Abstract:
An apparatus and a method provide an output signal indicative of a speed of rotation and a direction of rotation of a ferromagnetic object capable of rotating. A variety of signal formats of the output signal are described.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates generally to integrated circuits and, more particularly, to integrated circuits for detecting and communicating a speed of rotation and direction of rotation of a ferromagnetic object. 
       BACKGROUND OF THE INVENTION 
       [0004]    Proximity detectors for detecting ferromagnetic objects are known. In proximity detectors, the magnetic field associated with the ferromagnetic is detected by a magnetic field-to-voltage transducer (also referred to herein as a magnetic field sensing element), such as a Hall effect element or a magnetoresistance element, which provides a signal (i.e., a magnetic field signal) proportional to a detected magnetic field. 
         [0005]    Some proximity detectors merely provide an output signal representative of the proximity of the ferromagnetic object. However, other proximity detectors, i.e., rotation detectors, provide an output signal representative of the approach and retreat of each tooth of a rotating ferromagnetic gear or of each segment of a segmented ring magnet having segments with alternating polarity. The proximity detector (rotation detector) processes the magnetic field signal to generate an output signal that changes state each time the magnetic field signal either reaches a peak (positive or negative peak) or crosses a threshold level. Therefore, the output signal, which has an edge rate or period, is indicative of a rotation and a speed of rotation of the ferromagnetic gear or of the ring magnet. 
         [0006]    In one type of proximity detector (rotation detector), sometimes referred to as a peak-to-peak percentage detector (or threshold detector), a threshold level is equal to a percentage of the peak-to-peak magnetic field signal. For this type of proximity detector (rotation detector), the output signal changes state when the magnetic field signal crosses the threshold level. 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” assigned to the assignee of the present invention and incorporated herein by reference. 
         [0007]    In another type of proximity detector (rotation detector), sometimes referred to as a slope-activated detector or as a peak-referenced detector (or peak detector), threshold levels differ 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 proximity detector (rotation detector), the output signal changes state when the magnetic field signal departs from a peak and/or valley by the predetermined amount. One such slope-activated detector is described in U.S. Pat. No. 6,091,239 entitled “Detection Of Passing Magnetic Articles With a Peak Referenced Threshold Detector.” which is assigned to the assignee of the present invention and incorporated herein by reference. Another such peak-referenced proximity detector is described in U.S. Pat. No. 6,693,419, entitled “Proximity Detector,” which is assigned to the assignee of the present invention and incorporated herein by reference. Another such peak-referenced proximity detector is described in U.S. Pat. No. 7,199,579, entitled “Proximity Detector,” which is assigned to the assignee of the present invention and incorporated herein by reference. 
         [0008]    It should be understood that, because the above-described peak-to-peak percentage detector (threshold detector) and the above-described peak-referenced detector (peak detector) both have circuitry that can identify the positive and negative peaks of a magnetic field signal, the peak-to-peak percentage detector and the peak-referenced detector both include a peak detector circuit adapted to detect a positive peak and a negative peak of the magnetic field signal. Each, however, uses the detected peaks in different ways. 
         [0009]    In order to accurately detect the positive and negative peaks of a magnetic field signal, some proximity detectors, i.e., rotation detectors, are 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. 
         [0010]    Some proximity detectors are configured to be able to identify a vibration, for example, either a rotational vibration or a linear vibration of a gear or ring magnet, which vibration can generate signals from a magnetic field sensing element (magnetic field signals) that might appear similar to signals that would be generated during a rotation of the gear or ring magnet in normal operation. Proximity detectors having vibration processors that can detect a vibration are described in U.S. patent application Ser. No. 10/942,577, filed Sep. 16, 2004, entitled “Methods and Apparatus for Vibration Detection,” and in U.S. patent application Ser. No. 11/085,648, filed Mar. 21, 2005, entitled “Proximity Detector Having a Sequential Flow State Machine,” both of which are assigned to the assignee of the present invention and incorporated herein by reference. 
         [0011]    As described above, an output signal generated by a conventional proximity detector used to detect a rotation of a ferromagnetic object (e.g., a ring magnet or a ferromagnetic gear) can have a format indicative of the rotation and of the speed of rotation of the ferromagnetic object or ring magnet. Namely, the conventional proximity detector can generate the output signal as a two-state binary signal having a frequency indicative of the speed of rotation. When the ferromagnetic object is not rotating, the conventional proximity detector can generate an inactive output signal. However the output signal generated by most conventional proximity detectors is not indicative of a direction of rotation of the ferromagnetic object. 
       SUMMARY OF THE INVENTION 
       [0012]    In accordance with one aspect of the present invention, a rotation detector includes a magnetic field sensor for providing an output signal proportional to a magnetic field associated with a ferromagnetic object capable of rotating. The rotation detector also includes one or more detector circuits coupled to receive the output signal from the magnetic field sensor. Each detector circuit is configured to detect a rotation of the ferromagnetic object. The one or more detector circuits are configured to generate a respective one or more output signals, each output signal having respective rising and falling edges. The rotation detector also includes an output protocol circuit coupled to receive the one or more output signals from the one or more detector circuits and configured to generate an output signal indicative of a speed of rotation of the ferromagnetic object and also indicative of a direction of rotation of the ferromagnetic object. The output signal generated by the output protocol circuit comprises at least one of: a first plurality of pulses, each one of the first plurality of pulses having a leading edge with a transition direction indicative of the direction of rotation, or a first number of pulses occurring in instances of the first number of pulses when the ferromagnetic object is rotating in a first direction and a second different number of pulses occurring in instances of the second number of pulses when the ferromagnetic object is rotating in a second different direction. 
