Back to Basics: Jitter

Figure 1: Jitter is short-term variation
of a signal with respect to its
ideal position in time

Anyone working in applications that involve digital data, clocks, and serial data in general will eventually bump up against issues concerning jitter. Jitter is a subject of keen interest to every strata of the electronics industry. Chip makers, board integrators, system integrators, you name it: Everybody wants, and needs, to come to terms with jitter. It impacts reliability, manufacturability, and cost at all levels. And, of course, it's of keen interest to purveyors of test instruments, including us here at Teledyne LeCroy. In this first post of a projected series on jitter, we'll look at some of the tools built into modern digital oscilloscopes for jitter measurement and analysis.

Oscilloscope Basics: Trigger Holdoff

As discussed in an earlier post, triggering is the means by which we can coax an oscilloscope into showing us what we're looking for in an input signal, and indeed even simply to display it in a stable fashion. Two of the most basic triggering types are edge triggers and pattern triggers. The latter applies to mixed-signal instruments, allowing users to trigger on a logical combination of analog and digital inputs.

Back to Basics: Probes (Part IV)

Figure 1: An example of
differential probes
measuring from test
point to test point.

In three earlier posts on the basics of oscilloscope probes, we've taken a broad overview approach, looked more deeply at passive probes and inductance effects, and most recently, dug into active probes. Next up is differential probes, a different animal entirely from the foregoing types.

Back to Basics: Probes (Part III)

Figure 1: Active oscilloscope probes
sport high resistance and low
capacitance at their tips, but
terminate into a scope's 50Ω input.

In the first two installments of this series on probe basics, we examined some broad probe categories (Part I) and some of the issues that come with probe inductance (Part II). In the present installment, we'll delve a bit deeper into the topic of active probes. We'll also discuss when it's best to use passive probes and when to use active types.

Video: Zooming In On Waveforms

Many modern oscilloscopes offer the ability to zoom in on select portions of a waveform trace, allowing users a much more detailed look at whatever anomalies may (or may not) be present. Zooming is a handy feature on any oscilloscope, but it's even handier if you happen to be using a Teledyne LeCroy HDO. These instruments bring 12 bits of vertical resolution to the table for even more detail and cleaner, crisper waveforms than any legacy 8-bit oscilloscope.

So, without further delay, here's a short tutorial video on how to implement zoom traces on an HDO.

Back to Basics: Probes (Part II)

In a previous post, we provided some basic information about oscilloscope probes, including a brief survey of the different types and what can happen when the probe is connected to a DUT. In this installment, let's continue along those lines and take a closer look at passive probes.

Back to Basics: Probes (Part I)

Figure 1: An example of an active

oscilloscope probe 

To speak of an oscilloscope probe is to open a fairly large can of worms. There are many kinds of probes on the market, with differing functions and characteristics (Figure 1). This is the first in a short series of posts on the basics on probes, what the various kinds are used for, and how they might be expected to affect measurements taken with them.

Oscilloscope Basics: Controlling an Oscilloscope (Part II)

Figure 1: An example of a
touch screen-equipped
oscilloscope.

In a recent post, we discussed how to control a modern digital oscilloscope using the front-panel controls. That was a natural place to begin, given that it's the "traditional" means of controlling the instrument and the one that most seasoned users cut their teeth on. But there's more than one way to skin this cat these days. Many of today's oscilloscopes carry touch screens that do everything the front-panel controls can do, plus some things they cannot do.

Oscilloscope Basics: How to Set Up and Use Cursors

As a follow-up to a recent post with an oscilloscope front-panel tour, we want to dig a little deeper into one aspect of controlling the instrument, and that's how to set up and use cursors. But instead of describing it in prose, it makes more sense to show you. So enjoy this brief tutorial video that will get you started with cursors! We're demonstrating on a Teledyne LeCroy HDO4054, but most of what we're showing you translates to other manufacturer's instruments.

Going From FFTs to Spectrum Analysis

Figure 1: Spectrum Analyzer software for the HDO series
oscilloscopes provides an intuitive user interface

In earlier posts, we looked at a) the basics of fast-Fourier transforms (FFTs) and b) how to set up an FFT on a modern digital oscilloscope. In this post, we'll take a brief look at what that modern scope can do with an FFT, provided that scope is outfitted with software that will let it take full advantage. After all, the object of an FFT is to transform a time-domain waveform into the frequency domain. Sounds kind of like a spectrum analyzer, no?

