FM tuner having adaptive bandpass filter for adjacent channel interference

An FM tuner comprising:

• an intermediate signal generating circuit for subjecting a reception signal to a frequency conversion wherein a carrier frequency of a desired reception FM signal is shifted to a predetermined intermediate frequency, and generating an intermediate signal;
• a detection circuit for detecting the intermediate signal, and generating a detection signal having a voltage value corresponding to an amount of frequency deviation;
• a band judgment circuit for generating a band judgment signal in relation to whether or not the detection signal is within a target voltage range that is set according to the band of the desired reception FM signal, wherein:
• the band judgment circuit includes a first comparator for determining if the detection signal is below an upper limit value of the target voltage range;
• a second comparator for determining if the detection signal is above a lower limit value of the target voltage range;
• a first digital-to-analog conversion circuit to supply the upper limit value based on the desired reception FM signal;
• a second digital-to-analog conversion circuit to supply the lower limit value based on the desired reception FM signal;
• and
• an AND circuit outputting the band judgment signal based on the signals received from the first comparator and the second comparator;
• a strength signal generating circuit for generating a field strength signal corresponding to a field strength of the reception signal;
• a strength judgment circuit for generating a strength judgment signal in relation to whether or not the field strength signal is equal to or higher than a predetermined reference strength;
• and
• a station detecting circuit for determining the presence or absence of the desired reception FM signal based on the strength judgment signal and the band judgment signal, and outputting a station detecting signal;
• wherein
• the station detecting circuit further determines that a state in which the field strength signal is equal to or higher than the reference strength and the detection signal is within the target voltage range and a state in which the field strength signal is lower than the reference strength indicates the absence of interference from the adjacent signal, and determines that a state in which the field strength signal is equal to or higher than the reference strength and the detection signal is not within the target voltage range indicates the presence of interference from the adjacent signal.