Method and system for diagnosing a magnetic sensor

Abstract

A magnetic sensor circuit (100) includes a plurality of magnetic sensors (104A-C) having bias input and bias output terminals and first and second measurement terminals. The circuit includes a diagnostic sensor (108) having bias input and bias output terminals (110A-C, 112A-C) and first and second measurement terminals (122A-B). The circuit includes a first multiplexer (S1) configured to selectively couple a current source to the bias input terminals of the magnetic sensors or the bias input terminals of the diagnostic sensor; and a second multiplexer (S2) configured to selectively couple the bias output terminals of the magnetic sensors or the bias output terminals of the diagnostic sensor to a first terminal of a switch. The circuit includes a third multiplexer (S3) configured to selectively couple the measurement terminals of the magnetic sensors or the measurement terminals of the diagnostic sensor to differential input terminals of an amplifier.

Description

[0001] This description generally relates to magnetic sensors. BACKGROUND

[0002] Magnetic sensors, such as Hall effect sensors, are devices used to measure the strength of a magnetic field. Magnetic sensors provide an output voltage that is proportional to the magnetic field strength. Magnetic sensors are used for proximity sensing, position and velocity detection, and current sensing. Hall effect sensors can be combined with threshold detection circuitry such that they act as a switch.

[0003] Due to safety requirements in automotive applications, it is necessary to run-time diagnose Hall effect sensors to verify their integrity. For run-time diagnosis, a known magnetic field is typically created and isolated from the external magnetic field. Current systems include an on-chip coil built into an integrated circuit to create a local magnetic field. Current systems require additional on-chip area and consume a large amount of power. Moreover, due to challenges associated with isolating the local magnetic field from the external magnetic field, current systems are typically unreliable. SUMMARY

[0004] In one aspect, a magnetic sensor circuit includes a plurality of magnetic sensors having respective bias input and bias output terminals and respective first and second measurement terminals. The magnetic sensor circuit includes a diagnostic sensor having bias input and bias output terminals and first and second measurement terminals. The magnetic sensor circuit includes a first multiplexer configured to selectively couple a current source to the bias input terminals of the magnetic sensors or to the bias input terminal of the diagnostic sensor. The magnetic sensor circuit includes a second multiplexer configured to selectively couple the bias output terminals of the magnetic sensors or the bias output terminal of the diagnostic sensor to a first terminal of a switch. The switch includes a second terminal coupled to a ground terminal and includes a gate. The magnetic sensor circuit includes a third multiplexer configured to selectively couple the measurement terminals of the magnetic sensors or the measurement terminals of the diagnostic sensor to differential input terminals of an amplifier.

[0005] In an additional aspect, the switch is an NFET, the first terminal of the NFET is a drain, and the second terminal is a source. The NFET is turned on to electrically connect the bias output terminals to the ground terminal.

[0006] In an additional aspect, the diagnostic sensor comprises four resistors connected in a Wheatstone bridge configuration defining first, second, third, and fourth terminals, with two opposite terminals selected as the bias input and bias output terminals, and the other two terminals selected as the measurement terminals.

[0007] In an additional aspect, the direction of current flow in the diagnostic sensor is periodically changed by switching to adjacent terminals and their opposite terminals as the bias input and bias output terminals, respectively, and switching to the other two terminals as the measurement terminals.

[0008] In an additional aspect, during a first phase, the first and third terminals are selected as the bias input and bias output terminals, and the second and fourth terminals are selected as the measurement terminals, wherein during a second phase, the second and fourth terminals are selected as the bias input and bias output terminals, and the first and third terminals are selected as the measurement terminals.

[0009] In an additional aspect, the magnetic sensor circuit includes a demodulator having differential input terminals coupled to the differential output terminals of the amplifier and having an output terminal. The magnetic sensor circuit includes an analog-to-digital converter having an input terminal coupled to the output terminal of the demodulator and having an output terminal. The magnetic sensor circuit includes an operational amplifier having first and second input terminals coupled to differential output terminals of the third multiplexer, and a third input terminal coupled to a common mode terminal, and having an output terminal coupled to the gate of the switch.

[0010] In an additional aspect, the diagnostic sensor generates a non-sinusoidal reference voltage at the differential output terminals, wherein the amplitude of the reference voltage alternates between a minimum value and a maximum value. The reference voltage includes a diagnostic sensor output voltage component in response to a magnetic field and a diagnostic sensor offset voltage component resulting from a mismatch of the diagnostic sensor.

