Inductive position sensor

Abstract

The invention discloses an inductive position sensor. A position sensor for determining a position of a target includes a center tapped transmit coil having three terminals: a first terminal, a center tap, and a second terminal. The sensor has a transmitter that applies an oscillating signal across a first terminal and a second terminal of a transmit coil. The receiver is connected to the first terminal, the second terminal and the center tap of the transmitting coil. The processing circuitry calculates the position of the target by applying transformations to the signals received from the three terminals.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of position sensing technology. More specifically, the present invention relates to an inductive method and apparatus for determining the position of a target. BACKGROUND

[0002] Inductive position sensors are widely used in various applications for accurately detecting the position of a target. In a conventional inductive position sensor, as illustrated in FIG. 1, an integrated circuit (IC) is used to excite a transmit (TX) coil, typically operating in the frequency range of several megahertz. This excitation induces eddy currents in the target. The eddy currents then induce currents in a set of three receive (RX) coils, where the induced signals depend on the angle of the target relative to the coils.

[0003] The process involves a two-step induction mechanism: first, the TX coil induces eddy currents in the target; and second, these eddy currents induce a response in the RX coils. This method, while effective, has several limitations. As the size of the target and coil system decreases, the strength of the received signal decreases, making it increasingly difficult to achieve accurate position sensing. This decrease in signal strength can lead to challenges in maintaining electromagnetic compatibility (EMC) immunity, as smaller signals are more susceptible to noise and other interference. Therefore, there is a need for a position sensing method that can overcome these challenges, particularly in applications requiring smaller and more compact designs.

[0004] Prior art inductive position sensors, such as for example illustrated in FIG. 2, typically employ a single transmit (TX) coil, a target, and three receive (RX) coils to generate signals. These signals are shown in FIG. 3 and can be mathematically described by specific equations, where the signal components are affected by the rotor angle and a common mode component.

[0005]

[0006] In these equations, IN0, IN1, and IN2 are the amplitudes of the currents or voltage amplitudes of the receive coils.

[0007] To eliminate the common mode signal and isolate the position-dependent information, anti- winding RX coils are used. This results in a three-phase amplitude-modulated signal that varies with the angle of the target.

[0008] The angle position of the target is then reconstructed using a transformation that calculates the angle position of the target from the three-phase amplitude-modulated signal.

[0009] Such a transformation can be a Clarke transformation, where the angle is determined as the arctangent of the ratio of the sine component and the cosine component, where the sine component and the cosine component are derived from the received signals.

[0010]

[0011] wherein:

[0012] SINN = IN0 - IN1

[0013]

[0014] However, achieving sufficient received signal strength to obtain reliable noise and electromagnetic compatibility (EMC) performance requires larger coil systems and target sizes. This necessity conflicts with the current trend in sensor design towards miniaturization and cost reduction. SUMMARY

[0015] It is an object of embodiments of the invention to provide a good method and device for determining a position of a target.

[0016] The above objects are achieved by a method and a device according to the invention.

[0017] In a first aspect, embodiments of the invention relate to a position sensor for determining a position of a target.

[0018] The position sensor comprises the following components:

[0019] a center-tapped transmit coil comprising a first terminal, a center tap, and a second terminal. The coil is divided into two parts, where a first part is located between the first terminal and the center tap, and a second part is located between the center tap and the second terminal.

[0020] a transmitter comprising a positive output terminal and a negative output terminal, the positive output terminal being connected to the first terminal of the transmit coil, and the negative output terminal being connected to the second terminal of the transmit coil. The transmitter is designed to apply an oscillating signal between the first terminal and the second terminal of the transmit coil.

[0021] a receiver comprising a first receive input, a second receive input, and a third receive input. The first terminal of the transmit coil is electrically connected to one of the receive inputs via a first electrical coupling.

[0022] The second terminal of the transmit coil is electrically connected to a different one of the receive inputs via a second electrical coupling.

[0023] The center tap of the transmit coil is electrically connected to the remaining one of the receive inputs via a third electrical coupling.

[0024] processing circuitry configured to apply a transformation to the signals received from the three receive inputs,

[0025] to calculate the position of the target relative to the center-tapped transmit coil.

[0026] In embodiments of the application, the position sensor comprises a target. In embodiments of the application, a change in the position of the target causes a change in the inductance imbalance of the center-tapped transmitter coil.

