Patent Application
20120249126
This invention relates generally to integrated circuits and, more particularly, to integrated circuits for detecting a movement of a ferromagnetic object.
Magnetic field sensors (e.g., rotation detectors) for detecting ferromagnetic articles and/or magnetic articles are known. The magnetic field associated with the ferromagnetic article or magnetic article is detected by a magnetic field sensing element, such as a Hall element or a magnetoresistance element, which provides a signal (i.e., a magnetic field signal) proportional to a detected magnetic field. In some arrangements, the magnetic field signal is an electrical signal.
The magnetic field sensor processes the magnetic field signal to generate an output signal that changes state each time the magnetic field signal crosses thresholds, either near to peaks (positive and/or negative peaks) or near to some other level, for example, zero crossings of the magnetic field signal. Therefore, the output signal has an edge rate or period indicative of a movement speed (e.g., a rotation speed) of the ferromagnetic or magnetic object, for example, a gear or a ring magnet.
One application for a magnetic field sensor is to detect the approach and retreat of each tooth of a rotating ferromagnetic gear, either a hard magnetic gear or a soft ferromagnetic gear. In some particular arrangements, a ring magnet having magnetic regions (including permanent or hard magnetic material) with alternating polarity is coupled to the ferromagnetic gear or is used by itself. The magnetic field sensor is responsive to approach and retreat of the magnetic regions of the ring magnet. In other arrangements, a gear is disposed proximate to a stationary magnet and the magnetic field sensor is responsive to perturbations of a magnetic field as the gear rotates.
In one type of magnetic field sensor, sometimes referred to as a peak-to-peak percentage detector (or threshold detector), one or more threshold levels are equal to respective percentages of the peak-to-peak magnetic field signal. One such peak-to-peak percentage detector is described in U.S. Pat. No. 5,917,320 entitled “Detection of Passing Magnetic Articles While Periodically Adapting Detection Threshold” and assigned to the assignee of the present invention.
Another type of magnetic field sensor, sometimes referred to as a slope-activated detector (or peak referenced detector), is described in U.S. Pat. No. 6,091,239 entitled “Detection Of Passing Magnetic Articles With a Peak Referenced Threshold Detector,” also assigned to the assignee of the present invention. In the peak referenced magnetic field sensor, the threshold signal differs from the positive and negative peaks (i.e., the peaks and valleys) of the magnetic field signal by a predetermined amount. Thus, in this type of magnetic field sensor, the output signal changes state when the magnetic field signal comes away from a peak or valley of the magnetic field signal by the predetermined amount.
It should be understood that, because the above-described threshold detector and the above-described peak referenced detector both have circuitry that can identify the positive and negative peaks of a magnetic field signal, the threshold detector and the peak referenced detector both include a circuit portion, which is configured to detect positive peaks and/or negative peaks of the magnetic field signal. The threshold detector and the peak referenced detector, however, each use the detected peaks in different ways.
In order to accurately detect the positive and negative peaks of a magnetic field signal, the rotation detector is capable of tracking at least part of the magnetic field signal. To this end, typically, one or more digital-to-analog converters (DACs) can be used to generate a tracking signal, which tracks the magnetic field signal. For example, in the above-referenced U.S. Pat. Nos. 5,917,320 and 6,091,239, two DACs are used, one (PDAC) to detect the positive peaks of the magnetic field signal and the other (NDAC) to detect the negative peaks of the magnetic field signal.
Some types of rotation detectors perform one or more types of initialization or calibration, for example, at a time near to start up or power up of the rotation detector, or otherwise, from time to time as desired. During one type of calibration, the above-described threshold level is determined. In some types of calibration, a time interval during which the calibration occurs is determined in accordance with a predetermined number of cycles of the magnetic field signal. Thus, for fast magnetic field signals (e.g., for fast rotating gears), the time available for calibration is small. In those applications for which the movement or rotation is rapid and the time available for calibration is small, the rotation detector might not provide accurate motion detection fast enough.
It would, therefore, be desirable to provide a movement detector (e.g., a rotation detector) that can provide accurate and reliable motion detection (rotation speed and/or rotation direction) within a relatively short time frame, as well as over relatively long time frames.
In general overview, the invention is directed to aspects of a circuit capable of detecting movement of an object within a relatively short period of time and, in some embodiments, detecting a speed and/or a direction of movement of an object within a relatively short period of time. The circuit detects object movement using one or more predetermined threshold detectors based on a predetermined threshold of a magnetic field signal associated with a magnetic field of an object. The circuit also detects object movement using one or more tracking threshold detectors by tracking the magnetic field signal over time. The predetermined threshold detectors can detect object movement quickly in comparison to the tracking threshold detectors, which require a calibration period (for example, a period which may include a period from startup or power up of a circuit) to track positive and negative peaks of the magnetic field signal. The circuit includes an output selector to generate an output related to the output of one of the predetermined threshold detectors or the tracking threshold detectors based on a predetermined condition. In some embodiments, the predetermined condition is related to a number of cycles of a magnetic field signal or the calibration time period of the tracking threshold detectors.