Waveform Generator Tricks: Pulse-Width Modulation

Figure 1: Teledyne LeCroy's WaveStation
waveform generator

Imagine that you're designing a digital control circuit but you really want it to behave like an analog circuit. Say, something like light dimmers, or a motor controller. A tried-and-true approach is to use pulse-width modulation (PWM) to have your digital control logic emulate the behavior of analog control. And your handy-dandy waveform generator, if so equipped, is a great way to generate a PWM signal to test out your design.

Oscilloscope Basics: Controlling An Oscilloscope (Part I)

Figure 1: Front of HDO4054 oscilloscope

At first glance, the front of today's oscilloscopes can be daunting. For starters, there's an array of physical "hard" controls. Relatively recent models may also sport touch screen displays with so-called "soft" controls. For one thing, getting familiar with the front of these instruments is only a matter of experimentation and common sense. And for another, what at first may seem complex is carefully designed to make the instrument as easy to operate as possible. This is the first installment of a projected series of posts that will explain how to control a modern oscilloscope. Here, we'll start with the front panel.

Back to Basics: What is an FFT?

Figure 1: An FFT of a 300-kHz square wave.

In an earlier post, we discussed the basics of setting up a fast-Fourier transform (FFT) on an oscilloscope, and why you'd want to use an FFT to get a frequency-domain view of a time-domain signal in the first place. It might be a good idea to take a step back and dig into just what an FFT is (Figure 1).

Back to Basics: Creating Pulsed Waveforms

Figure 1: The Pulse
waveform dialog box.

Many test applications call for the creation of pulsed waveforms ranging from clock signals to logic control to trigger signals, among others. Often, these waveforms are used in the characterization and debug of digital devices and circuits. Stand-alone pulse generators provide one way to generate pulsed waveforms but in many cases, a general-purpose waveform generator will do a fine job.

Don't Just Trigger, But Trigger Smart

Figure 1: The runt pulse and non-monotonic edge anomalies
in this signal are not apparent with a simple edge trigger.

In an earlier post, we looked at some of the basics of oscilloscope triggering and noted that there are two broad classes of triggers: simple triggers that sense particular characteristics of the input signal (transition edges, pulse widths, and so on), and more complex triggers that let you zero in on more specific attributes of the signal based on timing and amplitude parameters.

Oscilloscope Basics: Setting Up FFTs

Figure 1: Capture time determines the
frequency resolution, Δf.

For most of their history, oscilloscopes have been thought of chiefly as a time-domain instrument. That is, an oscilloscope facilitates the observation of changes in a signal's amplitude over time. However, many modern digital and mixed-signal oscilloscopes provide spectral analysis capabilities based on fast Fourier transforms (FFTs) that convert a time-domain waveform into the frequency domain. There are lots of good reasons for taking advantage of this capability. Perhaps the most important is to gain insight into characteristics of the signal that simply are not apparent from a time-domain perspective.

Waveform Generators, Arbitrary and Otherwise

Figure 1: Teledyne LeCroy's ArbStudio 1104 is a four-channel,
16-bit arbitrary waveform generator with a maximum interpolated
sampling rate of 1 GS/s.

Next to an oscilloscope and perhaps a digital multimeter, a waveform generator is one of the most versatile and useful pieces of test equipment on the bench. Often, a device or circuit under test will require some kind of signal stimuli with which to confirm proper function and/or ferret out faults. This can run the gamut from a simple swept sine or pulse waveform for purposes of characterizing signal response, to advanced serial-data protocols, and even to the playback of analog signals captured in the real world. A waveform generator is your ticket to creating the required stimuli for your device or circuit under test.

Back to Basics: Differential Probing

Figure 1: Emitter voltage measurement
in simplified schematic view

Whether or not we think of it in such terms, any voltage measurement taken with an oscilloscope or voltmeter is, in reality, a differential voltage measurement. A voltage is, by definition, the difference in electrical potential between two points in a circuit. It's impossible to take a voltage measurement with only one voltmeter lead. One lead must be attached to the point of interest while the other must be connected somewhere else as a reference point.

