Timeline for Common Mode Rejection Ratio of op-amp
Current License: CC BY-SA 3.0
11 events
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| May 8, 2013 at 17:45 | comment | added | Thanos |
@OliGlaser: How are the formulas of the two gains are calculated? Is there any refference book(s) which makes the calculation? I've seen those formulas in The art of electronics by Paul Horowitz and Winfield Hill but they don't prove them...
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| Oct 12, 2012 at 3:59 | comment | added | Oli Glaser | The CMMR is a positive number, so it is diff gain divided by common mode gain. Ideally the differential gain for an opamp is infinite (large) and the common mode gain is zero (small) I suggest you have a read of a decent opamp book - "Opamps for Everyone" is a pretty good free one from TI. | |
| Oct 12, 2012 at 2:24 | comment | added | nee | Differential gain has to to large and common mode gain has to to small, is it? How does the differential gain related to closed-loop gain since they seem like have the gain formula where equals to Vout/ (V+-V-). Please help to clarify. Thanks. | |
| Oct 12, 2012 at 2:09 | comment | added | nee | Thanks. One more question to ask. CMRR is the ratio of differential gain to common mode gain or the ratio of common mode gain to differential gain ? As I have gone through these 2 definition before, and I confused which one is correct ? | |
| Oct 11, 2012 at 16:00 | comment | added | Oli Glaser | @nee - for an IC opamp, you just have to go from the datasheet value, the CMRR is determined by the integrated circuit design (the above circuit is a very basic example of an input section) | |
| Oct 11, 2012 at 15:35 | comment | added | Oli Glaser | @nee - I added some calculations, hope this helps. The main factor is the Re/Rtail ratio. | |
| Oct 11, 2012 at 15:33 | history | edited | Oli Glaser | CC BY-SA 3.0 |
Added calculations
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| Oct 11, 2012 at 14:49 | history | edited | Oli Glaser | CC BY-SA 3.0 |
Corrected calculations
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| Oct 11, 2012 at 6:57 | comment | added | nee | Without using the simulation tools, how can I know the common-mode gain ? Is it can be calculated from the input resistor value on both inverting and non-inverting input ? | |
| Oct 10, 2012 at 9:23 | history | edited | Oli Glaser | CC BY-SA 3.0 |
added 262 characters in body
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| Oct 10, 2012 at 9:02 | history | answered | Oli Glaser | CC BY-SA 3.0 |