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Oscilloscopes Blog

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mike1305

How Signal Modulation Works

Posted by mike1305 Employee Jun 20, 2017

Have you ever wondered how radio stations work? What about WiFi, or cell phones? These technologies (and countless others) all use modulation to send data at the same time, without interfering with each other! If electromagnetics wasn’t part of your college coursework, or you haven’t spent hours browsing Wikipedia, modulation of waveforms can be difficult to understand. To understand how wireless data transfer happens, we need knowledge of a handful of topics, which I plan to cover briefly in this blog post. For details, check out the full article.

 

Sending a signal that is a pure sine wave is called a "tone". It carries no real information, and doesn't sound that great either.

 

Single Tone

Single tone (time domain)

 

How about a signal composed of many tones of varying frequencies? We can see the signal is too complex to understand in the time domain.

 

Multi-tone Signal

Multi-tone signal (time domain)

 

For complex signals, engineers use a different way of graphing a signal in the frequency domain by using something called a Fourier transform. Let's see what our three signals above look like in this representation (skipping to the solution). Instead of plotting a signal’s voltage in time, we are plotting the power of the signal by frequency.

 

Multi-tone Signal of 10 tones

Multi-tone signal (frequency domain) of 10 tones, of varying amplitude

 

Notice the clear spikes? That is the mathematical representation of a sine wave at that particular frequency (x-axis). The multi-tone signal that was unreadable in the time domain has been clearly chopped into small spikes, representing all the frequencies that were summed to create the signal. A final example would be to show an audio signal.

 

Audio Signal

Audio Signal

 

This is how the spectrum of most signals appear, especially analog ones. The human voice and instruments do not play as discreet frequencies, and thus there is frequency content over an entire range. In theory, we can represent this analog signal as the sum of an infinite number of tones added together. That’s a fun one to wrap your head around.

 

Modulation is what takes a signal from low frequencies (we call this the message) and pulls it up to a higher frequency (the carrier). The idea is simple: Multiply your message by a high frequency carrier, such as 680kHz. Let's look at a few mathematical relationships. In this case, theta is the message and phi is the carrier.

The nifty relationships above show us that two signals multiplied can be represented as two signals added together! What does an audio spectrum look like when it's been modulated? We basically shift the signal up and around the carrier frequency.

 

Modulation of a Sound Clip

Modulation of a sound clip to 700 kHz

 

Just as expected, we see two signals. One is carrier + message, one is carrier - message (even notice how it is reversed). We can change the carrier frequency (radio station) to transmit a second, different signal at the same time. This is basically how a transmitter works in a radio tower. Now let's talk about receivers. Fortunately, it’s easy to bring our audio signal back to "baseband" (near 0 Hz instead of the carrier). We simply multiply everything by the carrier again. More math!

 

equation for modulation

 

That's a bunch of cosines, parenthesis, and f's all over the place. But it's correct, and we see that there are four signals that result from it. fC is the carrier frequency, and fM is the message.

 

  • ¼ power signal, (2*carrier + message)
  • ¼ power signal, (message)
  • ¼ power signal, (2*carrier – message)
  • ¼ power signal, (-message)

 

Let’s immediately disregard the last term with a negative frequency. It is a mathematical artifact which occurs quite often when talking about modulation and the math involved, but isn’t really, well… real. The two signals at double the carrier (assuming the carrier is much larger than the message, they are almost the same) can be filtered out with a low pass filter, leaving us with the original message at 25% power. Here's a picture of it, but backwards. Using this process, we can now hear the audio message that was transmitted at the 700 kHz carrier!

 

 

In summary, the purpose of this post was to give a 30,000 foot view of how radio transmission and signal modulation works. By taking multiple audio (or baseband) signals and mathematically multiplying them by different higher frequencies (the carrier), we can successfully transmit multiple signals over the same channel (our atmosphere) without interference. Multiplying it by the carrier again brings the modulated signal back to baseband, and a low pass filter and amplifier clean up and magnify the signal for our listening pleasure! I highly recommend reading the full length article for more details, fun facts about the FCC, as well as more in depth examples of signals being modulated for better understanding.

 

Have you ever set up your oscilloscope without a proper trigger? If so, you probably experienced something a little bit like this:

*disclosure – don’t watch this on repeat if you’re prone to epileptic fits*

 

In this case, I had an edge trigger and the level was set above my waveform.  The oscilloscope could not find any waveform data at that threshold and therefore, didn’t know what waveform data to display on screen.

When you have a trigger set up, the oscilloscope is looking at the acquisition data to see when your trigger conditions are met. If they are met, the oscilloscope will display the waveform data centered around the trigger event, thus stabilizing your display.  

Triggering

The easiest way to set up a quick trigger and stabilize your display is to hit Auto Scale.  That will take care of your vertical and horizontal scaling, and sets up the most common trigger type (Edge) at an appropriate level. This gets you to straight to basic troubleshooting.

 

Below is a trigger diagram showing the conditions for Edge trigger:

Trigger Diagram

Figure 1- edge trigger diagram

 

But triggering isn’t just used to obtain a stable display. It can also help you find events in your waveform. And there are many different triggers to help you find many kinds of events – even the tricky, hard to find events like glitches, runts, patterns, and sequences.  Keysight’s Infiniium oscilloscopes provide both hardware and software triggers.  Hardware triggers are quick and address the most common use cases. They are looking for events happening in real-time acquisition data.  Software triggers are used when the event you want to trigger on is just too complex for hardware alone.  To perform a software trigger, first the oscilloscope triggers in hardware to acquire the waveform data.  Then analysis and event searching happens in software before the waveform is displayed for that trigger. Perhaps a more accurate name for software triggering is event identification software. 

 

Below, you’ll find a quick reference guide for all the hardware and software triggers available on Keysight’s Infiniium oscilloscopes.  This will help you understand what triggers are available and determine what triggers you want to use when.

Hardware Triggers:

Trigger Type

What it Does / When to Use

Edge

looks for slope and voltage level of the selected source - mostly used for general purpose viewing and trouble shooting

Glitch

looks for a pulse that is narrower than other pulses in your source - used to capture infrequent glitches

Pulse Width

looks for a pulse that is either wider or narrower than other pulses in your source based on the pulse width and polarity you set - used to capture pulses that are too short or too long in time

Pattern/State

looks for a user specified pattern - used when you want to find a specific pattern across analog and/or digital channels

Runt

looks for a pulse that is smaller in amplitude than other pulses with low and high thresholds - to find pulses that are too low in voltage

Setup and Hold

looks for violations of setup time, hold time, or both setup and hold time based on a reference clock waveform

Edge Transition

looks for edges that do not rise or fall across two voltage thresholds in the amount of time you specify - used to find violations in rise/fall time

Edge Then Edge

looks for the two events you specify delayed by the number of events or time you set

Timeout

looks for a pulse that is lasting too long either at a high or low level - to find potential timeout errors

Window

looks for an event of the waveform exiting, entering, or remaining outside a voltage range as specified to use when you want to view a waveform either within or without certain thresholds

Protocol

looks for certain packets or patterns in protocol-based data. (Hardware protocol is only available on some Keysight oscilloscopes, the S-Series being one of them, with others performing protocol trigger in software).

Sequence

any two of the above performed in sequence used when you want to capture the signal based on two trigger events

 

Software Triggers (Available with InfiniiScan N5414B):

Trigger Type

What it Does / When to Use

Measurement

After hardware triggering and the waveform data is acquired, the specified measurement is performed, and then if the measurement condition is met, the InfiniiScan trigger condition is set to true and the waveform is displayed on screen

Zone Qualifying

create up to 8 zones and combine them with logic expressions to set triggering conditions

Generic Serial

capture packets of customized protocols or generic patterns

Non-monotonic Edge

capture small glitches or edges that may be hidden by hysteresis

Runt

capture runts that they may be hidden by hysteresis

 

I’m hoping as you advance past Auto Scale and try out a couple of these triggers, you’ll be a wiz and won’t even need this lookup table!

 

So how do you set up these different triggers? Easy.  Here are the two simple steps:

  1. Choose the Trigger Menu, then select Setup
  2. Choose the trigger you want from the list on the left and set your desired conditions

Now you’re rockin’ and rollin’! You’re ready to find all sorts of different anomalies that could exist in your waveforms and find the root causes of your malfunctioning DUT faster.  

 

If you have any interesting test conditions in which you used one of these triggers, we’d love to hear about it in the comments. Happy Triggering!

Oscilloscope users are constantly reviewing the signals of their design in the “normal” time vs voltage display of the scope.  It is easy to overlook the FFT (Fast Fourier Analysis) view of the same signal. It is a completely different way of reviewing the signal characteristics that often reveals clues to some very difficult to solve problems. FFT can be an invaluable tool for identifying noise, crosstalk, and other common problem in many designs that can stall prototype development. In digital designs, it is often used to highlight and pinpoint the source by the frequency content on power rails.

FFT measurement with an input sine wave

By applying the FFT algorithms to the sampled data, you convert the time domain operation of the oscilloscope into a frequency view of the signal. This results in two primary benefits. One, you can easily identify each of the frequency components. Two, it reveals the magnitude of each contributing signal.

