help to evaluate noise

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glias

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Hello all,
I have some questions about noise measurement on op amp...
consider that I'm in the broadband zone, so a white noise only is present, I measure the max voltage value on the scope. How can I deduce the rms value ? then if I could have the rms value, I can deduce the noise of my stage by multiply this value by 3 to cover 99.7% of cases (gaussian distribution)...
 

You can never accurately measure noise that way. Even with an oscilloscope that does true RMS measurements you will get a different value every time you measure it - such is the randomness of noise.

A rule of thumb is that the RMS will be one fifth of the peak to peak value. That is based on the probability of a value being outside that range for Gaussian noise and seems to be a useful guide.

Keith.
 

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