Digital signal processed touchscreen system

• US 8,947,369 B2
• Filed: 03/30/2010
• Issued: 02/03/2015
• 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): Karimi, Pegeman
• Application Number:
  US12/750,644
• Publication Number:
  US 20100177061A1
• Time in Patent Office: 1,771 Days
• Field of Search: 345173-179, 178/18.5, 178/18.6, 178 1801- 1803
• 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 dielectric sheet having a frontside and a backside;

a resistive pattern that is attached to the backside of the dielectric sheet;

a plurality of drive signal circuits that are respectively coupled to a corresponding plurality of communicative coupling points of the resistive pattern on the backside of the dielectric sheet to produce a first pair of two amplitude ramped fields having inversed gradients with respect to each other in a first direction by applying full scale AC signals to a first set of the plurality of communicative coupling points and virtual ground signals to a second set of the plurality of coupling points at a first time and applying the virtual ground signals to the first set of the plurality of communicative coupling points and the full scale AC signals to the second set of the plurality of coupling points at a second time, each of the amplitude ramped fields communicatively coupling through the dielectric sheet to the frontside of the dielectric sheet, the plurality of drive signal circuits being further operable to measure current flow at the plurality of communicative coupling points coupled to the resistive pattern on the backside of the dielectric sheet, the first pair of amplitude ramped fields including;

a first amplitude ramped field extending across the dielectric sheet in the first direction at the first time, and

a second amplitude ramped field extending across the dielectric sheet in the first direction at the second time subsequent to the first time; and

a digital signal processor that is operable to;

extract a first unbalanced capacitive component of the measured current flow at the plurality of communicative coupling points at the first time and a second unbalanced capacitive component of the measured current flow at the second time; and

derive a location in the first direction of the user'"'"'s interaction or touch on the frontside of the dielectric sheet by deriving a ratio of the first unbalanced capacitive component to a sum of the first unbalanced capacitive component and the second unbalanced capacitive component.

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

sums currents corresponding to the first and second amplitude ramped fields.

3. 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.

4. The touchscreen system of claim 1, wherein:

the dielectric sheet 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 dielectric sheet with a full scale AC signal when the digital signal processor fails to detect a user'"'"'s interaction or touch on the frontside of the dielectric sheet 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 frontside of the dielectric sheet.

5. The touchscreen system of claim 4, wherein:

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

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

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 the first unbalanced capacitive component at the first time and the second unbalanced capacitive component at the second time.

7. The touchscreen system of claim 6, wherein the plurality of subtraction circuits are 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. The touchscreen system of claim 1, wherein the plurality of drive signal circuits further produce a second pair of amplitude ramped fields having inversed gradients with respect to each other in a second direction perpendicular to the first direction, the second pair of amplitude ramped fields including:

a third amplitude ramped field extending across the dielectric sheet in the second direction at a third time subsequent to the second time by applying full scale AC signals to a first set of the plurality of communicative coupling points and virtual ground signals to a second set of the plurality of communicative coupling points, and

a fourth amplitude ramped field extending across the dielectric sheet in the second direction at a fourth time subsequent to the third time by applying the virtual ground signals to the third set of the plurality of communicative coupling points and the full scale AC signals to the fourth set of the plurality of communicative coupling points, the fourth amplitude ramped field having an inversed gradient with respect to the third amplitude ramped field;

wherein the digital signal processor derives a second ratio of the third unbalanced capacitive component to a sum of the third unbalanced capacitive component and the fourth unbalanced capacitive component to produce a second position of the location in the second direction.

9. A touchscreen system, comprising:

a dielectric sheet having a frontside and a backside;

a resistive pattern that is attached to the backside of the dielectric sheet;

a plurality of drive signal circuits that are communicatively coupled to the resistive pattern on the backside of the dielectric sheet at respective ones 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 coupled to the resistive pattern on the backside of the dielectric sheet;

wherein the plurality of drive signal circuits are cooperatively operable to energize the resistive pattern thereby generating a plurality of amplitude ramped fields that each communicatively couple through the dielectric sheet to the frontside of the dielectric sheet, the plurality of amplitude ramped fields including;

a first amplitude ramped field extending across the dielectric sheet in a first direction at a first time by applying full scale AC signals to a first set of the plurality of communicative coupling points and virtual ground signals to a second set of the plurality of communicative coupling points,

a second amplitude ramped field extending across the dielectric sheet in the first direction at a second time subsequent to the first time by applying the virtual ground signals to the first set of the plurality of communicative coupling points and the full scale AC signals to the second set of the plurality of communicative coupling points, the second amplitude ramped field having an inversed gradient with respect to the first amplitude ramped field,

a third amplitude ramped field extending across the dielectric sheet in a second direction perpendicular to the first direction a third time subsequent to the second time by applying the full scale AC signals to a third set of the plurality of communicative coupling points and the virtual ground signals to a fourth set of the plurality of communicative coupling points, and

a fourth amplitude ramped field extending across the dielectric sheet in the second direction at a fourth time subsequent to the third time by applying the virtual ground signals to the third set of the plurality of communicative coupling points and the full scale AC signals to the fourth set of the plurality of communicative coupling points, the fourth amplitude ramped field having an inversed gradient with respect to the third amplitude ramped field;

