A Hall Sensor Analog Front End for Current Measurement With Continuous Gain Calibration

This paper presents a new technique for continuously calibrating the sensitivity of a current measurement microsystem based on a Hall magnetic field sensor. An integrated reference coil generates a magnetic field for calibration. Using a variant of the chopper modulation, the spinning current technique, combined with a second modulation of the reference signal, the sensitivity of the complete system is continuously measured without interrupting normal operation. Modulation and demodulation schemes allowing the joint processing of both external and reference magnetic fields are proposed. Additional techniques for extracting the very low reference signal are presented. The implementation of the microsystem is then discussed. Finally, measurements validate the calibration principle. A thermal drift lower than 50 ppm/degC is achieved. This is 6-10 times less than in state-of-the-art implementations. Furthermore, the calibration technique also compensates drifts due to mechanical stresses and ageing

I. Introduction

This paper presents a new sensitivity calibration technique for Hall sensors [1]–[3]. Hall sensors are widely used to measure magnetic fields [4]. They can easily be integrated in conventional CMOS technologies without additional processing steps. However, they suffer from imperfections that limit their precision, and thus their use in high-performance measurement systems. In particular, the sensitivity drift due to temperature variations, mechanical stresses and ageing, is one of their current main limitations [5].