Extremely accurate automatic frequency control circuit and method therefor

DETAILED DESCRIPTION The above and other objects are achieved by an automatic frequency control circuit which receives an input signal exhibiting an unknown frequency and resolves the frequency of the signal.
The signal is input to a mixer and combined with a signal from a variable frequency oscillator.
The output of the mixer couples to a phase detector which outputs a signal representing the instantaneous phase difference between the mixer's output signal and a signal from a fixed frequency oscillator.
The phase detector output coupled to a computer, and the computer has an output which couples back to the variable frequency oscillator.
The computer, under the influence of a predetermined program, controls the oscillation frequency of the variable frequency oscillator in response to the signal received from the phase detector.