GB917194A - Improvements in or relating to negative feedback transistor amplifiers - Google Patents

Abstract

917,194. Transistor amplifier circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. May 26, 1961 [May 30, 1960], No. 19093/61. Class 40 (6). [Also in Group XXXIX] The parallel connected transistor of the output stage of an amplifier move particularly for a telephone repeater, have a common emitter resistor across which a voltage is applied proportional to the voltage across the load so that feedback applied by this resistor to the output stage and from this resistor to an earlier stage is proportional both to the current and the voltage in the load. A telephone line connected at terminals 1 is coupled through a choke 2 and a filter 3 to the input of a common emitter stage 4. This is D.C. coupled to a second stage 5 feeding an output stage comprising two transistors 9, 10 in parallel having the primary winding of output transformer 11 connected to their collectors. Feedback to a common emitter resistor 7 is provided from a tertiary winding through a resistor 19 whereby negative feed back is provided around the output stage. A further feedback circuit through resistor 8 provides both current and voltage feedback to the input stage. Network 3 and negative feedback network 13 equalize the attenuation of the cable, the latter network having a high impedance compared with the emitter impedance of transistor 4 so that its frequency characteristic has no effect on the feedback from the output stage. D.C. stabilization is effected by the main feedback path, by feedback to the first stage base from the second stage emitter resistor 17 and by the provision of individual output stage emitter resistors 14 and 15.