Magnetometer having a dynamically adjustable bias setting and electronic vehicle compass incorporating the same

• US 6,653,831 B2
• Filed: 11/20/2001
• Issued: 11/25/2003
• Est. Priority Date: 11/20/2001
• Status: Active Grant

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Friend, Timothy R., Bechtel, Jon H.
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US09/989,559
• Publication Number:
  US 20030094942A1
• Time in Patent Office: 735 Days
• Field of Search: 324/244, 324/247, 324/249, 324/253, 324/258, 324/260, 333/61
• US Class Current: 324/244
• CPC Class Codes: G01C 17/30 Earth-inductor compasses
• CPC Class Codes: G01R 33/0206 Three-component magnetometers
• CPC Class Codes: G01R 33/028 Electrodynamic magnetometers

Abstract

According to some embodiments of the present invention, a magnetometer includes at least one sensor for sensing a magnetic field component, a biasing circuit, and a processor. The sensor generates an output signal having a signal characteristic that varies in response to the sensed magnetic field component and in response to an applied bias. The biasing circuit dynamically biases the sensor in response to a bias setting signal. The processor is coupled to receive the output signal from the sensor and coupled to the biasing circuit. The processor is operable to generate the bias setting signal and thereby control the biasing circuit to dynamically bias the sensor such that the signal characteristic of the output signal is maintained in a target range. The processor determines the magnetic field component sensed by the sensor as a function of the bias setting applied to the sensor.

Claims

1. A magnetometer comprising:

a sensor for sensing a magnetic field, said sensor generating an output signal having a signal characteristic that varies in response to the sensed magnetic field and in response to an applied bias;

a biasing circuit for dynamically biasing said sensor in response to a bias setting signal; and

a processor coupled to receive the output signal from said sensor and coupled to said biasing circuit, said processor operable to generate the bias setting signal and thereby control said biasing circuit to dynamically bias said sensor such that the signal characteristic of the output signal is maintained within a relatively small target range of levels, said processor determines the magnetic field component sensed by said sensor as a function of the bias setting applied to said sensor.

2. The magnetometer of claim 1, wherein said sensor includes a core material and a winding wound about said core material, wherein the inductance of the sensor varies in response to the sensed magnetic field.

3. The magnetometer of claim 1, wherein said sensor comprises:

a sensing element having a sensor characteristic that varies in response to the magnetic field; and

an amplifier having an input for receiving a drive signal, said sensing element being coupled within a feedback loop of said amplifier, said amplifier generates the output signal, which has a signal characteristic that varies at least partially in response to variance in the sensor characteristic.

4. The magnetometer of claim 3, wherein the sensor characteristic is the inductance of the sensing element.

5. The magnetometer of claim 3, wherein said sensing element includes an inductor and a capacitor coupled in parallel with the inductor.

6. The magnetometer of claim 3 and further comprising a driver circuit for generating said drive signal, wherein said processor controls said driver circuit to vary the drive signal applied to said amplifier input.

7. The magnetometer of claim 6, wherein said processor varies the bias current of the drive signal to maintain the signal characteristic of the output signal within the target range, and wherein said processor determines the magnetic field strength based on the bias current of the drive signal.

8. The magnetometer of claim 1, wherein the signal characteristic is the phase of the output signal.

9. The magnetometer of claim 1, wherein the signal characteristic is the frequency of the output signal.

10. The magnetometer of claim 1, wherein said sensor has an inductance that varies as a function of the strength of the sensed magnetic field.

11. The magnetometer of claim 1, wherein said processor determines the magnetic field component sensed by said sensor as a function of both the bias setting applied to said sensor and the level of the output signal in the target range to enhance the resolution of the reading.

12. The magnetometer of claim 1, wherein the bias setting serves to approximately balance the field to be measured in each of two target ranges of sensor response.

13. The magnetometer of claim 1, wherein the bias setting is selected to bring the output signal of said sensor within the target range for one of two different ranges where a targeted response value may be attained.

