43. A frequency sensing circuit comprising: means for sampling an input signal; means, coupled to said means for sampling, for digitally encoding the magnitude of each sample; an adder having a first input coupled to said means for encoding and having a second input and an output; delay means having an input coupled to the output of said adder, said delay means providing a delay that is an integral multiple of one-half of the period corresponding to the frequency to be sensed; a multiplier having a multiplier constant K and having an input coupled to the output of said delay means and having an output coupled to the second input of said adder, said multiplier clocked at a rate of N times the desired frequency to be sensed, where N is any integer greater than 1, said multiplier constant K being controllable and determining the bandwidth of the frequency sensitive circuit; and means coupled to said frequency sensing circuit for deriving an output signal therefrom having a magnitude indicative of the frequency sensed.
43. A frequency sensing circuit comprising: means for sampling an input signal; means, coupled to said means for sampling, for digitally encoding the magnitude of each sample; an adder having a first input coupled to said means for encoding and having a second input and an output; delay means having an input coupled to the output of said adder, said delay means providing a delay that is an integral multiple of one-half of the period corresponding to the frequency to be sensed; a multiplier having a multiplier constant K and having an input coupled to the output of said delay means and having an output coupled to the second input of said adder, said multiplier clocked at a rate of N times the desired frequency to be sensed, where N is any integer greater than 1, said multiplier constant K being controllable and determining the bandwidth of the frequency sensitive circuit; and means coupled to said frequency sensing circuit for deriving an output signal therefrom having a magnitude indicative of the frequency sensed. 48. A frequency sensing circuit according to claim 43 wherein said output deriving means is coupled to said adder.