Skip navigation
All Places > Keysight Blogs > Oscilloscopes Blog > Blog > Author: KeysightOscilloscopes
1 2 Previous Next

Oscilloscopes Blog

25 Posts authored by: KeysightOscilloscopes Employee

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

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.

Written by Rick Eads

The Need for a 16GT/s PCIe Interconnect

PCI Express represents one of the most successful computer interconnects yet devised and helped to enable high-speed connections between external devices such as displays and storage adapters to the internal CPU of the computer.  As networking speeds have increased (datacenter), as display resolution has increased (4K streaming) and as disk drive capacity and speed has increased (cloud computing), the need for an improvement in the speed of a host adapter to the CPU has also driven the development of the next generation of the PCI Express 4.0 Standard.  PCie 4.0 technology doubles the bandwidth of the previous generation of PCie 3.0 devices as PCIe 4.0 is able to achieve throughput of nearly 32 GBytes/s for 16 lanes.

 

PCie 4.0 technology doubles the bandwidth of the previous generation of PCie 3.0 devices as PCIe 4.0 is able to achieve throughput of nearly 32 GBytes/s for 16 lanes.

What’s New about the PCIe 4.0 standard versus PCie 3.0?

The biggest improvement brought by the PCIe 4.0 standard is a doubling of the speed to 16GT/s per lane.  Nevertheless, there are additional changes to the PCIe 4.0 specification versus the Gen3 Spec that is worth noting.  Due to the higher data rate, the maximum channel loss accommodated by the PCIe 4.0 standard is approximately -28dB, which implies a maximum channel length of about 12” (or 25cm) with a single CEM class connector.  To accommodate channels longer than 12”, the PCie 4.0 specification provides protocol and electrical requirements for a retimer device which can be used to extend the PCIe 4.0 channel and can help to accommodate multiple connector topologies.  Another new feature of the PCIe 4.0 specification has been the addition of a lane margining capability.  Lane margining allows for in-band (L0) based adjustment of the receiver sampling point which allows for an estimation of eye width, and an optional mode also allows for voltage margining which may provide information regarding eye height.  This feature is intended to help system integrators determine product readiness for shipment.

 

Testing PCIe 4.0 Card Electromechanical (CEM) Devices

While the PCI Express 4.0 BASE specification is nearing 1.0 status, it primarily is written to accommodate new silicon or ASIC devices operating at 16GT/s.  PCI Express also accommodates a system specification referred to as the Card Electromechanical (CEM) specification.  This is the specification that is used at PCISIG compliance workshops to determine if motherboards and add-in cards are compliant to the PCIe 4.0 application.  To accomplish this, the PCISIG has commissioned the development of both new CEM test fixtures and new test software.  As of this writing, both are still in development but are being used in US-based compliance workshops since April 2017.  One new aspect of testing CEM devices under the PCIe 4.0 specification is the addition of an external physical ISI channel that is chosen/calibrated to ensure the maximum CEM channel loss is achieved.

 

                      

Fig 1: Prototype CEM Test Fixtures (CBB4 and CLB4)

Oscilloscope bandwidth requirement

The minimum oscilloscope bandwidth required for PCI Express 4.0 is 25GHz.  As the minimum eye height is 15mV, it is important to utilize real-time oscilloscopes with the lowest noise floor to minimize error and to maximize the measured margins.

 

The minimum oscilloscope bandwidth required for PCI Express 4.0 is 25GHz.  As the minimum eye height is 15mV, it is important to utilize real-time oscilloscopes with the lowest noise floor to minimize error and to maximize the measured margins.

Making PCI Express BASE spec transmitter measurements

Keysight’s new N5393F PCI Express transmitter test application provides step-by-step instructions to guide you through the process of configuring the test setup, selecting the tests and connecting the signals to the oscilloscope.   The N5393F supports PCI Express 4.0 testing at 16GT/s for BASE spec tests and also supports legacy testing under the PCIe 3.0, 2.0, and 1.0a/1.1 standards.  The N5393F test provides visual connection aids to facilitate the connection of your DUT to the oscilloscope and with optional software also integrates the ability to de-embed test fixtures, provide DUT automation for test mode selection (2.5G, 5G, 8G).

 

                 

Figure 2: PCI Express 4.0 BASE spec connection diagram including replica channel for de-embedding

 

                  

Figure 3: Keysight N5393F PCI Express automated test application for the oscilloscope showing the PCIe 4.0 BASE specification tests for 16GT/s validation

Summary

Keysight has been a consistent and valued contributor to the development and authorship of the PCI Express specification since the initial 1.0a draft and continues to provide valuable guidance to the PCISIG for transmitter testing, receiver testing, and channel testing and characterization.  Other optional tools such as the N5465A InfiniiSim Waveform Transformation toolset and N5461A equalization application can provide deep analysis and debug capability. In addition, Keysight has other comprehensive test solutions from design simulation to physical layer testing that includes transmitter, receiver and channel for the PCI Express 4.0 standard as well as previous generations of PCIe.

Written by Doug Beck

What is mask testing?

A fundamental aspect of electrical engineering is finding problems with signal integrity. In the real world, systems don’t always work as simulation says they are supposed to. There is the concept of a “golden trace” where the waveforms are precisely where they need to be. But there are a great number of things that can cause a waveform to vary from the “golden trace.” Unfortunately, these problems can also be quite rare, which makes them difficult to find.

 

The idea of a mask on an oscilloscope is to provide a region around the golden trace where the waveform can vary without causing any problems. An example is shown in Figure 1. The gray area is the mask. This can be thought of as “out of bounds” because if the waveform strays into the gray areas, it is considered an error. However, if the waveform remains within the black areas, the waveform is considered fine.

 

Figure 1. An example of a mask on a waveform

 

The most common alternative to using a mask is to use triggers such as glitch, run, slow edge, fast edge, etc. However, a mask combines all of these triggers into a single test. In general, oscilloscope hardware does not allow all of these errors to be searched for at the same time. The bottom line is that using a mask test can save quite a bit of time.

 

Standards-based mask testing

Because mask tests can be so effective, it is very common for masks to be provided for common standards. Examples include Ethernet and FlexRay. The good news is that if your signal happens to be one where an industry standard mask is available, the job is very easy. Just load the mask into an oscilloscope that supports mask testing and you will quickly find errors.

 

However, it is very common for industry standard masks to be unavailable. An obvious case is proprietary buses. In my experience, not having an industry standard mask is the rule rather than the exception. Fortunately, there are alternatives which allow users to create a mask on their own.

 

Creating your own mask with Auto Mask

A very simple method to create a mask is known as Auto Mask. The idea behind an Auto Mask is to take a single waveform and add a tolerance of the desired size around it both vertically and horizontally. An example of an Auto Mask setup dialog from a Keysight Infiniium oscilloscope is shown in Figure 2. It should be noted that the selection of the source channel is made in the main Mask Test dialog.

 

Figure 2. Auto-mask setup dialog

 

In one single step, a mask is created, such as the one shown previously in Figure 1. It is easy to think that this solves the problem completely. Regrettably, it does not work for most situations where masks are needed.

 

Auto Mask only works where the waveform only follows a specific path and only that path. This means if there is an entire unit interval (or more) on screen, the mask will continually fail. Consider the example in Figure 3. We have what seems to be a perfectly good auto mask drawn on the screen. However, in this case, we only have a single run’s worth of waveforms.

