Abstract:
Disclosed in the present invention is a low-power magnetoresistive switch sensor, comprising an internal reference voltage circuit, a multiplexer, a magnetoresistive bridge circuit, a comparison circuit, a voltage stabilization circuit, a digital control circuit, and a digital output circuit; one end of the internal reference voltage circuit is grounded while the other end of the internal reference voltage circuit is connected to the output end of the voltage stabilization circuit; the comparison circuit comprises one or more comparators, one end of the comparison circuit is electrically connected with the voltage stabilization circuit while the other end is grounded, the comparison circuit is provided with one or more input ends and one or more output ends, and the one or more output ends of the comparison circuit are electrically connected with one input ends of the digital control circuit; one end of the magnetoresistive bridge circuit is electrically connected with the output end of the voltage stabilization circuit while the other end is grounded, and the output end of the magnetoresistive bridge circuit is electrically connected with one input end of the comparison circuit. The low-power magnetoresistive switch sensor has the advantages of high sensitivity, low power consumption, high frequency response, small size, and excellent thermal characteristics.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the technical field of sensors, and more particularly to a low-power magnetoresistive switch sensor. 
       BACKGROUND 
       [0002]    Magnetic switch sensors are widely used in consumer electronics, white goods, utility-meters (electricity meter, water meter, gas meter), automotive, and industrial applications. Presently mainstream magnetic switch sensors utilize Hall sensors and AMR (anisotropic magnetoresistive) sensors. For the Applications in consumer electronics and utility meters, Hall switch sensors and AMR switch sensors have power consumption of up to a few microamps. This is obtained at the expense of operating frequency. Hall switch sensors and AMR switch sensors are operate at a frequency of a dozen or so Hz with a switch point in the range of tens of gauss. In the automobile and other industrial fields requiring high frequency operation, Hall switch sensors and AMR switch sensors consume power on the order of mA at the kHz level. 
         [0003]    In recent years, a new type of magnetoresistive sensor utilizing magnetic tunnel junction (MTJ) has found application in industrial fields. These combine magnetic multilayers with the tunneling magnetoresistance effect. The electrical resistance of the magnetic multilayer depends on the magnitude and the orientation of the external magnetic field. In the low-power consumption fields, such as the consumer electronics and utility-meters, the MTJ sensors operating at a frequency of a dozen Hz with a switch point of tens of gauss. In the automobile and other industrial fields requiring high frequency operation, the MTJ sensors consume power on the order of microamps at the MHz level. 
         [0004]    Some technical descriptions of magnetic switch devices are known in the art. U.S. Patent No. 2010/0026281 A1 discloses a gradiometer comprising two sensors for measuring location and speed of magnetic targets. The use of MTJ elements in magnetic switch sensors is described by Chinese patent application # 201110125153.5. These patent applications are incorporated by reference. 
         [0005]    The power consumption for the existing switch sensors is high in both sleep working states, and they have low operating frequency. A need therefore exists for a switch sensor with high sensitivity, high frequency response, small volume, and low power consumption in sleep and working states. 
       SUMMARY OF THE INVENTION 
       [0006]    The purpose of the present invention is to provide a magnetoresistive sensor switch. 
         [0007]    The magnetoresistive switch sensor of the present invention includes an internal voltage reference circuit, a multiplexer, a magnetoresistive bridge circuit, a comparison circuit, a power supply, a voltage reference circuit, digital control circuits, and digital output circuits; 
         [0008]    Said reference voltage circuit is connected to ground at one end, the other end is electrically connected to the output terminal of the power supply regulator circuit; 
         [0009]    Said comparison circuit comprises one or more comparators, one end of which is electrically connected to said power regulator circuit, and the other end to ground, said comparison circuit has one or more inputs and one or a plurality of outputs, one or more of said comparison circuit output terminals are electrically connected to an input terminal said digital control circuit; 
         [0010]    The magnetoresistive bridge circuit is electrically connected to the power regulator circuit and to ground, and the magnetoresistive bridge circuit output is connected to one input of the comparator circuit; 
         [0011]    The multiplexer is controlled by the digital control circuit, said multiplexor determining which of the many said outputs of said reference voltage circuit are electrically connected to one of said comparator circuit inputs; 
         [0012]    The digital control circuit executes operations based on internal logic states and input signals changes, and it is electrically connected to the multiplexer and the digital output circuit. 
         [0013]    Preferably, a Low Pass Filter circuit is connected between said reference voltage circuit, said magnetoresistive bridge circuit and said comparator circuit, the inputs of said Low Pass Filter circuit is connected to said outputs of said MR bridge circuit and said outputs of said reference voltage circuit, the outputs of said Low Pass Filter circuit is connected to said inputs of said comparator circuit, it is used to attenuate the voltages above a cut-off frequency. 
         [0014]    Preferably, the power regulator circuit output voltage V Bias  is less than the supply voltage. 
         [0015]    Further, the comparator circuit comprises one or more comparator power switches that determine which of current source are connected to the power terminals of said comparator circuit, said current sources connected also to said power regulator circuit, said comparator power switches being controlled by said digital control circuit. 
         [0016]    Preferably, the digital control circuit is one part of digital control system. 
         [0017]    Further, the digital control system comprises a set of logical operating modes, and applied magnetic field trigger conditions, wherein the digital control system creates magnetic field-dependent output having the character of the bipolar switch, unipolar switch, or omnipolar switch. 
         [0018]    Preferably, the magnetoresistive bridge circuit comprises the first MR element and the second MR element, the first MR element and the second MR element are connected electrically to form one Push-pull half bridge. 
         [0019]    Further, the first MR element and said second MR element respectively comprises one or more MTJ elements in series or/and in parallel. 
         [0020]    Further, the sensitive direction of said push-pull half bridge is parallel to the magnetic moment direction of the pinned layer of said first magnetoresistive element and second magnetoresistive element. 
         [0021]    Preferably, the digital output stage circuit comprises a latch and driver circuit and the output stage, the input of said latch and driver circuit is connected to the output of said digital control circuit, the output of said latch and driver circuit is connected to the output stage. 
