Effect of output buffer design on 40Gb/s limiting amplifiers designed with InP HBT technology

An InP-based HBT technology with peak f/sub t/ /spl sim/ 135GHz is used to design and fabricate several 3-stage limiting amplifier with high margin at >40Gbps. Feedback techniques are used in all design for the first two stages. The different designs compare the conventional (resistive load) differential pair output buffer with a feedback (active load) transimpedance output buffer. The common differential specifications are S11 and S22 < -15dB and S21 > 25dB with output swing >500mV. Results show that the design with the negative feedback output buffer has a lower small-signal bandwidth but a larger 40Gb/s eye opening than design with the conventional differential pair output buffer.