# Patent

## Title
Magnetic field sensor and electronic circuit that pass amplifier current through a magnetoresistance element

## Abstract

Electronic circuits used in magnetic field sensors use transistors for passing a current through the transistors and also through a magnetoresistance element.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
FIELD OF THE INVENTION
This invention relates generally to magnetic field sensors and, more particularly, to a magnetic field sensor, or an electronic circuit used therein, that pass an amplifier supply current through a magnetic field sensing element.
BACKGROUND
Magnetoresistance elements are known. A magnetoresistance element changes resistance in response to a magnetic field. Magnetic field sensors having electronic circuits coupled to the magnetoresistance element can inject a current into the magnetoresistance element and use a voltage resulting across the magnetoresistance element as being representative of a sensed magnetic field.
Conventionally, the current used to drive the magnetoresistance element uses power.
It would be desirable to provide a magnetic field sensor and associated electronic circuit for which a magnetoresistance element requires no extra power beyond that which is otherwise used by the magnetic field sensor.
SUMMARY
The present invention provides a magnetic field sensor and associated electronic circuit for which a magnetoresistance element requires no extra power beyond that which is otherwise used by the magnetic field sensor.
In accordance with an example useful for understanding an aspect of the present invention, an electronic circuit includes a first magnetoresistance element having first and second terminals. The electronic circuit also includes a first transistor having a control node, a first current passing node, and a second current passing node. The electronic circuit also includes a first voltage source having first and second nodes between which a first voltage is generated. The first terminal of the first magnetoresistance element is coupled to the first current passing node of the first transistor. The first node of the first voltage source is coupled to the control node of the first transistor and the second node of the first voltage source is coupled to the second terminal of the first magnetoresistance element. The electronic circuit is operable to generate a first current signal at the second current passing node of the first transistor related to a resistance value of the first magnetoresistance element.
In accordance with another example useful for understanding an aspect of the present invention, a magnetic field sensor includes a substrate and an electronic circuit disposed upon the substrate. The electronic circuit includes a first magnetoresistance element having first and second terminals. The electronic circuit further includes a first transistor having a control node, a first current passing node, and a second current passing node. The electronic circuit further includes a first voltage source having first and second nodes between which a first voltage is generated, wherein the first terminal of the first magnetoresistance element is coupled to the first current passing node of the first transistor, and wherein the first node of the first voltage source is coupled to the control node of the first transistor and the second node of the first voltage source is coupled to the second terminal of the first magnetoresistance element. The electronic circuit is operable to generate a first current signal at the second current passing node of the first transistor related to a resistance value of the first magnetoresistance element. The electronic circuit further includes a second magnetoresistance element having first and second terminals and a second transistor having a control node, a first current passing node, and a second current passing node. The electronic circuit further includes a second voltage source having first and second nodes between which a second voltage is generated. The electronic circuit further includes a load coupled to the second current passing node of the first transistor, wherein the second current passing node of the first transistor is coupled to the second current passing node of the second transistor. The first terminal of the second magnetoresistance element is coupled to the first current passing node of the second transistor. The first node of the second voltage source is coupled to the control node of the second transistor and the second node of the second voltage source is coupled to the second terminal of the second magnetoresistance element. The electronic circuit is operable to generate a second current signal at the second current passing node of the second transistor related to a resistance value of the second magnetoresistance element, wherein a current passing through the load is equal to a difference between the first current signal and the second current signal.
In accordance with another example useful for understanding an aspect of the present invention, a magnetic field sensor includes a substrate and an electronic circuit disposed upon the substrate. The electronic circuit includes a first magnetoresistance element having first and second terminals and a first transistor having a control node, and first current passing node, and a second current passing node. The electronic circuit further includes a first voltage source having first and second nodes between which a first voltage is generated. The first terminal of the first magnetoresistance element is coupled to the first current passing node of the first transistor. The first node of the first voltage source is coupled to the control node of the first transistor and the second node of the first voltage source is coupled to the second terminal of the first magnetoresistance element. The electronic circuit is operable to generate a first current signal at the second current passing node of the first transistor related to a resistance value of the first magnetoresistance element. The electronic circuit further includes a second magnetoresistance element having first and second terminals and a second transistor having a control node, a first current passing node, and a second current passing node. The electronic circuit further includes a second voltage source having first and second nodes between which a second voltage is generated. The electronic circuit further includes a load coupled to the second current passing node of the first transistor. The second current passing node of the first transistor is coupled to the second current passing node of the second transistor. The first terminal of the second magnetoresistance element is coupled to the first current passing node of the second transistor. The first node of the second voltage source is coupled to the control node of the second transistor and the second node of the second voltage source is coupled to the second terminal of the second magnetoresistance element. The electronic circuit is operable to generate a second current signal at the second current passing node of the second transistor related to a resistance value of the second magnetoresistance element. A current passing through the load is equal to a difference between the first current signal and the second current signal. The electronic circuit further includes a third magnetoresistance element having first and second terminals and a third transistor having a control node, and first current passing node, and a second current passing node. The electronic circuit further includes a third voltage source having first and second nodes between which a third voltage is generated. The first terminal of the third magnetoresistance element is coupled to the first current passing node of the third transistor. The first node of the third voltage source is coupled to the control node of the third transistor and the second node of the third voltage source is coupled to the second terminal of the third magnetoresistance element. The electronic circuit is operable to generate a third current signal at the second current passing node of the third transistor related to a resistance value of the third magnetoresistance element. The electronic circuit further includes a fourth magnetoresistance element having first and second terminals and a fourth transistor having a control node, a first current passing node, and a second current passing node. The electronic circuit further includes a fourth voltage source having first and second nodes between which a fourth voltage is generated. The electronic circuit further includes a second load coupled to the second current passing node of the third transistor. The second current passing node of the third transistor is coupled to the second current passing node of the fourth transistor. The first terminal of the fourth magnetoresistance element is coupled to the first current passing node of the fourth transistor. The first node of the fourth voltage source is coupled to the control node of the fourth transistor and the second node of the fourth voltage source is coupled to the second terminal of the fourth magnetoresistance element. The electronic circuit is operable to generate a fourth current signal at the second current passing node of the fourth transistor related to a resistance value of the fourth magnetoresistance element, wherein a current passing through the second load is equal to a difference between the third current signal and the fourth current signal.



BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a schematic diagram of an example of an electronic circuit as may be used in a magnetic field sensor, and which has or is otherwise coupled to one magnetoresistance element;
FIG. 2 is a schematic diagram of another example of an electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to one magnetoresistance element;
FIG. 3 is a schematic diagram of another example of an electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to one magnetoresistance element;
FIG. 4 is a schematic diagram of another example of an electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to one magnetoresistance element;
FIG. 5 is a schematic diagram of another example of an electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to one magnetoresistance element;
FIG. 6 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to one magnetoresistance element;
FIG. 7 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to two magnetoresistance elements;
FIG. 8 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to two magnetoresistance elements;
FIG. 9 is a block diagram of a magnetic field sensor having a substrate with two magnetoresistance elements disposed thereon, the substrate disposed proximate to a ferromagnetic target object having ferromagnetic target object features;
FIG. 10 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to four magnetoresistance elements;
FIG. 11 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to four magnetoresistance elements;
FIG. 12 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to four magnetoresistance elements;
FIG. 13 is a block diagram of a magnetic field sensor having a substrate with four magnetoresistance elements disposed thereon, the substrate disposed proximate to a ferromagnetic target object having ferromagnetic target object features;
FIG. 14 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to eight magnetoresistance elements;
FIG. 15 is a block diagram of a magnetic field sensor having a substrate with eight magnetoresistance elements disposed thereon, the substrate disposed proximate to a ferromagnetic target object having ferromagnetic target object features;
FIG. 16 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to four magnetoresistance elements; and
FIG. 17 is a schematic diagram of an example of another electronic circuit as may be used in another magnetic field sensor, and which has or is otherwise coupled to four magnetoresistance elements.



DETAILED DESCRIPTION
As used herein, the term “magnetic field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. The magnetic field sensing element can be, but is not limited to, a Hall effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of Hall effect elements, for example, a planar Hall element, a vertical Hall element, and a Circular Vertical Hall (CVH) element. As is also known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, for example, a spin valve, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ). The magnetic field sensing element may be a single element or, alternatively, may include two or more magnetic field sensing elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge. Depending on the device type and other application requirements, the magnetic field sensing element may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).
As is known, some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, planar Hall elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall elements tend to have axes of sensitivity parallel to a substrate.
As used herein, the term “magnetic field sensor” is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or a ferromagnetic target (e.g., gear teeth) where the magnetic field sensor is used in combination with a back-biased or other magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.
As used herein, the term “processor” is used to describe an electronic circuit that performs a function, an operation, or a sequence of operations. The function, operation, or sequence of operations can be hard coded into the electronic circuit or soft coded by way of instructions held in a memory device. A “processor” can perform the function, operation, or sequence of operations using digital values or using analog signals.
In some embodiments, the “processor” can be embodied in an application specific integrated circuit (ASIC), which can be an analog ASIC or a digital ASIC. In some embodiments, the “processor” can be embodied in a microprocessor with associated program memory. In some embodiments, the “processor” can be embodied in a discrete electronic circuit, which can be an analog or digital.
As used herein, the term “module” is used to describe a “processor.”
A processor can contain internal processors or internal modules that perform portions of the function, operation, or sequence of operations of the processor. Similarly, a module can contain internal processors or internal modules that perform portions of the function, operation, or sequence of operations of the module.
As used herein, the term “predetermined,” when referring to a value or signal, is used to refer to a value or signal that is set, or fixed, in the factory at the time of manufacture, or by external means, e.g., programming, thereafter. As used herein, the term “determined,” when referring to a value or signal, is used to refer to a value or signal that is identified by a circuit during operation, after manufacture.
As used herein, the term “active electronic component” is used to describe and electronic component that has at least one p-n junction. A transistor, a diode, and a logic gate are examples of active electronic components. In contrast, as used herein, the term “passive electronic component” as used to describe an electronic component that does not have at least one p-n junction. A capacitor and a resistor are examples of passive electronic components.
While electronic circuit shown in figures herein may be shown in the form of analog blocks or digital blocks, it will be understood that the analog blocks can be replaced by digital blocks that perform the same or similar functions and the digital blocks can be replaced by analog blocks that perform the same or similar functions.
Both bipolar junction transistors (BJTs) (or more simply, bipolar transistors) and field effect transistors (FETs) are used in examples herein. It should be understood that, for a bipolar transistor, most of the current flowing through the bipolar transistor flows between a collector terminal and an emitter terminal. Similarly, it should be understood that, for a field effect transistor, most of the current flowing through the field effect transistor flows between a drain terminal and a source terminal. Therefore, for bipolar transistors, the collector terminal and the emitter terminal are both sometimes referred to herein as “current passing terminals.” Similarly, for field effect transistors, the drain terminal and the source terminal are also both sometimes referred to herein as “current passing terminals.”
It should be also understood that the current flowing through a bipolar transistor is controlled by a current at a base terminal. Similarly, it should be understood that the current flowing through a field effect transistor is controlled by a voltage at a gate terminal. Thus, for bipolar transistors, the base terminal is sometimes referred to herein as a “control terminal.” Similarly, for field effect transistors, the gate terminal is sometimes also referred to herein as a “control terminal.”
Both current sources and current sinks are described herein. As used herein, the term “current generator” is used to describe either a current source or a current sink.
Referring to FIG. 1, an example of an electronic circuit 100 can be used in a magnetic field sensor. The electronic circuit 100 can include a fixed resistor 106 having first and second terminals, wherein the first terminal of the resistor 106 is coupled to receive a voltage 102 and the second terminal of the resistor 106 is coupled to an emitter of a PNP bipolar transistor 108.
The electronic circuit 100 can include a voltage source 104 having first and second terminals, wherein the first terminal of the voltage source 104 is coupled to receive the voltage 102 and the second terminal of the voltage source 104 is coupled to a base of the PNP bipolar transistor 108.
The electronic circuit 100 can also include a magnetoresistance element 110 having first and second terminals, wherein the first terminal of the magnetoresistance element 110 is coupled to a collector of the PNP bipolar transistor 108 and the second terminal of the magnetoresistance element 110 is coupled to a voltage reference, for example, a ground voltage.
An output voltage 112 can be generated at the collector of the PNP bipolar transistor 108.
In some embodiments, the electronic circuit 100 can include a comparator 114 having first and second input terminals, wherein a first input terminal of the comparator 114 is coupled to the collector of the PNP bipolar transistor 108 and the second input terminal of the comparator 114 is coupled to receive a threshold voltage 116. The comparator 114 can be configured to generate a comparison signal 118. The comparison signal 118 can have two states.
It will be understood that, for embodiments here and below that use a comparator, the associated electronic circuits form an electronic switch, wherein a state of the comparison signal 118 is determined by a strength of a magnetic field experienced by the magnetoresistance element 110. It should also be understood that embodiments shown below that are not shown to include a comparator can be adapted to use a comparator to provide an electronic switch.
It should be appreciated that the voltage source 104, the resistor 106, and the PNP bipolar transistor 108 form a current source operable to provide a fixed current, I, to the magnetoresistance element 110. Thus, the output voltage 112 is generated according to the following relationships. In this and in all equations that follow in conjunction with other figures below, a base current of bipolar transistors is relatively small and is disregarded.




