GB989619A - Improvements in or relating to electrical circuits including transistors - Google Patents

Abstract

989,619. Transistor amplifying circuits. TEXAS INSTRUMENTS Ltd. March 2,1962 [March 13, 1961], No. 9175/61. Heading H3T. A stabilized amplifier of high input and low output impedance comprises a direct-coupled pair of emitter-follower stages VT2, VT3, Fig. 4, in cascade. The two transistors are of opposite conductivity type and the base bias of the first is derived, over an adjustable resistor R4, from a potentiometer in the emitter circuit of the second transistor comprising a load resistor R3 in series with a constant voltage dropping device. The latter may comprise a battery Eb, a Zener diode MZ, or in the case of an amplifier for A.C. only, a resistor shunted by a capacitor. The collector electrode of transistor VT3 is connected to the positive supply via series resistor R6; alternatively it may be connected to a source of low positive voltage, e.g. a potential divider connected between earth and the positive supply line. The arrangement reduces " drift " and minimizes noise. In an A.C. signal application the output may be taken across resistor R6. In a modification, the input impedance is increased by coupling the arrangement to a further circuit comprising two direct-coupled emitter-follower stages VT4, VT5, Fig. 5, of opposite conductivity types. The arrangement may alternatively be followed by a voltage amplifier which applies series voltage feedback to the input so as to multiply the input impedance by the overall loop gain.