[0027] An advantage of embodiments of the application is that it relies on single-step induction between the center-tapped transmitter coil and the target to determine the position of the target. In embodiments of the application, the position of the target relative to the transmitter coil causes an inductance imbalance in both parts of the transmitter coil. An advantage of embodiments of the application is that this single-step induction causes a larger useful signal amplitude compared to a position sensor using a coil system consisting of one transmitter coil and three receiver coils. Therefore, another advantage of a position sensor according to embodiments of the application is that it is suitable for miniaturized designs.

[0028] In embodiments of the application, the transformation used can be a transformation for calculating the angular position of the target from three-phase amplitude-modulated signals obtained using a single transmitter coil and three receiver coils, wherein the three-phase amplitude-modulated signals are offset from each other by 120°.

[0029] An advantage of such embodiments of the application is that existing conventional inductive position sensor ICs based on prior art transformations can be used to detect the target position.

[0030] In embodiments of the application, such a transformation can be a Clarke transformation.

[0031] An advantage of embodiments of the application is that existing conventional inductive position sensor ICs based on the Clarke transformation can be used to detect the target position.

[0032] In embodiments of the application, the center-tapped transmitter coil is a balanced center-tapped transmitter coil in the absence of the target or when the target is positioned at the center position of the center-tapped transmitter coil.

[0033] In embodiments of the application, the first electrical coupling, the second electrical coupling and the third electrical coupling are capacitive couplings.

[0034] In embodiments of the application, the center-tapped transmitter coil is a linear coil. An advantage of embodiments of the application is that the linear position of the target relative to the center-tapped transmitter coil can be determined.

[0035] In embodiments of the application, the center-tapped transmitter coil is an arc-shaped coil. An advantage of embodiments of the application is that the position of the target along the arc-shaped coil can be determined.

[0036] In embodiments of the invention, the position sensor comprises an additional center-tapped transmitter coil, resulting in at least two center-tapped transmitter coils. The additional center-tapped transmitter coil features a first terminal, a center tap, and a second terminal, wherein the coil is divided into two parts: one part between the first terminal and the center tap, and another part between the center tap and the second terminal.

[0037] In such embodiments, the transmitter comprises an additional positive output terminal connected to the first terminal of the additional transmitter coil, and an additional negative output terminal connected to the second terminal of the additional transmitter coil. The transmitter is configured to apply an oscillating signal between the first terminal and the second terminal of the additional transmitter coil.

[0038] In such embodiments, the receiver comprises an additional set of three receiving inputs: an additional first receiving input, an additional second receiving input, and an additional third receiving input. The first terminal of the additional transmitter coil is electrically connected to one of the additional receiving inputs via an additional first electrical coupling. The second terminal of the additional transmitter coil is electrically connected to a different one of the additional receiving inputs via an additional second electrical coupling. The center tap of the additional transmitter coil is electrically connected to the remaining additional receiving input via an additional third electrical coupling.

[0039] In such embodiments, the processing circuitry is further configured to apply a Clarke transform on the signals received from the additional set of receiving inputs to calculate the position of the target relative to the additional center-tapped transmitter coil. Furthermore, the receiver is designed to receive signals from two transmitter coils, and the processing circuitry is configured to calculate the position of the target relative to the two transmitter coils.

[0040] In embodiments of the invention, the additional center-tapped transmitter coil can be oriented in the same direction as the center-tapped transmitter coil.

[0041] In embodiments of the invention, the additional center-tapped transmitter coil can be oriented in a different direction than the center-tapped transmitter coil. Embodiments of the invention have the advantage that the position of the target can be obtained in different directions.

[0042] In embodiments of the invention, the processing circuitry is configured to compensate for variations in the offset in the center-tapped transmitter coil and / or for mismatches in the coupling network by calibration, such calibration being used to balance the inductance of the center-tapped transmitter coil without the target or when the target is positioned at the center position of the center-tapped transmitter coil.

[0043] In embodiments of the invention, the configuration register is used by the processing circuitry to linearize the target position obtained from the transformation.

[0044] One advantage of embodiments of the invention is that the configuration register present in existing conventional inductive position sensor ICs can be used to linearize the target position.

