Channel selecting apparatus employing frequency synthesizer

Abstract From the Canadian patent

A tuner comprises a local oscillator including a variable capacitance diode. The output signal of the local oscillator is frequency divided by a prescaler and the frequency divided output is applied to a phase locked loop. The phase locked loop is structured such that the phases of the output signal of the prescaler and a reference frequency signal are compared and the signal associated with the phase difference is smoothed by a low pass filter and the smoothed output is applied to the variable capacitance diode as a tuning voltage. The low pass filter includes a smoothing capacitor. A tuning unlocked state is detected when the terminal voltage of the smoothing capacitor is stabilized at …