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Reference
3-14
WFM700 Series Waveform Monitors User Manual
Bowtie Mode
The Bowtie display evaluates the relative amplitude and timing between the
three video channels. To access the Bowtie mode, press the MEASURE button,
touch the Measure Menu soft key, and then touch the Bowtie soft key.
The Bowtie display requires a special test signal to be sent from the monitored
source. The Tektronix TG2000 Signal Generation Platform can produce a Bowtie
test signal with 20 ns time marks, which aid in signal evaluation. The signal is a
500 kHz sinewave on CH 1 (luminance) and 502 kHz sine waves on CH 2 (Pb)
and CH 3 (Pr).
The Bowtie display is made up of two separate waveforms. The left waveform
always compares CH 1 to CH 2. The right waveform always compares CH 1 to
CH 3.
Timing Measurement. The timing measurement is based on the alignment of the
center marker and the null point at the center of the waveform. The generator
provides a center marker, which is centered on the null point when interchannel
timing is correct. In Figure 3--6, the chrominance channel, CH 3 (Pr), is
advanced relative to the luminance channel by 20 ns.
Relative Gain Check. The relative gain check is based on the null point at the
center of the Bowtie waveforms. If the gains are not equal, the center null point
will not be a complete null. If the gain error is in CH 1, neither waveform has a
complete null. If CH 2 gain is off, the left waveform will not null completely, but
the right one will. If the gain is off for CH 3, as in Figure 3--6, the left waveform
will be normal and the right one will not reach a complete null.
Shifted null point
Waveform showing timing error in CH 3
(20 ns advanced)
Incomplete null
Waveform showing gain error in CH 3
Figure 3- 6: Bowtie waveforms showing timing and relative gain errors
Measurements