I am trying to figure out how to estimate the total output noise voltage density when I connect a LT1460 reference, LTC2757 DAC, and a LT1468 output transimpedance amplifier together. The datasheet simply lists "output voltage noise density" with no information about how this is measured (although note 11 seems to indicate this is simply the johnson noise of some resistor).
I know how to calculate the noise of a TIA but I don't know how the DAC converts the reference voltage noise into output current noise. Can you explain?
Many thanks!
At the first level the reference noise that gets to the output will be proportional to the output code. This is because the reference drives the R2R ladder directly and is attenuated depending on which resistors are switched in.
This gets complicated if you are using a bipolar mode because there is an offset resistor that will feed reference noise directly into the output, it will be attenuated, but will be constant over code.
So I can assume that at the maximum output code, the noise out will be equal to the reference noise in plus an additional 13 nV/rtHz (listed in datasheet)?
Yes, that is correct.