Identifying the frequency

By identifying the frequency components, it reveals if there are any signals on that are not expected. For example, a digital signal should only have frequencies that are harmonics of the base signal. If you have a 10 MHz data, there should be only frequencies at 10 MHz (the primary harmonic), 30 MHz (the third harmonic), 50 MHz (the fifth harmonic), and the continuing odd harmonics up to the bandwidth of the source.

Any other frequency is a result of noise, or crosstalk, or some type of coupling on to the signal.

Frequency components of 10MHz clock

Figure 1: In this capture of a 10 MHz clock, we can easily identify the frequency components related to the fundamental frequency, but we can also see a 20 MHz signal that is -55 dB from the fundamental.

 

It’s important to understand how the oscilloscope sampling characteristics play into the quality of this FFT measurement. The oscilloscope analog bandwidth, sample rate, memory depth, and related time capture period all can have a profound effect on the measurement result. The math that is utilized for the calculation is using the data that was sampled at 5 GSa/sec, and it makes it possible to calculate a 10 GHz FFT. However, the front end of this scope is 1 GHz, so the FFT is only valid up to the bandwidth of the oscilloscope.

Identifying the Magnitude

The other key component of the signal is the power of each signal component. When looking at a signal in the time domain, it is only possible to see the very large signal power components. In the spectrum view (or FFT display) the horizontal axis is changed from a linear voltage scale to a logarithmic voltage scale (or dB for decibel).

The display on the right side of the display is listing the power level in dBV (decibel volts, or power relative to 1volt) of each frequency in order with the respective power level.  The first, or fundamental frequency of our signal is at just less than 10 MHz, and a power level of -13.9775 dBV, which is about 200mV rms. Looking at the time display of the signal (in green), you can see that it looks about right. We can also see that the next highest power signal is at 30 MHz and a power level of -30dBV, or about 3 mVrms-- something that cannot be seen in the time display that we are used to looking at.

FFT is just a button away

On Keysight oscilloscopes, the FFT operation is often enabled by simply pressing a button on the front panel. The new 1000X low cost oscilloscopes include this feature standard. The FFT view is a great way to examine a signal to find the frequency and power that you could not normally see any other way. Make sure to take advantage of this powerful tool that next time you are trying to find elusive signals in your design.

Learn other time-saving tips to get more out of your oscilloscope with this new eBook!

 Oscilloscopes are used to measure and evaluate a variety of signals and sources. They also play a major role in both design and manufacturing, providing a visual display of voltage over time. Many times oscilloscope users need more than a visual representation and want to validate the quality and stability of electronic components and systems. The Keysight Technologies mask test option, DSOX6MASK, for InfiniiVision Series oscilloscopes can save you time and provide pass/fail statistics in seconds. The mask test option offers a fast and easy way to test your signals to specified standards, as well as the ability to uncover unexpected signal anomalies and glitches. Mask testing on many industry oscilloscopes is based on software-intensive processing technology, which tends to be slow. Keysight’s mask test option is based on hardware-accelerated technology performing up to 270,000 real-time waveform pass/fail tests per second. This makes your testing throughout orders of magnitude faster. This Keysight InfiniiVision ground breaking Mask Technology is supported by their industry leading highest sampling rate at 1,000,000 waveforms per second allowing for improved display quality to catch subtle waveform details such as noise and jitter.

 

Mask Testing

Figure 1 shows a pulse-shaped mask using an input signal standard. You can easily specify horizontal and vertical tolerance bands in either divisions or absolute volts and seconds. You can set up the mask test to run continuously in order to accumulate valid pass/fail statistics. In this example, an infrequent glitch was quickly detected. In just six seconds, the mask test statistics show that the scope performed the pass/fail mask test on more than 1,000,000 waveforms and detected just two errors for a computed error rate of 0.0002%. In addition, you can see that this particular signal has a sigma quality relative to the mask tolerance of approximately 6.1 σ.

Mask Testing

Figure 1 - Mask testing uncovers an infrequent signal anomaly

 

Importing an industry-standard mask -

Figure 2 shows testing results of an industry standard imported eye-diagram mask. This particular polygon-shape mask is based on a published standard and was created using a simple text editor.

 Mask Testing

Figure 2 - Testing an eye-diagram with an imported industry standard mask.

 

You can also set up masks around areas of the signal that should be off-limits. That way you do not need a perfect signal; just an understanding of how a signal looks when it functions correctly. Mask testing provides more reliability than testing individual attributes because the entire signal can be evaluated against a correct signal to find glitches and/or errors. As a result, mask testing saves time and money in design and manufacturing and ensures customers receive higher-quality products sooner.

 

Keysight Mask Test Functions include -

  • Automatic mask creation using input standard
  • Easily download multi-region masks and setups based on industry standards
  • Detailed pass/fail statistics
  • Test to high-quality standards based on sigma
  • Multiple user-selectable test criteria

 

When setting up your specific mask test criteria, you can choose from multiple options including:

  • Run forever (with accumulated pass/fail statistics)
  • Run until a specified number of tests
  • Run until a specified time duration
  • Run until a maximum ideal sigma standard
  • Stop-on-failure
  • Save-on-failure
  • Print-on-failure
  • Trigger out-on-failure

 

Low Noise –

Lower inherent vertical noise is key when making quality and precise mask tests. Vertical noise can cause random increases (spikes) in all areas of the signal, including trigger timing issues. Figure 4 below shows test results in just 6 seconds, capturing 3 elusive failures out of one million waveforms sampled. A consistent trigger point is vital to prevent jitter and drift of the waveforms. If a signal drifts outside the mask limits due to noise and/or trigger jitter, mask testing will analyze the oscilloscope-induced error components as a failure, thereby corrupting the test results. A low noise floor is essential to attain the precision and reliability of Six Sigma testing.

 Mask Testing

Figure 3 - Mask testing to 6.2 sigma resolution takes only seconds using an InfiniiVision scope with a mask test rate of 270,000 waveforms/s

 

Conclusion –

Not only does Keysight provide the fastest, low-noise mask testing performance in the market, but the mask test application on InfiniiVision scopes also has a variety of features for customizing your measurements. The Keysight mask testing software allows you to setup the mask test to run for a specified time, until a certain sigma threshold is reached, continue running upon a failure, stop on a failure, or save the data on a failure. This allows you to run a complete six sigma test in around one second. If a failure occurs the waveform can be set to automatically stop or saved for viewing and later analysis work. The capability to assure the quality of products to Six Sigma in 1.1 seconds saves time and effort in R&D and manufacturing. In R&D environments, engineers can test signals they are developing through many waveform repetitions spending less time but still ensuring signal stability. The more waveforms they can test, the more confidence they have that the design functions correctly. In manufacturing environments engineers must test signals to ensure customers receive reliable products. Your company can save manpower hours and can invest the capital in profitable initiatives, such as new product design. At the same time, customer satisfaction will increase as you produce high-quality products and move them quickly into the market.

Here in Keysight Oscilloscopeland we talk a lot about our ASICs (application specific integrated circuits). But why? Who cares about the architecture of a cheap oscilloscope? All that matters is how well it works, right? We agree. That’s why we design and use oscilloscope-specific chips for all our scopes.

 

How, though? Custom ASICs don’t just materialize out of thin air, it takes years of planning and R&D effort. Here’s a high level look at what it takes to make an ASIC.

 

The making of an ASIC

There are several different steps (and teams) involved in the creation of an ASIC. Before anything is started, there must be a long-term product plan – what do designers want to have 5-10 years down the road? Future products will have new specs or features that will sometimes warrant an ASIC. To make that decision, product planners meet with the ASIC planners.

 

An oscilloscope's ADC ASIC

A custom 8 GHz oscilloscope ADC, used in Keysight S-Series Infiniium oscilloscopes.

 

Planning

First up is the planning team. They ask “what chips do we need to have in a few years? – Let’s make that.” And, “what will be available off-the-shelf in a few years? - Let’s not make that.” The planners will also make cost vs. performance trade-off decisions (device speed, transistor size, power consumption, etc.).

 

Also, ASICs generally fall into one of two categories: digital or analog. Analog chips are essentially signal conditioning chips designed to massage signals into a more desirable form. Digital chips are essentially streamlined FPGAs, designed for processing data inputs and providing coherent data outputs. For example, our MegaZoom ASICs take data from an oscilloscope’s front end circuitry + ADC and output waveforms, measurements, and other analytics. 

 

processor chips on 1000 X-Series scope

Fig 1: The Keysight-custom ADC and processor chips on the InfiniiVision 1000 X-Series oscilloscopes

 

It's worth noting there's a third type of ASIC - a mixed signal ASIC like an ADC (Fig 1.)

 

Digital ASICs

 

Now, let's take a closer look at process of creating digital ASICs, like the MegaZoom processor in the InfiniiVision oscilloscopes.

 

Front-end/RTL design

Once the chip is well defined by the planning, the front-end team gets to work. They are responsible for the “register-transfer level” (RTL) design (and typically spend their days with Verilog or VHDL). Their goal is to create a functioning digital model of the chip, but not a physical model. The RTL team is ultimately responsible for taking the chip design specs and turning it into actual logic and computation models. To do this, they use digital design components/building blocks and techniques like adders, state machines, pipelining, etc.

