Navy Electricity and Electronics Training Series Module (NEETS) - Introduction to Amplifiers, Video And RF Amplifiers, And Special Amplifiers

CHAPTER 1
AMPLIFIERS
LEARNING OBJECTIVES
Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a
preview of the information you are expected to learn in the chapter. The comprehensive check questions
are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met
the objectives and have learned the information. The learning objectives are listed below.
Upon completion of this chapter, you will be able to:

1. Define amplification and list several common uses; state two ways in which amplifiers are
classified.
2. List the four classes of operation of, four methods of coupling for, and the impedance
characteristics of the three configurations of a transistor amplifier.
3. Define feedback and list the two types of feedback.
4. Describe and state one use for a phase splitter.
5. State a common use for and one advantage of a push-pull amplifier.

INTRODUCTION
This chapter is a milestone in your study of electronics. Previous modules have been concerned more
with individual components of circuits than with the complete circuits as the subject. This chapter and the
other chapters of this module are concerned with the circuitry of amplifiers. While components are
discussed, the discussion of the components is not an explanation of the working of the component itself
(these have been covered in previous modules) but an explanation of the component as it relates to the
circuit.

The circuits this chapter is concerned with are AMPLIFIERS. Amplifiers are devices that provide
AMPLIFICATION. That doesn't explain much, but it does describe an amplifier if you know what
amplification is and what it is used for.

WHAT IS AMPLIFICATION?
Just as an amplifier is a device that provides amplification, amplification is the process of providing
an increase in AMPLITUDE. Amplitude is a term that describes the size of a signal. In terms of a.c.,
amplitude usually refers to the amount of voltage or current. A 5-volt peak-to-peak a.c.signal would be
larger in amplitude than a 4-volt peak-to-peak a.c. signal. "SIGNAL" is a general term used to refer to any
a.c. or d.c. of interest in a circuit; e.g., input signal and output signal. A signal can be large or small, ac. or
d.c., a sine wave or nonsinusoidal, or even nonelectrical such as sound or light. "Signal" is a very general
term and, therefore, not very descriptive by itself, but it does sound more technical than the word "thing".
It is not very impressive to refer to the "input thing" or the "thing that comes out of this circuit."

Perhaps the concept of the relationship of amplifier-amplification-amplitude will be clearer if you
consider a parallel situation (an analogy). A magnifying glass is a magnifier. As such, it provides
magnification which is an increase in the magnitude (size) of an object. This relationship of magnifiermagnification-
magnitude is the same as the relationship of amplifier-amplification-amplitude. The
analogy is true in one other aspect as well. The magnifier does not change the object that is being
magnified; it is only the image that is larger, not the object itself. With the amplifier, the output signal
differs in amplitude from the input signal, but the input signal still exists unchanged. So, the object (input
signal) and the magnifier (amplifier) control the image (output signal).

An amplifier can be defined as a device that enables an input signal to control an output signal. The
output signal will have some (or all) of the characteristics of the input signal but will generally be larger
than the input signal in terms of voltage, current, or power.

USES OF AMPLIFICATION
Most electronic devices use amplifiers to provide various amounts of signal amplification. Since
most signals are originally too small to control or drive the desired device, some amplification is needed.

For example, the audio signal taken from a record is too smal