Joris Pascal

3D Hall probe integrated in 0.35 μm CMOS technology for magnetic field pulses measurements

This paper presents a 3 dimensional magnetometer based on Hall effect sensors integrated without any post processing in a standard low cost 0.35 mum CMOS technology. The system is dedicated to magnetic pulses measurements under a strong static field. Two vertical Hall devices (VHD) are sensitive to the components of the magnetic field oriented in the plane of the chip, while a horizontal Hall device (HHD) is sensitive to the component of the magnetic field orthogonally oriented to the plane of the chip. 3 identical instrumental chains are integrated to perform amplification of the 3 Hall voltages. The system implements a compensation of the static magnetic field and allows to measure magnetic fields pulses with a resolution of 79 muT over a [5 Hz - 1.6 kHz] bandwidth. Pulses are in the range from hundreds of muT to tens of mT in the frequency range from 1 Hz to 10 kHz. The static field is compensated up to 1.5 T. The spatial resolution is 44 mum. The system power consumption has been optimized to 15 mW.

CMOS integrated system for magnetic field monitoring and gradient measurement in MRI environment

This paper reports on a standard CMOS integrated system for monitoring the magnetic fields in MRI environments. The sub-micron technology circuit features three horizontal hall devices and their associated electronics that form instrumental chains. Two of them are dedicated to millitesla range magnetic pulse and gradient measurement whereas the third one is for monitoring the strong static field of the MRI setup. The 0.35 mum technology prototype performs 130 muT gradient measurement with 20 muT resolution and can also map static fields as high as 1.5T.

A Vertical Hall Device in Standard Submicron CMOS Technology

In order to lower the short circuit effect due to the measurement contacts, vertical Hall devices (VHD) are generally designed either in bulky N-type silicon or in the deep N-well of high-voltage CMOS technologies. In this last case, VHD can benefit from on chip circuitry for offset and 1/f noise reduction, but HVCMOS remains a costly technology. Recently, using spinning-current, a HVCMOS compatible VHD with a resolution of 76 muT over a 1.6 kHz bandwidth has been demonstrated. The VHD presented here is designed in the shallow N-well of a low cost 0.35 mum standard CMOS technology. Unlike conventional VHD, its measurement contacts are located outside the sensor active area. FEM simulations and experimental results show that the new geometry suppresses the short circuit effect and strongly reduces the intrinsic offset and noise. Thus, without any noise and offset reduction method, this new small VHD (63 mum2) reaches a resolution of 79 muT over a [5 Hz - 1.6 kHz] bandwidth.

Chopper stabilized CMOS integrated front-end for magnetic field measurement

This paper presents an analogue front-end dedicated to magnetic field measurement that is intended to be used in a mixed signal submicron CMOS microsystem. The front-end features a Hall device and its biasing circuitry both associated to a nested chopper-like structure. This system efficiently removes 1/f noise and reduces offset. The biasing amplifier is chopped at a frequency fc in order to ensure steady ground referencing to the Hall device. This latter is operated using the spinning current technique at a frequency fs = fc/2. Sensitivities of 90 V/AT and resolutions of about 15 muT over a 1.6 kHz bandwidth extending from 5 to 1.6 kHz have been measured

Continuous calibration of Rogowski coil current transducer

Rogowski coils (RC) used for high-accuracy contact-less current measurement ask for precise sensor geometry and specific conditions, such as a centered primary conductor. To relax these constraints, we propose here a recently patented continuous calibration system which features a reference conductor added coaxially to the primary conductor and a proportional-integral controller integrated in CMOS technology. Experimental results obtained with commercial flexible and rigid RC show that the sensor immunity to the conductor position, as well as the dispersion between RC, is reduced to +/-0.1%, i.e. a 0.1 class measurement. In addition, the system may ensure an absolute calibration of the RC current transducer, avoiding any costly calibration procedure at the end of the sensor manufacturing.

Integrated front-end for on line continuous calibration of Rogowski coil current transducer

The Rogowski coil is a traditional current-to-voltage transducer. To use it for high-accuracy measurement of low frequency AC current, it is necessary to have a very precise sensor geometry and very specific conditions, such as a stable temperature and a centered primary conductor in order to minimize errors. Conversely, it is also possible to compensate for these errors by using a sensor calibration. This paper presents a new continuous calibration system for Rogowski coil current transducer (RCCT). It features a reference conductor added close to the primary conductor and a calibration circuit which has been integrated in CMOS technology. First experimental results obtained with a homemade RCCT show that we drastically improve the immunity of the sensor to the primary conductor position with an error below ±2 % when the calibration is active against -8% to +4% without calibration. Limitations of the method are also discussed.

Signal processing for electro-optic voltage sensor

We present an electro-optic sensor for accurate AC voltage measurement in high voltage substations. This paper focuses on the novel signal processing method developed to retrieve the applied voltage from the sensors periodic optical signals. The sensor head was presented in an earlier publication. The method is capable of extracting the sensor temperature directly from the optical signals and uses this information for temperature compensation. This enables the sensor to operate with an accuracy of ±0.2% between -40 °C and +80 °C. Compared with earlier solutions, robustness has been improved as the method can now determine the intrinsic birefringence of the optical sensing element and thereby remove a fundamental source adding to the measurement error. This allows relaxing the requirements for high quality optics.

ECG Signal Artifacts Suppression System Based on an MRI Environment Dedicated CMOS Magnetic Field Monitor and FPGA Implementation

This paper presents a system for correcting ECG signals perturbed by MRI environments. The proposed system is based on a dedicated ASIC for measuring with high resolution the MRI magnetic gradients, which are the cause of the ECG artifacts. The measured data are used to calculate the coefficients of an integration compliant adaptive LMS filter. The filter removes the artifacts from the perturbed ECG. The filter has been implemented together with a QRS complex detection algorithm on an FPGA target. The promising experimental results validate the principle and open new perspectives in terms of ASIC integration of the whole system.