GB973706A - Improvements in transistor amplifier-limiter devices - Google Patents

Abstract

973,706. Transistor limiter circuits. C.I.T. COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. Dec. 22, 1961 [Dec. 29, 1960], No. 46078/61. Heading H3T. In an amplifier-limiter circuit as shown in Fig. 2, one terminal of a sine wave generator 1 is connected to the base of transistor 2 and its other output terminal connected through a resistor 7 to the positive pole of a D.C. supply and to earth through a diode 6, the diode 6 limiting the base current when the latter reaches a predetermined value in the positive half-cycle of the generator output. During the negative cycles of the generator the transistor base is driven negative and the resistance of the base-emitter diode becomes very high so that when the transistor is cut off the collector voltage is determined by the battery 5 and not by the input voltage. During the positive cycles of the generator the transistor conducts normally so that the collector potential becomes more negative. However, when the current flowing through resistor 7 and diode 6 is balanced by the current flowing in the base circuit of the transistor the potential drop across the diode 6 becomes zero and the base circuit open-circuited with the result that no further increase in the base current is possible. Thus both positive and negative cycles of the collector voltage are limited. In addition, the inclusion in the circuit of resistor 7 results in an increase in the load resistance of the generator at all stages of the generator's output cycle so that the limiter does not produce any damping on the generator.