Device for production of a tachometry signal of infinite resolution and without ripple from an inductive position sensor

A device for production of a tachometry signal of infinitely fine resolution and without ripple from an inductive position sensor fed by a sinusoidal reference signal and supplying two phase signals, comprising:

• a resistance-capacitance circuit tuned to the frequency of the reference signal, said resistance-capacitance circuit connected to said stwo phase signals and supplying a sinusoidal signal whose phase angle is proportional to a rotation of the sensor;
• digitizing means connected to said resistance-capacitance circuit and said sinusoidal reference signal for converting said sinusoidal signal and said sinusoidal reference signal to first and second digital signals;
• inverter means connected to said digitizing means for producing a third digital signal which is the inverse of said first digital signal;
• a plurality of digital phase comparators connected to said digitizing means, each generating a square-wave width modulation signal and consisting of a circuit of simple flip-flops which produce a corresponding square-wave width modulation signal beginning with each transition from a determined direction of an input signal and ending with each transition from a determined direction of said second digital signal, said input signal being said first digital signal in at least one digital phase comparator and being said third digital signal in at least one additional digital phase comparator;
• each digital phase comparator having associated therewith a return to zero detector consisting of another flip-flop circuit which produces a corresponding return to zero signal when there occurs a transition in the input signal to begin the square-wave width modulation signal while the square-wave width modulation signal is already being produced;
• a storage flip-flop which produces a selection signal in response to said return to zero signals;
• a plurality of low pass filters each receiving one square-wave modulation signal to produce a filtered signal;
• an electronic switch controlled by the selection signal to sample from each of the filtered signals a second half of each cycle to obtain a single sawtooth signal;
• and
• a single differentiator with means for elimination of discontinuities for generating an outgoing tachometry signal from said single sawtooth signal.