[0045] In a second aspect, embodiments of the invention relate to a method for determining a position of a target. The method comprises the steps of:

[0046] applying an oscillating signal between a first terminal and a second terminal of a center-tapped transmit coil, the center-tapped transmit coil comprising a center tap, wherein a change in the position of the target causes a change in an inductance imbalance of the center-tapped transmit coil.

[0047] receiving a signal from the first terminal, the second terminal and the center tap of the transmit coil.

[0048] processing the received signal by applying a transformation to determine the position of the target relative to the center-tapped transmit coil.

[0049] In embodiments of the invention, the processing comprises linearizing the target position obtained from the transformation.

[0050] In embodiments of the invention, the transformation can be a transformation for calculating the angular position of the target from three-phase amplitude-modulated signals obtained using a single transmit coil and three receive coils, such as the Clarke transformation, wherein the three-phase amplitude-modulated signals are offset by 120° from each other.

[0051] In embodiments of the invention, the processing comprises compensating for a shift variation in the center-tapped transmit coil by calibration for balancing the inductance of the center-tapped transmit coil without the target or when the target is positioned at a center position of the center-tapped transmit coil.

[0052] In embodiments of the invention, the method is applied to at least two center-tapped transmit coils oriented in different directions from each other, and wherein the processing comprises calculating the position of the target relative to both transmit coils.

[0053] In embodiments of the invention, the method is applied to at least two center-tapped transmit coils oriented in the same direction, and wherein the processing comprises calculating the position of the target relative to both transmit coils.

[0054] Particular and preferred aspects of the present invention are set out in the appended independent and dependent claims. Features from the dependent claims can be combined with those of the independent claims and the claims of other dependent claims, without departing from the scope of the present invention as defined in the appended claims.

[0055] These and other aspects of the application will be apparent from the following description, reference being made to the following description and to the embodiments described hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0056] Fig. 1 shows a schematic diagram of the principle of a conventional inductive position sensor.

[0057] Fig. 2 shows a block diagram of a conventional inductive position sensor.

[0058] Fig. 3 shows a signal obtained using a receiving coil of a conventional position sensor.

[0059] Figure 4 A useful range of target positions in which the Clarke transform can be applied to obtain the target position using a method or apparatus according to embodiments of the application is shown.

[0060] Figure 5 A block diagram of a position sensor according to embodiments of the application is shown.

[0061] Figure 6 A detailed block diagram of an exemplary position sensor according to embodiments of the application is shown.

[0062] Figure 7 A variation of the signal at the input of the receiver of an exemplary position sensor according to embodiments of the application as a function of the target position is shown.

[0063] Figure 8 A variation of the output position (in degrees) at the output of the processing circuit obtained using a position sensor or method according to embodiments of the application as a function of the target position is shown.

[0064] Figure 9 A schematic diagram of a linear center-tapped transmitting coil for a position sensor according to embodiments of the application is shown.

[0065] Figure 10 A schematic diagram of an arc-shaped center-tapped transmitting coil for a position sensor according to embodiments of the application is shown.

[0066] Figure 11 A schematic diagram of two linear center-tapped transmitting coils oriented in different directions for a position sensor according to embodiments of the application is shown.

[0067] Figure 12 A block diagram of a position sensor according to embodiments of the application comprising two center-tapped transmitting coils is shown.

[0068] Figure 13 A flowchart of a method according to an embodiment of the application is shown.

[0069] Any reference signs in the claims should not be construed as limiting the scope.

[0070] In the different drawings, like reference numerals refer to same or similar elements. DETAILED DESCRIPTION

[0071] The application will be described with respect to particular embodiments and with reference to certain drawings but the application is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements can be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond exactly to actual reductions for the purposes of illustration.

[0072] The terms first, second, etc. used in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing the temporal or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the application described herein are capable of operating according to different sequences of events than are illustrated or otherwise described herein.

[0073] It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted that the term "comprising" means "consisting at least of the stated features", but that it does not exclude the presence of one or more additional features, integers, steps or groups of features, integers, steps. It is thus to be interpreted in accordance with the purposes for which the term is used in the legal context.

[0074] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but can refer to different embodiments. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0075] Similarly, it is to be appreciated that, in the description of exemplary embodiments of the application, various features of the application are sometimes grouped together in a single embodiment, figure, or description of related features. This method of disclosure, however, is not to be interpreted as reflecting an intention that the application requires more features than are explicitly recited in each claim. Rather, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby expressly incorporated into this detailed description, with each claim acting as a separate embodiment of the application. The application illustratively disclosed herein suitably can be practiced in the absence of any element(s) not specifically disclosed herein.

