Multichannel disc demodulation circuit

Claim 1

A circuit for demodulating a multichannel disc having recorded thereon a multiplex signal including a non-modulated audio signal and an angle-modulated carrier wave signal, said demodulation circuit comprising a voltage controlled oscillator means for generating a signal having a frequency which is varied in accordance with a control signal, a phase comparator circuit means including a differential amplifier for comparing the phase of the output signal of said voltage controlled oscillator with the phase of the angle-modulated wave signal and for producing an error signal corresponding to the detected phase difference, said error signal representing a demodulated audio signal, and means for applying a part of said error signal to said voltage controlled oscillator as said control signal therefor, whereby the frequency of the signal generated by said voltage controlled oscillator coincides with the frequency of the angle-modulated carrier, said phase comparator circuit means comprising a pair of transistor means connected in said differential amplifier configuration, a direct current biasing circuit including a series combination of two resistors connected across a power source means for applying a direct current bias voltage from the junction of the two resistors to the base electrodes of the pair of transistors, means for applying the angle-modulated wave signal from an amplifier through a preceding circuit to at least one of the base electrodes, said preceding circuit being constructed so that the AC impedance measured from the amplifier looking toward said phase comparator circuit is relatively large and the DC impedance looking back from the one base electrode is relatively small, whereby the angle-modulated wave signal is not phase-shifted when the amplitude of the envelope of the anglemodulated wave signal varies.

Claim 8

A system for demodulating the signals recorded on a multichannel disc, said demodulation system comprising means having a phase-locked loop phase comparator means including a differential amplifier means, means for applying to an input of said differential amplifier an angle-modulated wave signal picked up from a multichannel record disc, means comprising a voltage controlled oscillator for supplying a control voltage to said phase comparator means responsive to a fed back portion of the output of said phase comparator means, said phase comparator means having an input circuit for connecting it to a preceding stage, said input circuit including a pair of input transistors and base bias resistors for setting the AC impedance of said pair of input transistors at a relatively large impedance value and for setting the DC impedance at a relatively small value, whereby demodulation can be accomplished without causing a phase difference with respect to said input angle-modulated wave signal when the amplitude envelope of said input signal varies.

Claim 9

A system for demodulating the signals recorded on a multichannel disc, said demodulation system comprising means having a phase-locked loop phase comparator means including a differential amplifier means, means for applying to an input of said differential amplifier an angle-modulated wave signal picked up from a multichannel record disc, means comprising a voltage controlled oscillator for supplying a control voltage to said phase comparator means responsive to a fed back portion of the output of said phase comparator means, said phase comparator means having an input circuit for connecting it to a preceding stage, said input circuit including a pair of input transistors and base bias resistors for setting the AC impedance of said pair of input transistors at a relatively large impedance value and for setting the DC impedance at a relatively small value, whereby demodulation can be accomplished without causing a phase difference with respect to said input angle-modulated wave signal when the amplitude envelope of said input signal varies.