  
    
      
        
          
            
              Vout
              =
              
              ⁢
              
                I
                ×
                A
              
            
          
        
        
          
            
              =
              
              ⁢
              
                
                  
                    (
                    
                      V
                      -
                      Vbe
                    
                    )
                  
                  /
                  R
                
                ×
                A
              
            
          
        
      
    
    
      
        (
        1
        )
      
    
  




where:

    
    
        V=voltage of voltage source 204
        R=resistance of resistor 106
        A=resistance of the magnetoresistance element 110
        Vbe=base emitter voltage of PNP bipolar transistor 108=approx. 0.7 volts
    
    


In the electronic circuit 100, it should be appreciated that the same current, I. flows through the PNP bipolar transistor 108 and through the magnetoresistance element 110.
Referring now to FIG. 2, another example of an electronic circuit 200 can be used in another magnetic field sensor. The electronic circuit 200 can include a magnetoresistance element 206 having first and second terminals, wherein the first terminal of the magnetoresistance element 206 is coupled to receive a voltage 202 and the second terminal of the magnetoresistance element 206 is coupled to an emitter of a PNP bipolar transistor 208.
The electronic circuit 200 can include a voltage source 204 having first and second terminals, wherein the first terminal of the voltage source 204 is coupled to receive the voltage 202 and the second terminal of the voltage source 104 is coupled to a base of the PNP bipolar transistor 208.
The electronic circuit 200 can include a resistor 210 having first and second terminals, wherein the first terminal of the resistor 210 is coupled to a collector of the PNP bipolar transistor 208 and the second terminal of the resistor 210 is coupled to a voltage reference, for example, a ground voltage.
An output voltage 212 can be generated at the collector of the PNP bipolar transistor 208.
In some embodiments, the electronic circuit 200 can include a comparator 214 having first and second input terminals, wherein a first input terminal of the comparator 214 is coupled to the collector of the PNP bipolar transistor 208 and the second input terminal of the comparator 214 is coupled to receive a threshold voltage 216. The comparator 214 can be configured to generate a comparison signal 218.
It should be appreciated that the voltage source 204, the magnetoresistance element 206, and the PNP bipolar transistor 208 form a variable current source operable to provide a variable current, I, to the resistor 110. The variable current, I, varies in accordance with a variable resistance of the magnetoresistance element 206, which varies in accordance with a sensed magnetic field. Thus, the output voltage 112 is generated according to the following:




  
    
      
        
          
            
              Vout
              =
              
              ⁢
              
                I
                ×
                R
              
            
          
        
        
          
            
              =
              
              ⁢
              
                
                  
                    (
                    
                      V
                      -
                      Vbe
                    
                    )
                  
                  /
                  A
                
                ×
                R
              
            
          
        
      
    
    
      
        (
        2
        )
      
    
  




where:

    
    
        V=voltage of voltage source 204
        R=resistance of resistor 210
        A=resistance of the magnetoresistance element 206
        Vbe=base emitter voltage of PNP bipolar transistor 208=approx. 0.7 volts
    
    


In the electronic circuit 200, it should be appreciated that the same current, I, flows through the PNP bipolar transistor 208 and through the magnetoresistance element 206.
Referring to FIG. 3, another example of an electronic circuit 300 can be used in another magnetic field sensor. The electronic circuit 300 can include a magnetoresistance element 304 having first and second terminals, wherein the first terminal of the magnetoresistance element 304 is coupled to receive a voltage 302 and the second terminal of the magnetoresistance element 304 is coupled to a collector of an NPN bipolar transistor 306.
The electronic circuit 300 can include a resistor 308 having first and second terminals, wherein the first terminal of the resistor 308 is coupled to an emitter of the NPN bipolar transistor 306 and the second terminal of the resistor 308 is coupled to a reference voltage, for example, a ground reference voltage.
The electronic circuit 300 can include a voltage source 310 having first and second terminals, wherein the first terminal of the voltage source 310 is coupled to a base of the NPN bipolar transistor 306 and the second terminal of the voltage source 310 is coupled to the second terminal of the resistor 308.
An output voltage 312 can be generated at the collector of the NPN bipolar transistor 306.
In some embodiments, the electronic circuit 300 can include a comparator 314 having first and second input terminals, wherein a first input terminal of the comparator 314 is coupled to the collector of the NPN bipolar transistor 306 and the second input terminal of the comparator 314 is coupled to receive a threshold voltage 316. The comparator 314 can be configured to generate a comparison signal 318.
It should be appreciated that the voltage source 310, the resistor 308, and the NPN bipolar transistor 306 form a current sink operable to provide a fixed current, I, to the magnetoresistance element 304. Thus, the output voltage 312 is generated according to the following:




  
    
      
        
          
            
              Vout
              =
              
              ⁢
              
                I
                ×
                A
              
            
          
        
        
          
            
              =
              
              ⁢
              
                
                  
                    (
                    
                      V
                      -
                      Vbe
                    
                    )
                  
                  /
                  R
                
                ×
                A
              
            
          
        
      
    
    
      
        (
        3
        )
      
    
  




where:

    
    
        V=voltage of voltage source 310
        R=resistance of resistor 308
        A=resistance of the magnetoresistance element 304
        Vbe=base emitter voltage of NPN bipolar transistor 306=approx. 0.7 volts
    
    


In the electronic circuit 300, it should be appreciated that the same current, I. flows through the NPN bipolar transistor 306 and through the magnetoresistance element 304.
Referring now to FIG. 4, another example of an electronic circuit 400 can be used in another magnetic field sensor. The electronic circuit 400 can include a resistor 404 having first and second terminals, wherein the first terminal of the resistor 404 is coupled to receive a voltage 402 and the second terminal of the resistor 404 is coupled to a collector of an NPN bipolar transistor 406.
The electronic circuit 400 can include a magnetoresistance element 408 having first and second terminals, wherein the first terminal of the magnetoresistance element 408 is coupled to an emitter of the NPN bipolar transistor 406 and the second terminal of the magnetoresistance element 408 is coupled to a reference voltage, for example, a ground reference voltage.
The electronic circuit 400 can include a voltage source 410 having first and second terminals, wherein the first terminal of the voltage source 410 is coupled to a base of the NPN bipolar transistor 408 and the second terminal of the voltage source 410 is coupled to the second terminal of the magnetoresistance element 408
An output voltage 412 can be generated at the collector of the NPN bipolar transistor 406.
In some embodiments, the electronic circuit 400 can include a comparator 414 having first and second input terminals, wherein a first input terminal of the comparator 414 is coupled to the collector of the NPN bipolar transistor 406 and the second input terminal of the comparator 414 is coupled to receive a threshold voltage 416. The comparator 414 can be configured to generate a comparison signal 418.
It should be appreciated that the voltage source 410, the magnetoresistance element 408, and the NPN bipolar transistor 406 form a variable current sink operable to provide a variable current, I, to the resistor 404. The variable current, I, varies in accordance with a variable resistance of the magnetoresistance element 408, which varies in accordance with a sensed magnetic field. Thus, the output voltage 412 is generated according to the following:




  
    
      
        
          
            
              Vout
              =
              
              ⁢
              
                I
                ×
                R
              
            
          
        
        
          
            
              =
              
              ⁢
              
                
                  
                    (
                    
                      V
                      -
                      Vbe
                    
                    )
                  
                  /
                  A
                
                ×
                R
              
            
          
        
      
    
    
      
        (
        4
        )
      
    
  




where:

    
    
        V=voltage of voltage source 410
        R=resistance of resistor 404
        A=resistance of the magnetoresistance element 408
    
    


1Vbe=base emitter voltage of PNP bipolar transistor 406=approx. 0.7 volts
In the electronic circuit 400, it should be appreciated that the same current, I. flows through the NPN bipolar transistor 406 and through the magnetoresistance element 408.
Referring now to FIG. 5, another example of an electronic circuit 500 can be used in another magnetic field sensor. The electronic circuit 500 can include a magnetoresistance element 506 having first and second terminals, wherein the first terminal of the magnetoresistance element 506 is coupled to receive a voltage 502 and the second terminal of the magnetoresistance element 506 is coupled to an emitter of a PNP bipolar transistor 508.
The electronic circuit 500 can include a voltage source 504 having first and second terminals, wherein the first terminal of the voltage source 504 is coupled to receive the voltage 502 and the second terminal of the voltage source 504 is coupled to a base of the PNP bipolar transistor 508.
The electronic circuit 500 can include a resistor 514 having first and second terminals, wherein the first terminal of the resistor 514 is coupled to an emitter of an NPN bipolar transistor 510 and the second terminal of the resistor 514 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 500 can include another voltage source 512 having first and second terminals, wherein the first terminal of the voltage source 512 is coupled a base of the NPN bipolar transistor 510 and the second terminal of the voltage source 512 is coupled to the second terminal of the resistor 514.
A collector of the PNP bipolar transistor 508 can be coupled to a collector of the NPN bipolar transistor 510 at a junction node.
A load 518, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 518.
The load 518 is labeled Zload. The nomenclature, Zload, used here and in figures below is not intended to limit the load 518 or loads discussed below to one or more passive electronic components. Instead, the load 518 and loads discussed below can be comprised of passive electronic components, active electronic components, or both.
An output voltage 516 can be generated at the collector of the PNP bipolar transistor 508 (i.e., at the junction node).
In some embodiments, the electronic circuit 500 can include a comparator coupled to the junction node that is the same as or similar to the comparators shown above in conjunction with FIGS. 1-4.
It should be appreciated that the voltage source 504, the magnetoresistance element 506, and the PNP bipolar transistor 508 form a variable current source operable to provide a variable current, I1. The variable current, I1, varies in accordance with a variable resistance of the magnetoresistance element 506, which varies in accordance with a sensed magnetic field. It should be appreciated that the voltage source 512, the resistor 514, and the NPN bipolar transistor 510 form a current sink operable to provide a fixed current, I2. Thus, the output voltage 516 is generated according to the following:

