Digital signal processed touchscreen system

• US 7,714,846 B1
• Filed: 08/25/2005
• Issued: 05/11/2010
• 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.
• Primary Examiner(s): Nguyen; Chanh
• Assistant Examiner(s): SEYOUM, TSEGAYE H
• Application Number:
  US11/211,272
• Time in Patent Office: 1,720 Days
• Field of Search: 345173-179, 178/18.06, 340/706, 340/712, 340/146.03
• US Class Current: 345/173
• 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 communicatively coupled to the resistive pattern at communicative coupling points, each drive signal circuit within the plurality of drive signal circuits is also operable to measure current flow at the communicative coupling points of each drive signal circuit within the plurality of drive signal circuits to the touchscreen;

wherein each drive signal circuit within the plurality of drive signal circuits operates cooperatively 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 direction, the direction being selectable by applying full scale AC signals to some of the communicative coupling points and virtual ground signals to other communicative coupling points, the amplitude ramped field is operable to be selectively ramped in a plurality of directions across the touchscreen;

a plurality of subtraction circuits, each subtraction circuit being communicatively coupled to one of the plurality drive signal circuits and each subtraction circuit being operable to remove any substantially purely resistive current portion that is injected into one of the corners by one of the drive signal circuits, each of the subtraction circuits also being operable to perform high pass filtering and adding to remove any resistance portion of the current flow at the corners of the touchscreen thereby leaving a resulting current flow having an unbalanced capacitive reactance current portion;

a 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 a user'"'"'s touch on the touchscreen;

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

wherein the current flow at the points of communicative coupling includes an unbalanced capacitive reactance current portion wherein a change of the unbalanced capacitive reactance current portion includes a portion that is substantially attributable to a user'"'"'s interaction or touch on the touchscreen; 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, further comprising:

a digital wave generator chip that is operable to generate a wave function comprising a predetermined amplitude that is delivered to at least one of the drive signal circuits within the plurality of drive signal circuits.

3. The touchscreen system of claim 1, wherein:

the touchscreen comprises a dielectric material; and

the resistive pattern that is attached to the backside of the dielectric material.

4. The touchscreen system of claim 1, wherein:

the plurality of directions across the touchscreen includes at least four directions comprising a horizontal direction from left to right, a horizontal direction from right to left, a vertical direction from top to bottom, and a vertical direction from bottom to top.

5. The touchscreen system of claim 1, wherein:

each drive signal circuit within the plurality of drive signal circuits simultaneously energize all of the communicative coupling points with a full scale AC signal when the digital signal processor fails to detect a user'"'"'s touch for a predetermined period of time; and

the touchscreen system operates in an energy conservation mode.

6. The touchscreen system of claim 1, wherein:

each drive signal circuit within the plurality of drive signal circuits begins to energize the resistive pattern thereby generating the amplitude ramped field that extends across the surface of the touchscreen when the digital signal processor detects a user'"'"'s touch on the touchscreen.

7. The touchscreen system of claim 1, wherein:

the digital signal processor compensates for at least one of noise introduced into the touchscreen, a temperature variation of the touchscreen system, and a humidity variation of the touchscreen system when processing the digital version of the change of the unbalanced capacitive reactance current portion to discriminate the location of the user'"'"'s touch on the touchscreen.

8. The touchscreen system of claim 1, wherein:

the amplitude ramped field across the touchscreen effectuates an unbalanced capacitive load across the touchscreen.

9. The touchscreen system of claim 1, wherein:

the touchscreen includes four corners;

the plurality of drive signal circuits includes four drive signal circuits such that each of the four drive signal circuits is coupled to the resistive pattern at one of the four corners of the touchscreen; and

each of the four drive signal circuits is operable to measure current flow at its respective corner of the touchscreen.

10. 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 communicative coupling points, each drive signal circuit within the plurality of drive signal circuits is also operable to measure current flow at the communicative coupling points of each drive signal circuit within the plurality of drive signal circuits to the touchscreen;

wherein each drive signal circuit within the plurality of drive signal circuits operates cooperatively 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 direction, the direction being selectable by applying full scale AC signals to some of the communicative coupling points and virtual ground signals to other communicative coupling points, the amplitude ramped field is operable to be selectively ramped in a plurality of directions across the touchscreen;

wherein the current flow at the points of communicative coupling includes an unbalanced capacitive reactance current portion wherein a change of the unbalanced capacitive reactance current portion includes a portion that is substantially attributable to a user'"'"'s interaction or touch on the touchscreen;

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;

wherein the touchscreen includes four corners;

wherein the plurality of drive signal circuits includes four drive signal circuits such that each of the four drive signal circuits is coupled to the resistive pattern at one of the four corners of the touchscreen;

wherein each of the four drive signal circuits is operable to measure current flow at its respective corner of the touchscreen;

four subtraction circuits, each subtraction circuit being communicatively coupled to one of the four drive signal circuits and each subtraction circuit being operable to remove any substantially purely resistive current portion that is injected into one of the corners by one of the drive signal circuits, each of the four subtraction circuits also being operable to perform high pass filtering and adding to remove any resistance portion of the current flow at the corners of the touchscreen thereby leaving a resulting current flow having an unbalanced capacitive reactance current portion;

a 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 a user'"'"'s touch on the touchscreen; and

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

11. The touchscreen system of claim 10, wherein:

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 touch 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 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 touch on the touchscreen.

12. The touchscreen system of claim 11, 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 a user'"'"'s touch on the touchscreen.