JPS6489714A - Electrical channel selection device - Google Patents

Abstract

PURPOSE:To shorten a time until searching is completed by deciding the size relation of a searching starting tuning frequency and an input signal frequency and starting always the searching toward an input signal frequency. CONSTITUTION:A size deciding circuit 28 decides the size of an inherent intermediate frequency f0 and an actual intermediate frequency fIF at the time of starting the searching, and thus, decides the size relation of an input signal frequency fIN and a searching staring tuning frequency fS. When the searching starting tuning frequency fS is larger than the input signal frequency fIN, a high level deciding signal VPD is outputted and at the reverse time, a low level deciding signal VPD is outputted. An MPU26, at the time of starting the searching, updates the frequency-dividing ration of a counted 21 in the direction to lower the tuning frequency when the deciding signal VPD is a high level. Reversely, when the deciding signal VPD is a low level, the frequency-dividing ratio of the counter 21 is updated in the direction to raise the tuning frequency. Thus, in accordance with the size relation of the frequency fS and a frequency fin, the updating of the tuning frequency is negative-feedback-controlled, and thus, the frequency fIF is always controlled from the time of starting the searching to the intermediate frequency f0.