Amplifier for energy harvesting: Low voltage, ultra low current, rail-to-rail input-output, high speed

Abstract

An ultra low current and low voltage rail-to-rail input-output class AB amplifier is presented that is based on standard 0.18 micron digital CMOS. Operating under the subthreshold region, the amplifier is capable of running at high speeds, with a supply voltage (VDD) as low as ∼ 0.6V. The main contributions of this work are: First, a primarily current-mode rail-to-rail output stage is presented that employs Minimum Current Selectors (MCS) which monitor the sink-source currents of the output buffer transistors. Concurrently, Current Feedback Amplifiers (CFA) composed of Inverting Current Mirrors (ICM) regulate the minimum stand-by currents for either the non-sinking or non-sourcing output transistors, while allowing maximum currents to run through the sinking or sourcing transistors. As such, the output stage, in its basic configuration, can deliver a wide dynamic range at high speeds with VDD as low as ∼ VGS+2VDS. Second, a Floating Current Source (FCS) is utilized in the main amplifier that can also operate with VDD as low as ∼ VGS+2VDS. Montecarlo (MC) and worst case (WC) simulation show the following specifications are achievable: VDD minimum ∼ 0.6v; IDD ∼ 330nA; Input range rail-to-rail; offset voltage ∼ 6mV; Output range ∼ 25mV from the rails; open loop gain (Av) ∼ 78dB with unity gain frequency (fu) ∼ 1MHz and phase margin (PM) ∼ 40 degrees; power supply rejection ratio (PSRR) ∼ −83dB; common mode rejection ration (CMRR) ∼ −98dB; Slew rate (SR) ∼ 2V/us; Settling time (ts) ∼ 3uS to ∼ 2mV; rail-to-rail output voltage swing with RL ∼ 5K ohms, and size ∼ 120um/side.