 

 

Figure 3. An auto mask of multiple unit intervals

 

Figure 4 shows what happens when we do multiple runs. Suddenly, we get a whole bunch of errors. What happened? The key point is: unless we are zoomed in on a very small part of the waveform, there are many points where either a rising edge or falling edge are valid. This means that the Auto Mask finds a great number of errors when there is actually none at all, in this case.

 

Figure 4. Showing the same auto mask as Figure 3 with multiple runs

 

This problem is just as bad with a single unit interval, which is known as an eye diagram. Eye diagrams are a very powerful method to determine signal integrity but auto mask will never work. An example of an eye diagram is shown in Figure 5. The middle opening is known as the “eye”. The size of this opening is one key measure of signal integrity.

 

Figure 5. Eye diagrams show a single unit interval

 

Creating your own mask with Draw Mask

For a long time, users who needed to create their own mask needed to use Excel to create a mask file. This is very error prone and tedious. However, starting in Version 6.0, Keysight Infiniium oscilloscopes provide a Draw Mask dialog. An example is shown in Figure 6. There is the option for manual creation of polygons which are used to indicate the areas where the waveform should not go. Much of the focus is typically on the eye area itself, although users are free to put the polygons anywhere.

 

 

Figure 6. Manually creating a mask using the Draw Mask dialog

 

Up to eight polygons are allowed, and each polygon can have up to fifteen points. Each point can be editable simply by clicking it and moving it to a new location. Moving the entire polygon at once is done by clicking anywhere inside it and dragging it to a new location. The bottom line is that users can create a new mask visually which is far less error-prone because they can see the existing waveforms in the editor. This is a massive improvement over creating mask files by hand in Excel!

 

The readout at the bottom shows the numeric values for each of the points in the selected polygon. These can be manually edited as shown in Figure 7. This is useful because sometimes users have specific values in mind to match a specification.

 

Figure 7. Entering a specific value for a point in a polygon

 

Each polygon can consist of as few as three points or as many as fifteen points. The reason to allow this flexibility is to give users the option to be as accurate as they desire. Fifteen points are the most accurate, but it also takes the most time to create.

 

An example of a complex multi-polygon mask is shown Figure 8. Notice the use of a different numbers of points. Creating this example took me only a couple of minutes. With Excel, it could have taken hours to get right.

 

Figure 8. Creating a complex mask in the Draw Mask dialog

 

The final result in the oscilloscope is shown in Figure 9. In this case, the waveform is well behaved and we have no errors.


Figure 9a. An eye diagram with a complex mask

 

Figure 10 shows the same mask with some errors. Notice the edges of the mask are now in a bright red. These are waveforms which violate the mask. Optionally, users can stop as soon as a failure occurs to allow them to see what led up to the problem.

 

Figure 9b. An eye diagram with a complex mask

 

It gets better: Automatic mask creation

While creating polygons is pretty fast and definitely a big improvement over manually creating mask files, users asked for even more efficiency. Can’t the oscilloscope automatically create shapes based upon an eye diagram? An example of doing this is shown in Figure 10. To use “Auto Eye,” users need to specify a tolerance and the maximum number of points and then click in the region where they want the shape created.  These shapes are still editable so that users can tweak them if desired. But most of the time the points are fairly close to the desired location so the amount of editing isn’t large. The key point of Auto Eye is not that it always gets the points exactly right but rather that it reduces the amount of editing by putting the points in approximately the correct location. That way, users might only have to adjust a few points of the polygon instead of moving all of them.

 

Figure 10. Automatic creation of polygons for an eye diagram

 

Mask testing transformed

Mask testing has come a long way! Because of enhancements such as Keysight’s Draw Mask dialog, it is now an analysis that can be used on any waveform. This means mask testing has moved from a relatively small niche to a fast and effective tool that should be used early in the testing process to quickly detect errors. Debugging electronics is challenging and can often be time-consuming, but mask testing is now a huge asset to oscilloscope users.

 

 

About the Author

Doug Beck is an Expert Usability Engineer with Keysight Technologies focused on oscilloscopes. He holds a PhD in Industrial & Operations Engineering from the University of Michigan and has 12 patents.

Written by Min-Jie Chong

 

The Need for New SAS-4 Storage Standard

The increase of data traffic due to the advent of internet of things has driven the need for faster backbone and storage transmission to meet this need. The Serial Attached SCSI - 4 (SAS-4) is a new enterprise storage standard that is being created to meet this need. It supports data rate of 22.5 Gb/s which doubles the data throughput of previous generation SAS-3 standard.

 

What is SAS-4 standard?

The SAS-4 working committee decided to leverage the OIF-CEI 3.1 specification to speed up the development of SAS-4 specification. The consequence is the test methodology in SAS-4 will deviate from the previous SAS generations. In the previous generation, reference transmitter and receiver are defined, which describe how a “perfect” design would handle the outgoing and incoming signal. However, the OIF-CEI specification does not provide any reference designs, which changes how the SAS-4 designs are tested.

 

First thing first, accessing SAS-4 signals

SAS-4 specification has a new recommendation of the insertion loss profile of the test fixture being used for testing. The intents are to more accurately test the 22.5 Gb/s signal without the effect of test fixtures so the industry can get more consistent results and avoid marginal design from passing using better test fixtures, but not meet the actual performance in real world. Keysight has found the Wilder Technologies SAS-3 test fixtures to be suitable for SAS-4. They perform better than what the specification recommends. This is a good outcome because it is easier to supplement loss using the embedding methodology, using Keysight’s N5465A InfiniiSim software toolset.

 

Oscilloscope bandwidth requirement

The SAS-4 specification does recommend a minimum of 33 GHz oscilloscope bandwidth for transmitter test. Keysight’s Z and V Series oscilloscope models (i.e. DSAV334A, DSAZ334A and DSAZ504A) have bandwidth that meet this requirement.

 

Making SAS-4 transmitter measurements

Keysight’s new N5412E SAS-4 transmitter test application provides step-by-step instructions to guide an engineer through the process of configuring the test setup, selecting the tests and connecting the signals to the oscilloscope. After everything is setup correctly, the application will then make the necessary measurements and analysis, and then presenting a pass or fail status of the signal under test. A test report will also be automatically generated at the end of this process, documenting the test results and measurement screenshots. This can really remove the complexity of learning the specifications, which can save engineers a lot of time and effort.

 

 transmitter measurements

Figure 1: Keysight N5412E SAS-4 automated test application for the oscilloscope, which covers all the required transmitter test requirements.

 

The application includes all the transmitter requirements listed below.

  1. Spread spectrum clocking (SSC)
  2. Transmitter signal quality (TSG)
  3. Transmitter equalization (TXEQ) coefficient request and circuit response
  4. Out-of-band (OOB) signaling

 

SAS-4 is highly susceptible to crosstalk

SAS-4 interface packs a lot of high speed lanes densely in a connector, which makes it highly susceptible to crosstalk effect. It is important for oscilloscope jitter separation algorithm to be able to handle presence of crosstalk. The earlier, more common jitter separation with the “spectral” method is not capable of separating crosstalk from random jitter. Keysight oscilloscope uses a newer, more advanced “tail fit” method that can correctly separate the effect of crosstalk from the random jitter.  

