A Low-Power Chopper-Stabilized Readout Interface ASIC for High-Resolution TMR Magnetometers

Tunnel magnetoresistance (TMR) sensors have attracted considerable attention in high-resolution magnetic-field measurement owing to their high sensitivity, low power consumption, and excellent temperature stability. However, the weak differential output of TMR Wheatstone bridges is highly susceptible to DC offset and low-frequency flicker noise, which significantly limits the overall sensing performance. To address these issues, this paper presents a low-power readout interface ASIC based on a chopper-stabilized programmable instrumentation amplifier (PGIA) for TMR magnetic sensors. The proposed PGIA provides eight programmable gain settings from 1 V/V to 128 V/V. A transconductance equalization technique is introduced to maintain nearly constant input transconductance over the entire rail-to-rail common-mode input range, thereby improving gain stability and reducing input-referred noise. In addition, a dynamic slew-rate enhancement circuit is employed to improve transient response without increasing static power consumption, while a digitally assisted offset calibration circuit effectively suppresses input offset and enhances measurement accuracy. The proposed interface ASIC was fabricated using a standard 0.18 μm CMOS process and experimentally evaluated in a compact TMR magnetometer prototype. Measurement results demonstrate a full-scale nonlinearity of 0.1% FS over a ±100 μT magnetic-field range, a magnetic noise density of 0.13 nT/√Hz at 1 Hz, and a combined power consumption of 10 mW for the readout ASIC and TMR sensing bridge, with the prototype powered from a 5 V external supply and the ASIC core operating from a regulated 3.3 V rail. Compared with representative reported magnetometers, the proposed system achieves an excellent trade-off among power consumption, linearity, and magnetic-field resolution, making it well suited for portable and high-precision magnetic sensing applications.