In some embodiments, a circuit capable of detecting a speed and a direction of a moving object includes a pair of predetermined threshold detectors responsive to a first pair of magnetic field elements (operative to provide a first magnetic field signal) and a second pair of magnetic field elements (operative to provide a second magnetic field signal). The first and second magnetic field signals are proportional to responses of the first and second pairs of magnetic field elements. The circuit also includes a pair of tracking threshold detectors responsive to the first and second magnetic field signals. The output selector generates an output signal related to a combination of output signals generated by the pair of predetermined threshold detectors and the pair of tracking threshold detectors based on the predetermined condition.
The circuit may be used in applications in which it is desired, needed, or necessary to detect object movement quickly and to generate an output signal indicative of such object movement. The object is not limited to any particular type of object which may include, but is not limited to, a toothed gear, crankshaft, camshaft, mechanical component of a toy or tool, etc. The object may include a ferromagnetic object, such as a soft ferromagnetic object. By way of non-limiting examples, the circuit may be used to detect movement of gears in a vehicle (for example, direction of rotation of transmission gears during vehicle operation), movement of vehicle wheels (for example, to generate an output signal indicative of forward or backward movement of a vehicle), etc.
In accordance with one aspect of the invention, a circuit responsive to movement of an object includes a magnetic field sensing element operative to provide a magnetic field signal proportional to a magnetic field associated with the object, a predetermined threshold detector including a comparator having a first input responsive to the magnetic field signal, a second input responsive to a predetermined threshold, and an output at which is provided a predetermined threshold detector output signal, and a tracking threshold detector including a tracking circuit coupled to receive the magnetic field signal and configured to track positive and negative peaks of the magnetic field signal and to generate a tracking signal, and a comparator having a first input responsive to the magnetic field signal, a second input responsive to an input signal related to the tracking signal, and an output at which is provided a tracking threshold detector output signal. The circuit also includes an output signal selector having a first input responsive to the tracking threshold detector output signal, a second input responsive to the predetermined threshold detector output signal, and configured to generate a circuit output signal related to at least one of the predetermined threshold detector output signal or the tracking threshold detector output signal based upon a predetermined condition.
In further embodiments, the circuit includes one or more of the following features: the predetermined condition is related to a predetermined number of cycles of the magnetic field signal; the predetermined condition is related to a predetermined number of cycles of the predetermined threshold detector output signal; the predetermined condition corresponds to a predetermined time; at least one of an automatic gain control coupled to the magnetic field sensing element and configured to process the magnetic field signal, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to the magnetic field sensing element and configured to process the magnetic field signal, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment, and; the output signal selector is further configured to generate the circuit output signal related to the predetermined threshold detector output signal during a calibration time period of the tracking threshold detector and to generate the circuit output signal related to the tracking threshold detector output signal after the calibration time period wherein the predetermined condition corresponds to the end of the calibration time period.
In another embodiment, the circuit includes one or more of the following features: the magnetic field sensing element is a first pair of magnetic field sensing elements, the magnetic field signal is a first magnetic field signal, and the predetermined threshold detector is a first predetermined threshold detector responsive to the first magnetic field signal and operative to provide a first predetermined threshold detector output signal having a first predetermined threshold detector phase, the circuit further including a second pair of magnetic field sensing elements operative to provide a second magnetic field signal, and a second predetermined threshold detector including a comparator having a first input responsive to the second magnetic field signal, a second input responsive to the predetermined threshold, and an output at which is provided a second predetermined threshold detector output signal having a second predetermined threshold detector phase, wherein the signal selector further includes a third input responsive to the second predetermined threshold detector output signal and a difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object; the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first or second predetermined threshold detector output signals; the predetermined condition corresponds to a predetermined time, and; at least one of an automatic gain control coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control.
In a further embodiment, the circuit includes one or more of the following features: the magnetic field sensing element is a first pair of magnetic field sensing elements and the magnetic field signal is a first magnetic field signal, and the tracking threshold detector is a first tracking threshold detector responsive to the first magnetic field signal and operative to provide a first tracking threshold detector output signal having a frequency indicative of movement speed of the object and a first tracking threshold detector phase, the circuit further including a second pair of magnetic field sensing elements operative to provide a second magnetic field signal, and a second tracking threshold detector including a tracking circuit coupled to receive the second magnetic field signal and configured to track positive and negative peaks of the second magnetic field signal and to generate a second tracking signal and a comparator having a first input responsive to the second magnetic field signal, a second input responsive to an input signal related to the second tracking signal, and an output at which is provided a second tracking threshold detector output signal having a second tracking threshold detector phase wherein the signal selector further includes a third input responsive to the second tracking threshold detector output signal and a difference between the first and second tracking threshold detector phases is indicative of a movement direction of the object; the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first or second tracking threshold detector output signals; the predetermined condition corresponds to a predetermined time; at least one of an automatic gain control coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment; the predetermined threshold detector is a first predetermined threshold detector responsive to the first magnetic field signal and the first predetermined threshold detector comparator is responsive to a first predetermined threshold and is operative to provide a first predetermined threshold detector output signal having a frequency indicative of movement speed of the object and a first predetermined threshold detector phase, the circuit further including a second predetermined threshold detector including a second comparator circuit having an input responsive to the second magnetic field signal and another input responsive to a second predetermined threshold and operative to provide a second predetermined threshold detector output signal having a second predetermined threshold detector phase wherein the signal selector further comprises a fourth input responsive to the second predetermined threshold detector output signal and a difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object; at least one of the first or second predetermined threshold detectors includes a Schmitt trigger; the output signal selector further includes a third input responsive to the second tracking threshold detector output signal and a fourth input responsive to the second predetermined threshold detector output signal and is further configured to provide the circuit output signal corresponding to a combination of the first and second tracking threshold detector output signals or a combination of the first and second predetermined threshold detector output signals based upon the predetermined condition.
