A new quantitative model for weak inversion charge injection in MOSFET analog switches

摘要

This paper proposes a new model concerning the channel charges in weak inversion injected from a turn-off MOSFET into a holding capacitor. This portion of charge injection has recently been newly observed, showing a significant contribution to the switch-induced error voltage on the switched capacitor. Our model is derived at the critical point where the device is operated in the transition region between strong inversion and weak inversion. This point has been expressed explicitly as a function of the DC input voltage, the threshold voltage, and the fall time of the gate voltage. The ability of the model in accurately determining quantitatively the impact of the weak inversion charge injection on the error voltage has been extensively judged experimentally and by two-dimensional mixed-mode simulation for a wide variety of design parameters such as the channel width and length, the holding capacitance, the fall time of the gate voltage, and the DC input voltage The assumptions utilized in the model development have also been validated.