Large signal analysis of low-voltage MOS analogue functional elements using Fourier-series approximations

This paper discusses the large signal performance of low-voltage analogue functional elements built around MOS field-effect transistors (MOSFETs). Fourier-series approximations are obtained for the transfer characteristics of the basic building blocks; such as the balanced source-coupled pair, the unbalanced source-coupled pair with different transistor sizes, the source-coupled pair with bias offset and the squaring circuits. Using the Fourier-series approximations of these basic building blocks, closed-form expressions are obtained for the amplitudes of the harmonics and intermodulation products at the output of analogue functional elements; such as the basic differential pairs, half-wave rectifiers, full-wave rectifiers and multipliers excited by a multisinusoidal input signals. Using these expressions comparison between the large signal performance of analogue functional elements can be performed and the parameters required for a predetermined performance can be determined.