A CMOS implementation of the discrete time nonlinear energy operator based on a transconductor-squarer circuit

This paper presents a strategy for implementing the discrete time version of the Nonlinear Energy Operator (NEO). The proposed implementation approach is based on the utilization of a circuit that produces an output current proportional to the square of its input voltage, which we call transconductor-squarer circuit. In order to avoid adverse effects of mismatch between circuits that should be identical, we propose the reuse of a single transconductor-squarer circuit for the realization of the NEO formula. The NEO system was evaluated simulating its ability to emphasize the presence of neural spikes in a synthetic noisy extracellular neural signal. The circuit is designed aiming at a standard CMOS fabrication process with 90nm minimum channel length and its circuit simulation shows energy consumption of 60pJ per spike. Simulations also show that the circuit is capable of operating at about 30 Ksample/s, compatible with current state-of-the-art neural recording systems.