Analog MOSFET devices

摘要

The specification describes MOS transistors for analog functions which have increased output impedance. The increased output impedance is the result of reduced drain depletion width. This is accomplished without adverse effects on other device parameters. The MOS transistor structures have an implant added to the lightly doped drain (LDD) with a conductivity type opposite to that of the LDD and a doping level higher than the channel doping. The added implant confines the spread of the depletion layer and reduces its width. A relatively small confinement results in a significant increase in output impedance of the device, and a corresponding increase in transistor gain.