Area Efficient Methods to Increase the Reliability of Combinatorial Circuits

The boolean circuits we consider are directed acyclic graphs built from nodes, in the following called gates, of bounded fanin and bounded fanout. No further restriction is put on the boolean basis B from which the type of each gate has to be chosen, except that it should be complete every boolean function should be realizable using only those kinds of gates. For simplicity let us assume that the total number of edges or wires entering or leaving a gate is at most 4. Gates and wires will be called switching elements. If an ouput of some gate is needed as an input for many other gates it has to be duplicated because of the bounded fanout. For that purpose a special (passive) id-gate of fanin 1 and fanout 2 will be required, such that by a combination of such gates one can produce arbitrary many copies of a given boolean value. Special nodes of fanin 0, called input pads, receive a boolean value from the outside. Computation takes place in the obvious way. In addition some gates are marked as output gates, their values define the output of the circuit.