[0076] Furthermore, although some embodiments described herein include some features of other embodiments described herein, those implementations that include fewer than all features are within the scope of the present application and form different embodiments as would be understood by one skilled in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination.

[0077] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the application can be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0078] In embodiments of the application where a center-tapped transmit coil is mentioned, a transmit coil is meant that has a first terminal and a second terminal at its open end portions and has a center tap between the first terminal and the second terminal. In embodiments of the application, the center position of the target refers to the position at which the target is aligned with the midpoint of the range of motion of the sensor relative to the center-tapped transmit coil. In a linear shaped transmit coil, the center position can be substantially in the middle of the linear range of travel. In an arcuate shaped transmit coil, the center position can be substantially in the middle of the angular range of travel of the target.

[0079] In the present invention, such a position sensor and method are introduced which rely on the detection of an inductance imbalance caused by a change of the target position. The device and method require a single center-tapped transmit (TX) coil, the three terminals of which are coupled to a receiver, and wherein the processing of the received signals for calculating the position of the target is based on a transformation which is suitable for calculating the angular position of the target from three-phase amplitude-modulated signals obtained using a single transmit coil and three receive coils, wherein the three-phase amplitude-modulated signals are offset by 120° from each other. Thus, advantageously, a conventional inductive position sensor integrated circuit (IC) can be used for calculating the relative position of the target. In embodiments of the present invention, such a transformation can be a Clarke transformation.

[0080] In embodiments of the present invention, instead of using a coil system consisting of four coils (one Tx and three Rx), only one balanced center-tapped Tx coil is used in such a way that the balance between the inductances of the two parts is disturbed with respect to the target position. Thus, the signal on the center tap, which is proportional to the inductance imbalance, will carry the position information. The advantage is that the concept relies on a single step of induction between the TX coil and the target, which leads to a greater useful signal amplitude and thus is suitable for miniaturized designs.

[0081] The fact that the proposed solution involves a single step of induction compared to the conventional inductive position sensor coil system solution which involves two steps of induction allows for a greater strength of the received signal. Due to the requirement of fewer coils and due to the requirement of fewer coupling steps, the size of the printed circuit board (PCB) module can be reduced and better electromagnetic compatibility (EMC) performance can be obtained.

[0082] In a first aspect, embodiments of the present invention relate to a position sensor. Figure 5 An exemplary embodiment of a position sensor 100 according to embodiments of the present invention is shown in Fig. 1.

[0083] The position sensor 100 comprises a center-tapped transmit coil 110, which consists of a first terminal 111, a center tap 112, and a second terminal 113. The transmit coil 110 is divided into two parts: a first part 110a between the first terminal 111 and the center tap 112, and a second part 110b between the center tap 112 and the second terminal 113.

[0084] The sensor further comprises a transmitter 120. The transmitter 120 has a positive output terminal 121 which is electrically connected to the first terminal 111 of the transmit coil 110. Additionally, the transmitter 120 has a negative output terminal 122 which is electrically connected to the second terminal 113 of the transmit coil 110. The transmitter 120 is designed to apply an oscillating signal between the first terminal 111 and the second terminal 113 of the transmit coil 110. In embodiments of the invention, the frequency of the oscillating signal can for example be between 2 Mhz and 5 Mhz.

[0085] The sensor further comprises a receiver 130 comprising a first receive input 131, a second receive input 132 and a third receive input 133, wherein the first terminal 111 of the transmit coil 110 is electrically coupled to one of the first, second or third receive inputs via a first electrical coupling 114, and wherein the second terminal 113 of the transmit coil 110 is electrically coupled to a different one of the first, second or third receive inputs via a second electrical coupling 115, and wherein the center tap 112 of the transmit coil 110 is electrically coupled to the remaining one of the first, second or third receive inputs via a third electrical coupling 116.

[0086] Finally, the position sensor 100 contains a processing circuit 140. This processing circuit 140 is configured to apply a transformation to the signals received on the first, second and third receive inputs 131, 132, 133, thereby calculating the position of the target relative to the center-tapped transmit coil 110.

