Automatic frequency scanning radio receiver

Abstract

An automatic frequency scanning radio receiver which includes a phase-locked loop frequency synthesizer serving as a local oscillator circuit and a scan clock counter circuit to produce a program input signal. The program input signal is supplied to a programmable divide-by-N counter of the frequency synthesizer, whereby the frequency synthesizer has its output frequency automatically changed in steps to automatically scan channels within a desired received frequency band. A detection circuit is provided for detecting a tuning of the radio receiver to a broadcast signal above a predetermined input level on one channel, whereby scan clock counting of the scan clock counter circuit, or the automatic channel scanning is interrupted when the radio receiver is tuned to such a broadcast signal. The tuning detection circuit detects whether or not the receiver is tuned to a broadcast signal having an input level above the predetermined input level in response to a noise level and a DC voltage level indicating a tuning degree of the receiver at the output of a demodulator such as a frequency discriminator.