Fig. 1
The multi-memristive synapse concept. a The net synaptic weight of a multi-memristive synapse is represented by the combined conductance \(\left({{\sum} \;G_n} \right)\) of multiple memristive devices. To realize synaptic efficacy, a read voltage signal, V, is applied to all devices. The resulting current flowing through each device is summed up to generate the synaptic output. b To capture synaptic plasticity, only one of the devices is selected at any instance of synaptic update. The synaptic update is induced by altering the conductance of the selected device as dictated by a learning algorithm. This is achieved by applying a suitable programming pulse to the selected device. c A counter-based arbitration scheme is used to select the devices that get programmed to achieve synaptic plasticity. A global selection counter whose maximum value is equal to the number of devices representing a synapse is used. At any instance of synaptic update, the device pointed to by the selection counter is programmed. Subsequently, the selection counter is incremented by a fixed amount. In addition to the selection counter, independent potentiation and depression counters can serve to control the frequency of the potentiation or depression events
