Group Delay (Trace Format)

Menu Path: Trace > Format > Format:

Group Delay trace format configures the active trace to show group delay. By definition, group delay is the derivative (or slope) of the phase response. It is useful for measuring signal transit-time through a device and for measuring the device's phase linearity. The formula for group delay is:

 Group Delay = [- delta(ph)/delta(f)] ´ [1 cycle/360 degrees]

"delta(ph)" is the phase difference (in degrees) of two frequencies separated by delta(f); "delta(f)" is the difference between two frequencies, in Hertz (cycles/second). Dividing by 360 converts degrees to radians. The final units for group delay are seconds.

Delta(f) can be adjusted by adjusting the group-delay aperture and/or the frequency span, according to the following formula:

 delta(f) = (aperture) ´ (frequency span)

Group Delay in the Time Domain

The 89600 VSA also computes group delay for time-domain data. The same formula is used, except delta(f) is replaced with delta(t), as follows:

 Group Delay = [- delta(ph)/delta(t)] ´ [1 cycle/360 degrees]

• "delta(ph)" is the phase difference (in degrees) of two points separated by delta(t).
• "delta(t)" is the difference between two points, in seconds.
• Dividing by 360 converts degrees to radians.
• The final units for group delay in the time domain are Hertz.

Delta(t) can be adjusted by adjusting the group-delay aperture and/or the time-record length, according to the following formula:

 delta(t) = (aperture) ´ (time-record length)

See Also

Group Delay Aperture