Making ‘Real-Time Corrected' Parametric Measurements using a Digital Oscilloscope
While accurate rise time measurements have become easier to make, it remains, nonetheless, quite easy to overlook error contributions due to not only the oscilloscope but also the probe. And, while the error contributed by a scope's finite step-response (rise time) is often accounted for, that contributed by the probe is often overlooked. The probe contributes its own source of error due to its own characteristic rise time. In this article, we will examine rise time measurements made while using a Gaussian scope and a probe, each of a known BW. Furthermore, we will look at how to make a systematic on-the-fly corrected rise time measurement using the DL9000 oscilloscope.
For a test system with a low-pass Gaussian frequency response, every element between the test point and the display of an oscilloscope contributes to the measured rise time (1). In the case of a DUT's rise time, a probe's rise time, and an oscilloscope's rise time, these three rise times may be summed by:
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