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Oscilloscopes Blog

10 Posts authored by: ErinEast Employee

Different instrument form factors are used for each of the various design and test phases in a project to increase efficiency. Many engineers believe their only choices for high performance measurements are large bench instruments, or modular choices. The USB platform is a popular option for anyone needing a small, portable device. However, most USB instruments available are not comparable to benchtop performance, and utilize a different user interface (UI). Having inconsistent measurements and automated coding between each platform makes the transition between each development phase more time intensive due to the learning curve and adjustments that must be made.

 

With the new Keysight Streamline Series, you can expect a common UI, measurement capabilities, and automated code between all form factors: USB, benchtop, and modular. This allows you to move between product development phases more efficiently and effectively since knowledge and data can easily be transferred among the various platforms.  With the same applications and accuracy as comparable benchtop instruments, the new Keysight Streamline Series is the perfect compact USB option. It is portable, easy to use, and there is zero compromise in performance.

 

The new Keysight Streamline Series consists of USB oscilloscopes, vector network analyzers (VNA), and an arbitrary waveform generator (AWG). The oscilloscopes range from 200 MHz to 1 GHz with 2 analog channels. They feature many of the capabilities you would find in an InfiniiVision 3000T X-Series benchtop or M924xA modular scopes, including zone triggering and 1,000,000 waveforms/s update rate. You will also find many of the same applications that you are used to from your benchtop instruments, like mask testing, frequency response analysis, built-in arbitrary WaveGen, and serial decoding. With a soft front panel that has the same UI as all InfiniiVision oscilloscopes, it makes it easy to transfer your skills between the multiple platforms.

 

 

The new USB vector network analyzers (VNA) have a wide frequency coverage that operates from 300 kHz up to 26.5 GHz, with two ports. The software has the same intuitive GUI as our benchtop VNAs, which again allows you to reduce the transition time between platforms. It utilizes the same measurements, automated code capabilities, calibration and metrology as our other trusted Keysight VNAs, so you can have consistent measurement results between form factors. You are also able to extend the number of ports available to increase your testing capabilities.

The P9336A AWG provides multiple independent or synchronized signal outputs with exceptional performance in USB form. The small, compact form-factor makes it ideal for creating complex waveforms, without taking up much bench space.  It can supply digitally modulated waveforms for wideband communication systems and high-resolution waveforms for radar and satellite test. Industry standard waveforms for the AWG can be easily generated using Keysight software applications tools such as Signal Studio or Waveform Creator. In addition to these tools, you can generate your own waveforms using MATLAB or custom tools. The AWG provides standard IVI compliant drivers for integration with multiple application development environments.

 

The new Keysight Streamlines Series offers VNAs, oscilloscopes, and an AWG in compact form with zero compromise in performance. Check out the details of each of these new instruments at www.keysight.com/find/streamline-series.

Prove yourself as an engineer! The Schematic Challenge is the perfect opportunity to test your skills. On March 5, 6, and 7, we will be posting a new schematic or problem-solving challenge. If you, as a community, are able to answer questions 1, 2, and 3 correctly by Thursday, March 8 at 11:59 PM MST, we will add three 1000 X-Series oscilloscopes to the overall Wave 2018 giveaway! Answers should be posted in a comment on the #SchematicChallenge posts on the Keysight Bench or RF Facebook pages. Work with your family, friends, coworkers, or fellow engineers in the Wave community to solve these problems. If you haven’t already, be sure to register for Wave 2018 at wave.keysight.com.

 

Question 1:

By Ryan Carlino

 

Status: SOLVED! (minimum of 8 bits)

 

Week1 Question 1 SchematicYou need to design a circuit to determine the resistance of an unknown ID resistor.
A voltage divider provides a bias that creates a voltage at the input of an ADC.
You’d like to be able to distinguish between a 15K and 20K ID resistor.
The ADC has a 0.5% internal 3.3V reference. The resistors are all 1%.
What is the minimum number of bits of resolution that the ADC needs in order to have at least 10 codes (LSBs) between a 15K and 20K resistor?

