Abstract:
A single die MR array composed of a plurality of MR elements, wherein each MR element is composed of a number of serially connected MR segments. The MR elements are arranged and configured so as to produce a variety of MR array geometries. In one form, an MR array is formed to provide angular sensing schemes wherein angular measurement redundancy is incorporated therein. In a second form, an MR array is formed to provide angular sensing schemes wherein angular measurement redundancy and reference redundancy are incorporated therein.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to magnetoresistor arrays used for magnetic position sensors.  
         BACKGROUND OF THE INVENTION  
         [0002]    The use of magnetoresistors (MRs) and Hall devices as position sensors is well known in the art. For example, a magnetically biased differential MR sensor may be used to sense angular position of a rotating toothed wheel, as for example exemplified by U.S. Pat. Nos. 4,835,467, 5,731,702, and 5,754,042.  
           [0003]    In such applications, the magnetoresistor (MR) is biased with a magnetic field and electrically excited, typically, with a constant current source or a constant voltage source. A magnetic (i.e., ferromagnetic) object moving relative and in close proximity to the MR, such as a toothed wheel, produces a varying magnetic flux density through the MR, which, in turn, varies the resistance of the MR. The MR will have a higher magnetic flux density and a higher resistance when a tooth of the moving target wheel is adjacent to the MR than when a slot of the moving target wheel is adjacent to the MR.  
           [0004]    Increasingly more sophisticated spark timing and emission controls introduced the need for crankshaft sensors capable of providing precise position information during cranking. Various combinations of magnetoresistors and single and dual track toothed or slotted wheels (also known as encoder wheels and target wheels) have been used to obtain this information (see for example U.S. Pat. Nos. 5,570,016, 5,731,702, and 5,754,042).  
           [0005]    The shortcoming of MR devices is their temperature sensitivity. They have a negative temperature coefficient of resistance and their resistance can drop as much as 50% when heated to 180 degrees Celsius. Generally, this led to the use of MR devices in matched pairs for temperature compensation. Additionally, it is preferable to drive MR devices with current sources since, with the same available power supply, the output signal is nearly doubled in comparison with a constant voltage source.  
           [0006]    To compensate for the MR resistance drop at higher temperatures, and thus, the magnitude decrease of the output signal resulting in decreased sensitivity of the MR device, it is also desirable to make the current of the current source automatically increase with the MR temperature increase. This is shown in U.S. Pat. No. 5,404,102 in which an active feedback circuit automatically adjusts the current of the current source in response to temperature variations of the MR device. It is also known that air gap variations between the MR device and ferromagnetic materials or objects will affect the resistance of MR devices with larger air gaps producing less resistance and decreased output signals.  
           [0007]    Single element magnetic field sensors composed of, for example, an indium antimonide or indium arsenide epitaxial film strip supported on, for example, a monocrystalline elemental semiconductor substrate, are also known. The indium antimonide or indium arsenide film is, for example, either directly on the elemental semiconductor substrate or on an intermediate film that has a higher resistivity than that of silicon. A conductive contact is located at either end of the epitaxial film, and a plurality of metallic (gold) shorting bars are on, and regularly spaced along, the epitaxial film. Examples thereof are exemplified by U.S. Pat. Nos. 5,153,557, 5,184,106 and 5,491,461.  
           [0008]    Most noncontacting magnetic angle position sensors use a Hall sensor and a rotating magnetic field. Since the Hall sensor output signal is proportional to the normal component of the magnetic field, its output is a sinusoidal function of the angle of rotation. Only within a relatively small angular range is the output proportional to the angle of rotation. Depending on the required accuracy, this range may be as small as ±30 degrees with a ±1.3% full scale error and, practically, never greater than ±50 degrees with almost a ±10% full scale error. Another approach relies on varying the air gap between a Hall sensor and a magnetic target. This allows a greater angular range. However, it is an inherently error prone method due to the high degree of non linearity in the relation between the magnetic field strength and the air gap.  
