This paper describes a new pulse-mode digital neuron which is based on voting neuron. The signal level of the neuron is represented by frequency of pulse signals. The proposed neuron provides adjustable nonlinear function, which resembles the sigmoid function. The proposed neuron and experimental multilayer neural network (MNN) are implemented on field programmable gate array (FPGA) and various experiments are conducted to test the performance of the proposed system. The experimental results show that the proposed neuron has rigid adjustable nonlinear function.
Many self-organizing maps (SOMs) implemented on hardware restrict their neighborhood function values to negative powers of two. In this paper, we propose a novel hardware friendly neighborhood function that is aimed to improve the vector quantization performance of hardware SOM. The quantization performance of the hardware SOM with the proposed neighborhood function is examined by simulations. Simulation results show that the proposed function can improve the hardware SOM's vector quantization capability even though the function value is restricted to negative powers of two. Then, the hardware SOM is implemented on field-programmable gate array to find out the hardware cost and performance speed of the proposed neighborhood function. Experimental results show that the proposed neighborhood function can improve SOM's quantization performance without additional hardware cost or slowing down the operating speed. Due to fully parallel operation, the proposed SOM with 16×16 neurons achieves a performance of 25 344 million connections updates per second.
A new digital architecture of the frequency-based multilayer neural network (MNN) with on-chip learning is proposed. As the signal level is expressed by the frequency, the multiplier is replaced by a simple frequency converter, and the neuron unit uses the voting circuit as the nonlinear adder to improve the nonlinear characteristic. In addition, the pulse multiplier is employed to enhance the neuron characteristics. The backpropagation algorithm is modified for the on-chip learning. The proposed MNN architecture is implemented on field programmable gate arrays (FPGA's) and the various experiments are conducted to test the performance of the system. The experimental results show that the proposed neuron has a very good nonlinear function owing to the voting circuit. The learning behavior of the MNN with on-chip learning is also tested by experiments, which show that the proposed MNN has good learning and generalization capabilities. Simple and modular structure of the proposed MNN leads to a massive parallel and flexible network architecture, which is well suited for very large scale integration (VLSI) implementation.
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