Research Spotlight: The tiny circuit that could

Inside the LHC tunnel during constructionImagine a tiny integrated circuit so small it must be viewed through a microscope, but so powerful, fast and sturdy it can routinely transmit huge amounts of data at high speed in a highly radioactive environment, where temperatures might fall below an unimaginable 300 degrees F.

Yet despite those challenges, the circuit must dissipate very little heat and – because its location makes routine maintenance impossible – it must be highly reliable. An SMU team of physicists led by Associate Professor of Physics Jingbo Ye not only imagined it – they designed it.

The miniscule SMU link-on-chip (LOC) serializer was designed for ATLAS, which is the largest particle detector in the Large Hadron Collider (LHC) – a massive, high-tech tunnel about 100 meters underground. Within the LHC’s 17-mile-long ring, protons traveling at high energy are smashed together and broken apart so physicists worldwide can analyze the resulting particle shower detailed in a flood of electronic data.

The data transmit from the LHC via a tiny serializer circuit enabling electronic readouts. Physicists analyze the data to discover answers to unsolved scientific mysteries such as the Big Bang, dark matter, black holes, the nature of the universe and the Higgs particle that gives mass to quarks and electrons. SMU is a member of the ATLAS Experiment.

The LHC is a program of the Geneva-based international scientific consortium known as the European Organization for Nuclear Research, or CERN. In March CERN announced that the LHC had successfully begun colliding protons at an energy three and a half times higher than previously achieved at any particle accelerator.

SMU’s new LOC serializer is what the industry calls an integrated circuit made for a specific use, or “ASIC” (application-specific integrated circuit). It was designed for the LHC’s high-radiation environment, as well as for high data bandwidth, low-power dissipation and extremely high reliability, says Ye.

SMU physicist Jingbo YeThe serializer was perfected over the past three years in the SMU Research Laboratory for Optoelectronics and ASIC Development in the Department of Physics. It can operate at cryogenic temperatures and has been tested down to liquid nitrogen temperatures of -346 degrees Fahrenheit. The serializer was designed to transmit data for the optical link readout system of the ATLAS Liquid Argon Calorimeter, an ATLAS sub-detector that measures the energies of electrons and photons generated at the center of ATLAS where protons collide. Because the electronic readout components are in the center of the ATLAS detector, they are essentially inaccessible for routine maintenance, so reliability is paramount, Ye says.

With a data transmission rate of 5.8 billion-bits per second, the SMU LOC serializer represents the first milestone for the SMU-led team. The team plans to develop an even faster ASIC serializer that transmits data at up to 10 billion-bits per second. Faster circuits are critical as CERN continues increasing the LHC’s luminosity, thereby generating more and more data.

SMU’s next goal is to increase both the data speed and the number of data lanes to produce an even faster LOC serializer, Ye says. “In the next few years, we hope to increase the total speed by a factor of 62 more than what is installed in ATLAS.”

Ye presented the SMU LOC serializer design in February at CERN. Made of complementary metal-oxide-semiconductor transistors in silicon-on-sapphire, the serializer’s design details also will be presented to scientists in April in Hamburg during the ATLAS Upgrade Week at the DESY laboratory, Germany’s premier research center for particle physics. The SMU LOC serializer research was funded by the National Science Foundation and the U.S. Department of Energy.

The new LOC serializer is critical for the upgrade of the Large Hadron Collider, called the Super LHC, which is planned to go online in 2017, Ye says.

“The original ATLAS design used a commercial serializer that was purchased from Agilent Technologies,” Ye said. “But for the Super LHC there is no commercial device that would meet the requirements, so – being typical physicists – we set out to design it ourselves.”

The ATLAS Liquid Argon Calorimeter’s existing optical link system, delivered by SMU physicists, has a data bandwidth of 2.4 terabits per second over 1,524 fibers, or 1.6 billion bits per second per fiber, more than 1,000 times faster than a T1 line of 1.544 megabits per second. The next generation of this optical link system will be based on the new SMU LOC serializer, and it will reach 152.4 terabits per second for the whole system.

“Fast information transfer from the detector to the computer processing system is a necessity for handling the significantly increasing amounts of data expected in the next round of LHC experiments,” says Ryszard Stroynowski, U.S. Coordinator for the ATLAS Liquid Argon Calorimeter, and chair and professor of physics at SMU. “It will allow ATLAS to be more selective in the choices of events sent for further analysis.”

A radiation-tolerant, high-speed and low-power LOC serializer is critical for optical link systems in particle physics experiments, Ye said, noting that specialized ASIC devices are now common components of most readout systems.

“The ever increasing complexity of particle physics experiments imposes new and challenging constraints on the electronics,” Ye says. “The LOC serializer was a formidable task, but our team was up to the challenge.”

Written by Margaret Allen

(Above, the LHC tunnel during its construction; SMU physicist Jingbo Ye in the lab.)

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