Sensor and method of sensing

• US 8,552,995 B2
• Filed: 10/22/2009
• Issued: 10/08/2013
• Est. Priority Date: 10/22/2008
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Yilmaz, Esat, Philipp, Harald
• Primary Examiner(s): Lao, Lun-Yi
• Assistant Examiner(s): McLoone, Peter D
• Application Number:
  US12/604,258
• Publication Number:
  US 20100097077A1
• Time in Patent Office: 1,447 Days
• Field of Search: 345173-175, 178/18.01, 178 1805- 1807
• US Class Current: 345/173
• 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: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2017/9613 using two electrodes per touch switch

Abstract

A touch sensor senses the presence of an object at one of a plurality of channels on a surface of the touch sensor, wherein proximity of the object to the touch sensor results in a change in capacitance at the position of the channel. The touch sensor includes a drive circuit and a charge sensing circuit, each coupled to each of the channels. The charge sensing circuit includes at least one charge measurement capacitor. A measurement cycle is applied to the touch sensor having a drive portion and a sense portion. During the drive portion a charge is applied to the channels and therefore the charge measurement capacitors of the touch sensor, and during a sense portion the charge measurement capacitors are discharged by a predetermined amount and the remaining charge on the charge measurement capacitors is measured.

Claims

1. An apparatus, comprising:

a plurality of charge measurement capacitors configured to couple to a plurality of channels of a touch sensor; and

a controller configured to;

control transferring charge to each of the plurality of channels;

control coupling each of the plurality of charge measurement capacitors to one of the plurality of channels such that charge is transferred to each of the plurality of charge measurement capacitors;

control a first discharge of each of the charge measurement capacitors in parallel;

control, after the first discharge, a second discharge of each of the measurement capacitors sequentially; and

determine, based on the second discharge, an amount of charge that was remaining in each of the charge measurement capacitors after the first discharge.

2. The apparatus as claimed in claim 1, wherein during the first discharge, each of the charge measurement capacitors is discharged a predetermined discharge amount.

3. A touch sensor, comprising:

a plurality of channels;

a drive circuit coupled to each of the channels;

for each of the channels, a charge sensing circuit, each of the charge sensing circuits including a charge measurement capacitor; and

a controller coupled to the drive circuit and the charge sensing circuit, the controller being operable to;

control the drive circuit to induce charge onto each of the channels during a drive part of a measurement cycle;

control each of the charge sensing circuits to couple a respective charge measurement capacitor to one of the channels during a charge measurement part of the measurement cycle such that the charge induced onto the channel during the drive part of the measurement cycle is transferred to the respective charge measurement capacitor;

control a first discharge of each of the charge measurement capacitors in parallel;

control, after the first discharge, a second discharge of each of the measurement capacitors sequentially; and

determine, based on the second discharge, an amount of charge that was remaining in each of the charge measurement capacitors after the first discharge.

4. A touch sensor as claimed in claim 3, wherein during the first discharge, each of the charge measurement capacitors is discharged a predetermined discharge amount.

5. A touch sensor as claimed in claim 4, wherein the predetermined discharge amount is set in accordance with an expected amount of charge present on each of the signal measurement capacitors as a result of the presence of an object proximate a corresponding one of the channels of the touch sensor.

6. A touch sensor as claimed in claim 5, wherein the predetermined discharge amount is determined by measuring a range of values of the expected charge values on each of the charge measurement capacitors for each of the channels as a result of the presence and absence of an object and setting the predetermined discharge amount in accordance with the expected range of values.

7. A touch sensor as claimed in claim 3, wherein each of the channels of the touch sensor is an intersection of a drive line and a receiving line, each receiving line being coupled to a corresponding charge measurement capacitor of the charge sensing circuit, and the controller is operable to control the drive circuit to drive each of the plurality of drive lines during the drive portion of the measurement cycle, and to control the charge sensing circuit to transfer charge on the plurality of receiving lines to the plurality of charge measurement capacitors during the measurement portion of the measurement cycle.

8. A touch sensor as claimed in claim 3, wherein each of the plurality of channels of the touch sensor comprises a coupling plate, and the controller is arranged to control the drive circuit to:

charge the coupling plate of each of the plurality of channels during the drive part of the measurement cycle, and

control the charge sensing circuit to transfer charge from each coupling plate of each of the plurality of channels to a corresponding one of the charge measurement capacitors of the charge sensing circuit during the measurement part of the measurement cycle.

9. A touch sensor as claimed in claim 3, the touch sensor further comprising a plurality of drive circuits each of which is coupled to a first set of the plurality of channels via a common drive line, wherein the charge sensing circuit is coupled to a different set of the plurality of channels via common receiving lines, wherein the plurality of channels are disposed on a two dimensional surface to form a two dimensional touch sensor.

10. A method, comprising:

controlling a drive circuit coupled to each of a plurality of channels of a touch sensor to induce charge onto each of the plurality of channels during a drive part of a measurement cycle;

controlling a charge sensing circuit for each of the plurality of channels to couple a charge measurement capacitor respectively to the each of the plurality of channels during a charge measurement part of the measurement cycle to the effect that the charge induced on the at least one of the plurality of channels during the drive part of the measurement cycle is transferred to at least one respective capacitor of the charge measurement capacitors of the charge sensing circuits;

controlling a first discharge of each of the charge measurement capacitors in parallel;

controlling, after the first discharge, a second discharge of each of the measurement capacitors sequentially; and

determining, based on the second discharge, an amount of charge that was remaining in each of the charge measurement capacitors after the first discharge.

