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8-4 GROUP DELAY Group delay is the measure of transit time through a device at a par
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ticular frequency. Ideally, we want to measure a constant—or rela
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tively constant—transit time over frequency. The top waveform shown
in Figure 8-14 is measured at one frequency. The bottom waveform is
identical to the first, simply delayed in time.
Referring to Figure 8-15, the first waveform shown is the original
waveform. It is made up of many frequency components. After travel-
ing through a device the signal is delayed in time. Some frequencies
are delayed more than others and thus our waveform does not have ex-
actly the same shape as before.
When delay is nonlinear, as shown above, distortion occurs. By meas
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uring group delay with a network analyzer you can characterize the
distortion that occurs from a signal traveling through your test device.
GROUP DELAY MEASUREMENTS
8-20 37xxxE OM
M A G N I T U D E
T I M E
t
0
t
1
Figure 8-14. Two Waveforms Delayed in Time
I N P U T
O U T P U T
M A G N I T U D E
T I M E
Figure 8-15. Waveform with Frequency Differences