A Precision CMOS Amplifier Using Floating-Gate Transistors for Offset Cancellation

A long-term offset cancellation scheme that enables continuous-time amplifier operation is described. Offset cancellation is achieved by programming floating-gate transistors that form an integral part of the amplifier's architecture. The offset voltage of a single-stage folded cascode amplifier has been programmed to a minimum of plusmn25 muV in a 0.5 mum digital CMOS process. The long-term offset voltage drift has been calculated to be less than 0.5 muV over a period of 10 years at 55degC from a thermionic emission model for floating-gate charge loss. The offset voltage varies by a maximum of 130 muV over a temperature range of 170degC, thereby making this a viable approach to offset cancellation