Mixed -signal CMOS circuits for digital free -space optical interconnects: Design, optimization, and system integration

The integration of digital free-space optical interconnects (FSOI) into a VLSI computing or switching system requires the development of CMOS transmitter and receiver circuits. These circuits are the interface between the on-chip digital signals and the off-chip analog optical signals, and thus their design and optimization is complicated by requirements from both the digital and analog regimes. In the analog regime, their noise, frequency response and stability are important design criteria. In the digital regime, they must be fast, small, low-power, and reliable in an electrically noisy environment.;This thesis first examines the analysis, design, and optimization of CMOS receivers for FSOI. Circuits are optimized for sensitivity and power dissipation, and the effects of noise and device parameter variations are analyzed. It is found that in order to meet the noise margin and timing requirements for CMOS digital circuitry, free-space optical interconnects must operate at optical powers significantly above those determined by the thermal noise limit. A method of optimizing the total link power is introduced, and its effect on the optimal receiver design is investigated.;Then, experimental results are presented for a range of receiver designs. Good correlation is found between the modeled performance and the measured performance of the optimized receivers. Operation using CMOS integrated photodetectors is tested, and a coding scheme is proposed to compensate for the long diffusion time of carriers when using an integrated CMOS detector.;Finally, the total link power is compared for three transmitter technologies: PLZT modulators, MQW modulators, and VCSELs. CMOS transmitter circuits applicable to each technology are presented and optimized. The receiver power dissipation is found to be a significant portion of the total link power. Aggregate bandwidths in excess of 1 Tbs˙cm2 are predicted for MQW and VCSEL based links.