This paper presents an ultra-low-power class-AB bulk-driven operational transconductance amplifier operating in the subthreshold region. Employing the partial positive feedback in current mirrors, the effective transconductance and output voltage swing are enhanced considerably without additional power consumption and layout area. Both traditional and proposed OTAs are designed and simulated for a 180 nm CMOS process. They dissipate an ultra low power of 192 nW. The proposed OTA features not only a DC gain enhancement of 14 dB but also a slew rate improvement of 200%. In addition, the improved gain leads to a 5.3 times wider unity-gain bandwidth than that of the traditional OTA.

Low voltage (LV) analog circuit design techniques are addressed in this tutorial. In particular, (i) technology considerations; (ii) transistor model capable to provide performance and power tradeoffs; (iii) low voltage implementation techniques capable to reduce the power supply requirements, such as bulk-driven, floating-gate, and self-cascode MOSFETs; (iv) basic LV building blocks; (v) multi-stage frequency compensation topologies; and (vi) fully-differential and fully-balanced systems.