| 摘要 |
PROBLEM TO BE SOLVED: To provide a disturbance detecting/discrimination circuit for an onboard FM radio tuner that can detect and discriminate multi-path/adjacent disturbance and to provide an automatic tuning program. SOLUTION: A disturbance detection circuit 10 is configured such that an S meter output Vsm is passed through a high pass filter 11 with a cut-off frequency fL=38 kHz and a band pass filter with a pass band frequency fC=72 kHz and amplified by an amplifier 13, which outputs a noise component VN. A disturbance discrimination circuit 20 is configured to comprise a pulse conversion circuit 15 that applies pulse conversion to the noise component VN as a discrimination means for discriminating the presence of disturbance on the basis of the noise component VN, a pulse counter circuit 16 that counts number of pulses for a prescribed time and a discrimination circuit 17 that discriminates the presence of disturbance when number n of count pulses is a prescribed number or over, and a discrimination output VJ being a high level in the presence of disturbance or a low level in the absence of disturbance is fed to a base of a transistor for driving a band stop filter for high-cut control of an FM detection output of a noise reduction means 18.
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