         [0022]    The present invention has the following beneficial effects: 
         [0023]    The switch sensor of the present invention utilizes MTJ elements as sensor components in order to sense the approach of ferromagnetic material, thereby providing high sensitivity, low power consumption, high frequency response, and good thermal characteristics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    In order to more clearly illustrate the implementation of technical solutions to the invention, a brief introduction to the relevant diagrams along with technical details are provided below. Obviously, the following descriptions of the diagrams illustrate only some of the practical configurations of the present invention. For a person of ordinary skill in this field, they can easily arrive at other useful configurations from our described diagrams without any creative thinking. 
           [0025]      FIG. 1  is a schematic view of a prior art MTJ element material stack. 
           [0026]      FIG. 2  is a plot showing the relationship between the applied magnetic field and the resistance of the prior art MTJ element. 
           [0027]      FIG. 3  is a plot illustrating an integrated circuit combined with a push-pull half-bridge sensor of the prior art. 
           [0028]      FIG. 4  is a plot of the output voltage as a function of applied magnetic field of a push-pull half-bridge magneto-resistive sensor measured at two different temperatures. 
           [0029]      FIG. 5  is a schematic diagram of a reference voltage circuit used for the bridge circuit simulation. 
           [0030]      FIG. 6  is an analog filter and a comparator circuit diagram of bipolar and unipolar switch magnetoresistance sensor; 
           [0031]      FIG. 7  is a circuit diagram of bipolar and unipolar switch magnetoresistive switch sensors. 
           [0032]      FIG. 8  is a graph showing the relationship between magnetoresistive bipolar switch sensor output voltage and the applied magnetic field; 
           [0033]      FIG. 9  is a graph showing the relationship between the output voltage and the applied magnetic field for a unipolar magnetoresistive switch sensor; 
           [0034]      FIG. 10  is a diagram showing the relationship between the output voltage and the applied magnetic field of a push-pull bridge sensor; 
           [0035]      FIG. 11  is a graph showing the relationship between the output voltage and the applied magnetic field of an omnipolar magnetoresistive switch sensor. 
           [0036]      FIG. 12  illustrates a circuit diagram of a preferred implementation of the present invention of the analog filters and comparators of an omnipolar magnetoresistive switch sensor. 
           [0037]      FIG. 13  is a circuit diagram of an omnipolar magnetoresistive sensor switch according to a preferred embodiment of the present invention; 
           [0038]      FIG. 14  is a timing chart for an omnipolar magnetoresistive switch sensor operating in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    The following diagrams illustrate the implementation of technical solutions of the present invention, with specific examples of the present invention described clearly and completely. 
         [0040]    Implementation Example 
         [0041]    As shown in  FIG. 1 , the MTJ magnetic tunnel junction structure is made by the nano-scale multilayers: the anti-ferromagnetic layer  1 , a magnetic pinning layer  2 , non-magnetic oxide layer  3 , the magnetic free layer  4 . The orientation of the magnetic moment  5  of the magnetic pinning layer  2  is perpendicular or has an angle to the orientation of the magnetic moment  6  of the magnetic free layer  4 . The orientation of the magnetic moment  6  of the magnetic free layer  4  depends on the magnitude and the orientation of the external magnetic field  7 . The mechanism for the MTJ structure is shown below: the resistance of the MTJ structure depends on the angle between the orientation of the magnetic moment  5  of the magnetic pinning layer  2  and the orientation of the magnetic moment  6  of the magnetic free layer  4 . When the orientation of the magnetic moment  6  of the magnetic free layer  4  rotates under the external magnetic field  7 , the resistance of the structure also changes. 
         [0042]    Shown in  FIG. 2 , when the external magnetic field  7  is parallel with the magnetic pinned layer  2  and the applied magnetic field strength is greater than H 1 , the orientation of the magnetic free layer  4  is also parallel with the external magnetic field  7 . Therefore, it is parallel with the magnetic pinning layer  2 . Under this circumstance, the MTJ structure demonstrates the minimum resistance. When the external magnetic field  7  is anti-parallel with the magnetic pinned layer  2  and the applied magnetic field strength is greater than H 2 , the orientation of the magnetic free layer  4  is also anti-parallel with the external magnetic field  7 . Therefore, it is anti-parallel with the magnetic pinning layer  2 . Under this circumstance, the MTJ structure demonstrates the maximum resistance. The magnetic field range between H 1  and H 2  is the measuring range of the MTJ. 
         [0043]    The present invention uses the following ways or a combination of the following ways to bias the direction of the magnetic moment of the magnetic free layer. The following orientation of the magnetic moment of the magnetic free layer is perpendicular to or at an angle and magnetic with that of the magnetic pinning layer: With the deposition of a thin layer of anti-ferromagnetic material above or underneath the free layer, the direction of the magnetic moment is biased by the exchange coupling; The direction of the magnetic moment is biased by the Neel coupling between the magnetic free layer and the magnetic pinning layer; By the integration of the current coil with the sensor, the direction of the magnetic moment is biased by the following current in the same direction; The direction of the magnetic moment is biased by the permanent magnetic nearby. 
         [0044]    A shown in  FIG. 3 , the prior art push-pull magnetoresistive switch sensor comprises a first magnetoresistive element  11 , a second magnetoresistive element  12  and an ASIC (Application Specific Integrated Circuit) chip  13 . Wherein the ASIC and the first magnetoresistive element  11  and the second magnetoresistive element form an assembly, the two magnetoresistive elements,  11  and  12 , are also connected to form a push-pull half-bridge circuit. The sensing elements of  11  and  12  consist by one or more MTJ magnetoresistive elements in series and/or parallel. The MTJ magnetoresistive element is a multilayer nano scale structure including a ferromagnetic free layer and a ferromagnetic pinned layer. The magnetic moments of the free layers inside two MTJ elements,  121  and  122  are set to the anti-parallel orientation. Similarly, the magnetic moments of the pinning layers inside two MTJ elements,  111  and  112  are set to the anti-parallel orientation. The magnetic moments of the pinned layer  111  and pinned layer  112  are rotated perpendicularly to the direction of the magnetic moments of the free layer  121  and free layer  122  for each MTJ element. The sensing direction  70  of the pull-push half-bridge circuit is parallel with the magnetic moments  11  and  12  of the pining layers. When an external magnetic field is applied along the sensing direction  70 , the magnetic moment of one magnetoresistive element tends to be parallel with the external field and the pinned layer, thus its resistance will be reduced. Meanwhile, the magnetic moment of the other magnetoresistive element tends to be anti-parallel with the pinned layer, so that its resistance will be increased, resulting in the push-pull output V OUT  (V OUT =V Bridge  in all remaining diagrams). The output curve is shown in  FIG. 4 . 
