You need to test, we're here to help.

You need to test, we're here to help.

12 April 2021

Take a Coffee Break and Learn How to Use Measurement Statistics to Set Up Triggers

Figure 1.  Histogram of the different pulse widths occurring
in a pulse-width modulated rectangular pulse train.
Triggering is an essential element in all modern digital oscilloscopes.  The trigger synchronizes the oscilloscope’s data acquisition with a user-specified event on the signal, be that an edge, threshold crossing or a specific signal characteristic. Teledyne LeCroy Smart Triggers can trigger oscilloscope acquisitions based on properties such as a period, width, low signal amplitude, slew rate or signal loss. These trigger types are ideal for capturing transient events like glitches, but they require knowing at least a range of possible values for the trigger to detect.

Intermittent transient events and glitches are among the most frustrating problems to detect and solve. This is especially true if you have no idea about the nature of the transient. However, you can use the oscilloscope’s measurement tools to help locate these bothersome transients, then use that information to set up your trigger to capture them when they occur. Here’s how.

05 April 2021

How to Test the CMRR of Differential Probes

Figure 1: CMRR plots for two attenuation
settings of an HVD3106A differential probe.
While recently we told you not to connect two probes to the same place at the same time, there is a case where connecting two tips of a differential probe to the same place at the same time is useful, and that is when testing the probe’s common mode rejection ratio (CMRR). CMRR is frequency dependent, so part of developing “situational awareness” of your test environment is to know how your probe behaves with different signals at different frequencies. 

Although CMRR as a function of frequency is a principal specification for differential probes, manufacturer's CMRR plots are the result of testing with a narrowband source under strictly controlled laboratory conditions. In real-world applications of probes to broadband sources, you can expect a different result. This quick test will inform you how different.

29 March 2021

Take a Coffee Break and Learn How to "Layer" Measurement Tools

Figure 1: Multi-grid display "layers" multiple
measurement tools to find hidden glitch.
Teledyne LeCroy oscilloscopes have four, distinct sets of measurement tools, including measurement graticules, cursors, parameters and graphs. These tools developed historically and are designed to be “layered” on multi-grid MAUI® oscilloscopes so that each addition brings a new level of understanding and insight. Even on oscilloscopes that do not have multi-grid displays, as shown here, several measurement tools can be applied at once for added insight. Read on to see how, properly combined, they can help you find waveform anomalies and assess their frequency of occurrence in a few, simple steps.

22 March 2021

TDME Primer: Automated USB-C® Timing Measurements

Figure 1: Interleaved decoding of USB-PD and DP-AUX signals.
Increasingly, serial data analysis is analysis of the interoperability of the many protocols that must perform together within interconnects and embedded systems. Nowhere is this more true than for USB-C® devices, which we’ll focus on in this post, although these examples of cross-protocol timing measurements could apply to any protocols supported by our TDME and DME options.

The USB-C connector packs many protocols onto one, small pin set, and maintaining signal and power integrity is a compliance challenge. Besides high-speed data delivery, USB-PD (power delivery) provides flexible power distribution, while auxiliary sideband signals, like DisplayPort™, transport video. Troubleshooting these capabilities requires the ability to measure timing between serial data packets, as well as between data packets and analog signals. 

For example, DisplayPort over USB-C (DPoC) in alternate mode (alt-mode) can manifest as an interoperability failure if there is a timing issue between alt-mode initiation and the start of DP-AUX.

15 March 2021

The Important Difference Between ProtoSync™ and CrossSync™ PHY

Figure 1: CrossSync PHY captures everything from
physical through protocol layers at once.
With the recent release of our new CrossSync™ PHY for PCI Express® product, some of you may be wondering how it’s any different than ProtoSync™ for PCIe®, which has been around for quite a few years.

