I have a low level DC signal from a thermopile sensor of 0-9.1mV with 7uV increment. I feed this to an INA114 instrumentation amplifier with gain of 550 to get 0-5V output.
I tried introducing RF noise by means of GMS (phone call or SMS) with the output moving up from 0 – 1V (0 – 1.82mV input). I have a voltmeter on the input and output to monitor it at the same time. With the noise present, the input is perfectly fine while the output ruined.
I then set the gain to 1 so that input is equal to output. Still, the input is perfectly fine while the output is ruined. It seems that the interference is hitting the INA114.
Why is this happening and how would I overcome it?
Best Answer
It is well-known that Inamps can suffer from degraded performance in the presence of EMI. Here is a document from ADI that gives tips on this subject and below is a small extract: -
Of vital importance (of course) is the requirement for the engineer to read the data sheet and follow specific guidelines for the chip such as adequate power supply decoupling and layout methods. A lot of EMI issues are caused by bad layout and generally not following the data sheet.
I'm not saying the OP hasn't followed the guidelines in the data-sheet of course but it would be interesting to see a picture of the PCB layout. If it's a breadboard then basic EMI protection is out of the window!