Vout=Vb+[(I1−I2)×Zload]

I1=(V1−Vbe)/A
I2=(V2−Vbe)/R
I1−I2=(V1−Vbe)/A−(V2−Vbe)/R

Vout=Vb+[[(V1−Vbe)/A−(V2−Vbe)/R]×Zload]  (5)

where:

    
    
        V1=voltage of voltage source 504
        V2=voltage of voltage source 512
        R=resistance of resistor 514
        A=resistance of the magnetoresistance element 506
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 508 and of NPN bipolar transistor 510=approx. 0.7 volts
    
    


It should be understood that the load 518 can be made to have a high impedance to achieve a gain not obtained with the electronic circuits of FIGS. 1-4 described above.
In the electronic circuit 500, it should be appreciated that the same current, I1, flows through the PNP bipolar transistor 508 and through the magnetoresistance element 506.
Referring now to FIG. 6, another example of an electronic circuit 600 can be used in another magnetic field sensor. The electronic circuit 600 can include a resistor 606 having first and second terminals, wherein the first terminal of the resistor 606 is coupled to receive a voltage 602 and the second terminal of the resistor 606 is coupled to an emitter of a PNP bipolar transistor 608.
The electronic circuit 600 can include a voltage source 604 having first and second terminals, wherein the first terminal of the voltage source 604 is coupled to receive the voltage 602 and the second terminal of the voltage source 604 is coupled to a base of the PNP bipolar transistor 608.
The electronic circuit 600 can include a magnetoresistance element 614 having first and second terminals, wherein the first terminal of the magnetoresistance element 614 is coupled to an emitter of an NPN bipolar transistor 610 and the second terminal of the magnetoresistance element 614 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 600 can include another voltage source 612 having first and second terminals, wherein the first terminal of the voltage source 612 is coupled a base of the NPN bipolar transistor 610 and the second terminal of the voltage source 612 is coupled to the second terminal of the magnetoresistance element 614.
A collector of the PNP bipolar transistor 608 can be coupled to a collector of the NPN bipolar transistor 610 at a junction node.
A load 618, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 618.
The load 618 is labeled Zload. The nomenclature, Zload, used here and in figures below is not intended to limit the load 618 or loads discussed below to one or more passive electronic components. Instead, the load 618 and loads discussed below can be comprised of passive electronic components, active electronic components, or both.
An output voltage 616 can be generated at the collector of the PNP bipolar transistor 608 (i.e., at the junction node).
In some embodiments, the electronic circuit 600 can include a comparator coupled to the junction node that is the same as or similar to the comparators shown above in conjunction with FIGS. 1-4. Other electronic circuits described below can also include a comparator, though not shown.
It should be appreciated that the voltage source 604, the resistor 606, and the PNP bipolar transistor 608 form a current source operable to provide a fixed current, I1. It should be appreciated that the voltage source 612, the magnetoresistance element 614, and the NPN bipolar transistor 610 form a variable current sink operable to provide a variable current, I2. The variable current, I2, varies in accordance with a variable resistance of the magnetoresistance element 614, which varies in accordance with a sensed magnetic field.
Thus, the output voltage 616 is generated according to the following:

Vout=Vb+[(I1−I2)×Zload]

I1=(V1−Vbe)/R
I2=(V2−Vbe)/A
I1−I2=(V1−Vbe)/R−(V2−Vbe)/A

Vout=Vb+[[(V1−Vbe)/R−(V2−Vbe)/A]×Zload]  (6)

where:

    
    
        V1=voltage of voltage source 604
        V2=voltage of voltage source 612
        R=resistance of resistor 606
        A=resistance of the magnetoresistance element 614
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 608 and of NPN bipolar transistor 610=approx. 0.7 volts
    
    


It should be understood that the load 618 can be made to have a high impedance to achieve a gain not obtained with the electronic circuits of FIGS. 1-4 described above.
In the electronic circuit 600, it should be appreciated that the same current, I2, flows through the NPN bipolar transistor 610 and through the magnetoresistance element 614.
Referring now to FIG. 7, another example of an electronic circuit 700 can be used in another magnetic field sensor. The electronic circuit 700 can include a magnetoresistance element 706 having first and second terminals, wherein the first terminal of the magnetoresistance element 706 is coupled to receive a voltage 702 and the second terminal of the magnetoresistance element 706 is coupled to an emitter of a PNP bipolar transistor 708.
The electronic circuit 700 can include a voltage source 704 having first and second terminals, wherein the first terminal of the voltage source 704 is coupled to receive the voltage 702 and the second terminal of the voltage source 704 is coupled to a base of the PNP bipolar transistor 708.
The electronic circuit 700 can include another magnetoresistance element 714 having first and second terminals, wherein the first terminal of the magnetoresistance element 714 is coupled to an emitter of an NPN bipolar transistor 710 and the second terminal of the magnetoresistance element 714 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 700 can include another voltage source 712 having first and second terminals, wherein the first terminal of the voltage source 712 is coupled a base of the NPN bipolar transistor 710 and the second terminal of the voltage source 712 is coupled to the second terminal of the magnetoresistance element 714.
A collector of the PNP bipolar transistor 708 can be coupled to a collector of the NPN bipolar transistor 710 at a junction node.
A load 718, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 718.
The load 718 is labeled Zload. The nomenclature, Zload, used here and in figures below is not intended to limit the load 718 or loads discussed below to one or more passive electronic components. Instead, the load 718 and loads discussed below can be comprised of passive electronic components, active electronic components, or both.
An output voltage 716 can be generated at the collector of the PNP bipolar transistor 708 (i.e., at the junction node).
In some embodiments, the electronic circuit 700 can include a comparator coupled to the junction node that is the same as or similar to the comparators shown above in conjunction with FIGS. 1-4. Other electronic circuits described below can also include a comparator, though not shown or described below.
It should be appreciated that the voltage source 704, the magnetoresistance element 706, and the PNP bipolar transistor 708 form a variable current source operable to provide a variable current, I1. The variable current, I1, varies in accordance with a variable resistance of the magnetoresistance element 706, which varies in accordance with a sensed magnetic field. It should be appreciated that the voltage source 712, the magnetoresistance element 714, and the NPN bipolar transistor 710 form a variable current sink operable to provide a variable current, I2. The variable current, I2, varies in accordance with a variable resistance of the magnetoresistance element 714, which varies in accordance with a sensed magnetic field.
Thus, the output voltage 716 is generated according to the following:
Vout=Vb+[(I1−I2)×Zload]
I1=(V1−Vbe)/A
I2=(V2−Vbe)/B
I1−I2=(V1−Vbe)/R−(V2−Vbe)/A

Vout=Vb+[[(V1−Vbe)/A−(V2−Vbe)/B]×Zload]  (7)

where:

    
    
        V1=voltage of voltage source 704
        V2=voltage of voltage source 712
        A=resistance of magnetoresistance element 706
        B=resistance of the magnetoresistance element 714
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 706 and of NPN bipolar transistor 710=approx. 0.7 volts
    
    


It should be understood that the load 718 can be made to have a high impedance to achieve a gain not obtained with the electronic circuits of FIGS. 1-4 described above.
In the electronic circuit 700, noises of the two magnetoresistance elements 706, 714 add incoherently to result in the square root of two times the noise of one magnetoresistance element. However, signals resulting from resistance changes of the two magnetoresistance elements 706, 714 add coherently to result in an output signal 716 two times a signal that would result from one magnetoresistance element, for example, as provided by the electronic circuits of FIGS. 1-6. Thus, a signal to noise ratio improvement is obtained. Similar improvements in signal to noise ratio can be obtained for similar reasons with circuits described below.
In the electronic circuit 700, it should be appreciated that the same current, I1, flows through the PNP bipolar transistor 708 and through the magnetoresistance element 706. Also, the same current, I2, flows through the NPN bipolar transistor 710 and through the magnetoresistance element 714.
Referring now to FIG. 8, another example of an electronic circuit 800 can be used in another magnetic field sensor. The electronic circuit 800 can include a magnetoresistance element 806 having first and second terminals, wherein the first terminal of the magnetoresistance element 806 is coupled to receive a voltage 802 and the second terminal of the magnetoresistance element 806 is coupled to an emitter of a PNP bipolar transistor 808.
The electronic circuit 800 can include a voltage source 804 having first and second terminals, wherein the first terminal of the voltage source 804 is coupled to receive the voltage 802 and the second terminal of the voltage source 804 is coupled to a base of the PNP bipolar transistor 808.
The electronic circuit 800 can include a resistor 814 having first and second terminals, wherein the first terminal of the resistor 814 is coupled to an emitter of an NPN bipolar transistor 810 and the second terminal of the resistor 814 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 800 can include another voltage source 812 having first and second terminals, wherein the first terminal of the voltage source 812 is coupled a base of the NPN bipolar transistor 810 and the second terminal of the voltage source 812 is coupled to the second terminal of the resistor 814.
A collector of the PNP bipolar transistor 808 can be coupled to a collector of the NPN bipolar transistor 810 at a junction node.
A load 818, which can be a resistive or a complex load, can be coupled between the junction node and the second terminal of the resistor 814.
An output voltage 816 can be generated at the collector of the PNP bipolar transistor 808 (i.e., at the junction node).
It should be appreciated that the voltage source 804, the magnetoresistance element 806, and the PNP bipolar transistor 808 form a variable current source operable to provide a variable current, I1. The variable current, I1, varies in accordance with a variable resistance of the magnetoresistance element 806, which varies in accordance with a sensed magnetic field. It should be appreciated that the voltage source 812, the resistor 814, and the NPN bipolar transistor 810 form a current sink operable to provide a fixed current, I2. Thus, the output voltage 816 is generated according to the following:

Vout1=Vb+[(I1−I2)×Zload1]

I1=(V1−Vbe)/A
I2=(V2−Vbe)/R1
I1−I2=(V1−Vbe)/A−(V2−Vbe)/R1

Vout1=Vb+[[(V1−Vbe)/A−(V2−Vbe)/R1]×Zload1]  (8)

where:

    
    
        Zload1=impedance of load 818
        Vout1=voltage 816
        V1=voltage of voltage source 804
        V2=voltage of voltage source 812
        R1=resistance of resistor 814
        A=resistance of the magnetoresistance element 806
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 808 and of NPN bipolar transistor 810=approx. 0.7 volts
    
    


In the electronic circuit 800, it should be appreciated that the same current, I1 flows through the PNP bipolar transistor 808 and through the magnetoresistance element 806.
The electronic circuit 800 can also include a resistor 820 having first and second terminals, wherein the first terminal of the resistor 820 is coupled to receive the voltage 802 and the second terminal of the resistor 820 is coupled to an emitter of a PNP bipolar transistor 822.
The second terminal of the voltage source 804 can be coupled to a base of the PNP bipolar transistor 822.
The electronic circuit 800 can include a magnetoresistance element 826 having first and second terminals, wherein the first terminal of the magnetoresistance element 826 is coupled to an emitter of an NPN bipolar transistor 824 and the second terminal of the magnetoresistance element 826 is coupled to a voltage reference, for example, a ground voltage.
The first terminal of the voltage source 812 is coupled a base of the NPN bipolar transistor 824.
A collector of the PNP bipolar transistor 822 can be coupled to a collector of the NPN bipolar transistor 824 at a junction node.
A load 830, which can be a resistive or a complex load, can be coupled between the junction node and the second terminal of the magnetoresistance element 826.
An output voltage 828 can be generated at the collector of the PNP bipolar transistor 822 (i.e., at the junction node).
It should be appreciated that the voltage source 804, the resistor 820, and the PNP bipolar transistor 822 form a current source operable to provide a fixed current, I3. It should be appreciated that the voltage source 812, the magnetoresistance element 826, and the NPN bipolar transistor 824 form a variable current sink operable to provide a variable current, I4. The variable current, I4, varies in accordance with a variable resistance of the magnetoresistance element 826, which varies in accordance with a sensed magnetic field. Thus, the output voltage 828 is generated according to the following:

