Certain signal chain errors can be corrected through a single room-temperature calibration. The AMC131M02 can store calibration values and uses the values to correct the results in real time. Among the errors that can be corrected in real time with the AMC131M02 are offset error, gain error, and phase error.

Offset calibration is performed by determining the measured output of the signal chain when the input is zero voltage for a voltage channel or zero current for a current channel. The ADC conversion result for zero input can be measured and recorded in external nonvolatile memory for each channel. When the system is deployed, these values can be provided to the CHn_OCAL_MSB and CHn_OCAL_LSB registers for the corresponding channels. The AMC131M02 then subtracts these values from the conversion results prior to providing them to the host.

Similar to offset error correction, system gain error can be determined prior to deployment and can be used to correct the gain error on each channel in real time. Gain error is defined as the percentage difference in the ADC transfer function from the PGA gain corrected ideal value of 1. This error can be determined by measuring the results from both a maximum and minimum input signal, finding the difference between these results, and dividing by the difference between the ideal difference. Equation 11 describes how to calculate gain error.

Equation 11.

To correct for gain error, divide each offset-corrected conversion result by the measured gain. The AMC131M02 multiplies each conversion result by the gain calibration factor stored in the CHn_GCAL_MSB and CHn_GCAL_LSB registers according to the method described in the Calibration Registers section. The host can program the measured inverted gain values for each channel into these registers to have them automatically corrected for each sample.

The AMC131M02 can also correct for system phase error introduced by sensors. For this design, PCB routing from the shunt to the ADC input (and from the voltage measurement resistive divider) can introduce some phase error into the system. Some designs use a software method for phase correction, but the AMC131M02 can perform this function in real time. The system must first measure the phase relationships between the various channels. Then the AMC131M02 defines one channel as phase 0. Subsequently, the PHASEn bits in the CHn_CFG registers corresponding to the various other channels can be edited to correct the phase relationship relative to the phase 0 channels.