1. Introduction
Current-mode complementary metal-oxide semiconductor (CMCL) technology is a readily available binary technology that has been used to implement multiple-valued logic (MVL) circuits. In addition to being readily available, CMCL does not suffer from the logic level tightness, a major difficulty with voltage-mode MVL circuits. Four basic CMCL elements have been introduced in the literature [1] [2]. These are the constant, sum, mirror, and the switch. Fig. 1 shows the set of basic CMCL elements. The figure shows the symbol used for each element, the logic function realized, the CMCL circuit used, and the cost. The latter represents a measure of the chip area consumed. In considering a unary 4-valued function, , we assume that the radix and that the function is a mapping . A 4-valued unary function is represented as a 4-tuple , where . Since current mode circuits are used, then each value of a current (representing a logic value) is associated with a direction. We consider the set of 4-valued signed values . There exist a total of 4-valued signed functions. We define a Singed Function (SF) as a function that can assume both negative and positive values from the set . We show that SFs are useful in realizing any of the 256 4-valued unary functions (see Section 3). Fig. 2 shows the realization of the function using . The set of basic CMCL elements. Summary of the results obtained using two cost-table approaches.
Attribute | Approach in [7] | Approach in [8] |
---|---|---|
Number of functions in the original Cost-table | 55 | 48 |
Size of the cost-table | Fixed | Variable |
The number of Negative Functions used | 12 | 10 |
Average cost | 10.41 | 9.45 |
Maximum cost per function | 19 | 17 |