As shown in above circuit, PNP transistor is connected with emitter-base PN junction as forward bias by VEE whereas collector-base diode is reverse-biased by Vcc. AC signal is given by the source Vs through resistance Rs and output voltage is obtained across collector and base as voltage Vo’.
Two-Diode Analogy of CB Amplifier:
PNP Two-Diode Analogy of CB Amplifier
As shown above, PNP transistor is connected as two-diode analog. Both the diodes are connected in front-to-front position, since arrow on the emitter points inward.
Operation of Circuit:
With no input AC signal, the emitter current is DC bias current IE. Most of this current is swept into collector current of the transistor as base current IB is small. i.e. IE=IB+IC…………(1) In presence of input AC signal Vs, there will be DC as well as current in the circuit and therefor above equation becomes iE=iB+iC
The above graph of IE —–>VEB gives input characteristics of CB amplifier. Since diode is in forward-biased, this characteristic is similar to that of diode in forward bias. But input or controlling current is much larger than in the CE amplifier.
The above graph of Ic——>VCB for different values of IE gives output characteristics of a CB amplifier. Due to high output resistance, the output characteristics curve is almost horizontal.