ProtoSync is an option for Teledyne LeCroy oscilloscopes with bandwidths that support high-speed serial data analysis. We’ve released ProtoSync options for PCIe, USB, SAS/SATA and Fibre Channel. ProtoSync links the same Protocol Analysis Suite software that is used with our protocol analyzers to the oscilloscope application, so that you can see physical layer decodings in the familiar PETracer and BITracer views right next to the decoded analog waveform. 

CrossSync PHY differs from ProtoSync in the three, significant ways:

08 March 2021

TDME Primer: Serial Trigger and Sequence Mode Sampling

Figure 1: Sequence mode sampling packs multiple acquisitions
into memory with very little “dead time” between them.
Sequence mode sampling, also referred to as segmented acquisition, is a sampling mode that divides the oscilloscope’s acquisition memory into a user-defined number of equal length segments. Each segment stores a single acquisition of the triggering event, with as much buffer zone as will fit into that segment, given the total number of segments requested. Only after all segments have been acquired is the data processed and displayed. 

The real power of sequence mode becomes evident when you combine it with intelligent triggers, such as the serial data triggers delivered with TDME options

01 March 2021

TDME Primer: Selecting Sample Rate for Serial Bus Analysis

Figure 1. Sample rate of only four sample points per bit
decodes correctly and lengthens serial bus acquisition.
Teledyne LeCroy supports trigger, decode, measure/graph, and eye diagram (TDME) software options for over 20 serial data standards, and the list is growing. This series will address practical tips for using TDME software successfully, and showcase some examples of applying TDME capabilities to real-world problems.

Given the wide range of protocols supported, you might be curious about how to best choose the oscilloscope sampling rate for a given standard when acquiring serial data signals. The optimal sample rate is determined by three principal factors: 

1) the bandwidth of the signal being digitized by the oscilloscope’s analog-to-digital converter (ADC);

2) the desired duration of the acquisition;

3) what you are going to do with the acquisition.

22 February 2021

Don't Attach Multiple Probes to the Same Place at the Same Time!

Figure 1. Response of two different probes to an
upper-side gate drive measurement.
Along with using single-ended passive probes for high-voltage measurements, another probing "no no" to avoid is attaching multiple probes to the same place at the same time.

You are probably aware that all measuring instruments, including oscilloscopes, are subject to conditions of observability.  As we discussed in a recent post on The Impact of the Interconnect, the very act of connecting the oscilloscope to the circuit with a particular probe affects the measurement in a particular way. Probes affect the circuit by applying additional resistance and capacitance loads in parallel with the circuit at the test point. Moreover, the probes themselves limit the fidelity of the measurement due to limits of bandwidth, slew rate and common mode response. So, it is always a good idea when making a measurement to compare how different probes/interconnects will affect the measurement…but don’t try to do it all at once.  

15 February 2021

Don't Probe HV with Single-ended Passive Probes!

Figure 1. A simple 120 Vrms switch-mode power supply
has a +/- 170 V peak and a 340 V pk-pk, difficult for
most single-ended passive probes to ground safely.

The high-impedance passive probes distributed with oscilloscopes of every major brand are sturdy, reliable and accurate within their specification limits, but they’re not intended for all applications.  This is especially true when measuring switch-mode power devices or other (relatively) high-voltage systems. These applications require probes that are both rated for their high voltage levels and isolated from ground as a reference voltage.  

High-impedance passive probes generally have maximum voltage limits of about 500 V and are ground referenced—meaning, one side of the probe is connected physically to earth ground through the oscilloscope.  If you’re measuring a single-phase 120 V line input to a power supply or inverter, you should be careful when connecting the probe ground to power neutral, which may not always be at ground level.  Using a differential probe, which is not ground referenced, eliminates this concern.

08 February 2021

Using Spectrograms to Visualize Spectral Changes

Figure 1. The spectrogram shows a history of
change in a spectrum and highlights variations
in frequency or amplitude.

In our last post, we discussed spectral analysis of RF in the lab as part of developing situational awareness. Another tool for spectral analysis is the spectrogram.

