## Featured post

### What Is Fluid and Its Properties?

Science helps to understand things in a better way. We know about fluid but science helps to understand different aspects of it in a better ...

## 16/11/2020

### Voltage Gain & Bandwidth

Gain of the Amplifier

• The ratio of the output quantity to the input quantity of the amplifier is called as Gain of the Amplifier.

Gain of Multi Stage Amplifier

• Let us consider three amplifiers having respective gain of G1, G2 and G3. The total gain of the amplifier is

G = G1 × G2 × G3

• The gain of the multistage amplifier G is less than produce of G1 × G2 × G3 due to loading of next stages.

Decibel Gain

• The gain of the amplifier is very large therefore it is represented by common logarithm ( base 10 ). The unit of gain is bel or db.

Power gain

• The ratio of output power to the input power in log to the base 10 is called as power gain of the amplifier.

Power Gain = Log10 ( POUT / PIN ) bel

1 bel = 10 db

= 10 Log10 ( POUT / PIN ) db

Voltage Gain

• The ratio of the output voltage to the input voltage in log of base 10 is called as voltage gain of the amplifier.

Let POUT = VOUT2 / R

PIN = VIN2 / R

• Voltage gain = 10 Log10 ( POUT / PIN ) db

= 10 Log10 [ VOUT2 / R ] / [ VIN2 / R ] db

=  20 Log10 ( VOUT / VIN ) db

Current Gain

• The ratio of the output current to the input current in log of base 10 is called as voltage gain of the amplifier.

Let POUT = IOUT2R

PIN = IIN2R

• Current Gain = 10 Log10 ( POUT / PIN ) db

= 10 Log10 [ IOUT2R ] / [ IIN2R ] db

= 20 Log10 ( IOUT / IIN )

Finally

 Power Gain Log10 ( POUT / PIN ) bel 10 Log10 ( POUT / PIN ) db Current Gain Log10 ( IOUT / IIN ) bel 20 Log10 ( IOUT / IIN ) db Voltage Gain Log10 ( VOUT / VIN ) bel 20 Log10 ( VOUT / VIN ) db

Bandwidth

• It is range of frequencies over which the voltage gain is equal to or greater than 70.7% of the maximum gain.
• The f1 and f2 is range of frequencies over which the gain is equal / greater than 70.7% of the maximum gain.

Where f1 = Lower cut off frequency

f2 = Higher cut off frequency

• Bandwidth = f2 – f1
• It is important that the signal frequencies lie between f1 and f2 for distortion less amplification.

Bandwidth in terms of db

• Let us consider that the maximum gain of the amplifier is 100.
• Fall in voltage gain from 100 to 70.7%

= 20 Log10 ( 100 ) – 20 Log10 ( 70.7 ) db

= 20 Log10 ( 100 / 70.7 ) db

= 20 Log10 ( 1.414 ) db

= 3db

The bandwidth of the amplifier is defined as the range of frequency over which the voltage gain fall by 3 db from the maximum gain.

• The frequency f1 or f2 is called as half power frequency or 3 db frequency.

You may also like :

List of Power distribution Companies In India

What do you mean by AC Drive?

Effect of harmonics on Power factor

Types of Smoothing Reactor

Series Compensation