Well Chia
This is sort of a classic datasheet plot. This done with the device in high gain mode followed by normally a gain of 100X active filter implementing a multiple pole 0.1Hz to 10Hz bandpass filter, then a 10sec sweep on a scope is done (measuring really pretty high Vpp noise) then that data is input referred dividing by the net gain in the DUT + active filter stage. This does not look as "noisy" as they usually do, kind of rounded off, but in case this is showing about 75nVpp which seems quite low,
We can calculate what it should be from the spot noise plots, this is 7nV flatband with 0.7Hz 1/f corner
Getting an equivalent flat noise over the 0.1 to 10Hz span, used this equation, from this app note, I should probably have changed this article name to be for all op amps.
https://www.ti.com/lit/an/sboa066a/sboa066a.pdf
Evaluating this gives 8.05nV
Then getting the RMS noise in that 9.9Hz span, 8.05nV*sqrt(9.9) = 25.4nVrms, then using a 6X crest factor, should have been 152nVpp - so yes the plot is missing a factor of 2 adjustment is would seem, but still really low - that 1/f corner is remarkable.
I had put this kind of info into some AudioXpress articles, here is the preamp active filter one,
Low Frequency and Popcorn Noise in High Speed Amplifiers part 9 updated April20_2020.docx
And the spec lines do indeed show 200nVpp for the 0.1 to 10Hz input voltage noise. So yes, the plot has been scaled down by a factor of 2 by accident I am guessing, or maybe the y-axis in the plot just needed to be 100nV/div
Hi Chia,
I hope you are doing well. We remeasured the data this afternoon (please see below). We also made note of it and will be updating the data sheet soon.
Thank you for bringing this to our attention. It seems like the old data may have been averaged for some reason.
Thank you,
Daniel
