Yujia Huo

Low noise and low power neural recording amplifiers are required for implantable devices measuring action potentials. This paper presents a dynamic current pulsing technique combined with a special type of two-stage low-pass filter (LPF) that demonstrates an improvement in the noise efficiency factor (NEF) beyond that achievable using traditional design. A low NEF of 1.55 is achieved at an average power consumption of 587.8 nW and 5.18 µVrms noise, integrated from 0.1 to 9.8 kHz, inclusive of the impacts of sampling and aliasing. The NEF is improved from 1.76 in the static low current state (LCS) and 1.67 in the static high current state (HCS), measured on the same amplifier chip.

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.

The recording and analysis of bio-magnetic fields has widespread applications in medical research and diagnostics. Wearable magnetic field sensors offer a non-contact and portable method for sensing bio-potentials. This paper presents a readout circuit in 180 nm CMOS for strain modulated multiferroic vector magnetic field sensors. By utilizing a demodulator first architecture, the circuit bandwidth and dynamic range requirements are greatly reduced allowing for a low power consumption of 5.9 mW. The circuit bandwidth is from 76 mHz to 2.2 kHz, allowing for measurement across the range of interest for bio-magnetic signals. Utilizing a modulation noise cancellation technique, the noise performance of the sensor system is significantly improved, and the sensor modulation amplitude can be increased, resulting in improved sensor sensitivity. Measurements for the sensor-readout system demonstrate a 144 pT/√Hz magnetic noise floor at 1 kHz. The noise and power consumption are significantly lower than alternative magnetic sensor systems of similar volume.

Low noise sensors with low power consumption are needed for sensing the bio-magnetic potentials produced by the human body. Compared to their electrical counterparts, bio-magnetic sensors are non-invasive and non-contact. A strain modulated FeCo-Hf/AlScN based sensor with a bandwidth of 3.4 kHz and a magnetic noise spectral density at 1 kHz of 59.5 pT/√Hz before demodulation and 98.5 pT/√Hz after demodulation in an unshielded environment is presented. The footprint of the sensor including flux concentrators is 0.125 cm ² , and the total power consumption of the printed circuit board based readout electronics is 440 mW. A theoretical analysis for scaling of the sensitivity and the noise spectral density of modulated multiferroic sensor systems is presented.

Magnetic fields produced by the body can provide information for medical diagnoses, patient monitoring, and robotic control. Measuring biomagnetic signals locally allows for an external sensing mechanism that is non-invasive and non-contact. Despite these advantages, current sensing systems are either prohibitively large, consume excessive power, or both when applied to on-body applications. This study explores how multiferroic systems can provide an alternative to current biomagnetic sensing platforms. While maintaining a very small die size (2.25mm $^{\mathbf{2}}$ ) and low power consumption (13mW), multiferroic resonant MEMS magnetometers can provide high sensitivity and low noise at room temperature. Two resonant plate designs operating in the MHz regime are explored, implementing a strain modulation technique to upconvert low frequency magnetic field signals to the resonance band of the plates, utilizing the high device Q factors. When operated below the Duffing limit, sensitivities of 58.4mA/T and 37.7mA/T with resolutions of 5.03nT/ $\surd$ Hz and 2.72nT/ $\surd$ Hz, respectively, were observed for the two devices. Without electric modulation, the large sensor design shows a sensitivity of 1.56A/T and a resolution of 2pT/ $\surd$ Hz when sensing an AC magnetic field at the device resonance. 2022-0158