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There are many cases where certain signals can cause your device to malfunction. This may be a problem your customer ends up finding if you don’t properly test during product development. Designers and test engineers frequently use an Arbitrary Waveform Generator (AWG) to simulate worst-case conditions during design verification. An AWG is the ideal tool for creating degraded or stressed signals to verify product performance limits. System or product noise susceptibility, timing problems, signal-level abnormalities, bandwidth loss, harmonic distortion, or a host of related maladies can be determined.

 

The AWG is a very powerful tool and can create waveforms or waveform bursts needed for your specific application. An AWG combines the capabilities of a function generator with that of a pulse generator, modulation source, noise generator, sweep generator, and trigger generator. It is a good tool for everyday use in the design lab or test environment. You can create custom solutions for a wide range of applications spanning many industries. AWG applications range from high dynamic range to high bandwidth output requirements.

 

 Arbitrary Waveform Generator (AWG) applications

Figure 1. Arbitrary Waveform Generator (AWG) applications.

 

Below is a list of common applications covered in this blog:

  • Radio Frequency (RF) signals
  • Radar signals
  • Environment signals
  • Coherent optical
  • Generic Orthogonal Frequency-Division Multiplexing (OFDM)
  • High-speed serial
  • Simulating real-world aberrations in 100Base-T physical layer
  • Dual Tone Multi-Frequency (DTMF)
  • Pacemaker
  • Automobile suspension testing
  • Power line testing

 

Radio Frequency (RF) Signals

Creating the signals required for RF conformance and margin testing is increasingly difficult. Digital RF technologies require wide-bandwidths and fast-changing signals that other generators cannot produce. These types of signals are seen in RF communications and ultra-wide band radio applications.

 

Radar Signals

Radar signals demand AWG-level performance in terms of sample rate, dynamic range, and memory. AWGs can oversample the signal in instances where phase and amplitude quadrature signal generation is desired. This improves signal quality, creating a spurious free dynamic output. AWG’s also provide Linear Frequency Modulation (LFM), Barker and Polyphase codes, step FM, and nonlinear FM modulation signals. They also generate pulse trains to resolve:

  • Range and doppler shift ambiguity
  • Frequency hopping for electronic counter-counter measures
  • Pulse-to-pulse amplitude variation

 

Environment Signals

Radar signals must coexist with commercial signals and not affect each other. Use your AWG to thoroughly test all the corner case issues at the design or debug stage. An AWG can be programmed to output many industry-standard signals:

  • WiMAX
  • WIFI
  • GSM
  • GSM-EDGE
  • EGPRS-2A
  • EGPRS2B
  • CDMA
  • WCDMA
  • DVB-T
  • Noise
  • CW radar

 

You can also define the carrier frequency, power, start time, and duration of these signals. This allows control of the level of signal interaction or interference.

 

Coherent Optical

Today's web driven world is pushing the demand for high-speed short and long haul coherent optical solutions. Phase modulation, high baud rate, high sample rate, high bandwidth, and high resolution are all critical to optical applications. Multiple synchronized AWGs can be used to generate many desired coherent optical signals.

 

Generic Orthogonal Frequency-Division Multiplexing (OFDM)

OFDM has become the modulation method of choice for transmitting large amounts of digital data over short and medium distances. Wide bandwidths and multiple carriers are needed to test RF receivers in today’s wireless world. AWG OFDM packets can specifying the spacing between the symbols or frames or stressed by adding gated noise.

 

High-speed Serial

Serial signals are made of binary data (simple ones and zeros). These signals have begun to look more like analog waveforms with analog events embedded in the digital data. The textbook zero-rise time and flat top of the theoretical square wave no longer represent reality. Today’s serial communication environments are negatively impacted by noise, jitter, crosstalk, distributed reactances, and power supply variations. Your arbitrary waveform generator can create all these signals!

 

Using direct synthesis techniques, AWGs can simulate the effects of propagation through a transmission line.

 

 

Rise times, pulse shapes, delays, and aberrations can all be controlled by your AWG. You can also create a variety of digital data impairments such as jitter (random, periodic, sinusoidal), noise, pre/de-emphasis, duty cycle distortion, inter-symbol interference, duty cycle distortion, and spread spectrum clocking.

 

Simulating Real-World Aberrations in 100Base-T Physical Layer

To simulate physical layer test signals for 100Base-T transceivers, your AWG will create several analog parameters:

  • Undershoot and overshoot
  • Rise and fall time
  • Ringing
  • Amplitude variations
  • Specific timing variations such as jitter

 

AWGs provide an efficient method for generating signal impairments like these for testing product margins.

 

Dual Tone Multi-Frequency (DTMF)

Touch-tone signals on push button telephones are created by combining a low frequency and a high-frequency signal. Simulating the superimposed frequencies creates a special challenge if the frequencies are not harmonically related. An arbitrary waveform generator can generate these signals along with controlled levels of noise and harmonic content.

 

Pacemaker

A simple square wave or sine-wave pulse was used to test pacemakers in the past. Today’s AWGs can create a simulated heartbeat waveform that pacemakers are designed to detect.

The arbitrary waveform generator can customize pacemaker testing for particular heart rate types.

 

Automobile Suspension Testing

An AWG can simulate automobile sensor outputs just as a car would when it hits a bump. The suspension’s response and reliability can be tested under virtually any simulated road condition because the size of the “bumps” can be precisely controlled.

 

Power Line Testing

Multichannel AWGs can simulate three-phase power. Transients or glitches can be created to simulated problematic waveforms. For example, you could simulate a transient on one phase and signal dropout on another.

 

In addition to all the applications above, there are many more across several different industries, and the arbitrary waveform generator will support them all:

  • Sequencing and deep memory
  • Creating long scenario simulations
  • Leading edge physics, chemistry, and electronics research
  • Validation and compliance testing of high-speed silicon and communications devices
  • Stressing testing receivers with a wide array of signal impairments
  • Generating high Baud rate baseband signals with higher order, complex modulation
  • Radar, satellite, electronic warfare, and multilevel signals
  • Jitter margin testing for analog-to-digital converters

 

Conclusion

We have now covered the importance of an arbitrary waveform generator to ensure your device is working properly for your specific application. As you can see, AWGs excel in creating mixed-signal waveforms that can mimic real world conditions. To learn more about arbitrary waveform generators, check out: A High-Performance AWG Primer.

If you are using an oscilloscope, make sure you are using the right bandwidth! Choosing the wrong amount could adversely affect your measurement results. Let’s look at what oscilloscope bandwidth is and why you need just the right amount. 

 

What is Bandwidth?

 

Bandwidth is often regarded as the single most important characteristic of an oscilloscope. Measured in Hertz, the bandwidth of your oscilloscope is the range of frequencies that your oscilloscope can accurately measure. Without enough bandwidth, the amplitude of your signal will be incorrect and details of your waveform might be lost. With too much bandwidth, you will capture excessive noise, providing you with an inaccurate measurement. Here’s why: 

 

You can think of an oscilloscope like a low pass filter, meaning it will only pass frequencies from 0 Hz up to a specified frequency. An oscilloscope’s bandwidth is specified as the 3 dB down point of the filter. What the heck is a 3 dB down point? Read on. 

