I'll start by saying I'm new to electronics, and have only minor working knowledge. I am designing a transimpedance amplifier to measure the opacity of a surface that is changing over time. The resulting voltage is sent into an ADC for me to record. My circuit is below:
I am seeing a lot of voltage variation due to the ambient temperature of the room (I've put a temperature sensor next to my TIA, and noted a strong correlation between a rise in temperature and a decrease in voltage). This variation is relatively large, and causes my measurements to have long cyclic behaviour (due to room heating turning on and off). FYI the ambient temperature changes by ~0.5std. Below is an example of the relationship I'm seeing (Blue is temperature, green is voltage):
My questions are:
Is the variation in output caused by
- the LED warming up, causing a decrease in light output?
- the feedback resistor changing due to temperature changes?
- both? maybe the photodiode?
What are some possible solutions to correct for this, assuming I'll never have perfectly stable ambient temperature?
- I could add a thermsistor to the diagram, and use an input on the ADC to record the variation in temperature and use software to correct the op-amp output voltage. This makes sense to me, but I've can't seem to find ppl doing this after some searching.
- Measure temperature and use a calibration curve to "correct" the reading back to 20C - is this going to be robust though?
- Some electronic solution? Not sure what that looks like.
- A PID controller that tries to stabilize the LED output (assuming it's the LED that is causing the variation).
Thanks for any suggestions!