ASIC Current-Reuse Amplifier With MEMS Delta-E Magnetic Field Sensors

An application specific integrated circuit (ASIC) and a custom-made microelectromechanical system (MEMS) sensor are presented, designed to function together as a sensor system for measuring low amplitude low frequency magnetic fields. The MEMS system comprises several free-standing double-wing magnetoelectric resonators with a size of $900~\mu $ m x $150~\mu $ m to measure alternating magnetic fields in the sub-kilohertz regime. It utilizes piezolelectric (AlN) and magnetostrictive (FeCoSiB) layers to exploit the delta-E effect for magnetic field sensing. On the ASIC a three-channel current-reuse amplifier with lateral bipolar transistors in the input stage is implemented occupying a chip area of 0.0864 mm2. Measurements demonstrate a voltage gain of 40 dB with a 3-dB bandwidth of 75 kHz and an input referred noise floor of 8 nV/ $\surd $ Hz while consuming $199~\mu $ W per channel. The sensor system is capable of detecting magnetic fields with a limit of detection (LOD) of 16 nT/ $\surd $ Hz for single sensor elements. By operating three sensor elements in parallel, one on each amplifier channel, the LOD is further reduced to 10 nT/ $\surd $ Hz. Owing to the high reproducibility of the sensor elements, this improvement in the LOD is close to the ideal value of $\surd 3$ . The results imply that the system can be scaled to large numbers of sensor elements without principle obstacles.