The RTL team is ultimately responsible for taking the chip design specs and turning it into actual logic and computation models.

 

As the front-end team is working, there’s also test team that works to check the RTL for errors. The goal is to try to avoid situations like the infamous Pentium FDIV bug that cost Intel nearly $500 million in 1995.

 

Once the RTL is proven to be functional by the test team, it is synthesized into a netlist. This essentially means that the RTL is converted from logic blocks into individual logic gates. Today, software handles this, but historically it was done by hand and engineers used truth tables and Karnaugh maps. The netlist is then run through a formal verification tool to make sure it implements the functionality described in the RTL before being passed to the back end team. 

 

Back-end

Once the logic is verified, it’s time to physically implement the chip. This is typically known as “floorplanning.” Floorplanners use crazy-expensive software (hundreds of $k) to place the RTL onto the chip footprint. In reality, the back end team generally gets early versions of the netlists so they can get a head-start on floorplanning.

 

The back end work begins with an overall placement of design blocks on the chip. The general workflow for the back-end team is:

 

  1. Floorplanning
  2. Individual gate placement
  3. Clock tree building
  4. Routing
  5. Optimizing
  6. Static timing analysis

For the chip to function properly, gates involved in the same computational processes should be close together. Also, designers have to make sure that power can be distributed properly throughout the chip.

 

A clock tree is a clock distribution network designed to make sure the clock reaches each of the gates at the same time. If clock edges arrived up at different times to different parts of the chip, it could cause painful timing errors. Sometimes, designers also intentionally add some clock skew to keep an edge from arriving too soon.

 

The back end work begins with an overall placement of design blocks on the chip.

 

Once placement is complete, software then auto-routes the connections between gates. You’re probably familiar with the phrase “never trust the autorouter.” In this case though, that’s really the only option unless you want to manually route hundreds of thousands (or millions) of connections.

 

Oscilloscope acquisition board

Fig 2: Routing of an oscilloscope acquisition board

 

Finally, an ongoing concern throughout the whole process is whether or not the design is actually manufacturable. This is known as DRC (design rule checking). Basically, this is a set of rules designers provide to the software to tell it what architectures (aka physical shapes) are and aren’t physically possible. Then, there's a layout vs. schematic check (LVS) to verify that the physical geometries actually implement the desired circuitry.

 

Tape Out

Once the front end and back end teams are done, it’s party time. This stage, known as “tape out,” is when the final design is prepped for production. Massive files are sent to the fab, who creates photomasks for each layer of the ASIC. It’s not unusual for there to be 30-50 masks for a single chip.

In the final stage, known as “tape out,” the final design is prepped for production.

 

Manufacturing

Once the masks are created, a number of different techniques are used to manufacture the chip. Usually a combination of photolithography, acid baths, ion implantation, furnace annealing (baking), and metallic sputter deposition is used. Each silicon wafer holds dozens (or hundreds) of identical layouts that will later be cut up into discrete chips.

 

The completed wafer is then tested for manufacturing errors. Depending on the size of the wafer and complexity of the process, planners can usually predict the failure rate of each chip. Microscopic anomalies, like a speck of dust under mask, can cause a chip to fail. “Scan testing” is used to check each gate. Scan testing consists of applying a pre-determined pattern of signals that will test every single gate on the chip, and each chips’ output is compared to the expected output. Each die is tested, and the chips that pass are sent on to be packaged.

 

Packaging

Good dies are then placed into packages and tested again. The packaging team typically designs a custom package for the die, and needs to consider signal integrity, cost, thermal regulation, and reliability. Often, we at Keysight will re-design the package of an existing ASIC using updated technology to reduce hardware cost and improve reliability of our oscilloscopes.

The packaging team typically designs a custom package for the die, and needs to consider signal integrity, cost, thermal regulation, and reliability.

For example, the ADC on our inexpensive oscilloscopes is the same ASIC used in some legacy oscilloscopes, but by improving the packaging over time we’ve reduced the package cost by nearly 5x. Thanks to that cost reduction, what was once used for only for a top-of-the-line oscilloscope we can now use in our cheap oscilloscope.

 

Support Circuitry

Once a chip is manufactured, tested, and packaged, it still needs to be surrounded with support circuitry. For example, what good is an op amp if you never configure it with resistors? But, that’s a topic for another blog post.

 

How it’s made

So, while you wouldn’t want to use this description to go design your own ASIC, you should now have a better understanding of what it takes to produce an ASIC. It’s a lot of work, but the benefits they offer compared to FPGAs are often worth the investment. For any given Keysight oscilloscope, we use a few different ASICs. We use analog ASICs for the front end, a custom low-noise ADC, and often a custom processor as the brain of our oscilloscope. While this comes with a fairly large non-recoverable engineering expense (NRE), being able to use the same chip in our $45,000 oscilloscopes and our $450 oscilloscopes earns our oscilloscopes special place on the budget-conscious engineer’s bench.

Lab benches are many times cluttered with multiple pieces of test equipment. Keysight’s InfiniiVision Oscilloscopes are equipped with a built in digital voltmeter, frequency counter and totalizer giving the oscilloscope user additional measurement options that can reduce the amount of test equipment needed. In addition, when you only measure the frequency of a signal, you rarely get the whole story. A repetitive signal can have spurs, intermittent spikes and noise that you need to see during design and or debug. The oscilloscope counter will show you all these attributes in addition to the frequency in one screen shot giving you the “big” picture. Keysight InfiniiVision oscilloscopes include both a 3 digit voltmeter (DVM) and a 5-10 digit Integrated Counter depending upon the oscilloscope model number (Figure 1 below).

 

 

Figure 1 – Functionality, options and specifications across the Keysight InfiniiVision family of Oscilloscopes

 

Digital Volt Meter

The DVM and Integrated Counter operate through the same probes as the oscilloscope channels. However, these measurements are decoupled from the oscilloscope triggering system measuring 100 points per second. This flexibility allows engineers to make DVM and triggered oscilloscope measurements with the same connection. DVM results are presented with an always-on seven-segment display keeping these quick characterization measurements at the engineers' fingertips. You get the added flexibility of measuring five types of DVM measurements depending upon your application: Peak-Peak, AC rms, DC, and DC rms. As a user you should also note that the oscilloscope DVM is designed for quick rough measurements as needed in design or debug and not meant to replace exact measurements you would get from a calibrated external DVM.

 

Standard 5 digit counter resolution

The traditional oscilloscope counter measurements offer only five or six digits of resolution, which may not be enough for the most critical frequency measurements are being made. With a 10 digit counter you can see your measurements with the precision you would normally expect only from a standalone counter. The Keysight integrated counter’s ability to measure frequencies up to a wide bandwidth of 3.2 GHz, allows it to be used in many high-frequency applications. This integrated hardware counter allows users to make much more accurate frequency measurements on signals. 4 digits is 1 part in ten thousand, or ~0.01% of the displayed number. In addition, relative to an industry standard oscilloscope frequency measurement, the Keysight counter measurement is designed to be very easy to use. It uses the trigger level of the oscilloscope as the trigger level for the counter independent of the cycles shown on the screen.

 

Up to 8 to 10 digit resolution with external time base

If an external 10MHz reference is used, the counter is as accurate as the externally fed 10MHz signal and the measurement resolution is increased. The 10MHz REF BNC connector on the rear panel is provided so you can supply a more accurate clock signal to the oscilloscope. To drive oscilloscope’s time base from external clock reference, connect a 10MHz square or sine wave reference signal to the 10MHz REF BNC input on the rear panel and go to the Utility -> Options ->Rear Panel menu and select Ref signal mode to 10 MHz input. The working 10MHz input voltage is 180mV to 1V in amplitude, with a 0V to 2V offset. To get the highest resolution, the time/div setting should be at 200mS/div or slower. With this setting, the resolution is increased up to 8 digits, which is what would be displayed if an external 10MHz reference is used. When the internal reference is used, the oscilloscope displays counter measurement in 5 digits. The counter measurements can measure frequencies up to the bandwidth of the oscilloscope.

 

Accuracy

Basically, the counter is as accurate as the time base reference that is used.  The oscilloscope’s time base uses a built-in 10MHz reference that has an accuracy of 1.6 ppm to 50 ppm depending upon the oscilloscope model number. This means that the number displayed is within 0.00016% to 0.0050% respectively of the actual signal measured. For example, if you are making a counter measurement of 32,768 Hz signal using a model 6000X with 1.6 ppm accuracy, you are measuring the signal at ~0.05 Hz accuracy (see calculation below).

32,768 Hz x 1.6 ppm (0.00016%) = ±0.0524288 Hz

 

Totalizer

The totalizer feature of the DSOXDVMCTR counter option adds another valuable capability to the oscilloscope. It can count the number of events (totalize), and it also can monitor the number of trigger-condition-qualified events. The trigger-qualified events totalizer does not require an actual trigger to occur. It only requires a trigger-satisfying event to take place. In other words, the totalizer can monitor events faster than the trigger rate of an oscilloscope, in some cases as fast as 25 million events per second. Keep in mind that the number of events is a function of the oscilloscope’s hold off time.

