Phase locked loop system with improved acquisition

Details Phase locked loop system with improved acquisition Phase locked loop system with improved acquisition

H - Electricity

03

L

331/33

H03L 7/06 (2006.01) H03L 7/113 (2006.01) H03L 7/187 (2006.01)

Patent

CA 1155504

ABSTRACT A phase locked loop system having improved acquisition time is particularly suitable for use in a television receiver with frequency synthesizer tuning. A conventional phase locked loop is modified by the addition of a pair of transmission gates and a frequency discriminator/detector. The transmission gates are normally open, and the phase locked loop system operates in a conventional manner. When a programmable frequency divider connected between the output of the voltage controlled oscillator and the input to the phase locked loop phase comparator has its division ratio changed to select a new channel, the frequency discriminator, which also is connected to the output of the programmable frequency divider, applies an appropriate gating signal to one or the other of the transmission gates to close that gate. The two gates are connected respectively to sources of direct current potential which operate rapidly to force the maximum control signal on the voltage controlled oscillator in the desired direction to produce acquisition until the phase locked loop is nearly locked. When the frequency at the output of the programmable frequency divider comes within a range which is a predetermined amount above or below the desired center frequency of the frequency discriminator, the output of the frequency discriminator terminates, opening the one of the transmission gates which previously was closed to return the system back to operation as a conventional phase locked loop system.

356980

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