Spinning Current Technique Research Articles

Experimental evaluation of Hall-effect current sensors in BCD10 technology

A new version of the X-Hall broadband current sensor implemented in the BCD10 process by STMicrolectronics is experimentally characterized by means of static, magnetic, and thermal measurements. The results are comparatively assessed against the same topology implemented in a previous BCD generation as well as against a reference square-Hall sensor in the same BCD10 process and operated under the spinning current technique. The sensors realized in BCD10 technology are here presented for the first time. This experimental study demonstrates that the BCD10 technology generally improves sensor sensitivity for all the topologies under analysis. In particular, it offers a 10% increase of the current-to-magnetic field transduction factor, and almost a two-fold improvement of the current-related sensitivity for the X-Hall sensor.

The X-Hall Sensor: Toward Integrated Broadband Current Sensing

This article presents the X-Hall sensor, a viable sensing architecture for implementing a silicon-integrated, broadband, current/magnetic sensor. The X-Hall sensor overcomes the bandwidth limit of the state-of-the-art Hall sensors by replacing the spinning-current technique with dc-biased-based passive offset compensation. In this way, the X-Hall architecture removes the methodological bandwidth limit due to the spinning-current technique and allows for exploiting the Hall probe up to its practical limit, which is set by the parasitic capacitive effects. Moreover, the X-Hall architecture allows pushing the practical bandwidth limit at higher frequencies due to both the removal of the switches inherent in the spinning-current approach and a specially designed analog front end. To this end, a differential-difference current-feedback amplifier (DDCFA) is proposed as an analog front end in the X-Hall sensor. A prototype of the proposed X-Hall architecture is implemented in bipolar-CMOS- DMOS (BCD) 0.16-μm silicon technology to experimentally assess the performance of the X-Hall architecture. The passive offset compensation implemented into the X-Hall architecture is frequency-independent and preserves an adequate offset reduction performance, though less efficient than the spinning-current technique operated at low frequency. Experimental dynamic tests on the prototype identify the presence of an additive parasitic dynamic perturbation due to the package that prevents from fully exploiting the X-Hall prototype up to its designed bandwidth limit. However, the implementation of a postdeemphasis digital filter allows us to mitigate for the dynamic perturbation and experimentally achieve a sensor bandwidth of 4 MHz, which is the broadest bandwidth ever demonstrated by a purely Hall-effect based sensor.

Residual Offset in Silicon Hall-Effect Sensor: Analytical Formula, Stress Effects, and Implications for Octagonal Hall Plate Geometry

The Hall-effect magnetic sensors suffer from large offset that is described by the resistance mismatch in the Wheatstone bridge-like equivalent electrical circuit model of the Hall plate. After a first order cancellation of the raw offset using spinning current technique, a residual offset still exists, significantly limiting the accuracy of the Hall sensor in the detection of low magnetic field. In this paper we analyzed the residual offset in silicon Hall sensor using a nonlinear lumped resistor network model to derive a closed form expression. We further analyzed the residual offset in silicon Hall sensor under the influence of stress. Using these results, we show that eight-terminal, octagonal-shaped silicon Hall sensors employing eight-phase spinning current technique provide greater immunity to stress effects on residual offset due to a second order cancellation compared to the conventional four-phase spinning. The measurement results suggest superior offset performance of eight-terminal silicon Hall sensor.

Calibration and Characterization of a Reduced Form-Factor High Accuracy Three-Axis Teslameter

A new reduced form-factor three axes digital teslameter, based on the spinning current technique, has been developed. This instrument will be used to characterize the SwissFEL insertion devices at the Paul Scherrer Institute (PSI) for the ATHOS soft X-ray beamline. A detailed and standardized calibration procedure is critical to optimize the performance of this precision instrument. This paper presents the measurement techniques used for the corrective improvements implemented through non-linearity, temperature offset, temperature sensitivity compensation of the Hall probe and electronics temperature compensation. A detailed quantitative analysis of the reduction in errors on the application of each step of the calibration is presented. The percentage peak error reduction attained through calibration of the instrument for reference fields in the range of ±2 T is registered to drop from 1.94% down to 0.02%.