         [0013]    In accordance with another aspect of the present invention, a method of detecting a rotation of a ferromagnetic object includes generating a first signal proportional to a magnetic field associated with the ferromagnetic object. The method also includes detecting a rotation of the ferromagnetic object in response to the first signal, generating one or more second signals, each having respective rising and falling edges in response to the detecting, and generating a third signal in response to the one or more second signals. The third signal is indicative of a speed of rotation of the ferromagnetic object and is also indicative of a direction of rotation of the ferromagnetic object. The third signal comprises at least one of: a first plurality of pulses, each one of the first plurality of having a leading edge with a transition direction indicative of the direction of rotation, or a first number of pulses occurring in instances of the first number of pulses when the ferromagnetic object is rotating in a first direction and a second different number of pulses occurring in instances of the second number of pulses when the ferromagnetic object is rotating in a second different direction. 
         [0014]    With these arrangements, the rotation detector and the method provide an output signal indicative of a speed of rotation and also a direction of rotation of a ferromagnetic object capable of rotating. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    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: 
           [0016]      FIG. 1  is a block diagram showing a rotation detector proximate to a ferromagnetic object, the rotation detector having an output protocol circuit configured to generate an output signal indicative of a speed of rotation and also a direction of rotation of the ferromagnetic object; 
           [0017]      FIG. 2  has several graphs, each graph representative of a different exemplary output signal that can be generated by the output protocol circuit of  FIG. 1  in order to be indicative of the speed of rotation and also the direction of rotation of the ferromagnetic object; 
           [0018]      FIG. 3  is a block diagram of an exemplary output protocol circuit that can be used as the output protocol circuit of  FIG. 1  in order to generate one of the output signals shown in  FIG. 2 ; 
           [0019]      FIG. 4  is a block diagram of another exemplary output protocol circuit that can be used as the output protocol circuit of  FIG. 1  in order to generate another one of the output signals shown in  FIG. 2 ; 
           [0020]      FIG. 5  is a block diagram of another exemplary output protocol circuit that can be used as the output protocol circuit of  FIG. 1  in order to generate another one of the output signals shown in  FIG. 2 ; and 
           [0021]      FIG. 6  is a block diagram of another exemplary output protocol circuit that can be used as the output protocol circuit of  FIG. 1  in order to generate another one of the output signals shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Before describing the present invention, some introductory concepts and terminology are explained. As used herein, the term “rotation detector” is used to describe a circuit that includes a “magnetic field sensing element,” which detects a magnetic field. The rotation detector can sense movement, i.e., rotation, of a ferromagnetic object, for example, advance and retreat of magnetic domains of a ring magnet or advance and retreat of gear teeth of a ferromagnetic gear. The term “proximity detector” is used more broadly herein, to include rotation detectors, and also to include other circuits that merely detect proximity of a magnetic object. 
         [0023]    While magnetic field sensing elements are shown and described below to be Hall effect elements, in other arrangements, the magnetic field sensing elements can be, but are not limited to, Hall effect elements, magnetoresistance elements, magnetotransistors, or magnetoinductive devices. As is known, there are different types of Hall effect elements, for example, a planar Hall element, and a vertical Hall element. As is also known, there are different types of magnetoresistance elements, for example, a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ). 
         [0024]    Referring to  FIG. 1 , an exemplary rotation detector  10  can be used, for example, to detect passing gear teeth, for example, gear teeth  12   a - 12   c  of a ferromagnetic gear  12 . One of ordinary skill in the art will understand that a permanent magnet (not shown) can be placed at a variety of positions proximate to the gear  12 , resulting in fluctuations of a magnetic field proximate to the gear  12  as the gear  12  having the gear teeth  12   a - 12   c  rotates. 
         [0025]    The rotation detector  10  can have a first port  14  coupled to a power supply denoted as Vcc. The rotation detector  10  can also have a second port  16  coupled to a fixed voltage source, for example, a ground voltage source, denoted as GND. Thus, is some arrangements, the rotation detector  10  is a two port device, for which an output signal appears as a signal current at the first port  14 , superimposed upon the power supply voltage, Vcc. However, in other arrangements, one of ordinary skill in the art will understand that a rotation detector similar to the rotation detector  10  can have a third port (not shown) at which an output signal can appear as a voltage rather than a current. 
         [0026]    The rotation detector  10  can include first, second, and third magnetic field sensing elements  18 ,  20 ,  22 , respectively, here shown to be Hall effect elements. The first Hall effect element  18  generates a first differential voltage signal  24   a ,  24   b , the second Hall effect element generates a second differential voltage signal  26   a ,  26   b , and the third Hall effect element  22  generates a third differential voltage signal  28   a ,  28   b , each having an AC signal component in response to the rotating gear  12 . 
