I had a conversation with principals at Cadmos--actually, a difference of opinion--as to whether their soon-to-be-announced analysis tool was geared for "mixed-signal" ICs or "mixed-technology" ICs. Cadmos wants to say "mixed-signal," because that's where the market is. But in its emphasis on the substrate noise coupling between what it calls "high-speed digital and high-precision analog circuits," the tool is really geared toward "mixed technology." That's a much smaller market, right? Wrong, insisted Cadmos CEO Charlie Huang; it's a big market. But it's "too small to track," I thought I heard EDA analyst Gary Smith say.(See last week's Scarlet A on analog EDA.) Whose definition of reality is operative here?
As one who sees applications of mixed-signal technology everywhere--in communications, multimedia, data storage, automotive and consumer electronics--I'm still inclined to see "mixed signal" as a much abused term. Sure, the Semiconductor Industries Association (SIA) claims 67 percent of the world's ICs will embody some form of mixed-signal processing within the next five years. And I have no argument with that. But that does NOT create a big market for IC substrate noise analyzers like Snaketech's or Cadmos'.
As EE Times' editor of record on analog and mixed-signal technology, managing editor of the monthly Signals special section on signal processing and chair of the yearly Analog and Mixed-Signal Applications Conference, my reportage on mixed-signal companies and their activities has been pretty extensive. Yet, a year into that job I was confronted by Ed Ritter, an applications engineer at Linear Technology Corp. "I don't see too much analog in your stinking publication," said Ritter, always a gentleman. Agreed, there are not too many days when standard linear components like op amps, data converters or voltage regulators can make the front page of EE Times. Still, the view of Linear Technology engineering chief Bob Dobkin that voltage-regulation problems would doom a lot of Taiwan-made PC motherboards to early failure DID make headlines there.
What we obviously must do is make sure we carefully differentiate among the terms "analog," "mixed signal," "mixed analog-digital" (which is NOT quite the same as "mixed signal") and "mixed technology." I now believe that mixed signal and mixed analog-digital do NOT necessarily refer to the same things. The mixed-signal label has been attached, sometimes incorrectly, to strictly analog circuits. It probably doesn't help to know that analog and mixed signal (like the notion of digital signal processing) refer to a TECHNOLOGY and NOT A MARKET. It doesn't help to know that companies will say they are "a mixed-signal company" as a shorthand for saying they serve multiple markets, or that marketers abusing the term are in no mood to split hairs if the "mixed-signal" moniker helps their startup venture get funding or raises the stock price of their public offering.
Let me take a stab at it: MIXED-SIGNAL circuits are those that perform both analog and digital signal-processing functions. As I suggested last week, mixed-signal circuits are typically digital CMOS ICs, in which logic gates are put in the service of an analog function. MPEG compressors, Dolby Digital decoders, serial data formatters, Ethernet MACs (media access controllers)--even many of the processors shown at the Embedded Systems Conference--are all legitimately mixed-signal devices, even though there is no analog component on-chip. Even though the data enters and leaves in digital format, even though a separate data-conversion and signal-conditioning element will interface with the analog world, these are devices that effectively DO SOMETHING to an analog signal. That's why my coverage has been so broad; why Planet A turns out to be a rich place to live.
"Mixed-signal" is not synonymous with MIXED ANALOG-DIGITAL or mixed-technology, though a Venn diagram would put mixed analog-digital circuitry within the territory covered by mixed-signal circuits. Mixed analog-digital refers to circuits that not only perform analog and digital signal processing, but also have clearly identifiable sections devoted to analog and digital activity. These would include modems and Ethernet PHYs, disk drive read channels, computer graphics ICs (with built-in RAMDACs), the analog front ends for digital subscriber lines and new-generation RF ICs. These devices are not just large systems on chip (SoCs). Mixed analog-digital circuits could include microprocessor supervisor circuits, in which a simple trip comparator detects a drooping supply voltage, digitally shuts down the processor and sequences its return to normal operation. As a rule for mixed analog-digital, you have digital coming into (or going out of) one part of the circuit, and you have analog coming out of (or going into) the opposite end.
Be aware: ICs with mixed analog-digital elements are a much smaller proportion of the mixed-signal IC world, nowhere near the 67 percent forecast by the SIA. My seat-of-the-pants estimate: mixed analog-digital ICs represent maybe one-third of mixed-signal ICs and no more than 10 to 15 percent of the semiconductor industry as a whole.
An even smaller proportion of that is what you'd call MIXED TECHNOLOGY. An easy example to look at is BiCMOS, in which the analog functions (typically amplification) are performed by bipolar transistors on a digital CMOS substrate. A number of companies, like STMicroelectronics, are able to build lateral DMOS power transistors onto the BiCMOS substrate to creat a power driver/controller (like a disk drive motor control servo) on a single chip. But there are all-CMOS circuits that represent mixed-technology choices. Remember, if you are building digital logic, all the CMOS transistors have to do is distinguish data ones and zeroes, highs and lows. For block integration, these transistors must be as small as you can make them, 0.18, 0.15, 0.12 microns (angstrom units within the next few generations), but they can be pretty sloppy transistors. If they generate logical ones and zeroes, all they need to do is slam on and off. They generate a considerable amount of switching noise in the process.
Linear CMOS, in contrast, generally requires the transistors to do something different. In amplifier circuits, they must follow a linear ramp between off and on states. Since transistors are switches and not amplifiers, the amplification function generally requires the transistors to be biased with a small amount of current so they will never be fully on or fully turned off, but suspended in some linear region in between. Most transistor amplifiers are built this way, but seldom on the same chip with digital circuits. I'm sorry to rain on Cadmos' parade, but data converters (even disk drive read channels) are built on an awful lot of clacking CMOS switches. But the noise-sensitive signal conditioning circuitry is typically on another chip.
Hence, ANALOG includes a significant amount of territory on the Venn diagram which is neither mixed signal nor mixed analog-digital nor mixed technology. It refers to a very specific technology and skill set applied to amplifiers--both small-signal conditioners and high-current drivers--and linear voltage regulators (the error amp that regulates the base drive on a series pass transistor). This is the special skill set of the analog gurus at Linear Technology, Maxim, National Semiconductor, and the "Santa Clara Division" of Analog Devices (the old PMI). With its concentration on process variables and bias circuit techniques the analog-signal-conditioning world is a rich one, which Planet Analog and EE Times' Signals section will court and service with circuit-design articles and applications implementation tips. But as useful as these guys find a Cadmos, Snaketech or Barcelona tool, it is a relatively small proportion of the so-called mixed-signal design world.
This does not mean that this skill set and product group is insignificant in the market. Analog amplifier skills form the basis for RF antenna drivers and receivers and, driven by cellular network expansion and home and office wireless networking (the entire Bluetooth mania), this market is going to explode. In their efforts to reduce the size, cost and power consumption of RF transceivers in handheld portable devices (for example, PDAs that talk to the Internet) manufacturers will harness every integration trick in the book. That means mixed signal, mixed analog-digital, mixed technology, and--yes!--straight analog. It is on these future-looking applications that the fortunes of analog IC makers (Maxim already has a substantial investment in this area) and EDA tool developers like Cadmos and Xpedion will rise.