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 component that is substantially attributable to a user'"'"'s interaction or touch on the frontside of the dielectric sheet; and

a digital signal processor that is operable to;

extract a first unbalanced capacitive component of the measured current flow at the first time, a second unbalanced capacitive component of the measured current flow at the second time, a third unbalanced capacitive component of the measured current flow at the third time and a fourth unbalanced capacitive component of the measured current flow at the fourth time; and

derive a location of the user'"'"'s interaction or touch on the frontside of the dielectric sheet by deriving;

a first ratio of the first unbalanced capacitive component to a sum of the first unbalanced capacitive component and the second unbalanced capacitive component to produce, a first position of the location in the first direction; and

a second ratio of the third unbalanced capacitive component to a sum of the third unbalanced capacitive component and the fourth unbalanced capacitive component to produce a second position of the location in the second direction.

10. The touchscreen system of claim 9, wherein:

the dielectric sheet 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 dielectric sheet; and

each of the four drive signal circuits is operable to measure current flow at an associated corner of the dielectric sheet and to detect a respective one of the first, second, third and fourth unbalanced capacitive components of the measured current attributable to the user'"'"'s interaction or touch on the frontside of the dielectric sheet.

11. The touchscreen system of claim 10, 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 frontside of the dielectric sheet.

12. The touchscreen system of claim 9, 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.

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

cooperatively energizing a resistive pattern attached to a backside of a dielectric sheet at a plurality of communicative coupling points and generating a plurality of amplitude ramped fields that each communicatively couple through the dielectric sheet to a frontside of the dielectric sheet, the cooperatively energizing the resistive pattern including;

applying full scale AC signals to a first set of the plurality of communicative coupling points and virtual ground signals to a second set of the plurality of communicative coupling points to produce a first amplitude ramped field extending across the dielectric sheet in a first direction at a first time,

applying the virtual ground signals to the first set of the plurality of communicative coupling points and the full scale AC signals to the second set of the plurality of communicative coupling points to produce a second amplitude ramped field extending across the dielectric sheet in the first direction at a second time subsequent to the first time, the second amplitude ramped field having an inversed gradient with respect to the first amplitude ramped field,

applying the full scale AC signals to a third set of the plurality of communicative coupling points and the virtual ground signals to a fourth set of the plurality of communicative coupling points to produce a third amplitude ramped field extending across the dielectric sheet in a second direction perpendicular to the first direction a third time subsequent to the second time, and

applying the virtual ground signals to the third set of the plurality of communicative coupling points and the full scale AC signals to the fourth set of the plurality of communicative coupling points to produce a fourth amplitude ramped field extending across the dielectric sheet in the second direction at a fourth time subsequent to the third time, the fourth amplitude ramped field having an inversed gradient with respect to the third amplitude ramped field;

measuring current flow at the plurality of communicative coupling points coupled to the resistive pattern on the backside of the dielectric sheet at each of the first, second, third and fourth times;

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 component thereby generating a first unbalanced capacitive component at the first time, a second unbalanced capacitive component at the second time, a third unbalanced capacitive component at the third time and a fourth unbalanced capacitive component at the fourth time;

converting the first, second, third and fourth unbalanced capacitive component, being substantially attributable to a user'"'"'s interaction or touch on the frontside of the dielectric sheet, to first, second, third and fourth digital signals, respectively;

deriving, in a digital signal processor, a location of the user'"'"'s interaction or touch on the frontside of the dielectric sheet deriving including;

deriving a first ratio of the first digital signal to a sum of the first digital signal and the second digital signal to produce a first position of the location in the first direction, and

deriving a second ratio of the third digital signal to a sum of the third digital signal and the fourth digital signal to produce a second position of the location in the second direction.

14. The method of claim 13, 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.

15. The method of claim 13, wherein:

the dielectric sheet includes four corners; and

further comprising;

simultaneously energizing all four corners of the dielectric sheet with a full scale AC signal when the digital signal processor fails to detect a user'"'"'s interaction or touch on the frontside of the dielectric sheet 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 frontside of the dielectric sheet.

16. The method of claim 13, further comprising:

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

17. 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;

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.