Selecting op amps

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I agree with Paul in his article where he states that a five-pin device must be simple. Think about it. Two of the pins are reserved for the power supplies. As you can read from his article and the others mentioned in this blog, slugging through the various specifications can be overwhelming. That is, unless you start to think about why you need the amplifier and what your system characteristics are. For instance, if you are using an amplifier to filter higher frequency noise out of the signal path, you will select an amplifier that has very low input bias current (so that the resistors around the amplifier do not generate offset errors) and a bandwidth that is at least 100x higher than your filter corner frequency. These are only two specifications out of (usually) 40 or 50 specifications. You can reduce most of the requirements for amplifiers in one specific application in this manner. Not bad. After you narrow your list of amplifiers down with that exercise, you will add the criteria of power supply, input, and output swing limitations. Even further down the list would be the specifications that receive a lot of publicity; noise and offset voltage. Noise is very low on the list because your noise gain is probably 1V/V or 2V/V. Multiply that times the total RTI noise (also band-limit it with your filter cut-off frequency), and you will see that you won?t have to worry about it. Offset voltage is also low on the list because of the low gain. Oops ? I did leave a very important specification off my list ? $$. But the long and short of this discussion is that you have to look at what is coming into your amplifier circuit (voltages, noise, bandwidth), what you want the amplifier to do (gain, isolate, sum, take the difference, integrate), and what you want the output to look like to the next stage (stable, linear, low-impedance). And at the end of your design process, you do need to exercise due diligence and review all of the specifications to make sure they fit into your circuit.

It would be nice if there were a centralized location for finding components, or if Google could say "look for an op-amp" with these specs across all vendors.

I think much to the chagrin of the chip makers, designers find certain op amps with certain characteristics they like and trust and then design those into products until something (much) better comes along. This is just in my limited experience, but I can almost guarantee that the ones I know who stick with what they know do so at least partially because of the pain involved in finding a new favorite. Thanks for the links Paul!