         [0045]    The corresponding ASIC Chip  13  is connected to the push-pull half-bridge in order to provide pa steady voltage V DD  (V Bias  in remaining figures), and to convert the push-pull half-bridge output voltage signal is converted to a switching signal. ASIC chip  13  can be varied according to different technical requirements of different switch signal output signals. ASIC chip  13  can be configured to output a bipolar switching signal as shown in  FIG. 8 , a unipolar signal as shown in  FIG. 9  or an omnipolar switching signal as shown in  FIG. 11 . 
         [0046]    The foregoing example and  FIG. 1 ,  FIG. 2 , and  FIG. 3 , are provided as detailed background information, and they come from Chinese Patent Application No. 201110125153.5, which is herein included for reference. 
         [0047]    At high and low temperatures in both cases, the relationship between the push-pull half-bridge output voltage and the applied magnetic field between the curves shown in  FIG. 4 , Where the present embodiment magnetoresistance switch sensor the high temperature and low temperature range limits operation. In this example, the high temperature is 100° C., denoted HT; the low temperature is 0° C., denoted LT. In  FIG. 4 , curve  35  corresponds to that in  FIG. 2 , but the curve in  FIG. 4  but with a 180 degree rotation of the element pinning direction with respect to the sensing axis  7 . As a result, first magnetoresistive element  11  of the push-pull half-bridge has a magnetoresistive transfer curve with negative slope, and second magnetoresistive element  12  of the push-pull half-bridge has a magnetoresistive transfer curve with positive slope, so in  FIG. 4  push-pull half-bridge output, V Bridge  transfer curve, is balanced at midpoint V Mid    24 , and V Bridge  due to this relationship has a positive slope with respect to applied magnetic field. 
         [0048]    Push-pull half-bridge output voltage at low temperatures V Bridge  is indicated by the solid line curve  21 , from curve  21  we can see output  20 , the output voltage V B ridge has the minimum V Min  LT  23  and it gradually increase to the maximum V Max  LT  25 . First push-pull half-bridge magnetoresistive element  11  and the second magnetoresistive element  12  having a negative temperature coefficient of resistance (TCR: Temperature Coefficient of Resistance) and the corresponding negative temperature coefficient resister Sensitivity (TCRS: Temperature Coefficient of Resistance Sensitivity). When using a push-pull bridge structure, the corresponding temperature coefficient voltage sensitivity (TCV) is −1000 ppm/° C. This means that over the 100 C temperature difference, the VBridge would change −10% for a fixed V bias  and Applied Magnetic Field  7 . The high temperature curve for V Bridge  is plotted as dashed curve  22 , and Curve  22  goes from a minimum value of V Min  HT,  26  to a maximum value of V Max  HT,  27 . At half of V bias  is the midpoint of the curve is, V Mid    24 . A typical value for V bias  is 1 Volt, so V Mid  is 0.5 V. 
         [0049]    The output of the comparator circuit described below depends on two voltage input signals at its input, which is a voltage signal in  FIG. 4  push-pull half-bridge  87  provides an output voltage V Bridge , another voltage signal is provided by the internal voltage reference circuit, reference voltage V Ref . The value of V Ref  is controlled by Digital Control circuitry described later. The value of V Ref  is controlled by Digital Control circuitry described later. One possible value for V Ref  is shown in  FIG. 4  as  29 , Voltage Operate Point South (V OP S), another possible value for V Ref  is  28 , shown in  FIG. 4 , Voltage Operate Point North (V OP N). The low temperature curve for V Bridge    21 , crosses the voltage level V OP S  29  at Applied Magnetic Field value H OP S-LT  30 ; it crosses the voltage level V OP N  28  at Applied Magnetic Field value H OP N-LT  31 . The high temperature curve for V Bridge    22 , crosses the voltage level V OP S  29  at Applied Magnetic Field value H OP S-HT  32 ; it crosses the voltage level V OP N  28  at Applied Magnetic Field value H OP N-HT  33 . 
         [0050]    Thus, the circuit switching action of the comparator happens at Applied Magnetic Fields of increasing absolute value in proportion to the operating temperature of the magnetoresistive bridge sensor. This is called “temperature dependence of output” and is usually an undesirable effect for sensing applications. 
         [0051]    A detailed circuit schematic of the temperature compensation and push-pull bridge circuit is shown in  FIG. 5 . The right half of the bridge is formed as a push-pull half bridge magnetoresistive sensor enclosed by the dashed box  87 . This half bridge has two magnetoresistors,  56  and  56 ′ with characteristics that result in output  59 , V Bridge , following the curve  21  in  FIG. 4 . The left half of the bridge is set up as a voltage divider, enclosed by dotted line  86 , made of a series of 10 resistors  131 - 140  and these resistors  131 - 140  values do not change with magnetic field; it is on a circuit chip represented by dashed outline  86 . Internal reference circuit constitutes a half-bridge. Internal reference circuit  86  and push-pull half-bridge  87  form a full bridge. Internal voltage reference circuit  86  includes 7 voltage outputs, and these 7 voltage outputs output 7 different voltage signals, inside the circuit  86 , there are 9 Voltage Outputs available from the left side. Of these, 6 are used as switching thresholds: Voltage Operate Point South (V OP S), Voltage Reset Point South (V RP S), Voltage Standby Threshold South (V ST S), Voltage Standby Threshold North (V ST N), Voltage Reset Point North (V RP N), Voltage Operate Point North (V OP N), and are taken from connection nodes as shown in  FIG. 5 ; Another output is for Voltage Midpoint (V Mid ). The two dashed boxes  86  and  87  have components that may be integrated onto the same silicon chip. Or  87  could be one or more separate chips containing magnetoresistors. Wire bonds and other methods well known in the art are used to make electrical connection from one chip to another when needed. The entire bridge is powered between Ground and V Bias    63 , and V Bias    63  is a fixed voltage controlled by circuitry that is described later in this patent application. 
         [0052]    Unipolar, bipolar and omnipolar are three types of magnetoresistive switches have different behavior and values for V Ref S and magnetic field switching values. Table 1 below summarizes the names and values for thresholds. Note that the values shown are merely a representative example and can be tuned to meet specific requirements of a given application or user. This generality holds true so long as the Applied Field values are within the active, that is non-saturated, range of the magnetoresistive sensing elements  11  and  12 , and the V Ref  are less than  63 , V Bias . Take the Bipolar values for example. H OP S is set to be 59% of Vbias. Suppose V Bias =1.0 Volts, then H OP S is 590 mV. This switching occurs at an applied field value of +30 Oe. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Bipolar, unipolar and omnipolar type magnetoresistive switch sensors with 
               
