Crosstalk is the effect on a signal caused by the high-speed switching of a nearby signal. This effect can manifest itself as jitter, which is the deviation of a signal's edge from its expected location. A large amount of jitter can cause a timing budget failure in a parallel system or it can cause a clock and data recovery PLL to incorrectly recover the data in a serial system.
Due to the deleterious effects of crosstalk, it is important to determine the amount of it that exists during worst case scenarios. Currently, there are no standard crosstalk measurement techniques for the serial domain. This article describes effective measurement techniques and how to determine if the amount of crosstalk is acceptable for reliable data transfer. The techniques described include measuring the device's jitter output with a wide-bandwidth oscilloscope and spectral output with a high-bandwidth spectrum analyzer. Also discussed are the configurations that yield the highest crosstalk scenarios. Real measurement data of a multi-channel, independent rate device is provided. The measurements are performed at video serial digital interface (SDI) data rates, but the measurement techniques apply to any high-speed standard. To read more on this topic, click the download link above, or visit Planet Analog.
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