14. The magnetometer of claim 13, wherein the bias setting is subsequently selected to bring the output signal of said sensor within a second target range corresponding to the other one of the two different ranges where a targeted response value may be attained.

15. The magnetometer of claim 1, wherein said processor measures the output signal response and determines the bias needed to achieve a target response value based upon the present bias setting and the output signal response.

16. The magnetometer of claim 1, wherein said processor determines the magnetic field component sensed by said sensor as a function of two bias settings for which at least one targeted response value may be attained.

17. The magnetometer of claim 1 and further comprising a multiple pole filter coupled to an output of said biasing circuit for filtering the bias to be applied to said sensor.

18. The magnetometer of claim 17, wherein said filter is configured to utilize a single amplifier that also supplies current to a bias determining resistor.

19. The magnetometer of claim 17, wherein said filter has a dampening factor that is greater than that of a comparable Butterworth filter.

20. The magnetometer of claim 1, and further comprising a phase discrimination circuit coupled between said sensor and said processor.

21. The magnetometer of claim 20 and further comprising a multiple pole filter coupled to an output of said phase discrimination filter.

22. The magnetometer of claim 1, wherein said sensor is a resonant sensor, and said magnetometer further comprises an excitation circuit coupled to said resonant sensor for supplying an excitation signal thereto.

23. The magnetometer of claim 22, wherein said excitation circuit limits the amplitude of the excitation signal to prevent significant saturation of the response of said resonant sensor to the excitation signal.

24. The magnetometer of claim 22 and further comprising a filter for filtering the excitation signal prior to application to said resonant sensor, said filter making the excitation signal approximately sinusoidal.

25. The magnetometer of claim 24, wherein said filter is a multiple pole filter.

26. The magnetometer of claim 22 and further comprising an amplifier for driving said resonant sensor, an output of said amplifier is coupled to an input of said excitation circuit.

27. The magnetometer of claim 22, wherein said processor determines the magnetic field component sensed by said sensor by measuring a phase shift of the output signal of said sensor relative to the phase of the excitation signal.

28. The magnetometer of claim 27, wherein the excitation signal has a frequency that is approximately equal to the resonant frequency of said resonant sensor for a nominal center point for the operation of said resonant sensor.

29. The magnetometer of claim 22, wherein said processor determines the magnetic field component sensed by said sensor by measuring the frequency of the output signal of said sensor.

30. The magnetometer of claim 29, wherein the excitation signal is nominally in phase with the output signal of said resonant sensor.

31. The magnetometer of claim 29, wherein the excitation signal has a nominally constant phase with respect to the output signal of said resonant sensor.

32. The magnetometer of claim 22 and further comprising an amplifier, wherein the excitation signal and a bias signal supplied from said biasing circuit are linearly summed by said amplifier prior to application to said resonant sensor.

33. The magnetometer of claim 22 and further comprising an amplifier, wherein said biasing circuit biases said sensor by supplying a DC bias current, said amplifier drives both the DC bias current and the excitation signal.

34. The magnetometer of claim 22, wherein said resonant sensor includes a sensing element having a core and a coil wound about said core, said biasing circuit biases said sensor by supplying a DC bias current, and wherein both the DC bias current and the excitation signal are supplied to said coil.

35. The magnetometer of claim 1, wherein said processor controls said biasing circuit to dynamically bias said sensor such that the signal characteristic of the output signal is maintained in one of two target ranges.

36. The magnetometer of claim 35, wherein said processor determines in which of the two target ranges the signal characteristic of the output signal falls based upon the sign of the slope of the plot of the bias setting versus output signal characteristic.

37. The magnetometer of claim 35, wherein the total range through which said sensor may be biased by said biasing circuit approximately spans the range required for biasing said sensor to have output signal characteristics falling within both of the two target ranges plus the range required for sensing external magnetic field intensities to be measured.