[0087] An advantage of embodiments of the invention is that existing conventional inductive position sensor ICs can still be employed to detect the position of the target, which ICs utilize a transformation that calculates the angular position of the target from three-phase amplitude-modulated signals obtained using a single transmit coil and three receive coils, wherein the three-phase amplitude-modulated signals are offset from each other by 120°.

[0088] Such a transformation can be a Clarke transformation. However, other transformations for obtaining the angular position from signals obtained from a prior art device comprising a transmit coil and 3 receive coils are possible. For example, such another transformation can be based on the differences between the three-phase amplitude-modulated signals offset by 120°, and on the ratios of these differences. The angular position of the target is calculated from these ratios.

[0089] An advantage of embodiments of the invention is that the transformations that can be used to calculate the angular position from signals obtained from a prior art device comprising a transmit coil and 3 receive coils can also be used to calculate the angular position from signals from the center-tapped transmit coil of the invention.

[0090] In embodiments of the invention, the signal envelope from the center tap 112 of the TX coil can transition from positive to negative or from negative to positive as the target position changes, depending on the starting position of the target.

[0091] In embodiments of the invention, the first terminal 111 of the transmit coil 110 can be electrically coupled to a first receive input, and the second terminal 113 can be electrically coupled to a second receive input, and the center tap 112 of the transmit coil can be electrically coupled to a third receive input, for example.

[0092] In embodiments of the invention, the first electrical coupling 114, the second electrical coupling 115, and the third electrical coupling 116 are capacitive couplings. Figure 5 A diagram illustrating an example thereof is shown in FIG. 3. In this diagram, the capacitive coupling comprises a series connection of a capacitor (a), a resistor (b) between a terminal of the transmit coil and a receive input of the receiver, and a capacitor (c) between an input of the receiver and ground. In embodiments of the invention, the coupling capacitor (a) can be sufficient to make the capacitive coupling.

[0093] Figure 6 A detailed block diagram of an exemplary position sensor according to embodiments of the invention is shown in FIG. 4. In this example, a prior art integrated circuit is used for the transmitter 120, the receiver 130, and the processing circuit 140.

[0094] The capacitive couplings 114, 115, 116 are used to connect the terminals of the transmit coil to the receiver inputs of the receiver 130 of the prior art integrated circuit. In this exemplary embodiment of the invention, the coupling capacitor of the first capacitive coupling 114 between the first terminal 111 and the first receive input has a capacitance of 10 pF, and the coupling capacitor of the second capacitive coupling 115 between the second terminal 113 and the second receive input has a capacitance of 10 pF. In this exemplary embodiment of the invention, the coupling capacitor of the third capacitive coupling 116 between the first center tap 112 and the third receive input has a capacitance of 100 pF. However, the invention is not limited to these capacitance values.

[0095] In this example, the receiver 130 comprises an EMC filter for filtering the signal from the receiver inputs, an amplifier for amplifying the filtered signal, a baseband converter for converting the amplified signal to baseband, a multiplexer and a programmable gain amplifier, and an ADC for converting the processed analog signal to a digital signal.

[0096] The transmitter 120 comprises an LC oscillator for generating an oscillating signal.

[0097] The processing circuit 140 includes a digital signal processor for applying a transform (e.g., a Clarke transform) to the ADC-converted signals. The processing circuit includes configuration registers for controlling the implemented algorithm.

[0098] Consider a signal generated by a conventional coil system operating around 90° (in a range between 60° and 120°) as depicted in Figure 4 and connect the center tap 112 to the third input IN2, the positive terminal to the first input IN0, and the negative terminal to the second input IN1. The amplitudes of the signals on IN0, IN1, and IN2 are each assigned to a different input variable of the transform (e.g., the Clarke transform).

[0099] The three received signals then behave like Figure 7 as shown in When the target moves across its mechanical range, the IN2 signal linearly decreases from positive to negative, while the IN0 and IN1 signals remain constant.

[0100] Figure 8 It is important to note that by applying an offset angle using the configuration registers, the final output angle on the interface can be adjusted to be centered at any angle other than 90°. Additionally, the relationship between the final output angle and the target position can be linearized by utilizing the existing configuration registers, as is done in conventional rotary applications.

[0101] In embodiments of the invention, coupling capacitors connected between the transmit coil terminals and the receive inputs can be used to adjust the output angle range of the received signals.

