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The tunneling magnetoresistance micro-sensors (TMR) developed by magnetic multilayer material has many advantages, such as high sensitivity, high frequency response, and good reliability. It is widely used in military and civil fields. This work presents a high-performance interface circuit for TMR sensors. Because of the nonlinearity of signal con...
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... exchange coupling between ferromagnetic layer and anti-ferromagnetic layer determines the direction of the magnetic moment of a ferromagnetic layer; tunneling barrier layer is usually composed of MgO or Al2O3, located in the upper part of anti-ferromagnetic layer [11]. As shown in Figure 1 the arrows represent the direction of the magnetic moment of the pinning layer and the free layer. The magnetic moment of the pinning layer is relatively fixed under the action of a certain size of magnetic field. ...
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... is no nonlinearity in the integrator. When the amplitude of input signal increases to a certain value, the integrator output is determined by Equation (13). Obviously, the establishment process of integrator is non-linear at this time. ...
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... verify the analysis presented in the previous sections, the interface circuit chip was designed in a standard 0.35 μm CMOS process and Figure 10 shows that the interface ASIC chip with three pathways (X-axis, Y-axis, and Z-axis) of the TMR sensors is made on the four-layer printed-circuitboard (PCB). The TMR sensitive element is on the opposite side of ASIC chip. ...
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... digital bit stream output is collected from the Sigma-Delta interface circuit by the oscilloscope Agilent MSO9104A (Agilent Technologies Inc, Santa Clara, CA, USA). Transient response results of the interface circuit are shown in Figure 11. The results show that the interface circuit can achieve analog digital conversion function. ...
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... 98000-point digital output sequence of the sigma-delta modulator is captured by an Agilent Logic analyzer 16804A (Agilent Technologies Inc, Santa Clara, CA, USA). The ouput digital signal is used to calculate the output power spectral density (PSD) as shown in Figure 12 by a MATLAB program. We optimized the switches and integrators in the sigma-delta modulator. ...
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... optimized the switches and integrators in the sigma-delta modulator. Figure 12 shows the comparison of test results previous work with no optimization and after harmonic distortion optimized. The power dissipation of the interface circuit chip is 8.6mW at a sampling frequency of 6.4 MHz. ...
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... testing the interface ASIC chip, we tested the TMR sensitive element together with the interface circuit. In order to avoid the disturbance of geomagnetic field and other electrical equipment magnetic field, we build the high-precision test platform as shown in Figure 13. The TMR magnetometers are put into a three-layer shielding tube made of high-magnetoconductivity permalloy. ...
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... power supply of the interface circuit combined with sensitive element is supported by the Agilent 3631A (Agilent Technologies Inc, Santa Clara, CA, USA). The test results are as shown in Figure 14. The full scale range is ±10 5 nT, the TMR sensors system can achieve a linearity of 0.3% at full scale range as shown in Figure 14a. ...
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... test results are as shown in Figure 14. The full scale range is ±10 5 nT, the TMR sensors system can achieve a linearity of 0.3% at full scale range as shown in Figure 14a. The Σ-Δ TMR micro-sensors system can achieve a power dissipation of 20 mW at a supply voltage of 5 V. Figure 14b shows the normalized noise test results which can achieve -11.22 dB at 1 Hz corresponding to 0.25 nT/Hz 1/2 (@1 Hz). ...
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... full scale range is ±10 5 nT, the TMR sensors system can achieve a linearity of 0.3% at full scale range as shown in Figure 14a. The Σ-Δ TMR micro-sensors system can achieve a power dissipation of 20 mW at a supply voltage of 5 V. Figure 14b shows the normalized noise test results which can achieve -11.22 dB at 1 Hz corresponding to 0.25 nT/Hz 1/2 (@1 Hz). The TMR sensors system can achieve a resolution of 0.25 nT/Hz 1/2 over a signal bandwidth, which is limited by the low-frequency noise of the sensitive element. ...
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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 [Formula: see text]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 [Formula: see text]. 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 [Formula: see text], it can achieve a nonlinearity of 0.2% FS and a resolution of 0.15 nT/Hz[Formula: see text] over a signal bandwidth.
