Tunable television receiver circuits with automatic phase control

Claim 1

In a television receiver having a mixer stage coupled to a tunable local oscillator stage and to a source of television signals to provide picture and sound intermediate frequency signals, a tunable automatic phase control circuit comprising: synchronous demodulator detector means coupled to the output of said mixer stage for receiving said picture and sound intermediate frequency signals; amplitude limiting amplifier means coupled to said mixer stage and providing a first picture intermediate frequency signal of unmodulated amplitude; resonant circuit means coupled to said synchronous demodulator detector means and to said amplitude limiting amplifier means, said resonant circuit means including a variable reactance means in the form of a varactor diode; reference frequency resonant circuit means coupled to said resonant circuit means and providing a second picture intermediate frequency signal of unmodulated amplitude; phase difference detecting synchronous demodulator means coupled to said amplitude limiting amplifier means and said resonant circuit means and to said reference frequency resonant circuit means, said phase difference detecting synchronous demodulator means receiving said first and second picture intermediate frequency signals of unmodulated amplitude and providing a control signal which varies in accordance with the phase difference between said first and second picture intermediate frequency signals; and circuit means coupling said control signal from said phase difference detecting synchronous demodulator means to said variable reactance means of said resonant circuit means whereby said resonant circuit means provides a resonance oscillation for effecting demodulation of said first picture intermediate frequency signal by said synchronous demodulator detector means.