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

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

20 August 2014

Go Back to School on Signal Integrity

No matter how much we might think we know about signal integrity, there's always more to learn. The laws of physics never change but we might come across new scenarios in which to apply them. Circuits with higher levels of functionality are constantly being squeezed into smaller, more portable spaces; the closer together we pack active components and transmission lines, the more acute their sensitivity is to electromagnetic energy. Everything's either a transmitter or a receiver in some sense and everything has effects on other components, intended or otherwise.

A great deal of what any oscilloscope user is concerned with revolves around signal integrity. Often, engineers are tasked with quantifying and/or eliminating SI problems like reflections on transmission lines, ground bounce, and crosstalk. You have your aggressor nets and your victim nets, your impedance mismatches, and other issues that in one way or another degrade the performance of the system. Oscilloscopes and network analyzers are the primary tools for understanding these SI parameters. The more users know about SI, the better equipped they are to take advantage of the capabilities of test and measurement tools.

Continuing education is important in all fields of endeavor. In the signal integrity realm, one such resource is Signal Integrity Academy, the online home of an ongoing series of video classes conducted by renowned SI expert Dr. Eric Bogatin. SI Academy offers a wealth of material on SI for everyone from beginners to grizzled veterans. Of particular note is a compilation of presentations, Essential Principles of Signal Integrity, in which Bogatin covers basic SI concepts as well as topics such as differential pairs, reflections and terminations, reflections and routing topologies, ground bounce, crosstalk, and more. We're talking some 16 hours of presentations in this section of SI Academy alone. Subscribers should start with the Essentials Principles course, as the subsequent sections of the Academy build on these basics.

A second collection of related talks is Advanced Gigabit Channel Design, which homes in on the problems associated with interconnects in the range of 1 to 40 GB/s. Here, you'll learn about the design techniques, materials, and technologies with which to reduce Gigabit channel problems to acceptable levels. Also covered are analysis techniques and tools you can use to accurately predict signal quality at the channel's receiver.

In the section of SI Academy labeled "S-parameters for SI," Dr. Bogatin strips away the layers of FUD surrounding S-parameters. Looking behind the complicated math, Bogatin delves into essential principles of S-parameters. Fundamentally, S-parameters are used to describe the interactions of sine waves and interconnects. This course extends S-parameter concepts into the time domain, examining both single-ended and differential interconnects. Rather than being intimidated  by S-parameters, this course shows you how to make them a useful and relied-upon tool.

A fourth section of SI Academy delivers some 30 hours worth of Dr. Bogatin's videos, recorded presentations, and webinars on a host of SI-related topics. Here, you'll find tons of material on how the concepts and principles of SI are applied to real-world scenarios.

There's an old maxim that says, "Education costs, no matter how you get it," and it applies to SI Academy. There's a cost associated with subscriptions, but when you consider that a subscription gets you anytime virtual access to a world-renowned SI expert's knowledge, it's a worthwhile investment. Having said that, each section of SI Academy contains a number of videos that can be viewed without a subscription, so take a look and decide whether a subscription would be of use to you. 

05 August 2014

Back to Basics: History Mode

Back in the day, one of the biggest deficiencies of early digital oscilloscopes was their lack of memory depth. A memory of 500 or 1000 points was about as good as it got, and this didn't provide much in the way of detailed waveform capture. Today's instruments are very different animals; for example, Teledyne LeCroy's recently introduced WaveSurfer 3000 oscilloscopes offer up to 10 Mpoints of memory per channel.

All that memory comes into play when one invokes History Mode, a debug and analysis tool found in many Teledyne LeCroy oscilloscopes. History Mode lets users scroll back in time to isolate anomalies or other waveform events. Then, they can be measured with parameters or cursors to quickly turn up the sources of signal problems.

Initial setup of WaveSurfer 3000 oscilloscope
Figure 1: Initial setup of WaveSurfer 3000 with a
2-MHz pulse waveform fed into Channel 1
Often, when we view waveforms on an oscilloscope's display, unexpected events may occur and we'll want to stop the trigger and view these interesting little behaviors. The great thing about History Mode is that it automatically stops the trigger and displays a list of previously captured waveforms. This shortens the amount of time it takes to identify problems, enabling us to view, quantify, and analyze those anomalies in our signal.

Here's an example, in which we fed a 2-MHz pulse into Channel 1 of a WaveSurfer 3000 (Figure 1). The best way to access History Mode is directly from the front panel; it's also available in the Timebase drop-down menu. Pressing the History button stops the trigger and displays a list of previously captured waveforms alongside the waveform grid. Here's how the History Mode dialog box looks along with the waveform list (Figure 2).