         [0027]    While each one of the Hall effect elements  18 ,  20 ,  22  is shown to be a two port device, one of ordinary skill in the art will understand that each one of the Hall effect elements  18 ,  20 ,  22  is actually a four port device and the other two ports of the Hall effect elements can be coupled to receive and pass respective currents as might be provided, for example, by respective current sources or a voltage source (not shown). 
         [0028]    The first differential voltage signal  24   a ,  24   b  is received by a first differential preamplifier  30   a , the second differential voltage signal  26   a ,  26   b  is received by a second differential preamplifier  30   b , and the third differential voltage signal  28   a ,  28   b  is received by a third differential preamplifier  30   c.    
         [0029]    First and second output signals  32   a ,  32   b  generated by the first and second differential preamplifiers  30   a ,  30   b , respectively, are received by a “right” channel amplifier  34   a  and the second output signal  32   b  and a third output signals  32   c  generated by the second and third differential preamplifiers  30   b ,  30   c , respectively, are received by a “left” channel amplifier  34   b . Designations of “right” and “left” are arbitrary but are generally indicative of rotation of the gear  12  in first and second directions. 
         [0030]    A signal  38   a  generated by the right channel amplifier  34   a  is received by a right channel detector circuit  36   a  and a signal  38   b  generated by the left channel amplifier  34   b  is received by a left channel detector circuit  36   b . The signals  38   a ,  38   b  can be analog signals, generally sinusoidal in nature. 
         [0031]    Taking the right channel detector circuit  36   a  as representative of both of the detector circuits  36   a ,  36   b , the right channel detector circuit  36   a  includes a peak detector circuit  40   a  coupled to receive the signal  38   a . The peak detector circuit  40   a  is configured to detect positive and negative peaks of the signal  38   a  and to generate the threshold signal  42   a  that, for example, takes on a first static threshold value just below a positive peak of the signal  38   a  or a second static threshold value just above a negative peak of the signal  38   a , depending upon a direction of transition of the signal  38   a . A comparator  44   a  is coupled to receive the threshold signal  42   a  and is also coupled to receive the signal  38   a . As a result, the comparator  44   a  generates a binary signal  46   a  that has transitions when the signal  38   a  crosses both the first and second static thresholds, near to a time when the signal  38   a  achieves positive and negative peaks. 
         [0032]    A signal  46   b  generated by the left channel detector circuit  36   b  is generated in the same way as the signal  46   a . However, since the magnetic field sensing elements  18 ,  20  contribute to the signal  46   a , while the magnetic field sensing elements  20 ,  22  contribute to the signal  46   b , it should be appreciated that the signals  46   a ,  46   b  have edges that differ in time (which is equivalent to phase for a particular signal frequency, i.e., particular rotation speed). Furthermore, it should be appreciated that a direction of rotation of the gear  12  may be determined from a relative phase or relative time difference (e.g., lag or lead) of a particular edge transition in the signal  46   a  compared with a particular corresponding edge transition in the signal  46   b . Therefore, a relative lag or a lead of edges of the signals  46   a ,  46   b  can be used to identify a direction of rotation of the gear  12 . 
         [0033]    The rotation detector  10  can include an output protocol circuit  48  coupled to receive and process the signals  46   a ,  46   b  and configured to generate an output signal  52  as a current signal, which is indicative of the speed of rotation and the direction of rotation of the gear  12 . 
         [0034]    While the rotation detector  10  is shown to include the detector circuits  36   a ,  36   b , each having a particular topology, it should be understood that any form of peak-referenced detectors or peak-to-peak percentage detectors, including, but not limited to, the above-described peak-referenced detectors and peak-to-peak percentage detectors, can be used in place of or in addition to the detector circuits  36   a ,  36   b.    
         [0035]    Referring now to  FIG. 2 , a graph has a horizontal axis in units of time in arbitrary units. A curve  60  is representative of one of the signals  46   a ,  46   b  received by the output protocol circuit  48 . The curve  60  represents a binary (two-state) signal, having positive transitions  62   a - 62   c  at times trise 1 , trise 2 , and trise 3 , respectively, and negative transitions  64   a - 64   c  at times tfall 1 , tfall 2 , and tfall 3 , respectively, when the gear  12  is rotating at a rotational speed proportional to a frequency of the signal  60 . 
         [0036]    The signal  60  encounters reversals of direction of rotation of the gear  12  at times trev 1  and trev 2 . Prior to the time trev 1 , the gear  12  is rotating in a first direction. Between times trev 1  and trev 2 , the gear  12  is rotating in a second different direction. After the time trev 2 , the gear is again rotating in the first direction. 
         [0037]    A curve  66 , representative of the other one of the signals  46   a ,  46   b  of  FIG. 1 , has generally the same shape and transitions as the signal  60  but has a phase either leading or lagging the phase of the signal  60  according to the direction of rotation of the gear  12  of  FIG. 1 . 
         [0038]    Thus, transitions of the signal  66  lead the signal  60  prior to the time trev 1 , transitions of the signal  66  lag the signal  60  between the times trev 1  and trev 2 , and transitions of the signal  66  again lead transitions of the signal  60  after the time trev 2 . The curve  66  is shown with a small vertical offset from the signal  60  for clarity. 
