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THRESHOLD LOGIC IMPLEMENTATIONS - sreeku_princess - 10-04-2017 THRESHOLD LOGIC IMPLEMENTATIONS: THE EARLY DAYS [attachment=16005] I. INTRODUCTION Research on neural networks (NNs) goes back sixty years. The seminal year for the science of mind was 1943 when the paper of McCulloch and Pitts was published [58]. They introduced the first mathematical model of a neuron operating in an all-or-none fashion: the threshold logic (TL) gate (TLG). It computes the sign of the weighted sum of its inputs: f(X) = sign ( i = 1 n wi xi ), wi being the synaptic weight associated to xi, the threshold, and n the fan-in. II. VARIOUS TECHNOLOGIES In 1951 Marvin Minsky teamed with Dean Edmonds and designed the first 40-neuron neurocomputer Snark [60]. It was an electro-mechanical implementation using tubes, motors, and clutches, and successfully modeled the behavior of a rat searching for food in a maze. In 1957 Frank Rosenblatt generalized the McCulloch-Pitts neuron inventing the perceptron [70]. During 1957-1958, Rosenblatt together with Charles Wightman and others constructed the Mark I Perceptron having 512 adjustable weights (an 8 8 8 array of potentiometers). Shortly afterwards, Bernard Widrow together with his students developed the ADALINE (ADAptive LINear Element) [84]. They used an electrically adjustable resistor called a memistor, also founding the first neurocomputer hardware company: Memistor Corporation, producing neurocomputers during the early to mid 1960s. For a general overview of the evolution of the field of neural networks during those times the interested reader should consult [66], [16]. II. A HISTORICAL PERSPECTIVE The summing amplifier from 1946 [77] precedes even [58] by submission date: May 1, 1941. It seems to be the first hardware implementation of a TLG. The patent details an electrical calculating device [ ] for obtaining the sum of a plurality of electrical voltages using an electrical amplifier having a feedback. [ ] by adjustment of the impedances connected in series with the various sources of voltage, any one or more of the sources may be, in effect, multiplied by any desired factor [ ] (Fig. 1. (a)). Many other implementations followed. IV. CONCLUSIONS This paper has presented a brief account of the results on hardware implementations of TL obtained starting from the forties. It is quite amazing how much effort, ingenuity, and tenacity has been spent/invested over several decades to make TL a success, let alone the remarkable diversity of solutions and the numerous technologies which have been experimented with. Except a few very early solutions, all the others have mainly tried to cope with the major drawbacks of TLGs: power dissipation, reduced noise margins, and sensitivity to process variations |