38. The magnetometer of claim 1, wherein said biasing circuit comprises a pulse-width modulated digital-to-analog converter for setting a bias current for said sensor, said digital-to-analog converter having an accuracy that is substantially greater than its incremental resolution.

39. The magnetometer of claim 1, wherein said processor filters measurements from said sensor to reject cyclically varying magnetic field generated by current flowing through AC power lines.

40. The magnetometer of claim 1, wherein said processor uses the bias setting signal for a measurement from said sensor that is based on a previous reading from said sensor.

41. The magnetometer of claim 1, wherein said processor initiates a search sequence to find the bias setting for which a target response may be determined.

42. A magnetometer comprising:

a first sensor for sensing a first component of a magnetic field;

a second sensor for sensing a second component of the magnetic field, each of said sensors generating an output signal having a frequency that varies in response to the sensed component magnetic field and in response to an applied bias current;

a biasing circuit for generating bias currents to dynamically bias said first and second sensors; and

a processor coupled to receive the output signals from said sensors and coupled to said biasing circuit, said processor operable to control said biasing circuit to dynamically vary said bias currents applied to said sensors such that the frequency of the output signals is maintained within one or more target frequency ranges, said processor determines the magnetic field components sensed by said sensors as a function of the biasing currents applied to said sensors.

43. The magnetometer of claim 42, wherein said first and second sensors have an inductance that varies as a function of the strength of the sensed magnetic field.

44. The magnetometer of claim 42, wherein said first and second sensors each comprise a sensing element having a sensor characteristic that varies in response to the magnetic field, the sensors further include an amplifier having an input for receiving a drive signal, said sensing elements being selectively coupled within a feedback loop of said amplifier, said amplifier generates the output signal, which has a signal characteristic that varies at least partially in response to variance in the sensor characteristic of the selected sensing element.

45. The magnetometer of claim 44, wherein the sensor characteristic is the inductance of the sensing element.

46. The magnetometer of claim 44, wherein each said sensing element includes an inductor and a capacitor coupled in parallel with the inductor.

47. The magnetometer of claim 44 and further comprising a driver circuit for generating said drive signal, wherein said processor controls said driver circuit to vary the drive signal applied to said amplifier input.

48. The magnetometer of claim 47, wherein said processor varies the bias current of the drive signal to maintain the signal characteristic of the output signal within the target range, and wherein said processor determines the magnetic field strength based on the bias current of the drive signal.

49. The magnetometer of claim 44, wherein the signal characteristic is the phase of the output signal.

50. The magnetometer of claim 44, wherein the signal characteristic is the frequency of the output signal.

51. The magnetometer of claim 42, wherein said processor alternatingly reverses the polarity of the bias current generated by said biasing circuit.

52. An electronic compass for a vehicle comprising:

a first magnetic field sensor for sensing a first component of a magnetic field;

a second magnetic field sensor for sensing a second component of the magnetic field that is orthogonal to the first component, each of said sensors generating an output signal having a characteristic that varies in response to both the sensed component magnetic field and in response to an applied bias current;

a biasing circuit for generating bias currents to dynamically bias said first and second sensors;

a processing circuit coupled to receive the output signals from said sensors and coupled to said biasing circuit, said processor operable to control said biasing circuit to dynamically vary said bias currents applied to said sensors such that the characteristic of the output signals is maintained within one or more target ranges, said processing circuit computes a vehicle heading as a function of the biasing currents applied to said sensors; and

a heading indicator coupled to said processing circuit for indicating the vehicle heading.

53. The electronic compass of claim 52, wherein said processing circuit alternatingly reverses the polarity of the bias current generated by said biasing circuit.

54. The electronic compass of claim 52, wherein said characteristic is the frequency of the output signal.

55. The electronic compass of claim 52, wherein said processor determines the magnetic field component sensed by said sensor as a function of both the bias setting applied to said sensor and the level of the output signal in the target range to enhance the resolution of the reading.