 

Question 2:

By Ryan Gillespie

 

Status: SOLVED! ( V(d)=(0.72 - 0.13i) V )

 

Given the doubly terminated transmission line, calculate the voltage at d = 100 µm.

Hint: First you may want to solve for Zo, Wave Speed, Wavelength, V(x) and I(x)

Your answer should be in the form of V(d) = ( # + #i )  where # are the numerical answers.

 

 

 

Useful formulas:

 

Question 3:

By Patrick Mann

 

Status: SOLVED!

 

Given the block diagram in figure 1, is the additional explicit trigger input shown in blue in figure 2 required? Select the correct answer and post the respective letter on the Keysight Bench or RF Facebook pages:

 

  1. The explicit trigger is not required since the sampling oscilloscope can trigger off the data.
  2. The explicit trigger is required since the sampling oscilloscope cannot trigger off the data.
  3. The explicit trigger is not required because the precision waveform analyzer module can recover a clock and feed it to the sampling oscilloscope’s trigger circuitry.
  4. The explicit trigger is required because the precision waveform analyzer module cannot recover a clock and feed it to the sampling oscilloscope’s trigger circuitry.
  5. The explicit trigger is not required because the external time reference feeds into the sampling oscilloscope’s trigger circuitry.
  6. The explicit trigger is required because the external time reference feeds into the sampling oscilloscope’s trigger circuitry.

 

Figure 1: Precision Waveform Analyzer module (blue) and sampling oscilloscope mainframe block diagram (green)

 

Figure 2: Connection diagram of a sampling oscilloscope and module (left) to a pseudorandom binary sequence (PRBS) generator (right)

As power consumption and energy efficiency become more important, especially with battery-powered devices, it’s necessary to measure extremely low-level signals with higher sensitivity. Lowering your device’s current consumption will, in turn, lower its power consumption.

Power is defined as P = V x I

Having the ability to view the µA range with the highest accuracy possible allows you to analyze the power consumption of your design in detail. This ultimately leads to minimizing the power consumption, therefore maximizing battery life.

 

Download the "6 Essentials for Getting the Most Out of Your Oscilloscope" eBook.

 

One of the main challenges engineers run into is measuring the current consumption of a signal with wide dynamic range. In battery-powered devices, like a cell phone, the device will switch back and forth between active and idle states. During the active state, it will draw higher currents, in the A’s range. But when the device is idle, it draws very small currents, in the µA’s. In Figure 1, you can see the current signal of a cell phone making a phone call. The active peaks have a current of around 2 A, but during the idle states, the current is very small.

 

Graph showing current consumption during a cell phone call

Figure 1. Current consumption during a cell phone call

 

To measure on both of these extremes accurately, a specialized current probe is best. Clamp-on style current probes are typically enough for most measurements, especially if you are only trying to analyze the active periods. However, when measuring on the lower levels during the idle periods, a clamp-on current probe typically has too much noise. The Ohm’s law approach is the best option to measure on the µA or nA level. This means simply measuring the voltage drop across a sense resistor to derive the current. The only sense resistor current probe available with high sensitivity and a wide dynamic range is Keysight’s N2820A current probe, which can be seen in Figure 2

 

Image of measurement with N2820A 2-channel high sensitivity current probe

Figure 2. N2820A 2-channel high sensitivity current probe

 

This is a 2-channel active current probe. Each of the channels has a different gain in order to measure the two different current ranges. When you probe on your device with both channels:

  • One channel will give you a zoomed-in view of the µA level
  • The other will provide a zoomed-out view of the active, higher levels

The probe also has extremely low noise, which means you will have the highest accuracy possible when measuring on those really low levels. This will help to ensure you are saving even pA’s of current, which may seem small, but can make a huge difference in the system overall.

 

Graphical view of microamp level and Amp level current measurements with N2802A

Figure 3. Zoomed-in view (yellow) of the µA level and zoomed-out view (green) of the larger portions of the current signal in the A range

 

As I mentioned, this probe simply measures the voltage drop across a sense resistor. You can either cut a line and solder a resistor directly into the circuit, or you can use one of the temporary connectors that come with the probe. The probe comes with a 20 mΩ and a 100 mΩ resistor sensor head ready to use, along with a user-definable resistor head. You can use resistances from 1 mΩ to 1 MΩ.

