A Broadband, On-Chip Sensor Based on Hall Effect for Current Measurements in Smart Power Circuits

This paper presents a broadband ([dc--megahertz (MHz)]) current sensor for power applications, which is based only on a Hall-effect probe as the core sensing element. Unlike common solutions for broadband current sensing, the proposed architecture is suitable for integration of the measurement system on the same low-cost CMOS chip used for the power electronics (e.g., Bipolar-CMOS-DMOS), without the need for external transformers and allowing for the realization of ``smart power circuits.'' The Hall-effect probe is biased by implementing the offset compensation-oriented spinning-current technique through a novel front-end, designed to push the operative bandwidth toward the fundamental limit of the probe. Specifically, the proposed front-end employs switches, which are typical of spinning-current techniques, only for biasing the Hall probe, while the readout process is performed by minimum-sized differential amplifiers. In this way, the capacitive load seen by the Hall probe is minimized and the sensor practical bandwidth upper limit is strongly increased. A prototype of the proposed architecture was operated at 8-MHz spinning frequency and characterized by means of standard figures of merit, demonstrating the broadband capability and an adequate overall performance. At the same time, the prototype revealed a new bandwidth limit, masked in conventional architectures by stronger capacitance-induced effects, which is represented by a degradation of the effectiveness of the spinning-current technique. Measured performance is comparable to that of standard, nonintegrated, current sensors, demonstrating the effectiveness of the presented purely Hall approach for broadband current sensing. The architecture was validated by discussing two case studies typical of power applications.