           [0009]    Compound semiconductor MRs, such as those manufactured from lnSb, InAs, etc., are simply two-terminal resistors with a high magnetic sensitivity and thus, are very suitable for the construction of single die MR array geometries suitable for use as large range angular position sensors (in most cases one terminal of all the MR elements can be common).  
           [0010]    Ultimately, such MR arrays could be integrated on the same die with appropriate processing circuitry. For example, if the MR array was fabricated on a Si substrate then the processing circuitry would be also Si based. For higher operating temperatures, silicon-on-insulator (SOI) could be used. A potentially lower cost alternative to the SOl approach would be to take advantage of the fact that MRs are currently fabricated on GaAs, a high temperature semiconductor, and thus, to fabricate the integrated processing circuitry from GaAs (or related lnP) using HBT (Heterojunction Bipolar Transistor) or HEMT (High Electron Mobility Transistor) structures. This technology is now easily available and inexpensive through the explosive growth of the cellular phone industry.  
           [0011]    Accordingly, what remains needed is a compact and inexpensive die having at least one array of magnetic sensing elements and configured so as to produce a variety of array geometries suitable for specialized angular sensing schemes capable of self compensation over wide ranges of temperature and air gaps, wherein an array is defined as having three or more MR elements.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention is a compact and inexpensive single die having at least one MR array composed of a plurality of MR elements, wherein each MR element is composed of a number of serially connected MR segments. The MR elements are arranged and configured so as to produce a variety of MR array geometries suitable for specialized angular sensing schemes.  
           [0013]    The present invention is a noncontacting large angular range (approaching 180 degrees) angular magnetoresistor position sensor array incorporated on a die capable of self compensation over wide temperature ranges and air gaps.  
           [0014]    According to a first aspect of the present invention, an MR array is formed of a plurality of MR elements, wherein each MR element is composed of a plurality of uniformly arranged, serially connected MR segments. The arrangement is such as to provide an MR array suitable for angular sensing schemes wherein angular measurement redundancy is incorporated therein.  
           [0015]    According to a second aspect of the present invention, an MR array is formed of a plurality of MR elements, wherein each MR element is composed of a plurality of uniformly arranged, serially connected MR segments. The arrangement is such as to provide an MR array suitable for angular sensing schemes wherein angular measurement redundancy and reference redundancy are incorporated therein.  
           [0016]    According to a preferred method of fabrication, an indium antimonide epitaxial film is formed, then masked and etched to thereby provide epitaxial mesas characterizing the MR elements. Shorting bars, preferably of gold, are thereupon deposited, wherein the epitaxial mesa not covered by the shorting bars provides the MR segments. The techniques for fabricating epitaxial mesas with shorting bars are elaborated in U.S. Pat. No. 5,153,557, issued Oct. 6, 1992, U.S. Pat. No. 5,184,106, issued Feb. 2, 1993 and U.S. Pat. No. 5,491,461, issued Feb. 13, 1996, each of which being hereby incorporated herein by reference.  
           [0017]    Accordingly, it is an object of the present invention to provide an MR die comprising at least one MR array according to the first and second aspects of the present invention which is capable of detecting angular movement of a ferromagnetic or magnetic target in relation to the MR array.  
           [0018]    This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1A is a schematic representation of a single die MR array according to a first aspect of the present invention.  
         [0020]    [0020]FIG. 1B is a detailed depiction of an MR element of the single die MR array of FIG. 1A.  
         [0021]    [0021]FIG. 1C is a detail view of a portion of an MR element of FIG. 1A, seen by way of example at circle  1 C of FIG. 1B.  
         [0022]    [0022]FIG. 2 is a schematic representation of a single die MR array according to the second aspect of the present invention.  
         [0023]    [0023]FIG. 3A depicts a first example of the preferred environment of use of the present invention.  
         [0024]    [0024]FIG. 3B is a view seen along line  3 B- 3 B of FIG. 3A.  
         [0025]    [0025]FIG. 4A depicts a second example of the preferred environment of use of the present invention.  
         [0026]    [0026]FIG. 4B is a view seen along line  4 B- 4 B of FIG. 4A.  