[0102] With respect to Figure 5 and Figure 7 it is important to note, for example, that increasing the coupling capacitor 116a on the IN2 input increases the slope of IN2 with respect to the target position, while decreasing the coupling capacitors 114a and 115a on the IN0 and IN1 inputs decreases their respective signal amplitudes. Both effects contribute to expanding the output angle range, which is proportional to the ratio of IN2 to IN0.

[0103] In embodiments of the invention, the internal configuration registers of the position sensor can also be used, or alternatively, to adjust the output angle range.

[0104] A third way of adjusting the range of output angles, which can be used in combination with the other two ways, can be achieved by the design of the transmit coil. For example, a first part of the coil can be different from a second part of the coil. For example, its inductance can be larger than the inductance of the second part of the coil, or its length can be longer than the length of the second part of the coil.

[0105] In embodiments of the invention, the signals received on the first, second and third receive inputs are used as variables for a transformation, e.g. a Clarke transformation. The output range of the transformation depends on the amplitudes of the variables relative to each other, and thus on the choice of which input is used for each variable.

[0106] An advantage of embodiments of the invention is that the proposed solution is inherently resistant to changes in TX signal amplitude, due to its reliance on differential measurements. This differential approach allows the system to effectively distinguish between amplitude changes of the center tap signal caused by positional offsets and those caused by changes in TX signal amplitude.

[0107] In embodiments of the invention, the center-tapped transmit coil 110 is a balanced center-tapped transmit coil without a target or when the target is positioned at the center position of the center-tapped transmit coil.

[0108] In embodiments of the invention, the processing circuitry 140 is configured to compensate for variations in the offset in the center-tapped transmit coil 110 by a calibration for balancing the inductance of the center-tapped transmit coil without a target or when the target is positioned at the center position of the center-tapped transmit coil.

[0109] In embodiments of the invention, the existing PCB offset calibration hardware in a conventional inductive position sensor IC can be used for this calibration. The calibration may, for example, correct for mismatches in the TX coil or coupling capacitor.

[0110] In embodiments of the invention, the processing circuitry can be configured to adjust the received signals to their expected values when no target is present, ensuring that the system is balanced.

[0111] In particular, this involves adjusting the signals such that the sum of the three differential signals at the receiver inputs is equal to zero.

[0112] In a position sensor according to an embodiment of the application in which the center tap 112 is connected to the third input IN2, the positive terminal is connected to the first input IN0, and the negative terminal is connected to the second input IN1, the calibration can be such that IN2 is 0, and that IN1 is equal to -IN0. Since the compensation is done on differential signals, this means that: the goal is to make (IN1-IN2) equal to (IN2-IN0); and (IN0-IN1) is (-2) times each of (IN1-IN2) and (IN2-IN0). Finally, as usual, the sum of the three differential signals should be zero. It should be noted that it is often desirable to do the PCB offset calibration with the target mounted, since the target will also influence the offset. In that case, it is recommended to do the calibration described with the target in the center position with respect to the mechanical travel range.

[0113] In an embodiment of the application, the center tapped transmit coil 110 is a straight elongated coil (i.e. a linear coil). Figure 9 An example of which is shown in Fig. 2. It shows a loop of wire extending along a straight line. The loop can comprise a plurality of strands of wire. The loop is open and comprises a first terminal 111 and a second terminal 113 at open ends. Furthermore, the loop comprises a center tap 112 substantially at the midpoint of the linear travel range.

[0114] In an embodiment of the application, the travel range can extend over the entire size of the transmit coil. However, this is not strictly required. For example, the travel range can be smaller than the size of the transmit coil.

[0115] In an embodiment of the application, the center tapped transmit coil 110 is an arcuate coil. Figure 10 An example of which is shown in Fig. 3. It shows a loop of wire extending along an arcuate line. The loop can comprise a plurality of strands of wire. The loop is open and comprises a first terminal 111 and a second terminal 113 at open ends. Furthermore, the loop comprises a center tap 112 substantially at the midpoint of the arcuate travel range.

[0116] In an embodiment of the application, the position sensor 100 comprises an additional center tapped transmit coil 110’ which is oriented in a different direction than the original center tapped transmit coil 110. Figure 11 A schematic diagram of two center tapped transmit coils 110, 110’ oriented in different directions is shown. In this example, the transmit coils are linear transmit coils. Figure 12 A block diagram of such a position sensor 100 is shown.

