Introduction to common base configuration of Transistor

May 28 • Notes • 32568 Views • 8 Comments on Introduction to common base configuration of Transistor

Common Base Configuration

The common base terminology is derived from the fact that the base is common to both the input and output sides of the configuration.The base is usually the terminal closest to,or at,ground potential.
The figure below showing the notation and symbol used for npn transistor.

npn

npn2

In CB configuration, the base is common to both input (emitter) and output (collector). For normal operation, the E-B junction is forward biased and C-B junction is reverse biased.
In CB configuration, IE is +ve, IC is –ve and IB is –ve. So,
VEB=f1 (VCB,IE) and
IC=f2 (VCB,IB)
With an increasing the reverse collector voltage, the space-charge width at the output junction increases and the effective base width ‘W’ decreases. This phenomenon is known as “Earlyeffect”. Then, there will be less chance for recombination within the base region. With increase of charge gradient within the base region, the current of minority carriers injected across the emitter junction increases.The current amplification factor of CB configuration is given by,
α= ∆IC/ ∆IE

The input or driving point characteristics and the output or collector characteristics for a common-base transistor amplifier is shown below

123

The common-base amplifier can provide a reasonable level of voltage gain but suffers from low input impedance and a current gain of less than one. However, this circuit is used extensively for high-frequency applications because its terminal characteristics at high frequencies are better than those of a common-emitter configuration using the same
transistor.
The standard common-base configuration also requires two DC supplies rather than the one needed for the common-emitter and common-collector configurations. There is, however, a method to be introduced in this experiment that permits the proper biasing of a common-base amplifier with only a single supply.

Questions
1 What is the biasing rule of transistor?
Ans: Emitter base junction must be forward biased and collector base junction must be reversed biased.

2.What are three basic transistor connection,which mode is most preferred and Why?
Ans: Common-Emitter, Common-Base & Common-Collector connections.
Common emitter mode is most preferred because this modes gives Highest voltage gain.

8 Responses to Introduction to common base configuration of Transistor

  1. Anonymous says:
  2. himanshu patel says:

    not abe to understand the topic

  3. himanshu patel says:
  4. zeeshanmahmood says:

    bscs from punjab university

  5. zeeshanmahmood says:

    bscs from punjab university

  6. vishal prajapati says:

    To set up a common base transistor circuit and to study its input and output characteristic and to
    calculate its current gain. i need an investigatory project on it and i need it today please help me.

  7. EMILIA DEVI says:

    TO CONSTRUCT A SWITCH USING A TRANSISTOR AND DRAW THE GRAPH BETWEEN THE INPUT AND OUTPUT VOLTAGE AND MARK THE CUTOFF SATURATION AND ACTIVE REGION

  8. ARANI MONDAL says:

    I want each and every knowledge to be a good web and app developer

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