The A-196 contains a phase locked loop (PLL), which consists of a voltage controlled oscillator (VCO), phase comparator (PC), and low-pass filter (LPF). All parts are normally connected to form a closed-loop frequency-feedback system.
The output of the internal VCO is compared with an external signal in the phase comparator, this output is a digital signal that is low if both input signals have the same state and turns high if the input signals have different states.
This output is processed by a low pass filter to generate a smooth voltage that is used to control the frequency of the internal VCO. The VCO, PC and LPF form a feedback loop that increases as long as the external frequency is higher than the frequency of the internal VCO, remain the same when both frequencies become identical and decreases when external frequency is lower than the VCO frequency