Vout2=Vb+[(I3−I4)×Zload2]

I3=(V1−Vbe)/R2
I4=(V2−Vbe)/B
I3−I4=(V1−Vbe)/R2−(V2−Vbe)/B

Vout2=Vb+[[(V1−Vbe)/R2−(V2−Vbe)/B]×Zload2]  (9)

where:

    
    
        Zload2=impedance of load 830
        Vout2=voltage 828
        V1=voltage of voltage source 804
        V2=voltage of voltage source 812
        R2=resistance of resistor 820
        B=resistance of the magnetoresistance element 826
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 822 and of NPN bipolar transistor 824=approx. 0.7 volts
    
    


In the electronic circuit 800, it should be appreciated that the same current, I4, flows through the NPN bipolar transistor 824 and through the magnetoresistance element 826.
For the electronic circuit 800, the output voltages 816, 828 can be taken individually (i.e., each can be a single ended signal). In other embodiments, the electronic circuit 800 provides a differential signal, Vdiff=voltage 816−voltage 828=Vout1−Vout2.
It should be understood that the loads 818, 830 can be made to have high impedances to achieve single ended gains not obtained with the electronic circuits of FIGS. 1-4 described above. Furthermore, the above described differential signal has an amplitude that is double the amplitude of the single ended signals.
Referring now to FIG. 9, a magnetic field sensor 900 can include a substrate 902 having a surface 902a, which is one of two parallel major surfaces of the substrate 902.
Two magnetoresistance elements 904, 906 (also referred to herein as magnetoresistance elements A and B) can be disposed upon the surface 902a along an axis 908. The two magnetoresistance elements 904, 906 (A, B) can be part of or coupled to an electronic circuit 910, which is also disposed upon or within the surface 902a of the substrate 902. The two magnetoresistance elements 904, 906 (A, B) can be the same as or similar to the magnetic field sensing elements 706, 714 of FIG. 7 and the two magnetoresistance element 806, 812 of FIG. 3-8. The designations A, B can also be found in FIGS. 7 and 8 to represent resistance values.
Magnetoresistance elements, e.g., 904, 906 (A, B), are shown in all embodiments herein to be in the form of so-called “yokes,” which have a C-shape (or a reverse C-shape). In some embodiments, the yokes can have longest yoke axes substantially perpendicular to the axis 908. Advantages of yoke shapes are known. It will be understood that other magnetoresistance elements used in embodiments herein can have other shapes, for example, lines, polylines, or rectangles.
Maximum response axes of the magnetoresistance elements 904, 906 (A, B) can be parallel to and along the axis 908 and in the same direction. It should be understood that the magnetoresistance elements 904, 906 (A, B) having maximum response axes parallel to the axis 908 are also responsive to magnetic fields at other angles in the plane of the substrate 902 (and also out of the plane of the substrate 902). The degree to which the magnetoresistance elements 904, 906 (A, B) are responsive to magnetic fields at other angles not parallel to the axis 908 (and not perpendicular to the longest yoke axes) is determined by a magnitude of a geometric projection of the magnetic field at the other angle onto the axis 908. Thus, the term “projected magnetic field” is used below to describe this projection.
In some other embodiments, where the yoke shapes of the magnetoresistance elements 904, 906 may be rotated so that the longest yokes axes are not perpendicular to the axis 908, the degree to which the magnetoresistance elements 904, 906 (A, B) are responsive to magnetic fields at other angles not parallel to the axis 908 is determined by a magnitude of a geometric projection of the magnetic field at the other angle onto an axis that is perpendicular to the longest axes of the yoke shapes. This is also referred to herein as a projected magnetic field.
The magnetic field sensor 900 is responsive to movement of a ferromagnetic target object 912 having features, e.g., 912a, with width 914. For back-biased arrangements in which the magnetic field sensor 900 also includes a magnet (not shown), the ferromagnetic target 912 object can be, for example, a gear having gear teeth, in which case, the feature 912a of the gear can be one of a plurality of gear teeth or one of a plurality of gear valleys. In other arrangements, the ferromagnetic target object 912 can be a multi-pole ring magnet having alternating north and south poles, in which case, the feature 912a can be one of a plurality of magnetic poles, for example, a north pole or a south pole.
In some embodiments, the two magnetoresistance elements 904, 906 (A, B) have a separation 916 between about one half and about one and one half of the width 914 of the target feature 912a, for example, a gear tooth of a ferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet. In some other embodiments, the two magnetoresistance elements 904, 906 (A, B) have a separation 916 between about one half and about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 916 is much smaller than half of the width 914, for example, one one hundredth of the width 914, or larger than twice the width 914.
In some embodiments, the separation 916 is about equal to the width 914 of the target feature 912a, for example, a gear tooth of a ferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet.
In operation, the two magnetoresistance elements 904, 906 (A, B) can generate two output signals. FIGS. 7 and 8 above are representative of ways in which the two magnetic field sensing elements 904, 906 can generate two output signals. In FIGS. 7 and 8, the designation A and B are indicative of resistances and are also indicative of physical placement in relation to FIG. 9.
Using as an example the target feature 912a with a width 914 equal to the spacing 916 between the two magnetoresistance elements 904, 906, when the target feature 912a is centered about (i.e., between) the two magnetoresistance elements 904, 906 (A, B), it can be shown that any magnetoresistance element(s) (e.g., 904 (A)) on one side of a center of the target feature 912a experience a projected magnetic field pointed in one direction along the axis 908, and any magnetoresistance element(s) (e.g., 906 (B)) on the other side of the center of the target feature 912a experience a projected magnetic field pointed in the other direction.
Therefore, when the target feature 912a is centered about the two magnetoresistance elements 904, 906, any magnetoresistance element(s) (e.g., 904 (A)) on one side of the center of the target feature 912a changes resistance in one direction, and any magnetoresistance element(s) (e.g., 906 (B)) on the other side of the center of the target feature 912a changes resistance in the other direction.
In contrast, when an edge of the target feature 912a is centered about (i.e., between) the two magnetoresistance elements 904, 906 (A, B), it can be shown that the two magnetoresistance elements 904, 906 (A, B) experience projected magnetic fields pointed in the same direction along the axis 908. Thus, resistances of both of the two magnetoresistance elements 904, 906 (A, B) change in the same direction.
In view of the above, it should be understood that the electronic circuit 700 of FIG. 7 can operate as a so-called “edge detector,” generating a largest voltage 716 when the two magnetoresistance elements 706, 714 are on opposite sides of an edge of the feature 912a. Similarly, it should be understood that the electronic circuit 800 of FIG. 8 can operate as a so-called “feature detector,” generating a largest differential signal Vout1−Vout2 when the two magnetoresistance elements 806, 826 are on opposite sides of a center of the feature 912a. 
As described above, while a magnet is not shown, it should be understood that in some embodiments, the magnetic field sensor 900 can include a magnet.
Referring now to FIG. 10, another example of an electronic circuit 1000 can be used in another magnetic field sensor. The electronic circuit 1000 can include a magnetoresistance element 1006 having first and second terminals, wherein the first terminal of the magnetoresistance element 1006 is coupled to receive a voltage 1002 and the second terminal of the magnetoresistance element 1006 is coupled to an emitter of a PNP bipolar transistor 1008.
The electronic circuit 1000 can include a voltage source 1004 having first and second terminals, wherein the first terminal of the voltage source 1004 is coupled to receive the voltage 1002 and the second terminal of the voltage source 1004 is coupled to a base of the PNP bipolar transistor 1008.
The electronic circuit 1000 can include another magnetoresistance element 1014 having first and second terminals, wherein the first terminal of the magnetoresistance element 1014 is coupled to an emitter of an NPN bipolar transistor 1010 and the second terminal of the magnetoresistance element 1014 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 1000 can include another voltage source 1012 having first and second terminals, wherein the first terminal of the voltage source 1012 is coupled a base of the NPN bipolar transistor 1010 and the second terminal of the voltage source 1012 is coupled to the second terminal of the magnetoresistance element 1014.
A collector of the PNP bipolar transistor 1008 can be coupled to a collector of the NPN bipolar transistor 1010 at a junction node.
A load 1018, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1018.
The load 1018 is labeled Zload1. The nomenclature, Zload1, used here and in figures below is not intended to limit the load 1018 or loads discussed below to one or more passive electronic components. Instead, the load 1018 and loads discussed below can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1016 can be generated at the collector of the PNP bipolar transistor 1008 (i.e., at the junction node).
It should be appreciated that the voltage source 1004, the magnetoresistance element 1006, and the PNP bipolar transistor 1008 form a variable current source operable to provide a variable current, I1. The variable current, I1, varies in accordance with a variable resistance of the magnetoresistance element 1006, which varies in accordance with a sensed magnetic field.
It should be appreciated that the voltage source 1012, the magnetoresistance element 1014, and the NPN bipolar transistor 1010 form a variable current sink operable to provide a variable current, I2. The variable current, I2, varies in accordance with a variable resistance of the magnetoresistance element 1014, which varies in accordance with a sensed magnetic field. Thus, the output voltage 1016 is generated according to the following:

Vout1=Vb+[(I1−I2)×Zload1]

I1=(V1−Vbe)/A
I2=(V2−Vbe)/D
I1−I2=(V1−Vbe)/A−(V2−Vbe)/D

Vout1=Vb+[[(V1−Vbe)/A−(V2−Vbe)/D]×Zload1]  (10)

where:

    
    
        Zload1 =impedance of load 1018
        Vout1 =voltage 1016
        V1 =voltage of voltage source 1004
        V2 =voltage of voltage source 1012
        D=resistance of magnetoresistance element 1014
        A=resistance of the magnetoresistance element 1006
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 1008 and of NPN bipolar transistor 1010=approx. 0.7 volts
    
    


