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

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

3. 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. 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.  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 exhibits high voltage
gain and current gain. The output signal is 180º out of
phase with the input signal.

7.  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 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. 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 exhibits high
voltage gain. The output signal is in phase with
the input signal.

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