         [0027]    [0027]FIG. 5A is a schematic representation of a single die MR array according to the first aspect of the present invention depicting an angular displacement of the first or second example of the preferred environment of use of the present invention according to FIG. 3A or FIG. 4A.  
         [0028]    [0028]FIG. 5B is a schematic representation of a single die MR array according to the second aspect of the present invention depicting an angular displacement of the first or second example of the preferred environment of use of the present invention according to FIG. 3A or FIG. 4A.  
         [0029]    [0029]FIG. 6 shows a first example of an analog circuit implementing the first aspect of the present invention.  
         [0030]    [0030]FIG. 7 shows a second example of an analog circuit implementing the first aspect of the present invention.  
         [0031]    [0031]FIG. 8 shows an example of a circuit employing a digital processor implementing the first aspect of the present invention.  
         [0032]    [0032]FIG. 9 shows a first example of an analog circuit implementing the second aspect of the present invention.  
         [0033]    [0033]FIG. 10 shows a second example of an analog circuit implementing the second aspect of the present invention.  
         [0034]    [0034]FIG. 11 shows an example of a circuit employing a digital processor implementing the second aspect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]    [0035]FIG. 1A is a schematic representation of an MR die  10  on which an MR array  12  according to a first aspect of the present invention is depicted. The MR array  12  is comprised of four magnetoresistor elements, MR 1 , MR 21 , MR 22 , and MR 3  wherein MR 1  spans the angle A 1 , MR 21  spans the angle A 21 , MR 22  spans the angle A 22 , and MR 3  spans the angle A 3 . The shape of the MR array  12  is, preferably, circular, as depicted in FIG. 1A, but may be otherwise. MR 21  and MR 22  are the angle measuring elements whereas MR 1  and MR 3  are reference elements. MR 22  is intended to provide a redundant angle measurement as required by many throttle position sensor specifications. If redundancy is not required, MR 22  may be absent. Generally, and as shown in FIG. 1A, angles A 1  and A 3  are equal and angles A 21  and A 22  are equal, but this is not a fundamental requirement.  
         [0036]    [0036]FIG. 1B and 1C show a portion of the MR die  10 , in particular MR element MR 1  of the MR array  12 . Structurally, MR element MR 1  consists of a plurality of MR segments  22  demarcated by uniform shorting bars  24  which are preferably gold. The MR segments  22  are each uniformly matched to the others (that is, the MR segments are identical). By way of preferred example, each MR segment  22  is composed of indium antimonide (InSb) epitaxial film mesas. Each epitaxial film mesa is provided, by way of preferred example, by forming an indium antimonide epitaxial film, then masking and etching it. The shorting bars  24 , which demarcate the MR segments  22 , are composed of gold bars deposited upon the MR segments. Bonding pads (contacts or terminals)  26 , preferably also of gold, are provided at the ends of each MR element. Also, connecting strips  28  are also preferably of gold. The other MR elements of the MR array  12  are similarly constructed of MR segments demarcated by shorting bars, bonding pads and connecting strips.  
         [0037]    [0037]FIG. 2 is a schematic representation of an MR die  100  on which an MR array  120  according to a second aspect of the present invention is depicted. The MR array  120  is comprised of six magnetoresistor elements, MR 11 , MR 12 , MR 21 ′, MR 22 ′, MR 31 , and MR 32  wherein MR 11  spans the angle A 11 , MR 12  spans the angle A 12 , MR 21 ′ spans the angle A 21 ′, MR 22 ′ spans the angle A 22 ′, MR 31  spans the angle A 31 , and MR 32  spans the angle A 32 . The shape of the MR array  120  is, preferably, circular, as depicted in FIG. 2, but may be otherwise. MR 21 ′ and MR 22 ′ are the angle measuring elements whereas MR 11 , MR 12 , MR 31 , and MR 32  are reference elements. MR 22 ′ is intended to provide a redundant angle measurement as required by many throttle position sensor specifications and MR 12  and MR 32  provide redundant reference elements. Generally, and as shown in FIG. 2, angles A 11 , A 12 , A 31 , and A 32  are equal and angles A 21  ′ and A 22 ′ are equal, but this is not a fundamental requirement.  
