Electronic Design

T&M Puts Signal Integrity In The Cross Hairs

This year, signal-integrity issues stepped front and center in the test and measurement arena—not that SI is a new problem for designers. But with the proliferation of communications standards, especially serial data formats at rates that are well into the gigabit range, SI has become paramount.

Most new communications standards are for digital systems. When you're dealing with signals in the high megahertz and gigahertz range, however, calling them digital rather than analog signals can be the proverbial distinction without a difference. Their task may be to create ones and zeros, but the systems suffer from analog-type problems. Instruments that analyze SI are the means by which designers can find and eliminate those problems.

What makes covering T&M so interesting is that the new devices and standards can have all the speed they want, but they wouldn't be very useful without the ability to evaluate them—standalone and in-circuit. And T&M companies always seem to step up when needed. Here are some of the leading SI measurement systems introduced this year.

The MP1797A is a one-box solution for jitter testing of 40G transmission devices designed to ITU-T Standard O.172. With a built-in jitter generator and jitter-receiver and optical-to-electrical and electrical-to-optical conversion modules, the system automates jitter generation, jitter tolerance, jitter sweep, jitter transfer, and frequency-sweep tests. The generator section outputs a 39.81312-GHz clock with modulation frequencies to 320 MHz and amplitudes to 16,000 UI p-p. In addition to a 1/1 clock, the analyzer has 1/16 and 1/64 clock outputs so it can perform very accurate transponder tests.

First came the 81141A 7-GHz serial pulse data generator, followed three months later by the 81142A 13.5-GHz version (see the figure). The instruments are designed to stimulate new communication designs, especially under stress. Their pulses feature transition times below 20 ps and jitter of less than 1-ps rms. Multiple data formats include R1, RZ, and NRZ, with configurable width, duty cycle, and cross-point support. They also create pseudorandom binary sequences. Thanks to a 32-Mbit memory, designers can produce complex real-world patterns, with sequencing and looping capability available.

LECROY 11000
A DSO-based serial data analyzer, the SDA 11000 comes with a full complement of jitter and eyepattern analysis tools. The four-channel instrument features an 11-GHz bandwidth and an acquisition rate to 40 Gsamples/s. Standard memory is 8 Mpoints/channel (16 Mpoints in one-or two-channel operation), with upgrades to 100 Mpoints available. Automated functions include jitter filtering, multiple methods for total jitter measurement, ISI plotting for measuring data-dependent jitter without repeating a bit pattern, and a mask error violation locator.

This software package of automated measurements for Tek's WCA200A, RSA3300A, and RSA3408A real-time spectrum analyzers helps designers characterize phase noise, jitter, frequency deviation, and settling time for transient RF signals. Included are exclusive time-related measurements, like phase noise over time, for detecting intermittent effects. The software allows designers to display a spectrogram, which shows frequency horizontally, time vertically, and amplitude as a color scale, in addition to the traditional spectrum analyzer view of a signal with noise sidebands.

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