         [0039]    A curve  70  is representative of the output signal  52  generated by a first embodiment of the output protocol circuit  48  of  FIG. 1 , which embodiment is further described below in conjunction with  FIG. 3 . The output signal  70  has pulses  72   a - 72   c  and  76 . The pulses  72   a - 72   c  have rising leading edges  74   a - 74   c . The pulse  76  has a falling leading edge  78 . It will be understood that the output signal  70  has a plurality of pulses, each one of the plurality of pulses having a leading edge with a transition direction indicative of the direction of rotation. Thus, between times trev 1  and trev 2 , the leading edge of the pulse  76  is a falling leading edge and at other times, the leading edges of the pulses  72   a - 72   c  are rising leading edges. However, pulses with the opposite leading edge directions are also possible. 
         [0040]    As used herein, the term “pulse” is used to describe a portion of a binary signal, wherein a width of the pulse is less than about fifty percent of a period of the binary signal. Therefore, it will be understood that a pulse is a brief excursion of a signal from one signal value to another signal value. 
         [0041]    At a time trise 2 , during a time period between times trev 1  and trev 2  when the direction has changed to reverse, the pulse width of the high state changes from the width of the pulses  72   a ,  72   b  to be longer, having a length depending on speed of rotation. As a result, the output protocol circuit  48  of  FIG. 1  can identify that the direction of rotation has changed. The rising edge at the time trise 2  still conveys the edge information, but the expected high state time duration changed because the direction changed. Also, at time trise 3 , the falling edge of the signal  70  conveys the edge position, but the expected low state time duration changed, indicating that the direction of rotation changed again. 
         [0042]    In the signal  70 , the pulses are inverted in the reverse direction of rotation. For example, if the pulses, e.g.,  72   a ,  72   b , have forty-five millisecond high states (pulse widths) when the direction of rotation is forward, when the direction of rotation is in reverse, the pulses, e.g., the pulse  78 , have forty-five millisecond low states (pulse widths). As speed varies in the forward direction, the high state of the pulses (pulse width) remains forty-five milliseconds, and as speed varies in the reverse direction, the low state (pulse width) of the pulses remains forty-five milliseconds. 
         [0043]    A curve  80  is representative of the output signal  52  generated by a second embodiment of the output protocol circuit  48  of  FIG. 1 , which embodiment is further described below in conjunction with  FIG. 4 . The output signal  80  has pulses  82   a - 82   d , each of which is referred to herein as an “instance” having one pulse. The output signal  80  also has pulses  86   aa ,  86   ab ,  86   ba ,  86   bb , which appear in double pulse groups  86   a ,  86   b , and each double pulse group  86   a ,  86   b  is referred to here as an instance having two pulses. All of the pulses  82   a - 82   d ,  86   aa ,  86   ab ,  86   ba ,  86   bb  have rising leading edges  84   a - 84   d ,  88   a - 88   d , respectively. It will be understood that the output signal  80  has a first number of pulses (i.e. one pulse, e.g., the pulse  82   a ) occurring in instances (e.g.,  82   a ,  82   b ) of the first number of pulses when the ferromagnetic object (e.g., gear  12  of  FIG. 1 ) is rotating in a first direction, and a second different number of pulses (i.e., two pulses, e.g., the pulses  86   aa ,  86   ab ) occurring in instances (e.g.,  86   a ,  86   b ) of the second number of pulses when the ferromagnetic object (e.g., gear  12  of  FIG. 1 ) is rotating in a second different direction. 
         [0044]    While one pulse (e.g.,  82   a ) is shown to be representative of a first direction of rotation, and two pulses (e.g.,  86   aa ,  86   ab ) are shown to be representative of a second different direction of rotation, other numbers of pulses can also be used, so long as there are different numbers of pulses representative of each respective direction of rotation. 
         [0045]    Also, while the single pulses (e.g.,  82   a ) and the multiple pulses (e.g.,  86   aa ,  86   ab ) are shown to have leading edge transitions in the same positive direction, in other arrangements, the leading edge transitions of the single pulses  82   a - 82   d  can be in a direction opposite from the leading edge transitions of the multiple pulses  88   aa - 88   ab  and  86   ba - 8   bb.    
         [0046]    A curve  90  is representative of the output signal  52  generated by a third embodiment of the output protocol circuit  48  of  FIG. 1 , which embodiment is further described below in conjunction with  FIG. 5 . The curve  90  is shown in conjunction with a vertical amplitude scale of signal currents represented by lines  92   a ,  92   b ,  92   c . The line  92   a  is indicative of a signal current of about four to eight milliamps, the line  92   b  is indicative of a signal current of about twelve to sixteen milliamps, and the line  92   c  is indicative of a signal current of about twenty to twenty-six milliamps. It should be appreciated that the indicated current ranges are illustrative only and that other current ranges can be used. 
         [0047]    The output signal  90  has pulses  94   a - 94   d  with a first amplitude between currents represented by the lines  92   b  and  92   c . The output signal  90  also has pulses  98   a ,  98   b  with a second different amplitude above a current represented by the line  92   c . All of the pulses  94   a - 94   d ,  98   a ,  98   b  have rising leading edges  96   a - 96   d ,  100   a ,  100   b , respectively. In some embodiments, at times when pulses are not present, for example, at a baseline signal level  98 , the signal  90  can take on a third different amplitude above a current represented by the line  92   a , but below a current represented by the line  92   b.    
