TINA-TI : about indication of noise analysis graph

Hello rogin,   

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~Leonard   

Hi Rogin, I also was running into this issue, you can get to the actual < 100fA numbers dumping the data out into excel, attached steps, Well I am having trouple attaching the file, here is the contents, 

Testing the input current noise for the OPA350

Michael Steffes, 8/20/2023

I was also testing the input current noise for the OPA350 as it was called out in this app not as having a rising current noise, The app note implies this comes from the input voltage noise injecting a current through the input Cdiff term – I kind of doubt that as the differential voltage across that Cdiff cap is just the error voltage – in a noise test, the error voltage will be a very low noise so not really a term. I vaguely recall the BurrBrown PA designers talking about this term coming from the device model itself. This  effect is probably in quite a number of other FET or CMOS input devices, but as far as I can tell, rarely modeled.

https://www.ti.com/lit/an/sboa570/sboa570.pdf

Here is the result, where the marker goes to 0 below 100fA

One idea is to dump out the curve into a text file and reopen in excel. Well it won't let me keep that window open to snip, but

1.left click on the curve to highlight it

2. click on the file button inside the plot window, a drop down will open
3. pick the export as text option and save the data to a notepad file,
4. open the notepad file and copy all to an excel sheet (cntl a, cntl c, then paste), Here I did all of that and the data is there just not being picked up by the marker,

frist of all, thank you for your reply. i definitely agree your comment and i also know to see the data below 100 fA/Hz by excel. but i just want to see the data simply and iam not sure but the software is locked on measuring small value such. so i tried to ask the question to TINA technical designers 

and. now i regonized to be difference current input nosise charaterisctic between bioplar and FET. other referecens usually used bioplar type of opamp for noise analysis. but i want to know FET type of opamp for noise analysis. do you know how to revise the noise information by TINA-macro viewers ? 

for example, i'm running simulation about OPA355. there has a current noise spectral density compared to opa350. if you know the noise information in Tina-macro viewer. can you share the code of macro view ?

Well Rogin, I am not in TI. Clearly their modeling guys have developed a subckt for this as I see it in the OPA350 and OPA810. They would have to either update the model or (less likely) provide the macro. 

Hi Rogin, Michael,

Both TINA and PSPICE have limitations on the order of magnitudes of numbers they can process.  Whether or not the data that can be extracted from TINA at < 100 fA levels are meaningful without some additional resolution/tolerance changes, I don't know for sure.

Let me loop our modeling expert on this and see what he thinks, please give me until next Monday to get back to you.

Regards,
Mike

All,

In order to show the input current noise spectra density below 100fA you need to use on vertical axis logarithmic scale - see below.

OPA350 Noise.TSC

It's been a week since last reply, thus I'll close this post.  If you have further questions, please respond or open a new thread.