A LUT-Based Calibration Approach of the ESP32 ADC for a Power Quality Analyzer

Low-cost electronic circuits for Internet-of-Things (IoT) applications are based on system-on-chips (SoCs) with wireless connectivity. Among them, the ESP32 is a well-known microcontroller family adopted by a wide developer community. This SoC is selected in this work to implement a wireless remote power meter for energy quality analysis. The ESP32 provides a 12-bit analog-to-digital converter (ADC), but its performance is not suitable for precision applications. In this work, an offline ADC calibration is performed and the correction codes are stored in the ESP32 internal memory to optimize the analog-to-digital conversion to meet high-precision energy quality measurement standards. The results before and after calibration are shown to verify the effects of ADC linearity especially when measuring total harmonic distortion. We demonstrate that the ADC nonlinearity distorts the signal and introduce odd harmonic components that affect the reliability of the measured values, especially at the end of the scale. The look-up table based correction method can mitigate these effects and allows the use of a low-cost ADC with poor linearity in high-precision applications.