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FS8108
the wireless IC company
Page 8
June 2001
Phase/Frequency Detector (PFD)
The PFD compares an internal input frequency divider output signal, f
V, with an internal
reference frequency divider output signal, f
R, and generates an error signal, DO, which is
proportional to the phase error between f
V and fR. The DO output is intended for use with
a passive filter as shown in Fig. 3.
The input/output waveforms for the PFD are shown in Fig. 4.
Fig. 3 – Passive low-pass filter circuit
Fig. 4 – PFD input/output waveforms
DO
to VCO
R1
R2
C
high-Z
high-Z
high-Z
f
R
f
V
DO
LD
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