Tone signal detector

Abstract From the Canadian patent

A tone signal detector comprises a clock signal generator for generating clock signals of a frequency equal to N times (where N is an integer) the frequency of the tone signals detected. An N-path filter selects the tone signals according to the output of the clock generator. A low-pass filter connected to the output of the N-path filter eliminates the frequency component of the clock signals. A wave shaping circuit shapes the signals passed by the low-pass filter. A gate circuit controls the clock signals in accordance with the output of the wave shaping circuit. A counter counts the number of the output pulses provided by the gate circuit. A timing circuit determines the count of the …