 

Selecting the correct sense resistor for your device can be difficult,
but is critical in order to measure different current ranges and characteristics accurately.

If you use a larger resistor, you will get a great signal to noise ratio, which makes for more accurate measurements. The downside to using a larger resistance value is the burden voltage. Burden voltage is the unwanted voltage drop caused by increased power dissipation at the resistor. Using a smaller sense resistor will lower the power dissipation and, in turn, the burden voltage. However, this lower resistor value also comes with downsides, especially with measurement accuracy. Figure 4 below can be used to help determine whether a high or low resistor value would be better for the measurements you are trying to make. 

 

Figure shows the balance Rsense, Burden Voltage, Noise, Sensitivity and Bandwidth

Figure 4. The balance between sense resistor values and measurement specifications

 

Once you have this wide range of currents accurately captured on the oscilloscope screen, you can learn from it to understand how to adjust your design to increase power efficiency. Area under the curve measurements allow you to understand the charge and easily calculate current consumption over time. You will be able to see where there may be areas where power is being wasted. There could be points where the device should be in its idle state, but some functionality is staying on that is causing for power to be drawn unnecessarily.

 

Now, you can easily analyze power consumption and see the big picture on the dynamic current waveforms to improve the energy efficiency of your devices. And, built-in automatic measurements make it even easier to take your analysis to the next step and find the root cause of any problems you see.

 

To learn about which current probe is right for your applications, take a look at the Application Note, How to Select the Right Current Probe.

 

To measure current with an oscilloscope, you have to use a current probe. The problem is, there are so many types of current probes available now, and it’s hard to know when to use what. When you think about current probing, there are three main categories that most applications fit into:

  1. High current

  2. General purpose

  3. Low current

Each of the current probes fits into a specific category. Breaking it up like this makes it a little bit easier to identify which probe will be the best for your test.

 

Table 1: Current probing categories

 

High Current

When I say high current, I mean HIGH current, as in hundreds or thousands of amperes. You will run into large currents like this when measuring inrush currents or switching transients of switching power supplies, motors, and more. How do you think it would go clamping on a standard current probe to something like this? For this special type of measurement, you need a special type of probe: a Rogowski coil. The technology used in a Rogowski coil allows for measuring extremely high currents, something that no other probing technology can do. This is due to the fact that it uses an air core, where traditionally a metalcore would be used. Normally, we would worry about the metal core getting saturated when measuring too high of a current, but with air we don’t have to worry about that. Make sure you check back in a couple weeks for more details on the N7040A/41A/42A Rogowski coil probes!

 

Image 2: N7040A/41A/42A Rogowski coil probes

 

There are a few other reasons why you would want to use the N704xA probes rather than the other one you see listed in this category in Table 1, besides the fact that the Rogowski coil can measure much higher current. One reason is the other probe listed is a clamp-on style. One of the big problems you can run into with this is that you aren’t able to actually fit the larger devices you want to measure in the clamp itself. You may have to add in some additional wires and do some extra work to get the measurement you need, often causing changes in the characteristics of the DUT. The N704xA has been getting a lot of attention from engineers because it’s extremely easy to use and connect directly to your device under test. The probe head is just a flexible loop that you can wrap around anything you want to test, as you can see in image 2.

 

General Purpose

Typically for more general current measurements, the most commonly used current probe is the clamp-on style, or the magnetic core current probe. This refers to measurements such as current consumption of high frequency digital circuit, ICs, or power supplies. You can also make measurements on motor drives, power inverters, to test lighting fixtures, and the list goes on.

 

Clamp-on style probes are convenient because they are really easy to use.

 

To use this style probe, all you have to do is clamp it around a wire and you’re ready to start measuring, there are no accessories or extra components to worry about. You’re able to quickly and easily make accurate measurements with low loading and a very flat response. Most Keysight clamp-on current probes employ a hybrid AC/DC measurement technology, integrating both the Hall effect sensory element for measuring DC/low-frequency contents and the current transformer for measuring AC into a single probe. With clamp-on probes, you can have the ability to measure AC and DC current, so you are able to account for the DC offset in your signal rather than blocking it out and not knowing what is going on there.