 

Summary

The voltmeter and counter functions discussed in this article are just two of the “6 instruments in one oscilloscope” of the Keysight InfiniiVision family. The six instruments are the oscilloscope, 16 digital channels (mixed signal), serial protocol analyzer, Dual channel 20 MHz function/arbitrary waveform generator, 3-digit voltmeter and 5 to 10-digit counter with totalizer.

 

The voltmeter operates through the same probes as the oscilloscope channels. However, the DVM measurements are made independently from the oscilloscope acquisition and triggering system so you can make both the DVM and triggered oscilloscope waveform captures with the same connection.

 

Traditional oscilloscope counter measurements offer only five or six digits of resolution. While this level of precision is fine for quick measurements, it falls short of expectations when critical frequency measurements are needed. With the integrated counter within the five Keysight oscilloscope families summarized in Figure 1, you can select between 5 and 10 digit counter options and see your measurements with the precision you would normally expect only from a standalone counter. Because the integrated counter measures frequencies up to a wide bandwidth of 3.2 GHz, you can use it for many high-frequency applications as well

Keysight continues to invest in the very popular InfiniiVision X-Series oscilloscopes with new oscilloscope models, new options, and customer-requested enhancements. Every 6 to 8 months, Keysight releases new firmware that our customers can download into their InfiniiVision scopes at no cost. The latest release of firmware (version 7.10) for the InfiniiVision 3000T, 4000, and 6000 X-Series oscilloscopes includes three new licensed “pay for” options as well as several FREE upgrades/enhancements including the following:

 

  • User-definable Manchester/NRZ Trigger & Decode Option
  • Frequency Response Analyzer (FRA) Option
  • CXPI Trigger & Decode Option (new on 6000X, existing on 3000T & 4000)
  • DVM/Counter Option – Now standard!
  • Education Training Kit Option – Now standard!
  • On-screen grid scaling factors – Standard!
  • FFT RF power measurements -Standard!

 

 

User-definable Manchester/NRZ Trigger & Decode Option (DSOXT3NRZ, DSOX4NRZ, & DSOX6NRZ)

 

Keysight’s InfiniiVision X-Series oscilloscopes support triggering on and decoding a broad range of today’s most popular serial bus protocols including I2C, SPI, UART, CAN, USB, etc.  But what happens if you are working with one of the less popular — or perhaps proprietary — serial bus protocols that isn’t supported? Available now on InfiniiVision 3000T, 4000, and 6000 X-Series oscilloscopes is a “user-definable” Manchester- & NRZ-encoded serial bus option. This new trigger and decode option allows you to define the specifics parameters and structure of your particular serial bus including:

 

  • Encoding type (Manchester or NRZ)
  • Baud Rate
  • Start edge
  • # of Synchronization bits
  • Word size
  • Header field size
  • Data field size
  • Trailer field size
  • Decode Base (binary, hex, ASCII, or unsigned decimal)

 
Also available are three new application notes that provide step-by-step instructions on how to set up triggering and decoding for three specific Manchester-encoded serial bus measurement applications including the automotive PSI5 sensor bus, automotive RF-modulated key fob signals, and NFC-F signals. Figure 1 show an example of triggering on and decoding the automotive PSI5 sensor bus, which is often used in airbag systems.

 

Figure 1: Triggering on decoding the Manchester-encode PSI5 sensor bus using Keysight’s user-definable serial bus option.

 

In the above PSI5 measurement example, after detecting the 2-bit Start field, the scope triggered on and decoded a 10-bit payload field followed by a parity bit. The scope also automatically detected a Manchester timing error in the frame that immediately followed the trigger frame (155h). To learn more about triggering on and decoding the PSI5 serial bus, download the new application note on this topic.


 


Figure 2 above shows an example of decoding automotive key fob signals.

 

Decoding RF-modulated key fob signals requires hardware digital demodulation. The new application note on this topic shows you how to capture the RF signal with a “sniffer” probe, how to demodulate the captured signal in hardware, and then how to decode each “code-hopping” RF burst. To learn more about how to set up the scope to demodulate and then decode RF-modulated key fob signals, download the new application note on this topic.


  
Figure 3 above shows an example of decoding NFC-F signals.

 

With NFC-F signals, the scope automatically demodulates the captured RF-modulated waveform if based on a baud rate of either 212 kbps or 424 kbps. When the new Manchester trigger and decode option is used along with the recently-introduced NFC automated test software, the designer of NFC-enabled device now has a very powerful set of debug and test tools. To learn more about how to set up the scope to decode NFC-F signals, download the new http://literature.cdn.keysight.com/litweb/pdf/5992-2337EN.pdf on this topic.

 

 

Frequency Response Analyzer (FRA) Option (DSOXT3FRA, DSOX4FRA, & DSOX6FRA)

 

Using the InfiniiVision oscilloscope’s built-in function generator (WaveGen), these scopes can now perform automatic frequency response analysis (Bode gain & phase plots) as shown in Figure 4 below.

 

 

Figure 1: Triggering on decoding the Manchester-encode PSI5 sensor bus using Keysight’s user-definable serial bus option.

 

Frequency Response Analysis (FRA) is often a critical measurement used to characterize the frequency response (gain & phase versus frequency) of a variety of today’s electronic designs including passive filters, amplifier circuits, and negative feedback networks of switch mode power supplies (loop response). Engineers typically use network analyzers or standalone low-frequency FRAs to perform these types of measurements today. To learn more about the new FRA option, download the data sheet.

 

 

Free InfiniiVision Enhancements with Firmware Upgrade

 
In addition to the new “pay-for” options listed above, there are also free enhancements available for InfiniiVision X-Series oscilloscopes with an upgrade to the latest firmware (v7.10). The built-in DVM and hardware counter option shown in Figure 5 will no longer be an option. These measurement capabilities will now be standard features of all InfiniiVision oscilloscopes.

 

 

Figure 5: The DVM/HW Counter option is now a standard feature in all InfiniiVision X-Series oscilloscopes.

 

The measurement example shown above shows output ripple riding on top of a 5 V dc output from a switch mode power supply (SMPS) with a switch rate of approximately 2 MHz. The scope’s built-in DVM shows that the actual DC output measures 4.97 V and the actual switching rate is 2.0112 MHz as measured by the 5-digit hardware counter.

 

Another new free enhancement is on-screen vertical and horizontal grid scaling factors along the left vertical axis and lower horizontal axis, which is also shown in Figure 5. This has been a very popular feature in Keysight’s higher-performance Infiniium oscilloscopes. Labeling each grid with scale factors can help you quickly estimate voltage levels and timing of your signals. 


In addition to making the DVM/Counter option standard, the education training kit (EDK) option is now standard as well on all InfiniiVision 3000T, 4000, and 6000 X-Series oscilloscopes with the latest firmware upgrade. Using the built-in training signals shown in Figure 6 along with available online training guides, users unfamiliar with the operation of Keysight InfiniiVision oscilloscopes can get up-to-speed quickly. To learn more about the EDK training kit and to download the training guides, go to the InfiniiVision http://www.keysight.com/en/pd-1952427-pn-DSOXEDK/educators-training-kit-for-infiniivision-2000-and-3000-x-series-oscilloscopes?cc=US&lc=eng webpage.

 

 

 Figure 6: The education training kit (EDK) is now standard and includes multiple built-in training signals and online training guides.

 

Also available at no cost in this latest firmware release are new automatic RF power measurements that can be performed on FFT math functions. Figure 7 shows an example of an Adjacent Power Ratio measurement performed on an RF-modulation sideband measurement. Other new RF measurements include Channel Power, Occupied Bandwidth, and Total Harmonic Distortion (THD).

 

Figure 7: New FFT analysis measurements.

In oscilloscopes and oscilloscope probes, bandwidth is the width of a range of frequencies measured in Hertz. Specifically, bandwidth is specified as the frequency at which a sinusoidal input signal is attenuated to 70.7% of its original amplitude, also known as the -3 dB point. Most scope companies design the scope/probe response to be as flat as possible throughout its specified frequency range, and most customers simply rely on the specified bandwidth of the oscilloscope or oscilloscope probes. This often leaves them wondering if they are indeed getting the bandwidth performance at the probe tip. This article provides some step-by-step instructions on how to simply measure and verify the bandwidth of your probe with an oscilloscope you may already have.

Oscilloscope Gaussian frequency response

Figure 1 An example of an Oscilloscope Gaussian frequency response

 

To measure the bandwidth of an oscilloscope probe, a VNA (vector network analyzer) is often used, which can be very expensive and difficult to learn how to use. Also, because typical passive probes are high impedance probes that should be terminated into 1 Mohm of an oscilloscope, it makes the traditional VNA s21 method hard to implement because it is 50 ohm based system.

 

The other way to get bandwidth is to use a sine wave source, a splitter, and a power meter and sweep the response directly. If you do this, you must set this up to run using a remote interface such as GPIB or USB. Doing it manually is very laborious, subject to mistakes, and requires extensive effort every time you want to evaluate a tweak, etc.