[0011] In an additional aspect, a self-diagnosing magnetic sensor circuit includes a plurality of magnetic sensors having respective bias input and bias output terminals and respective first and second measurement terminals. The magnetic sensor circuit includes a diagnostic sensor having bias input and bias output terminals and first and second measurement terminals. The magnetic sensor circuit includes a first multiplexer configured to couple a current source to the bias input terminals of the magnetic sensors during an operational phase and to the bias input terminals of the diagnostic circuit during a diagnostic phase. The magnetic sensor circuit includes a second multiplexer configured to couple the bias output terminals of the magnetic sensors to a first terminal of a switch during the operational phase and to couple the bias output terminals of the diagnostic sensor to the first terminal of the switch during the diagnostic phase, and a third multiplexer configured to couple the measurement terminals of the magnetic sensors to differential input terminals of an amplifier during the operational phase and to couple the measurement terminals of the diagnostic sensor to the differential input terminals of the amplifier during the diagnostic phase.

[0012] In an additional aspect, a method of diagnosing a signal chain of a magnetic sensor circuit includes generating a reference voltage by periodically switching a direction of current flow in a diagnostic sensor. The reference voltage is a non-sinusoidal differential voltage whose amplitude alternates between a minimum value and a maximum value, where the reference voltage includes a diagnostic sensor output voltage component responsive to an external magnetic field and a diagnostic sensor offset voltage component resulting from a mismatch of the diagnostic sensor. The method includes amplifying the reference voltage, where the amplified reference voltage is a differential voltage having an amplifier offset voltage component. The method includes demodulating the amplified voltage by filtering the diagnostic sensor offset voltage component and the amplifier offset voltage component, and digitizing the demodulated voltage. The method includes comparing the digitized voltage to the reference voltage to diagnose the signal chain.

[0013] In an additional aspect, the method includes generating the reference voltage by periodically switching a direction of current flow in the diagnostic sensor by switching to adjacent terminals and their opposite terminals as the bias input and bias output terminals, respectively, and to the other two terminals as the measurement terminals.

[0014] Additionally, a method for diagnosing a magnetic sensor includes generating a reference voltage by periodically switching the direction of current flow in the magnetic sensor, wherein the reference voltage is a non-sinusoidal differential voltage whose amplitude alternates between a minimum and a maximum value. The reference voltage includes a sensor output voltage component responsive to a magnetic field and a sensor offset voltage component resulting from a mismatch in the magnetic sensor. The method includes amplifying the reference voltage, wherein the amplified reference voltage is a differential voltage including an amplifier offset voltage component. The method includes demodulating the amplified reference voltage by filtering the sensor offset voltage component and the amplifier offset voltage component, and digitizing the demodulated voltage. The method includes using the digitized voltage to determine the sensitivity of the magnetic sensor. Attached Figure Description

[0015] Figure 1 This is a block diagram of a magnetic sensor circuit in an example embodiment.

[0016] Figure 2 Explain the timing diagram.

[0017] Figure 3 This is a schematic diagram of a magnetic sensor in an example embodiment.

[0018] Figure 4 This is a block diagram of the test circuit in an example embodiment.

[0019] Figure 5 This is a flowchart of an example implementation. Detailed Implementation

[0020] Figure 1 This is a block diagram of a magnetic sensor circuit 100 according to an example embodiment. The magnetic sensor circuit 100 operates in two modes: a diagnostic mode and a normal mode. In the diagnostic mode, the magnetic sensor circuit 100 performs self-diagnostics to verify the integrity of the signal chain of the circuit 100. In the normal mode, the magnetic sensor circuit 100 measures the external magnetic field and provides an output voltage representing the external magnetic field.

[0021] The magnetic sensor circuit 100 operates in a working cycle with sleep and active states. For example... Figure 2 The timing diagram illustrates that in sleep state 204, the magnetic sensor circuit 100 is inactive, and in active state 208, the magnetic sensor circuit 100 performs signal chain diagnostic checks 210 and sensor diagnostic checks 214. Afterward, the magnetic sensor circuit 100 performs normal operation 218, also known as Hall effect sensor operation.

[0022] The magnetic sensor circuit 100 includes three magnetic sensors 104A, 104B, and 104C, which are respectively oriented to measure an external magnetic field in the x, y, and z directions. The magnetic sensor circuit 100 can be constructed with any suitable number of magnetic sensors. The magnetic sensors 104A, 104B, and 104C can be, for example, Hall effect sensors that provide an output voltage representative of the strength of the external magnetic field.

