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Improving Analog Circuits
A solution to heavy analog circuit power consumption
Hae-Seung Lee, professor, MIT Microsystems Technology Labs Laboratory Inc. -- Design News, June 3, 2007
Why is there a need for a new class of analog circuits?
There may be drawbacks down the road, but we have successfully demonstrated the proof of concept. We are researching these comparator-based circuits and zero-crossing-based circuits to push for higher performance. The prototypes we've demonstrated performed at a relatively modest rate — so now we're trying for high accuracy and high speed. We are also working on applying these concepts to different applications. Our prototypes are built for analog-to-digital converters, but they can also be applied to amplifiers, filters or delta sigma modulators. It is my hope that these technologies will enter the mainstream and provide longer battery life and smaller battery volume for portable electronic applications.
What other factors contribute to increased analog power consumption?
Analog circuits require large amounts of gain. Predominantly, you need gain in a circuit from an operational amplifier, or op-amp. These op-amps are necessary, but very difficult to build. They require anywhere from 10,000 to 100,000 in gain, but as device dimensions get smaller, the physical property dictates that the gain must get smaller and smaller. Building an amplifier with a large amount of gain becomes extremely difficult. So, you have to build a lot of circuitry around the amplifier to encourage the gain. These gain requirements and the smaller signal range that comes with scaling ultimately require more power consumption and keep analog from advancing at the same pace as digital.
How do your analog advances improve on the old circuits?
With our new class of analog circuits, power consumption will be a lot less. We have eliminated the necessity for op-amps. Instead, we can provide exactly the same functionality by using comparators or zero-crossing detectors. Comparators compare two voltages and decide which is bigger. The comparator gives out a digital output, based on two inputs. If the first input is bigger than the second, the output will be 1 and so on. A zero-crossing detector has one or two inputs. When there are two inputs, the detector determines the instant when one input crosses the other and changes the output from 1 to 0 or 0 to 1.
Have you encountered any drawbacks with these new circuit technologies?
There may be drawbacks down the road, but we have successfully demonstrated the proof of concept. We are researching these comparator-based circuits and zero-crossing-based circuits to push for higher performance. The prototypes we've demonstrated performed at a relatively modest rate — so now we're trying for high accuracy and high speed. We are also working on applying these concepts to different applications. Our prototypes are built for analog-to-digital converters, but they can also be applied to amplifiers, filters or delta sigma modulators. It is my hope that these technologies will enter the mainstream and provide longer battery life and smaller battery volume for portable electronic applications.
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