 

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

 

Low pass filters allow signals to pass through them at full amplitude until the signal frequency approaches the high end of the frequencies that the filter can pass. Then a filter attenuates signals passing through them until the signal’s amplitude is dampened to nothing. When the signal is attenuated by three decibels (3 dB), that is the cutoff point for an oscilloscope’s bandwidth specification. If you aren’t familiar with decibels, the 3 dB down point is when the amplitude of a sine wave is 70.7% of its actual height. Look at the diagram below to visualize the frequency response of a low pass filter, depicted in blue.

 

Oscilloscope bandwidth: Frequency response of a low pass filter, depicting the 3 db down point and cutoff frequency.

Figure 1. Frequency response of a low pass filter, depicting the 3 dB down point and cutoff frequency.

 

So, if you have an oscilloscope that has a bandwidth of 200 MHz, you know that the cutoff frequency of that oscilloscope’s filter is 200 MHz. Why does this matter for your measurements? 

 

Too Little Bandwidth

 

You can see from Figure 1 that if you are measuring a signal that has a higher frequency than the cutoff frequency, you’ll either see an attenuated and distorted version of your signal or not much of a signal at all. Even measuring a signal as fast as the bandwidth of the scope is not a good idea. Measuring a 200 MHz signal on a 200 MHz oscilloscope will not provide you with the best representation of your signal, as the filter has already begun to roll off and distort your input.

 

Measuring with too little bandwidth will provide distorted results

 

Here is the rule of thumb for choosing the right bandwidth:

  • Digital signal measurements: five times higher bandwidth than the fastest digital clock rate in your system
  • Analog signal measurements: three times higher bandwidth than the maximum signal frequency on an oscilloscope with a flat frequency response

 

For more detail on these rules, read Evaluating Oscilloscope Bandwidths for Your Application.

 

So why not just use an oscilloscope with the highest bandwidth possible?

 

Too Much Bandwidth

 

Oscilloscopes can capture environmental noise. Oscilloscopes also add noise to your signal from filtering, processing, and digitizing (though a high-quality oscilloscope will do all of this properly and add less noise than a poorly-designed scope). And noise occurs at all frequencies. So if you have a 200 MHz oscilloscope, that scope is only going to show noise up to 200 MHz. But, if you have a 33 GHz oscilloscope, it will add noise to your measurement through its entire measurement range up to 33 GHz, regardless of the frequency of your signal. 

 

Increasing bandwidth increases noise

 

If you want to measure a 50 MHz signal, a 200 MHz oscilloscope will give you plenty of bandwidth to clearly display your signal without attenuation and filter distortion but not so much that it adds high frequency noise content to your measurement.

 

Insider tip: If all you have access to is a high bandwidth oscilloscope, but you are measuring low frequencies, turn on hardware filters in the oscilloscope to eliminate that high frequency noise and get a cleaner measurement.

 

The other reason why you probably don’t want to buy the highest bandwidth oscilloscope out there is price. The higher the bandwidth, the higher the price. If you are worried the bandwidth you need today will not be enough for future measurements, look for an oscilloscope that lets you upgrade the bandwidth with a software license. That way you can buy the bandwidth you need now and upgrade later without having to purchase a new oscilloscope or send it in to the factory for a hardware update. (Most Keysight oscilloscopes can be bandwidth upgraded with a software license for this very reason.)

 

Demonstration

 

Don’t be afraid to be the Goldilocks of bandwidth. Did she settle for the porridge that was too hot or too cold? No. She went for the one that was just right. And lucky for us, we won’t be eaten by bears if we set our bandwidth to just the right amount. Here is an example of how even a simple sine wave can be falsely represented on an oscilloscope without the right bandwidth.

 

In this demonstration, I am measuring a sine wave oscillating with a frequency of 80 MHz and a peak-peak voltage of about 2 volts.

 

Oscilloscope bandwidth: Measuring a sine wave oscillating with a frequency of 80 MHz and a peak-peak voltage of about 2 volts

 

I am using an 8 GHz oscilloscope. This is an excessive amount of bandwidth for an 80 MHz signal. The rule of thumb for analog signals is to use about 3 times the frequency of the signal. While this measurement doesn’t look horrible, let’s see how much better it can get when I apply the rule of thumb.

 

With only 240 MHz of bandwidth, look at how much cleaner my measurement is.

 

Oscilloscope bandwidth: Clean measurement with only 240 MHz of bandwidth

 

If I just want a quick check on the basics like voltage and frequency, the difference might not be crucial. But if I’m proving the quality of my design or attempting to pass strict performance or compliance specs, I would want the best (and cleanest) representation of my signal.

 

Now, I’ll decrease the bandwidth even further. As I mentioned earlier, you shouldn’t measure a signal at the bandwidth of the oscilloscope. The signal will be passing right through the 3 dB down point of the filter.

 

Oscilloscope bandwidth: Bandwidth decreased further

 

Here I’m measuring my 80 MHz signal with 80 MHz of bandwidth. You can see that the voltage is decreased from 1.92 V to 1.36 V. This is 70.8% of the voltage we should be seeing. The signal is attenuated by the filter. 

 

To demonstrate the effects of the filter above the cutoff frequency, here is my measurement of the same signal with only 75 MHz of bandwidth. The signal is attenuated even further to 161 mV. The period of my measured signal is displayed as 12.74 ns. This would imply that the frequency of my signal is only 78 MHz, which we know to be false.

 

Oscilloscope bandwidth: Measure the same signal with only 75 MHz of bandwidth

 

And here I’ve measured the same signal again with only 70 MHz of bandwidth. It barely looks like there is a signal at all.

 

Oscilloscope bandwidth: Measured same signal with only 70 MHz of bandwidth

 

You can see how dramatically the signal is attenuated when you try to measure a signal with frequency beyond the bandwidth of the oscilloscope.

 

Summary

 

Bandwidth is the most important characteristic of an oscilloscope

 

While there are many important features of an oscilloscope that you’ll need to evaluate before choosing one for your measurements, clearly bandwidth is the number one spec that you must check before any other. If you don’t have enough bandwidth you’ll see distorted or attenuated signals, giving you inaccurate measurements. If you have too much bandwidth, your measurements will be noisier than necessary. You have to choose a bandwidth that can support a clean and accurate representation of your test signals.

 

Now that you understand why bandwidth is the most important characteristic of an oscilloscope, check out Basic Oscilloscope Fundamentals to learn the other important oscilloscope characteristics and how to use an oscilloscope.

 

Picture the heart rate monitor that you always see next to hospital beds on “House” or “Grey’s Anatomy.” You hold your breath as you wait for the next beep and jump of the line on the screen, and you dread the flat line as the TV show reaches its apex.


Well, when my family asks me what I do for a living, this is how I describe an oscilloscope. But instead of displaying the signal of a human heart, oscilloscopes show the heartbeat of electronic devices. They give us all kinds of insights into whether or not an electronic device is operating correctly, allowing us to check its vitals.

 

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


The vitals of our devices could be voltage or current. And just like we don’t want our hearts to beat too fast or too slow, we want those voltages to oscillate at the right pace or frequency. We all know heart murmurs are bad. Well, we don’t want any glitches in our electrical signals either, and an oscilloscope can help us find them. Having insights like this into your electronic devices allows you to validate it is operating as expected. And if it’s not, oscilloscopes help you diagnose the problem and correct it. If you are an electrical engineer, chances are you could use an oscilloscope ─ whether you’re a test engineer or student or work in manufacturing, repair, research, or development.

