GB1002632A - Electrical signal amplifier - Google Patents

Abstract

1,002,632. Transistor amplifiers. ADAGE Inc. Dec. 27, 1962, No. 48722/62. Heading H3T. The invention relates to supply arrangements for D.C. amplifiers and more particularly for amplifiers having a high input impedance. A basic circuit arrangement according to the invention is illustrated in Fig. 1, in which input signals are applied through a network 24 to a D.C. amplifier 28 feeding a transistor output stage 34 having a constant current emitter supply, the circuit having common input, output and supply terminals 12, 16 and 18 and a D.C. supply for the amplifier comprising two stabilized voltage sources 44 and 46 with a common point connected to an output terminal 14. Fig. 2 shows more details of this circuit. The input terminal 10 is connected to a main D.C. amplifier 28 through an A.C. path comprising capacitor 50 and through a chopper type D.C. amplifier 60, 66 described later. The output from the main amplifier 28 is fed to a transistor 34 having output terminal 14 connected to its emitter. The emitter supply is obtained from a constant current source 38 formed from a transistor 88 having a constant current emitter supply provided from a Zener diode 90 and resistor 96. The collector-emitter voltage of transistor 34 is maintained constant by a series transistor 80 operated as an emitter follower with its base coupled through a constant voltage source 86 to the emitter of transistor 34. This constant voltage source comprises a 10-volt Zener diode fed with a constant current supply from a source 84. The constant 10 volts with reference to the emitter of transistor 34 which exists at the emitter of transistor 80 is used as a supply voltage for circuits 60, 64 and 28. A five-volt Zener diode 76 reduces this ten volts to five volts and this is used as a supply for amplifier 28. A multivibrator 64 operates a chopper 62 and a demodulator 66, the chopper being connected in a negative feedback path from output terminal 14 to the input terminal. When the transistor 34 has to operate from a higher voltage supply, further transistors may be added between the battery 22 and transistor 80 (Fig. 3, not shown). A diode 118 prevents false operation of the amplifier when the load is capacitive and a feedback circuit 120 improves the stability of the circuit. In addition overall feedback may be provided, for example, to make the circuit into an "operational" amplifier (Figs. 4 and 5, not shown).