In accordance with another aspect of the invention, a circuit responsive to movement of an object including a first pair of magnetic field sensing elements operative to provide a first magnetic field signal proportional to a magnetic field associated with the object, a second pair of magnetic field sensing elements operative to provide a second magnetic field signal proportional to the magnetic field, a first predetermined threshold detector including a first comparator circuit having an input responsive to the first magnetic field signal and another input responsive to a first predetermined threshold and an output at which is provided a first predetermined threshold detector output signal having a frequency indicative of movement speed of the object and a first predetermined threshold detector phase, a second predetermined threshold detector including a second comparator circuit having an input responsive to the second magnetic field signal and another input responsive to a second predetermined threshold and an output at which is provided a second predetermined threshold detector output signal having a second predetermined threshold detector phase, wherein a difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object, a first tracking threshold detector responsive to the first magnetic field signal and an output at which is provided a first tracking threshold detector output signal having a frequency indicative of a tracking threshold speed of the object and a first tracking threshold detector phase, a second tracking threshold detector responsive to the second magnetic field signal and an output at which is provided a second tracking threshold detector output signal having a second tracking threshold detector phase different than the first tracking threshold detector phase, wherein a difference between the first and second tracking threshold detector phases is indicative of the movement direction of the object. The circuit also includes an output signal selector coupled to receive the first predetermined threshold detector output signal, the second predetermined threshold detector output signal, the first tracking threshold detector output signal, and the second tracking threshold detector output signal and configured to generate a circuit output signal related to at least one of the received detector signals based upon a predetermined condition.
In a further embodiment, the circuit includes one or more of the following features: the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first predetermined threshold detector output signal, second predetermined threshold detector output signal, first tracking threshold detector output signal, or second tracking threshold detector output signal; the predetermined condition corresponds to a predetermined time, and; at least one of an automatic gain control coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment.
In accordance with yet another aspect, a method of detecting a movement of an object includes generating a magnetic field signal proportional to a magnetic field associated with the object, generating a tracking signal responsive to the magnetic field signal to track positive and negative peaks of the magnetic field signal, generating a predetermined threshold output signal responsive to the magnetic field signal and to a predetermined threshold, generating a tracking threshold output signal responsive to the magnetic field signal and to the tracking signal, and providing an overall output signal related to a selected one of the predetermined threshold output signal or the tracking threshold output signal based upon a predetermined condition.
In another embodiment, the method includes one or more of the following features: the predetermined condition is related to a predetermined number of cycles of the magnetic field signal; the predetermined condition is related to a predetermined number of cycles of the predetermined threshold output signal; the predetermined condition corresponds to a predetermined time; processing the magnetic field signal using at least one of an automatic gain control, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic adjustment control, wherein the predetermined condition corresponds to a condition of the automatic adjustment control; said providing the overall output signal further includes selecting the overall output signal to be related to the predetermined threshold output signal during a calibration time period, and selecting the overall output signal to be related to the tracking threshold output signal after the calibration time period, wherein the predetermined condition corresponds to the end of the calibration time period; said magnetic field signal is a first magnetic field signal proportional to a magnetic field of the object at a first position, said tracking signal is a first tracking signal responsive to the first magnetic field signal, said tracking threshold output signal is a first tracking threshold output signal responsive to the first magnetic field signal and to the first tracking signal, wherein the first tracking threshold output signal has a frequency indicative of a movement speed of the object and a first tracking threshold output signal phase, and said predetermined threshold output signal is a first predetermined threshold output signal responsive to the first magnetic field signal and to a first predetermined threshold, the first predetermined threshold output signal having a frequency indicative of the movement speed of the object and having a first predetermined threshold output signal phase, further including generating a second magnetic field signal proportional to a second magnetic field associated with the object at a second position offset from the first position, generating a second tracking signal responsive to the second magnetic field signal to track positive and negative peaks of the second magnetic field signal, generating a second tracking threshold output signal responsive to the second magnetic field signal and to the second tracking signal and having a second tracking threshold output signal phase, a difference of the first and second tracking threshold output signal phases indicative of a movement direction of the object, and generating a second predetermined threshold output signal responsive to the second magnetic field signal and to a second predetermined threshold and having a second predetermined threshold output signal phase, a difference of the first and second output signal phases indicative of movement direction of the object, wherein said overall output signal is further related to a selected one of a combination of the first and second predetermined threshold output signals or a combination of the first and second tracking threshold output signals based upon the predetermined condition; the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first predetermined threshold detector output signal, second predetermined threshold detector output signal, first tracking threshold detector output signal, or second tracking threshold detector output signal; the predetermined condition corresponds to a predetermined time, and; further including processing one of the first or second magnetic field signals using at least one of an automatic gain control, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment.
