Keysight 4000 X-Series, Руководство по продвинутой подготовке

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68 4000 X-Series Oscilloscopes Advanced Training Guide
3
Advanced Triggering, Search & Navigation, and Segmented Acquisition Labs
change polarity (high-to-low or low-to-high), then it must switch polarities a
minimum amount of time before the occurrence of the clocking signal. This is
commonly referred to as the device’s minimum specified “setup” time. And then
the data signal must remain stable (“hold” high or low) for a minimum amount of
time after the occurrence of the clocking signal before switching to the opposite
polarity. This is commonly referred to as the device’s minimum specified “hold”
time.
Let’s assume that data is being clocked into a device on the rising edge of our
clock signal (yellow trace). To determine the setup time of our signals we could
use the scope’s timing cursors to measure the time from the rising/falling edges of
the data signal to the rising edge of the clock signal. If you make this measurement
based on the brighter green traces, then you should measure a setup time in the
range of 37 ns. But notice the fainter green traces. It appears that our data signal
is occasionally shifting closer to the clock signal. If you make the setup time
measurement based on the fainter green traces you should measure a setup time
in the range of just 17 ns. Let’s now assume that our device has a minimum
specified setup time of 25 ns. This would mean that the timing of our signals
usually meet specification, but sometimes they are in violation of the specification.
Rather than triggering on any rising edge of the clock (current trigger condition),
triggering on clock signals that are preceded by a data setup time violation might
help us to debug this timing problem. Let’s do it.
7
Press the
[Trigger]
front panel key.
8
Select the Setup & Hold trigger type.
9
Double-tap the < Setup softkey and enter 25 ns .