Wide band aft circuit for television receivers

Abstract From the Canadian patent

A wide-band automatic fine tuning (AFT) circuit capable of a ?2 MHz pull-in range without false lockups responds to the output of a picture carrier discriminator a sound carrier discriminator and a vertical synchronizing signal sensing means to operate a reversible digital counter in either its count up or count down direction depending upon the relationship of the outputs of the two discriminators and the synchronizing signal sensing circuit. The output of the counter is supplied to a digital-to-analog converter which produces a tuning control voltage used for controlling the frequency of operation of the local oscillator of the receiver. The output of the digital-to-analog converter is …