. Electronic apparatus for biological research . Figure We have seen that the inclusion of resistance in the emitter circuit serves to off"set the effects of temperature. We have also seen that such a resistance introduces negative feedback and reduces gain. In coupled circuits, where there is a definite minimum frequency at which the circuit is required to operate, this feedback may be eliminated by shunting the emitter resistance with a large capacitance; in direct-coupled circuits there is no such frequency and another method is necessary. The technique is to use the transis
. Electronic apparatus for biological research . Figure We have seen that the inclusion of resistance in the emitter circuit serves to off"set the effects of temperature. We have also seen that such a resistance introduces negative feedback and reduces gain. In coupled circuits, where there is a definite minimum frequency at which the circuit is required to operate, this feedback may be eliminated by shunting the emitter resistance with a large capacitance; in direct-coupled circuits there is no such frequency and another method is necessary. The technique is to use the transistor equivalent of the long-tailed pair in valves {Figure ). This is a differential current amplifier which will discriminate against in-phase input signals. Inputs in opposite phase produce equal and opposite changes in collector current; there is no net change in the current through the common emitter resistance, and no 46A 697
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