[0023] The magnetic sensor circuit 100 includes a diagnostic sensor 108 that provides an output voltage that is not affected by the external magnetic field. In an example embodiment, the diagnostic sensor is constructed using a resistor (e.g., a polysilicon resistor) that does not generate a voltage in response to the external magnetic field. The resistor in the diagnostic sensor can be connected in a Wheatstone bridge network. The diagnostic sensor 108 is used to perform a self-diagnosis to check the integrity of the signal chain of the circuit 100. The diagnostic sensor 108 may, for example, be a resistor network that is not sensitive to the external magnetic field.

[0024] The magnetic sensors 104A, 104B, and 104C include respective bias input terminals 110A, 110B, and 110C configured to receive a bias current. During a normal mode of operation, switches SI couple the bias input terminals 110A, 110B, and 110C to a current source I bias The switches SI can be implemented with multiplexers.

[0025] The magnetic sensors 104A, 104B, and 104C include respective bias output terminals 112A, 112B, and 112C. During the normal mode of operation, switches S2 couple the bias output terminals 112A, 112B, and 112C to a first terminal 116 of a switch Ml. The switches S2 may, for example, be multiplexers. The switch Ml has a second terminal 118 coupled to a ground terminal. The ground terminal can be coupled to a ground voltage. The switch Ml may, for example, be an n-channel field effect transistor (NFET) with the first terminal 116 being the drain and the second terminal 118 being the source. The switch Ml also has a gate. When Ml is turned on, a conduction path is provided for the bias current to flow from the current source I bias to the ground.

[0026] Magnetic sensor 104A includes measurement terminals 122A and 122B, magnetic sensor 104B includes measurement terminals 124A and 124B, and magnetic sensor 104C includes measurement terminals 126A and 126B. In response to an external magnetic field, magnetic sensors 104A, 104B, and 104C provide output voltages at the measurement terminals. The output voltages at the measurement terminals are indicative of the strength of the external magnetic field. Switch S3 (e.g., a multiplexer) selectively couples the measurement terminals to differential output terminals 128 and 130. During a normal mode of operation, the output voltages generated by magnetic sensors 104A, 104B, and 104C are available at differential output terminals 128 and 130.

[0027] Diagnosis sensor 108 includes a bias input terminal 134 and a bias output terminal 136. Diagnosis sensor 108 includes measurement terminals 138 and 140. During a diagnosis mode, switch SI couples bias input terminal 134 to current source I bias , and switch S2 couples bias output terminal 136 to first terminal 116 of transistor Ml, thus providing a conduction path between current source I bias and ground. Also, during the diagnosis mode, switch S3 couples measurement terminals 138 and 140 to differential output terminals 128 and 130. Diagnosis sensor 108 provides an output voltage at measurement terminals 138 and 140 that is not affected by an external magnetic field.

[0028] Magnetic sensor circuit 100 includes an analog front end (AFE) 150, which can be an amplifier. AFE 150 includes differential inputs 152 and 154 coupled to differential outputs 128 and 130, respectively. During the diagnosis mode, switch S4 connects current source I diagsrc to input 152 of AFE 150, and switch S5 connects current sink I diagsnk to input 154 of AFE 150. AFE 150 applies a predetermined gain to the differential voltage provided by magnetic sensors 104A-104C or diagnosis sensor 108 and provides an amplified differential signal at outputs 156 and 158. Magnetic sensor circuit 100 includes a demodulator 160 coupled to receive the amplified differential signal at inputs 162 and 164. Demodulator 160 demodulates the amplified signal and provides a filtered signal at output 166. An analog-to-digital converter (ADC) 168 digitizes the filtered signal.

[0029] In an example embodiment, the magnetic sensor circuit 100 includes an operational amplifier 170 having first and second input terminals 172 and 174 coupled to respective differential output terminals 128 and 130 of the third switch S3, and a third input terminal 176 coupled to a common mode terminal to which a common mode voltage can be applied. The operational amplifier 170 also includes an output terminal 178 coupled to the gate of the switch Ml. In response to the differential voltage at terminals 128 and 130 and the common mode voltage, the operational amplifier 170 applies a gate voltage to the switch Ml to control the current through Ml, and thus the current in the magnetic sensors 104A-C and the diagnostic sensor 108.

