Method and apparatus for reducing noise in an electrostatic digitizer

• US 6,081,259 A
• Filed: 11/25/1997
• Issued: 06/27/2000
• Est. Priority Date: 11/25/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Inventors: Teterwak, Jerzy A.
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Kovalick, Vincent E.
• Application Number:
  US08/978,394
• Time in Patent Office: 945 Days
• Field of Search: 178/18.01, 178/18.03, 178/18.05, 178/18.06, 178/18.07, 178/18.08, 178/19.01, 178/19.02, 178/19.03, 345/173, 345/179
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04107 Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds
• CPC Class Codes: G06F 3/04164 Connections between sensors and controllers, e.g. routing lines between electrodes and connection pads
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

An electrostatic digitizing panel capable of filtering offset loads such that stylus or fingertip position information is more accurately obtained. The present invention utilizes a new method of calculating the stylus position such that the digitizer surface is sensitive only to the electric field concentrated in the area occupied by the stylus or fingertip. Thus, the panel has a substantially reduced sensitivity to fields emitted from a user'"'"'s hand or noise fields emitted from the surface of a display, or the like, coupled to the panel.

Claims

1. An electrostatic stylus or fingertip driven digitizing panel, comprising:

a generally rectilinear non-conductive surface;

a plurality of first non-overlapping resistive members each of said members having a first and a second end, said members forming an array overlaying said generally rectilinear non-conductive surface so as to form an active region on said generally rectilinear non-conductive surface;

a plurality of second non-overlapping resistive members forming a second array generally perpendicular to said first end of said first array members and operably electrically coupled with said first array members, said second array not overlaying said active region of said generally rectilinear non-conductive surface; and

a plurality of third non-overlapping resistive members forming a third array generally perpendicular to said second end of said first array members and operably electrically coupled with said first array members, said third array not overlaying said active region of said generally rectilinear non-conductive surface.

2. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 1 wherein the number of second non-overlapping resistive members is equal to one fourth (1/4) the number of first non-overlapping resistive members and wherein the number of third non-overlapping resistive members is equal to one fourth (1/4) the number of first non-overlapping resistive members.

3. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 2 wherein there are at least sixteen (16) first non-overlapping members.

4. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 2 wherein there are at least four (4) second non-overlapping members and wherein there are at least four (4) third non-overlapping members.

5. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 1 wherein said first, second, and third array members are formed of indium-tin-oxide ("ITO") strips.

6. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 5 further comprising a layer for insulating said indium-tin-oxide ("ITO") strips.

7. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 6 wherein said layer for insulating is a dielectric layer.

8. The electrostatic stylus or fingertip driven digitizing panel apparatus of claim 7 wherein said layer for dielectric layer is formed of a ceramic composition.

9. A method for reducing noise in a digitizing panel, comprising:

obtaining an output current value of the digitizing panel wherein the digitizing panel has an active region where coordinate data may be obtained and wherein corner current values are divided by a first array of non-overlapping resistive members acting to substantially cover the active region and a second array of non-overlapping resistive members not covering the active region, the second array operably connected to the first array, and wherein the output current value includes position current corresponding to the position of a stylus in contact with the digitizing panel and noise current corresponding to offset load currents conducting through grounded pathways; and

filtering the offset load current from the corner current values whereby the position of a stylus being in contact with said panel may be given as a function of the output current value.

10. The method of claim 9 wherein said second array has an output for each of said digitizing panel corners and the output of each of said corner output is split into a number equal to the number of panel corners.

11. The method of claim 10 wherein said digitizing panel has four corners and wherein said second array splits each of said four corner currents into four corner current values and wherein each of said four current values for each of said four corner currents is phase shifted such that four phase shifted signals corresponding to each of said four corner current values is obtained and wherein each of said four phase shifted signals corresponding to each of said four corner current values for each panel corner is summed and multiplied by the square root of two so as to obtain four values each of said four values corresponding to the current value at one corner of the digitizing panel.

12. An electrostatic digitizer assembly having an active region adapted to accept input from a stylus or a fingertip, said digitizer assembly comprising:

a generally rectilinear non-conductive surface;

a first array of non-overlapping resistive members overlaying said generally rectilinear non-conductive surface, said first array acting to substantially cover said active region;

a second array of non-overlapping resistive members overlaying said generally rectilinear non-conductive surface wherein said second array does not cover said active region, said second array operably electrically coupled to said first array wherein said first and second array are adapted to provide digitizing panel corner current values including position providing current consisting essentially of current injected by at least one of a fingertip and a stylus in contact with said digitizing panel and noise current consisting essentially of offset load currents from conductive grounded objects; and

a circuit for filtering at least part of said noise current from said corner current values so as to determine the position of at least one of a fingertip and a stylus in contact with said digitizing panel wherein said position of said at least one of a fingertip and a stylus in contact with said digitizing panel is given by said position providing current.

13. The digitizer assembly of claim 12, wherein said first and second arrays of non-overlapping resistive members are formed of indium-tin-oxide ("ITO") strips.

14. The digitizer assembly of claim 12, further comprising a layer for insulating said first and second arrays of non-overlapping resistive members.

15. The digitizer assembly of claim 14, wherein said layer for insulating is a dielectric layer.

16. The digitizer assembly of claim 15, wherein said dielectric layer is formed of a ceramic composition.

17. The digitizer assembly of claim 12, further comprising a layer for insulating said second array of non-overlapping resistive members.

18. The digitizer assembly of claim 17, wherein said layer for insulating comprises Kapton foil.

19. The digitizer assembly of claim 12, further comprising a grounded electrical shielding layer adapted to provide electrical shielding to said first and second arrays.

20. The digitizer assembly of claim 19, wherein said electrical shielding layer is comprised of indium-tin-oxide ("ITO").

21. The digitizer assembly of claim 12, further comprising a spall shield mounted to said generally rectilinear non-conductive surface, said spall shield including a grounded electrical shielding layer adapted to provide electrical shielding to said first and second arrays.

22. The digitizer assembly of claim 21, wherein said electrical shielding layer is comprised of indium-tin-oxide ("ITO").

23. A computer having an electrostatic digitizer assembly including an active region adapted to accept input from a stylus or a fingertip, said digitizer assembly comprising:

a generally rectilinear non-conductive surface;

a first array of non-overlapping resistive members overlaying said generally rectilinear non-conductive surface, said first array acting to substantially cover said active region;

a second array of non-overlapping resistive members overlaying said generally rectilinear non-conductive surface wherein said second array does not cover said active region, said second array operably electrically coupled to said first array wherein said first and second array are adapted to provide digitizing panel corner current values including position providing current consisting essentially of current injected by at least one of a fingertip and a stylus in contact with said digitizing panel and noise current consisting essentially of offset load currents from conductive grounded objects; and

a circuit for filtering at least part of said noise current from said corner current values so as to determine the position of at least one of a fingertip and a stylus in contact with said digitizing panel wherein said position of said at least one of a fingertip and a stylus in contact with said digitizing panel is given by said position providing current.