Accurate 3-axis measurement of inhomogeneous magnetic fields

Abstract Hall effect based Teslameters/Gaussmeters measure DC and AC magnetic flux densities in the range from a few µT to about 30 T. For accurate measurement a 3-axis Hall probe is applied with small magnetic field sensitive volume (MFSV) of 100 µm × 10 µm × 100 µm, with vertical and horizontal Hall elements integrated on a single chip. The planar Hall effect, that produces additional measurement errors is suppressed by the spinning current technique. The orthogonality error of the 3-axis Hall probe is reduced to smaller than 0.1° by the described calibration procedure. This paper explains why the above features are crucial for some applications in industry and modern science for accurate measurement of inhomogeneous magnetic fields and how to achieve them. The future technology trends in magnetic metrology are introduced and the newly developed Nanomapper that incorporates a 3-axis Hall probe with a MFSV of smaller than 10×10×10 micrometer is presented.

Bandwidth enhancement in Hall probe by X-Hall DC biasing

The spinning-current technique is the state-of-the-art method for offset cancellation in Hall-effect probe. This technique achieves the best results in terms of offset reduction but limits the acquisition bandwidth to less than 1 MHz; therefore, it precludes the use of purely Hall-effect sensors in broadband current measurement. We present the X-Hall probe, a DC bias approach combined with an octagonal 8-contact morphology of the Hall-effect probe, which overcomes the bandwidth limitations of spinning-current-operated Hall sensors while reducing the offset. A prototype of the X-Hall probe is realized in CMOS-like technology and can potentially achieve a bandwidth wider than 40 MHz with an acceptable residual offset.

Low-Frequency Noise Correlation in Current-Mode Magnetic Transducers: The CHOPFET Case

This paper is about low-frequency noise correlation in current-mode magnetic field transducers. The analysis methodology specifically focuses on the chopper-stabilized MAGFET (CHOPFET), a magnetotransistor that is compatible with the spinning current technique for low-frequency noise and offset cancelation. Experiments performed on a prototype circuit fabricated in the Austria Mikro Systeme 0.35 $\mu \text{m}$ CMOS process show a minimum value of 0.75 noise correlation between the two consecutive switching phases on an arbitrary-chosen terminal and whatever the operation region of the CHOPFET. This includes the contributions of uncorrelated sources, which cannot be separated from the correlated ones in the analysis process.

A Broadband, On-Chip Sensor Based on Hall Effect for Current Measurements in Smart Power Circuits

This paper presents a broadband ([dc—megahertz (MHz)]) current sensor for power applications, which is based only on a Hall-effect probe as the core sensing element. Unlike common solutions for broadband current sensing, the proposed architecture is suitable for integration of the measurement system on the same low-cost CMOS chip used for the power electronics (e.g., Bipolar-CMOS-DMOS), without the need for external transformers and allowing for the realization of “smart power circuits.” The Hall-effect probe is biased by implementing the offset compensation-oriented spinning-current technique through a novel front-end, designed to push the operative bandwidth toward the fundamental limit of the probe. Specifically, the proposed front-end employs switches, which are typical of spinning-current techniques, only for biasing the Hall probe, while the readout process is performed by minimum-sized differential amplifiers. In this way, the capacitive load seen by the Hall probe is minimized and the sensor practical bandwidth upper limit is strongly increased. A prototype of the proposed architecture was operated at 8-MHz spinning frequency and characterized by means of standard figures of merit, demonstrating the broadband capability and an adequate overall performance. At the same time, the prototype revealed a new bandwidth limit, masked in conventional architectures by stronger capacitance-induced effects, which is represented by a degradation of the effectiveness of the spinning-current technique. Measured performance is comparable to that of standard, nonintegrated, current sensors, demonstrating the effectiveness of the presented purely Hall approach for broadband current sensing. The architecture was validated by discussing two case studies typical of power applications.