56. The electronic compass of claim 52, wherein said characteristic is the phase of the output signal.

57. The electronic compass of claim 56 and further comprising:

a signal generator for generating a reference signal having a predetermined frequency; and

a driver circuit coupled to said signal generator and to said biasing circuit for generating a drive signal having a DC bias current level established by said biasing circuit combined with the reference signal of a predetermined frequency, the drive signal is applied to a selected one of said first and second magnetic field sensors,

wherein said processing circuit compares the phase of the output signal to the phase of the reference signal to determine whether the phase offset is in the target range.

58. The electronic compass of claim 52, wherein said heading indicator is a display.

59. The electronic compass of claim 52, wherein each of the first and second magnetic field sensors includes an inductive sensing element, the sensing elements are coupled to an amplifier that outputs said output signal.

60. The electronic compass of claim 59, wherein each sensing element is coupled in a separate feedback loop of said amplifier.

61. The electronic compass of claim 59, wherein each sensing element includes an inductor and a capacitor coupled in parallel with the inductor.

62. The electronic compass of claim 61, wherein each sensing element is coupled in a separate feedback loop of said amplifier.

63. The electronic compass of claim 62 and further including a sensor selection circuit coupled to said processing circuit and including first and second switches, said first switch being coupled in series with the sensing element of said first magnetic field sensor for selectively coupling and decoupling the sensing element of said first magnetic field sensor from said amplifier, and said second switch being coupled in series with the sensing element of said second magnetic field sensor for selectively coupling and decoupling the sensing element of said second magnetic field sensor from said amplifier.

64. The electronic compass of claim 52, wherein said first magnetic field sensor comprises:

a first sensing element having a sensor characteristic that varies in response to a magnetic field; and

an amplifier having an input for receiving a driving signal, said first sensing element being coupled within a first feedback loop of said amplifier, said amplifier generating an output signal having a signal characteristic that varies at least partially in response to variance in the sensor characteristic, wherein said first sensing element and said amplifier together form a resonant element that is driven in a mode that is substantially current sourcing.

65. The electronic compass of claim 64 wherein said processing circuit is coupled to said amplifier for receiving said output signal, wherein said processing circuit determines the strength of the sensed magnetic field.

66. The electronic compass of claim 65 and further comprising a driver circuit for generating said driver signal, wherein said processing circuit controls said drive circuit to vary the drive signal applied to said amplifier input.

67. The electronic compass of claim 64, wherein the signal characteristic is the phase of the output signal.

68. The electronic compass of claim 64, wherein the signal characteristic is the frequency of the output signal.

69. The electronic compass of claim 64, wherein the sensor characteristic is the inductance of the sensing element.

70. The electronic compass of claim 64, wherein said second magnetic field sensor comprises a second sensing element having a sensor characteristic that varies in response to a magnetic field, said second sensing element being coupled within a second feedback loop of said amplifier, and wherein said electronic compass further comprises:

a sensing element selection circuit including a first analog switch coupled in series with said first sensing element within the first feedback loop of said amplifier, and a second analog switch coupled in series with said second sensing element within the second feedback loop of said amplifier, said selection circuit selectively coupling one of said first and second sensing elements within a feedback loop of said amplifier while disconnecting the other sensing element from said amplifier,

wherein said amplifier generating an output signal having a signal characteristic that varies at least partially in response to variance in the sensor characteristic of the selected sensing element.

71. The electronic compass of claim 64, wherein the first sensing element includes an inductor and a capacitor coupled in parallel with said inductor.

72. The electronic compass of claim 52, wherein:

said first magnetic field sensor comprises a first sensing element having a sensor characteristic that varies in response to a magnetic field;

said second magnetic field sensor comprises a second sensing element having a sensor characteristic that varies in response to a magnetic field;

said electronic compass further comprises a single first analog switch provided for selecting said first sensing element and a single second analog switch provided for selecting said second sensing element; and

said processing circuit is coupled to receive output signals from a selected one of said first and second sensing elements and coupled to said first and second analog switches to select one of said first and second sensing elements.

