SDAA451 July   2026 ADS131M08

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2What is phase shift and phase error?
  6. 3How to calibrate out phase error with the ADS131M08
    1. 3.1 Determining the phase error
    2. 3.2 Converting to the time domain
    3. 3.3 Converting to modulator clock cycles
    4. 3.4 Converting to binary and writing to the PHASEn[9:0] bits
    5. 3.5 Phase calibration considerations
    6. 3.6 Summarizing the phase calibration process
    7. 3.7 Using the Phase Calibration Feature
      1. 3.7.1 Phase calibration considerations examples
  7. 4Synchronizing the ADS131M0x
    1. 4.1 The SYNC/RESET pin on the ADS131M0x
    2. 4.2 The importance of routing the clock signal
      1. 4.2.1 Single Clock Buffer
      2. 4.2.2 Multiple Clock Buffers
  8. 5Summary
  9. 6References

3.1 Determining the phase error

Determining the system phase error is the first step to implement the ADS131M08 phase compensation feature. CTs, potential transformers (PT), and any front-end circuit including amplifiers and RC filters can introduce phase errors. This application note uses a CT as an example to demonstrate the phase calibration process, but the ADS131M08 phase calibration feature can compensate for any of these error sources. CTs are commonly used to measure AC current in power measurement systems. However, CTs inherently introduce a phase shift between the measured current and the actual current due to the magnetic characteristics of the core. The CT manufacturer typically specifies the phase error in arc minutes or degrees. Table 1 shows the phase error of multiple CT accuracy classes.

Accuracy ClassPhase error in angular minutesPhase error in degree
0.1±5 minutes±0.083°
0.2±10 minutes±0.0167°
0.5±30 minutes±0.5°
1.0±60 minutes±1°
3.0±180 minutes±3°

Table 1. Common CT specification by accuracy class

Revenue grade meters use a CT with a 0.2 accuracy class and a ±0.0167° phase error.