8 - Optical-Link Transmitter Circuits

Summary

This chapter builds on the basic transmitter building blocks presented in Chapter 5 and applies them to optical links. The section on direct modulation discusses CML and SST circuits for driving laser diodes, along with how equalization can be added, incorporating concepts from Chapter 4. One aspect of laser diodes that is presented is their nonlinear behaviour that favours having different equalization for rising and falling edges, something not typically done in electrical links where channels are linear. Circuit design for modulator drivers is discussed in Section 8.2, including an overview of distributed amplifiers. Finally, microring modulator drivers are presented in Section 8.3. Since the basic IC building blocks have already been introduced in Chapter 5, this chapter emphasizes aspects particular to driving optical devices, such as the electrical modelling of the electronics/photonic packaging and the challenges in producing voltage swings beyond the breakdown voltage of the underlying CMOS technology.