Other Parts Discussed in Thread: LMP91000, LMC6081, , LMC6482, LMP2232, LMC6492
Dear Forum,
I am currently trying to design a dissolved oxygen device using a 2-wire polarographic probe. The max output of this probe is roughly 40-80 nA when biased at 670 mV. I was going to use the LMP91000 AFE in my design with a 5 meg Resistor for the TIA, but I've gotten feedback k the OpAmps in this chip are inot deal for such a high impedance signal.
So I was planning to recreate the circuit shown below with a low input offset current OpAmp like the LMC6082 (or LMC6081). I would dispense with amplifier A1 and simply send VE- to ground. I would feed A2 with a 670 mV potential from a buffered VDAC to the noninverting terminal of TIA and configure the rest of A2 as shown in the figure below: Inverting input tied to VE+ and through the R(TIA) resistor to Output. I would probably include a Cap (2.2-22 pF) in parallel with R(TIA) as well.
My question is whether my choice of OpAmp is wise and if this design is inherently flawed. Cost at this level is not a huge issue, and I'm looking at the LMC6081/2, LMC6492, LMP2232, and LMC6482.