         [0048]    It will be understood that the output signal  90  has a plurality of pulses  94   a - 94   d ,  98   a ,  98   b , each one of the plurality of pulses having a respective pulse amplitude selected from among a first pulse amplitude (e.g., the pulse  94   a ) and a second different pulse amplitude (e.g., the pulse  98   a ), wherein the first and second pulse amplitudes are indicative of respective directions of rotation of the ferromagnetic object (e.g., gear  12  of  FIG. 1 ). 
         [0049]    A curve  110  is representative of the output signal  52  generated by a fourth embodiment of the output protocol circuit  48  of  FIG. 1 , which embodiment is further described below in conjunction with  FIG. 6 . The output signal  110  has pulses  112   a - 112   d  and  116   a - 116   b . The pulses  112   a - 112   d  have rising leading edges  114   a - 114   d , respectively. The pulses  116   a - 116   b  have falling leading edges  118   a - 118   b , respectively. It will be understood that the output signal  110 , like the signal  70 , has a plurality of pulses, each one of the plurality of pulses having a leading edge with a transition direction indicative of the direction of rotation. Thus, between times trev 1  and trev 2 , the leading edges of the pulses  116   a - 116   b  are falling leading edges and at other times, the leading edges of the pulses  112   a - 112   d  are rising leading edges. However, pulses with the opposite leading edge directions are also possible. 
         [0050]    While pulses having particular directions of leading edge transitions are shown, in other arrangements, the signals  70 ,  80 ,  90 ,  110  can be inverted, resulting in leading edge transitions in the opposite directions from those shown. 
         [0051]    In some arrangement the pulses  72   a - 72   c , and  76 , the pulses  82   a - 82   d  and  86   aa - 88   ab  and  86   ba - 86   bb , the pulses  94   a - 94   d  and  98   a - 98   b , and the pulses  112   a - 112   c  and  118   a - 118   b  have time durations (pulse widths) of about forty-five milliseconds. However, it will be apparent that the pulse widths of the various pulses can be predetermined in accordance with a frequency at which the pulses (or instances of groups of pulses in the signal  90 ) occur. 
         [0052]    The frequency at which the pulses or instances occur can be indicative of a rotational speed of the rotating ferromagnetic object (e.g., the gear  12  of  FIG. 1 ). The frequency at which the pulses or instances occur is shown to be the same as the frequency of the signals  60  and  66  in  FIG. 2 , which signals are representative of output signals  46   a ,  46   b  from the detector circuits  36   a ,  36   b  of  FIG. 1 , and which signals are representative of the rotational speed of the ferromagnetic object. However, in other arrangements, the frequency at which the pulses or instances occur is not the same as the frequency of the output signal of the detector circuits. Nevertheless, the frequency at which the pulses or instances occur can still be indicative of the rotational speed of the rotating ferromagnetic object  12 . 
         [0053]    While the signals  70 ,  80 ,  90 , and  110  are representative of current signals, e.g., the current signal  52  of  FIG. 1  appearing at the node  14 , in other arrangements, the signals  70 ,  80 ,  90 , and  110  are voltage signals appearing at another port (not shown) of the rotation detector  10  of  FIG. 1 . 
         [0054]    While positive and negative pulses having pulse widths of forty-five milliseconds are described above, in other embodiments, the pulse widths can be within a range of about five to five hundred milliseconds. 
         [0055]    It should be apparent that the low states of the signals  70 ,  80 ,  110  need not be representative of zero current or zero volts. Instead, in some embodiments, any of the signals  70 ,  80 ,  110  can have respective low states that are at a positive voltage or current. However, in some other embodiments, any of the signals  70 ,  80 ,  110  can have respective low states that are at a negative voltage or current. 
         [0056]      FIGS. 3-6  are block diagram showing exemplary circuits that can form the output protocol circuit  48  of  FIG. 1 . The circuits of  FIGS. 3-6  can be used to generate the output signals  70 ,  80 ,  90 , and  110  of  FIG. 2 , respectively. 
         [0057]    Referring now to  FIG. 3 , an exemplary output protocol circuit  150  has a power supply/signal port  152  coupled to receive a power supply voltage signal denoted Vcc. At the port  152 , and as further described below, the output protocol circuit  150  can also generate an output signal in the form of a current signal  193   a  superimposed upon the power supply voltage signal Vcc. It will become apparent from discussion below that the output protocol circuit  150  is configured to generate the current output signal  193   a  at the node  152  that is the same as or similar to the signal  70  of  FIG. 2 . The output protocol circuit  150  also has a reference port  154 , which can be coupled to a reference voltage, for example, ground. 
         [0058]    The output protocol circuit  150  also has two input ports  156   a ,  156   b  coupled to receive a respective two input signals  155   a ,  155   b  from a respective two detector circuits, for example, from the detector circuits  36   a ,  36   b  of  FIG. 1 , wherein the two input signals  155   a ,  155   b  can be the same as or similar to the signals  46   a ,  46   b , respectively. As described above, the signals  46   a ,  46   b  generated by the detector circuits  36   a ,  36   b  are binary two-state signals. The signals  46   a ,  46   b  can be digital signals having high and low state values that can be operated upon by convention digital circuits, for example, CMOS digital circuits. 
