Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1998-08-24
2000-05-16
Patidar, Jay
Electricity: measuring and testing
Magnetic
Magnetometers
327511, 324225, G01R 3306
Patent
active
060642025
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is in the field of integrated micro sensors, in particular sensors for measuring a magnetic field (Hall devices).
BACKGROUND OF THE INVENTION
A Hall device usually has the form of a plate, but not necessarily. This plate consists of conducting material provided with at least four electrical contacts at its periphery. A bias current I is supplied to the device via two opposite contacts, called the current contacts. The two other contacts are placed at two equipotential points at the plate boundary. These contacts are called the voltage contacts or the sense contacts. If a magnetic field perpendicular to the surface is applied to the device, a voltage appears between the sense contacts due to the Hall effect. This voltage is called the Hall voltage. An example of a Hall device is shown in FIG. 1, where for the basic function only the contact pairs AC and BD are used.
A major problem of Hall devices is their offset voltage. The offset voltage is a static or a very low frequency output voltage at the sense contacts of the Hall device in the absence of a magnetic field. The causes of offset voltages in integrated Hall devices are imperfections of the fabrication process and nonuniformity of materials. An offset reduction method according to the state of the art is the switched spinning current method. This method uses a Hall plate with eight or more contacts which are symmetrical with respect to rotation by e.g. 45.degree.. The direction of the current is made to spin discretely by contact commutation. Averaging the consecutive Hall voltages reduces the offset.
SUMMARY OF THE INVENTION
An object of the invention is to simplify and to generalize the switched spinning current method as described, for example, in the article "Offset Reduction in Spinning-Current Hall Plates" by Bellekom and Munter, Sensors And Materials, Vol. 5, No. 5, (1994) pages 253-263, and to further reduce the offset voltage.
The inventive method serves for dynamically compensating the offset voltage of a Hall device. The Hall device can have either a platelike structure with a circular conductive area and at least four contacts arranged in pairs of opposite contacts on the circumference of the conductive area, the pairs of contacts being spaced from each other by equal spatial angles or it can have any form deriveable from such a circular arrangement by conformal mapping. It can e.g. be a so called vertical Hall device. The contact pairs are angled by e.g. 90.degree.. Each pair is supplied with a periodically alternating current whereby the phase shift of the supply currents corresponds to the spatial phase shift of the contact pairs and is e.g. 90.degree.. Superposition of the supplied currents results in a continuously spinning current vector in the Hall device. By measuring simultaneously the voltages between corresponding terminals, a signal consisting of the Hall voltage and a periodic offset voltage can be isolated. The offset voltage is eliminated by averaging the signal over at least one period. The advantages achieved compared to already existing methods are the following: different current directions is limited to the number of terminals of the Hall device. The continuous spinning current method allows the use of more current settings than device terminals. Thus, aliasing effects as a consequence of discrete sampling can be reduced significantly. In the case of fully time-continuous spinning, these aliasing effects can be avoided completely. increase in size, which makes them more susceptible to material inhomogeneity. The continuous spinning current method is applicable on minimal size Hall plates, and therefore, the lowest possible offset resulting from material inhomogeneity is achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a micrograph of an eight-contact Hall plate in CMOS technology;
FIG. 2 is a vector diagram of the two biasing currents I.sub.AC (B,.phi.), I.sub.BD (B,.phi.) and the resulting continuous spinning current vector I.sub.0 ;
FIG. 3 is a vector
REFERENCES:
patent: 4037150 (1977-07-01), Taranov et al.
patent: 4668914 (1987-05-01), Kersten et al.
Munter, P.J.A., "Electronic Circuitry for a Smart Spinning-Current Hall Plate with Low Offset", Sensors and Actuators A, vol. A27, No. 1-3, May 1, 1991.
Bellekom & Munter, "Offset Reduction in Spinning-Current Hall Plates", Sensors and Materials, vol. 5, No. 5 (1994) pp. 253-263., 1994. Month not available.
Haeberli Andreas
Maier Christoph
Steiner Franz-Peter
Steiner Ralph
Farley Walter C.
Patidar Jay
Physical Electronics Laboratory
LandOfFree
Spinning current method of reducing the offset voltage of a hall does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spinning current method of reducing the offset voltage of a hall, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spinning current method of reducing the offset voltage of a hall will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-261410