Capacitive position sensor system

• US 9,977,061 B2
• Filed: 09/26/2013
• Issued: 05/22/2018
• Est. Priority Date: 10/02/2012
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Suwald, Thomas
• Primary Examiner(s): Phan, Minh
• Assistant Examiner(s): Ferdous, Zannatul
• Application Number:
  US14/038,554
• Publication Number:
  US 20140091815A1
• Time in Patent Office: 1,699 Days
• Field of Search: 324658, 345173, 345174
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A capacitive position sensor system for determining the position of an object, in particular on a surface of a contactless smartcard, is provided. The object is positioned within a sensitive area of the capacitive position sensor system and changes the capacitance of capacitors being arranged underneath the object. The capacitive position sensor system comprises a set of sensing elements being arranged in the form of a column. Each sensing element includes a first capacitor having a first electrode and a second electrode and a second capacitor having a first electrode and a second electrode. A specific weighting factor is assigned to each capacitor. A control unit is adapted to determine the position of the object in one dimension by analyzing the results of a plurality of sensed voltage levels for the first capacitors and the second capacitors of a plurality of integration cycles.

Claims

1. A capacitive position sensor system for determining the position of an object, in particular on a surface of a contactless smartcard, wherein the object is positioned within a sensitive area of the capacitive position sensor system and changes the capacitance of sensing capacitors being arranged underneath the object, the capacitive position sensor system comprising

a set of sensing elements being arranged in the form of a column, each sensing element comprising a first sensing capacitor having a first electrode and a second electrode and a second sensing capacitor having a first electrode and a second electrode, wherein each first electrode is coupled via a switch to a voltage supply to form a switched capacitor filter, wherein the second electrodes of the first sensing capacitors are coupled to form a first sensing line and the second electrodes of the second sensing capacitors are coupled to form a second sensing line, wherein the electrodes of the first and second sensing capacitors are configured relative to a substrate such that a human finger in close proximity to the substrate causes distortion of a fringe field,

a sensing unit, wherein the sensing unit is adapted to sense a voltage level representing the amount of charge being present on the first sensing line and the second sensing line, and

a control unit, wherein the control unit is adapted to apply a drive signal to each of the switches being coupled to the first electrodes,

wherein a specific sensor position weighting factor is assigned to each sensing capacitor, wherein the capacitances of the first and the second sensing capacitor of one sensing element corresponds to a constant capacitance value, wherein the first sensing capacitors of the set of sensing elements are weighted with sensor position weighting factors that increase relative to each other in one direction along the column and the second sensing capacitors of this set of sensing elements are weighted with sensor position weighting factors that decrease relative to each other in the same direction along the column, wherein the sensor position weighting factor assigned to each sensing capacitor is a multiplier that is a function of the distance of the corresponding sensing capacitor from an origin,

wherein the control unit is adapted to, in one integration cycle, close a part of the switches being coupled to the first electrodes so that a part of the first sensing capacitors is driven by a first drive signal and close a part of the switches being coupled to the second electrodes so that a part of the second sensing capacitors is driven by a second drive signal, wherein the sensing unit is adapted to sense the voltage level representing the sum of the amount of charge of the part of the first sensing capacitors and the voltage level representing the sum of the amount of charge of the part of the second sensing capacitors,

wherein the control unit is adapted to determine the position of the object in one dimension by analyzing the results of a plurality of sensed voltage levels for the first sensing capacitors and the second sensing capacitors of a plurality of integration cycles, wherein analyzing the results of a plurality of sensed voltage levels comprises multiplying the sensor position weighting factor assigned to a sensing capacitor by a value corresponding to the sensed voltage level of the corresponding sensing capacitor and using the product of the multiplication to determine the position of the object.

2. The capacitive position sensor system according to claim 1, wherein analyzing the results of a plurality of sensed voltage levels comprises computing the charge of each of the first sensing capacitors and the second sensing capacitors.

3. The capacitive position sensor system according to claim 1, wherein the second electrodes of the first sensing capacitors are arranged equally spaced between the second electrodes of the second sensing capacitors.

4. The capacitive position sensor system according to claim 1, wherein the number of integration cycles corresponds to the number of the first sensing capacitors.

5. The capacitive position sensor system according to claim 1, wherein the sensing unit comprises an integration capacitor being indicative for the sum of the amount of charge of the part of the first sensing capacitors and the second sensing capacitors, and

a comparator for comparing the voltage level sensed via the integration capacitor with a reference voltage.

