1. TYPES OF COUPLING IN AMPLIFIER
The types of coupling used in amplifiers
1. Resistance – capacitance (RC) coupling.
2. Inductance (LC) coupling.
3. Transformer coupling (TC)
4. Direct coupling (D.C.)
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2. Two stage transformer coupled amplifier.

3. Advantages:
Transformer coupling is mostly employed for impedance matching
It is used as final stage. It is used to transfer power to the low impedance lad such as loudspeaker.
For amplification of radio frequency (RF) signal.
In power amplifiers.

4. single stage CE amplifier

5. Operation of Single stage CE amplifier
The circuit diagram of a voltage amplifier using single transistor in CE configuration is shown in figure. It is also known as a small-signal single-stage CE amplifier or RC coupled CE amplifier. It is also known as a voltage amplifier.
The potential divider biasing is provided by resistors R1, R2 and RE.
It provides good stabilization of the operating point. The capacitors CC1 and CC2 are called the coupling capacitors used to block the AC voltage signals at the input and the output sides.
The capacitor CE works as a bypass capacitor. It bypasses all the AC currents from the emitter to the ground and avoids the negative current feedback. It increases the output AC voltage.
The resistance RL represents the resistance of whatever is connected at the output. It may be load resistance or input resistance of the next stage

6. Types of Coupling in Multistage
In multistage amplifiers, the output signal of preceding stage is to be connected to the input of next stage.
Coupling techniques:
R-C coupling
Transformer Coupling
Direct Coupling

7. Two stage RC coupled amplifier

9. Advantages of RC coupled Amplifier
Wide frequency response
It is most convenient coupling
It is inexpensive way of coupling distortion in output is low
It is high fidelity amplifier
No core distortion

10. Application In Public Address amplifier system Tape Recorder
TV, VCR and CD player
Stereo amplifiers
RC coupled amplifiers are basically voltage amplifiers

11. Transformer Coupled Amplifier

12. Coupling transformer is expensive and bulky
Advantages
Impedance matching between the stages is possible
Higher voltage gain than RC coupled amplifiers
DC biasing of individual stages will remain unchanged even after cascading.
Disadvantages
Coupling transformer is expensive and bulky
Frequency response is not perfectly flat
There is possibility of core saturation
Low frequency due to losses in transformer

13. Applications For Impedance matching
For amplification of radio frequency (RF) signal
In power amplifiers
For transferring power to low impedance load and such as a loude speaker

14. Direct coupled amplifier

15. Advantages
Due to absence of coupling capacitor, the gain does not reduce on the lower frequency side
Wide frequency response
This amplifier can amplify even the DC signal
Reduced cost and complexity due to absence of coupling capacitor
Disadvantages
DC biasing conditions of the individual stages do not remain same after cascading
Poor frequency response at higher frequencies
Output waveform has DC shift
Poor temperature stability

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Application
In operation Amplifiers (OP-AMP)
In analog computation
In linear Power supplies
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