 

An easier way of measuring probe bandwidth, especially for the lower bandwidth probes (say, <1 GHz passive probe) is the time domain approach utilizing only an oscilloscope with the built-in step signal source, the ‘differentiate’ function, and the ‘FFT’. To be able to use this method, your oscilloscope should support the function of another function output. If you don't, an alternative is to pull the time domain waveform data out of the oscilloscope, import it into the PC based analysis tool such as Mathlab or Excel, and apply the math functions on the step data there.

 

When you apply a step function to your system, then you will get the step response. If you then apply the differentiate (or derivative) to this step response, you obtain the impulse response, and then take the FFT of the impulse response to obtain the frequency response of the system.

 

Keysight’s Infiniium real-time oscilloscope is an excellent tool for this quick bandwidth testing. Here is the step by step procedure of the testing. For this bandwidth measurement example, a N2873A 500MHz 10:1 passive probe with an Infiniium MSOS804A 8 GHz oscilloscope is used.

  • Use a performance verification fixture such as Keysight’s E2655C with a 50 ohm BNC cable to connect the Aux output of the oscilloscope to the input of the oscilloscope. The Infiniium oscilloscope has an Aux output port with fast edge speed (~140 psec, 10-90% for Infinium S Series) for probe calibration. It is very important to note that the rise time of the signal source should be faster than the probe’s rise time, and the frequency response of the source is reasonably flat over frequency.

Probing 25 ohm signal source with Keysight E2655C

Figure 2 Probing 25 ohm signal source with the Keysight E2655C performance verification fixture

 

  • Connect the probe to the PV fixture to measure one edge of the source. Use as short a probe ground as possible to reduce probe loading associated with ground leads.

Ch 1 (yellow) = signal source (Aux output) as loaded by the probe

Ch 2 (green) = the measured output of the probe

 

Probing fast edge

Figure 3 Probing fast edge

 

  • Place the rising edges at center of the screen. Trigger on the measured output of the probe (ch2) and use the averaging or high resolution acquisition to reduce the noise on the waveform.
  • Use the oscilloscope’s built-in math function to differentiate the step response. Now you get the impulse response of the channel 2 where the probe is connected to. Assign the differentiated output of the step response into the F1 of the oscilloscope.

 

Built-in math function to differentiate the step response

Figure 4  -- Use the oscilloscope’s built-in math function to differentiate the step response.

 

  • Apply the built-in FFT Magnitude function on the impulse response (F1) of the measured step signal. Rescale the FFT to 100MHz/div (the center frequency at 500 MHz with the 1 GHz of frequency span across the screen) and 3dB/div vertically.

 

FFT magnitude function

Figure 5 -- Apply the built-in FFT Magnitude function on the impulse response

 

  • Now you have a plot of bandwidth. Since the vertical scale of the FFT plot is set to 3 dB/div with the horizontal scale set to 100 MHz/div, you can see the probe has ~660 MHz, as you pick the point in the FFT trace falling by 3 dB.

 

Plot of bandwidth

Figure 6 Now you have a plot of bandwidth

 

There is one catch to this. The way we do differentiate in some of the oscilloscopes is taking the best fit slope to three adjacent points and then assign this slope to the center point. This can really hose the bandwidth measurement up if you don't have enough sample density on the edge, so experiment with sample density and make sure it doesn't affect the bandwidth.

 

Conclusion

Utilizing the built-in mathematical capabilities available in modern digital oscilloscopes, it is possible to derive the frequency response or the bandwidth characteristics of a probe based on the measured step response of a fast step signal. Among those several test methods, the time domain approach is the easiest for an oscilloscope user to duplicate without having a need to use expensive test instruments.

Lab benches are many times cluttered with multiple pieces of test equipment. Keysight’s InfiniiVision Oscilloscopes are equipped with a built in digital voltmeter, frequency counter, and totalizer giving the oscilloscope user additional measurement options that can reduce the amount of test equipment needed. In addition, when you only measure the frequency of a signal, you rarely get the whole story. A repetitive signal can have spurs, intermittent spikes, and noise that you need to see during design and or debug. The oscilloscope counter will show you all of these attributes in addition to the frequency in one screen shot giving you the “big” picture. Keysight InfiniiVision oscilloscopes include both a 3-digit voltmeter (DVM) and a 5-10-digit integrated counter depending upon the oscilloscope model number (Figure 1 below).

 

 Digital Voltmeter

Figure 1 – Functionality, options and specifications across the Keysight InfiniiVision family of Oscilloscopes

 

Digital Volt Meter

The DVM and integrated counter operate through the same probes as the oscilloscope channels. However, these measurements are decoupled from the oscilloscope triggering system measuring 100 points per second. This flexibility allows engineers to make DVM and triggered oscilloscope measurements with the same connection. DVM results are presented with an always-on seven-segment display keeping these quick characterization measurements at the engineers' fingertips. You get the added flexibility of measuring four types of DVM measurements depending upon your application: Peak-Peak, AC rms, DC, and DC rms. As a user you should also note that the oscilloscope DVM is designed for quick rough measurements as needed in design or debug and not meant to replace exact measurements you would get from a calibrated external DVM.

 

Standard 5-digit counter resolution

The traditional oscilloscope counter measurements offer only five or six digits of resolution, which may not be enough for the most critical frequency measurements being made. With a 10-digit counter you can see your measurements with the precision you would normally expect, only from a standalone counter. The Keysight integrated counter’s ability to measure frequencies up to a wide bandwidth of 3.2 GHz allows it to be used in many high-frequency applications. This integrated hardware counter allows users to make much more accurate frequency measurements on signals. Four digits is one part in ten thousand, or ~0.01% of the displayed number. In addition, relative to an industry standard oscilloscope frequency measurement, the Keysight counter measurement is designed to be very easy to use. It uses the trigger level of the oscilloscope as the trigger level for the counter independent of the cycles shown on the screen.

 

Up to 8 to 10-digit resolution with external time base

If an external 10MHz reference is used, the counter is as accurate as the externally fed 10MHz signal, and the measurement resolution is increased. The 10MHz REF BNC connector on the rear panel is provided so you can supply a more accurate clock signal to the oscilloscope. To drive oscilloscope’s time base from external clock reference, connect a 10MHz square or sine wave reference signal to the 10MHz REF BNC input on the rear panel, and go to the Utility -> Options ->Rear Panel menu and select Ref signal mode to 10 MHz input. The working 10MHz input voltage is 180mV to 1V in amplitude, with a 0V to 2V offset. To get the highest resolution, the time/div setting should be at 200mS/div or slower. With this setting, the resolution is increased up to 8 digits, which is what would be displayed if an external 10MHz reference is used. When the internal reference is used, the oscilloscope displays counter measurement in 5 digits. The counter measurements can measure frequencies up to the bandwidth of the oscilloscope.

 

Accuracy

Basically, the counter is as accurate as the time base reference that is used.  The oscilloscope’s time base uses a built-in 10MHz reference that has an accuracy of 1.6 ppm to 50 ppm depending upon the oscilloscope model number. This means that the number displayed is within 0.00016% to 0.0050% respectively of the actual signal measured. For example, if you are making a counter measurement of 32,768 Hz signal using a model 6000X with 1.6 ppm accuracy, you are measuring the signal at ~0.05 Hz accuracy (see calculation below).

32,768 Hz x 1.6 ppm (0.00016%) = ±0.0524288 Hz

 

Totalizer

The totalizer feature of the DSOXDVMCTR counter option adds another valuable capability to the oscilloscope. It can count the number of events (totalize), and it also can monitor the number of trigger-condition-qualified events. The trigger-qualified events totalizer does not require an actual trigger to occur. It only requires a trigger-satisfying event to take place. In other words, the totalizer can monitor events faster than the trigger rate of an oscilloscope, in some cases as fast as 25 million events per second. Keep in mind that the number of events is a function of the oscilloscope’s hold off time.

 

Summary

The voltmeter and counter functions discussed in this article are just two of the “6 instruments in one oscilloscope” of the Keysight InfiniiVision family. The six instruments are the oscilloscope, 16 digital channels (mixed signal), serial protocol analyzer, Dual channel 20 MHz function/arbitrary waveform generator, 3-digit voltmeter, and 5 to 10-digit counter with totalizer.

 

The voltmeter operates through the same probes as the oscilloscope channels. However, the DVM measurements are made independently from the oscilloscope acquisition and triggering system, so you can make both the DVM and triggered oscilloscope waveform captures with the same connection.

 

Traditional oscilloscope counter measurements offer only five or six digits of resolution. While this level of precision is fine for quick measurements, it falls short of expectations when critical frequency measurements are needed. With the integrated counter within the five Keysight oscilloscope families summarized in Figure 1, you can select between 5 and 10 digit counter options and see your measurements with the precision you would normally expect only from a standalone counter. Because the integrated counter measures frequencies up to a wide bandwidth of 3.2 GHz, you can use it for many high-frequency applications as well.

This blog was written by Ailee Grumbine- Keysight Memory Solutions Product Manager

 

As a design engineer, your job is to design the best product. Your manager’s job is to reduce the number of redesigns and deal with engineering shortages and budget constraints. Your manager asked for test results to decide if your product is ready for release to production. You would spend days analyzing the test results to gain confidence that your product is good. You then translate the information into graphs and test reports that are presentable to your manager. Does this all sound familiar?