The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which:
Before describing the inventive systems, methods, and techniques, some introductory concepts and terminology are explained. As used herein, the term “magnetic field sensing element” is used to describe a variety of types of electronic elements that can sense a magnetic field. The magnetic field sensing elements can be, but are not limited to, Hall effect elements, magnetoresistance elements, or magnetotransistors. As is known, there are different types of Hall effect elements. These Hall effect elements may be made of a IV type semiconductor material such as Silicon (Si) or Germanium (Ge), or a III-V type semiconductor material such as Gallium-Arsenide (GaAs) or an Indium compound, for example, Indium-Antimonide (InSb).
As is also known, there are different types of magnetoresistance elements, for example, anisotropic magnetoresistance (AMR) elements, giant magnetoresistance (GMR) elements, tunneling magnetoresistance (TMR) elements, and magnetic tunnel junction (MTJ) elements.
Some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, most, but not all, types of magnetoresistance elements tend to have axes of maximum sensitivity parallel to the substrate and most, but not all, types of Hall elements tend to have axes of sensitivity perpendicular to a substrate.
As used herein, the term “magnetic field sensor” is used to describe a circuit that includes a magnetic field sensing element. Magnetic field sensors are used in a variety of applications including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch or proximity detector that senses the proximity of a ferromagnetic or magnetic object, a motion detector (e.g., a rotation detector) that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or teeth of a ferromagnetic gear, and a magnetic field sensor that senses a magnetic field density of a magnetic field. Rotation detectors are used as examples herein. However, the circuits and techniques described herein apply also to any magnetic field sensor capable of detecting a motion of an object.
Operation of a magnetic field sensor in a so-called “calibration mode,” also referred to herein as an “initialization mode,” is described herein. Reference is also made herein to operation of a magnetic field sensor in a so-called “running mode.” The calibration mode can occur at the beginning of operation (or from time to time as desired) and the running mode is achieved at other times. Operation of the running mode is described in greater detail in one or more of the above-mentioned patents, notably, U.S. Pat. No. 5,917,320 and U.S. Pat. No. 7,362,094, which are incorporated by reference herein in their entirety.
While a calibration time period is discussed herein, and end of which ends the calibration mode discussed herein in accordance with certain criteria, it should be recognized that other calibrations can be performed after the end of the indicated calibration time period. For example, an automatic gain control can continue calibrating after the end of the indicated calibration time period. At some point after the end of the indicated calibration time period, but not necessarily coincident with the end of the indicated calibration time period, the magnetic field sensors described herein can enter the running mode, during which updates to values of circuit parameters can update in a different way than during the calibration mode.
Referring to
The object 124 can be an object configured to rotate, for example, a ferromagnetic gear. The circuit 100 can include an amplifier 106 coupled to receive the differential signal 104A, 104B from the magnetic field sensing element 104 and configured to generate a signal 106A (also a magnetic field signal).
Circuit 100 also includes a predetermined threshold detector 120. In some embodiments, the predetermined threshold detector 120 includes an amplifier 122 coupled to receive the signal 106A and configured to generate a signal 122A (also a magnetic field signal). In some embodiments, the amplifier 122 includes an automatic gain control (AGC) amplifier and/or the circuit 100 includes an automatic offset adjustment (AOA).
The predetermined threshold detector 120 can include a comparator 128 having a first input 128A responsive to the magnetic field signal 122A, a second input 128B responsive to a predetermined threshold 130, and an output 128C at which is provided a predetermined threshold detector output signal 140. In some embodiments, the predetermined threshold 130 is an electrical signal having a reference voltage value, for example 1.5 volts.
Circuit 100 also includes a tracking threshold detector 110. In some embodiments, the tracking threshold detector 110 includes an amplifier 112 coupled to receive the signal 106A and configured to generate a signal 112A (also a magnetic field signal). In some embodiments, the amplifier 112 includes an AGC amplifier and/or the circuit 100 includes an AOA.
The tracking threshold detector 110 can include a tracking circuit 116 coupled to receive the signal 112A and configured to track positive and negative peaks of the signal 112A and to generate a tracking signal 117. The tracking threshold detector 110 can also include comparator 118 having a first input 118A responsive to signal 112A, a second input 118B responsive to an input signal related to the tracking signal 117, and an output 118C at which is provided a tracking threshold detector output signal 145.
In further embodiments discussed in detail herein below, the tracking threshold detector 110 includes a peak-to-peak percentage detector (
In some embodiments, detectors 110, 120 are rotation detectors to detect rotational movements of the object 124, while in some other embodiments, detectors 110, 120 are translation detectors to detect translational movements of the object 124. It should be noted that detectors 110, 120 are not limited to detection of stated kinds of object movement, and may detect other types of object movements, including combinations of object rotation and translation.
It should be noted that signals 104A, 104B, 106A, 112A, 122A are all magnetic field signals, and are all indicative of a magnetic field experienced by the magnetic field sensing element 104.
Circuit 100 can also include an output signal selector 150 having a first input 150A responsive to the tracking threshold detector output signal 145, a second input 150B responsive to the predetermined threshold detector output signal 140, and configured to generate a circuit output signal 155 related to at least one of the predetermined threshold detector output signal 140 or the tracking threshold detector output signal 145 based upon a predetermined condition.
As will be described more fully below in conjunction with
In some embodiments, the predetermined condition is related to a predetermined number of cycles of the magnetic field signal 106A, for example, three cycles.
