Tektronix WFM8200 User Manual page 183

Usage Notes
WFM8200 and WFM8300 Waveform Monitors
To use the Timing display to time a signal to a reference.
1. Select a tile in which to time the active input.
2. Apply the input signal to be timed to the appropriate input, terminate it
properly and select it.
3. Apply the house reference signal to the external reference input, terminating it
properly.
4. Press the EXT REF button to select External Reference mode.
5. Press the MEAS button to select the Timing display for the tile selected in
step 1.
6. If only one circle is displayed, adjust the timing offset of the black generator
to match the timing to the external reference. Adjust for a perfect coincidence
of the circle around the reference target (circle turns green at coincidence) and
null values of the vertical and horizontal timing readouts.
7. If multiple circles are displayed, the timing is complex, and you must choose
the one you want. The measurement that is closest to zero offset is displayed
with emphasis and appears in the readouts.
NOTE.
See Timing Displays for Simple Versus Complex Timing for more
information about complex timing displays and their elements. (See page 45.)
9. Repeat step 6 or 7 for any other signals.
NOTE. As you adjust timing, the circle representing the input timing may jump
occasionally. This is because the color frame detection circuit can be temporarily
disrupted as the signal shifts. The jump is often a multiple of the field time. The
circle will settle back to the correct location in a second or so.
The resolution of the timing display for Composite and SD signals is one
27 MHz clock cycle or 37 ns. For HD signals, it is one clock at 74.25 MHz,
which equates to about 13.5 ns. To get the greater accuracy needed for a
composite signal, first use the timing display to get close, then use a vector
display for the final burst phase alignment. Since this instrument can display
both the timing display and a vector display simultaneously (each in its own
tile), this process can still be easy and quick.
For composite signals the definition of time aligned is obvious but for an
SDI input relative to a analog reference the situation is more complex. For
the timing display, the definition of zero offset on an SDI input uses the
methodology described in SMPTE RP168. This method specifies the SDI
signal will be converted to analog. The converted analog signal is then
Application Example
167