Moore's Law: a mixed-signal perspective

April 20, 2015 //By Steve Taranovich
Moore's Law: a mixed-signal perspective
Steve Taranovich, editor of EE Times' Planet Analog website, interviews Dave Robertson, product line director with Analog Devices Inc. and a member of the technical program committee for the International Solid State Circuit Conference (ISSCC) from 2000 to 2008. Taranovich asked Robertson about Moore's Law, as it reached its 50th anniversary on April 19, 2015.

Steve Taranovich: The 50th anniversary of Moore’s Law coincides with Analog Devices’ 50th anniversary. How has the industry’s singular focus on Moore's law impacted analog innovation?

Dave Robertson: Gordon Moore’s observation was about the number of transistors on a chip doubling at a certain pace, and focused on integration, scale, and density. By the time “Moore’s Law” celebrated its 25th birthday in 1990, it had also come to represent the driving pace of cost reduction, increased processing speed, increased performance, and shrinking size that has enabled the electronics revolution to migrate from industrial applications to business applications to consumer applications. Today, this continuous exponential improvement is taken for granted as an economic entitlement.

For example, consider the way you think about the newest electronic device splashed across the headlines. If it is too expensive today, you can count on it following a lower price curve in six months, 12 months, and 24 months. In the digital world, scaling drives everything, or at least, so it has seemed. While scaling is important in the analog world, it is not always the dominant consideration. In digital signal processing, for example, we are dealing with the abstractions of binary 1s and 0s. We can scale capacitance, resistance, and supply voltages downward because there are no absolutes. This is true at least until noise or quantum effects start to impact our ability to distinguish a 1 from a 0. In analog electronics, on the other hand, we have to deal with absolutes of voltage, charge, current, capacitance and resistance. Information from real sensors has to be recovered, real loads have to be driven – be that a motor, a relay, or an antenna. Non-scalable impedances may constrain how much we can “shrink” a circuit. Limitations in electromagnetic propagation may constrain what frequencies a radio can work in. The FM radio band, for example, has not moved in frequency with Moore’s Law. Shrinking dimensions mean shrinking supply voltages, and for analog circuits, with their associated signal-to-noise ratio (SNR) limits, it can be shown that lowering the supply voltage may actually increase the power consumption of analog amplification stages.

Still, scaling, density, and integration have had an enormous impact on analog innovation. Even in high-performance mixed-signal circuits, most of the circuitry is not limited by SNR, so scaled technologies on lower supply voltages have been able to deliver performance and power efficiency improvements – though admittedly not at the pace of digital advancements [ref. 1]. Furthermore, the integration afforded by lithography scaling and yield improvements has been exploited in the analog and mixed-signal domains. We now have full audio systems-on-a-chip, single-chip cell phones, ICs that integrate the sensor, signal conditioning, data conversion, and digital communication functions all in a power-efficient solution. To realize these great analog advances, “Moore’s Law” type scaling was necessary, but not sufficient by itself since numerous other innovations also were required.

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