PULSE
BACK TO BASICS: JITTER David Maliniak Technical Marketing Communication Specialist Teledyne LeCroy
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.
There are a number of measurement and analysis techniques one can turn to for quantifying and estimating jitter. Among them are: Histograms Measurement track Time Interval Error (TIE) Jitter breakdown and extrapolation Persistence display of jitter A traditional means of investigating a signal for jitter is to use the oscilloscope’s persistence display mode (Figure 2). It’s relatively easy to set up and get a quick eyeball estimate of total jitter. However, it’s not a method you’d use for serious diagnostics. The results are skewed by any trigger jitter that is present, and it’s also subject to human interpretation.
Figure 1: Jitter is short-term variation of a signal with respect to its ideal position in time
What’s all this “jitter” stuff, anyhow? A broad definition is “the short-term variations of a signal with respect to its ideal position in time.” Jitter can manifest as instability in signal period, frequency, phase, duty cycle, or other timing characteristics. It’s of interest from pulse to pulse, over many consecutive pulses, or as a longer-term variation. Figure 2: Persistence display can serve for a quick eyeball estimate of total jitter in a signal
10
Visit: eeweb.com