A Hybrid Multi-Path CMOS Magnetic Sensor With 76 ppm/°C Sensitivity Drift and Discrete-Time Ripple Reduction Loops

This paper presents a temperature-insensitive magnetic sensor system for contactless current measurements. To simultaneously achieve wide bandwidth and low noise, the proposed system employs a multi-path structure with a set of spinning current Hall sensors in its low-frequency path and a set of pick-up coils in its high-frequency path. The Hall sensors and pick-up coils are used in a differential sensing arrangement that naturally rejects common-mode magnetic field interference, e.g., due to the earth's magnetic field. A common-mode ac reference field can then be used to continuously stabilize the sensitivity of the Hall sensors, which, unlike that of the pick-up coils, is quite temperature dependent. In this design, the ripple reduction loops in the Hall sensor readout are implemented in a discrete-time manner, and so occupy 20% less area than a previous continuous-time implementation. Over a -45 °C to 105 °C temperature range, the proposed system reduces the Hall sensor drift from 22% to 1%, which corresponds to a temperature coefficient of 76 ppm/°C.