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 $\mu$m 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 $3\mathrm{\text{mm}}\times 3\mathrm{\text{mm}}$. 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 $\pm 100\mu \mathrm{\text{T}}$, it can achieve a nonlinearity of 0.2% FS and a resolution of 0.15 nT/Hz${}^{1/2}$ over a signal bandwidth.

具有高分辨率数字输出的隧道磁阻（TMR）广泛应用于军事和民用领域。在这项工作中，我们提出了一种用于 TMR 传感器的低噪声读出电路和四阶全差分 Sigma-Delta 调制器。在读出电路中，我们使用对称级联来实现良好的匹配。我们使用相关双采样 (CDS) 技术来提高调制器的转换精度。在开关电容器电路中，我们使用时分复用来抑制电荷注入和时钟馈通。高精度专用集成电路 (ASIC) 芯片由 0.35$\mu$m 来自上海华虹代工厂的 CMOS 工艺。将 TMR 传感器置于三层磁屏蔽环境中进行测试。ASIC 的活跃区域只有大约$3\mathrm{\text{毫米}}\times 3\mathrm{\text{毫米}}$. 在 20 kHz 的采样频率下，TMR 磁力计从 5 V 单电源消耗 77 mW；用于 TMR 的 Sigma-Delta 调制器可以实现 -141 dBV 的平均本底噪声。磁力计在满量程 (FS) 下工作$\pm 100\mu \mathrm{\text{吨}}$, 它可以实现 0.2% FS 的非线性和 0.15 nT/Hz 的分辨率${}^{1/2}$ 超过信号带宽。