In other embodiments, the predetermined condition is related to a predetermined number of cycles of the predetermined threshold detector output signal 140, for example, three cycles.
In still other embodiments, the predetermined condition corresponds to a predetermined time, for example, 1.0 second. In some embodiments, the predetermined time is related to the rotation speed and/or a predetermined time after rotation is detected. For faster rotation speeds, the time can be shorter while for slower rotation speeds the time can be longer.
In other embodiments, the circuit 100 includes at least one of an AGC or an AOA coupled to the magnetic field sensing element 104 and configured to process the signal (as may be similar to signal 106A). In these embodiments, the predetermined condition corresponds to a condition of the AGC, for example, a gain of the AGC that has not changed for 3 cycles of the signal or a condition of the AOA, for example, an offset value of the AOA.
The predetermined condition should not be construed as limited to the above described conditions but can also be based on various algorithms to determine when tracking threshold detector 110 is calibrated and to determine proper rotation speed and/or direction information.
In some arrangements, the magnetic field sensing element 104 can be responsive to motion of the object 124, for example, motion of ferromagnetic gear teeth upon a gear, of which gear teeth 124A-124C upon the gear 124 are representative. To this end, a fixed magnet (not shown) can be disposed proximate to the magnetic field sensing element 104 and the gear teeth can disturb the magnetic field generated by the magnet as the gear rotates. However, in other arrangements, the magnetic field sensing element 104 can be responsive to movement of magnetic regions upon a magnet, for example, magnetic regions 126A-126C upon a ring magnet 126. In some particular arrangements, the ring magnet 126 and the gear 124 are coupled together with a shaft or the like. In these particular arrangements, the ring magnet 126 can be proximate to the magnetic field sensing element 104.
The magnetic field sensing element 104 is responsive to proximity of the ring magnet 126 and, in particular, to proximity of passing magnetic regions north (N) and south (S) 126A-126C. In operation, the magnetic field sensing element 104 produces the differential magnetic field signal 104A, 104B (and also the magnetic field signals 106A, 112A, 122A) having a generally repeating pattern when the ring magnet 126 rotates, wherein each peak (positive and negative) of the pattern is associated with one of the magnetic regions N, S.
Referring now to
In some embodiments, the first predetermined threshold detector 220A can include an amplifier 222A coupled to receive the signal 276A and configured to generate a signal 272B (also a magnetic field signal). In some embodiments, the amplifier 222A includes an AGC amplifier and/or the circuit 100 includes an AOA.
The first predetermined threshold detector 220A can include a comparator 228A having a first input 278A responsive to the magnetic field signal 272B, a second input 278B responsive to a predetermined threshold 230A, and an output 278C at which is provided a first predetermined threshold detector output signal 240A. The predetermined threshold 230A may include a plurality of predetermined thresholds, for example, a first predetermined threshold and a second predetermined threshold.
The circuit 200 can also include a second pair of magnetic field sensing elements 205B, including magnetic field sensing element 204B and magnetic field sensing element 204C, operative to provide a second differential magnetic field signal 284A, 284B, 294A, 294B proportional to the magnetic field associated with object 224. In some embodiments, circuit 200 can include an amplifier 206B coupled to receive the differential signal 284A, 284B, 294A, 294B from the second pair of magnetic field sensing elements 205B and configured to generate a signal 286A (also a magnetic field signal).
In further embodiments, the second predetermined threshold detector 220B includes an amplifier 222B coupled to receive the signal 286A and configured to generate a signal 282B (also a magnetic field signal). In still further embodiments, the amplifier 222B includes an AGC amplifier and/or the circuit 100 includes an AOA.
The second predetermined threshold detector 220B can also include a comparator 228B having a first input 288A responsive to the magnetic field signal 282B, a second input 288B responsive to a predetermined threshold 230B, and an output 288C at which is provided a second predetermined threshold detector output signal 240B. In some embodiments, the predetermined threshold 230B of detector 220B is the same as the predetermined threshold 230A of detector 220A, while in some other embodiments, the predetermined thresholds 230A, 230B are different.
In some embodiments, the tracking threshold detector 210A of circuit 200 includes an amplifier 212A coupled to receive the signal 276A and configured to generate a signal 272A (also a magnetic field signal). In some embodiments, the amplifier 212A includes an AGC amplifier and/or the circuit 100 includes an AOA.
The tracking threshold detector 210A can include a tracking circuit 216A coupled to receive the signal 272A and configured to track positive and negative peaks of the signal 272A and to generate a tracking signal 277A. The tracking threshold detector 210A can also include a comparator 218A having a first input 278A responsive to signal 272A, a second input 278B responsive to an input signal related to the tracking signal 277A, and an output 278C at which is provided a first tracking threshold detector output signal 245A.
The circuit 200 can also include an output signal selector 250 (as may be similar to output signal selector 150 described in conjunction with
Output signal selector 250 selects signals 245A, 245B, 240A, 240B based on a predetermined condition and includes logic for example to determine speed and/or direction and/or vibration information based on one or more of these signals. For example, higher signal edge rates can correspond to relatively fast object movement and lower signal edge rates can correspond to relatively slow object movement. In embodiments in which the object is a rotating gear, for example, signal frequency (related to edge rate) is indicative of rotation speed of the gear. The relative phase sequences of rising and falling edges of two of the signals can be used to determine a direction of object movement. It will be understood that logic to determine speed and/or direction information may include analog logic, digital logic, and/or mixed logic.