[0117] The additional center-tapped transmit coil 110’ comprises a first terminal 111’, a center tap 112’ and a second terminal 113’. The coil is divided into two parts: a first part 110a’ between the first terminal 111’ and the center tap 112’, and a second part 110b’ between the center tap 112’ and the second terminal 113’.

[0118] The transmitter 120 comprises an additional positive output terminal 121’ electrically coupled to the first terminal 111’ of the additional transmit coil, and an additional negative output terminal 122’ electrically coupled to the second terminal 113’ of the additional transmit coil. The transmitter 120 is configured for applying an oscillating signal between the first terminal 111’ and the second terminal 113’ of the additional transmit coil 110’.

[0119] The receiver 130 comprises an additional set of inputs: an additional first receive input 131’, an additional second receive input 132’ and an additional third receive input 133’. The first terminal 111’ of the additional transmit coil 110’ is electrically coupled to one of these inputs using an additional first electrical coupling 114’. The second terminal 113’ of the additional transmit coil 110’ is electrically coupled to a different input using an additional second electrical coupling 115’. The center tap 112’ of the additional transmit coil 110’ is electrically coupled to the remaining input using an additional third electrical coupling 116’.

[0120] In a second aspect, embodiments of the application relate to a method 300 for determining a position of a target 200. Figure 13 An exemplary flowchart of such a method is shown in Fig. 2. The method comprises applying (310) an oscillating signal between a first terminal 111 and a second terminal 113 of a center-tapped transmit coil 110, the transmit coil 110 comprising a center tap 112 between the first terminal 111 and the second terminal 113. The method further comprises receiving (320) signals from the first terminal 111, the second terminal 113 and the center tap 112. Finally, the method comprises processing (330) the received signals by applying a transformation (e.g. Clarke) to compute a position of the target relative to the center-tapped transmit coil.

[0121] In embodiments of the application, the processing (330) comprises linearizing the target position obtained after the transformation.

[0122] In embodiments of the application, the processing comprises compensating for variations in the offset in the center-tapped transmit coil 110 by calibration, such calibration being used to balance the inductance of the center-tapped transmit coil without a target, or when the target is positioned at the center position of the center-tapped transmit coil.

[0123] In an embodiment of the invention, the method is applied to at least two center-tapped transmitting coils 110 oriented in different directions from each other, and wherein the process (330) includes calculating the position of a target relative to the two transmitting coils.

[0124] In an embodiment of the invention, the method is applied to at least two center-tapped transmitting coils 110 oriented in the same direction, and wherein the process (330) includes calculating the position of the target relative to the two transmitting coils.

[0125] In an embodiment of the invention, the method includes a calibration step for balancing the inductance of a center-tapped transmitting coil in the absence of a target. In another embodiment, calibration is performed when a target is positioned at the center of the center-tapped transmitting coil. This calibration step compensates for offset variations in the center-tapped transmitting coil 110.

Claims

1. A position sensor (100) for determining a position of a target (200), the position sensor comprising: a center-tapped transmit coil (110) comprising a first terminal (111), a center tap (112) and a second terminal (113), wherein a first part (110a) of the transmit coil is between the first terminal (111) and the center tap (112) and a second part (110b) of the transmit coil is between the center tap and the second terminal; a transmitter (120) comprising a positive output terminal (121) and a negative output terminal (122), the positive output terminal (121) being electrically coupled with the first terminal (111) of the transmit coil, the negative output terminal (122) being electrically coupled with the second terminal (113) of the transmit coil, and the transmitter (120) being configured for applying an oscillating signal between the first terminal (111) and the second terminal (113) of the transmit coil (110); a receiver (130) comprising a first receive input (131), a second receive input (132) and a third receive input (133), wherein the first terminal (111) of the transmit coil (110) is electrically coupled with one of the first receive input, the second receive input or the third receive input using a first electrical coupling (114), and wherein the second terminal (113) of the transmit coil (110) is electrically coupled to a different one of the first receive input, the second receive input or the third receive input using a second electrical coupling (115), and wherein the center tap (112) of the transmit coil (110) is electrically coupled to the remaining one of the first receive input, the second receive input or the third receive input using a third electrical coupling (116); a processing circuit (140) configured for applying a transformation to signals received on the first receive input (131), the second receive input (132) and the third receive input (133) to calculate a position of the target relative to the center-tapped transmit coil.

