Device and method for determining an angular position of inductive position sensor

1. A method of determining an angular position of a target of an inductive angular position sensor system, wherein the inductive angular position sensor system further comprises: a substrate with at least one transmitter coil and a plurality of receiver coils, and a target which is movable relative to said substrate, the method comprising:

a) receiving a plurality of input signals from said receiver coils;

b) demodulating and optionally pairwise subtracting said plurality of input signals, and providing a plurality of sinusoidal baseband signals, each having a respective amplitude and a respective DC-offset;

c) digitizing said plurality of sinusoidal baseband signals or digitizing pairwise difference signals derived therefrom, and providing a set of digital signals;

d) reducing the respective DC-offset-value for each of the digital signals in an iterative manner, thereby providing a plurality of DC-compensated signals;

e) determining an angular position of the target based on the DC compensated signals;

wherein step d) comprises:

i) initializing a DC correction value;

ii) subtracting the DC correction value from the digital signal to obtain a DC-shifted signal;

iii) clipping the DC-shifted-signal to obtain clipped signals;

iv) calculating a first sum by summing values of the clipped signal over one period;

v) calculating a second sum by summing absolute values of the clipped signal over said period;

vi) adjusting the DC-correction value by a function of a ratio of the first sum and the second sum.

2. The method of claim 1 , wherein step d) comprises:

i) initializing each DC offset value to a predefined value;

and repeatedly performing the following steps:

ii) subtracting the DC-correction value from the respective digital signal, thereby obtaining DC-shifted signals;

iii) clipping the DC-shifted-signals to a predefined symmetrical range, thereby obtaining clipped signals;

iv) calculating the first sum value by summing values of the clipped signal over one period of the respective signal;

v) calculating the second sum value by summing absolute values of the clipped signal over said one period;

vi) updating the DC-correction values using the following formulas:

DC0: =DC0+ K *( s 0/ a 0);

DC1: =DC1+ K *( s 1/ a 1);

DC2: =DC2+ K *( s 2/ a 2);

where “:=” is an assignment operator, s0, s1, s2 are the first sum values; a0, a1, a2 are the second sum values; and K is a predefined constant; and going back to step ii).

3. The method according to claim 2 , wherein an amplitude of the symmetrical range is a value from about 75% to about 85% of the nominal or average value of the signal amplitude.

4. The method according to claim 2 , wherein step iii) further comprises: dynamically adjusting the symmetrical range such that an amplitude of the symmetrical range is a value from about 75% to about 85% of the nominal or average value of the signal amplitude.

5. The method according to claim 1 , further comprising:

providing an AC signal for exciting said transmitter coil; and

wherein the demodulation of step b) is performed in synchronism with said AC signal.

6. The method according to claim 1 , wherein the plurality of sinusoidal baseband signals or the plurality of pairwise difference signals are three-phase signals;

wherein step b) comprises:

converting the three-phase signals to quadrature signals;

determining the angular position using an arctangent function of a ratio of the quadrature signals.

7. The method according to claim 1 ,

wherein step c) comprises:

digitizing said signals using an analog-to-digital convertor that provides at least 12 bits; and

wherein step iii) comprises: providing the clipped values with at most 8 bits.

8. The method according to claim 1 ,

wherein step c) comprises:

digitizing said signals using an analog-to-digital convertor that provides at least 12 bits; and

wherein step iii) comprises: providing the clipped values with at least 2 bits.

9. The method according to claim 1 , wherein the method further comprises estimating or calculating an angular speed of the target.

10. The method according to claim 9 , wherein step c) comprises:

digitizing said signals using an analog-to-digital convertor that provides at least 12 bits; and

wherein step iii) comprises: providing the clipped values with a number of bits in the range from 2 to 8, the number of bits being dynamically adjusted depending on the estimated speed.

11. The method according to claim 1 , wherein the moment of start and the moment of end of each respective period is determined based on the moment at which the DC-compensated signals cross a corresponding DC offset value.

12. An inductive position sensor device for use in an inductive angular position sensor system, wherein the inductive angular position sensor system further comprises a substrate with at least one transmitter coil and a plurality of receiver coils, and a target which is movable relative to said substrate;

wherein the inductive position sensor device comprises:

a plurality of inputs for receiving a plurality of input signals obtained from said plurality of receiver coils;

a demodulation circuit for demodulating and optionally pairwise subtracting said plurality of input signals, and providing a plurality of sinusoidal signals;

at least one analog-to-digital convertor for digitizing said plurality of sinusoidal baseband signals or for digitizing pairwise difference signals derived therefrom, and providing a set of digital signals;

a digital processing circuit configured for performing step d) and e) of the method of claim 1 .

13. An inductive position sensor system comprising:

an inductive position sensor device according to claim 12 ;

a substrate with at least one transmitter coil and a plurality of receiver coils;

a target which is movable relative to said substrate.