Transition Logic Circuits and a Synthesis Method

A transition signal is a change of binary level, either from 0 to 1 or from 1 to 0, regardless of the direction. It is often more convenient to describe a switching circuit in terms of level transitions, and a circuit with at least one input variable represented as a transition signal is called a transition logic circuit. Transition logic circuits are essentially level sequential circuits and, as such, Huffman´s synthesis method can be applied. However, Huffman´s synthesis rapidly becomes too laborious as the number of transition variables increases. The first part of this paper presents a synthesis approach which is simpler than Huffman´s in such cases, although its applicability is more limited. In this approach, one considers a level transition as if it were a pulse, and then synthesizes the circuit following the standard pulse sequential circuit synthesis method. Circuits are constructed from two basic transition logic elements, the G element and the M element, together with ordinary gates.