SENSOR AND METHOD OF SENSING

• US 20100214259A1
• Filed: 07/31/2008
• Published: 08/26/2010
• Est. Priority Date: 07/31/2007
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Philipp, Harald, Yilmaz, Esat
• Granted Patent: US 9,600,124 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/044 by capacitive means
• 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
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

A sensor is arranged to determine the presence of an object from a change in a capacitance of a sensing element. The sensor includes a capacitance measurement circuit operable to perform measurement cycles to measure a capacitance of the sensing element, and a controller circuit. The control circuit is operable to detect a periodic noise signal induced on the sensing element, to determine a first part, of a repeating pattern of the periodic noise signal, which causes a change in an amount of charge present on the sensing element, which affects the measurement of the capacitance of the sensing element by the capacitance measurement circuit, to determine a second part of the repeating pattern of the periodic noise signal, which does not cause a change in the amount of charge present on the sensing element, and to control the measurement cycles of the capacitance measurement circuit to perform the measurement cycles during the second part of the periodic noise signal and not to perform the measurement cycles during the first part of the periodic noise signal.

Claims

1. A sensor for determining the presence of an object from a change in a capacitance of a sensing element, the sensor comprising

a capacitance measurement circuit operable to perform measurement cycles to measure a capacitance of the sensing, element, and

a controller circuit operable

to detect a periodic noise signal induced on the sensing element,

to determine a first part of a repeating pattern of the periodic noise signal, which causes a change in an amount of charge present on the sensing element, which affects the measurement of the capacitance of the sensing element by the capacitance measurement circuit,

to determine a second part of the repeating pattern of the periodic noise signal, which does not cause a change in the amount of charge present on the sensing element, and

to control the measurement cycles of the capacitance measurement circuit to perform the measurement cycles during the second part of the periodic noise signal and not to perform the measurement cycles during the first part of the periodic noise signal.

2. A sensor as claimed in claim 1, wherein the sensing element includes a key and the controller is operable to control the capacitance measurement circuit to detect a change in the capacitance of the sensing element by

generating a plurality of the measurement cycles, each measurement cycle including inducing charge onto the key during a charging part of a measurement cycle, and measuring an amount of charge induced on the key during a signal measurement part of the measurement cycle, and

detecting the presence of the object proximate the key from a change in an amount of charge transferred from the key, thereby to detect a change in the capacitance of the sensing element.

3. A sensor as claimed in claim 2, wherein the controller circuit is operable to control the measurement cycles of the capacitance measurement circuit, to perform the measurement cycles during the second part of the periodic noise signal and not to perform the measurement cycles during the first part of the periodic noise signal by

generating one or more measurement bursts, each measurement burst providing a plurality of the measurement cycles, and

synchronizing the generation of the plurality of bursts and the measurement cycles within the bursts to coincide with the second part of the periodic noise signal.

4. A sensor as claimed in claim 3, wherein the controller circuit is operable to synchronize the generation of the plurality of bursts of the measurement cycles with respect to the periodic noise signal by

determining a temporal length of each of the bursts of the measurement cycles, and

adjusting the timing of the bursts of measurement cycles to coincide with the part or parts of the noise signal which are less likely to affect the capacitance measurements.

5. A sensor as claimed in claim 3, wherein the first part of the periodic noise signal includes rising or falling edges and the controller circuit is operable to synchronize the generation of the plurality of bursts and the measurement cycles within the bursts by

detecting the rising and falling edges in the periodic noise signal, and

synchronizing the generation of the bursts and the measurement cycles within the bursts to avoid rising and/or falling edges in the detected noise signal.

6. A sensor as claimed in claim 1, wherein the controller circuit is operable to control the measurement circuit to generate the measurement cycles for a plurality of periods of the periodic noise signal and not to generate the measurement cycles in the first part of the repeating noise signal.

7. A sensor as claimed in claim 1, wherein the controller circuit is coupled to the sensing element and is arranged to detect the noise signal induced on the sensing element from the sensing element itself.

8. A sensor as claimed in claim 1, wherein the controller circuit is operable to detect the noise signal during a noise sensing phase, in which the capacitance measurement circuit does not perform any measurement cycles and the key or keys of the sensing element are floated.

9. A sensor as claimed in claim 1, wherein the key includes a key matrix forming a two dimensional capacitive transducer.

