Francis Braun

CMOS microsystem for AC current measurement with galvanic isolation

In this paper, we present an integrated AC current sensor based on sensitivity-optimised horizontal Hall effect devices (HHDs) and a differential readout chain. It has been designed for 5A nominal AC current measurement with 5 kV galvanic isolation and 0.5% accuracy over 1.5 kHz bandwidth, which allows up to 30/sup th/ (25 th) harmonic detection in 50 Hz (60 Hz) applications. From the sensing element to the instrumental chains output the signal conditioning is exclusively performed by low-noise standard CMOS analog blocks. Moreover the whole microsystem features a mixed signal structure dedicated to auto-balancing.

Horizontal Hall effect sensor with high maximum absolute sensitivity

Sensitivity of conventional Hall sensors is strongly limited by the well known short-circuit effect. Many researches were devoted to reduce offset and noise but few works were carried out to improve sensitivity. Here, a new shape of integrated horizontal Hall device is presented. This particular shape has been developed to minimize the short-circuit effect of the sensor, allowing one to shrink the device length and consequently to reduce the biasing resistance. Then the biasing current of this sensor can be significantly increased to obtain an absolute sensitivity higher than for conventional devices. Such a Hall effect device needs a specific biasing circuit which is also presented.

A chopper stabilized biasing circuit suitable for cascaded wheatstone-bridge-like sensors

Many sensitive devices are based on Wheatstone bridge structures or can be modeled as Wheatstone bridges like Hall effect magnetic sensors. These sensors require a biasing circuit, and many solutions were proposed. However, up to now, none of them gives the opportunity to cascade several sensors, while such a cascade can help in improving the signal-to-noise-ratio (SNR) or in removing some parasitic effects through the direct summing/subtraction of sensing/parasitic effects. The circuit this paper presents is based on an operational transconductance amplifier with n output stages, and allows to cascade n Wheatstone-bridge-like sensors. It is shown that the maximal number of bridges which can be efficiently cascaded is limited by the output resistance of the output stages. Nevertheless, this number remains sufficient in practical cases, easily up to n=10. To remove the 1/f noise coming from the output stages, a chopper stabilization is used. We also establish formulas which allow quick hand calculation of the main parameters of the circuit. A prototype where 10 Hall effect sensors are cascaded is presented as well as experimental results.

A Hall effect sensors network insensitive to mechanical stress

Hall effect devices are widely used as magnetic sensors in integrated technology. Since they are very sensitive to mechanical stress, they are not suitable for the design of systems subjected to vibrations (portable systems, automotive applications,...). To cancel this cross-sensitivity, the spinning current method may be used. Nevertheless, this method does not remove, but modulates, the mechanical signal. Vibrations whose frequencies are close to the spinning frequency are thus rejected in the base band. Here, we propose an alternative based on a Hall effect sensor network. This method totally removes the mechanical signal and may be combined with the spinning current method in order to reject the flicker noise of the sensor. Compared experimental results obtained with Hall effect sensors subjected to vibrations are presented and discussed.

A two-axis magnetometer using a single magnetic tunnel junction

Based on a qualitative study of the Stoner-Wohlfarth model, we point out that driving a magnetic tunnel junction (MTJ) with an alternative two-dimensional magnetic field allows to measure simultaneously two components of an external magnetic field. Only one single MTJ without a pinning layer is needed to measure both components of a magnetic field parallel to the junction plane. The response of the magnetometer does not depend on the resistance of the junction or the amplitude of its variations. A prototype has been manufactured and encouraging experimental results are presented. Sensitivities higher than 500 V/T and a noise level of 2 /spl mu/T//spl radic/Hz are reported.

Compact modeling of a magnetic tunnel junction using VHDL-AMS: computer aided design of a two-axis magnetometer

Currently, the lack of compact magnetic tunnel junction (MTJ) model is a truly limiting factor for the design of spintronics circuits. In this paper, we present a compact MTJ model written in VHDL-AMS. This behavioral model is based on the Stoner-Wohlfarth model and takes most of the important phenomena such as magnetic coupling, capacitance, and magnetization dependent conductance into account. The method employed to model a two layer magnetic tunnel junction is detailed. Applications of this model such as the simulation of the operation of a magnetometer is also presented.

CMOS Microsystem Front-End for MicroTesla Resolution Magnetic Field Measurement

In this paper we discuss the conception and performances of a monolithic microsystem for magnetic field measurement built in standard 0.6 μm CMOS technology. It is shown that 5.2 microTesla resolution over 1 kHz bandwidth (5 Hz to 1 kHz) can be achieved by combining a particular Hall effect based sensing device and appropriate analog conditioning electronics. The study focuses on the methods used to drive up the sensors sensitivity and to drive down the systems noise level in order to achieve the above-mentioned resolution. A specific circuitry is proposed for biasing the sensor.

Analytical Modeling of Hot-Carrier Induced Degradation of MOS Transistor for Analog Design for Reliability

A CMOS transistor ageing analytical model is presented and the procedure that allows to extract its parameters is proposed in this paper. By using a simple, example, we show how such a model can be used to forecast the drifts of the main characteristics of a CMOS circuit Further, we demonstrate that this model can also be used to help the designer to choose and/or modify a circuit in order to minimize the hot-carrier induced degradations. Simulation results compared to the analytical study are also shown

VHDL-AMS based design methodology of very large scale integration fully digital controller for intelligent power control

This paper presents a methodology to design very large scale integration fully digital controller for intelligent power control. Step by step, top-down methodology for virtual prototyping based on very high speed integrated circuits hardware description language-analog-mixed signal (VHDL-AMS) with associated mixed simulation tools was used to study digital adaptation and architecture implementation of the control algorithm. Modeling, mixed simulation and virtual prototyping are achieved in an unique design environment. An application using the proposed methodology was studied: a digital controller for a single-phase parallel active power filter. The controller is described and virtual prototyping examined. Analog and digital models were used to define the algorithm implementation, specific binary format and architecture. The register transfer level model for this digital controller was finally validated by mixed simulation

A 100 MHz Current Conveyor in 0.35 μm CMOS Technology

In this paper a new 0.35 μm CMOS technology second generation current conveyor (CCII) is presented. It is a low power (60 μA @ ± 1.5 V power supply) circuit, featuring 88 × 100 μm2 area, 100 MHz bandwidth and 10 GHz equivalent gain bandwidth (GBW) product. Its static and dynamic characteristics when used both as a voltage and current buffer are described. The chip has been fabricated and tested, and experimental results are discussed. Its use in an application as an instrumentation amplifier (IA) is also presented. The CCII based IA has weaker offset and better CMRR than its voltage mode equivalent. In order to cancel output offset voltage and reduce noise, the IAs input and output signals are chopped at high frequency.