1000 X Series Oscilloscopes1000 X-Series oscilloscopes making a variety of measurements.

 

Oscilloscope Basics

The basic operation of an oscilloscope displays voltage versus time, with voltage on the vertical axis and time on the horizontal axis. This allows you to double check that your device’s signal is as you expect, both in magnitude and frequency. And because oscilloscopes provide a visual representation of the signal, you can view any anomalies or distortion that might be occurring. But before you start testing, there are some things for you to consider.

 

Oscilloscope displayOscilloscopes display voltage on the vertical axis and time on the horizontal axis.

 

Oscilloscopes come in many flavors. You want to select an oscilloscope with the right bandwidth, signal integrity, sample rate, and channel inputs. You also want to make sure it is compatible with any applications and probes you may need. Here is a list of some of the features you should check when deciding what oscilloscope to use:

 

  • Bandwidth – The range of frequencies the oscilloscope can measure accurately. Oscilloscope bandwidths typically range from 50 MHz to 100 GHz.
  • Sample Rate – The number of samples the oscilloscope can acquire per second. The greater the samples per second, the more clearly and accurately the waveform is displayed.
  • Signal Integrity – The oscilloscope’s ability to represent the waveform accurately. This is a topic I’m particularly passionate about and you’ll find me writing about this a lot. You wouldn’t want a heart rate monitor that displays incorrect information. It would do no good to declare a patient dead whose heart is still beating. The same is true for your device under test. You wouldn’t want to declare your device is malfunctioning and spend weeks trying to find the root cause when there isn’t actually a problem.
  • Channels – The input to the oscilloscope. They can be analog or digital. There are typically 2 to 4 analog channels per oscilloscope.
  • Probe Compatibility – A probe is the tool used connect the oscilloscope to your device under test. There are a large variety of passive and active probes, each made for specific use cases. You want an oscilloscope that is compatible with the type of probe you need for your specific tests.
  • Applications – Signal analysis, protocol decode, and compliance test software can greatly reduce the time it takes to identify and capture errors in your designs. Analysis software can help you find and evaluate jitter, perform Fourier transforms, create eye diagrams, and even identify and quantify crosstalk. Protocol decoding software can identify digital packets of information, trigger on different packet conditions, and identify protocol errors. Not all oscilloscopes are compatible with every application.

 

What are Oscilloscopes Used for?

Now that you’re armed with the lingo, you’re ready to get going. The most basic testing only requires an oscilloscope with 50 to 200 MHz of bandwidth, a passive probe, and sufficient sample rate, signal integrity, and channel inputs.


Armed with these basics, you can spot-check your printed circuit boards (PCBs) to find faulty parts, noisy power lines, shorts, and I/Os (inputs and outputs) that are not working; dive into different trigger modes to search for runts, glitches, and timing errors; and capture signals and data to prove the quality of your designs. Some basic oscilloscopes even provide Bode or frequency and phase response analysis. And this is just the start.

 

Frequency response analysis on InfiniiVision oscilloscopeFrequency response analysis performed on an InfiniiVision oscilloscope.

 

Oscilloscopes are versatile and widely used instruments. Automotive technicians use oscilloscopes to diagnose electrical problems in cars. University labs use oscilloscopes to teach students about electronics. Research groups all over the world have oscilloscopes at their disposal. Cell phone manufacturers use oscilloscopes to test the integrity of their signals. The military and aviation industries use oscilloscopes to test radar communication systems. R&D engineers use oscilloscopes to test and design new technologies. Oscilloscopes are also used for compliance testing such as USB and CAN protocols where the output must meet certain standards.

 

Get Started

Now that you know what an oscilloscope is and some of the crucial oscilloscope specs, it’s time to get testing. So throw on your scrubs (or maybe an ESD strap instead) and get started!


To learn more about how to operate an oscilloscope and understand measurement fundamentals, you can read the Basic Oscilloscope Fundamentals application note.

 

Quick note: We usually post oscilloscope tips and tricks to this blog, but today we want to share with you about another test & measurement tool often used with or alongside scopes.

 

In my previous post, I outlined the different types of signal generators in the market today, and what you need to consider when selecting the right fit for your application. I also highlighted why the arbitrary waveform generator (AWG) is my recommendation for you to simulate real world stimulus.

 

Arbitrary waveform generators (AWGs) are the most versatile signal generators available. An AWG can generate any mathematically-characterized signal, including sine wave, pulse, modulated, multitone, polarized, and rotated signals. The AWG is commonly seen as the workhorse piece of test equipment and can perform the functions of any other generator type. A typical block diagram of an AWG is shown below. The signal flow through the functional blocks starts with a numeric description of a waveform stored in memory. Then the selected waveform samples are sent to a digital-to-analog converter (DAC), filtered, conditioned, amplified and output as an analog waveform.

 

Diagram of a common Arbitrary Waveform GeneratorA common AWG block diagram

 

 

A Closer Look at Each Arbitrary Waveform Generator (AWG) Functional Block

 

1. Memory

A digital representation of a waveform is loaded into AWG memory through a variety of software applications, such as MATLAB, LabView, Visual Studio Plus, IVI, and SCPI. The memory is clocked at the highest sampling rate supported by the AWG. The size of the memory will dictate the amount of signal playback time available. A rule of thumb to determine the playback time is: memory depth divided by sample rate equals playback time. The faster your sample rate, the quicker you will use up the available memory.

 

2. Sequencer

The sequencer circuitry can solve memory depth limitations by arranging (sequencing) the waveform into segments to create your desired waveform. Memory sequencing (or memory ping-pong) does this by only enabling memory during critical waveform portions and then shutting off. You can think about it like this: when recording a round of golf, imagine how much recording time you would save if you only recorded the players striking the ball and not all the walking and setup time. The sequencer does the same thing by only recording waveform transitions and not idle time. Synchronization is maintained by the trigger generator, which enables the waveform. Trigger events can be internal, external, or linked to another AWG.


3. Markers and Triggers

Marker outputs are useful for triggering external equipment. Trigger inputs are used to alter sequencer operation, resulting in the desired waveform entering the DAC. Hardware or software triggers can be used for applications requiring exact timing, like wideband chirp signals. They can also be used where multiple AWGs are synchronized together and need to be triggered simultaneously.

 

4. Clock Generator

The timing of the waveform is controlled by an internal or external clock source. The memory controller keeps track of waveform events in memory and then outputs them in the correct order to the DAC. The memory controller saves space by looping on repetitive elements so that the elements are listed only once in the waveform memory. Clocking circuitry controls both the DAC and the sequencer.

 

5. Digital-to-Analog Converter (DAC)

Waveform memory contents are sent to the DAC. Here the digital voltage values are converted into analog voltages. The number of bits within the DAC will impact the AWG’s vertical resolution. The higher the number of bits, the higher the vertical resolution and the more detailed the output waveform will be. DACs can use interpolation to reach an even higher update rate than what was supplied by the waveform memory.

 

6. Low Pass Filter

Because the DAC output is a series of voltage stair steps, it is harmonic-rich and requires filtering for a smooth sinusoidal analog waveform.

 

7. Output Amplifier

After the signal passes through the filter, it will enter an amplifier. The amplifier controls both gain and offset. This gives you the flexibility to adjust output gain and offset depending on your application. For example, you may need high dynamic ranges for radar and satellite solutions or high bandwidth for high-speed and coherent optical solutions.

