SYSTEM AND METHOD FOR DETERMINING TOUCH POSITIONS BASED ON PASSIVELY-INDUCED POSITION-DEPENDENT ELECTRICAL CHARGES

• US 20100127717A1
• Filed: 11/26/2008
• Published: 05/27/2010
• Est. Priority Date: 11/26/2008
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Geaghan, Bernard O., Cordeiro, Craig A.
• Granted Patent: US 8,183,875 B2
• Time in Patent Office: Days
• US Class Current: 324/678
• 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 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

Systems and methods determine the position of a touch on a surface of a device, such as a touch-sensitive device, by using passively-induced position-dependent electrical charges. In such a method, the position of a touching implement is determined on the sensing surface of a device. The method includes charging the sensing surface during a first time period by connecting all four corners of the sensing surface to a reference voltage, and over a second time period discharging two adjacent corners of the sensing surface into an integrator capacitor while connecting the two opposite corners to ground. The first and second time periods together form a charge/discharge cycle that is repeated a plurality of times, after which an output of the integrator capacitor is measured. This sequence is performed for each of the four pairs of adjacent corners of the sensing surface, resulting in four integrator capacitor output measurements, each of the four measurements being associated with a different sensing surface edge. The position of the touching implement on the sensing surface is then calculated using the four charge measurements.

Claims

1. A method for determining the position of a touching implement on a sensing surface of a touch-sensitive device, the method comprising:

(a) over a plurality of cycles of first and second time periods,

connecting all four corners of the sensing surface to a reference voltage during the first time period, and

during the second time period, discharging two adjacent corners of the sensing surface into an integrator capacitor while connecting the two opposite corners to ground;

(b) after the plurality of cycles, measuring an output of the integrator capacitor;

repeating steps (a) and (b) for each of the four pairs of adjacent corners of the sensing surface, resulting in four integrator capacitor output measurements, each of the four measurements being associated with a different sensing surface edge; and

calculating the position of the touching implement on the sensing surface using the four charge measurements.

2. The method of claim 1, wherein the ratio between the first and second time periods is fixed.

3. The method of claim 2, further comprising varying the sum of the first and second time periods so that the measured output of the integrator capacitor is within a predetermined range after a predetermined number of cycles.

4. The method of claim 1, wherein the sum of the first and second time periods is fixed.

5. The method of claim 4, further comprising varying the ratio of the first and second time periods so that the measured output of the integrator capacitor is within a predetermined range after a predetermined number of cycles.

6. The method of claim 1, wherein the sum of the first and second time periods is in a range of about 0.5 microseconds to 5 microseconds.

7. The method of claim 1, wherein the plurality of cycles includes at least 100 cycles.

8. The method of claim 1, wherein the duration of the first time period is sufficient to charge the sensing surface to the reference voltage.

9. The method of claim 1, wherein the duration of the second time period is less than the time required to fully discharge the sensing surface from the reference voltage to zero volts.

10. An apparatus for determining the position of a touching implement on the sensing surface of a device, comprising:

a signal drive circuit, coupled to the surface of the device, to simultaneously drive all four corners of the sensing surface to a reference voltage over a first time period; and

a charge measurement circuit, coupled to the sensing surface, to passively induce a position-dependent electrical charge and to measure the position-dependent electrical charge by discharging two adjacent corners of the sensing surface into an integrator capacitor while simultaneously connecting the two opposite corners to ground during a second time period alternated with the first time period, the charge accumulated in the integrator capacitor indicating a coordinate on the sensing surface for establishing the position of the touching implement.

11. The apparatus of claim 10, further comprising switches to couple each of the four corners of the sensing surface to the charge measurement circuit.

12. The apparatus of claim 11, further comprising a pulse width modulation gate disposed between the switches and the integrator capacitor.

13. The apparatus of claim 10, wherein the duration of the first time period is sufficient to charge the sensing surface to the reference voltage.

14. The apparatus of claim 10, wherein the reference voltage is in a range of about 3 to 5 volts.

15. The apparatus of claim 10, wherein the duration of the second time period is less than the time required to fully discharge the sensing surface from the reference voltage to zero volts.

16. A method for use in calibrating a touch-sensitive device for determining the position of a touching implement on the sensing surface of the device, the method comprising:

(a) connecting all four corners of the sensing surface to a reference voltage during a first time period;

(b) responsive to completing the first time period, discharging two adjacent corners of the sensing surface into an integrator capacitor while connecting the two opposite corners to ground during a second time period;

(c) responsive to repeating steps (a) and (b) a predetermined number of times, comparing a voltage output of the integrator capacitor to a selected voltage range; and

(d) responsive to the comparing step, determining adjustments to the second time period according to the following;

decreasing the second time period if the voltage output of the integrator capacitor is below the selected voltage range, and repeating steps (a) through (d); and

increasing the second time period if the voltage output of the integrator capacitor is above the selected voltage range, and repeating steps (a) through (d).

17. The method of claim 16, further comprising increasing the first time period when the second time period is decreased, and decreasing the first time period when the second time period is increased.

18. The method of claim 17, wherein any adjustments to the first and second time periods are made so that the sum of the first and second time periods remains constant.

19. The method of claim 17, wherein after adjustment, the duration of the first time period is sufficient to charge the sensing surface to the reference voltage.

20. The method of claim 16, further comprising repeating the recited steps for each of the four pairs of adjacent corners of the sensing surface.