An overview of commercially available Teslameters for applications in modern science and industry

<p>The Hall-effect based Teslameters (also called Gaussmeters) are the mostly applied instruments for measuring DC and AC magnetic flux densities in modern science and industry. This paper gives an overview of commercially available Teslameters at the high-end performance level. The Teslameters have been evaluated by following characteristics that are published by suppliers: probe dimensions, magnetic field sensitive volume, accuracy, magnetic resolution, measurement range, frequency bandwidth, temperature coefficient sensitivity, and price/performance ratio.</p><p>The Teslameter that best matches the measurement needs in various application fields incorporates a 3-axis integrated Hall probe, analog electronics based on the spinning-current technique, an analog-to-digital converter, an embedded computer, and a touch-screen display. The 3-axis Hall probe is a single silicon chip integrating both horizontal and vertical Hall magnetic sensors and a temperature sensor. The spinning-current eliminates most of the Hall probe offset, low-frequency noise, and the planar Hall voltage. The errors due to the Hall sensor non-linearity and the variations in the probe and electronics temperatures are eliminated by a calibration procedure. The errors due to the angular imperfections of the Hall probe are eliminated by a calibration of the sensitivity tensor of the probe. This Teslameter can measure magnetic field vectors from about 100 nT to 30 T, with the spatial resolution of 100 µm, magnetic resolution ±2 ppm of the range, the accuracy 0.002 % of the range, a temperature coefficient less than 5 ppm/°C, and angular errors less than 0.1°.</p>

High resolution shallow vertical Hall sensor operated with four-phase bi-current spinning current

Vertical Hall-effect devices (VHDs) are CMOS integrated sensors dedicated to the measurement of magnetic field in the plane of the chip. At low frequency, their performances are severely reduced by 1/f noise. This paper presents the capability of a bi-current biasing combined to a four-phase spinning current technique (SCT) to lower 1/f noise and improve the resolution of shallow VHD designed in low-voltage CMOS technologies (LV-VHD). It has been shown that applying the highest achievable biasing current on each phase of the SCT and combining it with a switched gain, the sensor resolution can be optimized. A practical way to implement this technique is proposed, and experiments obtained from a 3μm wide, 25μm long LV-VHD integrated in the AMS 0.35μm CMOS technology show that 1/f noise is efficiently reduced, leading to a resolution of 51μT over a 1.6kHz bandwidth with an average biasing current of only 825μA.

Performance prediction of four-contact vertical Hall-devices using a conformal mapping technique**Project supported by the Natural Science Foundation of Jiangsu Province, China (Nos. BK20131379, BK20141431) and the Graduate Research and Innovation Projects of Jiangsu Province (No. SJLX_0373).

Instead of the conventional design with five contacts in the sensor active area, innovative vertical Hall devices (VHDs) with four contacts and six contacts are asymmetrical in structural design but symmetrical in the current flow that can be well fit for the spinning current technique for offset elimination. In this article, a conformal mapping calculation method is used to predict the performance of asymmetrical VHD embedded in a deep n-well with four contacts. Furthermore, to make the calculation more accurate, the junction field effect is also involved into the conformal mapping method. The error between calculated and simulated results is less than 5% for the current-related sensitivity, and approximately 13% for the voltage-related sensitivity. This proves that such calculations can be used to predict the optimal structure of the vertical Hall-devices.

High-accuracy teslameter with thin high-resolution three-axis Hall probe

The new digital teslameter system (also called Gaussmeter) incorporates a 3-axis Hall probe, analog electronics based on the spinning-current technique, 24-bit analog-to-digital converter, computer, and 7-digit touch-screen display. The Hall probe is a single silicon chip with monolithically integrated horizontal and vertical Hall magnetic sensors and a temperature sensor. The Hall sensor chip is encapsulated in a robust ceramic package, a version of which is only 250 μm thick. The spinning-current eliminates most of the Hall probe offset, low-frequency noise, and the planar Hall voltage. The errors due to the Hall element non-linearity and the variations in the probe electronics temperatures are eliminated by a calibration procedure based on a three-variable second-order polynomial. The errors due to the angular errors of the Hall probe are eliminated by a calibration of the sensitivity tensor of the probe. These new developments resulted in a teslameter that can measure magnetic field vectors from about 1 μT to 30 T, with the spatial resolution 100 μm, magnetic resolution ±2 ppm of the range, the accuracy ±0.0001% of reading +0.001% of range, temperature coefficient less than 5 ppm/°C, and angular errors less than 0.1 deg.