6. The capacitive position sensor system according to claim 5, wherein parasitic capacitances of connection nodes being coupled to the integration capacitor between the sensing capacitors of the sensing elements and the sensing line may be used as a fly capacitor during charging and/or discharging.

7. The capacitive position sensor system according to claim 1, wherein the first sensing capacitors are interconnected on a first layer and the second sensing capacitors are interconnected on a second layer.

8. The capacitive position sensor system according to claim 1,

further comprising a dummy capacitor being adapted to equalize the parasitic capacitance of each sensor capacitor node to AC-ground.

9. The capacitive position sensor system according to claim 1,

wherein the set of sensing elements are arranged surrounded by a guard fence electrode being adapted to provide a reference ground.

10. The capacitive position sensor system according to claim 1,

wherein the set of sensing elements corresponds to one column and wherein the capacitive position sensor system comprises a plurality of sets of sensing elements being arranged parallel to each other in order to form a two-dimensional sensor system.

11. The capacitive position sensor system according to claim 1, further comprising an electronic device, in particular a keypad, a smart card or a mobile device, for receiving an input from a user, wherein the input corresponds to the positioning of an object of the user.

12. A method of determining the position of an object, in particular on a surface of a contactless smartcard, wherein the object is positioned within a sensitive area of a capacitive position sensor system and changes the capacitance of sensing capacitors being arranged underneath the object,

wherein the capacitive position sensor system comprises a set of sensing elements being arranged in the form of a column, each sensing element comprising a first sensing capacitor having a first electrode and a second electrode and a second sensing capacitor having a first electrode and a second electrode, wherein each first electrode is coupled via a switch to a voltage supply to form a switched capacitor filter, wherein the second electrodes of the first sensing capacitors are coupled to form a first sensing line and the second electrodes of the second sensing capacitors are coupled to form a second sensing line, wherein the electrodes of the first and second sensing capacitors are configured relative to a substrate such that a human finger in close proximity to the substrate causes distortion of a fringe field,

the method comprising

sensing, by a sensing unit, a voltage level representing the amount of charge being present on the first sensing line and the second sensing line,

applying, by a control unit, a drive signal to each of the switches being coupled to the first electrodes,

wherein a specific sensor position weighting factor is assigned to each sensing capacitor, wherein the capacitances of the first and the second sensing capacitor of one sensing element corresponds to a constant capacitance value, wherein the first sensing capacitors of the set of sensing elements are weighted with sensor position weighting factors that increase relative to each other in one direction along the column and the second sensing capacitors of this set of sensing elements are weighted with sensor position weighting factors that decrease relative to each other in the same direction along the column, wherein the sensor position weighting factor assigned to each sensing capacitor is a multiplier that is a function of the distance of the corresponding sensing capacitor from an origin,

wherein, in one integration cycle, a part of the switches being coupled to the first electrodes is closed so that a part of the first sensing capacitors is driven by a first drive signal and a part of the switches being coupled to the second electrodes is closed so that a part of the second sensing capacitors is driven by a second drive signal, wherein the sensing unit is adapted to sense the voltage level representing the sum of the amount of charge of the part of the first sensing capacitors and the voltage level representing the sum of the amount of charge of the part of the second sensing capacitors, and

determining, by the control unit, the position of the object in one dimension by analyzing the results of a plurality of sensed voltage levels for the first sensing capacitors and the second sensing capacitors of a plurality of integration cycles, wherein analyzing the results of a plurality of sensed voltage levels comprises multiplying the sensor position weighting factor assigned to a sensing capacitor by a value corresponding to the sensed voltage level of the corresponding sensing capacitor and using the product of the multiplication to determine the position of the object.

13. The method according to claim 12,

wherein the set of sensing elements corresponds to one column and wherein the capacitive position sensor system comprises a plurality of sets of sensing elements being arranged parallel to each other in order to form a two-dimensional sensor system,

wherein the method further comprises

determining, by the control unit, the position of the object in a second dimension by analyzing the results of a plurality of sensed voltage levels for the first sensing capacitors and the second sensing capacitors of a plurality of integration cycles being determined for the first dimension.

14. The method according to claim 13,

wherein the determination of the position in the second dimension comprises analyzing the sensing elements being relevant for the first dimension.