Noise reduction in digitizer system

• US 20050189154A1
• Filed: 02/24/2005
• Published: 09/01/2005
• Est. Priority Date: 02/27/2004
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: N-Trig Ltd (Microsoft Corporation)
• Inventors: Rimon, Ori, Perski, Haim
• Granted Patent: US 7,995,036 B2
• Time in Patent Office: Days
• US Class Current: 178/18.60
• CPC Class Codes: G06F 2203/04106 Multi-sensing digitiser, i.e. digitiser using at least two different sensing technologies simultaneously or alternatively, e.g. for detecting pen and finger, for saving power or for improving position detection
• CPC Class Codes: G06F 2203/04108 Touchless 2D- digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface without distance measurement in the Z direction
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/04162 for exchanging data with external devices, e.g. smart pens, via the digitiser sensing hardware
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/0441 using active external devices, e.g. active pens, for receiving changes in electrical potential transmitted by the digitiser, e.g. tablet driving signals
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser
• CPC Class Codes: G06F 3/046 by electromagnetic means

Abstract

A method for noise reduction in a digitizer, the digitizer comprising a plurality of detecting elements for detecting an electromagnetic signal at one of a number of predetermined frequencies: the method comprising: sampling at least two of said detecting elements substantially simultaneously to obtain outputs therefrom, and reducing the output on one of said two elements in accordance with the output on the other of said elements.

Claims

1. A method for noise reduction in a digitizer, the digitizer comprising a plurality of detecting elements for detecting an electromagnetic signal at one of a number of predetermined frequencies:

the method comprising;

sampling at least two of said detecting elements substantially simultaneously to obtain outputs therefrom, and

reducing the output on one of said two elements in accordance with the output on the other of said elements.

2. The method of claim 1, wherein one of said at least two elements is selected as a candidate carrier of a stylus signal and the other of said at least two elements is selected as a candidate carrier of mere noise.

3. The method of claim 2, comprising detecting at each of said elements said one predetermined frequency and another arbitrary frequency.

4. The method of claim 3, comprising utilizing said arbitrary frequency to estimate the amount of noise at said predetermined frequency.

5. The method of claim 3, comprising:

determining a ratio between signals of the one predetermined frequency and the arbitrary frequency at said candidate carrier of mere noise,

from said ratio and the arbitrary signal at the candidate carrier of the stylus signal determining an amount of noise at the one predetermined frequency, and

reducing a signal at said one predetermined frequency at said candidate carrier of a stylus signal by said determined amount of noise.

6. The method of claim 5, wherein said arbitrary frequency is selected as a frequency within a preset detection range having a relatively high noise.

7. The method of claim 5, wherein said digitizer is also for touch detection and said arbitrary frequency is selected as a frequency already used for said touch detection.

8. The method of claim 5, further comprising deliberately generating noise at said arbitrary frequency.

9. The method of claim 5, wherein said predetermined frequency is changed to a new frequency during use, the method comprising changing said arbitrary frequency from a frequency relatively close to said predetermined frequency to a second frequency relatively close to said new frequency.

10. The method of claim 2, wherein said candidate carrier of mere noise is selected from a group of elements exhibiting more than a threshold amount of noise, as the element in said group which is furthest away from a stylus previously known location.

11. The method of claim 2, wherein said candidate carrier of mere noise is selected as an element exhibiting a strongest noise signal as long as it is beyond a determined distance from a stylus previously known location.

12. The method of claim 2, wherein:

said candidate carrier of mere noise is selected,

noise subtraction is carried out over a group of elements on the basis of said selection being correct,

a resulting signal pattern over said group of elements is analyzed, and

said arbitrary selection is allowed if said resulting signal pattern is indicative of a correct selection, otherwise a new arbitrary selection is made.

13. The method of claim 12, comprising using as patterns indicative of a correct selection a first pattern indicative of a stylus at one of non-selected elements, and a second pattern indicative of no stylus being present.

14. The method of claim 12, comprising verifying the presence of a stylus before carrying out said reduction.

15. The method of claim 1, comprising verifying the presence of a stylus, beforecarrying out said reduction, by comparing magnitudes at the arbitrary frequency and magnitudes at the predetermined frequency.

16. The method of claim 2, wherein:

said candidate carrier of mere noise is selected,

noise subtraction is carried out over a group of antennas on the basis of said selection being correct,

a resulting signal pattern over said group of antennas is analyzed, and

said arbitrary selection is rejected if said resulting signal pattern is indicative of an incorrect selection, and a new arbitrary selection is made.

17. The method of claim 16, comprising using as a pattern indicative of an incorrect selection a pattern indicative of a stylus at or near said selected candidate.

18. The method of claim 1, comprising using a complex proportion to compensate for at least one of phase and magnitude differences between respective antennas during said compensating.

19. The method of claim 1, comprising sampling a group of antennas of an array, selecting at least one antenna which is least affected by the stylus and reducing respective outputs of at least some remaining antennas in accordance with the output of said selected antenna.

20. The method of claim 3, comprising using a plurality of arbitrarily selected frequencies to calculate said reduction.

21. The method of claim 20, comprising using an average output of said plurality of arbitrarily selected frequencies to calculate said reduction.

