SiGe BiCMOS integrated circuits for optical communication transmitters
Telecommunications play a crucial role in our daily lives, not only because of their significance in allowing interaction between all of us, but also due to the forthcoming expansion of connection and exchange of data between machines, the so-called Internet of Things (IoT), which will result in a massive network of thousands of millions of devices around the world. Such growth of the internet calls for simultaneous development of the underlying network, as it needs to support faster speeds in current devices. Consequently, metro areas tend to experience much of this throughput concentration, demanding electro-optical transceivers with types of modulation featuring higher spectral efficiency. This thesis focuses on the development of new designs to improve the performance of electro-optical transmitters by making use of advanced manufacturing processes in SiGe BiCMOS technology. In the first part, the capability of a silicon photonics platform for the implementation of driver and Mach-Zehnder modulator (MZM) is investigated. With the aim to implement a high-speed solution using this platform, a segmented topology is used for the investigation. With this scheme the driving voltage can be effectively applied along the whole modulator length and velocity matching between optical and electrical waves can be achieved, overcoming the bandwidth impairments. With the implemented module, transmission over 60 km of fiber at up to 112 Gb/s data rate is demonstrated. In the second part of the thesis, stand-alone MZM driver implementations are presented which serve to explore different techniques in the electrical design of this integrated circuit (IC). First, the design of a 40-Gb/s driver compatible with a modulator with a custom impedance of 25 Ω is presented, which investigates a topology to overcome the additional power dissipation due to the lower load impedance. Secondly, a low-power solution driver implemented in a complementary BiCMOS technology is demonstrated, achieving 28 Gb/s and an efficiency of 6.4%, the highest in the literature. Finally, the implementation of a 100-Gb/s driver is investigated which includes a 2-bit RF digital-to-analog converter (DAC), eliminating the need for external DAC and therefore reducing power dissipation and footprint. The last part of the thesis deals with solutions targeting data rates higher than 100 Gb/s. A high-speed driver using a distributed amplifier topology in a differential manner is presented, achieving a record bandwidth of 90 GHz. Test equipment must also be able to cope with the increasing data rates in optical transmissions; in this context a pseudo-random bit sequence (PRBS) generator to ease measurements of the electro-optical devices is also designed, with eye-diagram measurements showing a PRBS7 of 115 Gb/s and demonstrating a state-of-the-art figure-of-merit (FoM) value of 0.87 pJ/b.
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