               
                 V Bias  corresponding reference voltage and magnetic field strength 
               
             
          
           
               
                   
                   
                   
                   
                 Room 
                 Voltage 
                 Magnetic 
               
               
                   
                   
                   
                 Voltage 
                 Temperature 
                 Value 
                 Field 
               
               
                   
                   
                 Variable 
                 Reference 
                 Voltage 
                 (V Bias  = 1 V) 
                 Strength 
               
               
                 Output Type 
                 Threshold Name 
                 Name 
                 Name 
                 (% × V Bias ) 
                 (mV) 
                 (Oe) 
               
               
                   
               
             
          
           
               
                 Bipolar 
                 south magnetic 
                 H OP S 
                 V OP S 
                 59.0 
                 590 
                 +30 
               
               
                   
                 field operate point 
               
               
                 Bipolar 
                 north magnetic 
                 H RP N 
                 V RP N 
                 41.0 
                 410 
                 −30 
               
               
                   
                 field release point 
               
               
                 Unipolar 
                 south magnetic 
                 H OP S 
                 V OP S 
                 59.0 
                 590 
                 +30 
               
               
                   
                 field operate point 
               
               
                 Unipolar 
                 south magnetic 
                 H RP S 
                 V RP S 
                 56.0 
                 560 
                 +20 
               
               
                   
                 field release point 
               
               
                 Omnipolar 
                 south magnetic 
                 H OP S 
                 V OP S 
                 59.0 
                 590 
                 +30 
               
               
                   
                 field operate point 
               
               
                 Omnipolar 
                 south magnetic 
                 H RP S 
                 V RP S 
                 56.0 
                 560 
                 +20 
               
               
                   
                 field release point 
               
               
                 Omnipolar 
                 south standby 
                 H ST S 
                 V ST S 
                 53.6 
                 536 
                 +12 
               
               
                   
                 threshold 
               
               
                   
                 magnetic field 
               
               
                 Omnipolar 
                 north standby 
                 H ST N 
                 V ST N 
                 46.4 
                 464 
                 −12 
               
               
                   
                 threshold 
               
               
                   
                 magnetic field 
               
               
                 Omnipolar 
                 north magnetic 
                 H RP N 
                 V RP N 
                 44.0 
                 440 
                 −20 
               
               
                   
                 field release point 
               
               
                 Omnipolar 
                 north magnetic 
                 H OP N 
                 V OP N 
                 41.0 
                 410 
                 −30 
               
               
                   
                 field operate point 
               
               
                   
               
             
          
         
       
     
         [0053]    Through a simple linear relationship, in  FIG. 4  it can be seen the output voltage V OUT  and magnetic field have a linear relationship curve  21  from the magnetic field in units of Oe can be converted into a percentage of V Bias , as shown in Table 1, column 5; Table 1 column 6 “voltage value (mV)(V Bias =1.0V)” shows the condition V Bias =1 V under this circumstance, the voltage value changes with differing reference voltage output. It is important to notice that V Bias  is not necessarily fixed at 1V, that is just a typical value. Table 1 column 7 is a compilation of necessary switch sensor magnetic field value, with typical units of Oe. 
         [0054]      FIG. 6  is a circuit block diagram of the analog filter and comparator stage for the Bipolar and Unipolar type magnetoresistive switch. The comparator  61  is a high-gain amplifier. When comparator  61  output, V A    67 , is H or 1, the output voltage V A    67 , is in the high state. When comparator  61  output, V A    67 , is L or 0, the output voltage V A    67 , is in the low state. The High state occurs when the voltage present at the positive input  65  is greater than the voltage present at negative input  66 . The high voltage value for V A  is less than but nearly equal to V CC    81 , the low voltage is greater than but nearly equal to ground  64  or 0 volts. The comparator is connected to power supply V CC  through its positive power input  62 . 
         [0055]    The voltage inputs are  71 ′ V Ref  that comes from the voltage reference portion  86  of  FIGS. 5, and 71  V Bridge  from the right side magnetoresistive chip  87 . V Ref  can be either V OP  or V RP  depending on the state of a multiplexer MUX 1   88  shown in  FIG. 7 . Each input passes through a standard RC low pass filter  72  and  72 ′. Each filter has a resistance  73 ,  73 ′, and a capacitor  74 ,  74 ′. The 3 dB roll off frequency is calculated by the usual 
         [0000]      Frequency  F= 1/[(2π)*( RC )]  equation (1)
 