 

There are some advantages to the new N7026A over the other clamp-on current probes used for general purpose measurements. Keysight’s clamp-on current probe with 0.1V/A (or 10:1) conversion factor can only go down to 10 mA/div of vertical scale setting, which isn’t good enough for most lower level current measurements. The new N7026A now allows for more accurate low-level measurements, down to 1 mA/div sensitivity with much lower noise and higher accuracy. The higher sensitivity means you will find about 5x lower noise with this probe, which makes a huge difference when measuring in the mA range. This is evident in images 3 and 4 below. The N7026A also introduces a wider range, going from the mA’s up to 30 Arms or 40 Apk, along with the highest bandwidth of any clamp-on current probe available, at 150 MHz.

 

Image 3: 10mApp, 100kHz sine wave showing dramatically improved noise and sensitivity (Ch1 in yellow = N7026A 1V/A, Ch2 in green = N2893A 0.1V/A)

 

Image 4: CAN bus current shows improved noise means higher accuracy with low-level measurements (Ch1 in yellow = N7026A 1V/A, Ch2 in green = N2893A 0.1V/A)

 

Low Current

As power consumption becomes more important with battery powered devices, it becomes necessary to measure extremely low-level currents accurately.

 

To maximize battery life, engineers must minimize the power consumption.

 

Low current here refers to measuring down from the µA to the A range, on components like charging devices, memory chips, battery-powered devices, and more. When you need to measure at these low levels, your probe must be more sensitive than ever before with much lower noise and have high enough dynamic range to cover the input signal range.

 

To have sensitivity this high, Keysight offers breakthrough technology in the N2820A/21A high sensitivity current probe that allows you to connect a sense resistor directly to your current path and make high sensitivity measurements. This will allow you to measure the voltage drop across the resistor, which is proportional to the current flow through the resistor. The N2820A/21A current probes are optimized for measuring current flow within the DUT to characterize sub-circuits, allowing the user to see both large signals and details on fast and wide-dynamic current waveforms.

Many times, when engineers are working on these devices that require low-level measurements, they also must be able to analyze larger currents at the same time, such as analyzing a phone’s idle state. The solution to this is the 2-channel version of the N2820A. One channel will act as the low gain side that allows you to see the entire waveform, or the “zoomed out” view. The other channel is the high gain amplifier that provides the “zoomed in” view of the extremely low-level currents. Now, with the N2820A/21A current probes, engineers are able to see the details and the big picture on dynamic current waveforms like never before.

 

Image 5: 2-Channel N2820A shows “zoomed in” and “zoomed out” view

 

Conclusion

There are so many probes available! Now you are an expert and know exactly which current probes to use for your measurements. Using the probe that aligns with your corresponding category will enable you to make the most accurate measurements possible, therefore creating the best product possible.

 

To further help you select the correct probe for your applications, check out this probes and accessories selection guide

To learn more about the high current and general current measurements we discussed, download this application note

To learn more about the N2820A for extremely low-level current measurements, check out this application note 

Eye diagrams are extremely helpful in testing the physical layer fidelity of clock or serial data, but many engineers don’t know:

  • What they are
  • Why they should use one
  • How to easily set one up

 

They actually aren’t that complex when broken down.

Eye diagrams can quickly give you insight into your signal, along with any jitter or anomalies that may be present that you might know exist.

 

What they are

What is an eye diagram? Eye diagrams are a layered view of every bit transition combination. There are eight of these in total. You can see in Figure 1 how each of these are layered to make up the eye. This provides a composite picture of the overall quality of a system’s physical layer characteristics like amplitude variation, timing uncertainties, or infrequent glitches.

 

Figure 1: Bit transition combinations

 

Why you should care

An eye diagram is used to detect jitter, but what is jitter and why is jitter bad?

 

Jitter can cause errors in the data that you are trying to transmit. If there is too much of it riding on your signal, the data that is sent will be interpreted incorrectly by the receiving end because the edge crossings aren’t occurring when they should be.