In the electronic circuit 1000, it should be appreciated that the same current, I1, flows through the PNP bipolar transistor 1008 and through the magnetoresistance element 1006. Also, the same current, I2, (different than I1) flows through the NPN bipolar transistor 1010 and through the magnetoresistance element 1014.
The electronic circuit 1000 can also include a magnetoresistance element 1020 having first and second terminals, wherein the first terminal of the magnetoresistance element 1020 is coupled to receive the voltage 1002 and the second terminal of the magnetoresistance element 1020 is coupled to an emitter of a PNP bipolar transistor 1022.
The second terminal of the voltage source 1004 can be coupled to a base of the PNP bipolar transistor 1022.
The electronic circuit 1000 can include another magnetoresistance element 1026 having first and second terminals, wherein the first terminal of the magnetoresistance element 1026 is coupled to an emitter of an NPN bipolar transistor 1024 and the second terminal of the magnetoresistance element 1026 is coupled to a voltage reference, for example, a ground voltage.
The first terminal of the voltage source 1012 is coupled a base of the NPN bipolar transistor 1024.
A collector of the PNP bipolar transistor 1022 can be coupled to a collector of the NPN bipolar transistor 1024 at a junction node.
A load 1030, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1030.
The load 1030 is labeled Zload2. The nomenclature, Zload2, used here and in figures below is not intended to limit the load 1030 or loads discussed below to one or more passive electronic components. Instead, the load 1030 and loads discussed below can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1028 can be generated at the collector of the PNP bipolar transistor 1022 (i.e., at the junction node).
It should be appreciated that the voltage source 1004, the magnetoresistance element 1020, and the PNP bipolar transistor 1022 form a current source operable to provide a variable current, I3. The variable current, I3, varies in accordance with a variable resistance of the magnetoresistance element 1020, which varies in accordance with a sensed magnetic field.
It should be appreciated that the voltage source 1012, the magnetoresistance element 1026, and the NPN bipolar transistor 1024 form a variable current sink operable to provide a variable current, I4. The variable current, I4, varies in accordance with a variable resistance of the magnetoresistance element 1026, which varies in accordance with a sensed magnetic field. Thus, the output voltage 1028 is generated according to the following:

Vout2=Vb+[(I3−I4)×Zload2]

I3=(V1−Vbe)/C
I4=(V2−Vbe)/B
I3−I4=(V1−Vbe)/C−(V2−Vbe)/B

Vout2=Vb+[[(V1−Vbe)/C−(V2−Vbe)/B]×Zload2]  (11)

where:

    
    
        Zload2==impedance of load 1030
        Vout2=voltage 1028
        V1=voltage of voltage source 1004
        V2=voltage of voltage source 1012
        C=resistance of magnetoresistance element 1020
        B=resistance of the magnetoresistance element 1026
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 1022 and of NPN bipolar transistor 1024=approx. 0.7 volts
    
    


In the electronic circuit 1000, it should be appreciated that the same current, I3, (different than I1, I2) flows through the PNP bipolar transistor 1022 and through the magnetoresistance element 1020. Also, the same current, I4, (different than I1, I2, I3) flows through the NPN bipolar transistor 1024 and through the magnetoresistance element 1026.
For the electronic circuit 1000, the output voltages 1016, 1028 can be taken individually (i.e., each can be a single ended signal). In other embodiments, the electronic circuit 1000 provides a differential signal, Vdiff=voltage 1016−voltage 1028=Vout1−Vout2.
It should be understood that the loads 1018, 1030 can be made to have high impedances to achieve single ended gains not obtained with the electronic circuits of FIGS. 1-4 described above. Furthermore, the above described differential signal has an amplitude that is double the amplitude of the single ended signals.
Referring now to FIG. 11, in which like elements of FIG. 10 are shown having like reference designations, in an electronic circuit 1100, the voltage source 1012 of FIG. 10 is replaced with a circuit portion 1102, which will be recognized to be a reference leg of a current mirror. The circuit portion 1102 can include a current source 1104 having an output node. A collector of an NPN bipolar transistor 1106 can be coupled to the current source. A base of the NPN bipolar transistor 1106 can be coupled to the collector of the NPN bipolar transistor 1106, such that the NPN bipolar transistor operates merely as a diode. A resistor 1180 having first and second terminals can be coupled such that the first terminal of the resistor is coupled to an emitter of the NPN bipolar transistor 1106 and the second terminal of the resistor 1108 is coupled to a reference voltage, for example, a ground voltage. The base or the NPN bipolar transistor 1106 is coupled to the bases of the NPN bipolar transistors 1010, 1024,
The electronic circuit 1100 operates in substantially the same way as the electronic circuit 1000 of FIG. 10, and has the same operating equations.
Referring now to FIG. 12, in which like elements of FIGS. 10 and 11 are shown having like reference designations, in an electronic circuit 1200, the voltage source 1004 of FIGS. 10 and 11 is replaced with a circuit portion 1202, which operates as a common mode voltage detector. The circuit portion 1202 can include a common mode voltage detector 1204 coupled to receive the two output voltages 1016, 1028 and operable to generate a common mode detection signal 1204a indicative of a common mode voltage of the output voltages 1016, 1028. A voltage buffer or level translator 1206 can be coupled to receive the common mode detection signal 1204a and operable to generate a signal coupled to the bases of the PNP bipolar transistors 1008, 1022.
In operation, if a common voltage of a differential signal Vout1−Vout2 is not at a desired operating point, the common mode voltage detector 1204 can detect the error condition and adjust the current flowing through the two PNP bipolar transistors 1008, 1022 to remove the error condition.
The electronic circuit 1200 operates in substantially the same way as the electronic circuit 1000 of FIG. 10 and the electronic circuit 1100 of FIG. 1, and has the same operating equations.
Referring now to FIG. 13, in which like elements of FIG. 9 are shown having like, reference designations, a magnetic field sensor 1300 can include a substrate 1302 having a surface 1302a, which is one of two parallel major surfaces of the substrate 1302.
Four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can be disposed upon the surface 1302a along an axis 1314. The four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can be part of or coupled to an electronic circuit 1312, which is also disposed upon or within the surface 1302a of the substrate 1302. The four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can be the same as or similar to the magnetic field sensing elements 1006, 1026, 1020, 1014, respectively, of FIGS. 10 and 11.
Maximum response axes of the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can be parallel to and along an axis 1314, and in the same direction. Angles of magnetic fields are discussed above in conjunction with FIG. 9.
The magnetic field sensor 1300 is responsive to movement of the ferromagnetic target object 912.
In some embodiments, the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) are disposed along the axis 1314 proximate to the ferromagnetic target object 912.
In some embodiments, the two magnetoresistance elements 1304, 1308 (A, C) have a separation 1320 between about one half and about one and one half of the width 914 of the target feature 912a, for example, a gear tooth of a ferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet. In some other embodiments, the two magnetoresistance elements 1304, 1308 (A, C) have a separation 1320 between about one half and about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1320 is much smaller than half of the width 914, for example, one one hundredth of the width 914 or larger than twice the width 914.
In some embodiments used in examples below, the separation 1320 is about equal to the width 914 of the target feature 912a. 
Similarly, in some embodiments, the two magnetoresistance elements 1306, 1310 (B, D) have a separation 1322 between about one half and about one and one half of the width 914 of the target feature 912a, for example, a gear tooth of a ferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet. In some embodiments, the two magnetoresistance elements 1306, 1310 (B, D) have a separation 1322 between about one half and about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1322 is much smaller than half of the width 914, for example, one one hundredth of the width 914 or larger than twice the width 914.
In some embodiments used in examples below, the separation 1322 is about equal to the width 914 of the target feature 912a. 
In some other embodiments, the two magnetoresistance elements 1304, 1306 (A, B) have a separation 1324 between about one half and about one and one half of the width 914 of the target feature 912a. In some other embodiments, the two magnetoresistance elements 1304, 1306 (A, B) have a separation 1324 between about one half and about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1324 is much smaller than half of the width 914, for example, one one hundredth of the width 914 or larger than twice the width 914.
In some embodiments used in examples below, the separation 1324 is about equal to the width 914 of the target feature 912a. 
Similarly, in some other embodiments, the two magnetoresistance elements 1308, 1310 (C, D) have a separation 1326 between about one half and about one and one half of the width 914 of the target feature 912a. In some other embodiments, the two magnetoresistance elements 1308, 1310 (C, D) have a separation 1326 between about one half and twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1326 is much smaller than half of the width 914, for example, one one hundredth of the width 914 or larger than twice the width 914.
In some embodiments used in examples below, the separation 1326 is about equal to the width 914 of the target feature 912a. 
In operation, the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can generate at least two output signals. FIGS. 10, 11, and 12 above are representative of ways in which the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can generate at least two output signals. In FIGS. 10, 11, and 12, the designation A, B, C, and D are indicative of resistances and are also indicative of physical placement in relation to FIG. 13.
Using as an example the target feature 912a with a width 914 equal to the spacings 1320, 1322, when the target feature 912a is centered about (i.e., between) the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D), it can be shown that any magnetoresistance element(s) (e.g., 1304, 1306 (A, B)) on one side of a center of the target feature 912a experiences a projected magnetic field pointed in one direction along the axis 1314, and any magnetoresistance element(s) (e.g., 1308, 1310 (C, D)) on the other side of the center of the target feature 912a experiences a projected magnetic field pointed in the other direction.
Therefore, when the target feature 912a is centered about four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D), any magnetoresistance element(s) (e.g., 1304, 1306 (A, B)) on one side of the center of the target feature 912a change resistance in one direction, and any magnetoresistance element(s) (e.g., 1308, 1310 (C, D)) on the other side of the center of the target feature 912a change resistance in the other direction.
In contrast, when an edge of the target feature 912a is centered about (i.e., between) the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D), it can be shown that the two magnetoresistance elements 1304, 1310 (A, D) experience projected magnetic fields pointed in the same direction along the axis 1314. Thus, resistance of both of the two magnetoresistance elements 1304, 1310 change in the same direction.
At the same time, when an edge of the target feature 912a is centered, the two magnetoresistance elements 1306, 1308 (B, C) experience projected magnetic fields pointed in the same direction along the axis 1314, but opposite in direction from the projected magnetic fields experienced by the two magnetoresistance elements 1304, 1310 (A, D). Thus, resistance of both of the two magnetoresistance elements 1306, 1308 (B, C) change in the same direction but opposite to the resistance change of the two magnetoresistance elements 1304, 1310 (A, D).
While a particular example of the spacings 1320, 1322 relative to the width 914 of the target feature 912a is given above, it should be appreciated that for other relative dimensions, magnetic fields at the four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) may not be exactly as described above and some resistance changes may be in other directions.
In view of the above, it should be understood that the electronic circuits 1000, 1100, 1200 of FIGS. 10, 11, 12 can operate as a feature detectors, generating a largest differential voltage Vout1−Vout2 when the four magnetoresistance elements 1004 (A), 1026 (B), 1020 (C), 1014 (D) of FIGS. 10, 11, 12 are arranged as shown in FIG. 13 by designations A-D, arranged relative to a center of the target feature 912a. 
While a magnet is not shown, it should be understood that in some embodiments, the magnetic field sensor 1400 can include a magnet.
Referring now to FIG. 14, another example of an electronic circuit 1400 can be used in another magnetic field sensor. The electronic circuit 1400 can include a magnetoresistance element 1404 having first and second terminals, wherein the first terminal of the magnetoresistance element 1404 is coupled to receive a voltage 1402 and the second terminal of the magnetoresistance element 1404 is coupled to an emitter of a PNP bipolar transistor 1406.
The electronic circuit 1400 can include a voltage source in the form of a common mode voltage detector circuit 1435 coupled to the base of the PNP bipolar transistor 1406.
The electronic circuit 1400 can include another magnetoresistance element 1410 having first and second terminals, wherein the first terminal of the magnetoresistance element 1410 is coupled to an emitter of an NPN bipolar transistor 1408 and the second terminal of the magnetoresistance element 1410 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 1400 can include a voltage source in the form of a current mirror reference leg 1428 coupled to the base of the NPN bipolar transistor 1408.
A collector of the PNP bipolar transistor 1406 can be coupled to a collector of the NPN bipolar transistor 1408 at a junction node.
A load 1414, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1414.
The load 1414 is labeled Z1. The nomenclature, Z1, is not intended to limit the load 1414 to one or more passive electronic components. Instead, the load 1414 can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1412 can be generated at the collector of the PNP bipolar transistor 1406 (i.e., at the junction node).
The output voltage 1412 is generated according to the following:

