Perhaps you have connected an oscilloscope to a circuit for troubleshooting,
only to have the circuit operate correctly after connecting the probes. The
capacitive loading of the probes can attenuate a glitch, remove ringing or
overshoot, or slow an edge just enough that a setup or hold time violation no
longer occurs.
Summary of Transient Response Errors
Minimize the effects of transient response on time-interval measurements by
following these guidelines.
•
Choose an oscilloscope and probe with a combined rise time less than 1/3
the fastest rise time or pulse width to be measured.
•
Consider probe loading effects, particularly capacitive loading. The RC
time constant of the output impedance of the circuit under test and the
capacitance of the probe should be very small compared to the signal rise
time.
Measurements
Time-interval measurements
13–45
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