A Josephson adder employing high-gain direct-coupled logic gate

A wide-margin adder with a simple configuration employing high-gain direct-coupled logic gates (HDCL's) was studied. A wide-margin half-adder circuit, consisting of a single junction and three HDCL buffer gates, is proposed. In order to obtain a wide-margin circuit, gates were designed to be protective against a noise signal. The experimental circuit fabricated by a conventional Pb alloy Josephson technology with 5-µm minimum line width has shown wide-margin (more than a ± 30-percent bias signal margin) characteristics, as predicted by a computer simulation. This paper also demonstrates that the adder can be simply modified into a wide-margin full adder with a simple configuration by connecting an additional single junction and a buffer gate for a carry signal.