There are times when I would need to measure relative propagation delay characteristics of digital waveforms my scope. Usually i would resort to the use of manual cursors until I peeked at the  measurement delay menu and wondered the meaning of FFR, FRF, FFR among other parameters.

More so I did not find any articles on the subject so I decided to jot down what I had learnt as this can be a problem especially when the scope in reach does not readily describe the measurement parameters visually.

 

sds00001-fs8

Each delay measurement is described by a 3 letter mnemonic ABC Examples include those in the scope screen shot above such as FRR, LFR, FFF and so on.

In the case of an arbitrary delay measurement ABC, this is what each letter means:

  • A-Refers to First(F) or last(L) edge of channel 2 in the oscilloscope view. It is closely related to C, the type of falling edge on channel 2.
  • B-Refers to Falling(F) or rising(R) edge of channel 1.
  • C-Refers to Falling(F) or rising(R) edge of channel 2.

Note: Every digital delay measurement is related to the first B edge of channel 1 so it is omitted in ABC.

scope-fs8

USE CASE

This is what each of the 3 letters mean in 2 of the 8 cases:

FRR

  • F-Refers to First(F) edge of channel 2 in the oscilloscope view
  • R-rising(R) edge of channel 1.
  • R-Refers to rising(R) edge of channel 2.

This measurement measures time delay from the first rising edge on channel 1 to the first rising edge on channel 2 in the scope view .

scope_frr-1-fs8

LRR

  • L-Refers to Last(L) edge of channel 2 in the oscilloscope view
  • R-rising(R) edge of channel 1.
  • R-Refers to rising(R) edge of channel 2.

This measurement measures time delay from the first rising edge on channel 1 to the last rising edge on channel 2 in the scope view .

scope_lrr-fs8

 

The rest should now be fairly easy to figure out.

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