         [0038]    The MR array  120  is generally fabricated according to the method previously described for the MR array  12 ′ of FIG. 1B, including the respective conductive contact at each opposing end of each MR element.  
         [0039]    [0039]FIGS. 3A and 3B depict a first example of the preferred environment of use of the present invention. The single MR sensor  30 , preferably stationary, employs an MR die  10  of FIG. 1A or an MR die  100  of FIG. 2 which is biased by a permanent magnet  32 , wherein the MR sensor is coaxially aligned with the axis  36  of a magnetic (i.e. ferromagnetic) shaft  34  such that the surface of the MR die lies in a plane perpendicular to the axis of the magnetic shaft. The magnetic shaft  34  can rotate clockwise  38  or counterclockwise  40  about the axis  36  of the shaft. The end  42  of the shaft  34  adjacent the sensor  30  has a notch  44  such that a tooth  46  and slot  48  are formed, thereby creating a rotating tooth and slot such that the die  10  or  100  experiences a maximum magnetic flux density on those portions thereof adjacent to the tooth and a minimum magnetic flux density on those portions thereof adjacent to the slot.  
         [0040]    [0040]FIGS. 4A and 4B depict a second example of the preferred environment of use of the present invention. The single MR sensor  50 , preferably stationary, is comprised of an MR die  10  of FIG. 1A or an MR die  100  of FIG. 2, a magnetic (i.e. ferromagnetic) layer  52 , and a circuit board  54 . The circuit board  54  may be located elsewhere, if desired. The layer  52 , preferably less than one millimeter thick, increases the sensitivity of the sensor to magnetic fields and is optional. The sensor  50  is coaxially aligned with the axis  56  of a nonmagnetic shaft  58  such that the surface of the MR die  10  or  100  lies in a plane perpendicular to the axis of the shaft. The shaft  58  can rotate clockwise  60  or counterclockwise  62  about the axis  56  of the shaft. On the end  64  of the shaft  58  adjacent the sensor  50  is attached a magnet assembly  66  which rotates with the shaft and is coaxially aligned with the shaft  58 . The magnet assembly  66  has a permanent magnet  68 , preferably in the form of a semicircular disk, such that one half of the area of the end  64  of the shaft  58  is covered, thereby forming a tooth whereas the other half of the area of the end of the shaft is covered with a nonmagnetic material  70  thereby forming a slot by which a rotating tooth and slot is created such that the die  10  or  100  experiences a maximum magnetic flux density on those portions thereof adjacent to the tooth and a minimum magnetic flux density on those portions thereof adjacent to the slot.  
         [0041]    [0041]FIG. 5A is a schematic representation of a single die MR array  10  according to the first aspect of the present invention of the first or second example of the preferred environment of use of the present invention according to FIG. 3A or  4 A. The shaded portion  72  of the overlay  74  represents the tooth  46  or  68 , respectively, whereas the unshaded portion  78  represents the slot  48  or  70 . FIG. 5A depicts, in this case, a clockwise rotation  76  of the tooth  46  or  68  through an angular displacement A from an initial position of zero degrees wherein at the initial position of zero degrees, MR 21  is totally under the slot  48  or  70  and MR 22  is totally under the tooth. The angular displacement A is limited during clockwise rotation  76  such that the tooth  46  or  68  always covers MR 1  and the slot  48  or  70  always covers MR 3  ensuring that MR 1  always experiences a maximum magnetic flux density and MR 3  always experiences a minimum magnetic flux density whereas the coverage of MR 21  or MR 22  varies from being totally under the slot to being totally under the tooth by which the resistance of MR 21 , R 21 , and MR 22 , R 22 , varies, preferably linearly, from a minimum, R MIN , to a maximum, R MAX . MR 1  is designed such that its resistance, R 1 , is a fraction p of R MAX  when exposed to the maximum magnetic flux density and MR 3  is designed such that its resistance, R 3 , is a fraction q of R MIN  when exposed to the minimum magnetic flux density where p and q have, preferably, values between greater than zero and one. Hence, R 1 /p=R MAX  and R 3 /q=R MIN . Values for p and q greater than one are permissible but there does not appear to be any benefit in doing so.  