 

Figure 2: Jitter causes errors in the interpreted waveform.

 

How to create an eye diagram

One of the first things many people think when they see an eye diagram on an oscilloscope is “how do you get it to look like that?”

 

This layered view of bit transitions is not something that a normal trigger would be capable of displaying. The answer is, the oscilloscope utilizes a built-in clock recovery system. Clock recovery is actually pretty straightforward. Some signals have an explicit clock signal, and some have an embedded clock. An explicit clock can be driven right into one of the oscilloscope channels, but embedded clocks have to somehow be de-embedded, or recovered, hence “clock recovery.”

 

Figure 3: Clock recovery dialog

 

There are three different ways to utilize the clock recovery system, which all depends on how well you know the bitrate of your signal (the width of each bit):

  1. Fully automatic
    1. The oscilloscope will calculate the ideal bitrate (or nominal data rate) of your signal.
    2. This should be used when you have no idea what the bitrate is and you need the oscilloscope to figure it out.
    3. However, this method is only about 80% accurate.
  2. Semi-automatic
    1. In most situations, you should have a rough idea of what the bitrate should be. You can very easily make a bitrate measurement on the oscilloscope to find this estimation. This method allows you to enter your rough measurement and then use that information as a seed as it calculates the exact ideal bitrate.
    2. This method is significantly more accurate.
  3. Manual
    1. This method should be used if you know the exact ideal bitrate of your signal.
    2. This is the most accurate method of clock recovery.

 

There are a few other settings within the clock recovery menu. To learn more about these, make sure you check out episode 3, How to set up an Eye Diagram, and episode 5, How to Measure Jitter, of Scopes University video series.

 

Once you have your clock recovery system set up, all you have to do to set up the eye is press “auto setup”. You will see in just a few seconds that the eye diagram has begun to form. Over time, you will be able to see if there is any jitter or anomalies in your signal. Generally, you will want to let the test run for a longer period of time.

 

The longer you let it run, the more data is collected, and the more jitter, anomalies, or any infrequent events you can see.

Figure 4: Eye diagram with jitter

 

From here, you can analyze the eye diagram further by using the color grading key. This allows you to visually analyze the frequency of each edge crossing. You can also very easily turn on a histogram on the eye to determine whether the jitter is deterministic or random. This will help you decide if this is something you can fix with a phase locked loop filter or if you have to redesign the component. Perhaps this is a topic for the next blog, though!

Figure 5: Histogram of the eye diagram

 

To learn more about what I talk about here, check out these Scopes University videos.

Episode 3: How to set up an Eye Diagram

Episode 5: How to Measure Jitter

Keysight oscilloscopes are loaded with various applications. So many, that there may be some you don’t know how to use or don’t even know they exist. In the new Scopes University video series, Erin East and Melissa Spencer dive into when and how to use some of the different capabilities of the InfiniiVision and Infiniium oscilloscopes. Gain familiarity with features that will help save you time in your measurements, further your analysis, and deepen your insight.

 

Scopes University with Erin and Melissa

 

In the first couple episodes, Melissa and Erin start out with some of the basics, including some handy touchscreen tricks that will speed up your setup. Then, you’ll learn about some of the more advanced applications, like eye diagrams, jitter analysis, and frequency response analysis. Throughout the series, they will be covering the entire range of the oscilloscope family, from the low cost 1000 X-Series, to the deeper analysis Infiniium oscilloscopes.

 

Stay up to date on when new episodes come out by subscribing to our YouTube channel

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. 

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 oscilloscope 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 oscilloscope. Let’s learn a little bit more about everything your signal encounters along this journey to understand how an oscilloscope works.

Oscilloscope Signal

 

Your signal’s journey begins with traveling from your device through a series of resistive and capacitive components inside the oscilloscope probe. The attenuation specification of your probe will determine what resistive components are inside. Most standard passive voltage probes that come with digital storage oscilloscopes (DSOs) 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 oscilloscope 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 oscilloscope 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 you 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 you 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 oscilloscope’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 oscilloscope, 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 oscilloscope 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 oscilloscope’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 digital storage 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 oscilloscopes 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 how an oscilloscope works, download Keysight’s application note, Evaluating Oscilloscope Fundamentals. 