         [0059]    The first and second input signals  155   a ,  155   b  are received at respective D inputs of first and second D-type flip-flops  158   a ,  158   b , which are clocked by a common master clock signal  162  generated by a master clock circuit  160 . In some embodiments, the master clock signal  162  is synchronous with the input signals  155   a ,  155   b . Furthermore, the master clock signal  162  has clocking transitions occurring after transitions of one of the input signals  155   a  or  155   b  and before corresponding transitions of the other one of the input signals  155   a  or  155   b . For example, referring briefly to  FIG. 2 , the clocking transitions of the master clock signal  162  can occur after the rising transitions of the signal  66  and before corresponding rising transitions of the signal  60 . 
         [0060]    Outputs signal  164   a ,  164   b  generated by the first and second D-type flip-flops  158   a ,  158   b  are received by D inputs of third and fourth D-type flip-flops  166   a ,  166   b , respectively. An exclusive OR gate  170  is coupled to receive the output signal  164   a  from the first flip-flop  158   a  and to receive the output signal  168   b  from the fourth flip-flop  166   b . In response, the exclusive OR gate  170  generates an output signal  172  having a state representative of a direction of rotation of a ferromagnetic object, for example, of the ferromagnetic gear  12  of  FIG. 1 . The state of the signal  172  is static for any one static direction of rotation. Thus, the signal  172  is also referred to herein as a “direction signal.” 
         [0061]    Another exclusive OR gate  174  is coupled to receive the output signals  164   a ,  164   b ,  168   a ,  168   b  from the first, second, third, and fourth flip-flops  158   a ,  158   b ,  166   a ,  166   b , respectively. In response, the exclusive OR gate  174  generates an output signal  176  having pulses generally at times of each transition of the input signals  155   a ,  155   b . Thus, the signal  176  is also referred to herein as a “count signal.” 
         [0062]    The count signal  176  is received by a one-shot circuit  178  (monostable multivibrator), that generates a pulse signal  180  having pulses, each having a predetermined pulse width, upon each transition of the signal  176  having a predetermined direction of transition. For example, in one particular embodiment, the pulses within the pulse signal  180  are generated by the one-shot circuit  178  upon each rising edge of the count signal  176 . 
         [0063]    The pulse signal  180  provides a clocking signal to a fifth D-type flip-flop  184 . The direction signal  172  is received at the D input of the D-type flip-flop  184 . Another exclusive OR gate  188  is coupled to receive an output signal  186  from the D-type flip-flop  184  and to receive the pulse signal  180 . In operation, an output signal  190  generated by the exclusive OR gate  188 , which is a voltage signal, appears similar to the signal  70  of  FIG. 2 , which is described above to be a current signal. 
         [0064]    The voltage signal  190  is converted to a current signal  193   b  by a switch  204  in combination with a current source  196 . The switch  204  has an input node  202 , a control node  192 , and an output node  204 . The current source  196  has an input node  194  coupled to the node  152  and an output node  198  coupled to the input node  202  of the switch  204 . A current signal  200  (and  193   b ) having a positive current value passes from the output node  198  of the current source  196  to the input node  202  of the switch  204  only when the switch  204  is closed, otherwise the current signal  200  (and  193   b ) has a current value of zero. The switch  204  is coupled to receive the voltage signal  190  at the control node  192 , and therefore, the switch  204  is configured to open and close in accordance with states of the signal  190 . 
         [0065]    In operation, when the direction signal  172  is in a low state indicative of a first direction of rotation, pulses in the pulse signal  180  pass through the exclusive OR gate  188  and appear in the signals  190 ,  193   a , and  193   b . Alternatively, when the direction signal  172  is in a high state indicative of a second different direction of rotation, pulses in the pulse signal  180  are inverted by the exclusive OR gate  188  and appear inverted in the signals  190 ,  193   a , and  193   b . Therefore, the current signals  193   a ,  193   b  are the same as or similar to the signal  70  of  FIG. 2 . 
         [0066]    It will be apparent that the current signal  193   a  can include an Icc current component as shown, which can result in the current signal  193   a  being offset from the current signal  193   b . The Icc current component can be a current signal corresponding to a DC current used to power other portions of the circuit  150 . However, in other embodiments, the current signal  193   a  can be further offset in a positive or in a negative direction by use of a current source or current sink in parallel with the Icc current signal. 
         [0067]    Referring now to  FIG. 4 , another exemplary output protocol circuit  220  has a power supply/signal port  222  coupled to receive a power supply voltage signal denoted Vcc. At the port  222 , and as further described below, the output protocol circuit  220  can also generate an output signal in the form of a current signal  258   a  superimposed upon the power supply voltage signal Vcc. It will become apparent from discussion below that the output protocol circuit  220  is configured to generate the current output signal  258   a  at the node  222  that is the same as or similar to the signal  80  of  FIG. 2 . The output protocol circuit  220  also has a reference port  224 , which can be coupled to a reference voltage, for example, ground. 
