- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
211
Internal phase comparison
The separated horizontal direction signal (EXT-HD) and the MCK-frequency-divided HD (MCK-HD) signal are
phase-compared inside the CXD3172AR, and the result of the comparison is output through PCOMP (pin 42).
The PCOMP signal is applied to the LPF (H-PLL) and fed back to the VCXO circuit on the MCK side to form
the horizontal direction PLL. The polarity of the PCOMP signal may be switched using PCMPINV
(CAT7_Byte2_bit4).
An active or passive filter can be selected, to match the specifications of the external LPF. Note that we
recommend an active filter since active filters have better performance.
shows the PCOMP output waveform when the lock is on.
shows the PCOMP output
waveform when the lock is off. (These waveforms are the results of measurements made using our evaluation
board.) Apply a trigger to the external video signal and look at the PCOMP output waveform to check whether
the lock is on.
Fig 12.2-23 PCOMP output waveform (locked)
Fig 12.2-24 PCOMP output waveform (unlocked)
PCOMP
output
EXT-VIDEO
EXVIDEOY
input
Ch1
Ch2
Ch1:500mV / DIV
Ch2:1.00V / DIV
20.0us / DIV
[TRIGGER]
PCOMP
output
Ch1
Ch2
[TRIGGER]
PCOMP Waveforms
Instability
20.0us / DIV
EXT-VIDEO
EXVIDEOY
input
Ch1:500mV / DIV
Ch2:1.00V / DIV