Staying within an op amp's specified output voltage range, how does a difference in output swing affect the op amp's noise applied to the output signal? Obviously by increasing gain, we amplify the op amp's injected noise as well, but in practical applications, is this a perfectly linear increase?
For context, I am looking at designing a transimpedance stage for the differential current-output DAC PCM1794A. At the output, it sources between 2.3mA and 10.1mA, with a center current "zero" of 6.2mA. I'd like to minimize added noise, and I will need two identical transimpedance stages to bring to a differential summer in order to receive a single-ended signal at the circuit's output (snip from the datasheet below).
Why would the reference schematic's designer not maximize the gain of the transimpedance stage? Conversely, why would it not be lower? From other posts and articles I've read (here for example), assuming identical noise figures from each op amp (which will never happen, but assume I at least plan to use identical op amps for all stages in my circuit), it seems like it would be best to try and form the circuit such that each amplifier's gain is the same to achieve the desired output voltage (in this case 4.5Vrms). To add to my confusion, there is another example in the datasheet that, among other things, replaces R3 with a 560-ohm and R5 with a 270-ohm (in addition to R4 and R6), negating the desire for a differential summer with input coefficients being 1.
Also, would there be any benefit to biasing the transimpedance stages such that the "zero" output of the DAC resulted in 0V at the output of the transimpedance stage? Seems to me that this would be unnecessary since both signals go through the differential summer together. I would also think that this would produce more noise as a result of deriving the bias voltage, but they do just this in TI Application Report SBOA237.
Thank you, I'm just trying to wrap my head around the "practical theory" here.