It is useful classify the amplifiers into four types.they are,
1.Voltage amplifier
2.Current amplifier
3. Transconductance amplifier
4. Transresistance amplifier
This classification based on the magnitudes of the input and output impedance of an amplifier relative to the source and load impedance.
1.Voltage amplifier :
The figure given in below shows the thevenin's equivalent circuit of a two port network which is represents the voltage amplifier.
from above voltage amplifier circuit consists of
Ri = Input resistance Rs = source resistance Vs = supply voltage
Ro = output resistance RL = load resistance .
- If the amplifier input resistance Ri is large as compared with source resistance Rs.
Ri >> Rs Then
Vi = Vs
- If the external load resistance RL is large as compared with the output resistance Ro of the amplifier.
- The amplifier provides a voltage output proportional to the voltage input,so the proportionality factor is independent of the magnitudes of the source and the load resistance.such a circuit is called a voltage amplifier.
- An ideal voltage amplifier must have infinite input resistance Ri and zero output resistance Ro.
