The digi-neocognitron: a digital neocognitron neural network model for VLSI

One of the most complicated ANN models, the neocognitron (NC), is adapted to an efficient all-digital implementation for VLSI. The new model, the digi-neocognitron (DNC), has the same pattern recognition performance as the NC. The DNC model is derived from the NC model by a combination of preprocessing approximation and the definition of new model functions, e.g., multiplication and division are eliminated by conversion of factors to powers of 2, requiring only shift operations. The NC model is reviewed, the DNC model is presented, a methodology to convert NC models to DNC models is discussed, and the performances of the two models are compared on a character recognition example. The DNC model has substantial advantages over the NC model for VLSI implementation. The area-delay product is improved by two to three orders of magnitude, and I/O and memory requirements are reduced by representation of weights with 3 bits or less and neuron outputs with 4 bits or 7 bits