Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – By integrating
Reexamination Certificate
2002-07-09
2003-12-02
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
By integrating
C327S344000, C327S510000, C327S511000
Reexamination Certificate
active
06657476
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to signal-conditioning methods and systems. The present invention is also related to magnetic sensor devices, such as Hall sensors and magnetoresistive devices. The present invention is also related to techniques for minimizing errors due to signal amplitude variations in magnetic sensors.
BACKGROUND OF THE INVENTION
Magnetic sensing devices for detecting the presence of a ferromagnetic object in the vicinity of the sensing device are utilized widely in a variety of fields, including automotive applications. Such sensing devices typically utilize a magnetic field and employ sensing components that are capable of detecting variations in the strength of a magnetic field. Magnetic field strength generally can be defined as the magnetomotive force developed by a permanent magnet per the distance in the magnetization direction. As an example, an increase in the strength of a magnetic field, corresponding to a drop in the reluctance of a magnetic circuit, can occur as an object made from a high magnetic permeability material, such as iron, is moved toward the magnet.
Magnetic permeability is generally defined as the ease with which the magnetic lines of force, designated as magnetic flux, can pass through a substance magnetized with a given magnetizing force. Magnetic permeability can be quantitatively expressed as the ratio between the magnetic flux density (i.e., the number or lines of magnetic flux per unit area which are perpendicular to the direction of the flux) produced and the magnetic field strength, or magnetizing force. Because the output signal of a magnetic field sensing device is generally dependent upon the strength of the magnetic field, the output signal can be effective in detecting the distance between the sensing device and an object within the magnetic circuit. The range within which the object can be detected is limited by the flux density, as measured in Gauss or Teslas.
Where it is desired to determine the speed or rotational position of a rotating object, such as a disk mounted on a shaft, the object is typically provided with surface features that project toward the sensing device, such as teeth. The proximity of a tooth to the sensing device will increase the strength of the magnetic field. Accordingly, by monitoring the output of the sensing device, the rotational speed of the disk can be determined by correlating the peaks in the sensor's output with the known number of teeth on the circumference of the disk. Likewise, when the teeth are irregularly spaced in a predetermined pattern, the rotational position of the body can be determined by correlating the peak intervals with the known intervals between the teeth on the disk.
One prominent form of such a sensing device is a Hall effect sensor. A Hall effect sensor relies upon a transverse current flow that occurs in the presence of a magnetic field. The Hall effect sensor is primarily driven by a direct current voltage source tied to electrodes at both ends of the Hall effect sensor, creating a longitudinal current flow through the sensor's body. In the presence of a magnetic field, a transverse current is induced in the sensor, which can be detected by a second pair of electrodes transverse to the first pair. The second pair of electrodes can be connected to a voltmeter to determine the potential created across the surface of the sensor. Transverse current flow increases according to a corresponding increase in the magnetic field's strength.
The Hall effect sensor can be mounted within and perpendicular to a magnetic circuit, which can include a permanent magnet and an exciter. The exciter can be configured as a high magnetic permeability element having projecting surface features, which increases the strength of the magnet's magnetic field as the distance between the surface of the exciter and the permanent magnet is reduced. Typically, the exciter can be configured in the form of a series of spaced teeth separated by slots, such as the teeth on a gear. The exciter generally moves relative to the stationary Hall effect sensor element and, in doing so, changes the reluctance of the magnetic circuit so as to cause the magnetic flux through the Hall effect element to vary in a manner corresponding to the position of the teeth. With the change in magnet flux there occurs the corresponding change in magnet field strength, which increases the transverse current of the Hall effect sensor.
With the increasing sophistication of products, magnetic field sensing devices have also become common in products that rely on electronics in their operation, such as automobile control systems. Common examples of automotive applications are the detection of ignition timing from the engine crankshaft and/or camshaft and the detection of wheel speed for anti-lock braking systems and four-wheel steering systems. For detecting wheel speed, the exciter is typically an exciter wheel mounted inboard from the vehicle's wheel, the exciter wheel being mechanically connected to the wheel so as to rotate with the wheel.
The exciter wheel can be provided with a number of teeth, which typically extend axially from the perimeter of the exciter wheel to an inboard-mounted magnetic field sensor. As noted before, the exciter wheel is generally formed of a high magnetic permeability material, such as iron. As each tooth rotates toward the sensor device, the strength of the magnetic field increases as a result of a decrease in the reluctance of the magnetic circuit. Subsequently, the magnetic circuit reluctance increases and the strength of the magnetic field decreases as the tooth moves away from the sensing device. In the situation where a Hall effect device is utilized, there should be a corresponding peak in the device's potential across the transverse electrodes as each tooth passes near the device.
One type of magnetic sensing device utilized in automotive applications, in particular, is a magnetoresistor. In general, a magnetoresistor has higher sensitivity than a Hall element, which potentially can improve sensor performance. A magnetoresistor is a device whose resistance varies with the strength of the magnetic field applied to the device (magnetoresistance). Generally, the magnetoresistor is a slab of electrically conductive material, such as a metal or a semiconductor.
There are three different physical effects, which can cause magnetoresistance to occur. The first type of magnetoresistance is generally referred to as Anisotropic Magnetoresistance (AMR). This effect occurs in thin ferromagnetic films (on the order of several hundred Angstroms thick). The AMR effect results from deflection of magnetization of the ferromagnetic layer by an applied field, which lowers the resistance. The magnetoresistance effect is approximately 2.5% of the base resistance for permalloy (i.e., a specific alloy of approximately 78% nickel and 22% iron), which is favored because it generally is known to not possess any magneto restrictive properties. The AMR effect generally occurs in response to the in-plane component of the applied magnetic field.
The second type of magnetoresistance is referred to generally as Giant Magnetoresistance (GMR). These materials can be generally arranged in a sandwich configuration of several very thin (e.g., 15 to 25 Angstroms) alternating layers of ferromagnetic material and highly conductive material. The ferrormagnetic layers have alternating magnetization, which is rotated into alignment by an applied field to lower the resistance. The GMR effect is from 5% to 35% of the base resistance, resulting in a substantially larger signal than AMR. GMR typically responds to the in-plane component of the applied magnetic field.
The third type of magnetoresistor can be generally formed as a thin elongated body of a high carrier mobility semiconductor material, such as indium antimonide (InSb) having contacts at its ends. Such a configuration responds to the perpendicular component of the magnetic field and, because current through the slab i
Fredrick Kris T.
Honeywell International , Inc.
Lam Tuan T.
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