Analog Electronics – Page 32
Multistage Amplifiers
A multistage amplifier consists of two or more amplifier stages connected in cascade to increase overall gain.
Each stage amplifies the signal and passes it to the next stage.
Why Multistage Amplifiers are Used
- To obtain very high voltage gain
- To improve power amplification
- To drive heavy loads
- To increase signal strength
Types of Coupling
- RC Coupling
- Transformer Coupling
- Direct Coupling
Overall Voltage Gain
The total gain of a multistage amplifier is the product of gains of individual stages.
Av = Av1 × Av2 × Av3 × ... × Avn
Gain in Decibels
Gain is often expressed in decibels.
Gain(dB) = 20 log10(Av)
For multistage amplifier:
Total Gain(dB) = Gain1 + Gain2 + Gain3
Example Problem
A two-stage amplifier has gains:
- First stage gain = 50
- Second stage gain = 20
Find total voltage gain.
Av = Av1 × Av2
Av = 50 × 20
Av = 1000
Gain in dB
Gain(dB) = 20 log10(1000)
Gain = 60 dB
Key Points for GATE
- Overall gain is multiplication of stage gains
- In decibel scale gains are added
- RC coupling is most common in voltage amplifiers
- Transformer coupling used for power amplification
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