OTA based 200 G{\Omega} resistance on 700 {\mu}m2 in 180 nm CMOS for   neuromorphic applications
  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. 
Christian Mayr, Michael Schultz, Marko Noack, Stephan Henker, Johannes   Partzsch, Rene Sch\"uffny
q-bio.NC cs.ET