Digital signal processed touchscreen system

• US 20100177061A1
• Filed: 03/30/2010
• Published: 07/15/2010
• Est. Priority Date: 08/26/2004
• Status: Active Grant

• Current Assignee: Wacom Co Limited (Wacom)
• Original Assignee: Wacom Co Limited (Wacom)
• Inventors: Gray, Patrick T.
• Granted Patent: US 8,947,369 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

Digital signal processed touchscreen system. The invention employs amplitude ramped signals across a touchscreen. The pattern to which the amplitude ramped electric signals are provided may be located on the surface of the touchscreen, or alternatively on the backside of the touchscreen. The signal processing employed by the invention, using digital signal processing techniques, is operable to discern a user'"'"'s touch and to determine its location. A dielectric, protective surface is used to enable implementation into a wide variety of applications, including those applications that are environmentally rugged and have, until now, been too rugged for prior art touchscreen systems. The invention employs a user generated unbalanced capacitive load generated on the touchscreen to identify the location of the user'"'"'s touch.

Claims

1. A touchscreen system, comprising:

a touchscreen having a frontside and a backside;

a resistive pattern that is attached to the backside of the touchscreen;

a plurality of drive signal circuits that are respectively coupled to a corresponding plurality of communicative coupling points of the resistive pattern to produce an amplitude ramped field that communicatively couples through the touchscreen to the frontside of the touchscreen and extends across the frontside of the touchscreen in a selectable direction and also operable to measure current flow at the plurality of communicative coupling points;

a plurality of subtraction circuits, each of the plurality of subtraction circuits being communicatively coupled to one of the plurality of drive signal circuits operable to produce a resulting current flow having a changed unbalanced capacitive reactance current portion that results from a user'"'"'s touch of the touchscreen that results from current flowing from the resistive pattern through the touchscreen responsive to the user'"'"'s touch; and

a digital signal processor that is operable to process a digital version of the change of the unbalanced capacitive reactance current portion to discriminate a location of the user'"'"'s interaction or touch on the touchscreen.

2. The touchscreen system of claim 1, wherein:

the plurality of drive signal circuits generates the amplitude ramped field in a direction, the direction being selectable by applying full scale AC signals to some of the plurality of communicative coupling points and virtual ground signals to other plurality of communicative coupling points.

3. The touchscreen system of claim 2, wherein:

the amplitude ramped field is operable to be selectively ramped in a plurality of directions across the touchscreen.

4. The touchscreen system of claim 1, wherein the touchscreen system:

generates at least two amplitude ramped fields across the touchscreen in different directions relative to each other.

5. The touchscreen system of claim 1, wherein the touchscreen system:

generates at least two amplitude ramped fields across the touchscreen in different directions relative to each other; and

sums currents corresponding to the at least two amplitude ramped fields.

6. The touchscreen system of claim 1, further comprising:

nulling and adding circuitry that is operable to reduce a non-user touched portion of the unbalanced capacitive reactance current portion and to increase an overall resolution of the unbalanced capacitive reactance current portion that is substantially attributable to the user'"'"'s interaction or touch on the touchscreen.

7. The touchscreen system of claim 1, wherein the touchscreen system:

the plurality of subtraction circuits being operable to remove any substantially purely resistive current portion that is injected into one of the corresponding plurality of communicative coupling points by one of the plurality of drive signal circuits.

8. A touchscreen system, comprising:

a touchscreen having a frontside and a backside;

a resistive pattern that is attached to the backside of the touchscreen;

a plurality of drive signal circuits that are communicatively coupled to the resistive pattern at one of a plurality of communicative coupling points, wherein each of the plurality of drive signal circuits is respectively operable to measure current flow at a respective one of the plurality of communicative coupling points;

wherein the plurality of drive signal circuits are cooperatively operable to energize the resistive pattern thereby generating an amplitude ramped field that communicatively couples through the touchscreen to the frontside of the touchscreen and extends across the frontside of the touchscreen in a selectable direction;

a digital signal processor that is operable to process a digital version of a change in unbalanced capacitive reactance current portion corresponding to at least one of the plurality of communicative coupling points to discriminate a location of a user'"'"'s interaction or touch on the touchscreen;

subtraction circuitry operable to remove any substantially purely resistive current portion that is injected by one of the drive signal circuits, the subtraction circuitry also operable to remove current not having an unbalanced capacitive reactance current portion based on the user'"'"'s interaction or touch on the touchscreen; and

an analog to digital converter that converts the unbalanced capacitive reactance current portion that is substantially attributable to the user'"'"'s interaction or touch on the touchscreen to a digital signal.

9. The touchscreen system of claim 8, wherein:

the selectable direction is selected by applying full scale AC signals to some of the plurality of communicative coupling points and virtual ground signals to other of the plurality of communicative coupling points, the amplitude ramped field is operable to be selectively ramped in a plurality of directions across the touchscreen.

