What are the conditions that the noise sources have, so that I can apply superposition principle to analyse the circuit having multiple noise sources?
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possible duplicate of How do I use superposition to solve a circuit? – The Photon Jul 22 '15 at 15:00
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You can use superposition to analyze noise response under exactly the same conditions as for any other type of sources. Therefore the answer to your question is the same as what's given in the previous linked question. – The Photon Jul 22 '15 at 15:02
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When multiple sources of noise are present, their contributions add in proportion to their noise powers, not the noise voltages. Uncorrelated noise adds by the sum of the individual noise powers. This is easy when working with power, but usually we work with voltages or currents, so we square the values. For example, given uncorrelated voltage noise sources e1, e2 ... en, the total noise, et, is given by the square root of the sum of the squares of the voltages.
John D
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I think the key word is "uncorrelated". So, I understand, If noise sources are correlated, this means they are not independent so I can't use superposition when noise sources are correlated. Am I right in this? – Aenid Jul 23 '15 at 05:44
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1No, if they are correlated then they will add just like an independent voltage source. It's only when they are uncorrelated that you add the squares of the noise voltages and take the square root. An example of uncorrelated noise would be resistor thermal noise. Correlated noise might be noise pickup from EMI. – John D Jul 23 '15 at 14:16