In these embodiments, the first predetermined threshold detector output signal 240A has a first predetermined threshold detector phase and the second predetermined threshold detector output signal 240B has a second predetermined threshold detector phase. A difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object 224. A frequency of either the predetermined threshold detector output signal 240A, the threshold detector output signal 245A, or the second predetermined threshold detector output signal 240B is related to a speed of rotation of the object 224.
In a further embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals 276A, 286A, for example, three cycles.
In another embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first or second predetermined threshold detector output signals 240A, 240B, for example, three cycles.
In a further embodiment, the predetermined condition corresponds to a predetermined time. In some embodiments, the predetermined time is related to the rotation speed and/or a predetermined time after rotation is detected.
In another embodiment, circuit 200 includes an AGC coupled to one of the first or second pair of magnetic field sensing elements 205A, 205B and configured to process a respective one of the first or second magnetic field signals (276A, 286A) wherein the predetermined condition corresponds to a condition of the AGC, for example, a gain of the AGC. Circuit 200 optionally includes an AOA coupled to one of the first or second pair of magnetic field sensing elements 205A, 205B and configured to process a respective one of the first or second magnetic field signals (276A, 286A) wherein the predetermined condition corresponds to a condition of AOA.
Referring again to
In some embodiments, the second tracking threshold detector 210B includes an amplifier 212B coupled to receive the signal 286A (from the second magnetic field sensing element 205B) and configured to generate a signal 282A (also a magnetic field signal). In some embodiments, the amplifier 212B is an AGC amplifier and/or the circuit 100 includes an AOA.
The second tracking threshold detector 210B can include a tracking circuit 216B coupled to receive the signal 282A and configured to track positive and negative peaks of the signal 282A and to generate a tracking signal 277B. The second tracking threshold detector 210B can also include a comparator 218B having a first input 288A responsive to signal 282A, a second input 288B responsive to an input signal related to the tracking signal 277B, and an output 288C at which is provided a second tracking threshold detector output signal 245B.
In this embodiment, the circuit 200 includes the output signal selector 250 (as may be similar to output signal selector 150 described in conjunction with
In this embodiment, the first tracking threshold detector output signal 245A has a first tracking threshold detector phase and the second tracking threshold detector output signal 245B has a second tracking threshold detector phase. A difference between the first and second tracking threshold detector phases is indicative of a movement direction of the object 224. A frequency of either the first tracking threshold detector output signal 245A, the first predetermined threshold detector output signal 240A, or the second tracking threshold detector output signal 245B is related to a speed of rotation of the object 224.
Referring yet again to
In a further embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals 276A, 286A, for example, three cycles.
In a further embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first predetermined threshold detector output signal 240A, the second predetermined threshold detector output signal 240B, the first tracking threshold detector output signal 245A, or the second tracking threshold detector output signal 245B, for example, three cycles.
In a further embodiment, at least one of the first or second predetermined threshold detectors 220A, 220B includes a Schmitt trigger.
It should be apparent to one of ordinary skill in the art that the circuit is not limited to above-described configurations, and may encompass other desired configurations including multiple tracking threshold detectors (i.e., more than two tracking threshold detectors) and/or multiple predetermined threshold detectors (i.e., more than two predetermined threshold detectors).
Operation of the circuits 100, 200 is described below in conjunction with
Referring now to
Magnetic field signal 18 is applied to a non-inverting input of a first comparator 400 and to the inverting input of a second comparator 404. The output signals of comparators 400 and 404 provide input signals GT_PDAC 458 and LT_NDAC 461, respectively, to an update controller 409 that provides control signals to counters 414 and 430, as shown.
The update controller 409 provides a p_updn signal 463 to an UPDN (up/down) input of a counter 414 to control the count direction. As will become apparent, the p_updn signal 463 normally causes the counter 414 to count up. Under certain conditions however, the p_updn signal 463 causes the counter 414 to count down for some clock cycles. The counter 414 is clocked by a system clock signal, CLK. A p_hold signal 465 is coupled to a HOLD input of the counter 414. The counter output is held constant (i.e., the counter is disabled) when the HOLD input signal is at a first logic level and is released (i.e., the counter is enabled) when HOLD input signal is at a second logic level. The counter 414 may be a six bit counter which is enabled when the HOLD input is low.
The outputs of the counter 414 are coupled to inputs of a positive digital-to-analog converter (PDAC) 403. The PDAC 403 is buffered by a buffer 424 to provide a PDAC signal 402, which may be a voltage that tracks positive peaks of the magnetic field signal 18 (i.e., a tracking signal).
The comparator 400, counter 414. PDAC 403, and buffer 424 comprise a “positive portion” of the detector circuitry. A “negative portion” of the detector 26 is similarly arranged, as shown. In particular, update controller 409 provides an n_updn signal 466 to an UPDN input of counter 430 to control the count direction. As will become apparent, the n_updn signal 466 normally causes the counter 430 to count down. Under certain conditions however, the n_updn signal 466 causes the counter 430 to count up for some clock cycles. The counter 430 is clocked by a system clock signal, CLK. An n_hold signal 468 is coupled to a HOLD input of the counter 430. The counter output is held constant (i.e., the counter is disabled) when the HOLD input signal is at a first logic level and is released (i.e., the counter is enabled) when the HOLD input signal is at a second logic level. The counter 430 may be a six bit counter which is enabled when the HOLD input is low.