         [0042]    At an angular displacement A, 
           R   21 =( A/A   21 )* R   1   /p +(1−( A/A   21 ))* R   3   /q   (1) 
         and 
           R   22 =(1−( A/A   22 )* R   1   /p+ ( A/A   22 ))* R   3   /q   (2) 
         from which, 
           A=A   21 ( R   21   −R   3   /q )/( R   1   /p−R   3   /q )  (3) 
         and 
           A=A   22 ( R   1   /p−R   22 )/( R   1   /p−R   3   /q )  (4) 
         [0043]    thereby enabling the angle A to be determined given p, q, R 1 , R 21 , R 3 , and A 21  or, redundantly, given p, q, R 1 , R 22 , R 3 , and A 22 . Preferably, p, q, R 1 , R 3 , A 21 , and A 22  are known from the die characteristics and R 21 , and R 22  are variables to be determined from measurements.  
         [0044]    [0044]FIG. 5B is a schematic representation of a single die MR array  100  according to the second aspect of the present invention depicting an angular displacement of the first or second example of the preferred environment of use of the present invention of FIG. 3A or FIG. 4A. The shaded portion  72 ′ of the overlay  74 ′ represents the tooth  46  or  68  of FIG. 3 or FIG. 4, respectively, whereas the unshaded portion  78 ′ represents the slot  48  or  70 . FIG. 5B depicts, in this case, a clockwise rotation  76 ′ of the tooth  46  or  68  through an angular displacement A′ from an initial position of zero degrees wherein at the initial position of zero degrees, MR 21 ′ is totally under the slot  48  or  70  and MR 22 ′ is totally under the tooth. The angular displacement A′ is limited during clockwise rotation  76 ′ such that the tooth  46  or  68  always covers MR 11  and MR 12  and the slot  48  or  70  always covers MR 31  and MR 32  ensuring that MR 11  and MR 12  always experience a maximum magnetic flux density and MR 31  and MR 32  always experience a minimum magnetic flux density whereas the coverage of MR 21 ′ or MR 22 ′ varies from being totally under the slot to being totally under the tooth by which the resistance of MR 21 ′, R′ 21 , and MR 22 ′, R′ 22 , varies, preferably linearly, from a minimum, R′ MIN , to a maximum, R′ MAX . MR 11  and MR 12  are designed such that their resistances, R 11 , and R 12 , are a fraction p′ of R′ MAX  when exposed to the maximum magnetic flux density and MR 31  and MR 32  are designed such that their resistances, R 31 , and R 32 , are a fraction q′ of R′ MIN  when exposed to the minimum magnetic flux density where p′ and q′ have, preferably, values between greater than zero and one. Hence, R 11 /p′=R 12 /p′=R′ MAX  and R 31 /q′=R 32 /q′=R′ MIN . Values for p′ and q′ greater than one are permissible but there does not appear to be any benefit in doing so.  
         [0045]    At an angular displacement A′, 
           R′   21 =( A′/A   2 l′)* R   12   /p′+ (1−( A′/A   21 ′))* R   32   /q′   (5) 
           R′   21 =( A′/A   2 l′)* R   11   /p′+ (1−( A′/A   21 ′))* R   31   /q′   (6) 
           R′   22 =(1−( A′/A   22 ′)* R   12   /p′+ ( A′/A   22 ′))* R   32   /q′   (7) 
         and 
           R′   22 =(1−( A′/A   22 ′)* R   11   /p′+ ( A′/A   22 ′))* R   31   /q′   (8) 
         from which, 
           A′=A   21 ′( R′   21   −R   32   /q′ )/( R   12   /p′−R   32   /q′ )  (9) 
           A′=A   21 ′( R′   21   −R   31   /q′ )/( R   11   /p′−R   31   /q′ )  (10) 
           A′=A   22 ′( R′   12   /p′−R′   22 )/( R   12   /p′−R   32   /q′ )  (11) 
         and 
           A′=A   22 ′( R′   11   /p′−R′   22 )/( R   11   /p′−R   31   /q′ )  (12) 
         [0046]    thereby enabling the angle A′ to be determined with full redundancy given p′, q′, R 11 , R 12 , R′ 21 , R′ 22 , R 31 , R 32 , A 21 ′ and A 22 ′. Preferably, p′, q′, R 11 , R 12 , R 31 , R 32 , A 21 ′, and A 22 ′ are known from the die characteristics and R′ 21  and R′ 22  are variables to be determined from measurements.  
