High-CMRR, Operational Transconductance Amplifier for Low-Voltage Applications Based on a Degenerative Current TRAM

This paper introduces an innovative circuit scheme named 'Current TRAM,' leveraging a degenerative current steering mechanism through the implementation of three current mirrors within a closed-loop configuration. This configuration undergoes transformation into a fully differential voltage-to-current converter, demonstrating its application in the design of an integrated operational transconductance amplifier (OTA). The OTA offers a high gain-bandwidth and common-mode rejection ratio at low power. Diode-connected topologies in the current mirrors adaptively bias other transistors, eliminating the need for a common-mode feedback circuit. A common-source amplifier is employed at the output stage of the OTA to enhance the slew rate performance. Implemented in a standard 0.18 µm CMOS process with a supply voltage of 0.4 V, the proposed OTA achieves a gain-bandwidth (GBW) product of 23 kHz, a DC gain of 75 dB, and a slew rate of 15.5 V/ms. Remarkably, it accomplishes this while consuming a mere 37 nW of power and driving a capacitive load of 2 × 15 pF.