Circuits that operate with power supplies of less than 1 Volt are presented. More particularly, circuits that operate with supply voltages near or lower than the threshold voltage of the transistors in those circuits are presented. Various circuits and embodiments such as operational transconductance amplifiers, biasing circuits, integrators, continuous-time sigma delta modulators, track-and-bold circuits, and others are presented. The techniques and circuits can be used in a wide range of applications and various transistors from metal-oxide-semiconductor to bipolar junction transistors may implement the techniques presented herein.