11. A method as claimed in claim 10, wherein during the first discharge, each of the charge measurement capacitors is discharged a predetermined discharge amount.

12. A method as claimed in claim 11, wherein the predetermined discharge amount is set in accordance with an expected difference in the amount of charge present on each of the measurement capacitors as a result of the presence of the object proximate a corresponding one of the plurality of channels of the touch sensor.

13. A method as claimed in claim 12, comprising determining, during an initialization phase, the predetermined discharge amount, by measuring a range of expected charge values on each of the charge measurement capacitors for each of the plurality of channels as a result of the presence of an object and setting the predetermined discharge amount in accordance with the range of expected charge values.

14. A method as claimed in claim 12, wherein the predetermined discharge amount is pre-set in accordance with the expected range in charge values on each of the measurement capacitors as a result of the presence and absence of an object.

15. A method as claimed in claim 10, wherein each of the plurality of channels of the touch sensor comprises a drive plate and a receiving plate, each of the drive plates being coupled to the drive circuit and each of the receiving plates being coupled to a corresponding charge measurement capacitor of one of the charge sensing circuits, and the controlling the drive circuit to induce charge onto each of the plurality of channels during a drive part of a measurement cycle, includes driving the drive plate of the plurality of channels during the drive part of the measurement cycle, and the controlling the charge sensing circuit for each of the plurality of channels to couple the charge measurement capacitor respectively to each of the plurality of channels during the charge measurement part of the measurement cycle includes, for each channel controlling the charge sensing circuits to transfer the charge induced on the receiving plate to the charge measurement capacitor during the measurement portion of the measurement cycle.

16. A method as claimed in claim 10, wherein each of the plurality of channels of the touch sensor comprises a coupling plate, and the controlling the drive circuit to induce charge onto each of the plurality of channels during the drive part of the measurement cycle, includes driving the coupling plate of the plurality of channels during the drive part of the measurement cycle, and the controlling the charge sensing circuit for each of the plurality of channels to couple the charge measurement capacitor respectively to one of the plurality of channels during the charge measurement part of the measurement cycle includes, for each of the plurality of channels controlling the charge sensing circuits to transfer the charge induced on the coupling plates of each of the plurality of channels to a corresponding one of the charge measurement capacitors of the charge sensing circuits during the measurement part of the measurement cycle.

17. A method as claimed in claim 13, wherein the controlling the drive circuit to induce charge onto each of the plurality of channels during the drive part of the measurement cycle, includes controlling a plurality of drive circuits, each of which is coupled to the plurality of channels via common drive lines, to induce charge onto each of the plurality of channels, and the controlling the charge sensing circuit for each of the plurality of channels to couple one of the charge measurement capacitors respectively to one of the plurality of channels during the charge measurement part of the measurement cycle to transfer the charge to each of the respective charge measurement capacitors, includes controlling each of the charge sensing circuits to couple a different set of the plurality of channels via common receiving lines to transfer the charge induced on each of the plurality of channels to one of the charge measurement capacitors, the plurality of channels being disposed on a two dimensional surface to form a two dimensional touch sensor.

18. A touch sensitive control panel comprising:

a channel matrix comprising

a first plurality of drive lines having N drive lines,

a second plurality of sense lines, having M sense lines,

wherein the channel matrix includes a number of channels equal to N multiplied by M, each of the channels being arranged to sense the presence of an object, each of the channels being disposed adjacent a respective intersection of one of the N drive lines and one of the M sense lines, each of the channels comprising a drive plate (X) connected to one of the N drive lines and a receiving plate (Y) connected to one of the M sense lines, each of the N drive lines is connected to a respective drive circuit, each of the M sense lines is connected to a respective charge sensing circuit including a charge measurement capacitor, and the channel matrix includes a controller, the controller being operable to;

control each drive circuit to induce charge onto each drive plate of each of the M sense lines connected to each of the N drive lines during a drive part of a measurement cycle;

control each charge sensing circuit to couple each charge measurement capacitor respectively to the receiving plate of each of the channels during a charge measurement part of the measurement cycle to the effect that the charge induced on each receiving plate of each channel during the drive part of the measurement cycle is transferred to each respective charge measurement capacitor;

control a first discharge of each of the charge measurement capacitors in parallel;

control, after the first discharge, a second discharge of each of the measurement capacitors sequentially; and

determine, based on the second discharge, an amount of charge that was remaining in each of the charge measurement capacitors after the first discharge.

19. A method, comprising:

controlling a first discharge of each of a plurality of charge measurement capacitors in parallel, each of the plurality of charge measurement capacitors corresponding to one of a plurality of channels of a touch sensor;

controlling, after the first discharge, a second discharge of each of the measurement capacitors sequentially; and

determining, based on the second discharge, an amount of charge that was remaining in each of the charge measurement capacitors after the first discharge.

20. An apparatus, comprising:

control circuitry operable to;

control a first discharge of each of a plurality of charge measurement capacitors in parallel, each of the plurality of charge measurement capacitors corresponding to one of a plurality of channels of a touch sensor;

control, after the first discharge, a second discharge of each of the measurement capacitors sequentially; and

determine, based on the second discharge, an amount of charge that was remaining in each of the charge measurement capacitors after the first discharge.