[0030] In an example embodiment, the magnetic sensors 104A-C and the diagnostic sensor 108 are implemented with four resistors connected in a Wheatstone bridge configuration. Figure 3 A sensor 300 is illustrated, which can be one of the magnetic sensors 104A-C or the diagnostic sensor 108. The sensor 300 includes four resistors Rl, R2, R3, and R4 connected in a bridge configuration defining first, second, third, and fourth terminals Tl, T2, T3, and T4, respectively. The sensor 300 operates in four phases, and in each phase, different pairs of opposite terminals are selected as bias input and bias output terminals, while another pair of opposite terminals is selected as measurement terminals. For example, in phase 1, terminals Tl and T3 can be selected as bias input and output terminals, respectively, while the two opposite terminals T2 and T4 can be selected as measurement terminals. During phase 1, the switch S1 couples the current source I bias to terminal Tl. Thus, the bias current flows through resistors Rl, R2, R3, and R4, and out via terminal T3. In response to the external magnetic field Hl, the sensor 300 provides an output voltage at the measurement terminals T2 and T4. The switch S3 couples the measurement terminals T2 and T4 to the differential output terminals 128 and 130 during phase 1.

[0031] In phase 2, terminals T2 and T4 can be selected as bias input and output terminals, respectively, while the two opposite terminals Tl and T3 can be selected as measurement terminals. During phase 2, the switch S1 couples the current source I bias to terminal T2. Thus, the bias current flows through resistors Rl, R2, R3, and R4, and out via terminal T4. In response to the external magnetic field Hl, the sensor 300 provides an output voltage at the measurement terminals Tl and T3. The switch S3 couples the measurement terminals Tl and T3 to the differential output terminals 128 and 130 during phase 2.

[0032] In phase 3, respectively, terminals T3 and Tl can be selected as the bias input and output terminals, while the two opposite terminals T2 and T4 can be selected as the measurement terminals. During phase 3, switch SI couples the current source I bias to terminal T3. Thus, the bias current flows through resistors Rl, R2, R3, and R4, and out via terminal Tl. In response to the external magnetic field HI, sensor 300 provides an output voltage at measurement terminals T2 and T4. Switch S3 couples measurement terminals T2 and T4 to differential output terminals 128 and 130 during phase 2.

[0033] In phase 4, respectively, terminals T4 and T2 can be selected as the bias input and output terminals, while the two opposite terminals Tl and T3 can be selected as the measurement terminals. During phase 4, switch SI couples the current source I bias to terminal T4. Thus, the bias current flows through resistors Rl, R2, R3, and R4, and out via terminal T2. In response to the external magnetic field HI, sensor 300 provides an output voltage at measurement terminals Tl and T3. Switch S3 couples measurement terminals Tl and T3 to differential output terminals 128 and 130 during phase 2.

[0034] By coupling the current source I bias to a different bias input terminal during each phase, the direction of the current flow in sensor 300 is periodically changed. Thus, a periodic non-sinusoidal voltage is generated at the measurement terminals of sensor 300. The amplitude of the non-sinusoidal voltage at the measurement terminals alternates between a minimum value and a maximum value.

[0035] During the diagnostic mode, magnetic sensor circuit 100 is configured to check the integrity of magnetic sensors 104A-104C by measuring the magnetic sensor offset and the offset of AFE 150. In this mode, current source I bias is provided to the magnetic sensors with a predetermined value. The direction of the current flow in magnetic sensors 104A-104C is periodically switched. In response to the external magnetic field, the magnetic sensors provide a periodic non-sinusoidal voltage at differential output terminals 128 and 130, which is referred to as the Hall voltage. The output voltage includes a diagnostic sensor offset voltage component corresponding to the current source I bias , the resistance of the magnetic sensors, and the external magnetic field, and a magnetically sensitive diagnostic sensor output voltage component. The offset component is generated due to the mismatch of the resistors of the sensors, and the magnetically sensitive voltage component is generated by the magnetic sensors in response to the external magnetic field. Since the external magnetic field can be an unknown value during the diagnostic mode, it is necessary to ignore its influence. The signals at differential output terminals 128 and 130 are amplified by AFE 150. At the output of AFE 150, the offset component is increased due to the mismatch in AFE 150. The signal at the output of AFE 150 can be represented as:

[0036] V ph(i) = (-1) i+1 V Hall + V OS,Hall,ph(i) + V OS,AFE where:

