2.5 GB/S LASER-DRIVER GAAS IC

A laser-diode driver GaAs IC incorporating an optional NRZ/RZ conversion facility, having ECL and SCFL compatible inputs and providing a 0-60 mA adjustable output current into a 50 OMEGA/5V termination at bit rates up to 2 Gb/s NRZ and maintaining a clear eye opening of 50 mA at 2.5 Gb/s NRZ bit rate has been designed using a commercial 1 mum gate length (F(tau) = 12 GHz) GaAs MESFET foundry service. The high maximum output current is obtained despite a low drain-to-gate breakdown voltage by implementing the output driver as a cascode differential amplifier. The logic circuitry incorporating two data input buffers, a clock input buffer, a retiming MS-DFF, a NRZ/RZ-converter and a 2-bit selector is implemented using a novel SCFL family, DCAL type SCFL, which is based on gate-width scaling rather than on absolute values. As a result, the on-chip logic voltage swing is less sensitive to process variations than conventional SCFL. A 60% improvement in noise margin over that of conventional SCFL is also obtained. Finally, in order to verify laser driving performance a back-to-back optical-fiber transmission experiment using a Siemens DFB laser was performed giving good optical eye diagrams at 2.5 Gb/s. Further, the electro/optical interplay between laser-diode driver and laser-diode has been demonstrated using SPICE simulations employing a large-signal model of an Ortel SL-620 laser-diode module.