Automatic gain control circuit for a subscriber line interface

An automatic gain control circuit for a subscriber line interface including separate transmit and receive gain control differential pair multipliers (Q11, Q12), (Q13, Q14) to which respective transmit and receive signal currents are applied, and means for applying to the multipliers a gain control voltage having a predetermined relationship to the DC differential line voltage of the subscriber line to control the current gains thereof, each multiplier being designed to have substantially linear change of gain with respect to line voltage over the same predetermined range of line voltages. Transistors (Q3, Q4) form a differential input stage for the transmit signal. Transistors (Q5, Q6) provide a current source for the transmit input stage. The receive signal is input via an emitter follower stage (Q15).