Two Transistor Synapse with Spike Timing Dependent Plasticity

We present a novel two transistor synapse (“2TS”) that exhibits spike timing dependent plasticity (“STDP”). Temporal coincidence of synthetic preand postsynaptic action potentials across the 2TS induces localized floating gate injection and tunneling that result in proportional Hebbian synaptic weight updates. In the absence of correlated preand postsynaptic activity, no significant weight updates occur. A compact implementation of the 2TS has been designed, simulated, and fabricated in a commercial 0.5 μm process. Suitable synthetic neural waveforms for symmetric STDP have been derived and circuit and network operation have been modeled and tested. Simulations agree with theory and preliminary experimental results.