Vout1=Vb+[(I1−I2)×Z1]

I1=(V1−Vbe)/A1
I2=(V2−Vbe)/C2
I1−I2=(V1−Vbe)/A1−(V2−Vbe)/C2

Vout=Vb+[[(V1−Vbe)/A1−(V2−Vbe)/C2]×Z1]  (12)

where:

    
    
        Z1=impedance of load 1414
        Vout1=voltage 1412
        V1=voltage of common mode voltage detector circuit 1435
        V2=voltage of current mirror reference leg 1428
        C2=resistance of magnetoresistance element 1410
        A1=resistance of the magnetoresistance element 1404
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 1406 and of NPN bipolar transistor 1408=approx. 0.7 volts
    
    


The electronic circuit 1400 can also include a magnetoresistance element 1416 having first and second terminals, wherein the first terminal of the magnetoresistance element 1416 is coupled to receive the voltage 1402 and the second terminal of the magnetoresistance element 1416 is coupled to an emitter of a PNP bipolar transistor 1418.
The common mode voltage detector circuit 1435 can be coupled to a base of the PNP bipolar transistor 1418.
The electronic circuit 1400 can include another magnetoresistance element 1422 having first and second terminals, wherein the first terminal of the magnetoresistance element 1422 is coupled to an emitter of an NPN bipolar transistor 1420 and the second terminal of the magnetoresistance element 1422 is coupled to a voltage reference, for example, a ground voltage.
The current mirror reference leg 1428 is coupled to a base of the NPN bipolar transistor 1420.
A collector of the PNP bipolar transistor 1418 can be coupled to a collector of the NPN bipolar transistor 1420 at a junction node.
A load 1426, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1426
The load 1426 is labeled Z2. The nomenclature, Z2, is not intended to limit the load 1426 to one or more passive electronic components. Instead, the load 1426 can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1424 can be generated at the collector of the PNP bipolar transistor 1418 (i.e., at the junction node).
The output voltage 1424 is generated according to the following:

Vout2=Vb+[(I3−I4)×Z2]

I3=(V1−Vbe)/C1
I4=(V2−Vbe)/A2
I3−I4=(V1−Vbe)/C1−(V2−Vbe)/A2

Vout2=Vb+[[(V1−Vbe)/C1−(V2−Vbe)/A2]×Z2]  (13)

where:

    
    
        Z2=impedance of load 1426
        Vout2=voltage 1424
        V1=voltage of common mode voltage detector circuit 1435
        V2=voltage of current mirror reference leg 1428
        C1=resistance of resistor 1416
        A2=resistance of the magnetoresistance element 1422
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 1418 and of NPN bipolar transistor 1024=approx. 0.7 volts
    
    


In the electronic circuit 1400, it should be appreciated that the same current, I3, (different than I1, I2) flows through the PNP bipolar transistor 1418 and through the magnetoresistance element 1416. Also, the same current, I4, (different than I1, I2, I3) flows through the NPN bipolar transistor 1024 and through the magnetoresistance element 1422.
For the electronic circuit 1400, the output voltages 1412, 1424 can be taken individually (i.e. single ended signals). In other embodiments, the electronic circuit 1400 provides a differential signal, Vdiff=voltage 1412−voltage 1424=Vout1−Vout2.
It should be understood that the loads 1414, 1426 can be made to have high impedances to achieve single ended gains not obtained with the electronic circuits of FIGS. 1-4 described above. Furthermore, the above described differential signal has an amplitude that is double the amplitude of the single ended signals.
The electronic circuit 1400 can also include a magnetoresistance element 1440 having first and second terminals, wherein the first terminal of the magnetoresistance element 1440 is coupled to receive a voltage 1402 and the second terminal of the magnetoresistance element 1440 is coupled to an emitter of a PNP bipolar transistor 1442.
The electronic circuit 1400 can include a common mode voltage detector circuit 1471 coupled to a base of the PNP bipolar transistor 1442.
The electronic circuit 1400 can include another magnetoresistance element 1446 having first and second terminals, wherein the first terminal of the magnetoresistance element 1446 is coupled to an emitter of an NPN bipolar transistor 1444 and the second terminal of the magnetoresistance element 1446 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 1400 can include a current mirror reference leg 1464 coupled a base of the NPN bipolar transistor 1444.
A collector of the PNP bipolar transistor 1442 can be coupled to a collector of the NPN bipolar transistor 1444 at a junction node.
A load 1450, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1450.
The load 1450 is labeled Z3. The nomenclature, Z3, is not intended to limit the load 1450 to one or more passive electronic components. Instead, the load 1450 can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1448 can be generated at the collector of the PNP bipolar transistor 1442 (i.e., at the junction node).
The output voltage 1448 is generated according to the following:

Vout3=Vb+[(I5−I6)×Z3]

I5=(V3−Vbe)B1
I6=(V4−Vbe)/D2
I5−I6=(V3−Vbe)/B1−(V4-Vbe)/D2

Vout3=Vb+[[(V3−Vbe)/B1−(V4−Vbe)/D2]×Z3]  (14)

where:

    
    
        Z3=impedance of load 1450
        Vout3=voltage 1448
        V3=voltage of common mode voltage detector circuit 1471
        V4=voltage of current mirror reference leg 1464
        D2=resistance of magnetoresistance element 1446
        B1=resistance of the magnetoresistance element 1440
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 1442 and of NPN bipolar transistor 1444=approx. 0.7 volts
    
    


The electronic circuit 1400 can also include a magnetoresistance element 1452 having first and second terminals, wherein the first terminal of the magnetoresistance element 1452 is coupled to receive the voltage 1402 and the second terminal of the magnetoresistance element 1452 is coupled to an emitter of a PNP bipolar transistor 1454.
The common mode voltage detector circuit 1471 can be coupled to a base of the PNP bipolar transistor 1454.
The electronic circuit 1400 can include another magnetoresistance element 1458 having first and second terminals, wherein the first terminal of the magnetoresistance element 1458 is coupled to an emitter of an NPN bipolar transistor 1456 and the second terminal of the magnetoresistance element 1458 is coupled to a voltage reference, for example, a ground voltage.
The current mirror reference leg 1464 is coupled to a base of the NPN bipolar transistor 1456.
A collector of the PNP bipolar transistor 1454 can be coupled to a collector of the NPN bipolar transistor 1456 at a junction node.
A load 1462, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1462
The load 1462 is labeled Z4. The nomenclature, Z4, is not intended to limit the load 1462 to one or more passive electronic components. Instead, the load 1462 can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1460 can be generated at the collector of the PNP bipolar transistor 1454 (i.e., at the junction node).
The output voltage 1460 is generated according to the following:

Vout4=Vb+[(I7−I8)×Z4]

I7=(V3−Vbe)/D1
I8=(V4−Vbe)/B2
I7−I8=(V3−Vbe)/D1−(V4−Vbe)/B2

Vout4=Vb+[[(V3−Vbe)/D1−(V4−Vbe)/B2]×Z4]  (15)

where:

    
    
        Z4=impedance of load 1462
        Vout4=voltage 1460
        V3=voltage of common mode voltage detector circuit 1471
        V4=voltage of current mirror reference leg 1464
        D1=resistance of magnetoresistance element 1452
        B2=resistance of the magnetoresistance element 1458
        Vb=bias voltage
        Vbe=base emitter voltage of PNP bipolar transistor 1454 and of NPN bipolar transistor 1456=approx. 0.7 volts
    
    


