photo by Gary Meek Associate Professor Farrokh Ayazi, left, and graduate student Mina Raieszadeh work in a laboratory at the Georgia Electronic Design Center at Georgia Tech. (300-dpi JPEG version - 1.1MB)

Paul Hasler, an associate professor in ECE and a GTAC team leader, has discovered techniques to program analog circuits in ways reminiscent of digital processors. Traditionally, analog circuits have been fixed-function – hard-wired to perform a specific task. Working frequently with David Anderson, an ECE associate professor and GEDC researcher who focuses on mixed-signal design, Hasler has been researching core analog capabilities for many years.

“Just saying that the world ‘went digital’ doesn’t address the crucial point,” Hasler says. “What’s key is that a programmable technology overtook a fixed-function technology.”

In their research, Hasler and his team have developed programmable analog circuits made with conventional materials and techniques but capable of taking over many functions from digital ICs.

“Digital may be a little better for communication, but in terms of computation that’s not necessarily the case at all,” Hasler says. “Programmable analog could be part of the entire-signal processing engine used by mobile devices.”

Analog is important, he explains, because analog chips use up to a thousand times less power than their digital counterparts. That makes them far better for mobile uses.

“When you’re looking at an hour versus a month in terms of your battery life, that’s pretty impressive,” Hasler says. “It just changes the entire game.”

Hasler’s research has led to GTronix, a startup company developing novel technology to extract real-world sensory information for portable consumer electronic products. The company, supported by Menlo Ventures, a major venture capital group, is poised to announce its first product soon.

Farrokh Ayazi, an ECE associate professor and GEDC team leader, is using micro-electromechanical analog technology to develop a frequency-spectrum analyzer and processor on a chip that can offer both the performance and power efficiency needed for mobile use. This technology, known as analog spectral processing, guides an RF signal to lesser-used frequencies and has similarities to GEDC’s cognitive-radio work. The research is supported by DARPA.

Ayazi is also researching the integration of microscale MEMS devices with analog, RF and mixed-signal circuits. These micro-mechanical structures could have various applications including minute, highly sophisticated motion sensors.

By converting mechanical signals into electrical signals and processing them using low-power electronics, this motion-sensing technology holds promise in handheld wireless applications such as gaming equipment and for mobile devices that navigate without GPS signals.

Qualtré, a semiconductor-design company based on work at the Integrated MEMS Lab that Ayazi leads, offers six-degree-of-freedom motion sensing devices (three-axis gyroscopes and accelerometers) with low-power integrated read-out and control circuits for consumer products. Qualtré is a member of the Advanced Technology Development Center (ATDC), a startup-company incubator at Georgia Tech.

Ayazi and his team are also investigating silicon arrays of low-power gravimetric gas and bio sensors that are capable of detecting even a single molecule of a target substance. By coating a MEMS device with a molecular-recognition layer, the researchers are bringing the advantages of low-power analog technology to these tiny devices.

In work supported by the National Science Foundation and industry, Ayazi is also studying whether tiny MEMS-based resonators, micromachined into silicon, could replace frequency-producing quartz in mobile devices such as cell phones. The MEMS technology handles higher frequencies than quartz can, while maintaining high performance.

The Silicon-Germanium Connection
John Cressler, Ken Byers Professor in ECE and a GEDC team leader, develops analog, RF and mixed-signal circuits

photo by Gary Meek Graduate student Steven Finn, left, and Professor John Cressler display a silicon-germanium integrated circuit – a transceiver designed for NASA for use on the moon. (300-dpi JPEG version - 848KB)

that exploit the special properties of silicon-germanium (SiGe) alloys. Combining silicon – a common microchip material – with germanium at nano-scale dimensions, Cressler is helping to develop next-generation microelectronic technologies that promise important gains in speed, flexibility and toughness.

Cressler recently made news when IBM and Georgia Tech research teams collaborated to produce a silicon-germanium transistor able to operate at frequencies above 500 GHz – far higher than plain silicon has ever reached. The record was attained at very cold temperatures, but the results suggested that SiGe chips could also attain record speeds at room temperature.

Cressler and his team are also leading a four-year, $14 million NASA program aimed at developing analog/mixed-signal systems for use in exploration of the moon. The work is challenging because of the lunar environment’s extremely wide, 300-degrees Celsius temperature swings and its exposure to space radiation.

The aim: to use silicon-germanium’s robust qualities to replace the bulky, power-hungry, shielded “warm boxes” currently used in space electronics.

“We’re taking legacy parts that are the size of a shoebox and putting a single piece of unprotected silicon-germanium in their place,” he says.

In the core analog realm, Cressler and his team are investigating the application of silicon-germanium to BiCMOS (SiGe transistors plus CMOS) technology used in very high-performance analog ICs. His team is helping industry researchers understand how to improve the design of these high-end analog circuits and find new applications areas for state-of-the-art analog technologies.

In addition, Cressler is studying the use of SiGe technology to improve data conversion in the very high-speed multi-gigabit range. For years, the problem of converting analog signals into digital code has created a bottleneck because analog-to-digital converters that are extremely fast yet affordable haven’t existed. New, faster data converters using SiGe could help redefine communications and radar capabilities.

“In terms of complexity and challenge in the analog design world, very high-speed data converters are at the top,” Cressler says.

Energy and Power – Better, Smaller
Gabriel Rincón-Mora, an ECE associate professor, is focusing analog expertise on powering integrated circuits and other microscale devices, and on using energy and power management to maximize a device’s operational life.

Energy/power generation and management for mobile devices will become ever more important in coming years, he says, as new, more capable chips nullify the gains made by advances in power conservation.