 

After determining the presence of crosstalk, the Keysight N8833A crosstalk analysis tool can provide deep analysis and debug capabilities. The tool is able to identify which potential aggressor is aggressing at the victim, quantify the amount of crosstalk the aggressor is coupling into the victim and then removing the crosstalk from the victim signal. We can check if the design can pass the specification and how much margins can be recovered without the crosstalk. This can assist in making important design decisions such as whether improving the crosstalk can make our design passes the specification, and which part of the design needs to be fixed.

 

eye diagram

Figure 2: Keysight N8833A crosstalk analysis application showing the eye diagram before (top) and after (bottom) removing crosstalk from the signal. The eye height and width can be measured to see the improvements of the signal without crosstalk.

 

Vendor specific SAS-4 receiver equalization implementation

While SAS-3 mandates 5 tap of decision feedback equalizer (DFE) implementation to recover a closed eye at the receiver, the SAS-4 does not mandate any specific number of taps. It is left to the vendor specific implementation how many taps will be sufficient to open up the eye. Keysight’s N5461A equalization tool with DFE allows engineers to recover the eye with up to 40 taps. Engineers can specify the value for each tap and check the effect on the eye opening or use the tap optimization feature that will compute the values based on the constraints given by the engineers. This feature is very useful to reproduce the eye opening that the receiver sees after the DFE process.

 

equalization tool

Figure 3: Keysight’s N5461A equalization tool is used to open up the closed eyes at various SAS data rates, and what the SAS receiver would see after DFE is performed.

 

Summary

Keysight has been a key contributor to SAS-4 and previous standards, and understand the test requirements. New test and interoperability challenges exist at 22.5 Gb/s and Keysight has the solutions to overcome these challenges. The automated N5412E SAS-4 test application covers the complete transmitter test requirements. Other tools such as the N8833A crosstalk analysis and N5461A equalization application can provide deep analysis and debug capability. In addition, Keysight has other comprehensive test solutions from design simulation to physical layer testing that includes transmitter, receiver and channel for SAS-4 standard.

Written by Sheri Detomasi

 

There are many similarities and differences between oscilloscopes and wideband digitizers.  How do you know which is the right tool for your measurement need? 

 

Oscilloscopes use wideband data converters and typically provide a broad range of functionality.  They provide probing and visualization of time variant waveforms.  When debugging or troubleshooting a project, it’s important to see as much signal detail as possible.  Oscilloscopes typically provide waveform reconstruction filters for improved signal visualization. If the ADC waveform data is displayed with no waveform reconstruction, you would see a confusing cluster of points as shown in (a) below.  Whereas (b) shows with the waveform reconstructions.  Same with fast rise-times in (c) and (d)

 Waveform reconstructions

 

For visualization purposes, an oscilloscope also has continuous waveform acquisitions in display memory.  An oscilloscope can produce an extremely high waveform update rate > 1,000,000 waveforms per second.   Shown below, with an oscilloscope’s high speed waveform update rate and its ability to pick up glitches or unexpected events.   

 

Different measurement capabilities

 

 

 

Many oscilloscopes have a wide range of automatic measurement capabilities like rise/fall time, delay, peak to peak, zone triggering, etc. In addition, with the wideband acquisition, oscilloscopes are also ideal for high speed digital test, emerging serial protocols, and advanced communications.  With the wide bandwidth, vast measurement capabilities and robust user friendly interface, weather in bench or modular form factor, an oscilloscope is a general purpose tool that can be used for many applications. Keysight’s modular oscilloscopes, the M924xA series, range from 200 MHz to 1 GHz and feature the same functionality you would find on a benchtop oscilloscope.

 Digitizers

 

Digitizers are more purpose built.  Their main goal is to capture many channels of data with high resolution to achieve the best measurement fidelity.  While oscilloscopes typically have 8- to 10-bit ADCs, a digitizer is usually 10- to 16-bits.  This doesn’t tell the whole story though.  There are other noise factors to consider such as ADC differential and integral nonlinearities, thermal and shot noise, input signal distortion, as well as sample aperture jitter and ADC sample clock noise.  Therefore, a better measure of the resolution is the ENOB, or Effective Number of Bits.  One technique digitizers use to get even more ENOBs is digital down conversion (DDC).  DDC is extremely valuable when analyzing a small slice of spectrum within a wideband acquisition, allowing the user to reduce the bandwidth and ‘tune and zoom’ into a specific part of the signal.  Here is the digitizer DDC block diagram.

 ACD memory

 

 

It’s common for oscilloscopes to provide extremely wide bandwidth while digitizers provide higher ENOBs over smaller bandwidths. 

 

In normal use a digitizer will acquire many channels of data over longer time periods, producing lots and lots of data.  The data is either analyzed onboard or sent to a PC or storage device for post processing. For this reason, digitizers typically have deep memory buffers behind each ADC and very high data transfer rates.   For on-board processing, it’s useful to access the digitizers internal FPGA to do some real-time signal processing.  This allows the data processing and manipulation routines to reside in the hardware at GS/s processing rates and is useful for embedding algorithms to implement onboard custom filtering, correction routines, data reduction schemes as well as application specific routines.  This provides very specific application needs at very high speeds.  Here you can see a process for acquiring the data, processing, extraction, analysis and playback.

 

 

A digitizer is always connected to a PC and is controlled through a computer soft front panel or an automated program.  With this, there is less of a need for high-speed waveform update rate to the computer display.  The purpose-built nature of a digitizer makes it more of a dedicated tool for specific applications.

 

Characteristic

Oscilloscope

Digitizer

Ideal use

Interactive test and analysis with high performance user interface

Data capture with deep dive software analysis

Resolution and dynamic range

Good

Better

Measurement and analysis

Better automatic measures

Better data collection for post processing

Bandwidth

Better

Good

Acquisition memory (record time)

Limited

Good, extendable to external storage

Number of channels

Limited

Good, expandable

Waveform update rate

Better visual (display) update rate

Limited

Data streaming

Limited

Better, high data throughput

Triggering

Better

Good

FPGA access

Not typically

Possible

Probing

Better

Limited

 

 

 

A word of caution: some test equipment vendors will promote a digitizer as an oscilloscope or an oscilloscope as  a digitizer.  This may cause some confusion and the wrong choice can cause headaches down the road. Ensure you understand your needs and select the right instrument for your test application.  To find out more, check out these resources as well as a video of Keysight experts talking about the blog:

 

 

App Note: Understanding the Differences Between Oscilloscopes and Digitizers for Wideband Signal Acquisitions  

Webcast: "Oscilloscope or Digitizer for Wideband analysis - Why care?" .

Keysight just announced our new Infiniium S-Series oscilloscope promotion, it’s called “Your Scope. Your Way.” 

The S-Series oscilloscope (500 MHz to 8 GHz) has unmatched measurement accuracy with the best signal integrity and the most comprehensive measurement software for signal analysis, compliance, and protocol analysis.   And now the Keysight S-Series oscilloscope just got better with a great offer allows you to tailor the product for your own needs for FREE.

 

Choose ONE of the following three offers for free with the purchase of each new S-Series oscilloscope:

 

Offer #1:  Get the new N8888A Infiniium Protocol Decode Bundle for free (supports 33 protocols)

protocol decodes


or

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

            probe

or

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

 

Take advantage of this offer:

Written by Ailee Grumbine and Brad Doerr

 

The design-to-manufacturing (D2M) process typically involves sequential stages from design to manufacturing. Each stage requires data collection that is specified in an initial design of experiments (DOE) and aimed at providing confidence that the design can meet critical requirements. Effective data analytics tools can help engineers evaluate the insights per the DOE in each stage of the design-to-manufacturing process. Time-to-market (TTM) can be greatly accelerated by utilizing modern data analytics tools while also increasing confidence in key technical decisions.

