Gain control circuit - has two transistor differential amplifiers with controlled transconductance and with negative feedback of different factors

摘要

The gain control circuit includes two transistor differential amplifier (T1 T2 and T3 T4). The input circuits of these amplifiers are connected in parallel to a signal voltage source (Us). The transistors in the amplifiers which carry signal currents having equal phase are connected together and to the input side of an amplifier (F). A current source (Is. T5. T6) is arranged to feed emitter currents to the amplifier the quotient of the emitter currents depending on a control signal (Uc) applied to the current source. The output of amplifier (F) is connected to the input of the differential amplifiers through a negative feedback network (R1 R2, R3). This network is so dimensioned that the differential amplifiers together with the feedback network have different loop again for the same emitter current.