OTA based 200 G{\Omega} resistance on 700 {\mu}m2 in 180 nm CMOS for neuromorphic applications

TL;DR

This paper introduces a highly area-efficient OTA with ultra-low transconductance for neuromorphic circuits, enabling dense integration of time constant circuits on a chip.

Contribution

It presents a silicon-verified OTA achieving 5 pS transconductance in only 700 μm², significantly reducing area compared to existing designs.

Findings

Achieved 5 pS transconductance in 700 μm² area

Enables high-density integration of neuromorphic circuits

Reduces circuit area by a factor of 10-100

Abstract

Generating an exponential decay function with a time constant on the order of hundreds of milliseconds is a mainstay for neuromorphic circuits. Usually, either subthreshold circuits or RC-decays based on transconductance amplifiers are used. In the latter case, transconductances in the 10 pS range are needed. However, state-of-the-art low-transconductance amplifiers still require too much circuit area to be applicable in neuromorphic circuits where >100 of these time constant circuits may be required on a single chip. We present a silicon verified operational transconductance amplifier that achieves a gm of 5 pS in only 700 {\mu}m2, a factor of 10-100 less area than current examples. This allows a high-density integration of time constant circuits in target appliations such as synaptic learning or as driving circuit for neuromorphic memristor arrays.