A Fully Analog CMOS Implementation of a Two-variable Spiking Neuron in the Subthreshold Region and its Network Operation

Edge computing requires the processing of real-time and personalized information with low power consumption. Neuromorphic devices are promising candidates for applications related to edge computing. Rate neurons, which are typically used in neuromorphic hardware, persistently consume power regardless of their outputs. To further reduce the power consumption of neuromorphic devices, spiking neurons are more suitable because they are event-driven, and information is transferred only when the neuron fires. Herein, we propose a two-variable spiking neuron circuit that operates in a fully analog manner by utilizing the physical properties of transistors as analog devices. By operating in the subthreshold region of the MOS transistor, the energy required to produce a spike is approximately tens of fJ/spike. Furthermore, the analog neuron can exhibit complex spike dynamics, such as chattering, as confirmed using post-layout simulations. The simulations indicated that a neural network comprising the proposed neuron circuits operates successfully and exhibits complex nonlinear behavior. These results provide a basis for dedicated hardware spiking neuron circuits, which could be used as ultra-low-power neuromorphic hardware in various applications, such as realizing liquid-state machines for processing time-series signals.