Alright, this tool may not actually be helpful in your search for dinosaurs if someone really were to figure out how to bring them back, but this makes a great example to help explain the concept of oscilloscope segmented memory.

So, let’s begin our journey to the greatest theme park of all time – we’ll call it “Dinosaur Island” for lack of a better name... Naturally you’re going to want as much footage as possible of your favorite dino so you can always remember this grand adventure (assuming it has a better outcome than in the movie). Let’s say you’re a huge T-rex enthusiast, so you want to capture them (and only them) running around the park each day. To do this, you can set up a video camera in a tree and retrieve the footage at the end of the day.

 

But when looking at the footage from the first day, not only do you see your beloved T-rex, but you also see all of the velociraptors, triceratops, diloposaurus, and whatever other Jurassic creatures were running through the park that day. Your camera only has so much memory, and it filled up half way through the day. So you’ve wasted the majority of the memory on these other dinos you don’t even care about. You only have two days left in the park and you really want more T-rex footage. What do you do now?

 

What if you could set up a sensor condition (or trigger condition) that tells the camera to only record when there is T-rex running by? Now, when you collect your camera at the end of the trip, the memory will only consist of T-rex footage! Not only do you save memory and use it more efficiently, but you also save yourself loads of time by not having to sift through all the footage you don’t care about.

 

Sadly, your amazing trip has come to an end and it is time for you to return to the real world as an engineer. However, you did learn some new skills that can be applied to making oscilloscope measurements. The concept of capturing T-rex footage using a sensor condition directly correlates to using segmented memory on an oscilloscope. Let’s say you have a signal that has infrequent pulses – like an RF burst (image below). There are about 4ms of dead time (miscellaneous dinosaurs) between each RF pulse while the pulses themselves (your T-rex) are about 700ns. If you were to acquire this signal as-is, including all dead time, you would use 0.0175% of that memory capturing the actual pulse (T-rex) and 99.98% of it on that dead time (misc. dinosaurs)! THAT’S INSANE! Almost all of your memory is being used on something that you don’t even want to see.

 

To solve this problem, you could always just buy an oscilloscope with significantly more memory, but that gets very expensive very quickly. A much cheaper solution would be to utilize the segmented memory tool, which is already integrated into Keysight oscilloscopes. This application comes standard on the 4000 and 6000 X-Series and all Infiniium oscilloscopes, and can be activated via software license on the 2000 and 3000T X-Series. With this application, you can set a specific trigger condition and tell the oscilloscope to only capture the waveform when that condition is met. So, once you set the trigger and segment parameters, your scope will only capture the pulses in the signal and ignore the dead time (image below). This means that 100% of your memory is being used to capture the pulses and 0% capturing dead time. It allows you to capture a long time span while still digitizing at a high sample rate. This way, you aren’t losing any signal detail for those pulses and you’ll be able to make even more accurate measurements.

 

Keysight Segmented Memory diagram

 

As I previously mentioned, this method will also save you a lot of time. Once all of the segments are acquired, you can easily scroll through a list of these segments and select which one you want to view (shown below). This list includes a time-tag of each of the segments which will give you insight into the frequency of each of the pulses. You can also view real-time and date information along the bottom of the screen, so you can see precisely when the pulse occurred. When using segmented memory for serial applications, the oscilloscope will automatically provide protocol decode for each of the captured packets.

 

 

Segmented memory can be especially helpful for many different applications, such as measuring an RF burst, decoding serial buses, finding glitches in repetitive signals, seeing the timing of single-shot events, the list goes on. This method gives you deeper insight in your design and helps you debug faster.

 

Want more detail? Check out these resources to understand how the segmented memory application works and how to set it up.

Segmented Memory Application Note

Using Segmented Memory for Serial Bus Applications

Let’s be honest, oscilloscopes aren’t exactly something you can just pick up and use without some sort of help or prior experience. Typically, it takes a bit of time and practice to understand how to use one correctly and make accurate measurements. We don’t want you wasting time trying to figure out how to use your oscilloscope – you should be able to spend your valuable time testing so you can get your designs to market faster. This means you need the right material that can quickly teach you how to use your scope. The Keysight Oscilloscopes team is constantly working to provide you with the materials you need, and expert help so you can spend more time characterizing your designs. We have a lot of resources for you, some of which you may not even know exist.

