Urs Bapst

Wireless in-house data communication via diffuse infrared radiation

A novel wireless broadcast/multi-access channel is described for flexibly interconnecting a cluster of data terminals located within the same room. The transmission medium is diffusively scattered infrared radiation at 950-nm wavelength. Transmission is low-to-medium speed and the range up to 50 m. Theoretical analysis indicates that the time dispersion limits the transmission bandwidth of the system to 260 Mbit ċ m/s, but background noise produced by ambient daylight reduces the transmission speed below 1 Mbit/s. The transmission properties of the diffuse optical channel are analyzed, and experimental digital links for baseband PCM at 125 kbit/s and PSK 64 kbit/s are demonstrated.

Development of a low-cost low-loss polymer waveguide technology for parallel optical interconnect applications

We report on the material evaluation, design, fabrication, and characterization of low-loss multimode polymer waveguides that are compatible with standard PCB manufacturing processes for use in large-area high-density high speed optical backplane interconnects.

Characterization of parallel optical-interconnect waveguides integrated on a printed circuit board

The development of optical interconnects in printed circuit boards (PCBs) is driven by the increasing bandwidth requirements in servers, supercomputers and switch routers. At higher data rates, electrical connections exhibit an increase in crosstalk and attenuation; which limits channel density and leads to high power dissipation. Optical interconnects may overcome these drawbacks, although open questions still need to be resolved. We have realized multimode acrylate-polymer-based waveguides on PCBs that have propagation losses below 0.04 dB/cm at a wavelength of 850 nm and 0.12 dB/cm at 980 nm. Transmission measurements at a data rate of 12.5 Gb/s over a 1-m-long waveguide show good eye openings, independent of the incoupling conditions. In the interconnect system, the transmitter and receiver arrays are flip-chip-positioned on the top of the board with turning mirrors to redirect the light. The coupling concept is based on the collimated-beam approach with microlenses in front of the waveguides and the optoelectronic components. As we aim for large two-dimensional waveguide arrays, optical crosstalk is an important parameter to be understood. Accordingly, we have measured optical crosstalk for a linear array of 12 optical channels at a pitch of 250 um. The influence of misalignment at the transmitter and the receiver side on optical crosstalk will be presented as a function of the distance between waveguide and transmitter/receiver.

Ion microbeam probing of sense amplifiers to analyze single event upsets in a CMOS DRAM

An ion microbeam radiation system has been used to probe the relative contribution of individual circuits and nodes of a CMOS DRAM to single event upsets (SEUs). This instrument, which uses monoenergetic collimated ions from a 3-MV tandem accelerator, can produce an ion beam with a diameter as small as 1 mu m. The precise alignment capability of the system allows positioning of the beam to any location in the circuit with an accuracy of better than 1 mu m. The monoenergetic beam with the device under vacuum simplifies the analysis of the experimental results. The results show that alpha-particle hits on sensitive nodes within the sense amplifiers dominate the SEU rate. This domination is due to the presence in the sense amplifiers of n-channel devices which can collect charge from the entire ion track. In contrast, the memory cells and bit lines contain only p/sup +/ nodes in an n-well, which shields them from charge generated in the substrate. >

Compact tunable FIR dispersion compensator in SiON technology

We present a tunable dispersion compensator, based on a sixth-order finite impulse response lattice filter. The filter has a free spectral range of 100 GHz and can be tuned for linear group delay slopes between -100 and 100 ps/nm with less than 1-ps ripple over a usable bandwidth of more than 60 GHz. Within this usable bandwidth, the average polarization-mode dispersion is low, reaching 2.4 ps only for extreme group delay slopes. The filter can also generate higher order group delay curves, for example for dispersion slope compensation.

Design and implementation of an optical interconnect demonstrator with board-integrated waveguides and microlens coupling

We discuss some of the trade-offs that we are facing when choosing design parameters for future optical backplane interconnects. We present some of our current choices, along with experimental module- and system-level results.

Ion microbeam radiation system

An ion microbeam radiation test system has been built for studying radiation-induced charge collection and single event upsets in advanced semiconductor circuits. With this system, it is possible to direct an ion beam of a diameter as small as 1 mu m onto a circuit or test structure with a placement accuracy of 1 mu m. The components of the system and its operation are described. Applications are described which demonstrate the capabilities of the system. >

Hierarchical system synchronization and signaling for high-performance-low-latency interconnects

We address a hierarchical synchronization distribution architecture for high-performance and low-latency operations. Furthermore, the bandwidth overhead is minimized, and the accuracy can be adjusted to the application. A novel signaling channel with an open, user-extendable protocol is proposed. An approximation method to estimate system-wide clock jitter is introduced and applied to the optical shared memory supercomputer interconnects system (OSMOSIS). First measurement results, which reveal the challenges of future system synchronization requirements and the potential of the defined architecture, are presented

A 5.9mW/Gb/s 7Gb/s/pin 8-lane single-ended RX with crosstalk cancellation scheme using a XCTLE and 56-tap XDFE in 32nm SOI CMOS

This work reports an 8-lane single-ended RX featuring compact and low power far-end crosstalk (FEXT) cancellation circuits. The RX data-path consists of a cross continuous-time linear equalizer (XCTLE) to remove FEXT by nearest aggressors within the channel bundle. Residual post-cursor FEXT is suppressed by a direct feedback 7×8-tap cross decision-feedback equalizer (XDFE). A CTLE and 8-tap DFE equalize single-ended channels with 28dB insertion loss at Nyquist frequency without TX FFE. The circuit, fabricated in 32nm SOI CMOS, was measured to receive 7Gb/s/pin PRBS11 data at BER<; 10-12 with 12.5%UI margin. Itoccupies 300×350μm2 with an energy efficiency of 5.9mW/Gb/s.