The outputs of the counter 430 are coupled to inputs of a negative digital-to-analog converter (NDAC) 405. The NDAC 405 is buffered by a buffer 436 to provide an NDAC signal 406, which may be a voltage that tracks negative peaks of the magnetic field signal 18 (i.e., a tracking signal).
The buffered PDAC and NDAC signals 402, 406 are coupled to a resistor divider comprising series-coupled resistors 408, 412, and 416 in order to generate peak-to-peak threshold signals THRESHHI and THRESHLO, as will be described more fully below in conjunction with
Each of the threshold signals THRESHHI and THRESHLO is a percentage of the difference between the PDAC and NDAC voltages, or, in other words, a percentage of the peak-to-peak magnetic field signal 18. As described more fully below in conjunction with
Referring now to
As illustrated in
Referring now to
Referring now to
It should be appreciated that method 600 could be implemented in a circuit, for example, circuit 100 described in conjunction with
Alternatively, one or more of the method steps may be performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC). The method does not depict the syntax of any particular programming language. Rather, the method illustrates the information one of ordinary skill in the art requires to fabricate circuits or to generate computer software to perform the processing required to implement at least a portion of the techniques described herein. It will be appreciated by those of ordinary skill in the art that the particular sequence of steps described is illustrative only and can be varied without departing from the spirit of the techniques described herein.
In a further embodiment of method 600, the predetermined condition is related to a predetermined number of cycles of the magnetic field signal. In a non-limiting example, a processor may process the magnetic field signal to recognize a predetermined number of cycles of the magnetic field signal (for example, three cycles of the magnetic field signal). The processor determines that the predetermined condition has been met (i.e., that three cycles of the magnetic field signal have occurred) and provides an overall output signal by selecting one of the predetermined threshold output signal or the tracking threshold output signal. In one configuration, the processor provides an overall output signal related to the predetermined threshold output signal before the predetermined condition is realized (i.e., before the processor recognizes the predetermined number of cycles of the magnetic field signal), and provides the overall output signal related to the tracking threshold output signal after the predetermined condition is realized (i.e., after the processor recognizes the predetermined number of cycles of the magnetic field signal).
In another embodiment of the method 600, the predetermined condition is related to a predetermined number of cycles of the predetermined threshold output signal. In a non-limiting example, a processor may process the predetermined threshold output signal to recognize a predetermined number of cycles of the signal (for example, three cycles of the predetermined threshold output signal). The processor determines that the predetermined condition has been met (i.e., that three cycles of the predetermined threshold output signal have occurred) and provides an overall output signal by selecting one of the predetermined threshold output signal or the tracking threshold output signal. In one configuration, the processor provides an overall output signal related to the predetermined threshold output signal before the predetermined condition is realized (i.e., before the processor recognizes three cycles of the predetermined threshold output signal), and provides the overall output signal related to the tracking threshold output signal after the predetermined condition is realized (i.e., after the processor recognizes the three cycles of the predetermined threshold output signal).
In a further embodiment of the method 600, the predetermined condition corresponds to a predetermined time. The predetermined time may optionally be related to a calibration time of a circuit, such as circuit 100 described in conjunction with
Accordingly, in a further embodiment, the method 600 includes selecting the overall output signal to be related to the predetermined threshold output signal during a calibration time period and selecting the overall output signal to be related to the tracking threshold output signal after the calibration time period. In this way, the predetermined condition corresponds to the end of the calibration time period.
In a non-limiting example, a processor provides a selected one of the predetermined threshold output signal or the tracking threshold output signal based upon the predetermined time (for example, in some embodiments, the time is related to target rotation speed). In a further embodiment, the predetermined time is defined relative to a time at which an object whose movement is to be detected begins to move or a time at which a circuit (as may be the same or similar to circuit 200) starts up or powers up. In a non-limiting example, the object is a rotating gear coupled to a rotating shaft of an engine. The rotating gear can be used to detect motion (and, more particularly, the speed and direction of motion) of engine components. By way of a non-limiting example, for a vehicle, this may include motion detection of a crankshaft, exhaust camshaft, intake camshaft, piston, connecting rods, valves, transmission gears, wheels, etc.
It should be noted that the predetermined time may be defined relative to various timing events. For example, the above-mentioned engine may be placed in a neutral state during which engine components are at rest (or at idle) and no movement detection is desired or necessary. However, once the engine is engaged and components begin to operate, the processor tracks the elapsed time and provides the predetermined threshold output signal until reaching the predetermined time, after which, the processor provides the tracking threshold output signal.
In another embodiment, the method 600 includes processing the magnetic field signal using an AGC, wherein the predetermined condition corresponds to a condition of the AGC, for example, at a time when the AGC stops updating. In still further embodiments, the method 600 includes processing the magnetic field signal using an AOA, wherein the predetermined condition corresponds to a condition of the AOA, for example, an offset value.
