Frequency translation phase-locked loop television sound detection system

Claim 1

In a television receiver including a source of intermediate frequency (IF) signal including picture and sound carriers modulated with video and audio information, respectively, apparatus for detecting said audio information comprising: a first filter having an input coupled to receive said IF signal and having a double-humped amplitude versus frequency response characteristic with peak amplitude portions centered at the frequency of said picture and sound carriers, respectively, for providing at its output said picture and sound carriers; an amplifier having an input coupled to the output of said first filter for amplifying said picture and sound carriers and providing said amplified carriers at the output of said amplifier; a controllable oscillator responsive to a control signal coupled to a control input and having an output at which is provided a controlled frequency output signal; mixer means having a first input coupled to be responsive to said amplified picture carrier, a second input coupled to be responsive to said oscillator output signal and an output for providing a frequency translated signal; a phase detector having a first input coupled to be responsive to said amplified sound carrier, a second input coupled to be responsive to said frequency translated signal and an output; lowpass filter means having an input coupled to the output of said phase detector and having an output for providing said control signal to the control input of said controllable oscillator and for providing said audio information; and a second filter coupled to one of said first and second inputs of said phase detector, said second filter having an amplitude versus frequency response characteristic for providing a predetermined attenuation at the frequency of said picture carrier and substantially less than said predetermined attenuation at the frequency of said sound carrier.