Philips Semiconductors
Frequency synthesizer
Product specification
HEF4750V
LSI
Fig.4 Phase characteristic of PC1.
PC1 is designed to have a high gain, typically 3200 V/cycle
(at 12,5 kHz). This enables a low noise performance.
Phase comparator 2
Phase comparator 2 (PC2) has a wide range, which
enables faster lock times to be achieved than otherwise
would be possible. It has a linear ± 360° phase range,
which corresponds to a gain of typically 5 V/cycle.
This digital phase comparator has three stable states:
• reset state,
• V’ leads R state,
• R leads V’ state.
Conversion from one state to another takes place
according to the state diagram of Fig.5.
Fig.5 State diagram of PC2.
Output PC2 produces positive or negative-going pulses
with variable width; they depend on the phase relationship
of R and V’. The average output voltage is a linear function
of the phase difference. Output PC2 remains in the high
impedance OFF-state in the region in which PC1 operates.
The resultant phase characteristic is shown in Fig.6.
January 1995
6