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I want to understand common mode and differential mode noise more intuitively.

I have read this article. But I would like some analogy or experience with real circuits with some example to understand better.

Can someone please help. I have read answers in this forum too. But it didn't provide clarity. I would be able to understand the answers if it is in the more basic level which is why I am asking some analogy.

Please help. Thanks

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  • \$\begingroup\$ Can someone please provide an answer \$\endgroup\$ – Newbie Nov 8 '19 at 9:05
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    \$\begingroup\$ There are lots of technical articles on this topic. Search using key words like: "electrical noise filtering, common mode noise, differential mode noise". For one basic example assume a two wire input to a system, maybe similar to a two wire AC power line entering a device. Common mode noise is when the offending noise is on both lines, differential mode noise is when the noise is on one line. There are many other examples, do more searching. \$\endgroup\$ – Nedd Nov 8 '19 at 9:20
  • \$\begingroup\$ I have researched many articles and app notes. But I am not able to get clarity. And how does a differential noise, attenuated only by adding a cap between the lines? \$\endgroup\$ – Newbie Nov 8 '19 at 10:12
  • \$\begingroup\$ Do these common mode and differential mode noise affect only the power supply lines or does it also affect the signal lines as well? \$\endgroup\$ – Newbie Nov 9 '19 at 1:58
  • \$\begingroup\$ Since you included more details into your newer question today, I'm voting to close this question, as a duplicate of your newer one here: "How is the differential mode noise suppressed by adding a capacitor across the Lines". In future, please update and add details to the original question, instead of posting a new one which is the same, just with more details. Thanks. \$\endgroup\$ – SamGibson Nov 9 '19 at 13:15
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Consider this drawing of two circuits; the 2nd circuit has many intentional IMBALANCES. These imbalances degrade the DC CMR and the AC CMR.

Notice the first circuit has gain of 1.

Notice the 2nd circuit has gain of 1,000.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I am sorry. I am unable to understand this. I require some basic and fundamental answer. Could you please help \$\endgroup\$ – Newbie Nov 8 '19 at 15:07
  • \$\begingroup\$ the top circuit is completely balanced. The lower circuit has many im-balanced. For good CMRR, you must be balanced. \$\endgroup\$ – analogsystemsrf Nov 9 '19 at 15:37

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