FROM EDN EUROPE: Software tracks jitter components to source—to 40 Gbps
By Graham Prophet -- EDN, February 5, 2004
As high-speed serial buses become more widely used, the need to measure jitter becomes ever more critical. With its DCA-J (digital-communications-analyser jitter) option instrument, Agilent says it is not only providing unprecedented levels of accuracy in jitter measurement, but also adding a layer of data analysis that helps you in identifying not only the amplitude of the jitter on a signal, but also its source and origin. With "one-button" analysis, you can decompose the jitter on a signal into its various components. The instrument, coded 86100C, spans 50 Mbps to 40 Gbps (Picture).
The basic instrument signal path is that of a sampling oscilloscope with low intrinsic jitter and an extremely stable timebase; there is no radically new architecture here, Agilent says, just close attention to the detail of the entire signal path to minimise the jitter component that is due to the measurement system. The instrument identifies a jitter component in a waveform and then statistically examines that jitter waveform with respect to the waveform's spectral components by extensive software analysis; this method allows the instrument with no further user intervention to isolate factors such as random jitter, deterministic jitter, data-dependent jitter, pattern jitter, intersymbol interference, and duty-cycle jitter. Agilent says you can now reduce to seconds analyses that would previously have taken hours.
You can use the instrument to measure both electrical and optical signals, and it is backward-compatible with all plug-in modules from the 86100A/B, 83480A, and 547-50A. Previously, the company asserts, measuring systems such as CMOS signal paths at up to 10 GHz would require special test rigs to get beyond 3 GHz. The intrinsic jitter of the instrument itself is quoted at 200 fsec.
The software separates random jitter from deterministic jitter and then treats the jitter as a frequency modulation on the base signal and analyses that modulation. An "eyeline-mode" facility can extract individual bit sequences from an eye diagram and identify features on them. In this new domain, Agilent says, of "digital-microwave" (or, if you prefer, "microwave-digital") measurements, and manufacturers have underestimated the need for such signal deconstruction. Agilent's DCA with the new option and the "extra button" for jitter analysis costs around €40,000.
Agilent, +31 20 547 2000, www.agilent.com.
