US Patent 8653857 Circuitry and layouts for XOR and XNOR logic

An exclusive-or circuit includes a pass gate controlled by a second input node. The pass gate is connected to pass through a version of a logic state present at a first input node to an output node when so controlled. A transmission gate is controlled by the first input node. The transmission gate is connected to pass through a version of the logic state present at the second input node to the output node when so controlled. Pullup logic is controlled by both the first and second input nodes. The pullup logic is connected to drive the output node low when both the first and second input nodes are high. An exclusive-nor circuit is defined similar to the exclusive-or circuit, except that the pullup logic is replaced by pulldown logic which is connected to drive the output node high when both the first and second input nodes are high.