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A high-precision interface for tunneling magnetoresistance sensors with 0.15 nT/√Hz resolution
Modern Physics Letters B  (IF1.668),  Pub Date : 2021-11-22, DOI:
Anqi Chen, Xiangyu Li, Yan Li, Xinpeng Di, Xiaowei Liu

The tunneling magnetoresistance (TMR) with high-resolution digital output is widely used in military and civil fields. In this work we proposed a low-noise read-out circuit and a four-order fully differential sigma-delta modulator for TMR sensors. In the read-out circuit, we used symmetrical cascade for good matching. We used correlated double sampling (CDS) technique to improve the conversion accuracy of the modulator. In switched capacitor circuits we used time-division multiplexing to suppress charge injection and clock feedthrough. The high-precision application specific integrated circuit (ASIC) chip was fabricated by a 0.35 μm CMOS process from Shanghai Huahong foundry. The TMR sensor was placed in an environment of three-layer magnetic shielding for test. The active area of the ASIC is only about 3 mm×3 mm. At a sampling frequency of 20 kHz, the TMR magnetometer consumes 77 mW from a single 5 V supply; the sigma-delta modulator for TMR can achieve an average noise floor of −141 dBV. The magnetometer works at a full scale (FS) of ±100 μT, it can achieve a nonlinearity of 0.2% FS and a resolution of 0.15 nT/Hz1/2 over a signal bandwidth.