Short distance optical links: Analysis, demonstration and circuit design.

摘要

Optical signaling has some fundamental advantages over electrical signaling. Some of these advantages like absence of parasitics have been utilized beneficially in long distance and medium distance interconnection networks. However, for optics to be useful in the highly optimized and constrained VLSI system space, we require more benefits from using optics.; In this dissertation, I identify electrical isolation of optical interconnects as an additional benefit. I study how this advantage can make optical interconnects beneficial in modern VLSI systems at short distances and have taken a step towards solving chip-to-chip and intra-chip interconnection issues.; I demonstrate using our proof-of-concept circuits, the benefits of using optical fanout in electrical links with fanout. I show improved signal latency with optical fanout even at link lengths of 200mum in a 0.25mum technology. This is the first physical demonstration of the advantages of using optics in silicon VLSI systems at these distances. I also demonstrated an advantage in energy-delay-squared product for fanout to more than 250 minimum sized inverters corresponding to a distance of 1.5 mm.; I also demonstrate an important step towards physical implementation of our proposed short-distance optical links via our design of a silicon-based detector. I developed our detector in a commercial process and it uses a low supply voltage 1.8V. These features make our detector extremely low-cost and readily available in commercial processes. I also demonstrate opto-electronic integration of detectors and receivers in the same silicon chip and show operation at 1Gbps link bit rate.; As a part of our circuit design efforts for optimal link design, I focused on creating process-invariant circuits. Fabrication related circuit variations lead to a significant power-performance-yield trade-off and introduce variability in the various branches of optical fanout. Addressing these issues is necessary in constructing a robust optical fanout.; As a step towards this, I developed a design methodology and two example current sources that reduce the effect of intrinsic process variations without the need for post-fabrication efforts. The example current sources demonstrate more than a factor of two reduction in normalized standard deviation over equivalent uncompensated current sources. To the best of our knowledge, these are the first measured results showing circuit design based variation reduction of such magnitude without post-processing.; The sum of this work not only helps solve a number of issues in enhancing performance using optics at short distances, but also presents practical results that have multiple applications in fields other than short-distance optical links, like slip-ring systems (MRIs, etc.), low crosstalk interconnects (cell phones), imaging systems and in precision circuit design. With these results, I hope to have made a contribution to VLSI system design in general.