The ADS1148 and ADS1248 family of devices are highly integrated delta-sigma (ΔΣ)
converters that are optimized for the measurement of temperature sensors, including
resistance temperature detectors (RTDs), thermocouples, and thermistors. In a
typical RTD measurement application, the ADS1148 and ADS1248 are configured in a
ratiometric topology using the built-in IDAC current sources feeding through an
external reference precision resistor. The ratiometric operation has an advantage
because the errors due to the excitation current source drift and noise tend to
cancel. In order to maintain good noise cancellation over the input signal range,
make sure that the analog-to-digital converter (ADC) external input filter is
matched to the filter at the reference input. This document focuses on the external
analog low-pass filter implementations and design considerations when performing RTD
sensor measurements using the ADS1148 and ADS1248 family of delta-sigma converters
in a ratiometric configuration.
Note: Although the ADS1248 24-bit device is referenced throughout
this document, the ADS1148 16-bit device can also be used. The same concept for
filtering applies to both device families, which also include the ADS1147 and
ADS1247.