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Chapter Seven<br />

Linear Amplifier <strong>Design</strong><br />

Tools<br />

This chapter establishes a basis for many modern amplifier design relationships,<br />

especially those related to generalized Smith charts and their bilinear<br />

functions. Impedance and power relationships will be investigated in detail.<br />

The linear two-port network will be analyzed in terms <strong>of</strong> Z, Y, and S<br />

parameters, as indicated in Figure 7.1. The network mayor may not be<br />

reciprocal, i.e., Yl2 may not be equal to Y21' The simplifying unilateral<br />

assumption that YI2=O will be considered only at the end <strong>of</strong> this chapter. The<br />

stability <strong>of</strong> such networks will be studied. Thus some <strong>of</strong> these results will be<br />

applicable to oscillator design. Further applications <strong>of</strong> this chapter will appear<br />

in Section 9.5, which deals with load effects on passive networks, especially<br />

dissipative filters.<br />

Impedance mapping will be the main analytic and computational tool. This<br />

technique establishes the position <strong>of</strong> a small Smith chart image <strong>of</strong> a branch- or<br />

port-terminating impedance plane embedded in a network impedance, admittance,<br />

or scattering response plane. For example, all possible values <strong>of</strong><br />

transducer gain S21 as a function <strong>of</strong> a network branch impedance are easily<br />

visualized and calculated. The generalized Smith chart is normalized to a<br />

complex number; it will be crucial to the impedance mapping concept.<br />

This chapter begins with the definition <strong>of</strong> bilinear functions and several<br />

methods for determining their three coefficients from a set <strong>of</strong> characterizing<br />

data. The generalized Smith chart bilinear form that maps the right-half plane<br />

onto a unit circle will be studied next. Some useful shortcuts and special<br />

features in its application will be considered. The bilinear theorem that relates<br />

all Z, Y, and S network functions will be derived by obtaining the three-port<br />

to two-port reduction formulas. The impedance-mapping relationship will<br />

then be derived, including the conversion <strong>of</strong> bilinear coefficients to the<br />

mapping displacement and orientation coefficients.

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