A 3.5MHz-BW 128nTrms Resolution TMR Readout Using Ping-Pong Auto-Zeroing and SAR-Assisted Offset Calibration for Contactless Current Sensing

This paper presents a tunnel magnetoresistance (TMR) sensor readout circuit for contactless current sensing. The proposed instrumentation amplifier utilizes ping-pong auto-zeroing to achieve a high resolution of 128n$\mathrm{T}_{\mathrm{r}\mathrm{m}\mathrm{s}}$ and can process sensor input signals up to 3. 5MHz. A SAR-assisted offset calibration eliminates the intrinsic offset of the TMR sensor, leaving a maximum sensor offset of 311nT (10 samples). By compensating the temperature coefficient (TC) of the TMR bias circuit, the temperature dependence of the sensor sensitivity is significantly reduced by 16×. Overall, the highly power-efficient sensor readout, including the TMR bias circuit, achieves a state-of-the-art FoM of 0. 57fW/Hz.