[Pease Porridge]
What's All This Analog Engineering Stuff, Anyhow?
Don't get dismayed by the rise of digital technologies. Analog engineers are still critical members of any design team.
For many years, aficionados of digital circuits and computers have bragged that their rapid advances will leave all analog circuits lying in the dust. The analog business is shrinking, at least compared to the success of digital computers. Moore’s law has made sure of that for many years. The tiny transistors are smaller and faster than ever, even if they can’t stand off 5 V (Fig. 1).
The efforts of a team of digital men who engineered and fit together a few hundred transistors has given way to automated schemes to assemble many thousands, many millions, and now billions of transistors. Boy, every circuit must cost millions of bucks! That means every microprocessor or systemon- a-chip (SoC) must be very profitable! Right?
Wrong. It ignores the fact that several thousand digital transistors may now sell for less than a penny. Digital IC makers must give away a million transistors to make a few bucks. This isn’t necessarily true for analog circuits. A couple dozen years ago, we handed out some license plate frames in Silicon Valley that said “One good op amp is worth 1000 microprocessors.” We still believe that!
A digital computer can do some things by computing the facts it is told. But to perform a useful function, it often needs a good bit of analog information. It needs to get information from the world or from its user. It also needs to get this data from sensors, where the information is channeled through analog preamps and/or filters. Usually, analog engineers have to engineer these channels. A brute-force approach generally doesn’t work.
Some sensors put out a signal that can be acquired directly by a fairly simple analog-to-digital converter (ADC) that interfaces to the sensor. But, typically, a high-performance ADC needs an anti-aliasing filter to prevent the sampling from turning high-frequency noises and spikes into low-frequency “artifacts.”
What kind of filter is needed, and how many dB of attenuation are needed at the sampling frequency? The person who designs that filter has to complete the filter engineering in the analog domain. You can’t do it with digital signal processing (DSP). You must have a good analog filter before you get the information converted into signals that can be processed by DSP.
Now, in theory, it sounds like an ADC or digitalto- analog converter (DAC) will be designed by one analog group and one digital group that sit down, shake hands across a table, and figure out how to get their circuits to do a handshake, too (Fig. 2). But in practice, most high-performance ADCs are designed by analog engineers. They have to figure out how all of the signals and waveforms will get along without causing trouble.
Yes, they do have to handle some digital signals, but that’s not too hard. We analog engineers know how to handle “digital” signals without excessive bounce or overshoot! We know how to design and lay out transmission lines, terminated as needed.
Sure, some ADCs are integrated onto the main SoC, but these are mostly the low-performance (slow or low-resolution) ones. High-performance ones are usually done off-chip. They are often more costeffective or time-effective.
Thus, analog circuits are also needed alongside modern microprocessors. Engineers used to try to add a lot of analog functions into the processor. But smaller feature sizes, faster logic, and low operating voltages have forced DIS-integration because a decent audio amplifier, low-noise preamp, bandgap reference, high-resolution ADC, or anti-aliassing filter can’t be made (profitably or at all) on such a low-voltage chip.
So, these functions are often being added as external chips. They don’t hurt the yield, as they might if they’re integrated on the main chip. They don’t delay release of a system that is nearly finished. Mindless attempts at further integration have, in many cases, been replaced with disintegration.
There are still applications for digital computers, where most of the work is just computation. When the computing is all done, after a few hours, the computer spits out the answer: “42.” But these days, there’s often a lot of interaction between the user and the computer.
Please refresh the page if you have trouble reading this text.
Search Electronic Design
Email Newsletter
Sponsored By:
Electronic Design UPDATE provides readers with late-breaking news, opinions from industry experts, and timely technology stories. It's a unique opportunity to get your product message in front of engineers, engineering managers, and corporate managers while they're reading about critical information online.
Reprints
