Tektronix WFM8200 User Manual page 185

WFM8200 and WFM8300 Waveform Monitors
Usage notes.
The resolution of the timing display is one 27 MHz clock cycle or 37 ns, for
Composite and SD video. To get the greater accuracy needed for a composite
signal, first use the timing display to get close, and then use a vector display
for the final burst phase alignment. Since these two displays can be present
simultaneously in separate tiles, this process is still easy and quick.
For composite signals, the definition of time aligned is straight forward, but
for an SDI input relative to an analog reference, the situation is more complex.
For the timing display, the definition of zero offset on an SDI input assumes
the SDI signal will be converted to composite. The converted composite
signal is then compared to the analog reference. For the conversion, a
half-band filter with a 33 clock-cycle delay and an analog reconstruction filter
are assumed. This conversion introduces a delay of about 3 µs.
In the Relative to: Rear Panel mode, this 3 µs conversion delay is removed
from the measured offset before the display is generated. In the Relative to:
Saved Offset mode, it has no effect.
This timing relationship between input and reference is also compatible with
the waveform mode. That is, if you have zero timing on the Timing display
and change from internal to external reference, the displayed waveform will
not shift position.
When timing analog composite signals, adjust the system phase with the
Vector display. (See page 45, Timing Displays for Simple Versus Complex
Timing.)
NOTE. If you have an input and reference combination that requires multiple
timing indicator circles, then it can be misleading to compare timing offsets
between multiple inputs. Because the timing display chooses the smallest of the
possible timing offsets, if a large timing difference exists between two inputs,
then they may not be matched. This problem also occurs using traditional timing
methods unless you use something similar to the SMPTE318 10 field flag to
identify a specific sub-multiple of the reference.
Application Example
169