ISSCC - MIT improves analogue circuit for consumer devices

Future models of consumer goods, from digital cameras to MP3 players, could take a leap forward with a new type of analogue circuit demonstrated at a trade show by researchers from the Massachusetts Institute of Technology (MIT).

The MIT team showed a comparator-based switched capacitor (CBSC) circuit, which could be manufactured with smaller size and better power efficiency than traditional analogue circuits using operational amplifiers. The team had presented a rougher version in 2006, and improved on the design by unveiling an 8-bit, 200MHz analoue-to-digital converter at the International Solid State Circuits Conference (ISSCC) in San Francisco.

The advance could help analogue technology catch up to the tremendous pace of improvement in digital circuits, which have shrunk in recent years thanks to software-aided design tools and to manufacturing processes such as complementary metal oxide semiconductor (CMOS) technology, one of the MIT professors involved in the work, Hae-Seung Lee, said.

Despite those enormous improvement in digital circuits, electronic devices will always need analogue circuits too, because the sights and sounds in the world around us exist as variable analogue data, not discrete digital bits.

Analogue circuits translated between those two languages by amplifying, processing, and filtering natural data and then converting it to digital signals, Lee said.

From playing songs on iPods to sending and receiving voices on cell phones, analogue circuits are part of most consumer devices.

"Analogue circuits sit on PC boards; when you put a disc in a CD-ROM drive to play music, the music is encoded in digital format, but what you're hearing is analogue. That's a digital-to-analogue converter doing that," Lee said.

Engineers could use the new CBSC circuit as a more efficient tool to filter and modulate analogue data, leading to less expensive, longer-lasting devices.

"Current analog circuits consume a disproportionate amount of power, which really drains the batteries. We think we can reduce the power consumption of analogue circuits by at least an order of magnitude," he said.

In addition to saving space and power, the CBSC circuits could also work with emerging technologies like carbon nanotube or nanowire and molecular devices, a looming challenge for conventional analogue circuits. And since they work with CMOS fabrication techniques, the new circuits are immediately applicable to those challenges.

Still, products using the new circuits will probably not reach store shelves for several years.

"We have demonstrated a proof of concept, so we know the technology is good. But there are still some practical questions to answer, like 'Is it robust enough to work in consumer electronics?' So it will be a couple of years before we see it in stores," Lee said.

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