| 摘要 |
PURPOSE:To obtain a gain controlling amplifier with very little distortion, by inserting a distortion cancelling circuit consisting of a semiconductor rectifier in a path of an amplifier signal having a variable current source changing a common emitter current of transistors (TRs) depending on a control voltage. CONSTITUTION:In a distortion cancelling circuit 2, a DC blocking capacitor (C) 18a and a diode (D) 14a are inserted in series between a signal input terminal 15 and a resistor (R) 16 and in parallel with them, a DC blocking C18b and D14b are inserted in series. A connecting point between the C18a and the D14a is connected to a positive power supply 9 via an R19a and a variable R20a. Further, a connecting point between the C18b and the D14b is connected to a negative power supply terminal 6 via an R19b and a variable registor 20b. In a variable gain amplifier 1, the emitter of TRs 3, 4 is connected in common via Ds 21, 22 and to the terminal 6 via a TR23 and an R24. A part consisting of the TR23 and R24 and a part consisting of a TR25 and an R26 constitute a current mirror circuit. Thus, the distortion in the circuit 1 can be cancelled at the circuit 2. |
