GB1525751A - Amplifiers - Google Patents

Abstract

1525751 Transistor amplifiers NIPPON GAKKI SEIZO KK 4 Sept 1975 [6 Sept 1974] 36525/75 Heading H3T An amplifier for low distortion, e.g. a Class B power amplifier, comprises first and second driver stages Tr21, 22 and Tr23, 24 respectively, and an output stage Tr25, 26, each driver stage including two complementary transistors with their control electrodes fed in parallel, their second electrodes connected to the control electrode of a respective output transistor Tr25 or 26, and their third electrodes respectively supplied from terminals +B1, -B1, the output transistors Tr25, 26 being complementary and feeding in parallel an output terminal of the amplifier. Biasing voltages for the control electrodes of Tr21-24 are provided by the networks E1-4, VR8 being for bias voltage adjustment. The input signal is applied to Tr54 which forms an emitter-coupled pair with Tr55, the latter receiving negative feedback from the amplifier output terminal via a network R101, R102, C88. The output from Tr54, 55 is applied to differential stage Tr52, 53, the outputs being taken from the collector circuit of Tr53 on each side of the network El, E2. Tr50, D51 provide constant current for the biasing networks and for Tr52, 53. In another embodiment complementary F.E.T.'s (Q21, Q22), Fig. 9 (not shown), feed an output F.E.T. (Q25). Stabilized biasing voltages for the F.E.T.'s are provided by the drops across resistors (R59, R60) in series with constant current transistors (Tr33, Tr34). A variable resistance (VR2) is included to adjust the bias. Circuits of the invention are stated to have the advantage over prior art, as exemplified by Fig. 1 (not shown), that they are substantially free from distortion caused by gate capacitance of the output transistors.