Integrated amplifier for telephony - has AC output impedance increased by eliminating DC component of positive feedback signal

摘要

The integrated amplifier is matched to the telephone network and has a wide drive range using few components. The amplifier's a.c. output impedance is increased compared to the differential impedance corresponding to the intermediate voltage output characteristics in the linear range. This increase is achieved by passing a positive feedback signal - obtained from a resistor - via a current mirror to the drive point of the output stage. A compensation signal is obtained from a point supplying the input stages and passed via two further current mirrors to the output stage's drive point in order to suppress the d.c. component of the positive feedback signal.