To hear more from the authors watch the video above

 

The first stages of the D2M process are design and simulation. The designer performs simulation to ensure that the design will meet the design specification. Simulation provides key statistics and produces waveforms that can be fed into compliance test applications. Simulation validation is a critical task prior to committing to expensive ASIC and PCB fabrication. The next stage is to perform design validation by using test equipment such as oscilloscopes and other measurement devices. The validation engineers will make measurements on multiple samples per the DOE created during the design stage. The DOE requires validation in a wide range of operating conditions, such as temperature and software configurations. The engineering team will then analyze the data with tools such as databases, PIVOT tables, JMP, R and/or other home-grown tools with data from instruments with data in CSV, XML or other formats. The challenge is that most engineering teams manage this data and the tools. This distracts from making measurements and promptly analyzing the findings. Next, the engineering team will perform compliance testing. Automated compliance test software saves a lot of time as it automates the measurements and produces the test report with statistical analysis to allow the engineers to determine the margins. This data is also very useful to determine if a second design cut is needed. Once the design is validated, the design can be released to manufacturing. The team will identify the production processes and measurements to ensure the design will meet the manufacturing goals derived from the original DOE. The manufacturing team will also seek efficiency improvements and/or yield improvements to improve. The data provides the basis for effective manufacturing management and optimization.

 

A capable data analytics platform integrates the DOE at the start of the process the engineering team will be able to achieve efficiency and confident decisions. The DOE is created in the early stages of design aimed at providing the data that can answer key questions about the design. This DOE defines the tests that need to be run in simulation and on the physical DUTs.  The DOE also identifies the test conditions and the number of tests that need to be run to achieve statistical confidence in the results. It is critical to choose a data analytics platform that can adapt alongside the DOE evolution. Nobody likes to delay a program while the team “re-architects the database schema”.            

 

There are many visualization tools in the market today that are used to help engineers analyze their test data. However, they are usually designed for a single user who has the time to acquire deep application expertise. These tools don’t fit well in the test and measurement D2M world especially as engineering teams are global and distributed. The visualization tool for D2M teams must provide data access to the entire team, with well-known visualization capabilities such as histogram, sweep, box-and-whisker and scatter plots.

 

Sweep or vector plots allow users to view 2-dimensional “sweep-data”. D2M and T&M applications rely heavily on sweep-data such as time-domain waveforms, frequency-domain magnitude plots and eye diagrams. The right analytics tool will enable the team to overlay for example, multiple eye diagrams with different test conditions. The overlay feature allows the user to determine test conditions that cause the eye to close or have less margin and allow the designer to optimize the design for best performance. Another example of a sweep/vector plot is a constellation diagram. Figure 1 shows an example of a 5G QAM4 constellation diagram. There are 3 sets of constellation data overlain which represent 3 different input voltages: 1V, 0.9V and 0.8V. The plot reveals that the constellation diagram with input voltage of 1V has the cleanest transmitted symbol. The constellation diagram with input voltage of 0.8V seems to be the one with the lowest received signal quality with potential phase noise issues.

Input voltages

Figure 1. Overlay of 3 different input voltages (1V, 0.9V and 0.8V) 5G QAM4 constellation data

Another visualization method in the test and measurement world is a box-and-whisker plot. Figure 2 shows an example of a box-and-whisker plot of a jitter measurement with multi-level split capability. The user can split on more than one property for analysis purposes. The plot on left is split by the three usernames: Sakata, Fernandez and Chang. The plot on right is split by username and input voltage. The plot indicated that most of Chang’s measurement values are higher than the upper limit especially for the input voltage of 0.8V.

Box-and-whisker plot

Figure 2. Box-and-Whisker plot of a jitter measurement with multi-level split capability.

In summary, successful D2M programs require a clear DOE and necessarily generate a great amount of data. With upfront planning and by choosing the right analytics platform, engineering teams can optimize effectiveness and time to market. This same data can also be leveraged into manufacturing ramp and manufacturing optimization.

 

Visit Keysight’s new Data Analytics Software here!

Want to show off your cool project? E-mail moreinfo@keysight.com and your project could be featured here!

 

Quinton Martins, the leader of the Mountain Lion Project at the Audubon Canyon Ranch (ACR) in Northern California, had a problem.  Mountain lions needed to be trapped and GPS-tagged for research, but traditional trapping methods were just not effective enough.

 

 

Trapping method of the past

 

The traditional technique for trapping mountain lions involves the use of a one-door “single- ended” cage, with bait to lure the cat inside.  A mechanical pressure plate on the cage floor triggers the door-closing mechanism.  There are two significant issues with this approach.

 

  1. Bait isn’t tempting enough. Where food is abundant, mountain lions may not be hungry enough to venture into a cage. It can also be very difficult to source mountain lion munchies, like roadkill deer.
  2. The wrong animals are caught! Often smaller animals like foxes and bobcats end up in the traps instead of mountain lions.

 

 

Catching more mountain lions

 

Mountain lions commonly re-use the same walking paths, so Quinton is able to use bushes and sticks to ‘funnel’ the animal into a walk-through cage that is open at both ends. This works well because it is far easier to convince a mountain lion to walk into a cage if it can see a clear path through the other side. It also eliminates the need for bait by taking advantage of the mountain lion’s natural walking path.

 

The challenge was to develop a reliable electronic system that would simultaneously close both doors of the walk-through cage while the mountain lion was inside.

 

In this new design, the doors operate very simply. They are held vertically in “U” channel guides and drop when actuator rods are pulled (Fig. 1). 

 

 Cage Operation

Fig 1: Mountain Lion Cage Operation

 

 

A single, high-power solenoid pulls a wheel, which is connected to both actuator rods. The electrical system is controlled by an Arduino Uno microcontroller and a high current relay to activate the solenoid (Fig 2).

 

Prototype Actuator Mechanism

Fig 2: The prototype actuator mechanism

 

 

System design

 

The system needed to detect the motion of a mountain lion without trapping smaller animals. I investigated several options for sensing mechanisms including a horizontal light beam sensor and ultrasonic range sensors.  The light beam sensor worked, but it was difficult to set up and align and involved hanging wires over the side of the cage. I ultimately decided to use less intrusive ultrasonic range sensors installed at the top of the cage.

 

The system needed to detect the motion of a mountain lion without trapping smaller animals.

 

By measuring the distance from the top of the cage to the animal, we could set it to trigger on large animals only (mountain lions are typically at least 20 inches tall at their shoulders). The system was designed with two range sensors spaced 14 inches apart that would trigger only when both sensors detected an object at least 20 inches tall.  This double-sensor set-up minimizes the chance of triggering on a smaller animal, such as a fox, that might sniff the top of the cage with its nose.  If that happens, the small animal would only trigger one of the sensors, so the doors would not close.

 

The system was designed with two range sensors spaced 14 inches apart that would trigger only when both sensors detected an object at least 20 inches tall.

Debugging & deployment

 

With the basic design established, the next challenge was to write and debug the code controlling the actuator mechanism, which proved to be challenging. Incorrect timing caused the ultrasonic sensors to interfere with each other.  We needed a way to debug the trap while in the field - the Keysight 1000 X-Series low cost oscilloscope proved to be just the right tool. The 2-channel oscilloscope allows the signals from both sensors to be viewed simultaneously, enabling us to adjust the timing and ensure reliable operation.

