Automatic broadcast wave tuning device for rds receiver

Claim 1

An automatic broadcast wave tuning device for a radio data system (RDS) receiver comprising: a front end unit for receiving a RDS broadcast wave carrying a list of alternative frequencies data (AF) and a program identification code (PI) of a group of broadcasting stations, which belong to the same broadcasting network, by tuning in a broadcasting station within the same broadcasting network; a phase-locked loop (PLL) circuit for performing the tune-in operation of the front end unit by varying a frequency divisional ratio thereof; a frequency discriminator for discriminating a frequency modulated (FM) signal output of the front end unit; a multiplex demodulator circuit for outputting an audio signal by demodulating a discriminated output of the frequency discriminator; a level detector for detecting a received signal level by accepting the discriminated output of the frequency discriminator; a RDS decoder for decoding the discriminated output of the frequency discriminator into prescribed readable data; an alternative frequencies (AF) data memory for storing the program identification code (PI) carried by the broadcast wave presently tuned in; and a controller connected to the phase-locked loop (PLL) circuit, the level detector and the RDS decoder for controlling the frequency divisional ratio of the phase-locked loop (PLL) circuit by receiving an detected output of the level detector and a decoded output of the RDS decoder, whereby the control is performed such that it is determined whether or not the program identification code (PI) is readable based on the detected output of the level detector, when it is determined that the program identification code (PI) is unreadable but a received signal level of the broadcast wave of the broadcasting station within the same broadcasting network is at or above a predetermined signal level, the frequency divisional ratio of the phase-locked loop (PLL) circuit is so controlled as to tune in the former broadcast wave by setting a forbidden flag to the corresponding frequency for forbidding the next tune-in to the broadcast wave of the broadcasting station within the same broadcasting network carrying the forbidden flag, whereas when it is determined that the program identification code (PI) is readable but the readable program identification code (PI) is not identical with that of the broadcast wave presently tuned in, the frequency divisional ratio of the phase-locked loop (PLL) circuit is so controlled, without discriminating a level of the received signal from the detected output of the level detector, so as to return to tune in the former broadcast wave by setting the forbidden flag to the corresponding frequency and so as to not switch to the broadcast wave of the broadcasting station carrying the forbidden flag in the next switching operation within the same broadcasting network.