         [0068]    The output protocol circuit  220  also has two input ports  226   a ,  226   b  coupled to receive the respective two input signals  155   a ,  155   b  from a respective two detector circuits, for example, from the detector circuits  36   a ,  36   b  of  FIG. 1 . The first and second input signals  155   a ,  155   b  are received by the circuit  151 , which is described more fully above in conjunction with  FIG. 3 , resulting in the direction signal  172  and in the count signal  176 . The count signal  176  is received by a first one-shot circuit  228  configured to generate a first pulse signal  230 . The first pulse signal  230  is received by a first inverter  232  configured to generate an inverted first pulse signal  234 . The inverted first pulse  234  is received by a second one-shot circuit  236  configured to generate a second pulse signal  238 . The second pulse signal  238  is received by a second inverter  240  configured to generate an inverted second pulse signal  242 . The inverted second pulse signal  242  is received by a third one-shot circuit configured to generate a third pulse signal  248 . 
         [0069]    The third pulse signal  248  and the direction signal  172  are received by an AND gate  250  configured to generate a signal  252 . The signal  252  and the first pulse signal  230  are received by an OR gate  254  configured to generate an output signal  256 . The output signal  256  generated by the OR gate  254 , which is a voltage signal, appears similar to the signal  80  of  FIG. 2 , which is described above to be a current signal. 
         [0070]    The voltage signal  256  is converted to a current signal  258   b  by a switch  270  in combination with a current source  262 . The switch  270  has an input node  268 , a control node  272 , and an output node  274 . The current source  262  has an input node  260  coupled to the node  222  and an output node  264  coupled to the input node  268  of the switch  270 . A current signal  266  (and  258   b ) having a positive current value passes from the output node  264  of the current source  262  to the input node  268  of the switch  270  only when the switch  270  is closed, otherwise the current signal  266  (and  258   b ) has a current value of zero. The switch  270  is coupled to receive the voltage signal  256  at the control node  272 , and therefore, the switch  270  is configured to open and close in accordance with states of the signal  256 . 
         [0071]    In operation, when the direction signal  172  is in a low state indicative of a first direction of rotation, only pulses in the first pulse signal  230  pass through the OR gate  254  and appear in the signals  256 ,  258   a , and  258   b . Alternatively, when the direction signal  172  is in a high state indicative of a second different direction of rotation, pulses in the first pulse signal  230  and also pulses in the third pulse signal  248  (i.e., two pulses) pass through the OR gate  254  and appear in the signals  256 ,  258   a , and  258 . Therefore, the current signals  258   a ,  258   b  are the same as or similar to the signal  80  of  FIG. 2 . 
         [0072]    It will be apparent that the current signal  258   a  can include an Icc current component as shown, which can result in the current signal  258   a  being offset from the current signal  258   b . The Icc current component can be a current signal corresponding to a DC current used to power other portions of the circuit  220 . However, in other embodiments, the current signal  258   a  can be further offset in a positive or in a negative direction by use of a current source or current sink in parallel with the Icc current signal. 
         [0073]    Referring now to  FIG. 5 , another exemplary output protocol circuit  300  has a power supply/signal port  302  coupled to receive a power supply voltage signal denoted Vcc. At the port  302 , and as further described below, the output protocol circuit  300  can also generate an output signal in the form of a current signal  312   a  superimposed upon the power supply voltage signal Vcc. It will become apparent from discussion below that the output protocol circuit  300  is configured to generate the current output signal  312   a  at the node  302  that is the same as or similar to the signal  90  of  FIG. 2 . The output protocol circuit  300  also has a reference port  304 , which can be coupled to a reference voltage, for example, ground. 
         [0074]    The output protocol circuit  300  also has two input ports  306   a ,  306   b  coupled to receive the respective two input signals  155   a ,  155   b  from a respective two detector circuits, for example, from the detector circuits  36   a ,  36   b  of  FIG. 1 . The first and second input signals  155   a ,  155   b  are received by the circuit  151 , which is described more fully above in conjunction with  FIG. 3 , resulting in the direction signal  172  and in the count signal  176 . The count signal  176  is received by a one-shot circuit  308  configured to generate a pulse signal  310 . 
         [0075]    A current signal  312   b  is generated by switches  322 ,  338  in combination with current sources  314 ,  330 . The switch  322  has an input node  324 , a control node  326 , and an output node  328 . The switch  338  has an input node  340 , a control node  342 , and an output node  344 . The current source  314  has an input node  316  coupled to the node  302  and an output node  318  coupled to the input node  324  of the switch  322 . The current source  330  has an input node  332  coupled to the node  302  and an output node  334  coupled to the input node  340  of the switch  338 . The output node  328  of the switch  322  is also coupled to the input node  340  of the switch  338 . 
         [0076]    A current signal  320  having a positive current value passes from the output node  318  of the current source  314  to the input node  324  of the switch  322  only when the switch  322  is closed, otherwise the current signal  320  has a current value of zero. The switch  322  is coupled to receive the direction signal  172  at the control node  326 , and therefore, the switch  322  is configured to open and close in accordance with states of the direction signal  172 . 
         [0077]    A current signal  336  having a positive current value passes from the output node  334  of the current source  330  to the input node  340  of the switch  338  only when the switch  338  is closed, otherwise the current signal  336  has a current value of zero. The switch  338  is coupled to receive the pulse signal  310  at the control node  342 , and therefore, the switch  338  is configured to open and close in accordance with states of the pulse signal  310 . 