For the electronic circuit 1400, the output voltages 1448, 1460 can be taken individually (i.e. single ended signals). In other embodiments, the electronic circuit 1400 provides a differential signal, Vdiff=voltage 1448−voltage 1460=Vout3−Vout4.
It should be understood that the loads 1450, 1462 can be made to have high impedances to achieve single ended gains not obtained with the electronic circuits of FIGS. 1-4 described above. Furthermore, the above described differential signal has an amplitude that is double the amplitude of the single ended signals.
As described above, for the electronic circuit 1400, the output voltages 1412, 1424, 1448, 1460 can be taken individually (i.e., single ended). However, in other embodiments, the output voltages 1412, 1424, 1448, 1460 can be combined in any way, for example, resulting in two differential signals.
Referring now to FIG. 15, in which like elements of FIG. 9 are shown having like reference designations, a magnetic field sensor 1500 can include a substrate 1502 having a surface 1502a, which is one of two parallel major surfaces of the substrate 1502.
The eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) can be disposed upon the surface 1502a along an axis 1514. The eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) can be part of or coupled to an electronic circuit 1512, which is also disposed upon or within the surface 1502a of the substrate 1502. The eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) can be the same as or similar to the eight magnetoresistance elements of FIG. 14.
Maximum response axes of the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) can be parallel to and along an axis 1514, and in the same direction. Angles of magnetic fields are discussed above in conjunction with FIG. 9.
The magnetic field sensor 1500 is responsive to movement of the ferromagnetic target object 912.
In some embodiments, the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) are disposed along the axis 1514 proximate to the ferromagnetic target object 912.
In some embodiments, the two magnetoresistance elements 1504a, 1504b (A1, A2) have a separation 1520 to the two magnetoresistance elements 1508a, 1508b (C1, C2) between about one half and about one and one half of the width 914 of the target feature 912a, for example, a gear tooth of a ferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet. In some embodiments, the two magnetoresistance elements 1504a, 1504b (A1, A2) have a separation 1520 to the two magnetoresistance elements 1508a, 1508b (C1, C2) between about one half and about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1520 is much smaller than half of the width 914, for example, one one hundredth of the width 914, or larger than twice the width 914.
In some embodiments used in examples below, the separation 1520 is about equal to the width 914 of the target feature 912a. 
Similarly, in some embodiments, the two magnetoresistance elements 1506a, 1506b (B1, B2) have a separation 1522 to the two magnetoresistance elements 1510a, 1510b (D1, D2) between about one half and about one and one half of the width 914 of the target feature 912a, for example, a gear tooth of a ferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet. In some embodiments, the two magnetoresistance elements 1506a, 1506b (B1, B2) have a separation 1522 to the two magnetoresistance elements 1510a, 1510b (D1, D2) between about one half and about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1522 is much smaller than half of the width 914, for example, one one hundredth of the width 914, or larger than twice the width 914.
In some embodiments used in examples below, the separation 1522 is about equal to the width 914 of the target feature 912a. 
In some other embodiments, the two magnetoresistance elements 1504a, 1504b (A1, A2) have a separation 1524 to the two magnetoresistance elements 1506a, 1506b (B1, B2) between about one half and about one and one half of the width 914 of the target feature 912a. 
In some other embodiments, the two magnetoresistance elements 1504a, 1504b (A1, A2) have a separation 1524 to the two magnetoresistance elements 1506a, 1506b (B1, B2) between about one half and twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1524 is much smaller than half of the width 914, for example, one one hundredth of the width 914, or larger than twice the width 914.
In some embodiments used in examples below, the separation 1524 is about equal to the width 914 of the target feature 912a. 
Similarly, in some other embodiments, the two magnetoresistance elements 1508a, 1508b (C1, C2) have a separation 1526 to the two magnetoresistance elements 1510a, 1510b (D1, D2) between about one half and about one and one half of the width 914 of the target feature 912a. In some other embodiments, the two magnetoresistance elements 1508a, 1508b (C1, C2) have a separation 1526 to the two magnetoresistance elements 1510a, 1510b (D1, D2) between about twice the width 914 of the target feature 912a. However, in other embodiments, the separation 1526 is much smaller than half of the width 914, for example, one one hundredth of the width 914, or larger than twice the width 914.
In some embodiments used in examples below, the separation 1526 is about equal to the width 914 of the target feature 912a. 
In operation, the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) can generate at least two output signals. FIG. 14 is representative of ways in which the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) can generate at least two output signals. In FIG. 14 the designations A1, A2, B1, B2, C1, C2, D1, D2 are indicative of resistances and are also indicative of physical placement in relation to FIG. 15.
Using as an example the target feature 912a with a width 914 equal to the spacings 1520, 1522, when the target feature 912a is centered about (i.e., between) the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2), it can be shown that any magnetoresistance element(s) (e.g., 1504a, 1504b, 1506a, 1506b (A1, A2, B1, B2) on one side of a center of the target feature 912a experiences a projected magnetic field pointed in one direction along the axis 1514, and any magnetoresistance element(s) (e.g., 1508a, 1508b, 1510a, 1510b (C1, C2, D1, D1)) on the other side of the center of the target feature 912a experiences a projected magnetic field pointed in the other direction.
Therefore, when the target feature 912a is centered about eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2), any magnetoresistance element(s) (e.g., 1504a, 1504b, 1506a, 1506b (A1, A2, B1, B2)) on one side of the center of the target feature 912a changes resistance in one direction, and any magnetoresistance element(s) (e.g., 1508a, 1508b, 1510a, 1510b (C1, C2, D1, D2)) on the other side of the center of the target feature 912a changes resistance in the other direction.
In contrast, when an edge of the target feature 912a is centered about (i.e., between) the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2), it can be shown that the four magnetoresistance elements 1504a, 1504b, 1510a, 1510b (A1, A2, D1, D2) experience projected magnetic fields pointed in the same direction along the axis 1514. Thus, resistances the four magnetoresistance elements 1504a, 1504b, 1510a, 1510b (A1, A2, D1, D2) change in the same direction.
At the same time, when an edge of the target feature 912a is centered, the four magnetoresistance elements 1506a, 1506b, 1508a, 1508b (B1, B2, C1, C2) experience projected magnetic fields pointed in the same direction along the axis 1514, but opposite in direction from the projected magnetic fields experienced by the four magnetoresistance elements 1504a, 1504b, 1510a, 1510b (A1, A2, D1, D2). Thus, resistance of four magnetoresistance elements 1506a, 1506b, 1508a, 1508b (B1, B2, C1, C2) change in the same direction but opposite to the resistance change of the four magnetoresistance elements 1504a, 1504b, 1510a, 1510b (A1, A2, D1, D2).
While a particular example of the spacings 1520, 1515 and 1524, 1526 relative to the width 914 of the target feature 912a is given above, it should be appreciated that for other relative dimensions, magnetic fields at the eight magnetoresistance elements 1504a, 1504b, 1506a, 1506b, 1508a, 1508b, 1510a, 1510b (A1, A2, B1, B2, C1, C2, D1, D2) may not be exactly as described above and some resistance changes may be in other directions. However, it should be apparent how to modify equations shown in figures below to accomplish both a feature signal and an edge signal.
While a magnet not shown, it should be understood that in some embodiments, the magnetic field sensor 1500 can include a magnet.
Referring now to FIG. 16, in which like elements of FIGS. 10, 11, and 12 are shown having like reference designations, another example of an electronic circuit 1600 can be used in another magnetic field sensor. In the electronic circuit 1600, a current mirror reference leg 1602 and a common mode voltage detector circuit 1609 are exchanged in position and couplings with the current mirror reference leg 1102 and a common mode voltage detector circuit 1202 of FIG. 12. Operation of the electronic circuit 1600 is similar to operation of the electronic circuit 1200 of FIG. 12.
It should be understood how a current mirror reference leg and a common mode voltage detector circuit can be coupled in either way to all of the above electronic circuits.
In FIG. 16, the designation A, B, C, and D are indicative of resistances and are also indicative of physical placement in relation to FIG. 13.
Referring now to FIG. 17, another example of an electronic circuit 1700 can be used in another magnetic field sensor. The electronic circuit 1700 can include a magnetoresistance element 1704 having first and second terminals, wherein the first terminal of the magnetoresistance element 1704 is coupled to receive a voltage 1702 and the second terminal of the magnetoresistance element 1704 is coupled to a source of a P-channel field effect transistor 1706.
The electronic circuit 1700 can include a common mode voltage detector circuit 1727 coupled to a gate of the P-channel field effect transistor 1706.
The electronic circuit 1700 can include another magnetoresistance element 1710 having first and second terminals, wherein the first terminal of the magnetoresistance element 1710 is coupled to a source of an N-channel field effect transistor 1708 and the second terminal of the magnetoresistance element 1710 is coupled to a voltage reference, for example, a ground voltage.
The electronic circuit 1700 can include a current mirror reference leg 1732 coupled a gate of the N-channel field effect transistor 1708.
A drain of the P-channel field effect transistor 1706 can be coupled to a drain of the N-channel field effect transistor 1708 at a junction node.
A load 1714, which can be a resistive or a complex load, can be coupled between the junction node and t a bias voltage, Vb. Current can flow into and/or out of the load 1714.
The load 1714 is labeled Zload1. The nomenclature, Zload1, is not intended to limit the load 1714 to one or more passive electronic components. Instead, the load 1714 can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1712 can be generated at the drain of the P-channel field effect transistor 1706 (i.e., at the junction node).
It should be appreciated that the common mode voltage detector circuit 1727, the magnetoresistance element 1704, and the P-channel field effect transistor 1706 form a variable current source operable to provide a variable current, I1. The variable current, I1, varies in accordance with a variable resistance of the magnetoresistance element 1704, which varies in accordance with a sensed magnetic field.
It should be appreciated that the current mirror reference leg 1732, the magnetoresistance element 1710, and the N-channel field effect transistor 1708 form a variable current sink operable to provide a variable current, I2. The variable current, I2, varies in accordance with a variable resistance of the magnetoresistance element 1710, which varies in accordance with a sensed magnetic field. Thus, the output voltage 1712 is generated according to the following:

Vout1=(I1−I2)×Zload1

Equations used to describe the voltage, Vout1, can be similar to the equations used to describe Vout1 in conjunction with FIG. 10 above, except that Vbe is replaced by Vgs, where Vgs=a gate source voltage of the field effect transistors (which can be different for P-channel and N-channel field defect transistors). A gate-source voltage can be near one volt.

In the electronic circuit 1700, it should be appreciated that the same current, I1 flows through the P-channel field effect transistor 1706 and through the magnetoresistance element 1704. Also, the same current, I2, flows through the N-channel field effect transistor 1708 and through the magnetoresistance element 1710.
The electronic circuit 1700 can also include a magnetoresistance element 1716 having first and second terminals, wherein the first terminal of the magnetoresistance element 1716 is coupled to receive the voltage 1702 and the second terminal of the magnetoresistance element 1716 is coupled to a source of a P-channel field effect transistor 1718.
The common mode voltage detector circuit 1727 can be coupled to a gate of the P-channel field effect transistor 1718.
The electronic circuit 1700 can include another magnetoresistance element 1722 having first and second terminals, wherein the first terminal of the magnetoresistance element 1722 is coupled to a source of an N-channel field effect transistor 1720 and the second terminal of the magnetoresistance element 1722 is coupled to a voltage reference, for example, a ground voltage.
The current mirror reference leg 1732 is coupled to a gate of the N-channel field effect transistor 1720.
A drain of the P-channel field effect transistor 1718 can be coupled to a drain of the N-channel field effect transistor 1720 at a junction node.
A load 1726, which can be a resistive or a complex load, can be coupled between the junction node and a bias voltage, Vb. Current can flow into and/or out of the load 1726.
The load 1726 is labeled Zload2. The nomenclature, Zload2, is not intended to limit the load 1726 to one or more passive electronic components. Instead, the load 1726 can be comprised of passive electronic components, active electronic components, or both.
An output voltage 1724 can be generated at the drain of the P-channel field effect transistor 1718 (i.e., at the junction node).
It should be appreciated that the common mode voltage detector circuit 1727, the magnetoresistance element 1716, and the P-channel field effect transistor 1718 form a variable current source operable to provide a variable current, I3. The variable current, I3, varies in accordance with a variable resistance of the magnetoresistance element 1716, which varies in accordance with a sensed magnetic field.
It should be appreciated that the current mirror reference leg 1732, the magnetoresistance element 1722, and the N-channel field effect transistor 1720 form a variable current sink operable to provide a variable current, I4. The variable current, I4, varies in accordance with a variable resistance of the magnetoresistance element 1722, which varies in accordance with a sensed magnetic field. Thus, the output voltage 1724 is generated according to the following:

Vout2=(I3−I4)×Zload2

Equations used to describe the voltage, Vout2, can be similar to the equations used to describe Vout2 in conjunction with FIG. 10 above, except that Vbe is replaced by Vgs where Vgs=a gate source voltage of the field effect transistors (which can be different for P-channel and N-channel field defect transistors). A gate-source voltage can be near one volt.

In the electronic circuit 1700, it should be appreciated that the same current, I1, flows through the P-channel field effect transistor 1706 and through the magnetoresistance element 1704. Also, the same current, I2, flows through the N-channel field effect transistor 1708 and through the magnetoresistance element 1710.
In the electronic circuit 1700, it should be appreciated that the same current, I3, flows through the P-channel field effect transistor 1718 and through the magnetoresistance element 1716. Also, the same current, I4, flows through the N-channel field effect transistor 1720 and through the magnetoresistance element 1722.
For the electronic circuit 1700, the output voltages 1712, 1724 can be taken individually (i.e., single ended signals). In other embodiments, the electronic circuit 1700 provides a differential signal, Vdiff=voltage 1712−voltage 1724=Vout1−Vout2.
It should be understood that the loads 1714, 1726 can be made to have high impedances to achieve single ended gains not obtained with the electronic circuits of FIGS. 1-4 described above. Furthermore, the above described differential signal has an amplitude that is double the amplitude of the single ended signals.
In FIG. 17, the designation A, B, C, and D are indicative of resistances and are also indicative of physical placement in relation to FIG. 13.
It should be understood that all of the above electronic circuits can use field effect transistors in place of bipolar junction transistors.
Some embodiments described above show two loads. Similar embodiments can instead drive different ends of the same load. Some embodiments described above show four loads.
Similar embodiments can instead drive different ends of two loads. Other load couplings are also possible.
While transistors are used in electronic circuits shown and described herein, it should be understood that any electronic component or element now known or later discovered that has a control node to control a current passing between two current passing nodes can be used in place of transistors.
Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent that other embodiments incorporating these concepts, structures and techniques may be used. Accordingly, it is submitted that the scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims.
Elements of embodiments described herein may be combined to form other embodiments not specifically set forth above. Various elements, which are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.

