| 摘要 |
PURPOSE:To enable to remove the adverse effect of noise caused in VCO circuit, by avoiding the operation of only VCO circuit of PLL circuit at AM,AUX, and PHONO which are functions other than FM. CONSTITUTION:The diode D19 is connected between the output terminal of DC power supply selection switch 3 to select the functions and the base terminal of the oscillation transistor Tr 11 of the VCO circuit 6. At FM function, since D19 is not connected, a given bias voltage is fed to the base of Tr11 and operation is conducted normally, but at the functins such as AUX, PHONO and AM, since D19 is connected to the output of the switch 3, forward voltage is fed to D19, being conductive, and the base potential of Tr11 is about Vcc-0.7V, that is, bias voltage more than required. Since only the circuit 6 is inoperative, the effect of noise caused at the circuit 6 is removed. |
