The digital circuits keep shrinking while the analog circuit designs remain relatively the same. These larger analog designs can drain more power and cause increased real estate needs, until now, according to MIT engineers. Now MIT engineers have devised new analog circuits they hope will change that. Their work was discussed at the International Solid State Circuits Conference (ISSCC) in San Francisco Feb. 11-15.
The focus of most design engineers has been mostly on processing and storing signals in digital form even though the real world is mostly analog. This makes analog signals an essential part of any electronic design. They 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.
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 typically require clever designs to be improved.
Analog designs need to keep improving to keep pace with digital designs. Presently, analog circuits are rather expensive and they consume a disproportionate amount of power compared with digital circuits.
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.
Professor Hae-Seung Lee, of MIT's Microsystems Technology Laboratories (MTL) and the Department of Electrical Engineering and Computer Science (EECS) 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.
Eliminating op amps and replacing them with circuit blocks may enable designs that are implemented on supply voltages of 1 volt or less. Additionally, according to Lee, the comparator-based switched capacitors may enable high-performance analog circuits in emerging technologies because it would be easier to implement comparators than op amps in these technologies.
The first prototype MIT CBSC was demonstrated in an analog-to-digital converter and presented at the 2006 ISSCC. The second prototype, an 8-bit, 200 MHz analog-to-digital converter, was presented at the conference this month at the 2007 conference.
More information can be found at mit.edu/newsoffice/2007/circuit.html