22. A sensor as claimed in claim 1, wherein the periodic noise signal is generated by a liquid crystal display screen.

10. A method of determining the presence of an object from a change in a capacitance of a sensing element, the method comprising

detecting a periodic noise signal induced on the sensing element,

determining a first part of a repeating pattern of the periodic noise signal, which causes a change in an amount of charge present on the sensing element, which affects the measurement of the capacitance of the sensing element,

determining a second part of the repeating pattern of the periodic noise signal, which does not cause a change in the amount of charge present on the sensing element,

performing measurement cycles to measure a capacitance of the sensing element during the second part of the periodic noise signal and not performing the measurement cycles during the first part of the periodic noise signal.

11. A method as claimed in claim 10, wherein the sensing element includes a key, and the performing measurement cycles to measure the capacitance of the sensing element includes

generating a plurality of measurement cycles, each measurement cycle including inducing charge onto the key during a charging part of a measurement cycle, and determining an amount of charge induced on the key during a signal measurement part of the measurement cycle, and

detecting the presence of the object proximate the key from a change in an amount of charge transferred from the key, thereby detecting a change in the capacitance of the sensing element.

12. A method as claimed in claim 11, wherein the performing measurement cycles to measure a capacitance of the sensing element during the second part of the periodic noise signal and not performing the measurement cycles during the first part of the periodic noise signal, includes

generating one or more measurement bursts, each measurement burst providing a plurality of the measurement cycles, and

synchronizing the generation of the plurality of bursts and the measurement cycles within the bursts to coincide with the second part of the periodic noise signal.

13. A method as claimed in claim 12, wherein the synchronizing the generation of the plurality of bursts and the measurement cycles within the bursts to coincide with the second part of the periodic noise signal, includes

determining a temporal length of each of the bursts of the measurement cycles, and

adjusting the timing of the burst of measurement cycles to coincide with the second part of the periodic noise signal

14. A method as claimed in claim 12, wherein the synchronizing the generation of the plurality of bursts and the measurement cycles within the bursts to coincide with the second part of the periodic noise signal, includes

detecting the rising and falling edges in the periodic noise signal, and

synchronizing the generation of the bursts and the measurement cycles within the bursts to avoid rising and/or falling edges in the detected noise signal.

15. A method as claimed in claim 10, wherein the performing the measurement cycles to measure the capacitance of the sensing element includes

generating the measurement cycles for a plurality of periods of the periodic noise signal, and

not generating the measurement cycles in the first part of the repeating noise signal.

16. A method as claimed in claim 10, wherein the detecting the periodic noise signal induced on the sensing element, includes

detecting the periodic noise signal induced on the sensing element from the sensing element itself.

17. A method as claimed in claim 16, wherein the detecting the periodic noise signal induced on the sensing element, includes

detecting the noise signal during a noise sensing phase, in which the capacitance measurement circuit does not perform any measurement cycles and the key or keys of the sensing element are floated.

18. A method as claimed in claim 17, wherein the key includes a key matrix forming a two dimensional capacitive transducer.

19. A controller for sensing the presence of an object from a change in an amount of charge present on a sensing element, the controller being operable

to detect a periodic noise signal induced on the sensing element,

to determine a first part of a repeating pattern of the periodic noise signal, which causes a change in an amount of charge present on the sensing element, which affects a measurement of a capacitance of the sensing element,

to determine a second part of the repeating pattern of the periodic noise signal, which does not cause a change in the amount of charge present on the sensing element, and

to control measurement cycles of a capacitance measurement circuit to perform the measurement cycles during the second part of the periodic noise signal and not to perform the measurement cycles during the first part of the periodic noise signal.

20. A controller as claimed in claim 19, wherein the sensing element includes a key and the controller is operable to detect a change in the capacitance of the sensing element by

generating a plurality of the measurement cycles, each measurement cycle including inducing charge onto the key during a charging part of a measurement cycle, and measuring an amount of charge induced on the key during a signal measurement part of the measurement cycle, and

detecting the presence of the object proximate the key from a change in an amount of charge transferred from the key, thereby to detect a change in the capacitance of the sensing element.

21. An apparatus for determining the presence of an object from a change in a capacitance of a sensing element, the apparatus comprising

means for detecting a periodic noise signal induced on the sensing element,

means for determining, a first part of a repeating pattern of the periodic noise signal, which causes a change in an amount of charge present on the sensing element, which affects the measurement of the capacitance of the sensing element,

means for determining a second part of the repeating pattern of the periodic noise signal, which does not cause a change in the amount of charge present on the sensing element,

means for performing measurement cycles to measure a capacitance of the sensing element during the second part of the periodic noise signal and not performing the measurement cycles during the first part of the periodic noise signal.