 

Data analytics is the answer for overcoming these challenges. In the test and measurement industry, designers use test equipment to help determine if their design meets the industry passing criteria for device certifications. Data sources include test results from compliance test software, simulation software, multiple vendors test equipment, and individual company’s proprietary measurement tools. Data collected is exported to a data repository server or cloud which is accessible by a globally distributed design team. Data analytics with visualization tools helps the decision making process more intuitive and a lot faster. The visualization tools include line and histogram charts with pass fail limits and statistical information. The image below shows an example of a measurement jitter histogram plot of different ASIC names. It reveals that the two ASICs, SERDES 700 and SERDES 701. Both have the same histogram mode and profile while SERDES 702 doesn’t have enough measurement to conclude its performance. You may want to hold off SERDES 702 for release to production.

Histogram Plot of jitter measurment

Histogram plot of jitter measurement on three different SERDES 

 

The next example is a bit error measurement against input voltage for different ASIC versions. Alpha, beta, and gamma versions have the same bit error measurements, while delta version is performing better with lower bit error measurement. You could conclude that delta version ASIC has better performance compared to the other versions. It could also be that there is discrepancy in the way the measurement is made that causes the outlier behavior.  You should also look at other possible contributing factors such as test equipment, test bench, and the engineer who made the measurement.  

 line plot of bit errors

Line plot of bit errors on four different ASIC versions

 

The visualization tool is the easy part of setting up data analytics capability. The hard part is setting up a web server that would interact with the data repository server for data upload and access. The data repository server has to be secured and has the support for backup, restore, and replication. It is highly recommended to have company’s internal IT department support in setting up the data repository server. The web server hosts the data analytics web server application software. It needs to support massive data upload via streaming or bulk transfer. It needs to be OS and programming language independent. It has to protect the data from any corruption and ensures consistency. It is recommended that the web server and the data repository server is setup using two separate servers to allow for scalability, performance, and data repository security.  You can collect the data in a .CSV file with measurements and properties information. Example of properties are temperature, test bench names, ASIC names, ASIC versions, and test engineers. Measurements can be jitter, bit error, input voltage, and power. For most measurements, there are upper and lower limits which would tell the design engineer the margins they have in their design.

 

Being ahead of the competition and doing it in the most cost efficient manner have a positive business impact. Hence, data analytics features are designed to work with all measurement data collection methods to allow for simple, quick, non-tedious integration into the design and characterization work flow. Important data analytics software features would include a web server application to enable real time huge data import and access. It would also support visualization tools with different chart options to enable fast and intuitive data analysis for making quick decisions. All of these elements should build an infrastructure that would support data analytics successfully in your company.

What does the piezoelectric effect have to do with oscilloscopes? If you follow any of the electrical engineering YouTube channels, you’re likely familiar with Dave Jones & the EEVBlog. His latest video caught my eye “EEVBlog #983 – A Shocking Oscilloscope Problem”. Now, this made me stop in my tracks. Not because he’s highlighting an oscilloscope “problem,” but because after waiting for 982 videos, Dave thought this topic was finally worth using the word “shocking” as a pun. I don’t know about you, but if I had made 982 videos, I’d probably have played that card already. Although, our Keysight Oscilloscopes YouTube channel just broke 250 videos and we haven’t done it yet, so you never know.

 

Anyways, what could be such a big deal? As it turns out the topic is actually, well (sigh) shocking. Who knew that simply bumping an oscilloscope the wrong way could cause mystery signals to appear on the screen? What makes this happen? It occurs because the ceramic capacitors in the oscilloscope’s acquisition system act as a piezoelectric material. Whether you are using a cheap oscilloscope or a high end oscilloscope, the piezoelectric effect is something to be aware of.

 

How does piezoelectricity work?

Piezoelectric materials are crystalline substances that produce an electric potential when subjected to mechanical stress.  Think about a crystal lattice. In general, a material’s molecules form into crystals because that is its most stable state. The molecular charges are arranged in an electrically neutral arrangement. Essentially, the positive and negative charges are all at a happy equilibrium. But as soon as an external physical pressure distorts the crystal structure, there will be an imbalance of charge. Take Fig 01 (GIF) for example. In a normal, non-compressed state the 2D lattice is at equilibrium. But as it’s compressed, the positive and negative charges “squish” out to opposite ends and create a potential across the structure. Basically, the lattice stops being an electrically neutral structure and has a charge distribution.

 

 

 Alternatively, you can apply a voltage to a crystalline structure and it will physically change the shape of the crystal – the “reverse piezoelectric effect.” This is especially useful if you want to generate or sense physical time-varying waves.

 

The piezoelectric effect and oscilloscopes

What does the piezoelectric effect have to do with oscilloscopes? Try this and see for yourself:

 

  1. Grab a standard 10:1 passive probe and connect it to your oscilloscope
  2. Zoom in vertically on your signal to a small voltage per division setting
  3. Set your trigger level slightly above your baseline signal
  4. Remove the probe’s grabber hat & tap the exposed probe tip on a hard surface
  5. Don’t panic and always carry a towel

 

You should then see a signal show up on your screen. Remember, you may have to put your oscilloscope into “Normal” trigger mode to keep the signal onscreen. Alternatively, you may be able to forgo the probe all together and simply tap on a bare BNC or even the top of the chassis (like in Figure 2). Now, don’t panic, this is a behavior that every scope in existence exhibits. It’s worth noting that I had to smack the oscilloscope pretty stinking hard to get this strong of an effect.

 

Scope Slap

A hand-numbingly hard slap demonstrates the piezoelectric effect on the Keysight InfiniiVision 1000 X-Series

 

A signal is showing up on the oscilloscope because designers use ceramic capacitors in both probes and in oscilloscope acquisition boards. Ceramic is a piezoelectric material, and the vibrations caused by physical force you exert on your probe and/or scope cause the capacitors to physically expand and contract slightly. This expansion and contraction creates an electric potential in the capacitors. Because these capacitors are part of the oscilloscopes acquisition system, that potential shows up on the oscilloscope screen. “So…” you ask me once you’re done hyperventilating, “have all of my measurements been bogus up to this point? Can I minimize this effect? Is this something I should worry about?”

 

No, yes, and probably not.

 

Unless you are working in the middle of a city-destroying earthquake or on the back of a kangaroo, you probably don’t have anything to worry about. Keysight oscilloscopes all go through extensive environmental and stress testing, including drop tests (up to 30 g’s of force!) and time on a vibration table (Fig 3). So, for Keysight oscilloscopes you can be confident that every-day vibrations won’t affect your measurements (but I can’t speak for other manufacturer’s testing procedures). If you are extra concerned about this or work on the back of a kangaroo, try using an equipment cart or table that has built-in suspension.

 

Drop Table

An Infiniivision 1000 X-Series oscilloscope being drop-tested. Just because it’s an inexpensive oscilloscope doesn’t mean it’s not rugged!

 

Wrapping up

Clearly, under the right circumstances, you can visibly observe the piezoelectric effect on your oscilloscopes. However, in my years at Keysight, I have not seen a single instance of this ever effecting an engineer’s measurements. To borrow the words of Mike from Mike’sElectricStuff:

Patient to Doctor: “Doc, it hurts when I do this!”

Doctor to Patient: “Don’t do that!”

The latest Infiniium software release (for Infiniium oscilloscopes and Infiniium Offline on your PC) includes a handful of new and improved tools to help you make more efficient measurements and documentation.

These updates include:

  • MIPI SPMI Protocol Decode
  • Generic Raw Decode for PAM-4 and NRZ
  • Symbolic Decode added to ARINC 429 and MIL-STD-1553 protocol decode 
  • Segmented Memory improvements
  • Measurement Reports
  • S-Parameter Viewer
  • Windows 10 Support

 

MIPI SPMI Protocol Trigger and Decode – N8845A

If you’re designing mobile devices, our new SPMI (System Power Management Interface) protocol decode license might interest you. SPMI is used to communicate from power controllers to one or multiple power management chips with up to 4 masters and 16 slaves on one bus. SPMI allows you to reduce the number of pins on your power controllers, reducing the size of your mobile designs. With Keysight’s SPMI protocol decode option you can decode and debug these designs. Like I always say when it comes to protocol decode software, have the oscilloscope decode for you so you can get right to the fun part - analyzing and debugging.

Figure 1 - MIPI SPMI protocol decode

 

Generic Raw Decode

You may have a proprietary bus or customized protocol that others may not have defined a specific protocol decode for. This means you don’t have the option of buying a convenient protocol decode license that will trigger and decode your serial bus, group bits, label packet types, and flag errors for you. However, you can still get the binary data extracted from your analog waveform. With Generic Raw, you can decode your NRZ and PAM-4 signals so you can process and analyze the data yourself. This software extracts the raw bit data from the analog signal based on the clock recovery and thresholds that you set. Generic Raw has one mode for NRZ* signals and another for PAM-4** signals.

Figure 2 - Generic Raw PAM-4 decode

 

Symbolic Decode – N8842A

If you’re working with ARINC 429 and MIL-STD-1553 protocols, this update is for you. How many of us sit with our protocol binders in our lap to translate the Hex values to meaningful English? It’s time to toss that binder in a desk drawer. Load your .xml file into the oscilloscope to view your protocol decode in ASCII instead of Hex. Look at the examples below to see the two versions side by side.

