Pulse-Firing Neural Chips for Hundreds of Neurons

Alister Hamilton II Song Han(l) H. Martin Reekie Dept. Electrical Eng. U niv. of Edinburgh We announce new CMOS synapse circuits using only three and four MOSFETsisynapse. Neural states are asynchronous pulse streams, upon which arithmetic is performed directly. Chips implementing over 100 fully programmable synapses are described and projections to networks of hundreds of neurons are made. 1 OVERVIEW OF PULSE FIRING NEURAL VLSI The inspiration for the use of pulse firing in silicon neural networks is clearly the electrical/chemical pulse mechanism in "real" biological neurons. Asynchronous, digital voltage pulses are used to signal states t Si ) through synapse weights { Tij } to emulate neural dynamics. Neurons fire voltage pulses of a frequency determined by their level of activity but of a constant magnitude (usually 5 Volts) [Murray,1989a]. As indicated in Fig. 1, synapses perform arithmetic directly on these asynchronous pulses, to increment or decrement the receiving neuron's activity. The activity of a receiving neuron i, Xi is altered at a frequency controlled by the sending neuron j, with state Sj by an amount determined by the synapse weight (here, T ij ). 1 On secondment from the Korean Telecommunications Authority 786 Brownlow, Tarassenko, Murray, Hamilton, Han and Reekie