Small-signal, high-frequency theory of field-effect transistors

Abstract

In this theory a field-effect transistor of planar geometry is considered as an active, distributed, nonuniform transmission line. The wave equation of this line is determined and solved by an approximation method. From this solution the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</tex> parameters are determined. By comparing the results for y <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> with van der Ziel's expression for the high-frequency gate noise of field-effect transistors, it is shown that the noise temperature of y <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> is of the order of the device temperature. The conductance part g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> of y <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> varies as ω <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over a wide frequency range. The high-frequency cutoff of the field-effect transistor is determined.