 

Use this blog’s functional building blocks to help you understand just what is happening within your AWG and fully utilize the AWG’s capabilities. For a deeper understanding of arbitrary waveform generator fundamentals, I recommend that you download the comprehensive "Fundamentals of Arbitrary Waveform Generation" guide. 

 

Takeaway and the Demands of Our Connected World

Image of a connected worldInternet technologies have driven advanced AWG solutions

 

Our connected world demands increased speed and data complexity. To support this demand, today’s AWGs must:

  • Reach higher frequencies while providing wider bandwidth
  • Handle complex modulation techniques that cram more data into available bandwidths
  • Work with ideal and real-world signals
  • Generate signals that stress devices to their limits
  • Provide reliable and repeatable results

 

More on this topic in my posts to come. 

Quick note: We usually post oscilloscope tips and tricks to this blog, but today we want to share with you about another test & measurement tool often used with or alongside scopes.

 

To develop or test your electronic design, you need to stress it beyond its real-world application. This will insure your device will operate flawlessly for your customers. In some cases, you may find real world stimuli, but most of the time you will need to use instrumentation.

 

Figure shows the stimulus test model with instrumentation to simulate real-world application

Figure 1. The stimulus test model

 

The instrumentation needed to develop and test today’s technologies has grown into many signal generator types over the years. The most popular signal generators provided by test and measurement manufacturers are:

  • Function Generators
  • RF Generators
  • Pulse and Pattern Generators
  • Arbitrary Waveform Generators (AWG)

There are many generators types out there, so choose yours wisely.

 

Function generators

These are the most well-known and cost-effective signal generators. But, they can only provide a limited set of waveforms such as sine, square, and triangle. They are designed to be very easy to use for simple waveforms with limited memory. You can also adjust the generator’s frequency, offset and other output variables as well as the types of modulation.

Function generators are a good general-purpose source. Use function generators when you need a stable and repeatable stimulus signal. You can use them in applications requiring only periodic waveforms such as stimulus response testing, filter characterization and clock source simulation. Some of the more modern function generators are even capable of generating simple AWG waveforms.

 

Radio Frequency Signal Generators (RF Signal Generators)

RF signal generators produce continuous wave tones with variable output power levels. RF generator outputs typically range from a few kHz to 6 GHz while microwave signal generators cover from 1 MHz to 20 GHz. Use them to service radio receivers and other RF applications. Keep in mind that there are many types and sub categories of these generators, and Keysight provides solutions from 9 kHz all the way up to 25 GHz.

 

Pulse Generators and Pattern Generators

Pulse generators and pattern generators have an advantage over function generators because the output repetition rate and pulse widths can be varied. Their internal circuits may be digital, analog, or a combination of both in order to create the desired outputs. The benefits of direct digital synthesis yield precise frequencies. Use them when working on digital circuits, whereas you should use a function generator primarily for analog circuits.

 

Arbitrary Waveform Generators (AWGs)

An arbitrary waveform generator (AWG) can create all the repetitive waveforms that the three generators above can provide. Plus, an AWG can provide single shot pulses and interpolate between defined points. This is helpful when you need to create triangular waveforms. By harnessing the power and versatility of an AWG’s digital signal processing techniques, you can create whatever signals you need to fully exercise your device under test. With this flexibility, you can either confirm proper operation or pinpoint faults within your system. Basically, with your AWG you can create custom solutions for a wide range of applications.

 

Image of Keysight M8195A Arbitrary Waveform Generator

Figure 2. M8195A Keysight AWG

 

Below is another view of the diverse generator market :-

Signal sourceCharacteristicsWave shape
RF Signal GeneratorsCW (continuous wave) sinusoidal signals over a broad range of frequencies. Modulation types include amplitude, frequency, phase and pulse modulation. May include the ability to sweep the output frequency over a user-set range for frequency response testing.Sine
Modulated sine
Swept sine
Vector Signal GeneratorsDigitally-modulated RF signals that may use any of a large number of digital modulation formats such as QAM, QPSK, FSK, BPSK, and OFDM.Sine
Modulated sine
Pulse GeneratorsPulse waveforms or square waves. Used for testing digital and pulsed systems.Rectangular pulse
Data or Data Pattern GeneratorsMultiple logic signals (i.e. logic 1s and 0s) used as a stimulus source for functional validation and testing of digital circuits and systems.Rectangular pulse
Function GeneratorsSimple repetitive waveforms like sine wave, saw tooth, step (pulse), square, and triangular. May include a modulation function such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM).Sine
Rectangular pulse
Square wave
Triangle
Ramp/saw tooth
Modulated waveforms
Noise
Arbitrary Waveform Generator (AWG)Digitally-based signal source generating any waveform, within published limits of bandwidth, frequency range, accuracy, and output level.All the above

 

Use your AWG to simulate real world stimulus

In many scenarios, you need real-world, non-repetitive stimulus to fully test your product. To do this, you need an AWG. In addition, you want to simulate the real-world signals early in the development cycle and fully test the robustness of your designs. An AWG allows you to do this and catch any intermittent or inherent design issues quickly and efficiently. This results in less revisions and gets products to market quicker.

 

Once the desired waveform is loaded into the AWG’s memory, it can be used to generate an output waveform. You can then adjust your frequency, amplitude, and DC offset and use tools such as triggering, gating, bursts, and modulation to further customize your stimuli. The advanced stimulus created by your AWG allows you to verify product performance limits under worst case conditions. Because of this, the applications for AWGs span virtually all industries.

 

What kind of signal generator do you need? Function, RF, Pulse or AWG? For real-world, non-repetitive stimuli creation, look to a function or arbitrary waveform generator. To fully utilize your AWG, you should have a basic understanding of the instrument's controls, features, and operating modes. To learn more about AWGs, download the “Fundamentals of Arbitrary Waveform Generation” guide.

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.

 

Enter now for free giveaways worth up to $44,000!

Keysight is launching Wave 2018, a first-of-its kind event created to connect you with our experts! Join us March 1-16 to learn helpful tips, discuss the latest ideas, and explore new advances in the industry via daily videos, exclusive content, and live Q&As. Plus, you can register for daily bench and RF giveaways worth up to $44,000! You won’t want to miss a minute of this event – or your chance to win. You can register now for a free early entry, and mark your calendar for March 1 when we’ll kick off Wave 2018 with a live stream. Get ready to discover an entire Keysight community focused on helping you become an engineering legend!

Enter Now button

 

Don’t leave it to chance!

Enter Keysight’s Test to Impress contest during Wave 2018 for even more ways to win. Simply submit a short video on why you need test and measurement equipment, and our panel of judges will be awarding one grand prize winner, who will get a bench or RF bundle prize of their choice, and four runner-up winners, who will get a DSOX1102G InfiniiVision 1000 X-Series oscilloscope. Want to see example entries? Check out the 2017 Test to Impress entries playlist.

Test to Impress 2017 Entries

 

What happened to Scope Month?

Wave 2018 is the next evolution of Keysight’s Scope Month, a 2016/2017 month-long oscilloscope-focused event that also featured measurement tips and giveaways. During Wave 2018 you’ll have access to helpful content beyond just oscilloscopes. Learn tips and tricks that will help you master all of the test and measurement tools on your bench. Scope Month had drawings for single oscilloscopes, but during Wave 2018 you could win giveaway bundles that include oscilloscopes, waveform generators, power supplies, digital multimeters, microwave analyzers, and more!

