A CMOS DRIVER

摘要

A CMOS input/output driver (200) having constant output impedance (Zo), the driver comprising a drive pMOSFET (208) and a drive nMOSFET (210) for driving an output node (202) HIGH and LOW, a pMOSFET (224) having a drain coupled to the output node and switchable so that its gate is coupled to the output node when the drive pMOSFET is driving the output node HIGH, and an nMOSFET having a drain coupled to the output node and switchable so that its gate is coupled to the output node when the drive nMOSFET is driving the output node LOW. The betas of the drive pMOSFET, the drive nMOSFET, the pMOSFET, and the nMOSFET are matched so that the output impedance of the drive is approximately independent of the output node voltage.