A 2 MHz Bandwidth TMR-Based Contactless Current Sensor With Ping-Pong Auto-Zeroing and SAR-Assisted Offset Calibration

• Published in: IEEE journal of solid-state circuits 2024-10, p.1-11
• Main Authors: Qu, Tianxiang, Dong, Tian, Qin, Wenhui, Pan, Yaohua, Sheng, Yun, Hong, Zhiliang, Zeng, Xiaoyang, Xu, Jiawei
• Format: Article
• Language: English
• Subjects: Bandwidth; Bridge circuits; Calibration; Coils; Contactless current sensing; Gain; instrumentation amplifiers; Linearity; Magnetic fields; magnetic sensors; Magnetic tunneling; offset calibration; ping-pong auto-zeroing (PPAZ); Power demand; SAR; Sensitivity; tunnel magnetoresistance (TMR)
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2024.3468955

This article presents a tunnel magnetoresistance (TMR)-based magnetic sensor for contactless current sensing. The TMR readout circuit utilizes a current-balancing instrumentation amplifier (CBIA) with ping-pong auto-zeroing (PPAZ), achieving an integrated magnetic noise of 206 nT _{\text{rms}} in a wide bandwidth of 2 MHz. Compared with chopping amplifiers, an auto-zeroed CBIA provides a ripple-free output, not only extending the available bandwidth but also ensuring a system linearity of 0.24%. In the gain configuration of 42 dB, the input magnetic field range is \pm 0.08 mT, corresponding to a dynamic range (DR) of 58 dB. The maximum offset of the TMR sensor is reduced to 311 nT (ten samples) through an SAR-assisted offset calibration scheme. Moreover, after compensating the temperature coefficient (TC) of the TMR bias generator, the sensitivity drift of the TMR sensor is reduced by 18 \times . Overall, the proposed TMR sensor readout, including the sensor bias circuit, achieves a state-of-the-art power efficiency in terms of figure-of-merit (FoM) of 2.5 fW/Hz or 146 dB. As a general bridge sensor readout, this work achieves 5.4 nV/ \surd Hz input-referred noise (IRN), 1 \mu V input offset, and bandwidth efficiency of I_{\text{supply}} /bandwidth = 0.44.