Sample and hold frequency to voltage converter circuit

Claim 1

An improved tachometer of the type including means for generating a periodically varying electrical input signal having a frequency proportional to the speed of rotation of a rotating member and a frequency to voltage converter circuit for converting the frequency of the periodically varying input signal to a voltage having a magnitude proportional to such frequency, wherein the tachometer has an improved frequency to voltage converter circuit comprising: circuit means, supplied with said input signal, for generating first and second pulse trains, said first pulse train comprising a pulsating signal having a repetition frequency proportional to the frequency of said input signal, said second pulse train comprising a pulsating signal having a repetition frequency and duty cycle proportional to the frequency of said input signal; integrator circuit means, supplied with said second pulse train, for generating an integrator voltage proportional to the duty cycle of said second pulse train; a transmission gate coupled to said circuit means for generating said first and second pulse trains; and a holding capacitor, said transmission gate when conductive coupling said integrator circuit means to said holding capacitor, said transmission gate being rendered alternately conductive and nonconductive by the pulsating signal of said first pulse train, said holding capacitor acquiring a voltage across it which varies as a function of said integrator voltage at those times in which said transmission gate is conductive.