Wave 2018 Giveaway Bundles

 

While you wait for Wave 2018 to begin...

we have other useful resources to help you with your measurement challenges:

Keysight Bench Facebook Page – Don’t miss out on information about Wave 2018 and other events by following us on social.

Keysight RF Test & Measurement Facebook Page – Keep up with the latest RF/microwave news and content

Keysight Lab’s YouTube Channel – Get a steady stream of how-to videos by subscribing to our YouTube channel.

“EEs Talk Tech” Electrical Engineering Podcast – Join Mike and Daniel as they cover a broad range of topics from the basics of electrical engineering to the tough engineering problems of tomorrow’s technologies.

Keysight Oscilloscopes Blog – Follow for the latest industry news, measurement tips and advice from Keysight oscilloscope experts.

Keysight General Electronics Measurement Blog – Follow for more information about Keysight solutions, new applications, measurement tips, and industry trends.

Keysight RF Test Blog – Follow to learn how to improve your RF test measurements.

*The specifics around this event are subject to change. View the latest information at www.wavekeysight.com

The internet got all kinds of angry at Apple recently. It turns out, Apple slows down the processor’s clock frequency on older iPhones. The internet took this as an opportunity to jump on “Evil Apple” for what it perceived as a marketing ploy to get people to upgrade.

But, the internet was wrong.

 

As it turns out, this was simply a case of good engineering by Apple’s engineers.

To understand why they would slow down the processor speed of old phones, you have to understand how lithium ion batteries work and have a basic understanding of processors.

Let’s start by taking a look at lithium ion battery technology.

Lithium Ion Battery Technology

Mobile devices use lithium ion batteries primarily because of their incredible energy density. They provide a lot of power and don’t take up much space.

We all want a battery that lasts a week. That is, until we have to carry it. Engineers must find a sweet spot somewhere between device usability and eternal battery life (known as “battery heaven”).

To understand Apple’s problem, you need to understand how lithium ion batteries (LIB) work. LIBs use a chemical reaction in which the anode (lithium-doped cobalt oxide) passes lithium ions to the cathode (graphite) through a special barrier. The ions, using an electrolyte as a conductor, can pass through this barrier. Electrons cannot, and therefore get provided to the circuit. Note the electrons in the half-reactions for the cathode and anode:

 

Figure 1.  Cathode half-reaction

 Figure 1.  Cathode half-reaction

 

Figure 2.  Anode half-reaction

Figure 2. Anode half-reaction

 

If there’s a path for the electrons, the chemical reaction will take place. If there’s not, the battery hangs in a balanced state and holds its charge.

But there’s a catch. LIBs age. A test from Battery University showed that LIBs experience a capacity drop of up to 20% after 250 charge cycles.

Not only do LIBs lose capacity, but they also lose the ability to generate high levels of current. The current production capability of an LIB is proportional to how fast its chemical reaction takes place. The faster the reaction, the higher the current.

When choosing a battery for your product, one spec you should consider is the current production capability. Typically, you know your required currents, so this is an easy call. Choose a battery that will give you enough current to power your design and enough extra headroom to be comfortable. But what happens a few years down the road? Your battery’s performance will degrade, but your device will still need the same amount of power.

The environment also takes a toll on LIBs. Like any proper chemical reaction, temperature is a factor. The colder an LIB, the slower the chemical reaction, the lower the peak current. Couple this with an old, degraded battery and you’re in for some trouble.

Eventually, you’re going to run out of extra power-generation capability. This is the problem Apple’s facing. Their older-model iPhones still require the same power that they did on day one, but their batteries aren’t holding up.

Now, Apple is slowing down your phone! Why? It’s actually for your own good. The reasoning comes down to how processors work.

Processors Need Power

Basically, processors are just an intelligently organized collection of transistors. When combined, they make up logic gates that form the core of modern processing (no pun intended). For gates to function properly, they need power. If a gate doesn’t get enough power, it’ll still work; it’ll just operate more slowly.

 

Figure 3. Low supply voltages mean increased propagation delay!

Figure 3.  Low supply voltages mean increased propagation delay!

 

Heavy processing tasks require a lot of power, and mobile devices are designed to handle this load. But what happens if a device’s battery is degraded to the point that it can’t provide enough power?

Without sufficient power to the processor, the gates won’t operate as fast. Put simply, their propagation delay increases. Processors operate expecting a certain propagation delay. The timing of its operations depend on logic blocks making decisions within an expected number of clock cycles. Low power to a processor slows down logic blocks.

Then things break.

Then what? If you have a well-designed device, it’ll realize there’s an issue and simply perform an emergency shutdown. If your device isn’t so well designed, the electronics can be damaged.

Don’t take it from me, Apple says as much in their statement on this matter:

"Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices. Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components.

Last year we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions. We've now extended that feature to iPhone 7 with iOS 11.2, and plan to add support for other products in the future."

So, what are Apple engineers actually doing to “prolong the life of their devices?” They’re slowing down the CPU frequency if the phone detects an insufficient battery voltage.

An iPhone owner on Twitter documented their iPhone 6’s CPU jumping from 600 MHz up to 1400 MHz after a battery replacement.

 

How iPhones Deal with Old Batteries

Apple is attacking this issue on two fronts.

The first is clear from the Twitter example – a slow down of the phone’s CPU frequency. The old battery’s lower power capability means a larger propagation delay in the processor. Slowing the CPU frequency ensures that there’s enough buffer time to cover a non-ideal propagation delay.

The second is addressed in Apple’s statement. Apple’s engineers are spreading out processor-heavy clock cycles to minimize the required battery power.

 

What Can You Do About It?

How do you avoid experiencing phone slow down?

First, take care of your battery. Don’t let it get too hot, especially if it’s fully charged. Also, don’t use off-brand chargers. A lower charging voltage is proven to prolong battery life, but it also takes longer to charge.

Second, expect to get a new battery every 350-500 charge cycles. They are not that expensive compared to a new device, and they can massively improve processing performance.

If you’re designing devices that use LIB, your users’ experience can hinge on battery management.

 

Make sure to have proper air flow around the battery. Also, think about whether or not the battery should be user-serviceable. Plan for battery degradation when selecting a battery and designing battery management circuitry.

 

Figure 4.  Design with battery limitations in mind!

Figure 4.  Design with battery limitations in mind!

 

It Seems Apple Isn’t Evil

Though some people may wish it were true, this wasn’t an evil corporate marketing scheme. It’s just good engineering. A closer look at processor basics and lithium ion battery technology shows that Apple is simply doing what they have to do to improve their users’ uptime – a noble goal.

I’d love to hear your thoughts on the issue. Let me know on Twitter(@Keysight_Daniel), the Keysight Bench Facebook page, or the Keysight Labs YouTube channel!

Good news! We're extending the end date for the Infiniium S-Series oscilloscope promotion, "Your Scope. Your Way." to March 31, 2018. 

