AlGaAs/GaAs HBT Circuits for Optical TDM Communications K. Runge, P.J. Zampardi, R.L. Pierson, R. Yu, P. B. Thomas, S.M. Beccue, and K. C. Wang Rockwell International Science Center 1049 Camino Dos Rios Thousand Oaks, California, 91360 We describe experimental ultra-high-speed HBT circuits for lightwave communications applications. High speed circuits such as multiplexer/demultiplexers, variable gain amplifiers, (VGAs), and transimpedance amplifiers operating at high bit rates (> 30 Gb/s) are required for the realization of high-performance lightwave systems using TDM or WDM. We have demonstrated 40 Gb/s 4:1 multiplexers, >30 Gb/s 1:4 demultiplexers, DC-26 GHz VGA’s, DC-25 GHz transimpedance amplifiers, 30 Gb/s data and clock regenerators, 40 Gb/s differentiate-and-rectify timing recovery circuits, and 40 Gb/s delay-and-multiply timing recovery circuits, for use in such systems using a manufacturable hybrid digital/microwave HBT process. 1. Introduction In this paper we discuss the application of the AlGaAs/GaAs HBT (heterojunction bipolar transistor) to high speed fiber optic systems operating at 30 Gb/s and beyond. In recent years the emphasis in both TDM (time division multiplexed) and WDM (wavelength division multiplexed) lightwave systems research has been on increasing the overall capacity of the system. In TDM systems, the emphasis has been on increasing the raw speed per channel from 2.5 Gb/s to 10 Gb/s with current laboratory work moving towards data rates of 40Gb/s, and beyond. WDM system capacity has also been growing dramatically with an increase in the number of wavelengths transmitted, and also with the per channel transmission rate. The WDM per channel transmission rate has traditionally lagged that of the TDM system. Fiber dispersion management may limit both the TDM and WDM systems capacity in the future. But current research is pointing the way for 40 Gb/s and beyond per channel transmission rates. The electronic circuits for ultra high-speed fiber optic transmission have always been seen as a bottleneck to systems performance. The perceived severity of this “bottleneck” has varied from year to year with the advancement of both optical technology (ex. fiber amplifiers, low drive voltage external modulators), coupled with improvements in circuit design techniques, and a great increase in the speed (f T /f MAX ) of IC technologies. The rapid development of optical and electrical technologies and design techniques shows no sign of slowing down. The design of high-speed circuits for lightwave systems requires not only advanced device technology, but also clever circuit design. In this paper we will talk about the AlGaAs/GaAs HBT transistor and its application to lightwave circuits. We will also show examples of key circuits will be shown which demonstrate circuit principles. The AlGaAs/GaAs heterojunction bipolar transistor (HBT) transistor is ideal for the design of lightwave circuits. The AlGaAs/GaAs transistor features high f T ,f MAX combined with high breakdown voltage. High f T is needed for circuits in the analog path, while high f MAX and f T , are need for the digital circuits. High breakdown allows for high drive voltage for the modulator driver, although recent progress in the development of modulators has relaxed this requirement. The semi-insulating substrate also aids with the design of high-speed circuits by having a lower C cs capacitance in comparison to silicon bipolar technology. It also allows for high-Q passive components, unlike conductive or highly resistive substrates in other technologies. The AlGaAs/GaAs technology also exhibits comparable power dissipation when compared to InP technology in circuit applications. This is attributable to the fact that a given f T /f MAX will be reached in both technologies at a comparable collector emitter voltage (V CE ) and collector current (I C ). A GaAs based substrate compares favorably to Si based substrates in that the GaAs is semi-insulating (S. I.). This reduces collector to substrate capacitance, which may play a key role in high-speed and high integration level silicon circuits.