73. The electronic compass of claim 72, wherein said first analog switch is coupled in series with said first sensing element, and said second analog switch is coupled in series with said second sensing element.

74. The electronic compass of claim 72, wherein said first and second analog switches are coupled in circuit paths where the signal to be provided to said sensing elements is in a substantially current sourced mode.

75. The electronic compass of claim 72, wherein said processing circuit filters measurements from said sensor to reject cyclically varying magnetic field generated by current flowing through AC power lines.

76. The electronic compass of claim 52 further comprising:

first and second high gain amplifiers each having an input, one of said amplifiers being coupled to said sensors,

wherein said biasing circuit being coupled between the inputs of said first and second high gain amplifiers.

77. The electronic compass of claim 52, wherein:

said sensors constitute resonant sensors;

said biasing circuit adjustably biases said sensors at two or more bias levels; and

the peak to peak excursion of the magnetic field level in said resonant sensors during a resonant cycle is a fraction of the field level excursion range due to the adjustment of the bias circuit over its total range of adjustment.

78. The electronic compass of claim 77, wherein the peak to peak excursion of the magnetic field level in said resonant sensors during a resonant cycle is less than one-half of the field level excursion range due to the adjustment of the bias circuit over its total range of adjustment.

79. The electronic compass of the claim 77, wherein peak to peak excursion of the magnetic field level in said resonant sensors during a resonant cycle is less than one-fourth of the field level excursion range due to the adjustment of the bias circuit over its total range of adjustment.

80. The electronic compass of claim 52, wherein:

said sensors are resonant sensors; and

the peak to peak excursion of the magnetic field level in said resonant sensors during a resonant cycle is less than the total range of the magnetic field to be measured.

81. The electronic compass of claim 80, wherein the peak to peak excursion of the magnetic field level in said resonant sensor during a resonant cycle is less than one-half of the total range of the magnetic field to be measured.

82. The electronic compass of claim 80 and further including a biasing circuit for dynamically biasing said resonant sensor in response to a bias setting applied by said processor and said processor determines the magnetic field component sensed by said sensor as a function of the bias setting applied to said sensor.

83. The electronic compass of claim 52, wherein said sensors are resonant sensors, and said electronic compass further comprises an excitation circuit coupled to said resonant sensors for supplying an excitation signal thereto, said excitation circuit limits the amplitude of the excitation signal to prevent significant saturation of the response of said resonant sensors to the excitation signal.

84. The electronic compass of claim 83, wherein said excitation circuit maintains a stable phase relationship between the output signals of said resonant sensors and the excitation signal which drives said resonant sensors.

85. The electronic compass of claim 83, wherein said processing circuit measures the frequency of the output signal from said resonant sensors by timing the period of a predetermined number of cycles of the output signals.

86. The electronic compass of claim 83, wherein said resonant sensors are inductive field sensors each having a winding, and said resonant sensors are configured such that substantially all DC current supplied thereto flows through said windings.

87. The electronic compass of claim 83, wherein the output signals of said resonant sensors are supplied to a high gain amplifier.

88. The electronic compass of claim 83, wherein the output signals of said resonant sensors are supplied to a comparator.

89. The electronic compass of claim 83, and further comprising a filter for filtering the excitation signal prior to application to said resonant sensors, said filter making the excitation signal approximately sinusoidal.

90. The electronic compass of claim 89, wherein said filter is a multiple pole filter.

91. The electronic compass of claim 83 and further comprising an amplifier for driving said resonant sensors, an output of said amplifier is coupled to an input of said excitation circuit.

92. The electronic compass of claim 83, wherein said processing circuit determines the magnetic field components sensed by said sensors by measuring a phase shift of the output signals of said sensors relative to the phase of the excitation signal.

93. The electronic compass of claim 92, wherein the excitation signal has a frequency that is approximately equal to the resonant frequency of said resonant sensors for a nominal center point for the operation of said resonant sensors.