We needed a way to debug in the field – the Keysight 1000 X-Series Oscilloscope proved to be just the right tool.

actuator circuitFigure 3:  Keysight EDUX1002A Oscilloscope being used to debug the actuator circuit.

 

 

 Setting up a trap in the field

Figure 4:  Quinton Martins, (Ecologist - in the cage!) and Neil Martin setting up the trap in the field (Picture by Jim Codington)

 

Mountain lions have very large territories, so patience is required when trapping these elusive animals.  After about two weeks, the waiting paid off, and we trapped our first mountain lion with this system, a female, and then caught a male 2 days later!

 

Trapped female mountain lion

Figure 5:  Trapped Female Mountain Lion

 

By Neil Martin 

 

More information about the ACR Mountain Lion project can be found here:

https://www.egret.org/acr-mountain-lion-project

 

 

Neil Martin is Keysight’s Corporate Marketing Director.  He used to be an R&D engineer and he can still remember a little engineering - which he makes use of in his spare time for volunteer projects.

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

 

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

 

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

Histogram Plot of jitter measurment

Histogram plot of jitter measurement on three different SERDES 

 

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

 line plot of bit errors

Line plot of bit errors on four different ASIC versions

 

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

 

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

When you are testing a crystal oscillator circuit with an oscilloscope probe, the oscillator may stop oscillating or the waveform may be severely distorted. Why?

 

Every probe functions as an external circuit connected to the device under test. Each probe has its own input resistance, capacitance and inductance, imposing additional load to the DUT. Connecting a probe to the oscillator circuit (or any electronic circuit) adds extra load to a signal or may distort the waveform displayed on the oscilloscope thanks to the loading effect. Therefore, probing an oscillator circuit requires special care, as the oscillator circuit is highly sensitive to capacitance. 

Connecting a probe to the oscillator circuit

Figure 1  Connecting a probe to the oscillator circuit adds extra loads to a signal

 

There are two main factors to consider in choosing a probe for oscillator testing. The first is that the oscilloscope probe is adding capacitance to the existing load capacitors (C1 and C2 in fig 2). The load capacitance is a parameter for determining the frequency of the oscillation circuit. It is important to note that the change in the value of the load capacitance may result in changes in the output frequency of the oscillator or at worst case, it may stop the oscillation. The second factor is that the probe is introducing resistive loading to the oscillator circuit. Both factors can be significant enough to keep the oscillator from working. At DC or low frequency ranges, probe loading is mostly caused by the resistance of the probe, and as the frequency goes up, capacitive component of the probe becomes the dominant factor in the loading effect.

A circuit diagram of a typical oscillator circuit

Figure 2 A circuit diagram of a typical oscillator circuit

 

A solution is to use a probe with high input resistance and low input capacitance in order to cause the lowest possible loading effect. In general, a passive probe with 100:1 attenuation ratio such as Keysight N2876A passive probe (with 2.6 pF of input capacitance) reduces capacitive loading significantly on the circuit, compared to a conventional 10:1 passive probe with ~10 pF of capacitive loading. Loading can be further reduced by switching the oscilloscope input coupling from DC to AC, as DC coupling mode on an oscilloscope presents additional loading to the oscillator and may cause it to stop.

 

Or, better yet, using an active probe with low input loading such as Keysight’s N2795A 1 GHz active probe or N2796A 2 GHz single-ended active probe may deliver better results. This active probe provides 1 Mohm input at DC and low frequencies for low resistance in parallel with <1 pF input capacitance loading to the circuits. Another good probe for oscillator circuit measurement is a Keysight InfiniiMax 1130A Series or N2750A Series InfiniiMode probe that presents even lower loading to the circuit.

Input impedance equivalent model of Keysight N2795A/96A single-ended active probe

Figure 3 Input impedance equivalent model of N2795A/96A single-ended active probe

 

Also, it’s important to note how to connect the probe to the DUT. If your probe connection has obviously longer input lead wires or a connector at the tip, you should suspect frequency response variation and degradation. In general, the longer the input wires or leads of a probe tip, the more it may decrease the bandwidth, increase the loading, cause non-flat frequency response and result in more variation in response. If at all possible, keep the input leads of the probe tip as small as possible, and keep the loop area of connection as small as possible.

Keep the input leads and loop area of connection small for more accurate results

Figure 4 Keep the input leads and the loop area of the connection as small as possible for more accurate results.

If your probe connection has longer input lead wires or a connector, look for frequency response variation and degradation

Figure 5 If your probe connection has obviously longer input lead wires or a connector at the tip, you should look for frequency response variation and degradation.

KeysightOscilloscopes

Scope Month 2017

Posted by KeysightOscilloscopes Employee Feb 15, 2017

It’s almost that time again, we’re only a few weeks away from Scope Month 2017! If you missed out last year, or are just getting ready for this year, here’s what you need to know.

 

Just like you, we love oscilloscopes. So Keysight created an entire month to celebrate oscilloscopes and the great engineers who use them, that’s you! March 1, 2017 kicks off Scope Month, which will run through March 31, 2017, and will offer new measurement tips, oscilloscope resources, a new Keysight oscilloscope, and of course oscilloscope giveaways!

Everyone’s favorite part of Scope Month is the oscilloscope giveaways, and this year won’t disappoint. For Keysight Scope Month 125 oscilloscope giveawaysScope Month 2017, Keysight is giving away more than 125 oscilloscopes! We will be drawing new winners each weekday during Scope Month and posting these drawings on our YouTube Channel along with a helpful measurement tip for you. You will be able to enter the drawing once per day during Scope Month, and all entries will be eligible for the entire drawing period. And the best part is that you can get an extra chance to win: if you enter now, you get an early entry into the sweepstakes (only one per person during the early-entry period).

 

Enter now

 

Any questions? Check out the FAQs on this page. Did we miss anything? Ask your questions in the comment section below and we’ll get back to you.

 

 

Keysight Test to Impress contestNot quite ready to leave a new oscilloscope up to chance? You can also participate in the Test to Impress video contest. Just create and submit a video explaining why you need a new Keysight oscilloscope and how you would use it, and you could win one! Eligible entries will be reviewed by a panel of recognized industry voices who will choose 1 Grand Prize winner to win a 6-GHz 6000 X-Series oscilloscope and 2 “Runner up” winners to receive brand new Keysight 350-MHz 3000T X-Series oscilloscopes. Entries will be accepted March 1-31st, 2017 at www.scopemonth.com. Be sure to stay tuned after Scope Month, because we’ll announce the winners April 14th, 2017.

 

 

Keysight new oscilloscope

But wait, there’s more… this year the start of Scope Month also means a big SURPRISE. We can’t give it away just yet, but we can tell you there’s a brand new oscilloscope coming to the Keysight family and Scope Month will give you the first chance to see it and even get your hands on one for free (and you’ll definitely want to get your hands on one)!

 

Add the live Scope Month kickoff to your calendar to make sure you’re the first to see it!

