GB926046A - Improvements in or relating to transistor amplifier circuit arrangements - Google Patents

Abstract

926,046. Transistor amplifier and limiter circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. Aug. 5, 1959 [Aug. 8, 1958], No. 26751/59. Class 40 (6). A transistor amplifier has the emitter base path of an auxiliary transistor connected for D.C. across the collector to base path of the amplifier transistor to produce a control signal in the auxiliary transistor which controls the level of the signal applied to the amplifier. In Fig. 1 transistor output stage 3 has the base emitter path of an auxiliary transistor connected between collector and base so that when the collector potential falls to a predetermined value the transistor 4 conducts, producing across a smoothing network 6, 7 a D.C. control voltage for reducing the amplification of a preamplifier stage 2. This avoids distortion due to the collector base junction of transistor 3 becoming forward biased on over load. The gain of transistor 2 could alternatively be controlled by applying the voltage across the network 6, 7 to the collector of the transistor. In an alternative embodiment (Fig. 2, not shown), transistor 4 is replaced by an NPN transistor, the smoothing networks 6, 7 is connected to the emitter of the pre-amplifier transistor 2. The voltage from the smoothing network could be applied in the reverse sense to the pre-amplifier, for example by connecting the output of the auxiliary transistor 4 in the second embodiment to the base of the pre-amplifier transistor so that peak limiting occurs. Capacitor 7 may be omitted, in which case negative feedback occurs when the transistor 4 becomes conductive.