         [0047]    [0047]FIG. 6 shows a first example of an analog circuit  600  implementing the first aspect of the present invention. V S  is the power supply voltage and i 1 , i 1 , i 3  and i 4  are matched constant current sources such that i 1 =i 2 =i 3 =i 4 . V 1 , V 21 , V 22 , and V 3  are given by: 
           V   1   =i   1   *R   1   (13) 
           V   21   =i   2   *R   21   (14) 
           V   22   =i   3   *R   22   (15) 
         and 
           V   3   =i   4   *R   3   (16) 
         [0048]    Amplifier  602  (i.e. an OP-AMP) has a preset gain of (1/p) whereas amplifier  604  (i.e. an OP-AMP) has a preset gain of (1/q). The output of differential amplifiers  606 ,  608 , and  610  are, respectively, (V 1 /p−V 22 ), (V 1 /p−V 3 /q), and (V 21 −V 3 /q). Single quadrant analog divider  612  has a preset gain of A 21  whereas single quadrant analog divider  614  has a preset gain of A 22  whereby, since the current sources are matched, 
           V   612   =A   21 ( V   21   −V   3   /q )/( V   1   /p−V   3   /q )= A   21 ( R   21   −R   3   /q )/( R   1   /p−R   3   /q )= A   (17) 
         and 
           V   614   =A   22 ( V   1   /p−V   22 )/( V   1   /p−V   3   /q )= A   22 ( R   1   /p−R   22 )/( R   1   /p−R   3   /q )= A   (18) 
         [0049]    thereby determining the angle of rotation A. Although not explicitly shown, it is understood that all components have appropriate power supply connections as needed and required, including ground.  
         [0050]    [0050]FIG. 7 shows a second example of an analog circuit  700  implementing the first aspect of the present invention. V′ S  is the power supply voltage and i′ 2  and i′ 3  are matched constant current sources such that i′ 2 =i′ 3 . Constant current sources i′ 1 , and i′ 4  are weighted such that i′ 1 =i′ 2 /p and i′ 4 =i′ 2 /q. V′ 1 , V′ 21 , V′ 22 , and V′ 3  are given by: 
           V′   1   =i′   2   *R   1   /p   (19) 
           V′   21   =i′   2   *R   21   (20) 
           V′   22   =i′   3   *R   22   (21) 
         and 
           V′   3   =i′   2   *R   3   /q .  (22) 
         [0051]    The output of differential amplifiers  702 ,  704 , and  706  are, respectively, (V 1 −V 22 ), (V 1 −V 3 ), and (V 21 −V 3 ). Single quadrant analog divider  708  has a preset gain of A 21  whereas single quadrant analog divider  710  has a preset gain of A 22  whereby, 
           V   708   =A   21 ( V   21   −V   3 )/( V   1   −V   3 )= A   21 ( R   21   −R   3   /q )/( R   1   /p−R   3   /q )= A   (23) 
         and 
           V   710   =A   22 ( V   1   −V   22 )/( V   1   −V   3 )= A   22 ( R   1   /p−R   22 )/( R   1   /p−R   3   /q )= A   (24) 
         [0052]    thereby determining the angle of rotation A. Although not explicitly shown, it is understood that all components have appropriate power supply connections as needed and required, including ground.  