[0037] V ph(i) = AFE output signal for each stage (1, 2, 3, and 4)

[0038] V Hall = Hall effect voltage component

[0039] V OS,Hall,ph(i) = Hall sensor offset voltage component

[0040] V OS,AFE = AFE offset voltage component

[0041] Based on the above:

[0042] V ph(1) + V ph(2) + V ph(3) + V ph(4) = 4(V OS,Hall,ph(i) + V OS,AFE )

[0043] As shown below, even in the presence of unknown external magnetic fields, the magnetic sensor integrity can be determined from the sum of the offsets of the magnetic sensor and the analog front end.

[0044] (V OS,Hall,ph(i) + V OS,AFE ) = (1 / 4)(V ph(1) + V ph(2) + V ph(3) + V ph(4) )

[0045] In normal operation, the sensor output corresponding to the external field is demodulated using demodulator 160, as follows:

[0046] V ph(1) - V ph(2) + V ph(3) - V ph(4) = 4(V Hall )

[0047] During the diagnostic mode, circuit 100 is configured to verify signal chain integrity using diagnostic sensor 108. In an example embodiment, in the diagnostic mode, in addition to bias current I bias , diagnostic current source I diagsrc and slot I diagsnk are applied to diagnostic sensor 108. Diagnostic current source I diagsrcThe diagnostic current sink I diagsnk may be connected to the differential terminals 128 and 130 through switch S4, and the diagnostic current source I diagsrc may be connected to the differential terminals 128 and 130 through switch S5. Switch S3 connects the differential terminals 128 and 130 to the diagnostic sensor 108, and thus the diagnostic current source I diagsnk and the diagnostic current sink I diagsrc are applied to the diagnostic sensor 108. The diagnostic current source I diagsnk and the diagnostic current sink I bias have a predetermined value, and can be referred to as a reference current of the diagnostic sensor 108.

[0048] The direction of current flow of I diagsrc , I diagsnk , and I bias is switched periodically in the diagnostic sensor 108. In phase 1 and phase 3, the terminal 180 of the diagnostic current source is switched to the terminal 152, and the terminal 182 of the diagnostic current sink is switched to the terminal 154. In phase 2 and phase 4, the terminal 180 of the diagnostic current source is switched to the terminal 154, and the terminal 182 of the diagnostic current sink is switched to the terminal 152. Without influence of an external magnetic field and I diagsrc , the diagnostic sensor 108 provides a periodic, non-sinusoidal voltage, referred to as a diagnostic reference voltage at the differential output terminals 128 and 130. The two diagnostic currents (I diagsnk , I diagsrc ) can have the same value (I diagsrc ). The diagnostic reference voltage includes a diagnostic sensor offset component corresponding to the resistance R diagsns of the diagnostic sensor and a known diagnostic reference voltage component. The diagnostic sensor offset component arises due to mismatch of the resistors of the diagnostic sensor 108, and the known diagnostic reference voltage component arises from the diagnostic sensor 108 being unaffected by an external magnetic field and due to a voltage drop created by the reference diagnostic current flowing through the diagnostic sensor. Since the diagnostic reference current has a known value, the resulting diagnostic reference voltage component also has a known value. The signal at the differential output terminals 128 and 130 is amplified by the AFE 150. At the output of the AFE 150, an offset component is added to the signal due to mismatch in the AFE 150. The signal at the output of the AFE 150 can be represented as:

[0049] V ph(i) = (-1) i+1 V ref,diag + V OS,Hall,ph(i) + V OS,AFE , where:

[0050] V ph(i) = AFE output signal for each phase (1, 2, 3, and 4)

[0051] V ref,diag = I diagsrc *R diagsns (diagnostic reference voltage component)

[0052] V OS,diag,ph(i) = diagnostic sensor offset voltage component

[0053] V OS,AFE = AFE offset voltage component

[0054] Based on the above:

[0055] V ph(1) -V ph(2) +V ph(3) -V ph(4) = 4(V ref,diag )

[0056] Thus, signal chain integrity can be determined by obtaining a known output reference voltage based on demodulation of the four different phases:

[0057] (V ref,diag ) = (1 / 4)(V ph(1) -V ph(2) +V ph(3) -V ph(4) ).

