Will the real Vos please stand up?

RE: Will the real Vos please stand up?

Tim Green1 — Mon, 08 Sep 2014 17:56:04 GMT

You are correct that the output of the op map will display a 9.12mV offset for a gain of 10 with a 912uV input offset voltage. The only way I know of is to use a lower input offset voltage op amp or to trim the offset out with a potentiometer voltage summed into the input. The problem with nulling the input offset voltage with a potentiometer is that over temperature and power supply fluctuations the initial offset you trim will change. Consider an Auto-Zero or Chopper op amp such as OPA333.....

RE: Will the real Vos please stand up?

Yasin J.I.1 — Mon, 01 Sep 2014 16:20:42 GMT

If the offset voltage is 912uV and the if the gain is 10 then whether the output of the op-amp will have a Dc offset of 9.12mV? How can I educe this offset voltage is there any method that can reduce the offset voltage other than trim pot offset correction correction

RE: Will the real Vos please stand up?

Tim Green1 — Sat, 14 Sep 2013 02:58:28 GMT

Please see link below to zip files that contain all of the old Burr-Brown Application Notes we are aware of. Happy Analog-ing!

e2e.ti.com/.../2573.burr-brown-application-notes.aspx

RE: Will the real Vos please stand up?

William Nurnberger — Thu, 12 Sep 2013 22:42:28 GMT

Tim,

You mentioned in one of your replies to a comment that the Burr-Brown App Notes were available in the pdf format. How might I access these files?

Thanks,

Bill Nurnberger

RE: Will the real Vos please stand up?

Tim Green1 — Mon, 26 Aug 2013 17:19:18 GMT

Howard:

You are so right regarding the Burr-Brown App notes. Most of op amp theory has not changed in the last 30 years (maybe longer but that's as far back as I can personally go for recollection). Parts have gotten smaller, features enhanced and cost reduced. We do have a collection of all of the Burr-Brown app notes in pdf format if you ever need one. We are also working on continuous expansion of the TI Precision Designs landing page to offer all relevant collateral such as the old BB App Notes. It is surprising to me that when I run into a subject I do not know in analog how little useful help I find on the web. Like most engineers today, time is precious and I just want a quick and exact definition by example so I can figure stuff out and move on. Much of the old literature has not been scanned or readily avaialble on analog. I guess we will just have to re-invent the wheel and hope it will last for a while. Thanks for your comments and let us know how we can help you succeed in your applications.

RE: Will the real Vos please stand up?

Howard Evans16256 — Sun, 25 Aug 2013 15:17:52 GMT

Hmmm. Looks like we may need to educate a whole new generation of "analog" design engineers! Burr-Brown (now absorbed by TI) published in the 1970s a slew of application notes on op-amp design, as did other manufacturers. The op-amps are better today, but the theory of design still holds true.

RE: Will the real Vos please stand up?

Tim Green1 — Mon, 12 Aug 2013 18:12:44 GMT

Ken:

You are absolutely right. Input bias and offset currents across input and feedback resistors will add additional error. Input noise times gain will also affect accuracy at the output. Looks like we need to put together a total op amp error budget white paper. I have seen such attempts in the past but nothing I can point to that is an easy definition by example to follow. Too many times customers are misguided by that Initial Vos number for DC. Thanks for the comment.

RE: Will the real Vos please stand up?

Ken Dillinger — Mon, 12 Aug 2013 17:59:27 GMT

I presume this is meant for static errors, so it would be nice to see input bias current, input bias offset, and gain error play a role.

What about noise density too!

It is only 3 terminals, what could possibly go wrong? Amiright?

-Ken