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Tool/software:
Hello for a new design I have to do a noise measurement. I found the application note SLYY076, "How to measure LDO noise" that is a great help for understanding.
Nevertheless, I have a question on the measurement. The spectrum analyzer that I use provides the measurment data in dBµV, the value is not yet normalized to 1Hz. As far as I know, I have to divide the measured value by the square root of the measurement bandwidth. Now I don't know whether I have to convert from dbµV to µV first and divide with sqrt(RBW) then, or vice versa.
Can you help me with this topic?
Best Regards
Markus
Hello Markus,
Have you taken a look at equation 5?
This is how you would convert to uV/sqrt(Hz).
Page 6 and 7 of the app note provide a great explanation on this conversion.
Please let me know if you have any additional questions.
Best regards,
Hannah
Hello Hannah,
thank you for your fast response.
Yes I took a look at this equation. But this one tells me how to convert dBµV to µV when RBW is already considered by the spectrum analyzer. Therefore, the unit is µV / sqrt (1Hz).
Is this correct?
Page 6 states: "Most spectrum analyzers record the measured noise in dBµV/√Hz."
=> Unfortunately my spectrum analyzer records in dBµV.
Page 7 states: "Once you have the spectral density in µV/√Hz, you can calculate the RMS noise ..."
For my measurement I set RBW to 100Hz, so the values are related to 100Hz. I don't know how to do the conversion to get the value related to 1Hz.
Can you tell me how to do the conversion?
Best regards;
Markus
Hi Markus,
The equation is not stating to take the sqrt of just 1 Hz. This value would be the RBW you used, which is 100Hz.
Hope this helps!
Best,
Hannah