[0058] In example embodiments, the magnetic sensor circuit 100 is configured to perform a sensor integrity check to verify the sensitivity of the magnetic sensors 104A-C. Figure 4 A simplified circuit 400 for a sensor integrity check for the magnetic sensor 104A is illustrated. The bias input terminal 110A of the magnetic sensor 104A is coupled to a current source, and the bias output terminal 112A is coupled to the drain 116 of the transistor Ml. During the sensor integrity check, the current source generates a current I diag and a resistor R diag using a known voltage V diag . In response to I diag with a known value, the magnetic sensor 104A provides a differential output voltage V(d1 -d2), which can be represented as:

[0059] V(d1 -d2) = (I diag )*(R Hall )

[0060] where R Hall is the equivalent resistance of the magnetic sensor 104.

[0061] After substituting I bg for (V diag / R diag ):

[0062] V(d1-d2) = (V bg / R diag )*R Hall = K*V bg

[0063] where K = R Hall / R diag and is defined as a sensitivity constant.

[0064] Thus, by measuring the differential voltage V(d1-d2) in response to a known current value, the sensitivity of the magnetic sensor 104A can be determined. As discussed previously, the differential voltage can be determined from the output of the ADC 168 converter that provides a digital signal representative of the differential voltage.

[0065] Figure 5 is a flowchart of a method of diagnosing a signal chain of a magnetic sensor circuit of an example embodiment. In block 504, a reference voltage is generated by periodically switching the direction of current flow in a diagnostic sensor. The reference voltage is a non-sinusoidal differential voltage whose amplitude alternates between a minimum value and a maximum value. The reference voltage includes a diagnostic sensor output voltage component in response to a magnetic field and a diagnostic sensor offset voltage component resulting from a mismatch of the diagnostic sensor. In block 508, the reference voltage is amplified by an analog front end. The amplified voltage is a differential voltage that includes an amplifier offset voltage component. In block 512, the amplified reference voltage is demodulated by filtering the diagnostic sensor offset voltage component and the amplifier offset voltage component. In block 516, the demodulated signal is digitized. The digitized signal is used to diagnose the signal chain in comparison to the reference voltage.

[0066] Various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0067] For simplicity and clarity, the full structure and operation of all systems suitable for use with the present disclosure is not depicted or described herein. Instead, only so much of a system as is unique to the present disclosure or necessary for an understanding of the present disclosure is depicted and described.

Claims

1. A magnetic sensor circuit, comprising: Multiple magnetic sensors, each having corresponding bias input and bias output terminals, as well as corresponding first and second measurement terminals; A diagnostic sensor having bias input and bias output terminals, as well as first and second measurement terminals; A first multiplexer is configured to selectively couple a current source to the bias input terminal of the magnetic sensor or the bias input terminal of the diagnostic sensor. A second multiplexer is configured to selectively couple the bias output terminal of the magnetic sensor or the bias output terminal of the diagnostic sensor to a first terminal of a switch. as well as A third multiplexer is configured to selectively couple the measurement terminal of the magnetic sensor or the measurement terminal of the diagnostic sensor to the differential input terminal of the amplifier.

2. The magnetic sensor circuit of claim 1, wherein the switch includes a second terminal coupled to a ground terminal and includes a gate.

3. The magnetic sensor circuit according to claim 2, wherein the switch is an NFET, the first terminal of the NFET is the drain and the second terminal is the source, and wherein the NFET is turned on to electrically connect the bias output terminal to the ground terminal.

4. The magnetic sensor circuit according to claim 1, wherein the direction of current flow in the magnetic sensor or the diagnostic sensor changes periodically.

5. The magnetic sensor circuit of claim 1, wherein the diagnostic sensor comprises four resistors connected in a Wheatstone bridge configuration defining the first, second, third and fourth terminals, wherein two opposite terminals are selected as the bias input and bias output terminals, and the other two terminals are selected as the measurement terminals.

6. The magnetic sensor circuit of claim 4, wherein the direction of current flow in the diagnostic sensor is periodically changed by switching adjacent terminals and their opposite terminals as the bias input and bias output terminals, respectively, and switching to two other terminals as the measurement terminals.

7. The magnetic sensor circuit of claim 5, wherein during a first stage, the first and third terminals are selected as the bias input and bias output terminals, and the second and fourth terminals are selected as the measurement terminals, and wherein during a second stage, the second and fourth terminals are selected as the bias input and bias output terminals, and the first and third terminals are selected as the measurement terminals.

