| 摘要 |
PURPOSE:To enable the FM detection with high fidelity, by broad FM detection band, through the control of oscillation frequency of the local oscillation circuit with the output frequency component, in the FM detection circuit using the solid-state resonators such as ceramic filters. CONSTITUTION:The output of the local oscillation circuit 8 is fed to the frequency mixing circuit 6, and the circuit 8 oscillates a given frequency to produce IF and the output frequency can be controlled with the control input. The voltage controlled oscillator VCO is used for the local oscillation circuit 8, in which the output audio frequency component is used for the control input. Further, the oscillation frequency controlled with the output audio frequency is mixed with the reception frequency at the circuit 6, to produce IF which is the difference of the two and is input to the IF amplifier circuit 10 at the next stage. Thus, the control of the oscillation frequency component in the FM detection circuit reduces the frequency shift at the input side of the FM detection circuit, allowing to make broad the detection band for FM detection with high fidelity. |
