Transconductance amplifier structures with very small transconductances:: A comparative design approach

A family of CMOS operational transconductance amplifiers (OTAs) has been designed for very small G(m)'s (of the order of nanoamperes per volt) with transistors operating in moderate 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-mum n-well CMOS process and operate at a power supply of 2.7 V. Chip test results are in good agreement with theoretical results.