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Circuit Description:

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

                                                                                                                             PNP Transistor

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                                                                                                                                                                                                  

 Input Characteristics:                                                                                                                                                                                                                                      

                                                                                                                  

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.

Output Characteristics:

                             

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.

                                                                                                                    

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Comments on: "The Basic Common-Base Amplifier,CB" (1)

  1. very helpful do v have lect notes j.d ryder fundamental of electronics

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