Module 8—Introduction to Amplifiers
Pages i - ix
1-1 to 1-10
, 1-11 to 1-20
1-21 to 1-30
, 1-31 to 1-40
2-1 to 2-10
, 2-11 to 2-20
2-21 to 2-30
, 2-31 to 2-35
3-1 to 3-10
,3-11 to 3-20
3-21 to 3-30
, 3-31 to 3-40
3-41 to 3-50
, 3-51 to 3-60
3-61 to 3-70
, AI-1 to AI-3
The CLASS OF OPERATION of a transistor amplifier is determined by the percent of time
that current flows through the transistor in relation to the input signal.
In CLASS A OPERATION,
transistor current flows for 100% (360º) of the input signal. Class A operation is the least efficient class of
operation, but provides the best fidelity.
In CLASS AB OPERATION, transistor current flows for more than 50% but less than
100% of the input signal.
In CLASS B OPERATION, transistor current flows for 50% of the input signal.
In CLASS C OPERATION, transistor current flows for less than 50% of the input signal.
Class C operation is the most efficient class of operation.
COUPLING is used to transfer a signal from one stage to another.
COUPLING is the connection of the output of one stage directly to the input of the next stage. This
method is not used very often due to the complex power supply requirements and impedance- matching problems.
RC COUPLING is the most common method of coupling and uses a coupling capacitor and
IMPEDANCE COUPLING uses a coil as a load for the first stage but otherwise functions just as
RC coupling. Impedance coupling is used at high frequencies.
TRANSFORMER COUPLING uses a transformer to couple the signal from one stage to the next.
Transformer coupling is very efficient and the transformer can aid in impedance matching.
MAXIMUM POWER TRANSFER occurs between two circuits when the output impedance of the first
circuit matches the input impedance of the second circuit.
A MAXIMUM VOLTAGE INPUT SIGNAL is present when the input impedance of the second circuit is
larger than the output impedance of the first circuit (mismatched).
The COMMON-EMITTER configuration of a transistor amplifier has MEDIUM INPUT and
MEDIUM OUTPUT IMPEDANCE.
The COMMON-BASE configuration of a transistor amplifier has LOW INPUT and HIGH OUTPUT
The COMMON-COLLECTOR (EMITTER FOLLOWER) configuration of a transistor amplifier as
HIGH INPUT and LOW OUTPUT IMPEDANCE.
FEEDBACK is the process of coupling a portion of the output signal back to the input of
POSITIVE (REGENERATIVE) FEEDBACK is provided when the feedback signal is in
phase with the input signal. Positive feedback increases the gain of an amplifier.
NEGATIVE (DEGENERATIVE) FEEDBACK is provided when the feedback signal is 180º out of
phase with the input signal. Negative feedback decreases the gain of an amplifier but improves fidelity and may
increase the frequency response of the amplifier.
The IDEAL FREQUENCY RESPONSE of an audio amplifier is equal gain from 15 Hz to 20 kHz
with very low gain outside of those limits.
A PHASE SPLITTER provides two output signals that are equal in amplitude but different in
phase from a single input signal. Phase splitters are often used to provide input signals to a push-pull
A PUSH-PULL AMPLIFIER uses two transistors whose output signals are added together to
provide a larger gain (usually a power gain) than a single transistor could provide. Push-pull amplifiers can be
operated class A, class AB or class B.
ANSWERS TO QUESTIONS Q1. THROUGH Q33.
A-1. Amplification is the control of an output signal by an input signal so that the output signal has
some (or all) of the characteristics of the input signal. The output signal is generally larger than the input
signal in terms of voltage, current, or power.
A-2. No, the input signal is unchanged, the output signal
is controlled by the input signal but does not effect the actual input signal.
A-3. To amplify the input
signal to a usable level.
A-4. By function and frequency response.
A-5. An audio power amplifier.
A-6. An RF voltage amplifier.
A-7. The amount of time (in relation to the input signal) in which current
flows in the output circuit.
A-8. A, AB, B, C.
A-9. Class B operation.
amplifier operates (and therefore uses power) for less time in class C than in class
A. A-11. Class A
A-12. To transfer energy (a signal) from one stage to another.
A-13. Direct, RC,
impedance, and transformer coupling.
A-14. RC coupling.
A-15. Transformer coupling.
A-17. Impedance coupling.
A-18. Equal impedance.
A-19. Lower than.
Common emitter-medium input, medium output; common base-low input, high output; common collector-high input, low
A-21. Common collector.
A-22. Transformer coupling.
A-23. The process of coupling a
portion of the output of a circuit back to the circuit input.
A-24. Positive and negative or regenerative
A-25. Positive (regenerative) feedback.
A-26. Negative (degenerative) feedback.
A-28. Negative (degenerative) feedback.
A-29. A device that provides two
output signals that differ in phase from a single input signal.
A-30. A phase splitter is used to provide
the input signals to a push-pull amplifier.
A-31. A push-pull amplifier is used when high power output and
good fidelity are needed.
A-32. A push-pull amplifier provides more gain than a single transistor
A-33. Class A, Class AB or Class B operation.
Introduction to Matter, Energy, and Direct Current, Introduction
to Alternating Current and Transformers, Introduction to Circuit Protection,
Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques,
and Schematic Reading, Introduction to Generators and Motors,
Introduction to Electronic Emission, Tubes, and Power Supplies,
Introduction to Solid-State Devices and Power Supplies,
Introduction to Amplifiers, Introduction to
Wave-Generation and Wave-Shaping Circuits, Introduction to Wave Propagation, Transmission
Lines, and Antennas, Microwave Principles,
Modulation Principles, Introduction to Number Systems and Logic Circuits, Introduction
to Microelectronics, Principles of Synchros, Servos, and Gyros,
Introduction to Test Equipment, Radio-Frequency
Communications Principles, Radar Principles, The Technician's Handbook,
Master Glossary, Test Methods and Practices, Introduction to Digital Computers,
Magnetic Recording, Introduction to Fiber Optics