 

 

While you wait for Scope Month to begin, we have quite a few great resources to help you with your measurement challenges:

  • Oscilloscope Learning CenterQuickly access video tutorials, application notes, white papers, and industry experts. Whether it’s your first time in front of a scope or you’ve been using one for decades, the oscilloscope learning center can help you stay ahead of next technology.
  • Oscilloscope blog – follow us to see a new post each week around topics from new releases to helpful tips to industry news
  • EEs Talk Tech – Join Mike and Daniel for an insider’s perspective on some of the latest technology trends and what they mean for you
  • Keysight 2 Minute Guru – Check out this series of 2-minute videos for tips on making better measurements
  • Digital Design and Test webcast series – Need a little more detail on some of the more complex measurements? Check out our free webcast series and join technology experts for more info on a range of topics

 

Check them out today!

In urban slang, signal-to-noise ratio (SNR) is a simple enough concept: the ratio of useful to useless information. We all know people whose SNR is not as high as we might hope. Unfortunately there’s no technology yet available to boost their SNR.

So engineers can be happy that’s not true for RF signals. We can now extend SNR in wideband oscilloscope-based RF measurements through what’s known as “processing gain.” Digital down-conversion lets you see small pulsed RF signals next to large signals by reducing the noise level in a particular measurement—whether it’s RF pulse envelope characteristics or frequency or phase shift across a pulse.

Increase in pulsed RF capture dynamic range

So how does it work? The trick is adding vector signal analysis (VSA) software. VSA in conjunction with an oscilloscope can extend the SNR. First VSA shifts a captured signal down to baseband I/Q. Then it bandpass filters the acquired oscilloscope data and finally resamples the data at a lower sample rate. The result is lower noise, higher dynamic range, and a wider SNR.

Let’s look at an example: An 8 GHz-wideband oscilloscope captures a pulse train in which a large pulse is immediately followed by a small pulse that is 50 dB down from the first pulse. This corresponds to being 100,000 times lower in power and ~316 times smaller in voltage (sqrt[100,000]) than the first pulse. The two-pulse sequence then repeats.

The large pulse has a +6 dBm power level (~1.4 mW), which results in a peak voltage of around 633 mV into 50 ohms. This can be represented as a -4 dBVpk level (20log 0.633). It also corresponds to a 1266 mV peak-to-peak signal into 50 ohms.

In contrast, the small pulse, being 316 times smaller in voltage, is only 4 mV peak to peak (-44 dBm, -54 dBVpk).

The VSA software, which also controls the oscilloscope front-end sensitivity, is set to +6 dBm (633 mV peak). This corresponds to an oscilloscope vertical range of 1266 mV.  There are eight vertical divisions, so this also corresponds to a ~160 mV/div setting.

At the full 8-Hz bandwidth for this ~160 mV/div setting, the broadband RMS noise for the 8 GHz bandwidth oscilloscope is around 5 mV, interpolating from a noise chart in the data sheet, as shown in Table 1.  The 5 mV of noise translates roughly into a peak-to-peak noise that is three times the RMS noise (assuming Gaussian noise). In other words, we’re looking at 15 mV of peak-to-peak noise.

8GHz bandwidth oscilloscope RMS noise levels

Table 1. 8-GHz bandwidth oscilloscope RMS noise levels at various V/div settings

The small pulse (4 mV p-p) is masked by the noise in the measurement (15 mV p-p). (Think how easily a big-mouth can drown out softer-spoken colleagues.) The small pulse can’t be well-discerned in the full 8-GHz measurement of the oscilloscope, with a linear scale and no averaging, as shown in Figure 1.

8-GHz bandwidth oscilloscope capture of +6 dBm pulse next to a 50 dB down pulse

Figure 1. 8-GHz bandwidth oscilloscope capture of +6 dBm pulse next to a 50 dB down pulse (2nd pulse cannot be seen)

Import of real-time captured pulsed RF signals into analysis software and digital down-conversion

Basic pulsed RF measurements can be made natively on a high-bandwidth oscilloscope. And there are certainly times that measurements on directly sampled signals are desired. But this isn’t one of those times. Instead we’re looking for advantages available through external signal processing and analysis on captured signals.  For example, through a process called digital down-conversion, it’s possible to make a range of RF pulse measurements with higher accuracy. That’s due to the lower noise present by using processing gain. Let’s take a closer look.

Figure 2 shows the basic process of digital down-conversion.  Through digital signal processing, the oscilloscope samples are multiplied by the sine and cosine of an imaginary oscillator of frequency fc, where fc is generally chosen to be the center frequency of the signal of interest. In effect, we’re “tuning” to the frequency of the input signal. This process converts the time samples into real and imaginary number pairs that completely describe the behavior of the input signal. To reduce noise, these samples can be low-pass filtered and then re-sampled at a lower rate to reduce the size of the data set and allow FFT processing of the data at a later stage. The resulting digitally down-converted samples can then be placed into memory for further processing.

Oscilloscope-captured samples input to VSA software for digital down-conversion

Figure 2. Oscilloscope-captured samples input to VSA software for digital down-conversion

Some important demodulation information comes from this digital down-conversion process. First, consider what happens when the digital local oscillator frequency Fc is equal to the carrier frequency of a modulated signal. The output of the digital filters, which includes the real part I(t) and imaginary part Q(t), consists of time-domain waveforms that represent the modulation on the carrier signal.

Do you want that in math? Here’s a representation of the captured input signal:

=  A(t) * Cos[2pfct +q(t)]

where the following equation describes the amplitude modulation:

amplitude modulation equation

And the equation here describes the phase modulation:

phase modulation equation

Displaying the I-Q results in terms of magnitude coordinates gives us a view of the amplitude modulation.  Displaying the I-Q results in terms of phase coordinates offers a view of the phase modulation. Taking the derivative of phase modulation yields the frequency modulation.

frequency modulation equation

By adjusting the width of the low-pass filters, you can set a defined span around the center frequency where the filter width is just wide enough to pass the signal of interest, but narrow enough to filter out a lot of the noise.

 

Results of digital down-conversion and processing gain on the 50-dB down RF pulse

So in short, processing gain “tunes” to the center frequency of the signal and “zooms” into the signal to analyze the modulation.

In this example, the original 8-GHz-wide measurement with the associated noise is reduced to a 500-MHz wide measurement, centered on the 3.7-GHz carrier with an instantaneous measurement bandwidth slightly wider than the width of the signal modulation.  This corresponds to an improvement in SNR as follows:

10log*(ScopeBW/Span) = 10log*(8E+09/500E+6) = 12 dB.

Taking advantage of this processing gain, combined with VSA software’s ability to have a log magnitude scale, and using averaging, the 50-dB down pulse is now visible, as shown in Figure 3.

down pulse seen with Keysight VSA software

Figure 3. 50-dB down pulse seen with VSA software “Center Frequency” and “Span” set to 3.7 GHz and 500 MHz

The improvement in SNR realized through narrowing down the span is depicted graphically in Figure 4.

achievable SNR

 

Figure 4. Plot of SNR achievable in time view verses span adjustment in VSA software

You can draw a similar plot to see improvement in dynamic range possible when measuring narrow band signals, as shown in Figure 5.

Plot of dynamic range in FFT vs. resolution BW setting in Keysight VSA software

Figure 5. Plot of dynamic range in FFT vs. resolution BW setting in VSA software

Here the dynamic range improvement when measuring narrowband signals in an FFT view is described as:

10log*(ScopeBW/RBW)

This does not describe the spur-free dynamic range (SFDR) or harmonic distortion characteristics of the oscilloscope response, but it does give an idea of where the noise floor will be in an FFT measurement.  As the resolution bandwidth is decreased, and the noise is divided among smaller time buckets, the noise floor drops.

