| 摘要 |
<p>1485682 Transistor amplifiers GENERAL ELECTRIC CO 22 Jan 1975 [22 Jan 1974] 2680/75 Heading H3T An audio amplifier with idling current controlled to be small, comprises a constant current source Q8, push-pull output transistors Q2, Q3 of the same conductivity type connected in series and with active regions of approximately equal area, a driver transistor Q1 driving Q3, and driving Q2 via an intermediate stage comprising a transistor Q5 of the same conductivity type as and related in active region area to Q3, and a control means Q6, connected to said current source for distributing portions of current to the output of Q5, and the input of Q2, whereby the idling currents of Q2 and Q3 are determined, the idling current of Q3 being determined by the output current of Q5 and the area ratio of Q3 to Q5. The V eb of Q2 and Q6 being approximately equal the P.D. across 16 is small so that the collector potentials of Q3 and Q5 are approximately equal. A constant currant determined by the large resistor 29 flows through Q7 and is mirrored in Q8, the area ratio of Q8 to Q7 being 9 to 1. Negative feedback is provided from the output to the base of Q1 via resistor 21, one effect being to reduce waveform asymmetry between the positive and negative half cycles, Figs. 3a, 3b (not shown). Transistor Q6 is a lateral type with current gain # adjusted to be low and independent of operating conditions. The amplifier may be fed by a preamplifier receiving an input signal from an AM or FM detector 22 via a volume control 23. A differential pair of transistors Q9, Q10 receives the signal at the base of Q9 and additional negative feedback at the base of Q10. The pair Q9, Q10 is fed by a current source Q16 in series with a 3k resistor, the potential thereacross being stabilized by D3 and the baseemitter potential of Q17. The collector currents of Q9 and Q10 are replicated by the current mirror or "turn-around" Q14, Q15. Thus the feedback applied to the base of Q10 reaches Q9 via the coupled emitters of Q9, Q10 and via Q15, Q14. The additional feedback path is through a resistor 27 and a transistor Q12 the latter having current source Q17. The output of Q9 is coupled to the input of Q1 via Q13, the current source for which is Q19. The D.C. voltage at output terminal 18 is stabilized to be slightly below half the supply voltage of source 12 by the controlled current of transistor Q20 flowing from 18 to earth via resistors 27 and 33, the base-emitter voltage of Q20 being stabilized by D1 in another current mirror arrangement. A further means for stabilizing the D.C. voltage is provided by current source Q18 feeding current from its collector via 33 and 27 to terminal 18. Resistor 33 isolates Q18 from the input to Q12. The combined amplifiers are intended for integrated form. A large capacitor 34 may be connected externally to the coupled collectors of Q18, Q20 to reduce output hum.</p> |