Invoking History Mode with the front-panel button opens the related dialog box at bottom.
Figure 2: Invoking History Mode with the front-panel button
opens the related dialog box at bottom. 
A neat feature of History Mode is its interactivity; tapping any line in the waveform table automatically brings up that acquisition. Scrolling up and down the table gives users direct access to any acquisition.

The Waveform History Navigation controls in the History Mode dialog give users a flexible means of traveling backward and forward through all of the acquisitions stored in memory. The controls offer slow/fast scrolling, single stepping, and a second scroll bar (Figure 2, again).

The top row of controls regulates scrolling with the two outer buttons starting a fast scroll and the two inner buttons a slower rate of scrolling. On the bottom row, the two outer buttons take the user to the oldest and newest acquisitions while the inner pair step through one at a time. You can tap the index box to directly enter a specific acquisition. The Relative Times check box toggles between the table displaying the absolute times of acquisitions and the relative time from the last acquisition.

Users can perform measurements and/or math operations on any History Mode acquisition.
Figure 3: Users can perform measurements and/or math
operations on any History Mode acquisition.
Any displayed acquisition in History Mode is saved by opening the File menu and selecting Save Waveform. Users may also apply measurements or math operations to any selected History Mode acquisition (Figure 3).

History Mode, then, is a great debug and analysis tool, automatically saving all acquisitions and giving users a convenient means of navigating amongst them with a tabular list.

30 July 2014

Video: WaveSurfer 3000 and the MAUI User Interface

Oscilloscopes are often an engineer's best friend, but that can change depending on how easy or difficult a given instrument is to use. Sure, the oscilloscope's capabilities and technical specs are critical, but if the machine is difficult or non-intuitive to interact with, the user ends up wasting time figuring out what should be simple.

Here at Teledyne LeCroy, we spend a lot of time and energy on our oscilloscopes' user interface. User efficiency is very important to us and we think that's reflected in our MAUI user interface. In this video, Applications Engineer Jeff Krauss takes you through a brief tour of MAUI as it appears in our recently launched WaveSurfer 3000 oscilloscopes.

24 July 2014

How Many Channels is Enough?

A switch-mode power supply driving a fixed load can be designed and optimized specifically for that load.
Figure 1: A switch-mode power supply driving a fixed load
can be designed and optimized specifically for that load.
The bulk of oscilloscope applications are well served by instruments with four analog input channels. Most basic debugging and design-related work involves probing of only one signal at a given time, and occasionally more than one, especially when differential signals are concerned. Thus, many users may never see a need for an oscilloscope with more than four channels.

Having said that, there are some applications that by their very nature surpass four channels. Moreover, some of these applications concern circuits and devices that are produced in extremely high volumes. A case in point is switch-mode power supplies, such as those typically found in notebook PCs, tablets, or embedded systems.

18 June 2014

Applying Selective Averaging to Waveform Acquisitions

Figure 1: Using pass/fail testing to average only those
waveforms which are inside the tolerance mask
In the course of using an oscilloscope, there are likely to be times when you'd like to separate pulses based on wave shape or some parametric value and average only those pulses that meet some criteria. Teledyne LeCroy's oscilloscopes, and others, provide pass/fail testing using masks and/or parametric readings to qualify waveforms before they're added into an average or other processing function. Let's take a look at how this works on a Teledyne LeCroy oscilloscope.

09 June 2014

Video: Vertical Controls on the HDO Oscilloscopes

Here's another in our continuing series of tutorial videos. This time, we'll review the use of the vertical controls on a Teledyne LeCroy HDO oscilloscope. These controls facilitate positioning and scaling of waveforms vertically on the oscilloscope's display. Note that although we're demonstrating these controls on an HDO, you'd be rather hard pressed to find an oscilloscope from any manufacturer without a volts/div and vertical offset control. Thus, this video is applicable to whatever oscilloscope you have on your bench.

There are quite a few tutorial videos for a broad range of Teledyne LeCroy products on our YouTube channel. Head on over whenever you need a refresher!

22 May 2014

The Effects of Passive Probe Ground Leads

Teledyne LeCroy's PP108, a representative passive probe
Figure 1: Teledyne LeCroy's PP108,
a representative passive probe
When you open the box containing your shiny new oscilloscope, one of the items you'll likely find inside is a set of basic 10:1 passive probes (Figure 1). Those probes have a ground lead that you'll want to use when you make measurements. Your probe has a bandwidth specification that's probably somewhere between a few hundred megahertz to 1 GHz; that spec was obtained at the factory with a specialized test jig having a specific ground inductance and source impedance. Now, the way in which you connect your ground lead can have a big impact on the real-world bandwidth and response of the probe.