| 摘要 |
PROBLEM TO BE SOLVED: To largely improve the distortion in an intermediate frequency (IF) stage in a superheterodyne FM receiver operable to perform FM detection.SOLUTION: In an FM receiver, a second FM detector 11 detects an output of an intermediate frequency (IF) filter 3; an error amplifier 10 compares a detection output of the second FM detector with a direct current (DC) voltage; and a capacitor 9 removes a DC component from an output signal of the error amplifier to input the resultant signal to a PLL oscillator 8. The PLL oscillator 8 outputs an FM modulated wave FM-modulated with the input signal. The FM modulated wave from the PLL oscillator 8 is input to a first mixer 2 and a second mixer 4. An output of the first mixer 2 is input to the IF filter 3, whereby a feedback loop for an AC component is formed. While a gain of the error amplifier can be set appropriately, the frequency shift of the output of the IF filter 3 can be reduced by increasing the gain.SELECTED DRAWING: Figure 1 |
