Analog circuit design using graded-channel silicon-on-insulator nMOSFETs

Abstract

An extended study of analog circuit design using graded-channel (GC) silicon-on-insulator (SOI) MOSFETs in comparison to conventional fully depleted (FD) transistors is performed. Performances of single-transistor operational transconductance amplifier (OTA) implemented using GC and conventional FD SOI nMOSFETs are compared. Improvements of the DC gain and unity-gain frequency resulting from the extremely reduced output conductance and the increased transconductance in the GC devices are discussed, based on experimental results, establishing design guidelines in order to aim at GC micropower or wide bandwidth OTAs. Two-dimensional simulations are used to analyze the intrinsic-gate capacitances in linear and saturation regions, establishing that GC transistors present almost the same capacitive amount than the conventional FD transistors in a typical analog range of operation. Current mirrors fabricated using GC and conventional MOSFETs are compared. It is demonstrated that GC MOSFETs can provide high precision current mirrors with enhanced output swing.