         [0053]    [0053]FIG. 8 shows an example of a circuit  800  employing a digital processor  802  (i.e. digital signal processor, microcontroller, microprocessor, etc.) implementing the first aspect of the present invention. V″ S  is the value of the supply voltage and is implicitly known to the digital processor  802 , for example, as an input, or stored in the digital processor&#39;s memory. The parameters p, q, A 21 , A 22 , R MAX , and R MIN  are, preferably, stored in memory also. The values of V″,, V″ 2 , and V″ 3  are input to the digital processor  802  and can be expressed as: 
           V″   1   =V″   S *( R   3   +R   1   +R   22 )/( R   21   +R   3   +R   1   +R   22 )  (25) 
           V″   2   =V″   S *( R   1   +R   22 )/( R   21   +R   3   +R   1   +R   22 )  (26) 
         and 
           V″   3   =V″   S   *R   22 /( R   21   +R   3   +R   1   +R   22 ).  (27) 
         [0054]    The value of the output voltages V D1  and V D2  are computed by the digital processor  802  and can be expressed as: 
           V   D1   =A   21 *{[( V″   S   −V″   1 )−( V″   1   −V″   2 )/ q ]/[( V″   2   −V″   3 )/ p −( V″   1   −V″   2 )/ q]}   (29) 
         and 
           V   D2   =A   22 *{[( V″   2   −V″   3 )/ p−V″   3 ]/[( V″   2   −V″   3 )/ p −( V″   1   −V″   2 )/ q]}   (30) 
         [0055]    which, using equations 25, 26, and 27, reduce to: 
           V   D1   =A   21 *(R 21   −R   3   /q )/( R   1   /p−R   3   /q )= A   (31) 
         and 
           V   D2   =A   22 ( R   1   /p−R   22 )/( R   1   /p−R   3   /q )= A   (32) 
         [0056]    thereby determining the angle of rotation A. The implementation of the above procedure for the digital processor  802  is well known in the art.  
         [0057]    [0057]FIG. 9 shows a first example of an analog circuit  900  implementing the second aspect of the present invention. V SS  is the power supply voltage and i 11 , i 22 , i 33 , i 44 , i 55 , and i 66  are matched constant current sources such that i 11 =i 22 =i 33 =i 44 =i 55 =i 66 . V 11 , V 12 , V″ 21 , V″ 22 , V 31  and V 32  are given by: 
           V   11   =i   11   *R   11   (33) 
           V″   21   =i   22   *R′   21   (34) 
           V   31   =i   33   *R   31   (35) 
           V   32   =i   44   *R   32   (36) 
           V″   22   =i   55   *R′   22   (33) 
         and 
           V   12   =i   66   *R   12 .  (33) 
         [0058]    Amplifiers  902  and  904  (i.e. OP-AMPs) have a preset gain of (1/p′) whereas amplifiers  906  and  908  (i.e. OP-AMPs) have a preset gain of (1/q′). The output of differential amplifiers  910 ,  912 ,  914 , and  916  are, respectively, (V 11 /p′−V 31 /q′), (V 21 −V 31 /q′), (V 12 /p′−V 32 /q′), and (V 12 /p′−V″ 22 ). Single quadrant analog divider  918  has a preset gain of A 21 ′ whereas single quadrant analog divider  920  has a preset gain of A 22 ′, whereby, since the current sources are matched, 
           V   918   =A   21 ( V″   21   −V   31   /q′ )/( V   11   /p′−V   31   /q′ )= A   21 ′( R′   21   −R   31   /q′ )/( R   11   /p′−R   31   /q′ ) A′   (39) 
         and 
           V   920   =A   22 ′( V   12   /p′−V″   22 )/( V   12   /p′−V   32   /q′ )= A   22 ′( R   12   /p′−R′   22 )/( R   12   /p′−R   32   /q′ )= A′   (40) 
         [0059]    thereby determining the angle of rotation A′. Although not explicitly shown, it is understood that all components have appropriate power supply connections as needed and required, including ground.  
