Project Leader: Dr. Edward Gebara and Dr. Chris Scholz

Motivation: The rapid development of multimedia communications in recent years calls for ever-increasing bandwidth, data throughput and high capacity transmission. These needs can be addressed by improving device technologies, expanding the bandwidth of the transmission medium or by utilizing improved modulation techniques. Modulation techniques such as PAM and QAM compared to conventional binary OOK transmission encode two or more bits in each transmitted symbol resulting in improvements in bandwidth, data throughput and spectral efficiency. The bandwidth of the transmission is predominantly determined by the symbol rate rather than the aggregate data throughput. This not only lowers the bandwidth requirements of the transmitter/receiver, but also allows for more channels on a given transmission medium.  Furthermore SCM, CDMA and Equalization are additional techniques to better utilize the transmission channel and increase data throughput.

Objective: The Objective of this project is to determine the optimum transmission scheme to achieve greater than 10 to 20Gbps data throughputs for Short Reach (SR) communication over copper interconnect and backplanes.  A thorough analysis of alternate modulation schemes (PAM, QAM, SCM, CDMA… etc.) and equalization techniques will be conducted and applied to SR communication. Copper Backplane and copper channels will be characterized and modeled. These models will be implemented in standard simulation tools (Matlab, ADS, VPI… etc.) allowing to evaluate the impact of alternate modulation and equalization to these channels as well as optimizing for the best system performance. Additionally, as these techniques are developed they will be evaluated for application to multi-mode fiber.  Such an evaluation and study can help improve the performance and efficiency of communication networks and provide accurate understanding of the effects of PAM, QAM, SCM, CDMA, and Equalization in such a system. Additionally, test beds and MMICs will be developed for proof of concept in pure CMOS. The current proposed projects and research include:

Dr. Edward Gebara
Dr. Chris Scholz
Anand Raghavan
Franklin Bien
Soumya Chandramouli
Hyungsoo Kim
Jean de Ginestous
Sarju Vasavada
Kil-Hoon Lee

Alternate modulation efforts: Optimum modulation scheme for SR communication

Alternate modulation schemes and equalization techniques will be analyzed for data throughput of 10 to 20 Gbps or greater for SR communication. System simulation as well as link characterization will be implemented and optimum schemes will be determined for various transmission mediums such as copper backplane and multi-mode fiber. The combination of equalization and alternate modulation schemes will be considered in order to improve non-linearity and loss in the transmission medium. CMOS circuits will be developed to demonstrate and reflect the high-level system simulation and analysis.

Short Reach, Backplane and Copper Communication: Backplane Channel modeling

Backplane Channels can be modulated at speeds ranging from DC to several GHz. The maximum frequency of operation depends solely on the material’s dielectric, the transmission length, and the interconnects. Operating backplanes at higher speeds requires equalization techniques to compensate for ISI and transmission loss proving the importance of Backplane channel modeling. Backplane interconnect signal integrity models, VIA models and PCB trace models (single- run, differential and on different layers) are being developed and validated with actual backplane measurements. De-embedding techniques are being adapted to backplanes in order to fully model a backplane for different dielectric material and transmission length. Models will be based on TDR impedance measurements. S-parameter measurements, and parameters such as propagation delay, reflections, cross talk, loss, ground bounce and dispersion, will be integrated in the models.

Short reach communication equalization/predistortion circuits

A continuous time transversal filter is being developed to meet the diverse equalization needs for Backplane, copper and short reach optics. The equalizer will compensate for chromatic dispersion in fiber and low pass effects of backplanes and copper. Additionally, it will compensate for reflections between closely spaced interfaces and filter noise. Furthermore a pre-distortion circuit for VCSELs will be implement using an anti-parallel diode circuit topology. The circuit will generate an arcsine transfer function that will minimize the non-linear effect of the VCSEL LI characteristics.