Transconductance Amplifier Structures With Very Small Transconductances: A Comparative Design Approach

Abstract—A family of CMOS operational transconductance amplifiers (OTAs) has been designed for very small ’s (of the order of nanoamperes per volt) with transistors operating in mod-erate inversion. Several OTA design schemes such as conventional, using current division, floating-gate, and bulk-driven techniques are discussed. A detailed comparison has also been made among these schemes in terms of performance characteristics such as power consumption, active silicon area, and signal-to-noise ratio. The transconductance amplifiers have been fabricated in a 1.2- m n-well CMOS process and operate at a power supply of 2.7 V. Chip test results are in good agreement with theoretical results. Index Terms—Bulk-driven transistors, current division, floating gates, OTA, small