         [0056]    where R and C are resistance and capacitance in Ohms and Farads, respectively. A typical cutoff frequency for this product is 100 kHz. This filter serves a few purposes: 1) it eliminates high frequency noise signals, 2) it reduces switching “bounce” where the high gain comparator bounces back and forth between its high and low output values when V Ref  is equal to or near V Bridge . 
         [0057]    The comparator  61  and filter  72 ,  72 ′ (together labeled Low Pass Filter  91 ) are part of a larger circuit whose block diagram is in  FIG. 7 . Power is connected between VCC  81  and Ground  64 . Voltage regulator  83  provides a steady analog voltage bias,  63  V Bias . Multiplexer  88  MUX 1  is a switch that connects one of the reference voltage outputs from  86  Internal Reference circuit to  71 ′ input to the Low Pass Filter  91 . The bridge output V Bridge  is connected to input  71  of Low Pass Filter  91 . Low-pass filter circuit  91  output terminal and the input of the comparator  61  are electrically connected. The comparator  61  utput V A  is connected to the input of Digital Control Circuit  92 . There are two outputs from Digital Control Circuit  92 : one is MUX 1 ,  88 , the other is a connection to Latch and Driver circuit  93 . This, in turn, drives the output stage. The output stage has a dual transistor  94  and  95  which is capable of switching rapidly without large power use. The circuit output is at  85 , V OUT . 
         [0058]    A digital control system  92  and a set of “logical operating modes” are two parts of the present invention. A “logical operating mode” has the following properties: 
         [0059]    1) an abstract logical or binary representation in “1”s and “0”s, 
         [0060]    2) an electronic circuit representation of the same mode, such as in digital memory, 
         [0061]    3) a set of “electronic operations” that occur as a result of being in a particular “logical operating mode”. Most interesting digital control systems have more than one “logical operating mode.” When this is the case, additional requirements are 
         [0062]    4) a well defined and finite set of distinct modes, and 
         [0063]    5) a well defined and self consistent set of “trigger conditions” that, when they are realized, cause the logical operating mode to switch from one to another well defined mode. 
         [0064]    Digital Control Circuit  92  contains the electronic representation of the binary mode names and the logical programs that carry out required “electronic operations” upon entering a logical mode, and also the programs that carry out switching from one mode to another upon realization of the “trigger conditions”. 
         [0065]      FIG. 8  shows Output Voltage vs. Applied Magnetic Field for Bipolar magnetic switch sensors. The magnetoresistive switch circuit shown in  FIG. 7  can put out two forms of output vs. an applied magnetic field  7 . The first form, Bipolar, is shown in  FIG. 8 . The output switches between two voltage values, V HIGH    103 , and V LOW    104 . The switching transitions  101  and  102  happen at magnetic field values H OP S and H RP N. For this behavior, the digital control circuit  92  must use MUX 1   88  to select V OP S and V OP N as the two reference voltages passed along to the comparator. A logic truth table is shown below in the top half of Table 2 for the Bipolar Switch operation. 
         [0066]      FIG. 9  shows Output Voltage vs. Applied Magnetic Field for Unipolar switch. The second possible form of output from the magnetoresistive switch circuit in  FIG. 7  is the Unipolar form, shown in  FIG. 9 . The output switches between two voltage values,  103  V High , and  104  V Low . The switching transitions  106  and  107  happen at magnetic field values H OP S and H RP S. For this behavior, the digital control circuit  92  must use MUX 1   88  to select V OP S and V OP S as the two reference voltages passed along to the comparator  61 . A logic truth table is shown below in the bottom half of Table 2 for the Unipolar Switch operation. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 bipolar and unipolar magnetoresistive sensor ASIC digital circuit  
               
               
                 switch truth table. 
               
             
          
           
               
                   
                 V Bridge   
                 VA 
                 (Mux1) 
                 V OUT   
               
               
                   
                 Bridge 
                 trigger 
                 V reference 
                 output 
               
               
                 Symbol 
                 Voltage 
                 condition 
                 select 
                 voltage 
               
               
                   
               
             
          
           
               
                 Bipolar Switch 
               
             
          
           
               
                 Power on 
                 =1/2 V bias   
                 1 
                 V OP   
                 1 
               
               
                 default 
                   
                   
                   
                   
               
               
                 H OP S 
                 &gt;V OP S 
                 1→0 
                 →V RP S 
                 →0 
               
               
                 H RP N 
                 &lt;V RP N 
                 1 
                 →V OP N 
                 →1 
               
             
          
           
               
                 Unipolar Switch 
               
             
          
           
               
                 Power on 
                 =1/2 V bias   
                 1 
                 V OP   
                 1 
               
               
                 default 
                   
                   
                   
                   
               
               
                 H OP S 
                 &gt;V OP S 
                 1→0 
                 →V RP S 
                 →0 
               
               
                 H RP S 
                 &lt;V RP S 
                 1 
                 →V OP S 
                 →1 
               
               
                   
               
               
                 When the behavior of Voltage A (VA) matches the trigger condition, MUX1 maintains, or switches to, the indicated reference voltage (V REF .) 
               
               
                 The character “→” indicates a change in value. 
               
             
          
         
       
