| 摘要 |
PURPOSE:To prevent the output signal of a high frequency amplifier circuit from leaking through a mixing circuit to a local oscillator circuit by providing an emitter follower circuit between the local oscillator circuit at a front end of a receiver. CONSTITUTION:The emitter follower 15 is provided between a DC amplifier 16 and the local oscillating circuit 14 in the front end comprising an RF circuit 12, mixing circuit 13, local oscillation circuit 14, DC amplifier 16 amplifying the output of the local oscillation circuit and an inverse amplifier 17. The emitter follower 15 is made to have a high impedance viewed from the output side. Thus, an output signal f0 of the RF circuit 12 prevents from invading to the circuit 14 via parasitic capacitors C12-C15. Moreover, the titled device is constituted so as to supply a bias voltage and a local signal to the upper stage differential amplifier constituting a part of the mixing circuit 13 based on the output signal of the DC amplifier 16 thereby preventing the generation of the DC offset voltage at the upper stage differential amplifier. |