The Realities of Oscilloscope Probes

Figure 1: Teledyne LeCroy's ZS2500

high-impedance active probe

Looking for a good, albeit very expensive, paperweight? Try using an oscilloscope without probes! Probes are often taken for granted but they are one of the most critical elements of the signal chain in any test scenario.

Back to Basics: Sequence Mode

Figure 1: Sequence mode enables fast trigger rates
and optimizes memory usage by
ignoring dead time.

Now and again, an oscilloscope user may need to capture either a large number of fast pulses in quick succession, or a small number of events separated by relatively long periods of time. Either of these scenarios are challenging with typical acquisition modes. Fortunately, most modern oscilloscopes offer what we call "sequence mode" (other oscilloscope makers refer to similar acquisition modes as "fast-frame" or "segmented memory" mode).

Back to Basics: Random Interleaved Sampling

Figure 1: This image illustrates the
general principle underlying RIS.

Modern oscilloscopes come with all kinds of bells and whistles, and users might be tempted to invoke them for all sorts of situations. But not every whiz-bang feature of an oscilloscope is applicable all the time. Rather, some features are great in the right applications but disastrous in others.

Oscilloscope Basics: Sampling Rate

In a recent overview post on oscilloscope banner specifications,
one of the topics covered is sampling rate. Let's do a somewhat deeper dive on that topic and look at what sampling rate means to oscilloscope users.

An Overview of Oscilloscope Banner Specs

"Banner specs" is a term that oscilloscope makers use often. If you've ever met with one of the vendors' salespeople, you're likely to have heard it. But what are banner specs and what do they mean to you?

Oscilloscope Basics: Triggering

At some point, it's likely you've had the experience of capturing a waveform on your oscilloscope only to see a wildly unstable trace displayed on the screen. Chances are that you hadn't adjusted the triggering correctly. Let's take a brief look at what triggering is and why it's important in an oscilloscope. Trigger modes determine when the oscilloscope acquires and what is displayed.

The Making of 12-Bit Scope Hardware

In many applications, the accuracy of a true 12-bit oscilloscope is not only desirable, but necessary. Going forward, this will become the case more and more often. When choosing one, it's a good idea to peek under the covers and gain a little insight into how the instrument operates. Having discussed in an earlier post the advantages of oscilloscopes with 12-bit vertical resolution, let's look at the ways in which that resolution is accomplished in hardware.

Oscilloscope Basics: Oscilloscope Bandwidth

Among the most important basic specifications of a digital oscilloscope is its bandwidth. Knowing a bit about bandwidth and the influences on the specification can be very helpful in selecting the right oscilloscope for your application. This post will cover some fundamental aspects of oscilloscope bandwidth.

Zero in on Power Analysis

Given the emphasis on "green" initiatives, in which anything and everything is touted as "energy efficient," there's been lots of chatter about low-power design. Naturally, much attention is focused on switched-mode power supplies, power devices, and power-conversion circuitry of all kinds. This is where a lot of power efficiency is either lost or gained, depending on how carefully you approach the design task. You know, a milliohm here, a milliohm there, and pretty soon you're talking about real voltage drops that are going to affect the performance of a power-distribution system.

Spectrogram Display Is Another Tool in the SI Shed

An oscilloscope with spectrum-analysis capability marries the best that both instruments offer in one package. You get the traditional oscilloscope view of signals in the time domain, but you also get the spectrum analyzer’s ability to take the same signal and look at it from the frequency perspective.

Check Constellation Diagrams for Digital Data Integrity

Data-communication systems that rely on quadrature signal generation to phase-encode data can run into a number of signal-corrupting snags. These can include things like Gaussian noise, non-coherent single-frequency interference, phase noise, and attenuation in the channel and/or receiver, to name a few. But did you know that you can use your digital oscilloscope to diagnose problems like these?

You Can’t Eliminate Noise You Can’t Measure

Noise within a circuit or system is, by most anyone’s definition, the bane of the engineer’s existence. It can be maddening to track down and even more so to solve. It can come from many different sources, from thermal problems to cold solder joints to grounding issues, and often from more than one at the same time. On top of that, it’s a random phenomenon by nature. Noise detection and analysis is a matter of having the right tool(s). It’s especially helpful if those tools span the time, frequency, and statistical domains. Naturally, an oscilloscope is the go-to tool for noise measurement and analysis.