Design of bioinspired tripartite synapse analog integrated circuit in 65-nm CMOS Technology

This paper presents the design of a bioinspired synaptic integrated circuit, which takes into account the interactions of astrocyte in a tripartite synapse. These interactions result in activation of Ca2+ ion waves through fast and slow activation pathways which affect the synapse and postsynaptic neuron. The circuit has been implemented in TSMC 65-nm CMOS technology with 1.2 V supply voltage. Dynamic and nonlinear characteristics of the interactions have been implemented based on nonlinear characteristics of field effect transistors and few external capacitors. This design used few components from previous works, including ML neuron and Ca2+ circuit. All components are scaled to 65 nm and implemented in weak inversion operating region. Simulation results confirm that the proposed circuit demonstrates the functionality of physical model with acceptable relative mean square error and low power consumption of about 37 nW. The effects of supply voltage sensitivity, variability of threshold voltage and noise on the Ca2+ circuit have been studied. Circuit layout for main components including presynaptic neuron, postsynaptic neuron and the synapse has been prepared, with the area of 80 µm2. Post-layout simulation of the neuron with parasitics demonstrates the feasibility of the proposed model for fabrication. This circuit structure can be used for the study and demonstration of various functionalities associated with astrocyte including self-repair.