GB809207A - Improvements in and relating to transistor amplifiers - Google Patents

Abstract

809,207. Transistor amplifier circuits. MURRAY, J. S. Oct. 23, 1956, No. 32314/56. Class 40 (6). A common emitter or common base transistor amplifier having an emitter bias resistor and a collector load has its collector to base voltage maintained constant by a negative feed-back circuit between collector and base including an emitter follower transistor stage with a grounded collector. The collector to base voltage may thus be maintained at a low value in order to reduce noise. In Fig. 2 a common emitter stage 11 feeds an emitter follower stage 22 and negative feed-back both for A.C. and D.C. is provided by a resistor 21. Further negative feed-back for A.C. is provided by a resistor 25. A low-pass filter may be included in series with resistor 21 to prevent the feed-back circuit shunting the input circuit. Transistor 22 may be an auxiliary transistor outside the main signal amplifying path and resistors 23 and 24 may be decoupled by a capacitor (Fig. 1, not shown). Two D.C. amplifiers according to the invention may be arranged in push-pull and D.C. coupled to a push-pull output circuit (Fig. 4, not shown) feeding a meter or a relay. In Fig. 3 a further amplifier stage 33 is added in the feed-back loop, the output being taken from the collector and the stabilizing feed-back taken from the emitter, a low-pass filter 21a being included in the latter path. Further A.C. negative feed-back is provided for the collector of transistor 33 and from the emitter of transistor 22 and this may be varied to vary the frequency response of the amplifier. The input signal may be applied to either the base or emitter electrode of transistor 11 according to whether switches 40 and 41 are in positions h or l. The circuit is made more stable by connecting a resistor 46 between base of transistor 11 and earth, a resistance capacity circuit 29, 31 between the emitter of transistor 22 and earth and a resistor 54 in the collector supply lead. '