The document discusses the common emitter configuration of a bipolar junction transistor (BJT), detailing its construction, operating modes, and the characteristics of common base and common collector configurations. It highlights the BJT's ability to act as an amplifier in active mode, its complete turnoff in cut-off mode, and its fully on condition in saturation mode. Additionally, it provides insights into input and output parameters along with their resistance characteristics.

1. Common Emitter Configuration

2. Bipolar Junction Transistor
 It is a three terminal device.
 It is constructed by connecting two P-N junction
diodes back to back
 It is of two types NPN and PNP.
 In NPN, P-type material is sandwiched between
N-type.

3. BJT operating modes
 Active mode: transistor operates as an amplifier
 Cut-off mode: complete turnoff mode
 Saturation mode: fully ON condition; collector
current equal to saturation current

4. Common base configuration
 Base terminal is common to both input and
output.
 It provides high voltage gain.

5. Common collector configuration
 In this collector terminal is common for both input
and output.
 It provides high current gain.

6. Common emitter configuration
 Emitter is common for both input and output.
 It provides both current and voltage gain.
 Output has a phase shift of 180 degree with
respect to input.

7. Bias computation

8. AC representation

9. Input characteristic
 Input parameters are base emitter voltage and
base current.
 Input resistance is

10. Output characteristic
 Output parameter are collector emitter voltage
and collector current.
 Output resistance is

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