Auto-selecting circuit of an intermediate frequency

Abstract

A circuit for automatically selecting an intermediate frequency which includes a single tuner having a plurality of local oscillators. The circuit amplifies a channel frequency received by an antenna and mixes it with a local oscillating frequency output from a designated local oscillator to output an intermediate frequency. The circuit also has a microprocessor which outputs a control signal to select a local oscillator for a particular broadcasting system from among the plurality of local oscillators, a switching circuit which selects an oscillating frequency of the designated local oscillator according to the control signal output from the microprocessor and outputs it to the mixer of the tuner, and a detector of an intermediate frequency which amplifies the intermediate frequency of the tuner to detect image signals and sound signals. The plurality of local oscillators for particular broadcasting systems are equipped in a single tuner, and an oscillating frequency output from a local oscillator suitable for a particular broadcasting system is selected. Cost of manufacture can be reduced, the circuit structure can be simplified, and the size of the receiving apparatus can be miniaturized because the intermediate frequency suitable for a particular broadcasting system is automatically output from a single tuner.