Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Reexamination Certificate
1998-09-15
2001-06-26
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
C324S11700H
Reexamination Certificate
active
06252390
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to ferromagnetic thin-film structures exhibiting relatively large magnetoresistive characteristics and, more particularly, to such structures used to sense magnetic fields.
Many kinds of electronic systems make use of magnetic devices including both digital systems, such as memories, and analog systems such as field sensors. Magnetometers and other magnetic sensing devices are used extensively in many kinds of systems including magnetic disk memories and magnetic tape storage systems of various kinds. Such devices provide output signals representing the magnetic field sensed thereby in a variety of situations.
One use for such magnetic field sensors is the sensing of magnetic fields generated by electrical currents in a conductor as a basis for inferring the nature of such current giving rise to these fields. While this has long been done for magnetic fields generated by substantial currents, such sensing becomes more difficult to accomplish in lesser ranges of currents that include relatively small currents. The need for sensing fields due to such small currents arises, for instance, in situations where the currents generating the fields to be measured are provided merely as a basis for conveying signal information rather than for transmitting substantial electrical energy.
Such a situation occurs in many medical systems, instrumentation systems and control systems where there is often a need to communicate signals to system portions over signal interconnections from an external source or from another portion of the system. Often, the conductors carrying signal currents for such purposes must be electrically isolated from the portion of the system containing the sensor arrangement for those signals to measure the resulting magnetic fields. As an example, a long current loop carrying signal information in the loop current may, through lightning or static electricity discharges, become subject to having large voltage potentials relative to ground developed thereon. Such potentials must in many instances be kept from the signal sensing and receiving circuitry to avoid damage thereto even though that circuitry must still be able to capture the signal information contained in the loop current.
Signal isolators for these purposes are often preferably formed in monolithic integrated circuit chips for reasons of cost, convenience and system performance. In such an arrangement, one or more solid state magnetic field sensors are used to detect the magnetic fields provided by the currents containing the signals. A kind of magnetic field sensor which has been used in this situation is a Hall effect device. Such devices are often not satisfactory for sensing the magnetic fields due to small currents because of the limited sensitivity they exhibit with respect to magnetic fields.
Furthermore, there is often a lack of satisfactory remedial or supplementary measures in such arrangements for improving the limited sensitivity of Hall effect devices. The use of field concentrators is difficult to provide in a monolithic integrated circuit containing a Hall device because of the magnetically sensitive axis of that device being perpendicular to the directions the Hall device in the monolithic integrated circuit extends over the substrate supporting that device, i.e. the device axis of sensitivity is parallel to the thickness of the device rather than to the width or length thereof. Also information provided by Hall devices as to the magnetic fields measured thereby is in the form of a voltage which limits the use of such devices in bridge circuits which might otherwise be used for purposes of increasing the output signal providing the current signal information.
Another possibility in either hybrid integrated circuits or monolithic integrated circuits for signal isolation is the use of a light source having its electromagnetic radiation intensities controlled by signal currents from a signal source. Such a light source is electrically isolated from a light detector provided in the integrated circuit that is used to infer the nature of the signal currents from the light transmitted to and received thereby. Difficult engineering and economic problems make this an unsatisfactory solution as they do various alternative capacitance based coupling solutions. Thus, there is a need for a signal isolation device exhibiting relatively high sensitivity which can be fabricated at a reasonably economic cost.
SUMMARY OF THE INVENTION
The present invention provides a current determiner having an output at which representations of input currents are provided for input currents that are supplied from a source, the current determiner comprising an input conductor and a first current sensor both supported on a substrate adjacent to and spaced apart from one another so they are electrically isolated with the first current sensor positioned in those magnetic fields arising from any input currents. The first current sensor is formed of a plurality of magnetoresistive, anisotropic, ferromagnetic thin-film layers at least two of which are separated from one another by a non-magnetic, electrically conductive layer positioned therebetween.
This first current sensor extends primarily along a first direction across the substrate and the input conductor extends primarily along a second direction across the substrate which is approximately orthogonal to the first direction. A layer of material exhibiting a substantial magnetic permeability can be used therewith positioned near both the input conductor and the first current sensor to serve as a magnetic field concentrator and as a shield against any unwanted external magnetic fields.
This sensor can be electrically connected to other electronic circuitry formed in the substrate. Such circuitry can include a nonlinearity adaptation circuit to provide more accurate representations of the input currents despite nonlinearities in the current sensor. Further current sensors also adjacent the input conductor or an output conductor can be provided to form bridge circuits to increase sensitivity.
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Black, Jr. William C.
Hermann Theodore M.
Karlsen Ernest
Kinney & Lange , P.A.
Kobert Russell M.
Nonvolatile Electronics Incorporated
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