| 摘要 |
PURPOSE:To prevent noise at switching based on the difference between the 1st and 2nd local oscillation frequencies by detecting the frequency difference of the 1st and 2nd local oscillators, differentiating the detection output and adding the result to the post-stage of an FM demodulation circuit in opposite phases. CONSTITUTION:The difference of the oscillated frequency between the 1st local oscillator 3a and the 2nd local oscillator 3b is detected by a frequency difference detection circuit 4. A differentiation circuit 12 differentiates the frequency difference output and the result is inputted to an adder 7 provided to the post-stage of the FM demodulation circuit 6. The adder adds the said differentiation output to the FM demodulation output in opposite phases. Through the constitution above, even when the oscillated frequency of the 1st and 2nd local oscillation circuits 3a,3b is subject to secular change and a frequency difference might be caused in the changeover of the IF stage, then hit noise attended with the frequency difference is cancelled by the said differentiation output.
|