         [0060]    [0060]FIG. 10 shows a second example of an analog circuit  1000  implementing the second aspect of the present invention. V′ SS  is the power supply voltage and i′ 22  and i′ 55  are matched constant current sources such that i′ 22 =i′ 55 . Constant current sources i′ 11 , i′ 33 =i′ 44 , and i′ 66  are weighted such that i′ 11 =i′ 66 =i′ 22 /p′ and i′ 33 =i′ 44 =i′ 22 /q′. V′ 11 , V′ 12 , V′″ 21 , V′″ 22 , V′ 31 , and V′ 31 , and V′ 32  are given by: 
           V′   11   =i′   22   *R   11   /p′   (41) 
           V′″   21   =i′   22   *R′   21   (42) 
           V′   31   =i′   22   *R   31   /q′   (43) 
           V′   12   =i′   22   *R   32   /q′   (44) 
           V′″   22   =i′   22   *R′   22   (45) 
         and 
           V′   12   =i′   22   *R   12   /p′ .  (46) 
         [0061]    The output of differential amplifiers  1002 ,  1004 ,  1006 , and  1008  are, respectively, (V′ 11 −V′ 31 ), (V′″ 21 −V′ 31 ), (V′ 12 −V′ 32 ), and (V′ 12 −V′″ 22 ). Single quadrant analog divider  1010  has a preset gain of A 21 ′ whereas single quadrant analog divider  1012  has a preset gain of A 22 ′ whereby, 
           V   1010   =A   21 ′( V′″   21   −V′   31 )/( V′   11   −V′   31 )= A   21 ′( R′   21   −R   31   /q′ )/( R   11   /p′−R   31   /q′ )= A′   (47) 
         and 
           V   1012   =A   22 ′( V′   12   −V′″   22 )/( V′   12   −V′   32 )= A   22 ′( R   12   /p′−R′   22 )/( R   12   /p′−R   32   /q′ )= A′   (48) 
         [0062]    thereby determining the angle of rotation A′. Although not explicitly shown, it is understood that all components have appropriate power supply connections as needed and required, including ground.  
         [0063]    [0063]FIG. 11 shows an example of a circuit  1100  employing a digital processor  1102  (i.e. digital signal processor, microcontroller, microprocessor, etc.) implementing the second aspect of the present invention. V″ SS  is the value of the supply voltage and is implicitly known to the digital processor  1102 , for example, as an input or stored in the digital processor&#39;s memory. The parameters p′, q′, A 21 ′, A 22 ′, R′ MAX , and R′ MIN  are, preferably, stored in memory also. The values of V A , V B , V C , and V D  are input to the digital processor  1102  and can be expressed as: 
           V   A   =V″   SS *( R′   22   +R   32 )/( R   12   +R′   22   +R   32 )  (49) 
           V   B   =V″   SS   *R   32 /( R   12   +R′   22   +R   32 )  (50) 
           V   C   =V″   SS *( R′   21   +R   31 )/( R   11   +R′   21   +R   31 )  (51) 
         and 
           V   D   =V″   SS   *R   31 /( R   11   +R′   21   +R   31 )  (52) 
         [0064]    The value of the output voltages V′ D1  and V′ D2  are computed by the digital processor  1102  and can be expressed as: 
           V′   D1   =A   21 ′*{[( V   C   −V   D )− V   D   /q′]/[ ( V″   SS   −V   C )/ p′−V   D   /q]}   (53) 
         and 
           V′   D2   =A   22 ′*{[( V″   SS   −V   A ) /p′−V   B   /q′]/[ ( V″   SS   −V   A )/ p′−V   B   /q′]}   (55) 
         [0065]    which, using equations 49, 50, 51, and 52 reduce to: 
           V′   D1   =A   21 ′( R′   21   −R   31   /q′ )/( R   11   /p′−R   31   /q′ )= A′   (55) 
         and 
           V′   D2   =A   22 ′( R   12   /p′−R′   22 )/( R   12   /p′−R   32   /q′ )= A′   (56) 
         [0066]    thereby determining the angle of rotation A′. The implementation of the above procedure for the digital processor  1102  is well known in the art.  
         [0067]    To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.