This paper presents an 11.6-GHz 1:4 regenerating demultiplexer (demux) and a 6.1-GHz phase aligner, implemented using high-current-gain baseline AlGaAs/GaAs /GaAs heterojunction bipolar transistor (HBT) technology. The demux features a hybrid tree/shift register-type architecture optimized for high-speed and low-power operation, and is the fastest demux with bit-rotation control ever reported. It consumes 1.4 W of power with a single -5-V supply, and has a phase margin of 270° and differential input data sensitivity of 56 mVp.p at 11.6 Gb/s. The phase aligner incorporates an auto-latching scheme which allows the data to be latched using a timing signal derived on-chip from the data, and is the fastest fully monolithic phase aligner ever reported. It dissipates 0.8 W of power with a single -5-V supply and has differential input data sensitivity of 60 mVp_p at 6.1 Gb/s.