Phase locked loop circuit - has constant voltage added to error voltage and switchable capacitor connected to control input of VCO

摘要

The phase locked loop consists of a VCO (1) controlled by the output of a phase comparator (2). An adder (4) adds a constant DC voltage to the phase comparator's output error voltage and applies the sum to the VCO's control input via a resistor (31). The frequency control input of the VCO is also connected via a second resistor (32) to an earthed capacitor (33). The capacitor is shunted by a controlled discharging switch (37).