Читать книгу Reversible and DNA Computing - Hafiz M. H. Babu - Страница 43

In a reversible circuit, correct output is found by applying correct input instance and controlling one or more inputs if needed. Feynman gate (FG) is already presented to illustrate the idea of garbage output, Feynman gate is 2 2 reversible gate where inputs are A, B, and corresponding functions are P = A, Q = A B. The Feynman gate is used here to show how to control input to produce expected output. Both the inputs A and B are used as control inputs, and their impact on output is shown below.

Figure 1.8 Toffoli gates as self‐reversible.

A as control input:

 For , output , and ,

 For , output , and .

B as control input:

 For , output , and .

 For , output , and .

It is better to note that when B is used as control input and , both the outputs P = B and Q = A. By controlling B, the copies of A can be created. This circuit can be easily used as a copying circuit.