GB848921A - Improvements in or relating to amplitude limited amplifiers - Google Patents

Abstract

848,921. Non-linear valve amplifier circuits. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. Jan. 26, 1959 [March 27, 1958], No. 9910/58. Class 40(6). In a circuit adapted to amplify a small part only of a relatively large input signal, comprising an amplifier having a resistance connected in series between the input terminal of the circuit and an input terminal of the amplifier and a negative feedback resistance connected between output and input terminals of the amplifier, a further negative feedback is connected between the output terminal and an intermediate terminal of the amplifier, the further feedback circuit including a pair of oppositely poled unilaterally conducted devices adapted to increase the amount of the further feedback when the signal is outside the given small range. Fig. 2 shows a "see-saw" type amplifier comprising a series input resistor 3 and a feedback resistor 4. A further feedback path is provided through a pair of oppositely directed biased diodes 15, 16 arranged to conduct when the signal extends beyond a given voltage range so that the feedback is greatly increased and the gain greatly reduced. The position of the range over which the diodes are non-conducting may be varied by adjusting the voltage on the grid of a valve 6. The Specification also describes a known alternative circuit in which the diodes are connected effective across the feedback resistor 4 instead of in an additional feedback path and in which the range of non-conduction of the diodes is varied by a bias voltage fed to the grid of valve 5.