ARINC 429 protocol decode:

Figure 3 - ARINC 429 decode in Hex

 

ARINC 429 protocol decode with symbolic decode:

 

 Figure 4 - ARINC 429 decode in ASCII

 

 

Segmented Memory Updates

Segmented memory is a great way to make the most of your oscilloscope’s memory, especially if you have specific events of interest separated by long amounts of time that you don’t really care about. An example of this is a serial bus. You’ll be looking at a waveform with packets of data separated by dead time. You can acquire waveform data just around the trigger conditions you set – for example, a specific packet type or an error. Then you can view this same packet type as it changes over time, comparing the packets captured in each acquisition. Now segmented memory has been improved to make your life even easier with the following:

  • Auto Play - automatically play through all the segments after acquisition is completed
  • Time between segment playback is reduced to zero – optimized performance saving you time
  • Persistent data is preserved – you can view all your segments laid on top of each other to see how your signal changes between packets in one view
  • Measurement Log – track the changes in measurements over the number of acquisitions you specify

 

 

Measurement Reports

 

Have you ever had to compile measurement reports to keep records of exact test conditions, equipment settings, and measurement results? Now, the oscilloscope can do it all for you in a couple clicks. No more copying and pasting screenshots, pulling together separate setup files and recording the software versions, and organizing them into your favorite text editor. The 6.0 Infiniium software now provides a way to generate hassle free reports that include all of the information you’d want to record and keep in your archives for proof of your test results.

 

Measurement reports provide, in a single file, measurement results and screenshots, plus all the information about your oscilloscope setup including:

 

  • Oscilloscope configuration with model number and software version
  • Calibration status of the frame and individual channels
  • Acquisition settings
  • Horizontal settings
  • Bandwidth limits and filter type
  • Vertical and channel settings
  • Trigger setup

 

You can save your report as PDF or as MHTML (*.mht) format files. MHTML is a webpage archive format that includes images and html all in one file so you don’t have to save images and text based content separately.

 

S-Parameter Viewer

If you are using InfiniiSim to apply transfer functions to your waveform – useful when you want to model the effects of a probe or RC circuit on your design – there is now an option to view the s-parameters. Being able to view the s-parameters before applying it to your waveform can be a nice sanity check before you end up spending hours trying to understand why your circuit behaves so unexpectedly because you accidentally uploaded the wrong file (it’s happened to the best of us).

 

Figure 5 - S-Parameter Viewer

 

Windows 10

Infiniium software now supports Windows 10. If you are running Windows 10 on your PC, Infiniium Offline is now compatible! For a free trial of the Infiniium software, click here.

_____________________________________________________________________________________________________________________

*Standard with SDA option

**Requires PAM-4 Compliance App and SDA option

If you are working on embedded designs such as automotive controllers, sensors, actuators, avionics, weapons systems, transmitting uncompressed audio and video data, or other chip-to-chip communications, you are probably using protocols and need a way to decode serial buses.

Protocol decode is the process of translating an electrical signal from a serial bus into meaningful bit sequences as defined by the standards of the protocol being analyzed. As we use serial buses in our designs to communicate from one device to another, we often need to debug our designs and verify we are sending the messages, or bit packets, that we intend to send.

One way to do this is to manually decode the signal. To do this, first you must capture the signal on an oscilloscope. Next, break apart the signal into one bit time slices and count the stream of ones and zeroes. Then group the sequence of bits and decode by the specifications of the protocol you are using. An example of this process is shown in the image below. This example is of a CAN bus.

Figure 1 - Decoding a CAN bus by hand

While this exercise might make an interesting learning experience for engineering students, this is a tedious and obsolete way to decode. Now days, you can decode your serial buses using a protocol analyzer or protocol decode software on your oscilloscope. This oscilloscope software will count the bits and compartmentalize the data into meaningful packets based on the definitions of the protocol you are using. With many oscilloscopes, you can even view the protocol decode results in a lister window.

 

Keysight InfiniiVision and Infiniium oscilloscopes display the original waveform, a time aligned decode trace for the data captured on screen, and a lister which is a text based table. The lister displays all the data packets, the time at which they occurred, the type of packet, and other relevant packet information specific to the protocol in use. Additionally, the lister will include the error type if an error was detected. Below is an example of CAN protocol decode performed on an InfiniiVision oscilloscope:

Figure 2 - CAN Protocol Decode performed by InfiniiVision oscilloscope

To find errors by hand you’d have to cross reference the packets you decoded with the packets you were trying to send at that point in the sequence and check if you have errors. Plus, you would be limited to the part of the waveform you could view on screen. As you can imagine, this is tedious. However, protocol decode software can find errors for you. Plus, with Keysight oscilloscopes, you can even trigger on errors or a specified packet type so you can easily find and analyze the events that interest you.

If you are looking for an entry level, affordable oscilloscope, the Keysight InfiniiVision 1000X-Series oscilloscopes have the ability to perform protocol hardware trigger and decode of I2C, SPI, UART/RS-232, CAN, and LIN buses.

1000 X-Series Oscilloscope

Figure 3 - Keysight 1000X-Series oscilloscope

If you are looking for an oscilloscope with higher bandwidth and additional capabilities, the Infiniium oscilloscopes offer several more protocol decode options including 8B/10B, ARINC 429, MIL-STD-1553, CAN, CAN-FD, LIN, FlexRay, DVI, HDMI, I2C, SPI, RS-232/UART, JTAG, several MIPI protocols, PCI Express, SATA/SAS, SVID, USB2.0, USB 3.0, USB 3.1, USB PD, and eSPI.

This variety of protocol decode addresses several industries. For example, the automotive industry often use CAN (Controller Area Network), CAN-FD (Controller Area Network – Flexible Data-rate), LIN (Local Interconnect Network), and FlexRay. These are the main buses used for automotive controllers, sensors, and actuators used throughout our vehicles. Designers in this space will want to be able to debug the physical layer of their designs. And because it is so important to have reliable systems in our automobiles, it is important to have reliable decode software.

Other buses that are important to have properly tested and reliable designs are ARINC 429 and MIL-STD-1553. These are often used in military equipment such as avionics, weapons systems, or ground vehicles.

As USB (Universal Serial Bus) has become so popular and continues to advance quickly, it is important to have the ability to decode both legacy USB protocols such as USB 2.0 and the newer USB protocols such as USB 3.1, and USB Power Delivery.   USB is everywhere now with its use in smartphones, computer peripheral devices, cameras, power chargers for hand held devices, and drones.

High definition televisions and displays usually use HDMI (High Definition Multimedia Interface) protocol for transmitting uncompressed audio and video data. DVI (Digital Visual Interface) is also used to transmit digital video.

Buses used for Short distances with integrated circuits include I2C and SPI.

Serial buses are used everywhere. With the ability to set up the decode in less than 30 seconds, set up specialized triggers and search on specific packet types or errors, and expand the amount of useful data captured with segmented memory, oscilloscopes make decoding serial buses much more efficient than decoding by hand. Protocol decode software on oscilloscopes help you quickly move from decoding to analysis and debugging.

Professor BodeWhen I was an electrical engineering student back in the 1970’s at the University of South Florida — go bulls! — two of my favorite classes were Control Systems and Analog Circuit Fundamentals. One reason I loved these classes so much was because we got to create Bode plots. I know, that sounds weird. I really enjoyed finding the theoretical poles and zeros and drawing Bode plots on my green engineering graph paper by hand (pencil, paper, and a ruler). Thank you Professor Bode; you are my hero! But when it came time to go into the lab to verify the frequency response of something like a passive or active filter design that we were assigned to build and test, there were no frequency response analyzers (sometimes called network analyzers) to be found.

 

In those days network analyzers were highly specialized and expensive multi-box systems from test and measurement vendors, including Hewlett-Packard (Keysight’s predecessor). Without

access to one of these expensive instruments in my EE lab, the testing process consisted of taking multiple VIN, VOUT, and Δt measurements on an oscilloscope while changing the input sine wave frequency on a function generator. After making 15 or 20 measurements, I would have enough measured data points to convert to gain (20LogVOUT/VIN) and phase shift (Δt/T x 360) using my trusty slide rule. I would then plot the results back onto that green engineering graph paper alongside the theoretical plots for comparison.

 

The days of plotting theoretical results by hand are over. Most engineering students today use MATLAB® to do that. And certainly the days of taking multiple VIN and VOUT measurements in the lab using an oscilloscope and a function generator set at discreet frequencies must be over, right? After all, the test and measurement industry now offers a broad range of frequency response analyzers (FRA) and vector network analyzers (VNA) that create gain and phase plots automagically. But those days aren’t over! Most undergraduate EE teaching labs are not equipped with frequency response analyzers. Almost all EE students today use the same tedious method of testing a circuit’s frequency response that I used back in ancient times. Why is that?

 

FRAs and VNAs are still considered by many to be a specialized instrument — especially in the university environment. In addition, the price of these instruments start at around US $5,000 and go up from there. This may not sound like much for someone in the high tech industry that depends on this type of instrument to get to their testing done quickly, but almost all universities have to operate on a tight budget. A typical student lab bench (consisting of an entry-level 2-channel oscilloscope, function generator, digital voltmeter (DVM), and power supply) can be purchased for about US $2,000 today. To equip an entire student teaching lab with an FRA at an additional US $5,000 per test station would blow most EE lab budgets out of the water.