S-Series Oscilloscope

The S-Series oscilloscopes (500 MHz to 8 GHz) provide you with unmatched measurement accuracy with the best signal integrity and most comprehensive measurement software for signal analysis, compliance, and protocol analysis. With "Your Scope. Your Way." promotion, you can choose ANY ONE of the following value-add offers with each S-Series oscilloscope purchase – at no additional cost:

 

Offer #1:  Get the new N8888A Infiniium Protocol Decode Software Bundle for free (supports 32 protocols)

I2C

eSPI

PCIe Gen 1Ethernet 10BaseTSVIDFlexRayUSB 2.0

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LIN

Ethernet 100BaseTXCANUFSUSB 3.1 Gen 1

USB 3.0 SuperSpeed Inter-Chip (SSIC)

RS232/UART

SASARNIC 429JTAGCAN-FDSPMI

SATA

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MIPI I3CMIPI RFFEMIPI UniProMIPI LLIMIPI D-PHYMIPI CSI-3

MIPI DigRF v4

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Offer #2:  Get two N2796A 2 GHz single-ended active probes for free

N2796A 2GHz single-ended active probe

 

Offer #3:  Get 400 Mpts/channel memory for free (DSOS000-400)

 

Offer details and T&C can be found here: www.keysight.com/find/yourscopeyourway. Promotion ends March 31, 2018 so hurry!

Sniffing the air

Dogs do it all the time. But there is much more in the air than just smells. There are RF signals of all kinds all around us. How do we 'sniff' these signals out of the air so that we can observe them on an oscilloscope?

Sniffing where you can’t probe

Probing electrical voltage signals in a circuit is typically achieved using an active or passive voltage probe. If you need to measure current, most engineers use a clamp-on Hall-effect current probe that converts the magnetic field around a conductor, created by the current flowing through it, into voltage. But what if you need to monitor and verify RF signals between two sealed devices (nothing to probe), such as signals transmitted from your key fob to the receiver in the car? Or perhaps Near Field Communication (NFC) signals between your mobile phone (transmitter) and a tag (receiver)? For this you can use a RF loop antenna — sometimes called “sniffers”.

 

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

 

Although RF loop antennas are typically used for spectrum analysis measurements, they can also be used for oscilloscope measurements. Loop antennas come in various sizes and are typically tuned for specific ranges of frequencies. In this post, I’m going to show you very briefly how you can capture key fob signals using a small RF loop antenna, based on amplitude shift-keying (ASK) modulation with a carrier frequency of 434 MHz. Detailed resources are listed at the bottom of this post.

RF_loop_antenna

Figure 1. A typical RF loop antenna

 

Sniffing and decoding automotive key fob RF signals

So, which oscilloscope would you need for the application? Since the carrier frequency in this measurement application is 434 MHz, I’ve used a 1.0 GHz bandwidth Keysight InfiniiVision X-Series oscilloscope (DSOX3104T). In brief, the steps to decode RF signals from an automotive key fob with a scope includes:

  1. Connecting the loop antenna to the scope’s Channel 1 input, terminated into 50
  2. Positioning the loop antenna near the key fob while one of its buttons is pressed to capture the single-shot burst of RF-modulated data packets (channel-1, yellow trace shown in Figure 2)
  3. As decoding the RF-bursted packets requires demodulation prior to digital decoding, you’ll also need to setup the scope to digitally demodulate the signal (hardware-based within the scope, channel-2, green trace shown in Figure 2)
  4. Decoding the digitally demodulated waveform. This can be achieved with the oscilloscope’s user-definable NRZ/Manchester trigger and decode option. Figure 2 shows the Manchester-decoded bits at the bottom of the trace display
  5. Screen display of the Keysight DSOX3104T scope

Figure 2. Screen display of the Keysight DSOX3104T oscilloscope that displays the captured single-shot burst RF-modulated signal (yellow trace), demodulated signal (green trace) and Manchester-decoded bits

 

Sniffing Near Field Communication (NFC) signals from a mobile phone

In Figure 3, I’m showing you the setup for how you can capture NFC signals generated by a mobile phone, using a larger PC trace loop antenna. Since the carrier frequency in this case is just 13.56 MHz, a 100-MHz bandwidth oscilloscope is sufficient for the measurement application.

 Capturing NFC signal from mobile phone

Figure 3. Setup to capture NFC signals from a mobile phone with a PC trace loop antenna and a 100-MHz bandwidth oscilloscope

 

Creating your own RF ‘sniffer’

What if you need a simple ‘sniffer’ that doesn’t have to be precision-tuned? Well, you can create a non-precision loop antenna yourself! Simply connect the ground clip of a standard high-impedance passive probe to the probe tip (shown in Figure 4) and – voilà – you have created an oscilloscope RF ‘sniffer’! Sure, it may not be tuned for a particular carrier frequency, meaning that the voltage levels that you measure on the oscilloscope may not be an accurate representation of the actual RF field strength. But you can still “sniff” signals out of the air to verify proper modulation and timing of your RF-modulated signals.

DIY of RF loop antenna using high-impedance passive probe

Figure 4. DIY your own RF loop antenna using a standard high-impedance passive probe

 

Detailed ‘sniffing’ resources

If you’re interested to learn in greater detail about ‘sniffing the air’ to verify modulated RF signals on an oscilloscope, here are excellent resources to get you started:

 

Decoding Automotive Key Fob Communication based on Manchester-encoded ASK Modulation – Application Note

Decoding Automotive Key Fob Communication based on Manchester-encoded ASK Modulation – YouTube Video

NFC Device Turn-on and Debug – Application Note

NFC Testing Using an Oscilloscope Part 1: Benchtop R&D Measurements

 

Written by David Liu

Routine electrical tests are time-consuming

Routine electrical tests can be mundane and quite time-consuming, especially when you’re required to repeat the same test procedure with just one or two parameter changes. Take the testing of a DC-DC converter, for example. In the diagram below, you’ll notice that setup requires a few instruments to work together, including a DC power supply, digital multimeters, a DC electronic load and an oscilloscope.

 

Typical schematic of a DC-DC converter test setup

 

Figure 1. Typical schematic of a DC-DC converter test setup

 

DC-DC converter testing

A typical DC-DC converter test procedure requires the recording of voltage, current and power values under different load conditions. The figure below simulates a table of results that you’d likely need to fill up as you complete the characterization of a DC-DC converter under test. Imagine the time that’s needed for you to manually change each instrument setting, measure the values at each test point and record them in the table. Not to mention, all those steps on repeat!

DC-DC Converter Test Table

Figure 2. Typical table for manual recording of DC-DC converter characterization results

 

Try automating routine electrical tests

The steps involved in a routine electrical test, such as the one described above, could be drastically simplified by programming the whole procedure and automating the test. But first, you need someone to write the program, and for efficiency, the program should cover steps from configuring instruments, to measuring outputs or inputs, and tabulating results.

 

 

BenchVue Test Flow saves on manual programming and testing

So, you could write your own program from scratch, or you could try Keysight BenchVue. With Keysight BenchVue, you don’t have to be a programming wizard. BenchVue’s drag-and-drop interface and its Test Flow feature lets you create simple test procedures or sequences – quickly and easily. Something that could take days with writing traditional programming languages from scratch.

 

With BenchVue Test Flow, you can:

  • Create custom test sequences easily and quickly
  • Combine multiple instruments into a sequence seamlessly for a more complete DUT characterization
  • Drag-and-drop controls for rapid test prototyping
  • Code flexibly with the capability to:
    • Incorporate various utility blocks that simplify programming including statistics, math function, step controls and loops
    • Run SCPI commands, integrated Command Expert sequence blocks, or external programs

BenchVue Test Flow intuitive interface

Figure 3. BenchVue Test Flow’s intuitive interface

 

BenchVue supports multiple Keysight instruments

Figure 4. BenchVue’s seamless support for multiple Keysight instruments

 

Using Keysight BenchVue Test Flow, you can complete the DC-DC converter test above within 10 seconds. Not only will you be able to export test results in a perfectly-filled spreadsheet, you will also be able to capture waveform files automatically.

