| 摘要 |
PURPOSE:To ensure an optional and independent control for each differential amplifying circuit, by providing a variable current circuit in addition to a constant current circuit to each differential amplifying circuit to control the gain of each of these amplifying circuits. CONSTITUTION:An input signal ei added with a base bias V1 is applied to a differential amplifying circuit. A constant current decided by a fixed bias V2 is supplied to diodes D1 and D2 via transistors Q1 and Q2. The signal ei is amplified by the differential amplifying circuit and undergoes a current-voltage conversion by the diodes D1 and D2 to be outputted as an output Vout by TRQ7 and TRQ8. The gain of the differential amplifying circuit can be controlled by controlling the current flowing to the D1 and D2 since the current-voltage conversions of D1 and D2 have different gains due to their current values. This current control is carried out by a variable current circuit consisting of current control transistors Q4, Q5 and Q6. This variable current circuit applies the control signal voltage to a base bias V3 or V4 to control the current. |
