| 摘要 |
PURPOSE:To improve the intermodulation distortion characteristic and the cross modulation distortion characteristic at a UHF receiving time, by increasing the emitter current when an IF signal is applied to the base of an emitter- grounded transistor, in a frequency converting circuit of the TV tuner circuit. CONSTITUTION:A local oscillator 11, a mixing amplifier 10, an operation state switching circuit 12, etc. are provided. When a power supply terminal F for UHF becomes a positive voltage at a UHF receiving time, the collector current of an emitter-grounded transistor of the mixing amplifier 10 is increased, and the operation state is transferred from an optimum point of intercept points as a mixing circuit to an optimum point of intercept points as an amplifying circuit. Consequently, at the UHF receiving time, the IF signal is supplied from an input terminal C to the cirauit 10 through a switching circuit 6. At this time, the circuit 10 is operated as an IF amplifier, and the emitter current is forcedly increased by the circuit 12, and the IF signal is transmitted from an output terminal (e) under the state where the current at the intercept point is increased. |