         [0078]    The current signals  320 ,  330  combine at the input node  340  of the switch  338  when the switch  322  is closed, but only the current signal  336  appears at the input node  340  of the switch  338  when the switch  322  is open. In this way, two current levels are achieved. 
         [0079]    In operation, when the direction signal  172  is in a low state indicative of a first direction of rotation, only the current signal  336  is in the current signal  312   b . Alternatively, when the direction signal  172  is in a high state indicative of a second different direction of rotation, the current signals  320  and  336  combine in the current signal  312   b . Therefore, the current signals,  312   a ,  312   b  are the same as or similar to the signal  90  of  FIG. 2 . 
         [0080]    It will be apparent that the current signal  312   a  can include an Ice current component as shown, which can result in the current signal  312   a  being offset from the current signal  312   b . The Icc current component can be a current signal corresponding to a DC current used to power other portions of the circuit  300 . However, in other embodiments, the current signal  312   a  can be further offset in a positive or in a negative direction by use of another current source or current sink in parallel with the Icc current signal. The Icc current (when both switches  322 ,  338  are open) can correspond to the baseline signal level  98  of  FIG. 2 . 
         [0081]    Referring now to  FIG. 6 , another exemplary output protocol circuit  350  has a power supply/signal port  352  coupled to receive a power supply voltage signal denoted Vcc. At the port  352 , and as further described below, the output protocol circuit  350  can also generate an output signal in the form of a current signal  366   a  superimposed upon the power supply voltage signal Vcc. It will become apparent from discussion below that the output protocol circuit  350  is configured to generate the current output signal  366   a  at the node  352  that is the same as or similar to the signal  110  of  FIG. 2 . The output protocol circuit  350  also has a reference port  354 , which can be coupled to a reference voltage, for example, ground. 
         [0082]    The output protocol circuit  350  also has two input ports  356   a ,  356   b  coupled to receive the respective two input signals  155   a ,  155   b  from a respective two detector circuits, for example, from the detector circuits  36   a ,  36   b  of  FIG. 1 . The first and second input signals  155   a ,  155   b  are received by the circuit  151 , which is described more fully above in conjunction with  FIG. 3 , resulting in the direction signal  172  and in the count signal  176 . 
         [0083]    The count signal  176  is received by a one-shot circuit  358  that generates a pulse signal  360  having pulses, each pulse having a predetermined pulse width, upon each transition of the count signal  176  having a predetermined direction of transition. For example, in one particular embodiment, the pulses within the pulse signal  360  are generated by the one-shot circuit  358  upon each rising edge of the count signal  176 . 
         [0084]    An exclusive OR gate  362  is coupled to receive the pulse signal  360  and to receive the direction signal  172  and configured to generate an output signal  364 . In operation, the output signal  364  generated by the exclusive OR gate  362 , which is a voltage signal, appears similar to the signal  110  of  FIG. 2 , which is described above to be a current signal. 
         [0085]    The voltage signal  364  is converted to a current signal  366   b  by a switch  372  in combination with a current source  368 . The switch  372  has an input node  374 , a control node  376 , and an output node  380 . The current source  368  has an input node  367  coupled to the node  352  and an output node  370  coupled to the input node  374  of the switch  372 . A current signal  371  (and  366   b ) having a positive current value passes from the output node  370  of the current source  368  to the input node  374  of the switch  372  only when the switch  372  is closed, otherwise the current signal  371  (and  366   b ) has a current value of zero. The switch  372  is coupled to receive the voltage signal  364  at the control node  376 , and therefore, the switch  372  is configured to open and close in accordance with states of the signal  364 . 
         [0086]    In operation, when the direction signal  172  is in a low state indicative of a first direction of rotation, pulses in the pulse signal  360  pass through the exclusive OR gate  362  and appear in the current signals  371 ,  366   a , and  366   b . Alternatively, when the direction signal  172  is in a high state indicative of a second different direction of rotation, pulses in the pulse signal  360  are inverted by the exclusive OR gate  362  and appear inverted in the current signals  371 ,  366   a , and  366   b . Therefore, the current signals,  366   a ,  366   b  are the same as or similar to the signal  110  of  FIG. 2 . 
         [0087]    It will be apparent that the current signal  366   a  can include an Icc current component as shown, which can result in the current signal  366   a  being offset from the current signal  366   b . The Icc current component can be a current signal corresponding to a DC current used to power other portions of the circuit  350 . However, in other embodiments, the current signal  366   a  can be further offset in a positive or in a negative direction by use of another current source or current sink in parallel with the Icc current signal. 
         [0088]    While the circuits shown above in  FIGS. 3-6  show particular circuit topologies that can generate the output signals shown in  FIG. 2 , which are indicative of a speed of rotation and a direction of rotation of a ferromagnetic object capable of rotating, it should be appreciated that other circuits can be used to generate any of the output signals of  FIG. 2 . For example, any of the voltage signal portions (e.g., the circuit  150  of  FIG. 3 , but without the current source  196  and the switch  204 ) of the circuits of  FIGS. 3-6  can be replaced with a programmable microprocessor or the like. 
         [0089]    All references cited herein are hereby incorporated herein by reference in their entirety. 
         [0090]    Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their 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.