     
         [0067]    The “logical operating modes” in the circuit examples so far are limited to two modes, “0” and “1” or “high” and “low”. The “electronic operations” that occur upon entering these modes are: Digital Control Circuit  92  uses MUX 1   88  to switch to a new Reference Voltage. The “trigger conditions” are defined in terms of observing the output of comparator  61  from High to Low, or Low to High. These trigger conditions are directly related to the externally applied magnetic field because the MR Sensor  87  V Bridge  is one of the comparator  61  input signals. These are called “applied magnetic field trigger conditions”. 
         [0068]      FIG. 10  is a graph showing the relationship between the output voltage and the applied magnetic field push-pull between the resistor bridge. The output V Bridge    59  from the tunneling magnetoresistive bridge sensor  87  is plotted as curve  21 . This is the same curve as in  FIG. 4 , but only one temperature is shown, and more switching field thresholds are shown. Curve  21  is antisymmetrical about the H=0 axis. The voltage midpoint, V Mid    24 , is approximately half way between V Max    25  and V Min    23 . Field values at which comparators switch are indicated as H Standby Threshold South H ST S  41 , H Reset Point South H RP S  43 , H Operate South H OP S  45 , H Standby Threshold North H ST N  42 , H Reset Point North H RP N  44 , H Operate Point North H OP N  46 . 
         [0069]      FIG. 11  shows the V OUT  vs. Output Voltage vs. Applied Magnetic Field  7  for of the Omnipolar magnetoresistive switch. This circuit uses the same analog bridge and reference voltage stages as the Bipolar and Unipolar. However, a different comparator and logic circuits are needed, they are shown below in  FIGS. 12 and 13 . The output switches between two voltage values,  103  V High , and  104  V Low . Switching transitions  47  and  48  happen at magnetic field values H OP S and H RP S. Switching transitions  47 ′ and  48 ′ happen at magnetic field values H OP N and H RP N. For this behavior, the digital control circuit  192  must use MUX 1   188  to select V ST S, V RP S, or V OP S as the reference voltages passed along to the comparators; and MUX 2   189  to select V ST N, V RP N, or V OP N as the reference voltages passed along to comparator  61 . 
         [0070]    The total magnetic field range is divided into six logical operating modes: Operate North, Reset North, Standby North, Standby South, Operate South, and Reset South. The Standby modes occur at fields between H ST N and H ST S. These standby modes have inventive properties. Specifically, they have new “electronic operations” that save power by actuating switches SW 1   170  and SW 2   270 . This is in addition to causing MUX 1   188 , and MUX 2   189 , to select new Reference Voltages. The digital labels [(111), (110), (101), (001), (010), (011)] for distinct logical operating modes for the 6 field regions are shown at the bottom of  FIG. 11  in their corresponding field range. A logic truth table is shown below Table 4 for the Omnipolar Switch operation. The “electronic operations” of MUX  1 , MUX  2 , SW  1 , SW  2 ; and, “trigger conditions” needed to switch from one mode to another, are shown in the table of logic modes in Table 5. A table of current consumption vs. operation mode is in Table 4. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Omnipolar switch sensor truth table. 
               
             
          
           
               
                   
                 Trigger 
                   
                   
                   
                   
                   
                   
               
               
                   
                 Condition 
                 VS 
                 VN 
                   
                   
                   
                 Operation 
               
             
          
           
               
                 Symbol 
                 V Bridge   
                 V A   
                 V B   
                 (Mux1) 
                 (Mux2) 
                 SW1 
                 SW2 
                 V OUT   
                 Mode 
               
               
                   
               
               
                 Standby 
                 =½vbias 
                 0 
                 0 
                 001 
                 101 
                 0 
                 0 
                 1 
                 Standby 
               
               
                 (power on 
               
               
                 default) 
               
               
                 S Out of 
                 &gt;V ST S 
                 0→1 
                 0 
                 →011 
                 →001 
                 →1 
                 0 
                 1 
                 South pole 
               
               
                 standby 
                   
                   
                   
                   
                   
                   
                   
                   
                 switch 
               
               
                 BOPS 
                 &gt;B OP S 
                 1 
                 0 
                 →010 
                 001 
                 1 
                 0 
                 →0 
                 mode 
               
               
                 BRPS 
                 &lt;B RP S 
                 1→0 
                 0 
                 →011 
                 001 
                 1 
                 0 
                 →1 
               
               
                 Re-standby 
                 &lt;V AT S 
                 0 
                 0 
                 →001 
                 →101 
                 →0 
                 0 
                 1 
                 Standby 
               
               
                 Standby 
                 V ST N 
                 0 
                 0 
                 001 
                 101 
                 0 
                 0 
                 1 
               
               
                   
                 &lt;V Bridge   
               
               
                   
                 &lt;V ST S 
               
               
                 N Out of 
                 &lt;V ST N 
                 0 
                 0→1 
                 →101 
                 →111 
                 0 
                 →1 
                 1 
                 North pole 
               
               
                 standby 
                   
                   
                   
                   
                   
                   
                   
                   
                 Switch 
               
               
                 BOPN 
                 &lt;B OP N 
                 0 
                 1 
                 101 
                 →110 
                 0 
                 1 
                 →0 
                 mode 
               
               
                 BRPN 
                 &gt;B RP N 
                 0 
                 1→0 
                 101 
                 →111 
                 0 
                 1 
                 →1 
               
               
                 Re-standby 
                 &gt;V ST N 
                 0 
                 0 
                 →001 
                 →101 
                 0 
                 →0 
                 1 
                 Standby 
               
               
                   
               
             
          
         
       
     
         [0071]    Table 3, when the voltage A and B (V A  and V B ) in columns 3 and 4 match the trigger conditions, MUX 1  and MUX 2  maintain or switch to the state shown in columns 5 and 6. In addition, SW 1  and SW 2  maintain or switch to the conditions shown in columns 7 and 8. The “→” character represents a change of values. In the SW 1  and SW 2  columns, “0” and “1” denote the “open switch” and “closed switch” states. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 MUX logic symbols related to reference voltage values for  
               
               
                 Omnipolar Switch. 
               
             
          
           
               
                   
                 Mux1 
                 V Ref S 
                 Mux2 
                 V Ref N 
               
               
                   
                   
               
               
                   
                 001 
                 V ST S 
                 000 
                 — 
               
               
                   
                 010 
                 V RP S 
                 101 
                 V ST N 
               
               
                   
                 011 
                 V OP S 
                 110 
                 V RP N 
               
               
                   
                 100 
                 — 
                 111 
                 V OP N 
               
               
                   
                   
               
             
          
         
       
