[Editors] MIT: New analog circuits could impact consumer electronics

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

======================================
MIT: New analog circuits could impact consumer electronics
======================================

For Immediate Release
THURSDAY, FEB. 15, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

PHOTOS AVAILABLE

CAMBRIDGE, Mass.--Advances in digital electronic circuits have 
prompted the boost in functions and ever- smaller size of such 
popular consumer goods as digital cameras, MP3 players and digital 
televisions. But the same cannot be said of the older analog circuits 
in the same devices, which process natural sights and sounds in the 
real world. Because analog circuits haven't enjoyed a similar rate of 
progress, they are draining power and causing other bottlenecks in 
improved consumer electronic devices.

Now MIT engineers have devised new analog circuits they hope will 
change that. Their work was discussed this week at the International 
Solid State Circuits Conference (ISSCC) in San Francisco Feb. 11-15.

"During the past several decades engineers have focused on allowing 
signals to be processed and stored in digital forms," said Hae-Seung 
Lee, a professor in MIT's Microsystems Technology Laboratories (MTL) 
and the Department of Electrical Engineering and Computer Science 
(EECS). "But most real-world signals are analog signals, so analog 
circuits are an essential part of most electronic systems."

Analog circuits are used to amplify, process and filter analog 
signals and convert them to digital signals, or vice versa, so the 
real world and electronic devices can talk to each other. Analog 
signals are continuous and they vary in size, whereas digital signals 
have specific or discrete values.

The reason the two different types of electronic signal circuits did 
not advance at the same pace, Lee said, is because they are very 
different. Digital circuits can be decreased in size more easily, for 
example, by using the popular complementary metal oxide semiconductor 
(CMOS) technology. And much of the design and performance enhancement 
can actually be done by computer software rather than by a human. 
That's not the case with analog circuits, which Lee said require 
clever designs by humans to be improved because of their variable 
nature.

"There is a lot of room for innovation in the human design," he said. 
"The importance of analog circuits is growing in light of the digital 
improvements, so engineers can make a difference in products by 
working on them." Currently, analog circuits are rather expensive and 
they consume a disproportionate amount of power compared with digital 
circuits.

Another blow to analog circuits is that the advancements in 
fabrication (manufacturing) technology to improve digital circuits 
have had a negative impact on them. Traditionally, many conventional 
analog circuits have relied upon devices known as operational 
amplifiers. Two negative side effects that advanced fabrication 
technologies have had on operational amplifier-based analog circuits 
are that when used in consumer or other devices, they have reduced 
the range of the analog signal and decreased the device's gain. To 
compensate for these shortcomings, analog circuits must consume much 
more power, thus draining precious energy from batteries.

In addition, it still is not clear whether traditional operational 
amplifier-based circuits can be applied to emerging technologies such 
as carbon nanotube/nanowire devices and molecular devices.

Lee's research group, in collaboration with Professor Charles 
Sodini's group in MIT's MTL and EECS, recently demonstrated a new 
class of analog circuits that Lee said eliminates operational 
amplifiers while maintaining virtually all benefits of operational 
amplifier-based circuits. These new comparator-based switched 
capacitor (CBSC) circuits handle voltage differently than 
conventional analog ones, resulting in greater power efficiency.

"The new work coming out of MIT offers the intriguing possibility of 
eliminating operational amplifiers by proposing an architecture that 
relies on circuit blocks that are much more readily implemented on 
supply voltages of 1 volt or less," said Dave Robertson, high-speed 
converter product line director at Analog Devices Inc. in Norwood, 
Mass., and data converter subcommittee chair at ISSCC.

Lee said CBSC may enable high-performance analog circuits in emerging 
technologies because it would be easier to implement comparators than 
operational amplifiers in these technologies.

The first prototype MIT CBSC was demonstrated in an analog-to-digital 
converter and presented at 2006 ISSCC. The second prototype, an 
8-bit, 200 MHz analog-to-digital converter, was presented at the 
conference this week.

Other key members of the research team are EECS graduate students 
John Fiorenza and Todd Sepke, who were involved in the work presented 
in 2006; EECS graduate student Lane Brooks, who worked on the current 
prototype; and Peter Holloway of National Semiconductor Corp.

The research leading to the 2006 ISSCC paper was funded by 
Microelectronics Advanced Research Corp. The research leading to the 
paper presented this week was funded by the MIT Center for Integrated 
Circuits and Systems and a National Defense Science and Engineering 
Graduate Fellowship.

--END--