OPA2991: Common mode testing circuit

Hi Archie,

ArTzy said:

what kind of test circuit is TI using for their Input offset voltage measurements depending on the Common mode voltage of the Op amp.

The image below is twi standard Vos test methods in ATE implementation. There are other variations, such as the one presented above. By toggling the relay switches, one circuit is capable to measure different op amp DUT parameters during ATE screen tests.  

I recently replied similar question, see the links below. 

https://www.edn.com/the-basics-of-testing-op-amps-part-3-configurable-circuit-tests-op-amps/  

https://www.edn.com/the-basics-of-testing-op-amps-part-4testing-op-amps-requires-stable-test-loops/

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/207116/how-to-test-an-op-amp-particularly-the-output-voltage-swing-using-servo-loop-test-method-for-work-bench-and-ate-set-up

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1454930/opa187-the-loop-test-of-the-dual---operational---amplifier-is-abnormal/5581636?tisearch=e2e-sitesearch&keymatch=servo%20test%20opa187#5581636

ArTzy said:

Then to get the Input offset voltage I would have to subtract the set Vcm from the output.

In difference amplifier topology, the Vout = Gain*(Vin+ - Vin-), so the Vcm will be subtracted from the difference amplifier by design, and it does not enter the transfer function. However, Vos may be affected slightly by Vcm variation, but this is typically plotted and presented in the datasheet.

If you have other questions, please let us know. 

Best,

Raymond