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A new CMOS VLSI implementation of an asymmetric programmable sigmoid neural activation function, as well as of its derivative, is presented. It consists of two coupled PMOS and NMOS differential pairs with different programmable bias currents that set the upper and lower limits of the sigmoid. The circuit works in the weak inversion region, for low power consumption and exponential envelope, or in strong inversion to achieve higher speeds. The results obtained from the theoretical transfer function, and from the simulations of the circuit implemented in AMI's 0.35 /spl mu/m technology, show a very good match. 相似文献
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Vítor Grade Tavares Sebastian Tabarce José C. Principe Pedro Guedes de Oliveira 《Analog Integrated Circuits and Signal Processing》2007,50(3):251-259
This paper presents the results of a CMOS-VLSI implementation of a realistic computational model proposed by Walter Freeman
for the olfactory system. This model, in later years, has been studied for engineering applications such as auto-association
and classification. The analogue nature of the model motivates analogue VLSI implementations. However, the dimension and complexity
of such system poses many obstacles to an analogue electronic implementation; one such is the massive interconnectivity which
size increases with the square of the number of inputs (channels). We suggest a multiplexing procedure that puts the burden
of interconnectivity over a digital system that is simpler to design and makes the analogue system more treatable. The procedure
naturally samples the signals. To avoid smoothing filters, a discrete-time solution was also employed. Although with such
approach the time resolution is reduced, the advantages overcome the detriments. Previous work has shown that the model can
be efficiently discretized using DSP techniques, resulting on a system that is able to predict, on sample-by-sample basis,
the behaviour of the VLSI circuit, allowing for a simple and flexible way to adjust the circuit parameters. We present the
measured circuit results that are further confronted with the digital implementation. 相似文献
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