The spectrogram is a display composed of the most recently acquired 256 spectra all stacked in a persistence display. It is a feature of the SPECTRUM-1 and SPECTRUM-PRO-2R options that highlights variations in acquired spectra, making dynamic changes immediately visible. 

The spectrogram in Figure 1 shows the timing dynamics of a power rail load variation in a three-dimensional (3D) plot with color persistence. The same data could also be rendered in a flat, two-dimensional (2D) spectrogram display, or using monochrome instead of color persistence.  

01 February 2021

Situational Awareness: RF Noise in the Lab

Fig. 1. Time domain (top) and spectral (bottom) views of
ignal shown in SPECTRUM-1 on a WaveSurfer 4000HD. 
Laboratories have multiple sources of RF that can affect measurements, like computers, cell phones, routers, local radio and TV stations, even a nearby airport. Knowing the RF background of your lab is another part of Situational Awareness. Only by knowing the background can you know what is actually due to the device under test.

One way to read RF is through spectral analysis of Fourier transforms (DFT and FFT). FFTs take a time domain view of a signal (e.g, amplitude versus time trace) and change it into a spectrum of amplitude plotted as a function of frequency. Frequency spectrums are great for observing signals than are asynchronous with the process being measured. They have a lower noise floor and offer better dynamic range than do time domain plots.  Consider the views of the same signal shown in the time domain and frequency domain in Fig. 1.

25 January 2021

Situational Awareness: The Impact of the Interconnect

Fig 1. Coaxial cable has little effect on signal rise time,
but that's not true for every connection method.
How you connect a signal to your oscilloscope affects your measurements, and knowing the impact of different connection methods is an important part of your situational awareness.  

Using the same 40 ps fast edge signal we used for the risetime measurements in the last post, we’ll compare connections made using coaxial cable and a 10x passive probe, with and without different accessories.

18 January 2021

Situational Awareness: Testing Oscilloscope Outer Limits

Fig 1. 40 ps signal measured full bandwidth on a
1 GHz oscilloscope shows visible over/undershoot.
Nothing is perfect. Every test instrument has its limits, and knowing the limits to your oscilloscope’s bandwidth in response to real-world signals helps to develop situational awareness when making measurements. This is especially true when testing signals that are at or very near the specified bandwidth limit of the instrument.

The measurements we’ll demonstrate were made on a WaveSurfer 4104HD, a 12-bit, 4-channel, 1 GHz bandwidth oscilloscope that samples at up to 5 GS/s.

11 January 2021

Four Measurement Best Practices

To start the New Year right, we’re going to talk about four measurement "best practices", which will help you get the most out of any oscilloscope you have. These are important when doing any type of measurement—and you can get a good start on them simply by asking yourself the four questions in the sidebar.

1. Anticipate the results

Those who are familiar with Dr. Eric Bogatin’s Rule #9 will know this one. Before you do any measurement, anticipate what you expect the result to be, because that is the most important way of identifying if there is a potential problem. 

04 January 2021

Decision Feedback Equalization in DDR

Figure 1. A transmitted rectangular pulse suffers
distortion by the time it reaches the receiver. 
Broadening and reflections from previous
transmitted bits add to the pulse response, 
creating inter-symbol interference.

High-speed serial links such as those used in DDR4 and DDR5 are subject to a variety of signal degradation challenges.  Insertion losses, frequency dependent attenuation and inter-symbol interference (ISI), as well as others, are among the most commonly encountered sources of signal degradation. 

Figure 1 shows how reflections can cause ISI on a rectangular pulse. When a rectangular pulse is transmitted, it suffers distortion which is apparent when it reaches the receiver.  It may be broadened due to group delay dispersion because different frequency components of the signal propagate along the signal path at differing velocities. In addition, there may be echo pulses, due to impedance mismatches in the channel.  These mismatches cause reflections that propagate back and forth over the channel and appear as these echoes where subsequent bits should be.