A programmable facilitating synapse device

We present a programmable dynamic charge transfer synapse (CTS) in a single semiconductor device. The CTS comprises a metal oxide semiconductor (MOS) transistor operating in subthreshold and two MOS capacitors in proximity to the transistor. One of the capacitors is permanently biased in strong inversion where the associated density of charge in the well implements the weighting. When a presynaptic spike is applied to the gate of the second MOS capacitor the charge density in the well falls producing a current spike at the output. The amplitude of the spike is correlated with the equilibrium charge density in the well, which is controlled by the associated gate voltage. Aggregation of spikes from an array of CTSs is achieved by using a current mirror configuration whose output postsynaptic potential can be used to stimulate a point neuron circuit. The function of the MOS transistor is to restore the charge in the well where the duration of this process is dictated by the associated gate voltage. Therefore, the synapse is capability of operating in the facilitating state over a large frequency range. The CTS is compact and since it operates in transient mode, its power consumption is negligible. Simulation results are presented which clearly demonstrate its operation.