MOS Pass transistor turn-off transient analysis

Errors induced by turn-off transients are one fundamental limit in precision switched capacitor circuits. This paper presents detailed pass transistor turn-off transient analysis. Conventional single-lump models which assume quasi-static operation can introduce substantial errors for high-speed analog applications. New distributed and two-lump models have been constructed to analyze pass transistor turn-off transients in the diffusion mode of operation. A pass transistor test chip including a new selectively doped pass transistor approach has been designed, fabricated, and tested to verify the transient analysis. Measured performance of the nonuniformly doped pass transistors shows advantages in reducing transient charge errors.