. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. EARTHED COLLECTOR CONFIGURATION Approximate equations for the earthed collector stage are very simple. The current gain is roughly j3, but the voltage gain is less than unity. The input resistance is merely f^Rj^ and the output resistance RqI^- Thus if i?^ is 10 k and /5 = 30, the input resistance is about 300 kQ. If the earthed collector transistor is being used as an output stage, Rq is the output resistance of the penultimate stage as a whole and is substantially the resistance of its c
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. EARTHED COLLECTOR CONFIGURATION Approximate equations for the earthed collector stage are very simple. The current gain is roughly j3, but the voltage gain is less than unity. The input resistance is merely f^Rj^ and the output resistance RqI^- Thus if i?^ is 10 k and /5 = 30, the input resistance is about 300 kQ. If the earthed collector transistor is being used as an output stage, Rq is the output resistance of the penultimate stage as a whole and is substantially the resistance of its collector load, perhaps 3 kQ. The output resistance of the earthed collector stage is then 3 kQ/30 = 100 In point of fact, high input resistance is not of first importance with grounded-collector stages. The power gain is so low that, as Jones and Hilbourne^ point out, the performance is no better than that of an earthed emitter stage with the input resistance raised by the simple expedient of connecting a resistance in series with it (Figure ). The low output impedance therefore remains its most valuable feature. Gain control In potentiometric gain control between valve stages V-^ and Fg {Figure ), the potentiometer is working between a generator of resistance, Low^ I Intermediate Figure Valve 2 the output resistance of F^, perhaps 50 kQ, and a load which is much higher, perhaps many hundreds of megohms. The potentiometer's own value is intermediate, say 2 MQ, and we saw in Chapter 2 that such an arrangement produces a satisfactory control characteristic. In transistor Intermediate I 1 I Low. Transistor 1 Transistor 2 Figure circuits the position is reversed. The output impedance of a transistor stage is larger than the input impedance of the stage which follows it, and under these conditions the arrangement of Figure gives poor control; a better scheme is shown in Figure , and this is the one usually used. It has another important advantage
Size: 2517px × 993px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodiversity, bookleafnumber745