Referring now to
Another portion 700C of the graph 700 includes a predetermined threshold detector output signal 740A representative of, for example, the predetermined threshold detector output signal 240A output from predetermined threshold detector 220A of
In some embodiments, the first and second states 776, 774 of the predetermined threshold detector output signal 740A are responsive to a time-varying magnetic field associated with an object and sensed by a pair of magnetic field sensing elements (as may be similar to first pair of magnetic field sensing elements 205A described in conjunction with
Another portion 700B of the graph 700 includes a time-varying magnetic field signal 772B representative of, for example, the magnetic field signal 282B of
Graph 700 (at portion 700C) includes a predetermined threshold detector output signal 740B representative of, for example, the predetermined threshold detector output signal 240B output from predetermined threshold detector 220B of
In some embodiments, the first and second states 786, 784 of the predetermined threshold detector output signal 740B are responsive to a time-varying magnetic field associated with an object and sensed by a pair of magnetic field sensing element (as may be similar to second pair of magnetic field sensing elements 205B described in conjunction with
An edge rate or period of the predetermined threshold detector output signals 740A, 740B are indicative of a speed of object movement. In other words, higher edge rates correspond to relatively fast object movement and lower edge rates correspond to relatively slow object movement. In embodiments in which the object is a rotating gear, signal frequency is indicative of rotation speed of the gear.
In
Referring now to
It should be noted that the PDAC signal 874A is generated at times before achieving a positive peak of the magnetic field signal 872A (such times denoted by dashed line box 890A), but is inaccurate and does not represent the true motion detection information and so is not shown in
Similarly, an NDAC signal 876A, which may be representative of the NDAC signal 406 described in conjunction with
It should be noted that the NDAC signal 876A is generated at times before achieving a negative peak of the magnetic field signal 872A (such times denoted by dashed line box 892A), but is inaccurate and does not represent the true motion detection information and so is not shown in
Another portion 800B of the graph 800 includes a time-varying magnetic field signal 872B representative of, for example, the magnetic field signal 282A of
It should be noted that the PDAC signal 872B is generated at times before achieving a positive peak of the magnetic field signal 872B (such times denoted by dashed line box 890B), but is inaccurate and does not represent the true motion detection information and so is not shown in
Similarly, an NDAC signal 876B, which may be representative of the NDAC signal 406 described in conjunction with
It should be noted that the NDAC signal 876B is generated at times before achieving a negative peak of the magnetic field signal 872B (such times denoted by dashed line box 892B), but is inaccurate and does not represent the true motion detection information and so is not shown in
Another portion 800C of the graph 800 includes a tracking threshold detector output signal 745A representative of, for example, the tracking threshold detector output signal 245A output from tracking threshold detector 210A of
The tracking threshold output signal 745A has edges 747A, 747B that align with positive and negative peaks, respectively, of the magnetic field signal 872A. It can be seen in
Portion 800C of the graph 800 also includes a tracking threshold detector output signal 745B representative of, for example, the tracking threshold detector output signal 245B output from tracking threshold detector 210B of
Similarly to the above-described signal 745A, the tracking threshold output signal 745B has edges 757A, 757B that align with positive and negative peaks, respectively, of the magnetic field signal 872B. It can be seen in
In
In
Successive edge 760C and edge 760B may be used to accurately determine and update the direction of object movement (as can be seen by triangular icon 877B and all successive icons). In embodiments in which the object is a rotating gear, icon direction is indicative of clockwise or counter-clockwise rotational movement of the gear.
Referring again to
Referring now to
A second graph 900B has a horizontal axis with a scale in arbitrary units of time and a vertical axis to indicate selected output information (an example of which is designated by reference number 955) related to one of the signals 940A, 940B, 945A, 945B of graph 900A. The selected output information 955 relates to movement of an object, as may be the same or similar to object movement information (e.g., speed and direction of object movement) described above in conjunction with
For example, at time t21, the selected object speed information 955A is related to the signal 940A and at time t24 the selected object speed information 955B is related to signal 945A. Here, during circuit start up or power up, an output signal selector (as may be the same or similar to output selector 250 of circuit 200 of
At time t22, the selected object direction information 955C is derived from signals 940A, 940B and at time t23 the selected object direction information 955D is derived from signals 945A, 945B. Here, during circuit start up or power up, the output signal selector selects relative phases of the predetermined threshold detector output signals (e.g., predetermined threshold detector output signals 940A, 940B) to derive direction information and at time t23 selects relative phases of the tracking threshold detector output signals (e.g., the tracking threshold detector signals 945A, 945B) to derive direction information. Time t23 (i.e., a time when output selector 250 of circuit 200 of
It will be appreciated that, in order to obtain a rapid determination of direction of movement, two predetermined threshold detectors should be used, so that a relative phase can be rapidly determined between the output signals of the two predetermined threshold detectors. However, use of only one predetermined threshold detector as in
While particular numbers of cycles, particular times, and other particular parameters are described above, it will be appreciated that other numbers of cycles, other times, and other particular parameters can be used.
It should be appreciated that a circuit as described herein may be used in applications in which it is desired, needed, or necessary to generate fast speed and/or direction information in sensor applications including, but not limited to, automotive engine management applications.
All publications and references cited herein are expressly incorporated herein by reference in their entirety.
Having described embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating these concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.