Four-phase Bi-current Spinning Current on Shallow Vertical Hall Sensor

Vertical Hall-effect devices (VHDs) are CMOS integrated sensors dedicated to the measurement of magnetic field in the plane of the chip. At low frequency, performances are severely reduced by the 1/f noise. We have recently assessed by FEM simulation the capability of the four-phase spinning current technique (SCT) to lower the 1/f noise on shallow VHD designed in low-voltage CMOS technologies (LV-VHD). It was shown than the highest biasing current could be used on each phase of the SCT, i.e. I13max for phases 1 and 3, and I24max for phases 2 and 4, if the signal on phases 2 and 4 is amplified by a ratio I13max/I24max. Here, we propose a practical way to implement this technique, and for the first time we show experimentally its efficiency to lower the 1/f noise, leading to 51 μT resolution over a 1.6 kHz bandwidth with a average biasing current of only 825 μA.

An improved compact model of the electrical behaviour of the 5-contact vertical Hall-effect device

This paper presents the improvement of an existing design-oriented compact model of the 5-contact vertical Hall-effect sensor integrated in CMOS technology. Such a model should facilitate the work of designers, permitting them to simulate the sensor, the biasing and processing electronics together with the same electrical simulator. Focus is put on the main aspects that alter the electrical response of the sensor: modulation of the conduction channel due to the bias-dependent space charge region thickness, saturation of carrier velocity, asymmetries, and effective channel conduction thickness. The model has been achieved with a subtle mix of theoretical considerations, numerical simulations performed with COMSOL Multiphysics® and experimental data. The parameters extraction procedure is also discussed. The model has been validated on experimental data gathered from two devices, one fabricated in a low-voltage CMOS technology and the other one in a high-voltage CMOS technology. Then, the model is used in order to study offset issues in VHD with external measurement contacts, i.e. VHD integrated in the shallow N-well of low-voltage technologies, and the way the spinning current technique can be used to suppress this offset. A new spinning-current technique is proposed for such a VHD. The simulation results are in perfect accordance with the analytical study. They pave the way for the design of an optimized readout circuitry that may improve the sensor sensitivity while maintaining a very low offset.

Magnetic noise of a frozen ferrofluid

The magnetic noise of a frozen ferrofluid made of maghemite nanoparticles dispersed in glycerin is measured using a two-dimensional electron gas based quantum well Hall sensor (QWHS) with the spinning current technique. The frozen ferrofluid shows a superspin glass transition at 67 K. Below this glass transition temperature, the relation between the imaginary part of the ac susceptibility of a bulk ferrofluid sample and the magnetic noise measured with the QWHS gives an indication of a violation of the fluctuation dissipation theorem.

A local noise measurement device for magnetic physical systems

We present an experimental setup developed to measure locally the fluctuations of themagnetization of physical systems such as spin and superspin glasses. It is based onmicronic and submicronic Hall probes. We present the noise reduction at ambienttemperature owing to the use of the spinning current technique. Finally, we show why, withsuch probes, the noise measured on a macroscopic sample probes only a microscopicvolume of the sample.

A Hall Sensor Analog Front End for Current Measurement With Continuous Gain Calibration

This paper presents a new technique for continuously calibrating the sensitivity of a current measurement microsystem based on a Hall magnetic field sensor. An integrated reference coil generates a magnetic field for calibration. Using a variant of the chopper modulation, the spinning current technique, combined with a second modulation of the reference signal, the sensitivity of the complete system is continuously measured without interrupting normal operation. Modulation and demodulation schemes allowing the joint processing of both external and reference magnetic fields are proposed. Additional techniques for extracting the very low reference signal are presented. The implementation of the microsystem is then discussed. Finally, measurements validate the calibration principle. A thermal drift lower than 50 ppm/degC is achieved. This is 6-10 times less than in state-of-the-art implementations. Furthermore, the calibration technique also compensates drifts due to mechanical stresses and ageing

Thermal behaviour of CMOS Hall sensors for different operating modes

Abstract New results obtained with CMOS Hall sensors are presented. The dependence of the sensitivity on temperature has been investigated for constant-current and constant-voltage operation modes. The current-related sensitivity varies with a very low value of 0.03%/°C in the constant-voltage mode. A new NMOS Hall sensor with eight contacts enables the spinning-current technique to be used for offset reduction. The averaged offset values of all eight possible current directions in this sensor exhibit an offset suppression by a factor up to 2000. This leads to a magnetic-field offset of the spinning-current sensor of less than ±200 μT for a wide temperature range.