Frequency synthesizer with numerically controlled scanning voltage

Claim 1

A frequency synthesizer including: a variable frequency oscillator providing an output frequency; scanning means for continuously applying a control signal to said variable frequency oscillator including means for varying said control signal so as to vary the frequency of said oscillator in steps, said scanning means comprising a step voltage generator and a clock pulse generator: a modulation and filter assembly connected to receive said output frequency from said oscillator; generator means providing a spectrum of harmonics of a high stability reference frequency connected to said modulation and filter assembly to provide beats between said output frequency and said harmonics; a counter connected to the output of said modulation and filter assembly to receive and store a quantity significant of the number of times a preselected value of beat frequency occurs in the modulation and filter assembly indicative of the number of coincidences between said output frequency of said variable oscillator and successive harmonics of the spectrum; coincidence circuit means connected to the output of said counter to compare the quantity stored in the counter with a second qUantity significant of the desired output frequency of the oscillator; and control means extending from said coincidence circuit to said scanning means for inhibiting said means for varying said control signal to thereby prevent further scanning when the two quantities compared in said coincidence circuit means have a predetermined relationship, said control means including an ANDgate connected to transmit the clock pulses from the clock pulse generator to the step voltage generator.