- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
194
Internal phase comparison
The CXD3172AR internally compares the phases of the ECK-DHD signal with the frequency-divided encoding
clock (ECK), against the MCK-HD signal with the frequency-divided MCK. The phase comparison result is
output through PCOMP (pin 42). The PCOMP signal should be applied to LPF (H-PLL) and fed back to the
MCK (pin 43) VCO. The PCOMP signal can be polarity-inverted by PCMPINV (CAT7_Byte2_bit4).
In addition, it is possible to select either active filtering or passive filtering in accordance with the external LPF
specifications. However, active filtering 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 ECK-DHD
signal output from S2 (pin 47) and view the PCOMP output waveform to check whether a lock has been
applied.
Fig 12.2-3 PCOMP output waveform (locked)
Fig 12.2-4 PCOMP output waveform (unlocked)
PCOMP
output
ECK-DHD
S2 output
Ch1
Ch2
Ch1:2.00V / DIV
Ch2:1.00V / DIV
20.0us / DIV
[TRIGGER]
PCOMP
output
Ch1
Ch2
[TRIGGER]
PCOMP Waveforms
Instability
ECK-DHD
S2 output
Ch1:2.00V / DIV
Ch2:1.00V / DIV
20.0us / DIV