Abstract: A full swing CMOS logic circuit provides fault tolerant, cold sparing of VLSI logic devices attached to a high speed bus. P-channel FET transistors are formed in an N-well which has a biasing transistor which effectively decouples the circuit when the circuit is not powered. The input/output interface of the cold spares have a high impedance and do not corrupt an interconnected electronic bus. The final drive transistors are reverse biased or clamped to zero to prevent any leakage paths.

Abstract: A digital adder circuit is disclosed which employs non-DC current configurations to significantly reduce power, device count, and delay in performing binary addition. The circuit features a carry propagate transfer FET device whose gate is controlled by a carry propagate control circuit which selectively gates on the transfer FET device at a particular adder bit stage when the carry-in binary bit is to be transferred as the carry-out binary bit, which takes place when the augend input bit and addend input bit at that stage are not equal. The circuit additionally features a carry generate control circuit which is connected to the carry-out node of the FET transfer device, which selectively connects that node to either a drain potential when both inputs are unity or to ground potential when both inputs are zero, thereby efficiently generating the carry-out bit without regard for the state of the carry-in bit.