GATE Electrical – Analog Electronics
Page 15: Emitter Follower (Common Collector Amplifier)
The Emitter Follower amplifier is also called the Common Collector (CC) amplifier. In this configuration, the collector terminal is common to both input and output circuits.
Circuit Configuration
In the emitter follower configuration:
- Input signal is applied between base and collector
- Output signal is taken from the emitter terminal
- The collector is connected to the supply voltage
Since the output voltage follows the input voltage, this amplifier is called an Emitter Follower.
Working Principle
When an input signal is applied to the base, the emitter voltage changes accordingly.
The emitter voltage is approximately:
VE ≈ VB − VBE
Where:
- VB = Base voltage
- VBE ≈ 0.7 V (for silicon transistor)
Voltage Gain
Voltage gain of emitter follower is approximately:
Av ≈ 1
Thus the output voltage nearly follows the input voltage.
Input Resistance
Input resistance is very high:
Rin ≈ β RE
Typical value ranges from:
100 kΩ – 1 MΩ
Output Resistance
Output resistance is very low:
Rout ≈ RE / β
Typical value ranges from:
10 Ω – 100 Ω
Applications
- Impedance matching
- Buffer amplifier
- Voltage follower circuits
- Signal isolation
Important GATE Points
- Voltage gain ≈ 1
- Very high input resistance
- Very low output resistance
- No phase inversion
- Used as buffer amplifier
Next Page → Multistage Amplifiers
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