I was looking closely at the data sheet of a new op-amp recently (don't ask why). Like most good op-amp data sheets, it had lots of performance curves and charts. The vendor name and model number are not relevant here. The entire data sheet for this functionally simple and ubiquitous analog building block ran about 16 pages, and pages 4-11 had between eight and 12 such figures each, so we're talking about 80 figures here. (The other pages had some up-front basics, pin-out information, absolute maximum numbers, and package/ordering information.)
The curves in the figures showed combinations of typical, minimum, and maximum performance for many static and dynamic parameters versus all sorts of operating conditions, depending on the parameter of interest. For some, min/max is actually hard to measure, so typical performance is all the vendor can show. These parameters included temperature extremes, voltage rails, signal levels, bias current, offset voltage, common-mode performance, drive levels, output loading, transient response… the list goes on. You get the picture.
To the non-analog enthusiast, this may seem like too much of a good thing, given the huge number of op-amps already available and the never-ending flow of new ones. (See: Do We Really Need Yet Another Op-Amp?.) Considering so many op-amps, each with so many curves, can give you a selection headache. Soon you'll feel like the fellow in this mid-20th-century painting by Dadaist Max Ernst: Young Man Intrigued by the Flight of a Non-Euclidean Fly.
It's easy to think vendors are overwhelming the users with needless data, simply because it's possible to generate so many a -versus-b graphs with automated test equipment and the software to drive it. But in my experience, that isn't the case at all. Most engineers looking at the universe of op-amps (or other analog building blocks) have a set of first-tier performance issues to consider as they try to drill down and select a few devices for extra consideration.
Then comes the real challenge of knowing and checking the second- and third-tier factors that are critical to your specific application. Many of those characteristic curves are not relevant to your situation, but some certainly will be. Knowing which ones you need to study — that's one of the marks of a seasoned analog engineer.
Have you ever been overwhelmed by the mass of performance specs and curves on the data sheet of a basic part such as an op-amp? Conversely, is there a spec rarely called out in detail that you have to ask about — knowing that a verbal answer from the vendor does not provide the same assurance as seeing it in black and white on the formal data sheet?
- Do We Really Need Yet Another Op-Amp?
- Improving the CMRR of Instrumentation Amplifiers
- Signal Chain Basics #78: How to Avoid Common-Mode Limitations on Instrumentation Amplifiers
- Low-Offset, Low-Noise, Wide-Bandwidth Chopper
- Do We Need Any New Op-Amps?
- New Instrumentation Amplifier Makes Sensing Easy