These days few people can say "system-on-a-chip" without also saying, "mixed-signal." A lot of these ASSPs are engineering feats and incredible moneymakers. But the analog lobby, which is pretty strong these days, is saying, "Never mind SoC integration; tell us more about specs."

In principle, mixed-signal ICs are devices with clearly identifiable analog and digital circuit blocks-you could call them "mixed analog-digital." But in practice, mixed-signal has become a buzz word for all sorts of processors, devices that once upon a time had analog signals but are now, for all practical purposes, big digital logic chips fashioned in TSMC CMOS.

Don't misunderstand: These CMOS devices are the workhorses of traditional analog applications like communications, multimedia, disk-drive read channels. It's just that their base technology-DSP-is far removed from the voltages and currents the hardcore analog community likes to manipulate.

The issues for analog designers are far more granular, much closer to the physics of the device. You want precision and speed, without a lot of noise or power consumption. It's difficult juggling all these specs without tweaking processes and circuitry. But unless they are working in BiCMOS, the mixed-signal designers don't get that close to bias currents and threshold voltages. Noise is something that'll cost 20,000 to 50,000 logic gates to filter, they figure, rather than a process tweak.

Though sometimes little more than a respin of a 10-year-old design, op amps, data converters and voltage regulators represent an incredible amount of engineering. Think about this: What kind of process builds a precision op amp with a 100-microvolt input offset and input bias current of 10 nanoamps? What process builds a 350-MHz amplifier that uses a little over 4 mA of supply current? Or a 100-mA low-dropout regulator with 40 microvolts of rms noise? Who engineered a 24-bit A/D converter that consumes only 200 microamps?

I hope to write more on this stuff in my columns here. After all, I'm the guy who moved to California-changed my whole life around-20 years ago because I thought 3 nV per square route of hertz was a good spec.