Tektronix TDS5054, User Manual

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Creating and Using Math Waveforms
TDS5000 Series User Manual
3- 159
display from +180 to --180 degrees. Phase unwrap will display the correct result
by unwrapping the phase.
Phase unwrap is only valid when the phase spectrum is a continuous function of
frequency. Therefore, do not use it when analyzing the harmonic content of the
typical repetitive signal.
Suppression Threshold:
Random noise in the spectrum may have phase values
over the entire range. This could make the phase display unusable. However, you
can set the suppression threshold control to a level in dB. The phase of any
complex spectral points with a magnitude below this threshold is set to zero.
--35 dB
0
°
Magnitude vs. frequency
Suppression threshold
Phase vs. frequency
Figure 3- 47: Example of the effects of setting the phase suppression threshold
Group Delay: When the phase spectrum is a continuous function of frequency,
group delay may be computed. This is true of impulse response testing where an
impulse is fed into the system, and the spectrum of the response of the system
output is computed.
Group delay measures how well a system passes a signal in terms of phase
distortion. Group delay is the derivative of the phase with respect to frequency.
This feature is not useful for analysis of harmonic content of signals where the
phase response is not continuous.