Chapter 5
Amplifiers
LEARNING OBJECTIVES
Learning objectives serve as a preview of the information you are expected to learn in this chapter.
The comprehensive check-on-learning questions, found at the end of the chapter, are based on the
objectives. Upon completion of this chapter, you will be able to perform the following learning
objectives:
Define amplification, list several common uses, and state two ways in which
amplifiers are classified.
List the four classes of operation for an amplifier.
List the four ways of coupling signals into and out of amplifier circuits.
Name the impedance characteristics of the three configurations of a transistor
amplifier.
Define feedback and list the two types feedback.
Describe and state one use for a phase splitter.
State a common use for and one advantage of a push-pull amplifier.
INTRODUCTION TO AMPLIFIERS
5-1.
This chapter, along with chapters 6 and 7, 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, but an explanation of the component as
it relates to the circuit.
5-2.
The circuits in this chapter are concerned with amplifiers. Amplifiers are devices
that provide amplification. That does not explain much, but it does describe an amplifier if
you know what amplification is and for what it is used.
AMPLIFICATION PROCESS
5-3.
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 AC, amplitude usually refers to the amount of voltage or current. A
5-volt peak-to-peak AC signal would be larger in amplitude than a 4-volt peak-to-peak AC
signal. "Signal " is a general term used to refer to any AC or DC of interest in a circuit (for
example, input signal and output signal). A signal can be large or small, AC or DC, a sine
wave or non-sinusoidal, or even non-electrical (such as sound or light). "Signal" is also 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."
5-4.
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 magnifier-magnification-magnitude is the same as the
relationship of amplifier-amplification-amplitude. The analogy is true in one other aspect
23 June 2005
TC 9-62
5-1
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