Current gain in the common emitter circuit is obtained from the base and the collector circuit currents.
12.
The most important parameter for transistors is usually the forward current gain, h 21, in the common emitter configuration.
13.
Only two resistors are necessary for the common collector stage and four resistors for the common emitter or common base stage.
14.
For example, a common base may be used as a current buffer at the output of a common emitter stage, forming a cascode.
15.
A practical solution to this low-input-impedance problem is to place a common emitter stage at the input to form a cascode amplifier.
16.
Q3 is a common emitter stage that provides amplification of the signal and the DC bias current through D1 and D2 to generate a bias voltage for the output devices.
17.
Other arrangements of amplifying device are possible, but that given ( that is, common emitter, common source or common cathode ) is the easiest to understand and employ in practice.
18.
The value of the supply voltage is chosen so that sufficient current flows through the compensating diodes D1 and D2 and the voltage drop across the common emitter resistor R E is adequate.
19.
They all together increase or decrease the voltage of the common emitter point ( figuratively speaking, they together " pull up " or " pull down " it so that it moves ).
20.
Common emitter amplifiers give the amplifier an inverted output and can have a very high Stability is another problem associated with such high gain circuits due to any unintentional positive feedback that may be present.
