Hey again guys.
I've been working from this document all day:
http://www.ti.com/lit/an/snva112a/snva112a.pdf They provide a lot of the theory right up to the calculation, and then leave you high and dry, without showing any work.
For an output divider + reference voltage circuit, the equation for variance is shown below:
First off, I'm confused as to the usage of "variance" here. For example, in the equation, V(R1), V(R2) and V(Vref) are the variances of these components. But the statistical variance is not something we are provided. Components are given a "tolerance", which we might assume is the spread of values out to 3 or 6 sigma. One sigma is the square root of the variance...
But they don't seem to talk about that at all. They only talk about 0.5%, 1% or 5%
tolerances. Is it possible that V(R1) is really the
tolerance of R1? Does that even make sense?
And then...once you get the
variance of the output voltage, do you have to take the square root of it to get sigma, and then multiple by 3 or 6 to get the expected spread? Yikes this is more confusing than it looked.