This graph does not account for limitations due to various spurs, so the spur-free dynamic range (SFDR) remains limited to around 50 dB.

Conclusion

Through the process of digital down-conversion, the SNR of an oscilloscope measurement can be significantly improved as a function of how much that measurement can be “spanned down” from the initial DC to 3dB bandwidth of the oscilloscope.  As our example showed, a 50-dB down pulse, not even visible on a normal scope screen, can be clearly seen once processed by VSA software and then displayed in a log-magnitude scale. This approach can be very helpful to speed system validation measurements on Aerospace/Defense pulsed-RF signals. With this process, you can significantly improve measurement accuracy when evaluating the spectral, pulse envelope, frequency chirp, and phase shift characteristics of an RF pulse train.

Introduction

In a previous post we described how phase noise information can be extracted from real-time oscilloscope waveform acquisitions using two different techniques to demodulate the phase. In this article we’ll take a look at the potential accuracy of the serial data clock recovery technique, what kinds of signals can reasonably be analyzed, and some ways to improve such measurements.

 

Accuracy

In order to check that the oscilloscope phase noise measurement is accurate we can use a clean signal source with a broadband random phase modulation source built-in. By injecting a relatively large PM amplitude over broad frequency we can verify the noise level by comparison with a measurement made on a Signal Source Analyzer such as the Keysight E5052B.

 

In the measurement below (Fig. 1), the SSA result is in blue and the oscilloscope measurement (using a Keysight MSOS804A) result is in green. There is excellent agreement over the range of injected PM. Above 2 MHz the SSA’s lower noise floor is the reason for the separation in the curves.

Fig 1

 

Measurement Noise Floor

The measurement floor of a jitter measurement on a real-time sampling oscilloscope is affected by both vertical (voltage) accuracy and timing accuracy. Vertical noise in the sampling system, stability of the timebase, the phase noise of the oscilloscope’s own oscillator & imperfections in the interleaving architecture of the scope will all contribute to errors in the jitter measurements and thus the measured phase noise.

 

An example of an oscilloscope jitter measurement floor specification is:

oscilloscope jitter measurement floor specification

The Intrinsic Jitter portion is dependent on the stability of the internal timebase reference. For the highest performance scopes such as the 63 GHz Keysight Z-Series this can be as low as 50 fs but it must be noted that this value is often only valid for fairly short acquisition times. To measure close-in phase noise we need to capture long acquisition times and the intrinsic jitter of the oscilloscope will increase due to its own phase noise.

 

Noise Floor & Signal Slew Rate

In most cases the first term in the equation dominates the jitter measurement floor. Both signal and oscilloscope vertical noise combine with the finite slew rate of the signal to create apparent horizontal displacement of edges, i.e.: jitter. Thus it is crucial to choose an oscilloscope with as low a vertical noise bandwidth density as possible. A further improvement in jitter measurement floor can be achieved if the oscilloscope also has the ability to limit the bandwidth to an arbitrary frequency. Since the phase noise information is contained within a bandwidth 2*fc we can drastically limit the measurement noise in many cases.

 

Below (Fig. 2) is a set of phase noise measurements made using a Keysight 8 GHz S-Series oscilloscope. The signal source was a 100 MHz sine wave from an ultra-low phase noise Performance Signal Generator, E8267D. The true phase noise of the E8267D (as verified with an SSA or other suitably low phase noise instrument) is well below the oscilloscope measurements so this enables us to see the measurement floor of the scope.

 

The oscilloscope bandwidth was adjusted for each measurement as follows:

 

Blue = 8 GHz, Green = 4 GHz, Red = 1 GHz, Cyan = 200 MHz.

Fig. 2

 

The phase noise floor at 1-10 MHz offsets drops from ~-124 dBc/Hz to -140 dBc/Hz when going from bandwidth of 8 GHz to 200 MHz. This can be explained by the fact that we’re reducing the bandwidth by a factor of 200 MHz / 8 GHz. If the noise of the oscilloscope is fairly flat with bandwidth we should expect a drop of about 10*log10(0.2/8) = -16 dB. This is not the case at all frequencies. At low frequencies the phase noise of the oscilloscope’s internal reference starts to dominate. At higher frequencies we see the limit of the ability to produce a perfect brick-wall bandwidth limit filter at 200 MHz. This means we are still getting some scope noise beyond 200 MHz included in our measurement.

 

The benefit gained in limiting the scope’s bandwidth is highly dependent on the slew rate of the signal to be measured and the ratio of the signal frequency to the full scope bandwidth.

 

Noise Floor & Scope Internal PLL/Oscillator

It is often the case with phase noise measurements that low frequency phase modulation is of particular interest. In addition to requiring responsive, deep memory acquisition as discussed in a previous article it is also important to have an oscilloscope with an extremely stable timebase and well-designed PLL circuitry as this will dominate the low frequency measurements.

 

In the measurement below (Fig. 3) you can see that an older technology oscilloscope (green) has higher phase noise at close-in offsets than the newer technology oscilloscope (blue).

 

Fig. 3

 

Further improvement of the close-in phase noise might be possible using an external reference clock to the oscilloscope which is cleaner than the internal oscillator. Below (Fig. 4) is a comparison measurement of a Keysight V-Series phase noise floor using the internal oscillator (blue) versus a Wenzel 10 MHz reference (red):

Fig. 4

 

Noise Floor & Sample Rate

Previously I mentioned that the oscilloscope sample rate must be kept high in order to accurately place the edges. It would be nice to be able to reduce the sample rate as it would allow us to use less acquisition points and thus either make faster measurements, increase averaging or go to lower frequency offsets. But we must be careful to make sure the sample rate does not impact our measurement accuracy significantly.

 

Below (Fig. 5) we can see the impact of reducing the sample rate (bandwidth is maintained at 200 MHz for all measurements) on the phase noise measurement of the same, clean 100 MHz sine wave.

 

Blue = 1 GSa/s, Green = 5 GSa/s, Red = 10 GSa/s, Cyan = 20 GSa/s.

Fig 5

 

You can see that eventually reducing the sample rate does impact the phase noise measurement floor. In this case there is not a significant difference between using 20 GSa/s and 10 GSa/s, but below that sample rate there is an increase in the results. The extent of the impact will also depend on the shape & slew rate of the signal edges.

 

Phase Noise of a Data Signal

Since the oscilloscope uses a clock recovery algorithm to extract the TIE information, an advantage of this approach is the ability to measure the phase noise of data signals. In the example below (Fig. 6) the phase noise of a high speed pattern generator is measured. The only difference in the measurements is the pattern used. Blue is a pseudo-random bit sequence and green is a repeating one-zero clock pattern:

Fig. 6

 

There is some difference in phase noise at high frequency offsets due to the nature of the generator.

 

Summary

To summarize, real-time sampling oscilloscopes – although perhaps not a first choice for phase noise measurements – can be an acceptable choice depending on the measurement requirements. For close-in phase noise measurements (typically less than 1 kHz or so) a dedicated phase noise analyzer or spectrum analyzer will provide a faster, more accurate measurement. However for measuring relatively low cost oscillators and PLL circuits or for wide bandwidth requirements an oscilloscope with a clean timebase and low noise front end may be very capable of making the required measurement. In addition using a real-time oscilloscope has the advantage of allowing you to extract phase noise from a serial data signal if a serial data clock recovery approach is used.

 

Questions? Visit the Infiniium phase noise forum.

What is Phase Noise?

