RADIO RECEIVER AND LOCAL OSCILLATION FREQUENCY CONTROL CIRCUIT FOR FM RECEIVER

摘要

PROBLEM TO BE SOLVED: To reduce the number of parts in a radio receiver for plural bands such as AM/FM, etc., and to change the local oscillation frequencies of the plural bands by a control terminal when the receiver is made into an IC. ;SOLUTION: A local oscillation circuit 20 for AM is provided with an oscillator 23 and the variable capacitance circuit 22 composing capacitance for resonating for determining the oscillation frequency of this oscillator 23. The variable capacitance circuit 22 is composed of a differential amplifier, a resistor and capacitor. By changing the amplification factor of the differential amplifier according to the control voltage from an input terminal, capacitance for resonating is equivalently changed and a local oscillation frequency is changed. A local oscillation circuit 14fm for FM broadcast is provided with a variable capacitance diode 142fm for tuning. The control voltage from the input terminal is amplified up to the necessary degree for FM by a voltage booster circuit 50 and the voltage is impressed on the variable capacitance diode 142fm which is biased to high voltage by the DC voltage from a high voltage generation circuit 15fm.;COPYRIGHT: (C)1997,JPO