Implementation of Threshold Logic

Traditionally, logic circuits have been, and are still being implemented using Boolean logic. Although there has been a tremendous increase in the performance of the technology used to implement Boolean logic primitives, the underlying paradigm has remained unchanged over the years. Since the early 1960's there is a fundamentally more powerful alternative for Boolean logic available, called Threshold Logic (TL). Although implementations of TL gates have grown with the advances in technology, none of these have ever proven widely applicable. Because of this TL was never a practical success. Recently a new technology called Capacitive Threshold Logic (CTL) was disclosed which holds the promise of being the rst practically applicable TL technology. This thesis investigates the issues related to the application of CTL, and particularly to the implementation of arithmetic operations. It starts with a very general introduction into TL. After this it deals with a number of problems which may occur when applications of TL need to be implemented in a less than perfect technology. The CTL concept is explored, and the rules governing its operation and programming are established. Based on the CTL concept, an alternative method of programming CTL gates is developed which is more practical than the plain CTL gate. A CTL gate using this method is called a Capacitor Programmable CTL (CP-CTL) gate. Finally, a 32-bit binary unsigned 2-1 adder is implemented at the layout level using (CP-)CTL gates. Although it was not the original objective of this thesis, this has given rise to an improved scheme for the 2-1 addition of binary unsigned numbers.

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