Television receiver with synchronous detection and automatic fine tuning

Claim 1

A circuit for receiving an AM signal comprising: tuner means including a local oscillator for converting said AM signal into an IF signal; phase detector means for providing a phase error signal containing AC and DC components in response to said IF signal; synchronous detector means for providing an output signal in response to said IF signal; means supplying said IF signal to said phase detector means and to said synchronous detector means; variable frequency reference oscillator means supplying a reference signal to said phase detector means and to said synchronous detector means; first low pass filter means connected between said phase detector means and said local oscillator of the tuner means and passing frequencies in a band ranging from DC to a first cut-off frequency for controlling said local oscillator; and second low pass filter means connected between said phase detector and said reference oscillator means and passing frequencies in a band ranging from DC to a second cut-off frequency; said first cut-off frequency being sufficiently less than said second cut-off frequency so that it is possible to affect automatic fine tuning for receiving said AM signal while both the AC and DC components of the phase error signal of said phase detector are permitted to pass to said reference oscillator means.