Radio Receiver Design
This reference focuses on understanding and designing radio receivers and systems, presenting the characteristics of individual receiver components and their interaction in cascade.
TABLE OF CONTENTS Radio Receiver Design
Chapter 6: Linearity
Nothing is more noble, nothing more venerable than fidelity.
-Cicero
6.1 Introduction
In Chapter 5, we found that thermal noise sets the limit on the smallest signal a receiver can process. Linearity, on the other hand, sets the limit on the largest signal that can be processed. A system will alter or distort any signal that is too large.
Definitions
Since there is some contention about describing the various harmonics of a signal, the following nomenclature is used throughout this book:
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Fundamental: The frequency is f 0.
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First Harmonic: The frequency is also f 0.
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Second Harmonic: The frequency is 2 f 0.
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Third Harmonic: The frequency is 3 f 0.
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n th Harmonic: The frequency is n f 0.
6.2 Linear and Nonlinear Systems
Although every system is nonlinear to one extent or another, this discussion focuses on linear systems for the following reasons:
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Almost every nonlinear system can be modeled as a linear system over a narrow operating range. For example, RF amplifiers are nonlinear devices but, if the input signal power is kept small enough, the amplifier can be modeled as a linear device.
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Even simple filters, which consists of common inductors and capacitors, are nonlinear devices. At very high power levels, the dielectrics of the capacitors behave in a nonlinear fashion and the inductors can saturate. As a result, the value of the component changes with the voltage across it or the current through it. This is a nonlinear process.
Copyright Noble Publishing Corporation 2000 under license agreement with Books24x7
