A Hybrid Multi-path CMOS Magnetic Sensor with 210µTrms Resolution and 3MHz Bandwidth for Contactless Current Sensing

Abstract

CMOS Hall sensors are widely used as magnetic sensors due to their linearity and ease of integration [1-3]. Being essentially n-well resistors, their resolution is determined by thermal noise and so decreases with bandwidth (Fig. 11.3.1), limiting their use in wide-band current-sensing applications, such as in switched-mode power supplies, electric motor control and short-circuit detection. In contrast, the differentiating characteristic of pick-up coils means that their resolution actually improves with bandwidth (Fig. 11.3.1). This paper describes a hybrid sensor in standard CMOS that achieves wide bandwidth and good resolution by employing a Hall sensor in a low-frequency (LF) path and a coil in a high-frequency (HF) path. The sensors' outputs are amplified by two transconductance amplifiers (gm,coil and gm,HS) and then combined by a transimpedance amplifier (TIA) (Fig. 11.3.1). The sensor achieves a resolution of 210μTrms in a 3MHz bandwidth; the latter represents an order of magnitude improvement over state-of-the-art CMOS magnetic sensors [1,4].