A Hybrid Magnetic Current Sensor With a Multiplexed Ripple-Reduction Loop

This article presents a hybrid magnetic current sensor for galvanically isolated measurements. It consists of a CMOS chip that senses the magnetic field generated by current flowing through a lead-frame-based current rail. Hall plates and coils are used to sense low-frequency (dc to 10 kHz) and high-frequency (10 kHz to 5 MHz) magnetic fields, respectively. With the help of on-chip calibration coils, the biasing current of the Hall plates is trimmed to match the sensitivity of the Hall and coil signal paths. The sensitivity drift of the coil path with temperature is compensated by using temperature-dependent gain-setting resistors, while the drift of the Hall path is compensated by biasing the Hall plates with a proportional-to-absolute-temperature (PTAT) current. The resulting sensitivity drift is less than 9% from -40 ^{\circ} C to 80 ^{\circ} C. The offset of the Hall plates is reduced by the current spinning technique, and the resulting ripple is suppressed by a multiplexed ripple-reduction loop (MMRL). Fabricated in a standard 0.18- \mu m CMOS process, the current sensor occupies 4.6 mm ^{2} and draws 7.8 mA from a 1.8-V supply. It achieves a gain variation of only \pm 2% in a 5-MHz BW. It also achieves high energy efficiency, with an figure of merit (FoM) of 1.6 fW/Hz.