22. The method of claim 1, wherein said detecting elements are conductive detectors of a flat array of said digitizer for digitizing signals of a movable object to indicate location of said object.

23. The method of claim 22, wherein said noise is at least in part a consequence of the presence of a finger.

24. The method of claim 1, wherein said digitizer comprises a detection surface for carrying said detecting elements, said detecting surface further being touch sensitive.

25. Apparatus for noise reduction in a digitizer, the digitizer comprising a plurality of detecting elements for detecting an electromagnetic signal at one predetermined frequency of a plurality of predetermined frequencies:

the apparatus comprising;

a sampler for sampling at least two of said detecting elements substantially simultaneously to obtain outputs therefrom, and

a noise reduction unit for reducing the output on one of said two detecting elements in accordance with the output on the other of said detecting elements.

26. Apparatus according to claim 25, wherein one of said detecting elements is selected as a candidate carrier of a stylus signal and the other of said detecting elements is selected as a candidate carrier of mere noise.

27. Apparatus according to claim 26, comprising a frequency detector for detecting outputs at each of said detecting elements at said predetermined frequency and another arbitrary frequency.

28. Apparatus according to claim 27, comprising:

a ratio finder for determining a ratio between outputs at the predetermined frequency and the arbitrary frequency at said candidate carrier of mere noise,

and wherein said noise reduction unit is operable with said ratio finder to;

determine from said ratio and the arbitrary signal at the candidate carrier of the stylus signal determining an amount of noise at the predetermined frequency, and

reduce the output at said predetermined frequency at said candidate carrier of a stylus signal by said determined amount of noise.

29. Apparatus according to claim 27, wherein said detecting elements are transparent conductors.

30. Apparatus according to claim 28, wherein said arbitrary frequency is selected as a frequency within a preset detection range having a relatively high noise.

31. Apparatus according to claim 28, wherein said arbitrary frequency is selected as a frequency already used for finger detection.

32. Apparatus according to claim 28, further comprising a noise generator for deliberately generating noise at said arbitrary frequency

33. Apparatus according to claim 28, wherein said predetermined frequencies are liable to change during use, the apparatus accordingly being configured to change said arbitrary frequency from a frequency relatively close to a first predetermined frequency to a second frequency relatively close to a second predetermined frequency.

34. Apparatus according to claim 26, wherein said candidate carrier of mere noise is selected from a group of detection elements exhibiting more than a threshold amount of noise, as the element in said group which is furthest away from a stylus previously known location.

35. Apparatus according to claim 26, wherein said candidate carrier of mere noise is selected as an element exhibiting a strongest noise signal as long as it is beyond a determined distance from a stylus previously known location.

36. Apparatus according to claim 26, wherein:

said candidate carrier of mere noise is selected,

noise subtraction is carried out over a group of elements on the basis of said selection being correct,

a resulting signal pattern over said group of elements is analyzed, and

said arbitrary selection is allowed if said resulting signal pattern is indicative of a correct selection, otherwise a new arbitrary selection is made.

37. Apparatus according to claim 36, comprising using as patterns indicative of a correct selection a first pattern indicative of a stylus at one of non-selected elements, and a second pattern indicative of no stylus being present.

38. Apparatus according to claim 36, wherein said analysis comprises determining a number of elements wherein an output exceeds a predetermined threshold.

39. Apparatus according to of claim 26, wherein:

said candidate carrier of mere noise is selected,

noise subtraction is carried out over a group of elements on the basis of said selection being correct,

a resulting signal pattern over said group of elements is analyzed, and

said arbitrary selection is rejected if said resulting signal pattern is indicative of an incorrect selection, and a new arbitrary selection is made.

40. Apparatus according to claim 25, comprising at least one of a phase compensator and a magnitude compensator using a complex proportion to compensate for at least one of phase and magnitude differences between respective elements during said compensating.

41. Apparatus according to claim 25, wherein said elements comprise an array, the apparatus configured to sample at least some elements of said array, said noise reduction unit being configured to choose at least one element and reduce respective outputs of at least some remaining elements in accordance with the output of another of said elements.

42. Apparatus according to claim 27, wherein said noise reduction unit is configured to use a plurality of arbitrarily selected frequencies to calculate said reduction.

43. Apparatus according to claim 42, wherein said noise reduction unit is configured to use an average noise level of said plurality of arbitrarily selected frequencies to calculate said reduction.

44. Apparatus according to claim 25, wherein said elements are conductive detectors of a flat array of said digitizer for digitizing signals of a movable object to indicate location of said object.

45. Apparatus according to claim 44, wherein said movable object is a stylus.

46. Apparatus according to claim 45, wherein said stylus is an electromagnetic stylus.

47. Apparatus according to claim 46, wherein said stylus comprises an active oscillator and an energy pick up circuit.

48. Apparatus according to claim 46, wherein said stylus comprise a resonance circuit.

49. Apparatus according to claim 25, wherein said detecting elements are arranged in a grid array.

50. Apparatus according to claim 25, wherein said detecting elements are loop elements.

51. Apparatus according to claim 44, wherein said noise is at least in part a consequence of the presence of a finger.