Forum Post: RE: ADS131M08: Abnormal reading data

Hi do Nghia, Welcome to the E2E forum. I noticed that you are using different ground planes, AGND is used for anti-aliasing RC filter and the ADC, GND is used for MCU and the ADC too, do you have a connection between the AGND and GND? Maybe I missed it in the schematic. Usually a single and solid ground plane can be used if there is no special requirement. Your RC filter on AIN7P/AIN7N (Temp1 and Temp2) uses GND1, but your ADS131M08 ADC uses AGND for analog circuit, where are both AGND and GND1 are shorted? I also noticed that you are using many ferrite beads on analog input and SPI digital signals. Please removed them by using a 0ohm resistors instead. You are using 1N4001 for input protection by connecting it to AVDD and AGND, it will actually affect your normal input signal when you signal is under the ground (negative input signal), and also 1N4001 has a high leakage current that will also affect your measurement performance in the future, so those are not recommended. If an input protection is desired, the solution in the application note is recommended: Circuit for protecting ADS131M0x ADC from electrical overstress After the ferrite beads are replaced and the ground connection issues are fixed, you can short the input to test again, e.g. short PE and GND1 that should be AGND, or short Tia1 and Tia2 to AGND. BR, Dale