Correlation learning rule in floating-gate pFET synapses

We study the weight dynamics of the floating-gate pFET synapse and the effects of the pFET's gate and drain voltages on these dynamics. We show that we can derive a weight update rule such that the equilibrium weight value is proportional to the correlation between the gate and drain voltages. In particular, we want a rule of the form /spl tau/' /spl Delta/W/spl dot/=-/spl Delta/W+/spl eta/E[xy], where x is a voltage signal on the gate terminal and y is a voltage signal on the drain terminal. We obtain this rule by making a linear approximation to the weight dynamics around a given equilibrium point. We develop this approximation by considering the basic functional form of the system dynamics and then examining the effects of the gate and drain voltages on the specifics of this form.