22.8 A 24-to-35Gb/s x4 VCSEL driver IC with multi-rate referenceless CDR in 0.13um SiGe BiCMOS

The optical interconnect technologies are a promising solution for high-speed and high-density interconnects because of the high-bandwidth and low-crosstalk properties of optical signals. The next challenge for optical interconnects is to move to a serial data-rate of 25Gb/s or higher [1,2]. To achieve flexible interconnects on a bandwidth demand, a CDR is required to operate at multiple rates in a wide tuning range. A selectable multi-VCO structure is one method to overcome this issue. However, when multi-VCOs are allocated in each channel, the large size of VCOs makes it difficult to achieve a high-density optical link. In this paper, we presenta dual-loop hybrid CDR including a phase interpolator (PI) loop for phase tracking and a common VCO loop situated outside the channel areas for frequency acquisition. We develop a quadrant-switching analog Pl-loop that has the ability to track the frequency mismatch corresponding to full-rate frequency up to 35Gb/s. The 4-channel driver IC with this dual-loop hybrid CDR is fabricated in 0.13μm SiGe BiCMOS technology. With these circuits, we achieve a driver IC with a multi-rate, ranging from 24 to 35Gb/s, reference-less CDR for flexible optical interconnects.