## Claims

1. An electronic circuit coupled to receive a power supply voltage, comprising:
a first magnetoresistance element having first and second terminals;
a first transistor having a control node, a first current passing node, and a second current passing node;
a first voltage generating source having first and second nodes between which a first fixed voltage is generated, wherein the first terminal of the first magnetoresistance element is coupled to the first current passing node of the first transistor, wherein the first node of the first voltage generating source is coupled to the control node of the first transistor and the second node of the first voltage generating source is coupled to the second terminal of the first magnetoresistance element, wherein the electronic circuit is operable to generate a first current signal at the second current passing node of the first transistor related to a resistance value of the first magnetoresistance element;
a second magnetoresistance element having first and a second terminals;
a second transistor having a control node, a first current passing node, and a second current passing node;
a second voltage generating source having first and second nodes between which a second fixed voltage is generated; and

a load coupled to the second current passing node of the first transistor, wherein the second current passing node of the first transistor is coupled to the second current passing node of the second transistor, wherein the first terminal of the second magnetoresistance element is coupled to the first current passing node of the second transistor, wherein the first node of the second voltage generating source is coupled to the control node of the second transistor and the second node of the second voltage generating source is coupled to the second terminal of the second magnetoresistance element, wherein the electronic circuit is operable to generate a second current signal at the second current passing node of the second transistor related to a resistance value of the second magetoresistance element, wherein a current passing through the load is equal to a difference between the first current signal and the second current signal, wherein the second terminals of the first and second magnetoresistance elements are not coupled together.

2. The electronic circuit of claim 1, wherein the first transistor is an NPN bipolar transistor and the second transistor is a PNP bipolar transistor.

3. The electronic circuit of claim 1, wherein the first transistor is a PNP bipolar transistor and the second transistor is an NPN bipolar transistor.

4. The electronic circuit of claim 1, further comprising:
a comparator coupled to the second current passing node of the first transistor for generating a two state output signal.

5. The electronic circuit of claim 1, wherein the first voltage generating source comprises a reference leg of a current mirror circuit.

6. The electronic circuit of claim 1, further comprising:
a comparator coupled to the second current passing node of the first transistor for generating a two state output signal.

7. The electronic circuit of claim 1, further comprising:
a third magnetoresistance element having first and second terminals;
a third transistor having a control node, and first current passing node, and a second current passing node;
a third voltage generating source having first and second nodes between which a third fixed voltage is generated, wherein the first terminal of the third magnetoresistance element is coupled to the first current passing node of the third transistor, wherein the first node of the third voltage generating source is coupled to the control node of the third transistor and the second node of the third voltage generating source is coupled to the second terminal of the third magnetoresistance element, wherein the electronic circuit is operable to generate a third current signal at the second current passing node of the third transistor related to a resistance value of the third magnetoresistance element, wherein the electronic circuit further comprises:
a fourth magnetoresistance element having first and second terminals;
a fourth transistor having a control node, a first current passing node, and a second current passing node;
a fourth voltage generating source having first and second nodes between which a fourth fixed voltage is generated; and
a second load coupled to the second current passing node of the third transistor, wherein the second current passing node of the third transistor is coupled to the second current passing node of the fourth transistor, wherein the first terminal of the fourth magnetoresistance element is coupled to the first current passing node of the fourth transistor, wherein the first node of the fourth voltage generating source is coupled to the control node of the fourth transistor and the second node of the fourth voltage generating source is coupled to the second terminal of the fourth magnetoresistance element, wherein the electronic circuit is operable to generate a fourth current signal at the second current passing node of the fourth transistor related to a resistance value of the fourth magnetoresistance element, wherein a current passing through the second load is equal to a difference between the third current signal and the fourth current signal.

8. The electronic circuit of claim 7, wherein the first voltage generating source and the third voltage generating source are a same first common voltage generating source.

9. The electronic circuit of claim 8, wherein the same first common voltage generating source comprises a reference leg of a current mirror circuit.

10. The electronic circuit of claim 8, wherein the second voltage generating source and the fourth voltage generating source are a same second common voltage generating source.

11. The electronic circuit of claim 10, wherein the same first common voltage generating source comprises a reference leg of a current mirror circuit and wherein the same second common voltage generating source comprises a common mode voltage detector circuit coupled to the first and second loads and configured to generate the first and third voltages as the same common mode voltage related to a common mode voltage between the first and second loads.

12. The electronic circuit of claim 7, wherein the second voltage generating source and the fourth voltage generating source are a same common voltage generating source.

13. The electronic circuit of claim 12, wherein the same common voltage generating source comprises a common mode voltage detector circuit coupled to the first and second loads and configured to generate the first and third voltages as the same common mode voltage related to a common mode voltage between the first and second loads.

14. A magnetic field sensor coupled to receive a power supply voltage, comprising:
a substrate; and
an electronic circuit disposed upon the substrate, the electronic circuit comprising:
a first magnetoresistance element having first and second terminals;
a first transistor having a control node, and first current passing node, and a second current passing node;
a first voltage generating source having first and second nodes between which a first fixed voltage is generated, wherein the first terminal of the first magnetoresistance element is coupled to the first current passing node of the first transistor, wherein the first node of the first voltage generating source is coupled to the control node of the first transistor and the second node of the first voltage generating source is coupled to the second terminal of the first magnetoresistance element, wherein the electronic circuit is operable to generate a first current signal at the second current passing node of the first transistor related to a resistance value of the first magnetoresistance element, wherein the electronic circuit further comprises:
a second magnetoresistance element having first and second terminals;
a second transistor having a control node, a first current passing node, and a second current passing node; and
a second voltage generating source having first and second nodes between which a second fixed voltage is generated;
a load coupled to the second current passing node of the first transistor, wherein the second current passing node of the first transistor is coupled to the second current passing node of the second transistor, wherein the first terminal of the second magnetoresistance element is coupled to the first current passing node of the second transistor, wherein the first node of the second voltage generating source is coupled to the control node of the second transistor and the second node of the second voltage generating source is coupled to the second terminal of the second magnetoresistance element, wherein the electronic circuit is operable to generate a second current signal at the second current passing node of the second transistor related to a resistance value of the second magnetoresistance element, wherein a current passing through the load is equal to a difference between the first current signal and the second current signal, wherein the electronic circuit further comprises:
a third magnetoresistance element having first and second terminals;
a third transistor having a control node, and first current passing node, and a second current passing node; and
a third voltage generating source having first and second nodes between which a third fixed voltage is generated, wherein the first terminal of the third magnetoresistance element is coupled to the first current passing node of the third transistor, wherein the first node of the third voltage generating source is coupled to the control node of the third transistor and the second node of the third voltage generating source is coupled to the second terminal of the third magnetoresistance element, wherein the electronic circuit is operable to generate a third current signal at the second current passing node of the third transistor related to a resistance value of the third magnetoresistance element, wherein the electronic circuit further comprises:
a fourth magnetoresistance element having first and second terminals;
a fourth transistor having a control node, a first current passing node, and a second current passing node;
a fourth voltage generating source having first and second nodes between which a fourth fixed voltage is generated;

a second load coupled to the second current passing node of the third transistor, wherein the second current passing node of the third transistor is coupled to the second current passing node of the fourth transistor, wherein the first terminal of the fourth magnetoresistance element is coupled to the first current passing node of the fourth transistor, wherein the first node of the fourth voltage generating source is coupled to the control node of the fourth transistor and the second node of the fourth voltage generating source is coupled to the second terminal of the fourth magnetoresistance element, wherein the electronic circuit is operable to generate a fourth current signal at the second current passing node of the fourth transistor related to a resistance value of the fourth magnetoresistance element, wherein a current passing through the second load is equal to a difference between the third current signal and the fourth current signal;
a fifth magnetoresistance element having first and second terminals;
a fifth transistor having a control node, and first current passing node, and a second current passing node;
a fifth voltage source having first and second nodes between which a fifth fixed voltage is generated, wherein the first terminal of the fifth magnetoresistance element is coupled to the first current passing node of the fifth transistor, wherein the first node of the fifth voltage generating source is coupled to the control node of the fifth transistor and the second node of the fifth voltage generating source is coupled to the second terminal of the fifth magnetoresistance element, wherein the electronic circuit is operable to generate a first current signal at the second current passing node of the fifth transistor related to a resistance value of the fifth magnetoresistance element, wherein the electronic circuit further comprises:
a sixth magnetoresistance element having first and second terminals;
a sixth transistor having a control node, an first current passing node, and a second current passing node; and
a sixth voltage generating source having first and second nodes between which a sixth fixed voltage is generated;
a load coupled to the second current passing node of the fifth transistor, wherein the second current passing node of the fifth transistor is coupled to the second current passing node of the sixth transistor, wherein the first terminal of the sixth magnetoresistance element is coupled to the first current passing node of the sixth transistor, wherein the first node of the sixth voltage generating source is coupled to the control node of the sixth transistor and the second node of the sixth voltage generating source is coupled to the second terminal of the sixth magnetoresistance element, wherein the electronic circuit is operable to generate a second current signal at the second current passing node of the sixth transistor related to a resistance value of the sixth magnetoresistance element, wherein a current passing through the load is equal to a difference between the first current signal and the second current signal, wherein the electronic circuit further comprises:
a seventh magnetoresistance element having first and second terminals;
a seventh transistor having a control node, and first current passing node, and a second current passing node; and
a seventh voltage generating source having first and second nodes between which a seventh fixed voltage is generated, wherein the first terminal of the seventh magnetoresistance element is coupled to the first current passing node of the seventh transistor, wherein the first node of the seventh voltage generating source is coupled to the control node of the seventh transistor and the second node of the seventh voltage generating source is coupled to the second terminal of the seventh magnetoresistance element, wherein the electronic circuit is operable to generate a third current signal at the second current passing node of the seventh transistor related to a resistance value of the seventh magnetoresistance element, wherein the electronic circuit further comprises:
an eighth magnetoresistance element having first and second terminals;
an eighth transistor having a control node, a first current passing node, and a second current passing node;
an eighth voltage source having first and second nodes between which an eighth fixed voltage is generated; and
a second load coupled to the second current passing node of the seventh transistor, wherein the second current passing node of the seventh transistor is coupled to the second current passing node of the eighth transistor, wherein the first terminal of the eighth magnetoresistance element is coupled to the first current passing node of the eighth transistor, wherein the first node of the eighth voltage generating source is coupled to the control node of the eighth transistor and the second node of the eighth voltage generating source is coupled to the second terminal of the eighth magnetoresistance element, wherein the electronic circuit is operable to generate a fourth current signal at the second current passing node of the eighth transistor related to a resistance value of the eighth magnetoresistance element, wherein a current passing through the second load is equal to a difference between the third current signal and the fourth current signal.

15. The magnetic field sensor of claim 14, wherein the first voltage generating source and the third voltage generating source are a same first common voltage generating source.

16. The magnetic field sensor of claim 15, wherein the same first common voltage generating source comprises a reference leg of a current mirror circuit.

17. The magnetic field sensor of claim 15, wherein the second voltage generating source and the fourth voltage generating source are a same second common voltage generating source.

18. The magnetic field sensor of claim 17, wherein the same first common voltage generating source comprises a reference leg of a current mirror circuit and wherein the same second common voltage generating source comprises a common mode voltage detector circuit coupled to the first and second loads and configured to generate the first and third voltages as the same common mode voltage related to a common mode voltage between the first and second loads.

19. The magnetic field sensor of claim 14, wherein the second voltage generating source and the fourth voltage generating source are a same common voltage generating source.

20. The magnetic field sensor of claim 19, wherein the same common voltage generating source comprises a common mode voltage detector circuit coupled to the first and second loads and configured to generate the first and third voltages as the same common mode voltage related to a common mode voltage between the first and second loads.

21. The magnetic field sensor of claim 14, wherein the first voltage generating source, the third voltage generating source, the fifth voltage generating source, and the seventh voltage generating source are a same first common voltage generating source, the second voltage generating source and the fourth voltage generating source are a same second common voltage generating source, and the sixth voltage generating source and the eighth voltage generating source are a same third common voltage generating source.