94. The electronic compass of claim 83, wherein said processing circuit determines the magnetic field components sensed by said sensors by measuring the frequency of the output signals of said sensors.

95. The electronic compass of claim 94, wherein the excitation signal is nominally in phase with the output signals of said resonant sensors.

96. The electronic compass of claim 94, wherein the excitation signal has a nominally constant phase with respect to the output signals of said resonant sensors.

97. The electronic compass of claim 52, wherein said processing circuit determines the magnetic field component sensed by said sensors as a function of the signal characteristic of the output signals from said sensors and as a function of a slope of the output signals versus bias level.

98. The electronic compass of claim 52, wherein said biasing circuit adjustably biases said sensors to at least a first bias level and a second bias level, and wherein said processing circuit determines the magnetic field component sensed by said sensors as a function of an average of the output signal levels when at the first and second bias levels.

99. The electronic compass of claim 52, wherein:

said first magnetic field sensor comprises a first sensing element having a sensor characteristic that varies in response to a magnetic field;

said second magnetic field sensor comprises a second sensing element having a sensor characteristic that varies in response to a magnetic field;

said biasing circuit adjustably biases said first sensing element to at least a first bias level and a second bias level, and adjustably biases said second sensing element to at least a third bias level and a fourth bias level; and

said processing circuit is coupled to said first and second sensing elements to receive the output signals from said sensing elements, said processing circuit measures the magnetic field components sensed by said sensing elements by sequentially;

sampling the output signal of said first sensing element at the first bias level,

sampling the output signal of said second sensing element at the third bias level,

sampling the output signal of said second sensing element at the fourth bias level,

sampling the output signal of said first sensing element at the second bias level,

determining the magnetic field component of said first sensing element as a function of the samples taken at the first and second bias levels, and

determining the magnetic field component of said second sensing element as a function of the samples taken at the third and fourth bias levels.

100. The electronic compass of claim 99 and further comprising a third sensing element having a sensor characteristic that varies in response to a magnetic field, wherein:

said biasing circuit adjustably biases said third sensing element to at least a fifth bias level and a sixth bias level; and

said processing circuit is further coupled to receive the output signal from said third sensing element, said processing circuit measures the magnetic field components sensed by said sensing elements by sequentially;

sampling the output signal of said first sensing element at the first bias level,

sampling the output signal of said second sensing element at the third bias level,

sampling the output signal of said third sensing element at the fifth bias level,

sampling the output signal of said third sensing element at the sixth bias level,

sampling the output signal of said second sensing element at the fourth bias level,

sampling the output signal of said first sensing element at the second bias level,

determining the magnetic field component of said first sensing element as a function of the samples taken at the first and second bias levels,

determining the magnetic field component of said second sensing element as a function of the samples taken at the third and fourth bias levels, and

determining the magnetic field component of said third sensing element as a function of the samples taken at the fifth and sixth bias levels.

101. The electronic compass of claim 52, wherein said first magnetic field sensor comprises a first sensing element having a sensor characteristic that varies in response to a magnetic field, said second magnetic field sensor comprises a second sensing element having a sensor characteristic that varies in response to a magnetic field, said electronic compass further comprising at least one analog switch provided for selecting said first or second sensing element, said at least one analog switch having a resistance, said biasing circuit supplying a biasing current to a selected one of said sensing elements, said processing circuit is coupled to receive output signals from a selected one of said first and second sensing elements and coupled to said at least one analog switch to select one of said first and second sensing elements, said processing circuit determines the magnetic field components sensed by said sensing elements, and said biasing circuit is configured to supply a biasing current that is substantially independent of the resistance of said at least one analog switch over a range of operation.