2. The position sensor (100) of claim 1, wherein, The transformation is a Clarke transformation.

3. The position sensor (100) of claim 1, wherein, The center-tapped transmit coil (110) is a balanced center-tapped transmit coil in absence of the target or when the target is located at a center position of the center-tapped transmit coil.

4. The position sensor (100) of claim 1, wherein, The first electrical coupling (114), the second electrical coupling (115) and the third electrical coupling (116) are capacitive couplings.

5. The position sensor (100) of claim 1, wherein, The center-tapped transmit coil (110) is a linear coil.

6. The position sensor (100) of claim 1, wherein, The center-tapped transmit coil (110) is an arc-shaped coil.

7. The position sensor (100) of claim 1, comprising an additional center-tapped transmit coil (110'), the additional center-tapped transmit coil (110') comprising a first terminal (111'), a center tap (112') and a second terminal (113'), wherein a first portion (110a') of the additional transmit coil is between the first terminal (111') and the center tap (112') and a second portion (110b') of the additional transmit coil is between the center tap (112') and the second terminal (113'); the transmitter (120) comprises an additional positive output terminal (121') and an additional negative output terminal (122'), the additional positive output terminal (121') being electrically coupled with the first terminal (111') of the additional transmit coil, the additional negative output terminal (122') being electrically coupled with the second terminal (113') of the additional transmit coil, and the transmitter (120) being configured to apply an oscillating signal between the first terminal (111') and the second terminal (113') of the additional transmit coil (110'); The receiver (130) comprises an additional first reception input (131'), an additional second reception input (132') and an additional third reception input (133'), wherein the first terminal (111') of the additional transmit coil (110') is electrically coupled with one of the additional first receive input, the additional second receive input or the additional third receive input using an additional first electrical coupling (114'), and wherein the second terminal (113') of the additional transmit coil (110') is electrically coupled to a different one of the additional first receive input, the additional second receive input or the additional third receive input using an additional second electrical coupling (115'), and wherein the center tap (112') of the additional transmit coil (110') is electrically coupled to the remaining additional receive input of the additional first receive input, the additional second receive input or the additional third receive input using an additional third electrical coupling (116'); wherein the processing circuitry (140) is additionally configured to apply a transformation to signals received on the additional first receive input (131), the additional second receive input (132) and the additional third receive input (133) to calculate the position of the target relative to the additional center-tapped transmit coil.

8. The position sensor (100) of claim 7, wherein, the additional center-tapped transmit coil (110') is oriented in a different direction than the center-tapped transmit coil (110).

9. The position sensor (100) of claim 1, wherein, the processing circuitry (140) is configured to compensate for variations in offset in the center-tapped transmit coil (110, 110') by calibration to balance the inductance of the center-tapped transmit coil without the target or when the target is positioned at a center position of the center-tapped transmit coil.

10. The position sensor (100) of claim 1, wherein, a configuration register is used by the processing circuitry (140) to linearize target positions obtained from the transformation.

11. A method (300) for determining a position of a target (200), the method comprising: applying (310) an oscillating signal between a first terminal (111) and a second terminal (113) of a center-tapped transmit coil (110), the center-tapped transmit coil (110) comprising a center tap (112); receiving (320) signals from the first terminal (111), the second terminal (113) and the center tap (112); processing (330) the received signals by applying a transformation to compute a position of the target relative to the center-tapped transmit coil.

12. The method (300) of claim 11, wherein The processing (330) comprises linearizing the target position obtained after the transformation.

13. The method (300) of claim 11, wherein, The processing comprises compensating for variations in the offset in the center-tapped transmit coil (110) by calibration to balance the inductance of the center-tapped transmit coil without the target or when the target is positioned at a center position of the center-tapped transmit coil.

14. The method (300) of claim 11, wherein The method is applied to at least two center-tapped transmit coils (110, 110’), wherein the processing (330) comprises computing a position of the target relative to both transmit coils.

15. The method (300) of claim 11, wherein The method comprises a calibration step to balance the inductance of the center-tapped transmit coil without the target or when the target is positioned at a center position of the center-tapped transmit coil to compensate for variations in the offset in the center-tapped transmit coil (110).

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