TABLE OF CONTENTS This chapter presents a digital gain calibration technique for Hall sensors. The gain is continuously measured using an integrated reference coil, without interrupting normal circuit operation. Appropriate modulation and demodulation schemes are implemented to separate the external and calibration magnetic fields. The gain drift is compensated by a digital compensation circuit. After an introduction and presentation of the state of the art, this chapter presents the system architecture, and chapter 6 its implementation.
The gain drift of integrated Hall sensors is one of their current main limitations. The drift is due to temperature variations, mechanical stresses and ageing. The technique presented in this chapter allows a continuous cancellation of the gain drift using a real-time digital calibration system. The detection and compensation circuit uses the digital correction techniques and methodology presented in the previous chapters. The proposed system allows a gain drift reduction by a factor of 6 to 10 compared to current commercial products.
Different techniques and corresponding sensor technologies allow the measurement of magnetic fields [60]. Among them, the Hall sensor [61] [62] [63] is one of the most widespread solid-state sensors. It can be realized without requiring additional fabrication steps in commercial CMOS technologies, allowing the design of single-chip microsystems [64] comprising both the sensor [65] and its analog front-end. Mixed-mode solutions further including an analog-to-digital converter even allow the complete integration of smart sensors [66], combining a sensor and a dedicated digital signal processing circuit.
