Consumer Electronics

CIRCUIT CONFIGURATION

The common-emitter circuit is the most convenient arrangement for low-frequency amplifier circuits. Its high current gain makes possible the use of resistance-capacitance coupling. Although the input resistance is normally of the order of one to two thousand ohms, it can readily be increased by inserting an unbypassed resistor in the emitter circuit. There will be a loss of signal across the emitter resistance, R_E and since it is common to both input and output circuits, it will also introduce negative feedback, thus reducing the stage gain. The input resistance can also be increased by including a resistor R_B in series with the input to the base. Again there will be a loss of signal across R_B. A third method of obtaining ...