Part Number: OPA301
Hello.In the data sheet, there is 40uVpp, 0.1-1MHz.I tried to get this number from the Noise density graph, but failed. Attached my calculations, based on you “Lecture Manual”.Data from the data sheet:Input Voltage Noise, f = 0.1Hz to 1MHz 40µVPP
From the Noise density graph: enf=0.3µV/√Hz at 10Hzf0=10 Hzennormal= enf√ f0=0.3*√10=0.95µV/√Hz at 1HzfL=0.1 Hz , fH=1 MHzenflicker= ennormal√(ln(fH/ fL))=0.95*√(ln(1M/ 0.1))= 0.95*√(ln(107))=0.95*√(ln(107))= 0.95*√(4)=3.8 µVrmsenflicker(pp)=6* enflicker=6*3.8=22.8 µVPP
Please advise where is my mistake.
It seems that the 40 uVpp in 0.1-1MHz range comes from this Application Report:
Enflicker = En_white*√Fcn*(ln(fH/fL)) - (1)
where, En_white (white noise) = 3 nV/√Hz from the datasheet
and Fcn is the frequency at which noise is √2 x white noise specification. For 3nV/rtHz white noise, the Fcn then will be 250kHz at √2x3nV/rtHz from the below noise spectral density figure.
If you plug-in the numbers into the Enflicker noise equation, you should get ~6.02 uVrms.
So, Enflicker (pp) = 6*Enflicker(rms) = 6*6.02 = 36.12 uVpp
I think there is some fudge factor or round off associated with making the Enflicker(pp) close to 40 uVpp (0.1-1MHz range) in the OPA301 datasheet.
In reply to Rohit Bhat:
Thanks for your answer. It took me some time to learn and understand your answer, and now it's clear.
What it is still not clear:
1. What is the explanation to use the method which I used?( get the Ennormal- the 1/f voltage noise spectral density normalized to 1Hz).
2. Why using this method gives a different result?
In reply to Shlomo Perlshtein:
Thanks again for completing the answer. I suppose that issue is resolved.
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