102. The electronic compass of claim 52, wherein said first magnetic field sensor comprises a first sensing element having a sensor characteristic that varies in response to a magnetic field, said second magnetic field sensor comprises a second sensing element having a sensor characteristic that varies in response to a magnetic field, said electronic compass further comprises at least one analog switch provided for selecting said first or second sensing element, said biasing circuit adjustably biases said sensing elements to at least a first bias level and a second bias level, said processing circuit is coupled to receive output signals from a selected one of said first and second sensing elements and coupled to said at least one analog switch to select one of said first and second sensing elements, said processing circuit determines the magnetic field components sensed by said sensing elements, and said biasing circuit biases one of said sensing elements at the first bias level and subsequently biases the same sensing element at the second bias level without any analog switch changing states.

103. The electronic compass of claim 52, wherein said biasing circuit includes a digital-to-analog converter;

and said processing circuit includes a readout device coupled to receive the output signal from said sensors, said processing circuit measures the magnetic field component sensed by said sensors by taking at least one reading of the output signals from said sensors, wherein the resolution in reading the output signals is a function of both said digital-to-analog converter and said readout device.

104. The electronic compass of claim 103, wherein said digital-to-analog converter is a pulse-width modulated digital-to-analog converter for setting a bias current for said sensors, said digital-to-analog converter having an accuracy that is substantially greater than its incremental resolution.

105. The electronic compass of claim 52, wherein said sensors are resonant sensors, and said electronic compass further comprising:

an excitation circuit coupled to said resonant sensor for supplying an excitation signal thereto having an AC component;

a filter for filtering the excitation signal prior to application to said resonant sensors, said filter making the excitation signal substantially sinusoidal.

106. The electronic compass of claim 105, wherein said filter is a multiple pole filter.

107. The electronic compass of claim 105, wherein said excitation circuit limits the amplitude of the excitation signal to prevent significant saturation of the response of said resonant sensors to the excitation signal.

108. The electronic compass of claim 105, and further comprising an amplifier for driving said resonant sensors, an output of said amplifier is coupled to an input of said excitation circuit.

109. The electronic compass of claim 52, wherein the bias setting selected to determine the magnetic field component is based on the difference in bias current at two points for which the output signal achieves a target response.

110. The electronic compass of claim 52, wherein the bias setting selected to determine the magnetic field component is based on no more than five prior raw readings obtained from said sensor.

111. A method of determining the strength of a magnetic field component comprising the steps of:

providing a magnetic field sensor that generates an output signal having a signal characteristic that varies in response to the strength of a sensed magnetic field component and in response to an applied bias setting;

dynamically varying a bias setting of the sensor such that the signal characteristic of the output signal is maintained within a target range; and

determining the strength of the sensed magnetic field component as a function of the bias setting of the sensor.

112. The method of claim 111, wherein the bias setting is a bias current applied to the sensor.

113. The method of claim 111, wherein the signal characteristic is the frequency of the output signal.

114. The method of claim 111, wherein the signal characteristic is the phase of the output signal.

115. A magnetometer comprising:

a sensor for sensing a magnetic field component, said sensor generating an output signal having a characteristic that varies substantially linearly in response to the sensed magnetic field components throughout a first range of magnetic field levels, wherein the magnetic field component varies throughout a second range of magnetic field levels;

a magnetic field generating mechanism for generating a magnetic field that is summed with any external magnetic field such that the resultant magnetic field is sensed by said sensor, the strength of the generated magnetic field being selectively variable; and

a processor coupled to receive the output signal from said sensor and coupled to said magnetic field generating mechanism, said processor operable to control said magnetic field generating mechanism to select the field strength of the generated magnetic field and thereby dynamically shift and/or maintain the second range within the first range, said processor being further operable to determine the magnetic field component sensed by said sensor in response to the output signal received from said sensor.

116. An electronic compass for a vehicle comprising the magnetometer defined in claim 115 and further comprising:

a second sensor for sensing a second component of the magnetic field, the second component being orthogonal to the first component as sensed by the other sensor;

a processing circuit for computing a vehicle heading as a function of the magnetic field components determined by said magnetometer; and

a heading indicator coupled to said processing circuit for indicating the vehicle heading.