KIP publications

year 2012
author(s) Thomas Pfeil, Tobias C. Potjans, Sven Schrader, Wiebke Potjans, Johannes Schemmel, Markus Diesmann, Karlheinz Meier
title Is a 4-bit synaptic weight resolution enough? - Constraints on enabling spike-timing dependent plasticity in neuromorphic hardware
KIP-Nummer HD-KIP 12-09
KIP-Gruppe(n) F9
document type Paper
Keywords neuromorphic hardware, wafer-scale integration, large-scale spiking neural networks, spike-timing dependent plasticity, synaptic weight resolution, circuit variations, PyNN, NEST
source Frontiers in Neuroscience 6:90 (2012)
doi 10.3389/fnins.2012.00090
Abstract (en)

Large-scale neuromorphic hardware systems typically bear the trade-off between detail level and required chip resources. Especially when implementing spike-timing-dependent plasticity, reduction in resources leads to limitations as compared to floating point precision. By design, a natural modification that saves resources would be reducing synaptic weight resolution. The FACETS wafer-scale hardware system, a pioneering neuromorphic device that implements a large amount of synapses, will offer a 4-bit resolution of synaptic weights. In this study, we give an estimate for the impact of synaptic weight discretization on different levels, ranging from random walks of individual weights to computer simulations of spiking neural networks. Within the scope of network benchmarks that have been used in this study, we conclude that 4-bit is indeed a sufficient weight resolution. Our results indicate that increasing the resolution may not even be useful in light of further restrictions of customized mixed-signal synapses. In addition, variations due to production imperfections are investigated using the already existing FACETS chip-based hardware system, and are shown to be uncritical in the context of the presented study. Our results represent a general framework for setting up and configuring hardware-constrained synapses. We suggest how weight discretization could be in addition considered for other backends dedicated to large scale simulations. Thus, our proposition of a good hardware verification practice may rise synergy effects between hardware developers and neuroscientists.

  author   = {Pfeil, Thomas and Potjans, Tobias C. and Schrader, Sven and Potjans, Wiebke and Schemmel, Johannes and Diesmann, Markus and Meier, Karlheinz},
  title    = {Is a 4-bit synaptic weight resolution enough? -- Constraints on enabling spike-timing dependent plasticity in neuromorphic hardware},
  journal  = {Frontiers in Neuroscience},
  volume   = {6:90},
  year     = {2012},
  pages    = {}
URL Online Article
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