Analysis of Second-Order Effect Components of Drain Conductance and Its Implication on Output Resistance of Wilson Current Mirror

Drain conductance gds is an important small signal parameter for analysis of small signal model of analog circuits as it influences the output resistance and voltage gain. The gds or reciprocal rds and Early voltage is a useful design parameter for designer as they appear frequently in intrinsic voltage gain and transresistance expression in general circuits. In this paper we analyze the different component of gds in which it can be decomposed to fifferent component as it is influenced by many second order effects like channel length modulation, vertical field mobility reduction, drain induced barrier lowering and velocity saturation. The analysis of impact of overdrive voltage and Inversion Coefficient (IC) for fixed drain voltage and shape factor on gds components is investigated. The validation of total drain conductance which is sum of its component is verified using BSIM3v3 model PTM generated data on 180nm technology node. The effect of component is shown in intrinsic voltage gain of single stage common source transistor and output resistance of Wilson current mirror as function of inversion level. The sensitivity of output resistance on process related parameters which give deeper insight of circuit performance is computed qualitatively. The interpolation equation as used by EKV model is taken for analysis and analytically computed for the different gds components.