8. The magnetic sensor circuit according to claim 1, further comprising: A demodulator having a differential input terminal coupled to the differential output terminal of the amplifier and having an output terminal; and An analog-to-digital converter having an input terminal coupled to the output terminal of the demodulator and having an output terminal.

9. The magnetic sensor circuit of claim 1, further comprising an operational amplifier having first and second input terminals coupled to the differential output terminal of the third multiplexer and a third input terminal coupled to the common-mode terminal, and having an output terminal coupled to the gate of the switch.

10. The magnetic sensor circuit of claim 1, wherein the diagnostic sensor generates a non-sinusoidal reference voltage at a differential output terminal, and wherein the amplitude of the reference voltage alternates between a minimum value and a maximum value.

11. The magnetic sensor circuit of claim 10, wherein the reference voltage includes a diagnostic sensor output voltage component responsive to a magnetic field and a diagnostic sensor offset voltage component resulting from a mismatch of the diagnostic sensor.

12. A self-diagnostic magnetic sensor circuit, comprising: Multiple magnetic sensors, each having corresponding bias input and bias output terminals, as well as corresponding first and second measurement terminals; A diagnostic sensor having bias input and bias output terminals, as well as first and second measurement terminals; A first multiplexer is configured to couple a current source to the bias input terminal of the magnetic sensor during the operation phase and to the bias input terminal of the diagnostic circuit during the diagnostic phase. A second multiplexer is configured to couple the bias output terminal of the magnetic sensor to a first terminal of the switch during the operation phase, and to couple the bias output terminal of the diagnostic sensor to the first terminal of the switch during the diagnostic phase. as well as A third multiplexer is configured to couple the measurement terminal of the magnetic sensor to the differential input terminal of the amplifier during the operation phase, and to couple the measurement terminal of the diagnostic sensor to the differential input terminal of the amplifier during the diagnostic phase.

13. The self-diagnostic magnetic sensor circuit of claim 12, wherein the switch includes a second terminal coupled to a ground terminal and includes a gate.

14. The self-diagnostic magnetic sensor circuit of claim 13, wherein the switch is an NFET, the first terminal of the NFET is the drain and the second terminal is the source, and wherein the NFET is turned on to electrically connect the bias output terminal to the ground terminal.

15. The self-diagnostic magnetic sensor circuit according to claim 12, wherein the direction of current flow in the magnetic sensor or the diagnostic sensor changes periodically.

16. The self-diagnostic magnetic sensor circuit of claim 12, wherein the diagnostic sensor comprises four resistors connected in a Wheatstone bridge configuration defining the first, second, third, and fourth terminals, wherein two opposite terminals are selected as the bias input and bias output terminals, and the other two terminals are selected as the measurement terminals.

17. The self-diagnostic magnetic sensor circuit of claim 15, wherein the direction of current flow in the diagnostic circuit is periodically changed by switching adjacent terminals and their opposite terminals as the bias input and bias output terminals, respectively, and switching to two other terminals as the measurement terminals.

18. The self-diagnostic magnetic sensor circuit of claim 16, wherein during a first phase, the first and third terminals are selected as the bias input and bias output terminals, and the second and fourth terminals are selected as the measurement terminals, and wherein during a second phase, the second and fourth terminals are selected as the bias input and bias output terminals, and the first and third terminals are selected as the measurement terminals.

19. The self-diagnostic magnetic sensor circuit according to claim 12, further comprising: A demodulator having a differential input terminal coupled to the differential output terminal of the amplifier and having an output terminal; and An analog-to-digital converter having an input terminal coupled to the output terminal of the demodulator and having an output terminal.

20. The self-diagnostic magnetic sensor circuit of claim 12, further comprising an operational amplifier having first and second input terminals coupled to the differential input terminals of the amplifier and a third input terminal coupled to a common-mode terminal, and having an output terminal coupled to the gate terminal of the switch.

21. The magnetic sensor circuit of claim 12, wherein the diagnostic sensor generates a non-sinusoidal reference voltage at a differential output terminal, and wherein the amplitude of the reference voltage alternates between a minimum value and a maximum value.

22. The magnetic sensor circuit of claim 21, wherein the reference voltage includes a diagnostic sensor output voltage component responsive to an external magnetic field and a diagnostic sensor offset voltage component resulting from a mismatch of the diagnostic sensor.

23. The magnetic sensor circuit of claim 21, wherein the transition between the minimum value and the maximum value is instantaneous.

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