I am working on an electronics project to design a transimpedance amplifier circuit. It involves an op amp chip in a PCB with a current input, 3.4 KOhm resistor, and the voltage output that I am measuring.
- Why might it be that for nearly 20 of the same OPA227P chips, the voltage offset is about .5V? I checked the chip's datasheet and its offset should be 75 uV maximum. The chip is in the PCB, no input, powered by a 12 V source, grounded to a metal table... how can this problem be fixed?
- And, why is the voltage output that I see not stabilizing on a single value? It fluctuates up and down a lot and is generally a lot lower than expected, the gain is lesser on a magnitude of 10-100. Is there something that I can do so that the voltage output stabilizes? Why might the gain be so lower than expected, is there something I could do to remedy that?
Thank you for any help!
Here is a diagram of the circuit:
The chip is being powered by a 12 V source (when I measure its voltage with a multimeter, it's actually 11.84 V). The current input is from a programmable current source. I've been using .1-1.0 mA in .1 mA increments. I've also been checking the current input with a multimeter. The op amp chip model is OPA227P, and it's in a socket which is soldered onto the PCB. I measured the resistance of the resistor, it is 3.398 KOhm. The other leads of the current source are grounded and the ground port of the PCB is grounded, all to a metal table in the lab but on different spots (there is no measurable voltage difference between those points).