China Electronics Technology Instruments AV3672 Series, User Manual

Page: 258 / 424

8 Basis of Network Measurement
8.5 Group Delay
254
8.5 Group Delay
The phase distortion of the DUT is measured in group delay measurement. The group delay refers to the actual
transition time of the signal through the DUT and changes over the frequency. The aperture of group delay
measurement must be specified to describe the group delay indicator.
8.5.1 What is group delay?
The group delay refers to:
1) Measure of phase distortion of the device.
2) Relationship between the signal transition time through the device and the frequency.
3) Derivative of the phase characteristic of the device relative to the frequency.
Fig. 8.11 Phase Shift and Group Delay
Group delay
Φ is in radian, ω in radian/second, θ in degree and f in Hz.
The phase characteristic of the device includes the linear phase shift component and high-order phase shift
component.
1) Linear phase shift component: refer to the average transition time of the signal, indicating the electrical length of
the device.
2) High-order phase shift component: refer to the transition time change over the frequency, a cause of signal
distortion.
Fig. 8.12 Group Delay
In the group delay measurement:
1) The linear phase shift component represents the average group delay.
2) The high-order phase shift component represents the average group delay deviation (group delay ripple).
3) Similar to the linear phase deviation resulting in distortion, the group delay deviation will also result in signal
distortion.
4) The trace of group delay measurement indicates the passing time of each frequency signal through the DUT.
The group delay of the analyzer is calculated in the following methods:
Group delay
Φ is in radian, ω in radian/second, θ in degree and f in Hz.