Memristor Based Circuit Design for Liquid State Machine Verified with Temporal Classification

Spiking neural networks represent a transition from deep networks and tensor engines to more dynamic systems better suited for carrying out decisions based on temporal patterns within data. Furthermore, memristor based hardware for synaptic computation provides the potential for dramatic gains in terms of portability, power reduction, and throughput efficiency. In this paper we combine these ideas and present a memristor crossbar based implementation of a liquid state machine based on spiking neurons. The design is verified by demonstrating successful classification of MIDI (Musical Instrument Digital Interface) signals. Given the temporal nature of musical works, this dataset is well suited to show the effectiveness of the proposed hardware. The proposed circuit implementing this LSM is designed using SPICE to ensure accuracy at the device level, which aids in detailed analysis and circuit optimizations. Liquid layer activity is converted to state vectors using custom hardware that does not bottleneck throughput. Along with the proposed architecture, a neuron modeling procedure is described to match the software and hardware spiking neuron outputs, proving the feasibility of a full-scale implementation of the LSM system. Furthermore, various non-idealities are analyzed in the network, including misfiring neurons and noise associated with updating memristor conductance. We find that the proposed architecture is resilient to noise and fault-tolerant. In simulation, the performance of the memristor-based LSM is demonstrated on a musical genre classification experiment, where a recognition accuracy of 90% is achieved, compared to 91% accuracy in software. To the best of our knowledge this work represents the first end to end circuit implementation of an analog spiking neural network based reservoir computing system where memristors are responsible for all computation, with custom CMOS hardware for sampling the liquid layer. Finally, we tie the work together with an energy and timing analysis of the proposed system.