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YLi.12
YLi.12
Visitor II
February 17, 2023
Solved

STM32L476 OPAMP CMRR Measurement methods

Currently doing academic research.

There are few descriptions in the specification, how to measure CMRR?0693W00000aH3ckQAC.png

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FBLBest answer
ST Technical Moderator
February 22, 2023

Hello @Community member​ 

CMRR is a basic electronic measurement and calculated as the ratio of the differential gain to the common-mode gain. You may refer to AN4586 as an example of an implementation to highlight the importance of having very accurate resistors.

Hope this could be an enhancement to guide you on how to calculate CMRR.

To give better visibility on the answered topics, please click on "Best answer" on the reply which solved your issue or answered your question.Best regards,FBL
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2 replies

FBLBest answer
ST Technical Moderator
February 22, 2023

Hello @Community member​ 

CMRR is a basic electronic measurement and calculated as the ratio of the differential gain to the common-mode gain. You may refer to AN4586 as an example of an implementation to highlight the importance of having very accurate resistors.

Hope this could be an enhancement to guide you on how to calculate CMRR.

To give better visibility on the answered topics, please click on "Best answer" on the reply which solved your issue or answered your question.Best regards,FBL
LCE
LCE
Principal III
February 22, 2023

The most simple way:

  • connect the signal output of a single-ended source to both differential inputs
  • connect the ground of the source to the same ground that the amp-under-test refers to
  • measure amp output, compare to input

Edit: careful, do not connect any signal generator directly to the controller!

In case of testing a "VCC"-supplied device, it's safest to use the output a single-supply-RRIO-opamp which is also supplied with VCC as a signal source

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