^CEA

^CEA

Output is 180⁰ out of phase with input.

Transconductance is also called mutual conductance.

As β > > α, thus the ac power gain of a CEA is much larger than that of a CBA. Remember the transistor is not generating any power. The energy for the higher ac power at the output is supplied by the battery.

Saturation state:

Both the junction are forward biased & here I_C is maximum & does not depend on the input current I_B.

Cut off state:  Both the junctions are reverse biased as a result I_C = 0. Between cut off & saturation state a transistor works as switch as here it turns over rapidly from OFF state (i.e. I_C = 0 or cut off) to the ON state (i.e. I_C is maximum or saturation state).

Active state: Emitter base junction is forward biased and the collector base junction is reverse biased. A transistor works as an audio amplifier in this regions.

Relation between α and β:

As the value of I_B is about 1 – 5 % of I_E or I_C is 95 – 99 % of I_E, α is about 0.95 and 0.99 and β is about 20 to 100.  It is found that α and β are independent of current if the emitter base junction is forward biased and the collector base junction is reverse biased. Also the above definitions of α and β do not hold when both the junctions of a transistor are forward biased or reverse biased.

The CE configuration is frequently used as it gives high current gain as well as voltage gain.