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Is it possible to measure the relative timing of two serial component signals with the WFM601M?


Is it possible to measure the relative timing of two serial component signals with the WFM601M?


Because many digital video systems are buffered, video sources may be out of time by several lines without causing a problem. Exact timing is less of an issue than with analog systems. Buffers, however, have a limited range and it is important that signals be timed close enough together to avoid buffer overflow. Relative timing between two synchronous serial component video signals is easily measured with the WFM601M.

To measure relative timing between two serial component signals, connect a synchronous analog reference to the WFM601M and use EXT REF mode. Select SERIAL A, Y-PB-PR waveform display, display CH1 only, CONFIG-WFM/VEC-EAV-PASS on, 1H, LIN SEL. Center the SAV pulse on the display and turn on MAG sweep. Watch for the SAV pulse to change shape between lines 19 and 20 as the V bit changes to indicate start of active video (the line number may read something else because the instrument is locked to the external reference signal). Also note that the SAV pulse and the ringing around the pulse is smaller in amplitude on field 1 than on field 2 because the F bit is 0 on field 1. You can't see the bits on the analog display; you just see changes in the value of the 27 MHz rate word (sample 1715). The peak of this SAV pulse will be the timing reference point for the signal on SERIAL A. Turn on the TIME CURSOR and set TIME1 to the peak of this SAV pulse. Note the number and line numbers displayed.

Now do the same for SERIAL B, using the LINE and FIELD selector and the TIME2 cursor without changing the TIME1 cursor. The difference between the line numbers and the field numbers for the two signals, and delta T (time between TIME1 and TIME2 cursors) is the timing difference between the two signals.

When this relative timing measurement is first made in your system, you may want to store the WFM601M setup for SERIAL A, the reference signal component video signal, in a PRESET.

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