GB1059112A - Improvements in and relating to buffer amplifiers - Google Patents

Abstract

1,059,112. Buffer amplifiers. BRITISH BROADCASTING CORPORATION. July 20, 1964 [Aug. 20, 1963], No. 32953/63. Heading H3T. In a transistor buffer amplifier having a parallel input stage and a push-pull output stage, and intended to have unity gain, the drop in voltage across the input transistors is compensated at least in part by the voltage drop in the second stage which is of opposite sign to that of the first. In the simplest arrangement, two emitter-follower stages are used, one having a PNP transistor and the other an NPN. If both transistors are of the same type they are connected in different configurations, e.g. common collector and common emitter, with negative feedback to equalize the gains of the two stages. In Fig. 2, the two parallel amplifiers comprise amplifiers, transistors 10 and 15, and transistors 18 and 19 respectively. If the load is capacitive, a sudden change in input voltage might tend to cut off one of the input transistors as the following transistor could not follow the voltage change immediately. The diode 21 then conducts and passes the signal through the second transistor of the other parallel pair. Resistor 22 reduces the standing current of the transistors. The gain can be increased by replacing or supplementing the emitter resistors by the emitter-to-collector paths of further transistors.