     
         [0072]    Do not need to care about states 101, 000 and 100, in the two stage floating output design. 
         [0073]    A circuit diagram of the Analog Filter and Comparator for the Omnipolar magnetoresistive switch is shown in  FIG. 12 . It performs similar functions to the comparator circuit in  FIG. 6 . But an additional comparator is needed for Omnipolar operation, and power saving features are added. 
         [0074]    The left side of  FIG. 12  shows an analog input filter. South pole reference voltage V REF    171  is connected to the low-pass filter  172 , a low-pass filter  172  includes a resistor  173  and a capacitor  174 . The output of Low pass filter  172  is electrically connected to negative input  166  of the comparator  161 . V Bridge    171 ′ is connected to the low-pass filter  172 ′, a low-pass filter  172  includes a resistor  173 ′ and the capacitor  174 ′. Low-pass filter  172 ′ is electrically connected to the negative input  266  of the second comparator  261  and to the first comparator  161  positive input  165 . V Bridge  opposite polarity and electrical connection between the comparator, make V OUT  versus applied magnetic field and having anti-symmetry. North pole reference voltage V REF    271  is electrically connected to a low pass filter  272 , low pass filter  272  includes a resistor  273  and a capacitor  274 , a filter  272  is electrically connected to the output of the second comparator  261  positive input  265 . 
         [0075]    Two comparator implementations of the present embodiment are given, a first Comparator  161 , and a second comparator  261 . The first comparator  161  has positive input  165  and negative input  166 . It has output V A  at  167 . It draws power between V Bias    163  and Ground  64 . Positive power supply  162  carries electrical current from current supplies  168  and  169 , which supply 0.05 μA and 2.0 μA, respectively. The first switch SW 1   170  determines whether the current supply  169  is connected or not. Current supply  168  is always connected. The second comparator  261  has positive input  265  and negative input  266 . It has output V B  at  267 . It draws power between V Bias    263  and Ground  64 . Positive power supply  262  carries electrical current from current supplies  268  and  269 , which supply 0.05 μA and 2.0 μA, respectively. The second switch SW 2   270  determines whether the current supply  269  is connected or not. Current supply  268  is always connected. 
         [0076]    The current supply first switch SW 1  and second switch SW 2  provide a way to reduce the amount of electrical power consumed during operation. Table 5 below shows totals of current consumed in various modes. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Current consumption in the modes of Omnipolar type  
               
               
                 magnetoresistive switch. 
               
             
          
           
               
                   
                   
                   
                 Total I in 
               
               
                 Magnetic field 
                 Switch 1 
                 Switch 2 
                 comparator 
               
               
                 (Oersted) 
                 (SW1) 
                 (SW2) 
                 (uA) 
               
               
                   
               
             
          
           
               
                 Magnetic field South 
               
             
          
           
               
                 H &lt; 12 
                 open 
                 open 
                  0.1 uA 
               
               
                 H &gt; 12 
                 connect 
                 open 
                 2.05 uA 
               
               
                 H &lt; 30 (B OP S) 
                   
                   
                   
               
               
                 H falling to 20 (B RP S) 
                   
                   
                   
               
             
          
           
               
                 Magnetic field North 
               
             
          
           
               
                 H &lt; 12 
                 open 
                 open 
                  0.1 uA 
               
               
                 H &gt; 12 
                 open 
                 connect 
                 2.05 uA 
               
               
                 H &lt; 30 (B OP N) 
                   
                   
                   
               
               
                 H falling to 20 (B + N) 
               
               
                   
               
             
          
         
       
     