10. The touchscreen system of claim 8, wherein:

the touchscreen system is operable to generate at least two pluralities of digital data corresponding to the selectable amplitude ramped field being ramped in at least two directions; and

the digital signal processor is operable to process the at least two pluralities of digital data to discriminate the location of the user'"'"'s interaction or touch on the touchscreen.

11. The touchscreen system of claim 8, wherein:

when the current flows at the plurality of communicative coupling points, the touchscreen system detects the unbalanced capacitive reactance current portion of the current; and

a change of the unbalanced capacitive reactance current portion is substantially attributable to the user'"'"'s interaction or touch on the touchscreen.

12. The touchscreen system of claim 8, wherein:

the touchscreen further includes four corners;

the plurality of drive signal circuits includes four drive signal circuits;

the four drive signal circuits are respectively coupled to the resistive pattern at the four corners of the touchscreen; and

each of the four drive signal circuits is operable to measure current flow at an associated corner of the touchscreen and to detect unbalanced capacitive reactance current attributable to the user'"'"'s interaction or touch on the touchscreen.

13. The touchscreen system of claim 12, further comprising:

four subtraction circuits, each subtraction circuit being respectively communicatively coupled to one of the four drive signal circuits and each subtraction circuit being respectively operable to subtract current not attributable to the user'"'"'s interaction or touch on the touchscreen.

14. The touchscreen system of claim 8, further comprising:

nulling and adding circuitry that is operable to reduce a non-user touch portion of the unbalanced capacitive reactance current portion and to increase an overall resolution of the unbalanced capacitive reactance current portion that is substantially attributable to the user'"'"'s interaction or touch on the touchscreen.

15. The touchscreen system of claim 14, wherein:

the touchscreen further includes four corners;

the plurality of drive signal circuits includes four drive signal circuits;

the four drive signal circuits simultaneously energize all four corners of the touchscreen with a full scale AC signal when the digital signal processor fails to detect a user'"'"'s interaction or touch on the touchscreen for a predetermined period of time;

the digital signal processor detects and compensates for at least one of a temperature variation of the touchscreen system and a humidity variation of the touchscreen system;

the touchscreen system operates in an energy conservation mode; and

the digital signal processor exits the energy conservation mode after detecting the user'"'"'s interaction or touch on the touchscreen.

16. The touchscreen system of claim 15, wherein:

the four drive signal circuits energize the resistive pattern thereby generating the amplitude ramped field that extends across the surface of the touchscreen when the digital signal processor detects the user'"'"'s interaction or touch on the touchscreen.

17. A method for operating a touchscreen system, the method comprising:

cooperatively energizing a resistive pattern attached to a backside of a touchscreen at a plurality of communicative coupling points and generating an amplitude ramped field that communicatively couples through the touchscreen to a frontside of the touchscreen and extends across the frontside of the touchscreen in a selectable direction;

measuring current flow at the plurality of communicative coupling points;

removing any substantially purely resistive current portion that is injected at the plurality of communicative coupling points and removing current not having an unbalanced capacitive reactance current portion thereby generating an unbalanced capacitive reactance current portion;

converting the unbalanced capacitive reactance current portion, being substantially attributable to a user'"'"'s interaction or touch on the touchscreen, to a digital signal; and

processing, in a digital signal processor, the digital signal thereby discriminating a location of the user'"'"'s interaction or touch on the touchscreen.

18. The method of claim 17, further comprising:

selecting the selectable direction by applying full scale AC signals to some of the plurality of communicative coupling points and virtual ground signals to other of the plurality of communicative coupling points; and

selectively ramping the amplitude ramped field in a plurality of directions across the touchscreen.

19. The method of claim 17, further comprising:

generating at least two pluralities of digital data corresponding to the selectable amplitude ramped field being ramped in at least two directions; and

processing the at least two pluralities of digital data to discriminate the location of the user'"'"'s interaction or touch on the touchscreen.

20. The method of claim 17, further comprising:

reducing a non-user touch portion of the unbalanced capacitive reactance current portion; and

increasing an overall resolution of the unbalanced capacitive reactance current portion that is substantially attributable to the user'"'"'s interaction or touch on the touchscreen.

21. The method of claim 17, wherein:

the touchscreen includes four corners; and

further comprising;

simultaneously energizing all four corners of the touchscreen with a full scale AC signal when the digital signal processor fails to detect a user'"'"'s interaction or touch on the touchscreen for a specified period of time;

compensating for at least one of a temperature variation of the touchscreen system and a humidity variation of the touchscreen system;

operating in an energy conservation mode; and

exiting the energy conservation mode after detecting the user'"'"'s interaction or touch on the touchscreen.

22. The method of claim 17, further comprising:

energizing the resistive pattern and generating the amplitude ramped field that extends across the surface of the touchscreen when the digital signal processor detects the user'"'"'s interaction or touch on the touchscreen.