“We’re putting a lot more functionality into a single IC,” he says. “So we are ultimately increasing power density while maintaining similar power-source levels.”

Rincón-Mora is investigating how to provide power to chip-based mobile sensors using a system composed of a proton exchange-membrane fuel cell and a thin-film lithium ion battery. Working with Paul Kohl, a Regents’ professor in the School of Chemical and Biomolecular Engineering, Rincón-Mora and his team are studying how to manage power throughout the whole system – fuel cell, battery and chip – in ways that maximize lifetime and minimize footprint.

Rincón-Mora is also investigating microscale techniques to harvest energy from the surrounding environment. In one project, he is working with Texas Instruments to develop an electrostatic harvesting chip that draws power from the kinetic energy in vibrations. He is also working with Sakis Meliopoulos, another ECE professor, to power wireless microsensors in a power grid by using the field that surrounds an electric cable.

photo by Gary Meek Pamela Bhatti, an assistant professor in the School of Electrical and Computer Engineering, is researching the use of analog microelectronics to help treat patients with total deafness. (300-dpi JPEG version - 1.1MB)

In another project, Rincón-Mora is studying how to scavenge energy from the human body. The aim is to power a biomedical implant called a vestibular prosthesis, a device being co-developed by ECE Assistant Professor Pamela Bhatti to help patients regain their sense of balance. Rincón-Mora plans to power the tiny device through piezoelectric harvesting – generating power from the motion of tiny materials that bend as bodily fluids in the inner ear flow around the implant.

Bhatti is also collaborating with Shreyes Melkote, a professor in the Woodruff School of Mechanical Engineering, to develop an electrode array that would provide better results to patients with a cochlear prosthesis, used to treat total deafness.

Cutting Costs with Analog
Analog expertise is an important asset at the Georgia Tech Research Institute (GTRI), Georgia Tech’s nonprofit applied-research arm. Several GTRI laboratories focus on the analog-heavy field of radar and RF technology for military and civilian applications. And GTRI researchers are often tasked with finding ways to replace older analog circuits, in aircraft and elsewhere, that are no longer manufactured.

“We’re developing applications as opposed to developing new technologies in analog,” says Richard Levin, a GTRI senior research engineer. “We find new ways to apply existing technology so that we can meet the customer’s needs.”

Levin has been performing analog design that’s helping to re-engineer an older circuit board in an Air Force radar-warning receiver. Key components in the all-analog board are no longer made, and obtaining custom replicas promised to be very expensive. Levin is part of a team that has crafted a plug-in replacement board, using mixed-signal technology that combines analog and digital functions.

“Basically, it’s a more modern, work-alike circuit made from available parts,” says Levin.

Mark Mitchell, a GTRI principal research engineer, reports that his group is working on numerous projects that employ analog-intensive technology to design and develop low-cost phased-array antennas.

“Phased-array antennas have historically been extremely expensive,” he says. “That’s limited the number of applications where they can be used.”

In one program, Mitchell and his colleagues are collaborating with ECE’s Cressler to create a single-chip, phased-array module using cutting-edge silicon-germanium technology.

Current phased-array antennas, which use many multi-chip modules, are bulky. Mitchell and Cressler want to pack that functionality into a single silicon-germanium chip.

“You can’t get the kind of high-frequency performance we want out of these analog circuits with conventional silicon,” Mitchell says. “Only silicon germanium can give us that performance and also cut the cost per element down by a couple of orders of magnitude.”

Communicating with the Body
At the Laboratory for Neuroengineering (NeuroLab), the team of Steve DeWeerth, a professor in the Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, is designing custom analog circuits. The twofold aim: to use analog systems to mimic biological performance and to interface with biological systems for medical applications development.

photo by Gary Meek Research engineer Edgar Brown, left, and Professor Steve DeWeerth demonstrate a custom analog integrated circuit. (300-dpi JPEG version - 1.2MB)

“I think Georgia Tech’s analog design strengths will provide some real opportunities to develop new areas in the biomedical field with real potential – biomedical devices, prosthetics and implants,” says DeWeerth.

Among other things, the NeuroLab team has developed circuitry for stimulation of neural tissue in vitro. They are using novel analog designs to minimize data loss caused by applying electric-stimulus power, and also to enable accurate feedback.

Thanks to the proliferation of foundries that serve circuit designers, the team now pursues its research using analog circuits made to its own specifications.

“One of the advantages of designing our own ICs is that we’re not confined to what exists out there,” says Edgar Brown, a research engineer on DeWeerth’s team. “It would be very difficult to do the kinds of things that we’re doing with off-the-shelf circuitry.”

Maysam Ghovanloo, an assistant professor with ECE and GEDC, focuses on design of integrated circuits and microsystems for implantable biomedical applications. His research involves state-of-the-art neuroprosthesis technology that could communicate with the human nervous system to address serious impairments ranging from from blindness to paralysis.

In his recently established lab, GT-Bionics, Ghovanloo is developing a multi-channel neural recording system to wirelessly monitor freely moving animal brain activities. He is also trying to establish a bidirectional telemetry link with the central nervous system at the cellular level for brain-computer interfacing.

At GEDC, Ghovanloo is initiating collaborations on wireless/RF and MEMS technologies to develop electrodes, antennas and packaging needed for implantable microelectronic devices.

Clearly, analog technology is here to stay. Analog engineers are likely to remain in short supply worldwide for years, says GEDC Director Laskar, as demand for both analog research and applications continues to grow.

“Analog and mixed-signal technologies are going to become more important, not less,” he says. “For the entire microelectronic revolution to proceed robustly, analog research has to keep pace – and here at Georgia Tech it’s an ongoing mission to supply the research and the people to help make that happen.”