Wikipedia defines phase noise as, “the frequency domain representation of rapid, short-term, random fluctuations in the phase of a waveform, caused by time domain instabilities (jitter)”. The inclusion of the word noise in the name tells us that this does not refer to any spurious or deterministic terms. The mention of “short-term” in the definition is meant to distinguish from other ways to determine the cleanliness of a clock source such as stability in points per million, ppm. This is usually measured over a much longer timescale such as seconds or minutes.

 

Phase Noise information is usually presented in a log frequency plot such as the one shown below (Fig 1) where the amplitude units are dBc/Hz (decibels relative to the carrier power normalized to a 1Hz bandwidth). The x-axis is the frequency offset from the nominal signal or “carrier” frequency.

Fig. 1

 

For a more complete explanation of what phase noise is I recommend the application note, “Using Clock Jitter Analysis to Reduce BER in Serial Data Applications.”

 

Why use an Oscilloscope?

Before describing how to measure phase noise using an oscilloscope it would probably be a good idea to ask “why use a real time scope for this kind of measurement?” There are instruments dedicated to the measurement of phase noise such as the Keysight E5052B Signal Source Analyzer which have a much lower phase noise measurement floor than any oscilloscope. An SSA is also able to accurately measure much closer-in phase noise offsets and much quicker than any oscilloscope. However there are typically some measurement restrictions such as limits on the maximum frequency offset range available. 100 MHz is a typical maximum offset for a phase noise analyzer. For clock frequencies greater than 100 MHz it may be desirable to measure out to higher frequency offsets than can be measured with these tools. Also an oscilloscope can measure the phase noise transferred onto a data signal, not just on a clock.

An oscilloscope may also simply be good enough for the measurement requirements if your budget doesn’t allow for a dedicated instrument for measuring phase noise.

 

Extracting the Phase

An oscilloscope captures and digitizes the complete signal waveform and there is more than one way to extract the phase noise information from the digitized waveform. In this article we will briefly describe two methods:

  1. Clock Recovery
  2. Phase Demodulation using Vector Signal Analysis

 

Phase Demodulation via Serial Data Clock Recovery

Oscilloscopes measure timing variations (jitter) of a serial data or clock signal by analyzing where a signal crosses a voltage threshold and comparing that to the edges of some reference clock. In the case of phase noise we want the reference clock to be an ideal, constant frequency clock. Most modern oscilloscopes have clock recovery algorithms to extract a clock from the signal. In many cases it is desirable that the algorithm emulates a Phase Locked Loop (PLL) but in our case we simply want to extract a constant period ideal clock so that we do not “track out” any of the phase variations like a PLL would. An example of the setup of clock recovery is shown below. (Fig 2) The algorithm can be set to adjust to the nominal signal frequency and phase based on each captured acquisition.

Fig 2

 

A time interval error (TIE) measurement on an oscilloscope will produce a time series of the absolute time error of each edge relative to the ideal clock. To convert to phase (radians) error we simply multiply by 2*pi*fc where fc is the clock carrier frequency.

φ[rad]=2*π*TIE(t)*fc

 

A Time Interval Error trend can be transformed to frequency space with an FFT to give something called a Jitter Spectrum. Most modern oscilloscopes have this capability built in or as an option (Fig 3).

 

Fig 3

 

Averaging of the jitter power spectrum over multiple acquisitions is necessary to get a clean view of the measured phase spectral density.

 

The Jitter Spectrum approach yields a maximum frequency offset (fφ_max) equal to the carrier frequency itself (when both rising and falling edges are included in the TIE).

 

The minimum frequency offset (fφ_min) is principally bounded by the length of time of the TIE capture. I.e.: no frequency content is captured lower than the inverse of the time between the first edge in the TIE trend and the last.

minimum frequency offset is bounded by the length of time of the TIE capture

Herein lies the difficulty with measuring phase noise on a real-time sampling oscilloscope. A high enough sampling rate must be maintained to accurately capture the edges in time, but in order to also get the low frequency content very large acquisition memory depths must be used to capture more time.

 

Example:

SaRate = 80 GSa/s

fφ_min = 100 Hz

Required Memory Depth = 800 Mpts

 

Each acquisition must then be processed to find the edges using clock recovery, Fourier transformed to create the jitter spectrum and then multiple acquisitions must be averaged. The oscilloscope must have deep memory available and be able to process it quickly.

 

We now have the fundamental information contained in a phase noise measurement but ideally we’d like to have units of dBc/Hz as is common practice for these measurements. Also most phase noise plots have a log frequency scale to enhance the viewing of close-in phase noise offsets.

 

As an example if we set up the TIE measurement in units of seconds rather than radians then to convert to units of dBc we do the following:

phase noise

 

However note that the phase noise above contains the energy from both sides of the carrier. Most often people think of the Single-Sideband (SSB) phase noise which is defined as the noise on a single side of the carrier spectrum & denoted by the use of the symbol L. Thus we must divide the above phase noise by 2 since L(fj) = 0.5*Sφ(fj) and also divide by the square root of the resolution bandwidth of the jitter spectrum to normalize to a 1Hz bandwidth.

 

Thus:

normalized phase noise calculation

 

An example of such a measurement and conversion is shown below.  (Fig.  4) This is a measurement of a very clean 100 MHz sine wave using a Keysight Infiniium DSAV334A oscilloscope in conjunction with an application called Infiniium Phase Noise. In addition to the averaging of the jitter spectrum, smoothing and spur removal techniques are employed in this application to get a better measure of the random phase noise floor.

 

 

 Fig. 4

 

Phase Demodulation via Vector Signal Analysis

Vector Signal Analysis software such as the Keysight 89600B can use a variety of hardware to acquire data including real-time oscilloscopes. Analog Phase Demodulation algorithms work differently than serial data clock recovery but with a very similar outcome.

Shown in Fig 5 is a high-level block diagram of how the phase demodulation is performed in the 89600B VSA software. An ideal local oscillator (LO) is mixed mathematically with 2 copies of the digitized signal – one of which is 90 degrees out of phase with the other. The resultant signals are then low-pass filtered to remove the high-frequency mixing products and leave just the phase (and frequency) error. This can then be displayed in many formats including the phase spectrum.

Fig 5

 

The VSA PM demodulation algorithm has optional automatic carrier frequency and phase tracking algorithms as shown below (Fig. 6):

 

Fig. 6

 

The auto-carrier frequency algorithm adjusts the clock frequency to the measured nominal signal clock frequency rather than the value input by the user (just like the serial data clock recovery). This frequency is re-calculated for each new waveform acquisition.

The auto-carrier phase algorithm also adjusts to the nominal phase of the incoming signal on each acquisition.

 

 

Below (Fig. 7) is a measurement of the same clean 100 MHz sine wave with the same DSAV334A oscilloscope but using the VSA software to control the scope acquisition, demodulate the phase and average the phase noise spectrum. There is excellent agreement between the two phase demodulation techniques.

Fig. 7

 

Summary

Different algorithms can be applied to digitized waveforms acquired by real-time oscilloscopes in order to recover the phase noise information and thus present phase noise plots. There are tradeoffs between the techniques which are outside the scope of this article but we can conclude that it is both possible and useful to be able to make phase noise measurements with an oscilloscope if the need arises. In part 2 of this article, we will explore tradeoffs and accuracy of using a real-time oscilloscope for these kinds of measurements. 

 

Questions? Visit the Infiniium phase noise forum.