Sweep output generator having a frequency modulated local oscillator for the station selector of a television receiver

Claim 1

A sweep output generator for a station selector comprising: a first electrically controlled oscillator including a variable reactance element, said oscillator having an oscillation frequency versus impressed voltage or current characteristic, means for applying a sweep signal to said first electrically controlled oscillator, a continuous oscillator for superimposing an a-c signal having an amplitude which is small compared to that of said sweep signal on said sweep signal for application to said variable reactance element, a frequency modulated sweep oscillation signal being generated at the output of said first electrically controlled oscillator, a second electrically controlled oscillator, mixer means combining the outputs of said first and second electrically controlled oscillators to produce an intermediate frequency signal, integrating means for integrating said demodulated intermediate frequency signal, the output of said integrating means having a sweep characteristic corresponding to the normalized oscillation frequency versus impressed voltage or current characteristic of said first electrically controlled oscillator, reference signal generating means for generating a reference signal corresponding to a station to be selected, comparison means for comparing the output of said integrating means with said reference signal, and means coupled to the output of said comparison means and to said first electrically controlled oscillator for terminating the sweep signal to said first electrically controlled oscillator when said compared voltages coincide, the desired station being thereby selected.