Quieting receiver during power interruption

Abstract

A receiver comprises a tuner circuit for detecting a selected input signal and an audio circuit for reproducing the audio content in the detected signal. The tuner circuit includes a local oscillator, a prescaler, a phase detector and an integrator, and has a tendency to uncontrollably detune during AC power interruption responsive to a spurious tuning control signal generated in the tuner circuit and generate audible noise during the detuning. The audible noise is introduced into the audio content of the detected signal. An AC power interruption detector monitors a run power supply and generates a power loss control signal when the run supply falls below a predetermined threshold. A control circuit responsive to the power loss control signal, absent a user command, first disables normal operation of the tuner circuit and then disables the audio circuit, thereby reducing the audible noise. The tuner circuit may be disabled by decoupling the output of the phase detector from the input to the integrator, enabling the input to float. In the absence of a corrective signal from the phase detector, which may be the spurious tuning control signal, the integrator maintains a substantially constant output tuning voltage and prevents sudden detuning.