A BiCMOS Circuit Interface for Low Power and Low Noise Magnetic Field Sensor Systems

Bio-magnetic sensing will have broad applications owing to its advantages of being non-invasive and having good spatial resolution. A wearable magnetic sensing device can realize long-term health monitoring for the purposes of medical research and diagnosis. The challenges underlying this technology are the simultaneous realization of low magnetic noise with low power consumption. Strain-modulated, multiferroic, vector magnetic field sensors have shown high sensitivity and low magnetic noise with small volume. To achieve a complete low power sensing system, this paper presents a low flicker noise readout circuit realized in SiGe BiCMOS 130 nm. The application specific integrated circuit (ASIC) achieves amplification and demodulation of the sensor output current using a differential, demodulation-first structure. The system includes demodulation noise cancellation to largely reduce the external noise from the modulation drive voltage, such that the magnetic noise of the sensor-readout system is improved. In the paper, we discuss the design requirements, implementation, innovation, and measurement results of a prototype readout ASIC and the complete sensing system. The presented sensor-readout system has small volume, low power consumption, and adequate bandwidth and resolution. It is able to measure magnetic fields with a bandwidth from 40 mHz to 3.1 kHz. A magnetic noise floor of 85 pT/ $\surd $ Hz at 1 kHz and 300 pT/ $\surd $ Hz at 10 Hz is achieved with a power consumption of 5.6mW when measuring the sensor device paired with small flux concentrators. This result is compared with other state-of-the-art magnetic sensing systems.