I've come across this part of a circuit from a precision multi-slope ADC, it is described as a "Dual op amp integrator", but I am left confused as to what U11 accomplishes in this circuit,
This part of the circuit is switched between an external input voltage and either a positive of negative reference voltage at about 50KHz, apparently done to use a much smaller integration capacitor, and have more residue resolution, this is just to give an idea of how it is used.
My goal is working out how each component in this circuit influences the total noise, and what frequency bands of external and internal noise it is susceptible to,
I am very limited when it comes to simulation knowledge, and have so far been deriving the relationship of what the AC gain vs frequency is of each part of the circuit moving forward, however without knowing exactly what this circuit accomplishes, I've been struggling with it.
My first thought was increasing the gain of the circuit, with U11 contributing about x16000, and U2 contributing x1000000 however this seems a little overkill, as U2 on its own could saturate on only 15uV difference across its inputs.
Second thought was some kind of sallen key low pass, that some how relied on parasitic capacitance, but every calculation for that I could find had results far above the gain bandwidth product.
The other thought was to reduce the offset voltage of U2, but in a part of the circuit where noise is critical, it seems odd.