I'm not talking just about I/O or interconnect analysis. The big comeback may be in the very place where analog has been most dramatically routed by digital: signal processing. DSPs have been incredibly popular for years now. They have in effect promised to turn a nasty analog design problem into a combination of simple digital interfacing and simple programming. But the promises may not have been entirely realistic, and now we are seeing a backlash.

To begin with, DSP could never banish analog entirely. It could only drive it back behind the barrier walls of A/D and D/A converters. Analog was still out there. In addition, in turned out that the programming was nontrivial for a lot of applications. And in some cases removing the artifacts of discrete-time processing proved almost as interesting an analog design challenge as the original processing task.

So we seem to be witnessing some of these signal-processing tasks going back to the analog domain. One could point in particular to signal conditioning for communications and feedback control, two closely related tasks. Often, it appears, not only does implementing a transfer function in analog require fewer components and less energy, but it can be easier to debug and less expensive, and it may perform better.

Set aside digital radio, where frequency-domain digital techniques make possible modulation schemes that may not be implementable in analog. I'm thinking more along the lines of audio frequency through the low-megahertz range-the kinds of things typically done with a microcontroller and a modest DSP chip.

One interesting bit of evidence along those lines is the emergence of field-programmable analog devices. Lattice Semiconductor has a line of field-configurable continuous-time analog blocks aimed at various applications. And Cypress Microsystems, a subsidiary of Cypress Semiconductor, is offering configurable chips that bundle a microcon-troller, programmable-logic blocks, configurable continuous analog blocks and configurable switched-capacitor analog blocks on a single die. Such a device could offer functionality and power savings for control applications that would be very interesting in comparison with a DSP-based approach.