| 摘要 |
PURPOSE:To stabilize a bias voltage by constituting the post-stage filter with an emitter follower transistor (TR) whose base and emitter are connected between a filter output terminal of the 1st stage and a bias output terminal and with a capacitor connected to said emitter. CONSTITUTION:A TRQ1 of emitter follower connection is used in place of a resistor constituting a post-stage LPF together with a capacitor C2. Through the constitution above, in viewing the post-stage filter circuit from the 1st stage LPF circuit comprising a diode D and a resistor R1 and a capacitor C1 connected in series therewith, the input impedance is very high, resulting that the time constant is very large. Since a base-emitter voltage of the TRQ1 is not so much changed even when a bias current iB changes largely, a bias voltage outputted at a bias output terminal K is not almost changed. |
