I've used EVAL-INAMP-82RZ as the main board for testing AD8421/AD8422/AD8221. With all of these amplifiers I've seen a lot of noise. The main setup consisted of:
- 2x18650 in series providing power to the system with: -Vs = -4.2V / +Vs = +4.2V / GND = 0V (middle point of 2 series battery setup)
- REF set to GND
- single-ended scope probe directly probing the output
- IN+ and IN- directly shorted to GND plane
- gain set on the INA to >350
With above setup we are seeing output noise in the range of 6.7mV - 8mV on the scope, while running in Normal Acquisition mode, at a sweep speed of 30kSPS, AC 1:1, BW limited.
Any idea on why such a bad noise performance?
I've also connected the INA output to a 24-bit AD7175-8 ADC and the same level of noise was observed with the sample rate being set to 31250SPS.