Two-Stage OTA With All Subthreshold MOSFETs and Optimum GBW to DC-Current Ratio

An approach for the design of two-stage class-AB OTAs with sub-
$1{\boldsymbol {\mu }}\text{A}$
current consumption is proposed and demonstrated. The approach employs MOS transistors operating in subthreshold and allows maximum gain-bandwidth product (GBW) to be achieved for a given DC current budget, by setting optimum distribution of DC currents in the two amplifier stages. Following this strategy, a class AB OTA was designed in a standard 0.5-
${\boldsymbol {\mu }}\text{m}$
CMOS technology supplied from 1.6-V and experimentally tested. Measured GBW was 307 kHz with 980-nA DC current consumption while driving an output capacitance of 40 pF with an average slew rate of 96 V/ms.