Bjt amplifiers

Objectives
Understand the concept of amplifiers
Identify and apply internal transistor parameters
Understand and analyze common-emitter, common-collector and common-base amplifiers
Introduction
One of the primary uses of a transistor is to amplify ac signals. It has to be able to do it without distorting the original input.
Amplifier
The collector curves and load lines help us to relate the Q-point and its proximity to cutoff and saturation. The Q-point is best established where the signal variations do not cause the transistor to go into saturation or cutoff. For perfect amplifier Q-point must be in the middle of the active region.
Amplifier Operation
The region between cutoff and saturation is called the linear region. A transistor which operates in the linear region is called a linear amplifier. Note that only the ac component reaches the load because of the capacitive coupling and that the output is 180º out of phase with input.
The Common-Emitter Amplifier
The common-emitter amplifier exhibits high voltage gain and current gain. The output signal is 180º out of phase with the input signal.
Characteristics
Voltage gain -High
Current gain - High
Power gain - High
Input or output phase relationship - 180 degree
Input resistance - Low
Output resistance -High

1. BJT Amplifiers D. Veera Vanitha Assistant Professor Avinashilingam Institute for Home Science and Higher Education for Women, Coimbatore, Tamil Nadu

2. Objectives Understand the concept of amplifiers Identify and apply internal transistor parameters Understand and analyze common-emitter, common-collector and common-base amplifiers

3. Introduction One of the primary uses of a transistor is to amplify ac signals. It has to be able to do it without distorting the original input.

4. Amplifier The collector curves and load lines help us to relate the Q-point and its proximity to cutoff and saturation. The Q-point is best established where the signal variations do not cause the transistor to go into saturation or cutoff. For perfect amplifier Q-point must be in the middle of the active region.

5. Amplifier Operation The region between cutoff and saturation is called the linear region. A transistor which operates in the linear region is called a linear amplifier. Note that only the ac component reaches the load because of the capacitive coupling and that the output is 180º out of phase with input.

6. The Common-Emitter Amplifier The common-emitter amplifier exhibits high voltage gain and current gain. The output signal is 180º out of phase with the input signal.

7. Characteristics Voltage gain -High Current gain - High Power gain - High Input or output phase relationship - 180 degree Input resistance - Low Output resistance -High

8. The Common-collector Amplifier The common-collector amplifier exhibits high current gain and voltage gain is unity. The output signal is in phase with the input signal. It is also known as emitter-follower.

9. Characteristics   Voltage gain -Zero Current gain -High Power gain -Medium Input or output phase relationship - Zero degree Input resistance - High Output resistance -Low

10. The Common-Base Amplifier The common-base amplifier exhibits high voltage gain. The output signal is in phase with the input signal.

11. Characteristics Voltage gain -High Current gain - Low Power gain -Medium Input or output phase relationship - Zero degree Input resistance - Low Output resistance -High

12. Thank You