SBAA201A March   2013  – March 2023 ADS1120 , ADS1120-Q1 , ADS1147 , ADS1148 , ADS114S06 , ADS114S06B , ADS114S08 , ADS114S08B , ADS1220 , ADS122C04 , ADS1247 , ADS1248 , ADS124S06 , ADS124S08

 

  1.   RTD Ratiometric Measurements and Filtering Using the ADS1148 and ADS1248 Family of Devices
  2.   Trademarks
  3. 1Introduction
  4. 2Low-Pass Filter Design Considerations in Ratiometric Measurements
    1. 2.1 Resistor and Capacitor Component Selection
  5. 3Noise Performance Using the ADS1248 in the Ratiometric Configuration
    1. 3.1 Noise Performance Using Mismatched RC Filters
    2. 3.2 Noise Performance Using The Four-Wire Configuration with Matched RC Filters
    3. 3.3 Noise Measurements Using the Three-Wire Configuration with Matched RC Filters
    4. 3.4 Other Considerations
  6. 4Conclusion
  7. 5References
  8. 6Revision History

4 Conclusion

Performing sensor measurements in a ratiometric configuration provide a significant advantage, where the voltage reference used for the analog-to-digital conversion is derived from the excitation source, and the errors due to the absolute value of the excitation and excitation drift are virtually eliminated. In addition, when performing measurements in a ratiometric configuration, the noise of the excitation source is reflected at the inputs of the ADC device and the reference path, and in this manner the noise cancels.

Although external RC filters are not required to achieve a ratiometric measurement, the addition of external filters may prove to be beneficial in noisy environments, where sensors are prone to RFI or EMI. In addition, appropriate printed circuit board (PCB) layout, shielding, and grounding techniques are essential in the design to mitigate interference. When adding RC filters to combat RFI noise, make sure to balance the input path low-pass filter and the reference path low-pass filter. The preceding discussion shows some of the trade-offs and design considerations to balance the filters using the ADS1248 in RTD ratiometric circuits. The information is provided to assist the design engineer when implementing the filter design and testing according to the specific application needs.