 

BenchVue Test Flow completes DC-DC converter test in 10 s

Figure 5. BenchVue Test Flow completes DC-DC converter test in 10 seconds and exports tabulated results in a spreadsheet for easy analysis

 

BenchVue Test Flow  eases data recording, export and analysis

BenchVue Test Flow incorporates features that are designed to speed up your data analysis, so you can focus on your next measurement tasks.

  • The “preview tool” helps you validate the sequence setup at a quick glance.
  • Customize how and what measurements you’d like to view on the X- and Y-axis
  • View data logs easily in tabular form
  • For reporting purposes, or for further analysis, export data easily to popular software applications including MATLAB, Microsoft Word and Microsoft Excel

BenchVue Test Flow features for quick data analysis

Figure 6. BenchVue Test Flow’s easy setup validation with the preview tool, customizable X-Y chart and exportability to popular software applications

 

If you are looking for a software app that can easily control your instruments and simplify automation, we recommend that you check out the latest updates and features on the Keysight BenchVue page.

mike1305

Keysight Crossword Fun!

Posted by mike1305 Employee Dec 6, 2017

Hey readers!

 

For today’s blog we decided to do something a bit different. I’m a big fan of the New York Times crossword puzzle (Monday record time 4m35s, let me know yours below) and thought this would be a fun way to share that with all of you. Grab a cup of coffee and give this puzzle a try! Let us know in the comments if you’d like to see more of these in the future, or if you need any extra hints to solve it.

 

Cheers!

-Mike

 

*Download the attachment and print for the best experience*

If you are dealing with more than a couple tens of amperes of AC current and want to make flexible current measurements, consider a Rogowski current probe.

 

A Rogowski coil is an electrical transducer used for measuring AC currents such as high-speed transients, pulsed currents of a power device, or power line sinusoidal currents at 50 or 60 Hz. The Rogowski coil has a flexible clip-around sensor coil that can easily be wrapped around the current-carrying conductor for measurement and can measure up to a couple thousand amperes of very large currents without an increase in transducer size.

 

How does a Rogowski coil work?

The theory of operation behind the Rogowski coil is based on Faraday’s Law which states that the total electromotive force induced in a closed circuit is proportional to the time rate of change of the total magnetic flux linking the circuit.

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

 

The Rogowski coil is similar to an AC current transformer in that a voltage is induced into a secondary coil that is proportional to the current flow through an isolated conductor. The key difference is that the Rogowski coil has an air core as opposed to the current transformer, which relies on a high-permeability steel core to magnetically couple with a secondary winding. The air core design has a lower insertion impedance, which enables a faster signal response and a very linear signal voltage.

 

An air-cored coil is placed around the current-carrying conductor in a toroidal fashion and the magnetic field produced by the AC current induces a voltage in the coil. The Rogowski coil produces a voltage that is proportional to the rate of change (derivative) of the current enclosed by the coil-loop. The coil voltage is then integrated in order for the probe to provide an output voltage that is proportional to the input current signal.

 

 

Advantages

Rogowski coil current probes offer many advantages over different types of current transducers or sensing techniques.

  • Large current measurement without core saturation -- Rogowski coils have the capability to measure large currents (a very wide range from a few mA to more than a few hundred kA) without saturating the core because the probe employs non-magnetic “air” core. The upper range of the measurable current is limited by either the maximum input voltage of a measuring instrument or by the voltage breakdown limits of the coil or the integrator circuit elements. Unlike other current transducers, which get bulkier and heavier as the measurable current range grows, the Rogowski coil remains the same small size coil independent of the amplitude of current being measured. This makes the Rogowski coil the most effective measurement tool for making several hundreds or even thousands of amperes of large AC current measurements.

 

 

  • Very flexible to use -- The lightweight clip-around sensor coil is flexible and easy to wrap around a current-carrying conductor. It can easily be inserted into hard-to-reach components in the circuit. Most Rogowski coils are thin enough to fit between the legs of a T0-220 or TO-247 power semiconductor package without needing an additional loop of wire to connect the current probe. This also gives an advantage in achieving high signal integrity measurement.
  • Wide bandwidth up to >30 MHz -- This enables the Rogowski coil to measure the very rapidly changing current signal – e.g., several thousand A/usec. High bandwidth characteristic allows for analyzing high-order harmonics in systems operating at high switching frequencies, or accurately monitoring switching waveforms with rapid rise- or fall-times.
  • Non-intrusive or lossless measurement -- The Rogowski coil draws extremely little current from the DUT because of low insertion impedance. The impedance injected into the DUT due to the probe is only a few pico-Henries, which enables a faster signal response and very linear signal voltage.
  • Low cost Compared to a hall effect sensor/transformer current probe, the Rogowski coil typically comes in at lower price point.

 

Limitations

  • AC only -- Rogowski cannot handle DC current. It is AC only.
  • Sensitivity - Rogowski coil has a lower sensitivity compared to a current transformer due to the absence of a high permeability magnetic core.

 

Applications

Rogowski coil current probes have a large number of applications in broad power industries and power measurement applications. The following are some examples of Rogowski coil applications:

  • Flexible current measurement of power devices such as MOSFET or IGBT device as small as TO-220 or TO-247 package or around the terminals of large power modules
  • To measure power losses in power semiconductors
  • To monitor currents in small inductors, capacitors, snubber circuits, etc.
  • To measure small AC current on a conductor with high DC current or in the presence of a high DC magnetic field.
  • To measure high frequency sinusoidal, pulsed, or transient currents from power line frequency to RF applications
  • To measure current in motor drives and, in particular, power quality measurements in VSD, UPS or SMPS circuits
  • To evaluate switching performance of power semiconductor switches (double pulse tester).
  • Power distribution line monitoring or utilities pole probe monitoring
  • Smart grid applications
  • Plasma current measurement

 

Conclusion

There are a number of different ways of measuring electric current where each method has advantages and limitations.

 

The Rogowski coil is similar to an AC current transformer in that a voltage is induced into a secondary coil that is proportional to the current flow through an isolated conductor. However, Rogowski coils have the capability to measure large currents (very wide range from a few mA to more than a few kA) without saturation because of its non-magnetic “air” core. The air core design also has a lower insertion impedance to enable a faster signal response and a very linear signal voltage and is very cost effective compared to its hall effect sensor/current transformer counterpart. This makes the Rogowski coil the most effective measurement tool to make several hundreds or thousands of amperes of large AC current measurement.

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 

Comparing different manufacturers’ oscilloscopes and their various specifications and features can be time-consuming and confusing. Streamline this process and select the oscilloscope that best fits your application with these top 10 considerations.

 

Streamline this process and select the oscilloscope that best fits your application with these top 10 considerations.

 

Bandwidth

The primary oscilloscope specification is bandwidth, and it is critical that you select an oscilloscope that has sufficient bandwidth to accurately capture the highest frequency content of your signals. Most oscilloscopes with bandwidth below 8 GHz have a Gaussian, or single-pole low-pass filter frequency response. The oscilloscope’s bandwidth is the frequency at which the input signal is attenuated by 3 dB. Because of this, you cannot expect to make accurate measurements near your oscilloscope’s specified bandwidth frequency.

