2-bit adder carry and sum logic circuits clocking at 19 GHz clock frequency in transferred substrate HBT technology

We report carry and sum circuits for a 2-bit adder. The 2-bit adders are designed to be part of a pipelined 2N-bit adder-accumulator. The ICs clock at a maximum of 19 GHz and were fabricated in InAlAs/InGaAs transferred substrate HBT technology. To obtain high clock rates in a design with multiple gate delays, we have employed a novel merged AND-OR logic structure using 4-level series-gated current-steering logic. Further, this logic is merged with the synchronizing latch circuit so as to minimize the overall gate delay. The 2-bit carry circuit has 250 transistors, a maximum clock frequency of 19 GHz, and dissipates 1.2 W. The sum logic circuit of a full adder was realized as a 4-level series-gated ECL XOR gate. This circuit has a maximum clocking frequency of 24 GHz, has 150 transistors and dissipates 750 mW.