Generalization of the integral function method to evaluate distortion in SOI FD MOSFET

Abstract

The harmonic distortion introduced by MOS transistors is a property of major importance regarding their analog applications. In recent papers we presented a new integral function method (IFM) to calculate total harmonic distortion (THD) and the third harmonic component (HD3) of MOSFET based on the direct analysis of the non-linearity of the DC I/sub DS/-V/sub DS/ characteristic of the device for a fixed gate voltage. To evaluate this non-linearity, we defined an integral function, which will be called D hereafter, to calculate an integral equation of the I/sub DS/-V/sub DS/ characteristic, and in order to eliminate the even harmonics, a second function, which we call D3 was also defined. In this paper we generalize the IFM to analyze the case where several MOSFET pairs (balanced 2-MOSFET and double balanced 4-MOSFET structures) are used in order to eliminate the even harmonics. Real transistors always show some mismatch in their parameters that become apparent even in these balanced circuits. For the generalized IFM a new function Da is defined and used to analyze the effect of variation of transistor parameters. The efficiency of the new method is demonstrated analyzing the harmonic distortion in a balanced circuit, where typical variations of the threshold voltage if the transistors is taken into account.