 

Rule of Thumb:

  • Analog applications: Choose a bandwidth at least 3x higher than the highest sine wave frequencies you will measure
  • Digital applications: Choose a bandwidth at least 5x the highest clock rate in your system.

 

This will allow you to capture the fifth harmonic with minimum signal attenuation. This fifth harmonic of the signal is critical in determining the overall shape of your digital signals. This 5-to-1 rule-of-thumb does not take into account lower clock-rate signals that may have relatively fast edge speeds. These clock signals may contain significant frequency components beyond the fifth harmonic and require even higher bandwidths.

 

Keysight’s S-Series oscilloscope has bandwidth options of 1, 2, 2.5, 4, 6, and 8 GHz  

 

 

Figure 1 – Keysight’s S-Series Oscilloscope from 500 MHz to 8 GHz

 

Sample Rate

A digital oscilloscope can spend a lot of time calculating between the trigger event, the signal displayed, and the next trigger. This can result in only a few captures of your signal each second. Your oscilloscope will fail to capture intermittent errors or faults in your signal without a high enough update date.  This happens because the oscilloscope is busy calculating the last acquisition captured instead of acquiring. The higher the update rate, the higher your chances are of capturing that rare event.

 

Memory Depth

Closely related to an oscilloscope’s maximum sample rate is its maximum available acquisition memory depth. You should select an oscilloscope that has sufficient acquisition memory to capture your most complex signals with high resolution. Even though an oscilloscope’s banner specifications may list a high maximum sample rate, this does not mean that the oscilloscope always samples at this high rate. Oscilloscopes sample at their fastest rates when the time base is set on one of the faster time ranges. But when the time base is set to slower ranges to capture longer time spans across the oscilloscope’s display, the scope automatically reduces the sample rate based on the available acquisition memory. Maintaining the oscilloscope’s fastest sample rate at the slower time base ranges requires that the scope have additional acquisition memory. Determining the amount of acquisition memory you require is based on the time span of your signal and your desired maximum sample rate:

 

Acquisition Memory = Time Span x Required Sample Rate

 

Even though an oscilloscope’s banner specifications may list a high maximum sample rate, this does not mean that the oscilloscope always samples at this high rate. 

 

To better understand the relationship between bandwidth, sampling rate, and memory depth, let’s look at a real-world example. Consider trying to capture one frame data that lasts 1 ms and has serial data transmitted at 12 Mbps. So let’s assume that we have to capture a 12 MHz square wave for 1 ms.

  • Bandwidth — to measure the 12 MHz signal, we need an absolute minimum of 12 MHz, however, this will give a very distorted signal. So a scope with at least 50 MHz bandwidth should be selected.
  • Sampling rate — to reconstruct the 12 MHz signal, we need around 5 points per waveform, so a minimum sampling rate of 60 MS/s is required.
  • Memory depth — to capture data at 60 MS/s for 1 ms requires a minimum memory depth of 60,000 samples.

 

Triggering

Triggering allows you to synchronize the oscilloscope’s acquisition and display particular parts of your signal under test. Most digital oscilloscopes trigger on simple edge crossings, but you should select your oscilloscope based on the types of advanced triggering needed to help you isolate your most complex signals. Some oscilloscopes have the ability to trigger on pulses that meet a particular timing qualification. For example, trigger only when a pulse is less than 20 ns wide. This type of triggering (qualified pulse-width) can be very useful for triggering on unsuspected glitches. Pattern triggering is also very common and allows you to set up the oscilloscope to trigger on a logical/Boolean combination of highs (or 1s) and lows (or 0s) across two or more input channels. More advanced oscilloscopes even provide triggering that can synchronize on signals that have parametric violations. In other words, trigger only if the input signal violates a particular parametric condition such as reduced pulse height (runt trigger), edge speed violation (rise/fall time), or perhaps a clock to data timing violation (setup and hold time trigger).

 

Most digital oscilloscopes trigger on simple edge crossings, but you should select your oscilloscope based on the types of advanced triggering needed to help you isolate your most complex signals.

 

Display Quality

The quality of your oscilloscope’s display can make a big difference in your ability to effectively troubleshoot your designs. You should select an oscilloscope that provides multiple levels of trace intensity gradation in order to display subtle waveform details like noise distribution, jitter, and other signal anomalies. For the highest oscilloscope display quality in the industry, go to Keysight.com. An example is shown in Figure 2 below.

 

 

Figure 2 – High levels of display quality are required when viewing complex modulated signals such as video

 

Serial Bus Applications

To help you debug your designs faster, select an oscilloscope that can trigger on and decode serial buses. Serial buses such as I2C, SPI, RS232/UART, CAN, USB, etc., are pervasive in many of today’s digital and mixed-signal designs. Verifying proper bus communication along with analog signal quality measurements requires an oscilloscope. Many of today’s oscilloscopes have optional built-in serial bus protocol decode and triggering capabilities. If your designs include serial bus technology, then selecting an oscilloscope that can decode and trigger on these buses can be a significant time-saver to help you debug your systems faster.

 

If your designs include serial bus technology, then selecting an oscilloscope that can decode and trigger on these buses can be a significant time-saver to help you debug your systems faster. 

 

Connectivity and Documentation

Selecting an oscilloscope that meets your hardware connectivity, test automation, and electronic documentation requirements are key. Automated testing requires that the oscilloscope’s ports be programmable. So make sure any measurement that can be performed using the oscilloscope’s front panel and menu controls can also be programmed remotely via LAN or USB connectivity.

 

Keysight’s InfiniiVision X-Series and Infiniium Series oscilloscopes are all fully programmable via SCPI commands as well as National Instruments IVI drivers. Saved images (screen-shots) and data (waveforms) can also be easily imported into various word processors, spreadsheets, and applications such as MATLAB. Keysight’s N8900A InfiniiView offline analysis software lets you easily capture waveforms on your oscilloscope, save them to a file, and recall the waveforms into the application. With Keysight’s > 50 standard automated measurements with statistics and 16 independent math functions, you’ll be able to analyze a wide variety of tests.

 

Probing

Your oscilloscope measurements can only be as good as the data your probe delivers to the oscilloscope’s BNC inputs. Always keep in mind that when probing your circuit, your oscilloscope and probe become part of your device-under-test. This means it can change the behavior of your device-under-test signals due to capacitive or inductive loading. Select an appropriate probe for your measurement to minimize these loading effects. This will prevent disturbance of the input signal and deliver a true representation of your signal as it existed in your circuit before the probe was attached.

 

Select an appropriate probe for your measurement to minimize these loading effects.

 

Ease of Use

Your oscilloscope should be user-friendly and intuitive. This can be just as important as specified performance characteristics.  Oscilloscopes have evolved over the years with many additional features and capabilities but ease of use should not be compromised. Although most oscilloscope vendors will claim that their oscilloscopes are the easiest to use, usability is not a specified parameter that you can compare against in a product’s data sheet. Ease-of-use is subjective, and you must evaluate it for yourself. However, there are a few things you can look for when evaluating ease of use:

  • Built-in help menus, which reduce the need to reference manuals
  • Large color displays, which allow views of waveforms and measurement data at the same time
  • Voice control, which allows for hands-free control

Always request a demo when picking out your oscilloscope with a reputable company providing field engineers to help demo the scope or go to trade shows that provide hands-on demos.

 

Learn more about these and other oscilloscope selection topics: