Noise reduction in digitizer system

• US 7,995,036 B2
• Filed: 02/24/2005
• Issued: 08/09/2011
• 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: Perski, Haim, Rimon, Ori
• Primary Examiner(s): Nguyen; Chanh
• Assistant Examiner(s): Karimi; Pegeman
• Application Number:
  US11/063,535
• Publication Number:
  US 20050189154A1
• Time in Patent Office: 2,357 Days
• Field of Search: 345/173, 345/174, 178/20.01, 178/18.07, 178/18.06, 178/18.04, 178/18.03, 178/18.01, 178/20.02
• US Class Current: 345/173
• 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 comprising:

sampling at least two elements of said plurality of detecting elements substantially simultaneously to obtain an output signal from each of the at least two detecting elements;

defining a noise signal based on the output signal from one element of the at least two elements, wherein one of said at least two elements is selected as a candidate carrier of stylus signal and the other of said at least two elements is selected as a candidate carrier of mere noise; and

reducing noise on the output signal of the other of the at least two elements in accordance with the noise signal,

wherein;

said candidate carrier of mere noise is selected,

noise reduction is carried out over a group of elements based on said selection being correct,

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

said selection is allowed if said resulting signal pattern is indicative of a correct selection, otherwise a new selection of candidate carrier of mere noise is made.

2. The method of claim 1, comprising detecting signals at each of said at least two elements of said one of the number of predetermined frequencies and of another arbitrary frequency.

3. The method of claim 2, comprising utilizing said signals of said arbitrary frequency to estimate the amount of noise at said signals of said predetermined frequency.

4. The method of claim 2, comprising verifying the presence of a stylus, before carrying out said reduction, by comparing output signal magnitudes of the arbitrary frequency and magnitudes of the predetermined frequency.

5. The method of claim 2, comprising detecting output signals of a plurality of arbitrarily selected frequencies to calculate said reduction.

6. The method of claim 1, wherein said candidate carrier of mere noise is selected from a group of said plurality of detecting elements exhibiting more than a threshold amount of noise, as an element in said group which is furthest away from a stylus previously known location.

7. The method of claim 1, 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.

8. The method of claim 1, 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.

9. The method of claim 1, comprising verifying the presence of a stylus before carrying out said reduction.

10. The method of claim 1, comprising sampling a group of said plurality of detecting elements, selecting at least one element which is least affected by the stylus and reducing respective output signal of at least some remaining elements in accordance with the output signal of said selected element.

11. The method of claim 1, wherein said plurality of detecting elements are conductive detectors arranged in an array associated with said digitizer.

12. The method of claim 1, wherein said noise is at least in part a consequence of presence of any member of a group of:

a finger, hand or palm.

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

14. The method of claim 1, wherein said plurality of detecting elements are arranged in a grid array.

15. The method of claim 1, wherein said plurality of detecting elements are loop elements.

16. The method of claim 1, wherein said plurality of detecting elements are transparent conductors.

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

18. The method of claim 1, wherein said stylus signal is produced by a stylus.

19. The method of claim 18, wherein the stylus is an electromagnetic stylus.

20. The method of claim 19, wherein said stylus comprises an active oscillator and an energy pick up circuit.

21. The method of claim 19, wherein said stylus comprises a resonance circuit.

22. The method of claim 1 comprising:

detecting signals at each of said elements of said one of the number of predetermined frequencies and of another arbitrary frequency;

determining a ratio between output signals of the arbitrary frequency at said candidate carrier of mere noise and said candidate carrier of stylus signal; and

estimating an amount of noise at the predetermined frequency on said candidate carrier of stylus signal from said ratio and the signal of the predetermined frequency at the candidate carrier of mere noise.

23. 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 elements of the plurality of detecting elements substantially simultaneously to obtain output signals from each of the at least two elements, wherein one of the at least two elements is selected as a candidate carrier of a stylus signal and the other of the at least two elements is selected as a candidate carrier of mere noise; and

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

wherein;

said candidate carrier of mere noise is selected,

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

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

said selection is allowed if said resulting signal pattern is indicative of a correct selection, otherwise a new selection of candidate carrier of mere noise is made.

24. Apparatus according to claim 23, comprising a detector for detecting output signals at each of said at least two elements of said predetermined frequency and another arbitrary frequency.

25. Apparatus according to claim 24, wherein said arbitrary frequency is selected as a frequency within a preset detection range having a relatively high noise.

26. Apparatus according to claim 24, wherein said arbitrary frequency is selected as a frequency already used for finger detection.

27. Apparatus according to claim 24, wherein said noise reduction unit is configured to detect output signals of a plurality of arbitrarily selected frequencies to calculate said reduction.

28. Apparatus according to claim 23, wherein said plurality of detecting elements are transparent conductors.

29. Apparatus according to claim 23, wherein said candidate carrier of mere noise is selected from a group of said plurality 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.

30. Apparatus according to claim 23, 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.

31. Apparatus according to claim 23, 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.

32. Apparatus according to claim 23, wherein analyzing the resulting signal pattern over said group of elements comprises determining a number of elements wherein an output signal exceeds a predetermined threshold.

33. Apparatus according to claim 23, 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.

34. Apparatus according to claim 23, wherein said plurality of detecting elements are arranged in 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 output signals of at least some remaining elements in accordance with the output signal of said at least one chosen element.

35. Apparatus according to claim 33, wherein said plurality of detecting elements are conductive detectors arranged in a flat array associated with said digitizer.

36. The apparatus of claim 23, wherein said noise is at least in part a consequence of presence of any one of:

a finger, hand or palm.

37. 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 elements of said plurality of detecting elements substantially simultaneously to obtain output signals from each of the at least two detecting elements, wherein one of the 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;

a detector for detecting output signals at each of said at least two elements of said predetermined frequency and another arbitrary frequency; and

a noise reduction unit for reducing noise on the output signal on one of said at least two elements in accordance with the output signal on the other of said at least two elements,

wherein said noise reduction unit is configured to detect output signals of a plurality of arbitrarily selected frequencies to calculate said reduction and calculating an average ratio in accordance with said output signals of a plurality of arbitrarily selected frequencies to calculate said reduction.

38. 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 comprising:

sampling at least two elements of said plurality of detecting elements substantially simultaneously to obtain an output signal from each of the at least two elements, 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;

detecting signal at each of said at least two elements of said one of the number of predetermined frequencies and of another arbitrary frequency;

determining a ratio between signals of the arbitrary frequency at said candidate carrier of mere noise and said candidate carrier of the stylus signal;

from said ratio and the signal of the one of the number of predetermined frequencies at the candidate carrier of mere noise, determining an amount of noise of the one of the number of predetermined frequencies at said candidate carrier of the stylus signal;

reducing a signal of said one of the number of predetermined frequencies at said candidate carrier of a stylus signal by said determined amount of noise; and

reducing the output signal on one of the at least two elements in accordance with the output signal from the other of the at least two detecting elements.

39. The method of claim 38, wherein said arbitrary frequency is selected as a frequency within a preset detection range having a relatively high noise.

40. The method of claim 38, wherein said digitizer is adapted for touch detection and said arbitrary frequency is selected as a frequency already used for said touch detection.

41. The method of claim 38, further comprising deliberately generating noise at said arbitrary frequency.

42. The method of claim 38, 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.

43. The method of claim 38, wherein said ratio is a complex proportion to compensate for at least one of phase and magnitude differences between respective detecting elements during said compensating.

44. The method of claim 38, comprising detecting output signals of a plurality of arbitrarily selected frequencies, and calculating an average ratio in accordance with said output signals of said plurality of arbitrarily selected frequencies to calculate said reduction.

45. 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 elements of said plurality of detecting elements substantially simultaneously to obtain output signals from each of the at least two elements, wherein one of said at least two elements is selected as a candidate carrier of stylus signal and the other of said at least two elements is selected as a candidate carrier of mere noise;

a detector for detecting output signals at each of said at least two elements of said predetermined frequency and another arbitrary frequency;

a ratio finder for determining a ratio between output signals of the arbitrary frequency at said candidate carrier of mere noise and said candidate carrier of stylus signal; and

a noise reduction unit for reducing the output signal on one of said at least two detecting elements in accordance with the output signal on the other of said at least two detecting elements,

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

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

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

46. Apparatus according to claim 45, further comprising a noise generator for deliberately generating noise at said arbitrary frequency.

47. Apparatus according to claim 45, 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.

48. A method for determining a noise signal 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 elements of said plurality of detecting elements substantially simultaneously to obtain output signals from each of the at least two elements;

selecting a first of said at least two elements as a candidate carrier of stylus signal and a second of said at least two elements as a candidate carrier of mere noise;

detecting signals at each of said at least two elements of said one of the number of predetermined frequencies and of another arbitrary frequency;

determining a ratio between output signals of the arbitrary frequency at said candidate carrier of mere noise and said candidate carrier of stylus signal; and

estimating an amount of noise at the predetermined frequency on said candidate carrier of stylus signal from said ratio and the signal of the predetermined frequency at the candidate carrier of mere noise; and

defining a noise level on the output signal of the candidate carrier of a stylus signal based on the output signal of the candidate carrier of mere noise.

49. The method of claim 48, wherein said arbitrary frequency is selected as a frequency already used for finger detection.

50. The method of claim 48, wherein said noise is at least in part a consequence of presence of any member of a group of:

a finger, hand or palm.

51. The method of claim 48, wherein said digitizer comprises a detection surface for carrying said plurality of detecting elements, said detecting surface further being touch sensitive.

52. The method of claim 48 comprising reducing effect of the noise level on the output signal of the candidate carrier of stylus signal based on the output signal of the candidate carrier of mere noise.