Wideband FM modulator and AFC control loop therefor

摘要

An AFC loop for controlling the frequency of a VCO including an A to D converter and divider for providing pulses at some frequency equal to or lower than the output of the VCO, a source of stable reference pulses and a counter constructed to count to a predetermined number and count the reference pulses in synchronism with the divided pulses, a second divider connected to divide the reference pulses by the predetermined number and means for subtracting the output of the second divider from the counter to provide a control voltage for the VCO which is proportional to the drift in frequency of the VCO from a mean frequency.