 1000 X-Series Oscilloscope

But now the process of making multiple VIN and VOUT oscilloscope measurements to create Bode gain and phase plots are about to be over for many EE students – at least for students at universities that equip their labs with a new Keysight oscilloscope. Keysight just introduced a family of low-cost oscilloscopes with an optional built-in function generator (Figure 2). And the best part is that automatic frequency response analysis (Bode gain and phase plots) can be performed on these student oscilloscopes at no additional charge on models that come equipped with the built-in WaveGen function generator and frequency response analysis (EDUX1002G and DSOX1102G). All of this functionality (oscilloscope, function generator, and frequency response analysis) can be had for just over US $600. Let’s take a look at a measurement example of characterizing a passive bandpass filter using this new oscilloscope.

Passive RLC bandpass filter

Figure 3 shows the schematic of a simple RLC circuit that we will test. At lower frequencies, the 1-µF capacitor dominates the impedance (XC = 1/2πfC) of this circuit and blocks most of VIN from getting to VOUT. At higher frequencies, the 10-µH inductor (XL = 2πfL) blocks most of the input from getting to the output. But in the mid-band frequencies, the 50-Ω load resistor dominates such that most of VIN reaches VOUT (~0 dB). By definition, this is a bandpass filter. We will now test it with Keysight’s new oscilloscope with the built-in function generator and frequency response analysis capability.

 

We begin by connecting the output of the generator to VIN and also probe VIN and VOUT with channel 1 and channel 2 of the oscilloscope, respectively. Figure 4 shows the frequency response analysis setup menu, which displays a block diagram to assist us in making proper connections. This is also where we can define which of the oscilloscope’s input channels is probing VIN, which channel is probing VOUT, the minimum test frequency, maximum test frequency, and test amplitude. For this test, we will use all the default settings. When we select Run Analysis, the oscilloscope executes the one-time  test, sometimes called a "sweep."

Figure 5 shows the test results. The blue trace represents gain (in dB) with scale factors shown on the left side of the display, while the orange trace represents phase (in degrees) with scale factors shown on the right side of the display. A pair of markers is also available to measure gain and phase at any frequency. The oscilloscope even optimizes magnitude and phase scaling factors automatically. But you also have the ability to establish your own scale factors manually after completion of the test. This is probably the easiest-to-use frequency response analyzer on the market today. At least that’s my opinion. And it has to be the least-expensive FRA because it comes standard (US $0) with the purchase of an EDUX1002G or DSOX1102G oscilloscope, which is only US $200 more than the baseline 1000 X-Series model (US $449). But performance is not sacrificed. Using a proprietary measurement algorithm, this instrument can achieve up to 80 dB of dynamic range based on a 0 dBm (224 mVrms) input.

 

Using this new Keysight oscilloscope capability has sure saved me a lot of time in my job. And I bet it will save EE students a lot of time as well so they can complete their lab assignments on time!

 

 

MATLAB is a registered trademark of MathWork, Inc.

The second the probe is connected to your device your signal begins a grand journey to the center of the scope. It has to pass through five phases in order to complete its journey to the center, then back up to the surface. First the signal has to find its way to the front of the scope through the probe. Then, once it enters the scope, it has to go through an attenuator, DC offset, and amplifier before it can reach the center. At the center, the signal goes through an analog to digital converter. In order to make its way back to the surface of the scope, it must venture to find the display DSP. Along the way, it finds evidence that signals have been here before. The timebase and acquisition blocks show that previous samples of signals have been collected. Once the signal passes through these two blocks, it will finally be displayed on the surface of the scope. Let’s learn a little bit more about everything your signal encounters along this journey.

Oscilloscope Signal

 

Your signal’s journey begins with traveling from your device through a series of resistive and capacitive components inside the probe. The attenuation specification of your probe will determine what resistive components are inside. Most standard passive voltage probes that come with DSO scopes have a 10:1 attenuation ratio. This type of probe would have a 9 MΩ probe tip resistor in series with the scope’s 1 MΩ input impedance. This would make the resistance at the probe tip 10 MΩ, which means that when your signal travels through the probe and reaches the scope’s input, it will be 1/10th of the voltage level that it was when it entered the probe at the tip from your device. This means that the dynamic range of the scope measurement system has been extended because you can now measure signals with 10x higher amplitude as compared to signals you could measure using a 1:1 probe. Also, this 10:1 passive probe ensures a high input impedance at the probe tip which will eliminate any loading on your device. Loading will change the way your device behaves, and we don’t want that.

Analog Input Signal Conditioning

 

Next the signal enters the scope to begin the first phase of processing, analog input signal conditioning. There are three stages to this conditioning process which are all done in order to scale the waveform correctly to be within the dynamic range of the analog-to-digital converter (ADC) and the amplifier. The processing done in these stages is dependent on what the V/div and offset settings are, which ultimately depends on whether you are measuring a low level or high level signal. First, the signal is scaled in the attenuator block, which is a network of resistor dividers. If you have a high level input signal, then the signal will be attenuated, or reduced. If you are inputting a low-level signal, then the signal will be passed through to the next step without any attenuation. You may often be inputting a signal that has a DC offset, but we want to be able to display that signal in the center of the screen at 0 V. In order to make that happen, there is an internal DC offset of the opposite polarity that is added to the signal to shift the scale. This way it will display on the center of the screen. Lastly, the signal travels into the variable gain amplifier. This type of amplifier will either increase or decrease the gain of your signal dependent on what your V/div setting. So, this again depends on whether you are looking at a low or high level signal. If you are working with a low level signal, you are likely at a low V/div setting which would tell the amplifier the gain should be increased so that we are utilizing the full range of the ADC. If you are working with a high level signal, then the signal would have been attenuated back in the first stage of this process, and the amplifier may then further attenuate the signal in this stage by decreasing the gain, again to scale the signal within the dynamic range of the ADC.

Analog to Digital Conversion and Trigger Blocks

 

Now that the signal is conditioned to be within the dynamic range of the ADC, it can enter the center of the scope and the analog to digital conversion can begin. The ADC block is the core component of all DSOs. This is where the analog input signal gets converted into a series of digital words. Most of today’s DSOs utilize 8-bit ADCs which will provide 256 unique digital output levels/codes. These digital binary codes are stored in the scope’s acquisition memory, which will be discussed later. In order to obtain the highest resolution and accurate measurements, the scope will try to use the full dynamic range of the ADC. While the signal is being converted in the ADC, the scope is also processing the trigger conditions needed to establish a unique point in time on the input signal upon which to establish a synchronized acquisition. Depending on what you set the trigger acquisition settings to on the scope, the trigger comparator block will output a non-inverted waveform with a duty cycle that is dependent on what you set the trigger level to. Then, depending on what you set the trigger type to (rising edge, falling edge, etc.) the trigger logic block will either invert the waveform before allowing it to pass through, or it will allow the non-inverted waveform to be passed through to the next step. This trigger signal is then used in the timebase block in the next step as the unique synchronization point in time.

Timebase and Acquisition Memory Blocks

 

              The timebase block controls when ADC sampling is started and stopped relative to the trigger event that was just determined in the previous step. In addition, the timebase block controls the ADCs sample rate based on the scope’s available acquisition memory depth and the timebase setting. When the Run key is pressed, the timebase block enables continuous storing of the digitized data into the scope’s “circular” acquisition memory at the appropriate sample rate. While the timebase block increments addressing of the circular acquisition memory buffer after each sample, it also counts the number of samples taken up to a certain number which is dependent on the memory depth of the scope along with the trigger position. Once the timebase block determines that the minimum required number of samples of your signal have been collected, the timebase block enables triggering and begins to look for the first qualifying point of the output trigger comparator. Once the trigger event is detected, the timebase block then begins collecting the required number of samples. Once all of the samples have been stored, the timebase block disables the sampling and the process is pushed on to the next step.

 Display DSP Block

             

              Your signal has now reached the final stage in its journey. Once the acquisition of all of the samples has been completed, the data in the acquisition memory is “backed out” in a last-in-first-out sequence. The signal is reconstructed from the samples and the data is put into the scope’s pixel display memory and it is ultimately displayed on the screen. Once all of the data has been “backed out” of the acquisition memory, the DSP block signals the timebase block that it can begin another acquisition. This is a technique that is unique to Keysight’s custom ASIC technology. Traditionally, most other DSO oscilloscopes would not include this DSP block, but would instead use the scope’s CPU system. That method greatly decreases the efficiency of the scope and slows down the waveform update rate, so you would lose accuracy in your measurements and miss important glitches. Using the DSP block allows Keysight scopes to always operate at high efficiency and display a waveform that is more true to what is actually coming out of your device.

 DSP block waveform oscilloscope

              You can see the signal goes through quite the lengthy journey before it is displayed on the scope’s screen, but this all happens in the blink of an eye. To learn more about the fundamentals of oscilloscopes, download Keysight’s application note, Evaluating Oscilloscope Fundamentals.