Pavel Kejik

Submicrometer Hall devices fabricated by focused electron-beam-induced deposition

Hall devices having an active area of about (500 nm)(2) are fabricated by focused electron-beam-induced deposition. The deposited material consists of cobalt nanoparticles in a carbonaceous matrix. The realized devices have, at room temperature, a current sensitivity of about 1 V/AT, a resistance of a few kilo-ohms, and can be biased with a maximum current of about 1 mA. The room-temperature magnetic field resolution is about 10 muT/Hz(1/2) at frequencies above 1 kHz.

A new compact 2D planar fluxgate sensor with amorphous metal core

A new compact 2D planar fluxgate sensor using a ferromagnetic amorphous metal core is described. The fluxgate sensor consists of two orthogonal planar metallic coils and a ring shaped amorphous magnetic ribbon mounted on a PCB substrate. Each planar coil is used alternatively as excitation or as pick-up coil. An electronic interface drives alternatively the two coils and performs a feedback on each sensing coil in order to compensate for the two measured magnetic field omponents. The sensing element has a magnetic sensitivity of 55 VrmT at an excitation frequency of 8.4 kHz with a 160 mApeak driving current. Used as an electronic compass, the reached precision angle is better than 1degree.

Circular Hall Transducer for Angular Position Sensing

We developed a new integrated magnetic sensor based on the Hall effect, suitable for contactless 360deg absolute angle encoding. The sensing device consists of a narrow n-well ring with a chain of 64 contacts equally distributed along the ring. It is connected to on-chip biasing and signal conditioning circuits that provides the magnitude and the phase of the in-plane component of the magnetic field. In a homogenous magnetic field, the transducer angular resolution is 0.01deg in the 1 kHz frequency bandwidth and the absolute accuracy is about 1deg and 0.1deg without and with output offset calibration, respectively.

Low-power 2-D fully integrated CMOS fluxgate magnetometer

In this paper, we present a low-power, two-axis fluxgate magnetometer. The planar sensor is integrated in a standard CMOS process, which provides metal layers for the coils and electronics for the signal extraction and processing. The ferromagnetic core is placed diagonally above the four excitation coils by a compatible photolithographic post process, performed on a whole wafer. The sensor works using the single-core principle, with a modulation technique to lower the noise and the offset at the output. In contrast to traditional fluxgate approaches, the sensor features a high degree of integration and minimal power consumption at 2.5 V of supply voltage that makes it suitable for portable applications. A novel digital feedback principle is integrated to linearize the sensor characteristics and to extend the linear working range.

True 2D CMOS integrated Hall sensor

We have designed and realized a new integrated Hall structure that converts the magnetic field vector in the chip plane, into an ac signal, whose amplitude and phase correspond to the magnitude and direction of the field. It is the first Hall sensor that provides the field angle without the need of computing an arctan function. The Hall structure is formed by a n-well ring with a large number of contacts equally distributed along the ring, like a circular railroad track. Each contact is connected to the control electronics through switches. The measurement consists in activating a small portion of the ring at the time, forming a vertical Hall probe and uses the switches to make this portion circulate. The measurement sequence suppresses the zero-field offset and the 1/f noise. At 100 Hz, the resolution is 14 muT and 0.008deg. We propose a measurement scheme to further reduce the offset, and remove the need for calibration.

Three-Axis Teslameter With Integrated Hall Probe

The first commercially available teslameter with a fully integrated three-axis Hall probe is described. The Hall probe chip contains horizontal and vertical Hall elements, analog electronics, and a synchronization circuit. A horizontal Hall element measures the perpendicular component, and two vertical Hall devices measure the two in-plane components of a magnetic flux density vector. Current spinning in the Hall devices cancels offset, 1/f noise, and the planar Hall voltage. The analog electronic module of the teslameter cancels the residual offset and compensates temperature dependence and nonlinearity of the Hall voltages. The digital module provides analog-to-digital conversion and communication to a computer.

Ultra low-power angular position sensor for high-speed portable applications

We present a technique for contactless angular position sensing that allows low power consumption while keeping dynamic properties comparable to existing sensors. The technique essentially consists in combining a recently developed sensing element, the so-called Circular Vertical Hall Device, with a simple and robust signal treatment based on phase detection. Because of its low startup time, this circuit is specially suited for pulsed mode operation, which enables to further decrease the power consumption. More generally, the absence of complex digital signal treatment makes this technique a natural method for measuring the magnetic field direction and therefore for designing an angular position sensor using Hall probes.

First fully CMOS-integrated 3D Hall probe

We present the first fully CMOS-integrated 3D Hall probe. The microsystem is developed for precise magnetic field measurements in the range from mT up to tens of tesla in the frequency range from DC to 30 kHz and with a spatial resolution of about 150 /spl mu/m. The microsystem is realized in a conventional CMOS process without any additional processing step and can be manufactured at very low cost. With the electronics circuit applying the so-called spinning-current technique to the Hall sensor block, we obtain low noise (a resolution better than 100 /spl mu/T) and low cross talk between the channels (less than 0.2% between the channels up to 2 T). The single chip configuration insures a precision of the orthogonality between the measurement axes better than 0.5/spl deg/. A temperature sensor based on a band-gap cell is integrated directly on the chip, which allows a good temperature drift compensation of the system.

Precise DC current sensors

Three novel DC current sensors are described. Portable 40 A DC current clamps have resolution of 1 mA and high immunity to unclamped currents and external fields. AC/DC comparator with amorphous core may serve for precise measurement of DC currents with AC component up to 1 kHz. Magnetoresistive sensor field has limited accuracy but potential bandwidth from DC to 1 MHz.

Purely CMOS angular position sensor based on a new hall microchip

This paper presents a new technique to sense the direction of the magnetic field, enabling a new generation of contactless 360deg absolute angle encoders. The sensor consists of a microchip that contains a special ring-shaped Hall element. It is the first sensor that gives the angle value without the need of computing an arctan function. In addition, we demonstrate that this system is compatible with a self calibration method. Measurements were performed with the microchip operating inside a hollow permanent magnet and an accuracy of 0.1deg was obtained without calibration.