         [0077]      FIG. 13  shows a circuit diagram of a preferred implementation of an omnipolar low-power magnetoresistive switch sensor of the present invention. It draws electrical power between Ground  64  and V CC    81 . Regulator  383  provides a stable and lower voltage power supply V Bias    163  to internal voltage reference circuit  86  and Magnetoresistive Bridge  87 . Multiplexer MUX 1   188  is a switch that connects one of the reference voltage outputs from the South end of Internal Reference circuit  87  to the V Ref  South  71 ′ input to the Low Pass Filter  190 . The bridge output V Bridge  is connected to input  171 ′ of Low Pass Filter  190 . Multiplexer MUX 2   189  is a switch that connects one of the reference voltage outputs from the North end  87  of Internal Reference circuit to the V REF  South  271  input to the Low Pass Filter  190 . 
         [0078]    The two comparator outputs V A  and V B  are connected to the input of Digital Control Circuit  192 . There are five outputs from Digital Control Circuit  192  (MUX 1   188 ; MUX 2   189 ; SW 1   170 ; SW 2   270 ) the Latch, and 5 output driver circuit  193 . This, in turn, drives the output stage. The output stage has a dual transistors  394 ,  395 , which are capable of switching rapidly without large power use. The circuit output is at  385 , V Out . The response of digital control circuit  192  to signals V A  and V B  at its input are detailed in Tables 4 and 5, and in the timing diagram in  FIG. 14 . A signal vs. time diagram for the Omnipolar Magnetoresistive Switch is shown in  FIG. 14 . The time axis is unitless and not precisely linear. It is scaled in a way to aid explanation, not to provide quantitative detail. Times are labeled T 0 , T 1 , . . . T 10 . There are two sets of analog scales. The upper analog scale has analog signals coming from the V Bridge , and V Ref . The lower analog scale shows digital values in the vertical direction. 
         [0079]    The output from the magnetoresistive bridge  87 , V Bridge  is plotted in the dashed curve  201 . It represents a signal that would be present as a magnet moves by the sensor and giving a quasi-sinusoidal Applied Magnetic Field signal to the magnetoresistive bridge. V Bridge  is directly proportional to the Applied magnetic Field, so these two curves are plotted on the same set of vertical axes as  201 . The left axis shows 7 Applied Magnetic Field values. The right vertical axis shows reference voltage values both as threshold labels and as percentage of V Bias . The upper half of the plot has positive (South) values for magnetic field, and positive values for V Bridge . The lower half of the plot has negative (North) values for magnetic field, and negative values for V Bridge . 
         [0080]    V REF  South is plotted as solid curve  202 . It has three steady state values V ST S, V OP S, and V RP S. V REF  North is plotted as solid curve  203 , which has three steady state levels V ST N , V OP N, and V RP N. There is a measurable time for curves  202  and  203  to switch from one state to another. These two signals are taken from the Voltage reference circuit  86 . MUX  1 , whose digital state vs. time is plotted in solid curve  210 , selects one of the three South V REF  values: V ST S , V OP S, or V RP S. MUX  2 , whose digital state vs. time is plotted in solid curve  211 , selects one of the three North V REF  values: V ST N , V OP N, or V RP N. These digital states are not voltage levels, but rather a representation of which V REF  to which they are to be connected. The output connections of the first comparator and the second comparator carry voltage signals V A  and V B , respectively. These two digital levels are plotted vs. time as solid curves  204  and  205  that switch between digital levels near Ground and V BIAS . The external output connection  385  of the circuit carries voltage level V OUT  whose signal vs. time is plotted as solid curve  206 . The V OUT  switches between levels near Ground and V CC . There are three mode logic lines whose output vs. time are plotted as solid curves: Standby  207 , South Operate  208 , and North Operate  209 . The states of Switch  1   170  (SW  1 ) and Switch  2   270  (SW  2 ) are plotted vs. time as solid curves  212  and  213 . A high level on these curves means the switch is closed and extra current is flowing to the power terminal of that comparator. The total Quiescent Current used by the circuit is plotted vs. time as solid curve  214 . This curve goes between values of 0.1 μA and 2 μA. When the circuit is in one of the active North or South switching modes, one but not both of SW  1  or SW  2  is open. When in “Standby” mode, both SW  1  and SW  2  are open. At no time are both SW  1  and SW  2  closed simultaneously. 
         [0081]    Now, a description of the entire circuit action vs. time using the example signal provided as V Bridge  curve  201 . The logic design was described above in Tables 3 and 4. At T 0 , V Bridge =0 Volts; the mode is Standby (001), V OUT =High. V Bridge  increases to and at T 1  crosses V ST S which is the current voltage threshold value on the first Comparator. This causes V A  to switch to 1 after a time dT=T 2 −T 1  has passed. dT is relatively long, say 1 millisecond, because the power to the first Comparator is low, which causes signal delays. Subsequent switching events happen within a time t, which is set by the logic circuit clock frequency, f. At time T 2 +t, the following occur: logic Standby line  207  goes 0 to 1, South Operate mode  208  goes 0 to 1, North Operate Mode  209  is 0, MUX  1   210  selects V OP S, SW 1   212  closes. The circuit is in South Operate Mode (011). 
         [0082]    V Bridge  continues to increase and at time T 3  crosses V OP S, the present voltage threshold value on the first comparator indicated by curve  202 . This causes V A  to switch to 0. At the next clock cycle within time □, at time T 3 +□, the following occur: output  206  goes Low, Standby line  207  is 0, South Operate mode  208  goes from 1 to 0, North Operate Mode is 0, MUX  1   210  selects V RP S causing curve  202  to shift towards V RP S. The circuit is in South Operate Mode (010). 
         [0083]    V Bridge  at some time begins to decrease and at time T 4  crosses curve  202  at value V RP S, the present voltage threshold value on Comparator  1 . This causes V A  to switch 0 to 1. At the next clock cycle within time t, at time T 4 +t, the following occur:  206  Output goes Low to High, logic (Standby line  207  is 0, South Operate mode  208  is 0, North Operate Mode is 0), MUX  1   210  selects V ST S causing curve  202  to shift towards V ST S. The circuit is in South Operate Mode (011). 
         [0084]    V Bridge  at some time begins to decrease and at time T 5  crosses curve  202  at value V RP S, the present voltage threshold value on the first comparator. This causes V A  to switch 0 to 1. At the next clock cycle within time t, at time T 5 +t, the following occur:  206  Output goes Low to High, Standby line  207  goes from 0 to 1, South Operate mode  208  is 0, North Operate Mode is 0, MUX  1   212  closes. The circuit is in Standy Mode (011). 
         [0085]    V Bridge  continues to decrease and at time T 6  crosses curve  203  at value V ST N, the present voltage threshold value on the second Comparator. This causes second comparator output V B    205  to switch from 0 to 1 at time T 7 . This comparator action takes relatively long dt=T 7 −T 6 , say 1 millisecond, because the power to the second Comparator is low At T 7 +t, the following occur: Output  206  is High, Standby line  207  goes from 1 to 0, South Operate mode  208  is 0, North Operate Mode  209  goes from 0 to 1. MUX  2   211  switches to V OP N causing V Ref  North curve  203  to shift towards V OP N. SW  2   213  closes, providing more power current to the second comparator. The circuit is in North Operate Mode (111). 
         [0086]    V Bridge  continues to decrease and at time T 8  and crosses curve  203  at value V OP N, the present voltage threshold value on the second comparator. This causes the second comparator output V B    205  to switch from 1 to 0. At T 7 +t, the following occur: output  206  switches from High to Low, Standby line  207  is 0, South Operate mode  208  is 0, North Operate Mode  209  goes from 1 to 0. MUX  2   211  switches to V RP N causing V Ref  North curve  203  to shift towards V RP N. The circuit is in North Operate Mode (110). 
         [0087]    V Bridge  begins to increase and at time T 9  crosses curve  203  at value V RP N, the present voltage threshold value on the second comparator. This causes the second comparator output V B    205  to switch from 0 to 1. At T 9 +t, the following occur: output  206  switches Low to High, logic lines Standby line  207  switches from 0 to 1, South Operate mode  208  is 0, North Operate Mode  209  is 0). MUX  2   21  switches to V ST N causing V Ref  North curve  203  to shift towards V ST N. The circuit is in North Operate Mode (111). 
         [0088]    V Bridge  continues to increase and at time T 10  crosses curve  203  at value V ST N, the present voltage threshold value on the second comparator. At the next clock cycle within time t, at time T 10 +t, the following occur: output  206  is High, logic levels Standby line  207  goes from 0 to 1, South Operate mode  208  is 0, North Operate Mode is 0. SW  2   203  closes. The circuit is in Standby Mode (001). 
         [0089]    Compared with Chinese patent application number 201110125153.5, this low power magnetoresistive switch sensor has the following advantages:
       1) Provides a filtering means for reducing the noise of a switch;   2) The method described for reducing power, provides only a slight decrease in operating frequency in the circuit.       
 
         [0092]    It should be understood that the above detailed description of the technical solutions used for the present invention are preferred embodiments that are illustrative and not restrictive. One of ordinary skill in the art upon reading the present specification can based on the technical solutions described in the embodiments modify or replace some technical features with equivalent replacements; and such modifications or replacements do not make the revised technical solutions of the various embodiments of the present invention depart from the spirit and scope of the present invention.