 

The Educators Training Kit

 

When I was learning how to use an oscilloscope as a young engineer, the resource I found to be most helpful is the Educator’s Training Kit. Don’t let the name fool you - this is not something that only applies to professors and students. It’s helpful for anyone who wants to learn how to use an oscilloscope. The Training Kit includes fifteen hands-on labs that walk you through how to use various features and applications. The labs range from basic concepts, such as triggering and probe compensation, to more advanced measurements such as capturing infrequent events, gated measurements, and using acquisition modes like peak detect. If you complete all of these labs and you still want more, you can also check out the Advanced Training Guide for your oscilloscope model. This guide starts out by reviewing basics, but also covers more advanced labs, including triggering on logic patterns and decoding serial buses. Most of these labs can be completed using the 11 built-in training signals that come with the Educator’s Training Kit, but some guides also include one or two labs that require you to build a very basic RLC circuit as your device under test (DUT). The kit also includes a slide-set on scope fundamentals so you can make sure you really understand the basics before diving into the hands-on labs. The Educators Training Kit is now a FREE option for all Keysight InfiniiVision oscilloscopes so you can learn more about how to properly use an oscilloscope without having to find extra money in the budget.

 

Built-in Help

 

Throw away that user’s manual! Well, maybe not - it could still come in handy. But seriously, everyone hates having to dig through a user’s manual just to figure out something like what one of the trigger options should be used for. There are so many different options and measurement types on an oscilloscope, including some you probably didn’t even know were there. For example, did you know you can get help in seconds right on the screen of your oscilloscope? If you don’t know what something is, just hold down the front panel key or menu button associated with it for a few seconds, and a built-in HELP screen will appear. These HELP screens provide quick information and set-up tips. Bye-bye, user’s manual.

 

Scope Tips from Experts

 

We’re here to help you. That means not only do we provide you with the most accurate test equipment on the market, but we are also available to help you use it. We are regularly posting new videos, blog posts, webcasts, and application notes to help you characterize your designs more easily.  

 

Our Oscilloscope YouTube channel has quick how-to videos, like the Keysight 2-Minute Guru series, along with detailed demonstrations, like Johnnie Hancock’s demo on NFC Testing. The Digital Design and Test Webcast Series is another free resource that offers live, one-hour presentations by some of our experts on various measurement techniques. If you don’t have time to watch the live stream during the workday, you can always watch (or re-watch) it on-demand at a time that works for you. Some of these recordings can also be found on our YouTube channel.

 

When the experts here aren’t working on new videos for you, they are spending their time writing up new blog posts and application notes. These blog posts are another quick way to learn about a topic, while application notes dive deep into the specifics of a certain measurement applications. The Oscilloscope Learning Center offers help on various topics such as scope basics, probing, and applications, and provides links to related videos and application notes for your convenience.


 

I know what you’re probably thinking right now, “Wow, those sound like great resources, but that’s a lot of websites to constantly be checking for new content.” To make your life easier, you can just like our Facebook page. Every time we post new content on all of those free resources I discussed, we usually post a link on our Facebook page as well. The Keysight Oscilloscope Facebook page is the perfect central place to stay up-to-date on all of the new content available.

 

BenchVue

 

BenchVue is a free software tool that can quickly and easily connect your Keysight instruments to your PC in seconds. You can use it to control your instruments remotely and analyze data from various tests. Not only is it a great extension of your oscilloscope’s functionality, but it also has a helpful education feature, the Library tab. The Library tab allows you to type in any Keysight product number and it will return any documentation it can find on that product such as a data sheet, application notes, video demos, user guides, etc.  This eliminates all of that time you would spend searching the web to find these documents and puts them in one convenient location for you.

 

I hope all of these resources prove to be helpful when learning how to use your oscilloscope. We will continue working hard to give you new content to help you in your testing. If you have any specific questions or content requests, just let us know in the comment section below.