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THS3491: Some THS3491 2018 model noise testing,

Michael Steffes
Guru 47505 points
Part Number: THS3491

So I was kind of working on Steve Smith's sim vs. measurement question and thought I would step through some things, 

Here is the input current noise for the 2018 model - I had some analysis options set in V11 that was messing this sim up, going back to default fixed the sim problem, the datasheet says 15pA for the V+ input and 20pA for the inverting input. 

And then here is the input voltage noise, 1.77nV in sim vs. 1.7nV in the datasheet, 

And then one more detail, is what temperature are the resistors set at, for some reason this file was at 0C, I changed the 2 R's to 25C, not sure I am doing this right? 

I had the feedback R in the wrong spot, would not effect the input noise sims, here is the total output noise 18nV

If you put all these numbers into a ideal output noise calculator, I get 17.5nV, not sure why we are not exactly on? note we have to use the noise gain of 3 line here, 

Anything look amiss here? 

  • 0
    Prodigy 230 points

    Hi Michael,

    I think there is a problem with the temperature setting, see this post: TINA-TI: How do you set temperature of components for noise simulation?

    So probably the thermal noise is higher.

    Best wishes, Zoltan

  • +1
    Guru 47505 points

    Hey Thanks Zotan, that was very useful, I went to relative on both R's with a 0C offset from the global 27C setting, I then went to 27C in the excel sheet and corrected my Rf to 786 not 768 (darn numeric dyslexia - an increasing issue for me), and I get 17.9nV calculated vs a 17.97nV in sim. This all seems to make sense and model to calc is close enough and the 2018 model is pretty close to the datasheet, Steve is having a problem  getting the sim to measured to match. I am suspecting this might be some slight peaking in his frequency response and or his integration span is not exactly the same as his assumed 150MHz.