Wednesday, August 01, 2007

Avoid Common Problems When Designing Amplifier Circuits

Modern op amps and in-amps provide great benefits to the designer, and a great many clever, useful, and tempting circuit applications have been published. But all too often, in one’s haste to assemble a circuit, some very basic issues are overlooked, leading to the circuit not functioning as expected—or perhaps at all. This article will discuss a few of the most common application problems and suggest practical solutions.

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3 Comments:

At 4:21 AM, Anonymous John Davies said...

Excellent article - a set of concise explanations that lives up to its name. I shall stuff it into my copy of The Art of Electronics! The final section on decoupling single-supply op-amps is particularly useful.

Only one complaint: I had trouble printing it - the pdf upset my version of Acrobat.

 
At 2:36 AM, Anonymous Matthias said...

Excellent article, I think. But: In figures 5 and 6 there are resistors providing a ground return path for input bias currents. In figures 12 and 13 not at all. What about bias currents charging the C1s in 12 and 13?

 
At 4:25 PM, Anonymous Chuck Kitchin said...

Dear Matthias: There actually is a DC return path for circuits 12 and 13. It is through the Ra, Rb voltage divider. Since an op-amp will do whatever it can do (with-in the limits of the amplifier) to keep the - input (summing) junction voltage equal to the + input voltage, the - input is also satisfied.

Bottom line: if the + input is maintained at Vs/2so also will the - input.

I hope this makes sense.

 

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