Noise measurement in capacitive touch sensors

• US 8,629,686 B2
• Filed: 07/18/2013
• Issued: 01/14/2014
• Est. Priority Date: 10/22/2008
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Yilmaz, Esat, Pickett, Daniel, Philipp, Harald
• Primary Examiner(s): Nguyen, Vincent Q
• Application Number:
  US13/945,820
• Publication Number:
  US 20130307569A1
• Time in Patent Office: 180 Days
• Field of Search: 324/658, 324/679, 324/684, 324/690
• US Class Current: 324/684
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 29/26 Measuring noise figure; Measuring signal-to-noise ratio
• 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 3/0443 using a single layer of sensing electrodes
• 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

In particular embodiments, an apparatus includes a charge-measurement capacitor having a first plate coupled to a second plate of a coupling capacitor and a non-transitory computer-readable storage medium embodying logic that is operable when executed to ground a first plate of the coupling capacitor; inject a pre-determined amount of charge onto the charge-measurement capacitor; and transfer an amount of charge accumulated on the second plate of the coupling capacitor to the first plate of the charge-measurement capacitor. The charge accumulated on the second plate of the coupling capacitor is due at least in part to noise. The logic is also operable when executed to determine, through a measured voltage across the charge-measurement capacitor, the amount of charge.

Claims

1. An apparatus comprising:

a charge-measurement capacitor having a first plate coupled to a second plate of a coupling capacitor; and

a non-transitory computer-readable storage medium bodying logic that is operable when executed to;

ground a first plate of the coupling capacitor;

inject a pre-determined amount of charge onto the charge-measurement capacitor;

transfer an amount of charge accumulated on the second plate of the coupling capacitor to the first plate of the charge-measurement capacitor, the charge having accumulated on the second plate of the coupling capacitor due at least in part to noise; and

determine, through a measured voltage across the charge-measurement capacitor, the amount of charge.

2. The apparatus of claim 1, wherein the injection of the pre-determined amount of charge is through a resistor coupled to a voltage source.

3. The apparatus of claim 2, wherein the logic is further configured to couple the resistor to the voltage source for a pre-determined amount of time.

4. The apparatus of claim 2, wherein the logic is further configured to:

ground the first plate of the charge-measurement capacitor; and

couple the second plate of the charge-measurement capacitor to the voltage source through the resistor.

5. The apparatus of claim 1, wherein the logic is further configured to ground a second plate of the charge-measurement capacitor subsequent to the injection of the pre-determined amount of charge.

6. The apparatus of claim 1, wherein the logic is further configured to float the second plate of the charge-measurement capacitor subsequent to the transfer of the pre-determined amount of charge.

7. The apparatus of claim 1, wherein the logic is further configured to calculate a noise factor to configure a filter based on the amount of charge.

8. A non-transitory computer-readable storage medium embodying logic that is operable when executed to:

ground a first plate of the coupling capacitor;

inject a pre-determined amount of charge onto the charge-measurement capacitor;

transfer an amount of charge accumulated on the second plate of the coupling capacitor to the first plate of the charge-measurement capacitor, the charge having accumulated on the second plate of the coupling capacitor due at least in part to noise; and

determine, through a measured voltage across the charge-measurement capacitor, the amount of charge.

9. The medium of claim 8, wherein the injection of the pre-determined amount of charge is through a resistor coupled to a voltage source.

10. The medium of claim 9, wherein the logic is further configured to couple the resistor to the voltage source for a pre-determined amount of time.

11. The medium of claim 9, wherein the logic is further configured to:

ground the first plate of the charge-measurement capacitor; and

couple the second plate of the charge-measurement capacitor to the voltage source through the resistor.

12. The medium of claim 8, wherein the logic is further configured to ground a second plate of the charge-measurement capacitor subsequent to the injection of the pre-determined amount of charge.

13. The medium of claim 8, wherein the logic is further configured to float the second plate of the charge-measurement capacitor subsequent to the transfer of the pre-determined amount of charge.

14. The medium of claim 8, wherein the logic is further configured to calculate a noise factor to configure a filter based on the amount of charge.

15. A method comprising:

grounding a first plate of the coupling capacitor;

injecting a pre-determined amount of charge onto the charge-measurement capacitor;

transferring an amount of charge accumulated on the second plate of the coupling capacitor to the first plate of the charge-measurement capacitor, the charge having accumulated on the second plate of the coupling capacitor due at least in part to noise; and

determining, through a measured voltage across the charge-measurement capacitor, the amount of charge.

16. The method of claim 15, wherein the injection of the pre-determined amount of charge is through a resistor coupled to a voltage source.

17. The method of claim 16, wherein the injection of the pre-determined amount of charge comprises coupling the resistor to the voltage source for a pre-determined amount of time.

18. The method of claim 16, further comprising:

grounding the first plate of the charge-measurement capacitor; and

coupling the second plate of the charge-measurement capacitor to the voltage source through the resistor.

19. The method of claim 15, wherein the transfer of charge comprises grounding a second plate of the charge-measurement capacitor subsequent to the injection of the pre-determined amount of charge.

20. The method of claim 15, further comprising floating the second plate of the charge-measurement capacitor subsequent to the transfer of the pre-determined amount of charge.