- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
197
Internal phase comparison
The CXD3172AR internally compares the phases of the external power supply square wave signal (S0 pin 44
input), and the VD (MCK-VD) signal obtained by frequency-dividing the MCK (pin 43). The phase comparison
result is output through PCOMP (pin 42).
The PCOMP signal is applied to LPF (V-PLL) and fed back to the MCK VCO circuit to form the vertical
direction PLL. The PCOMP signal’s polarity can be switched through PCMPINV (CAT7_Byte2_bit4).
In addition, it is possible to select either active filter or passive filter in accordance with the external LPF
specifications. However, active filter is recommended since it provides higher performance.
shows the PCOMP output waveform when a lock is applied.
shows the PCOMP output
waveform without a lock. (From measurements using our evaluation board.) Apply a trigger to the external
power supply square wave (S0 pin 44 input) and view the PCOMP output waveform to check whether a lock
has been applied.
Fig 12.2-6 PCOMP output waveform (locked)
Fig 12.2-7 PCOMP output waveform (unlocked)
PCOMP
output
S0 input
Ch1
Ch2
Ch1:2.00V / DIV
Ch2:1.00V / DIV
4.00ms / DIV
[TRIGGER]
3.3 V amplitude
digital signal
PCOMP
output
Ch1
Ch2
[TRIGGER]
PCOMP Waveforms
Instability
Ch1:2.00V / DIV
Ch2:1.00V / DIV
4.00ms / DIV
S0 input
3.3 V amplitude
digital signal