I know but 5nV/Sqrt (Hz) should already described the noise voltage. In the last 2 images in my original message. The noise voltage at 100Hz vs 1000Hz bandwidth should have similar nV/Sqrt(Hz) but it varies from 100nV/Sqrt (Hz) to 1uV/Sqrt (Hz), why? what components can make the noise density change?
You keep mentioning this 5nV/Sqrt(Hz) noise spec, but this is not relevant. That is only the noise of one of the stages in your amplifier, the programmable gain amplifier stage, and even then only in optimal circumstances.
Going from your previous threads, your amplifier has several stages:
1. An input buffer and offset/CMRR trim stage. This stage has at least 40 nV/Sqrt Hz noise, and is the most importnat source of noise in most circumstances.
2. The programmable gain stage (Amp01). At medium and high gains (approx G>=1000), this gives optimal noise performance, but this noise is negligible compared to the noise of the input stage. At low gains, then the noise performance is absolutely terrible, at 300-500 nV/sqrt Hz, but likely to be irrelevant because low gains are used for large signals.
3. Finally, there are 2 additional gain and filtering stages, used for bandwidth selection and increasing the overall amplifier gain up to a max of 50,000.
If you want to measure the noise floor of your amp, it is best to do so when it is in the exact operating mode you wish to use.
Your noise spectrum figures are difficult to read (you have chosen sub-optimal settings for the spectrum acquisition). However, in both the 100 Hz and 1 kHz bandwidth cases, taking a representative estimate of noise at 50 Hz - your plots read approx 2.5 uV/sqrt Hz - after correcting for gain (1.7 V FS sine rms), and taking into account the amplifer gain of 10, this gives an overall input referred noise of approx 400 nV/sqrt Hz. This is about what I would expect due to the contibution of all the amplifier stages at this low gain.
I'd suggest when doing a spectrum measurement, you use a modest number of points 32-64k, select "forever" averaging, and collect a large number of averages (hundreds or thousands). This makes it much easier to read - see my random example (not measuring anything in particular).
Once you are happy with the acquisition setup, then you can test the amplifer at the gain you intend to use.