Automatic intermediate frequency correction circuit for radio - determines maximum signal strength and uses it along with local frequency for digitally setting reception frequency

摘要

The correction circuit corrects the denominator N of an oscillator's frequency (Fosc) by a value X and uses it as a digital value for the received frequency. The oscillator's frequency is compared in a phase locked loop with a reference frequency (Fref). The vco of the AM/FM tuner is used as local oscillator. The input range of the tuner is disabled during testing. The frequency range of the vco is changed in steps until the field strength of the IF signal is a max. This max. is stored along with the value of the IF local oscillator frequency and used to digitally set the frequency of the receiver.