Analysis and simulation of MOSFET-based gate-voltage-independent capacitor

Abstract

In this paper, we analyze the gate capacitance of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and propose a method of realizing the capacitance less dependent on the gate voltage. We analyze the mechanism of capacitance formation in the cases of shorting the source and drain to the ground and floating them. The analysis also reveals the influence of channel length on gate capacitance. By floating the terminals of source and drain and tuning for an optimum channel length, the voltage dependence of the gate capacitance can be largely reduced. Simulation results verify our analysis, suggesting a possibility of applying a MOSFET capacitor for sample-and-hold circuits which has been applied to the standard-cell-based successive approximation analog-to-digital converter).