METHOD FOR SELECTING LOW IF OF FM RADIO TUNER, AND FM RADIO TUNER USING THAT IF

摘要

An FM radio tuner that, even when using a low IF frequency, is not affected by noise getting into an audio band. A radio tuner comprises at least a BPF (2) that attenuates, among signals received via an antenna (1), the signals other than a desired signal; a mixing circuit (3) that mixes the output signal from the BPF (2) with a signal from a local oscillator (4) to provide converted intermediate frequencies; a combination of the local oscillator (4) and a PLL circuit (5) that generate the signal to be mixed into the output signal of the mixing circuit (3) so as to tune to a desired FM signal; an IF BPF (6) that extracts, from the intermediate frequency signals outputted from the mixing circuit (3), only a desired signal; a limiting circuit (7) that keeps the amplitude of the FM signal constant; an FM detecting circuit (8) that detects the FM signal; and a stereo demodulating circuit (9) that demodulates the signal detected by the FM detecting circuit (8). This radio tuner uses, as the center frequency of the IF frequencies, a frequency near an even multiple of 38 kHz.