Capacitive sensing employing a repeatable offset charge

• US 7,124,312 B2
• Filed: 06/30/2005
• Issued: 10/17/2006
• Est. Priority Date: 07/26/2002
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Bathiche, Steven N., Casebolt, Mark W., Rensberger, Gary S., Albulet, Mihai
• Primary Examiner(s): BUTLER, DENNIS
• Application Number:
  US11/169,739
• Publication Number:
  US 20050240785A1
• Time in Patent Office: 474 Days
• Field of Search: 713/300, 713/320, 713/323, 345/163, 345/165, 345/166, 345/172, 345/156
• US Class Current: 713/323
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3231 Monitoring the presence, absence or movement of users
• CPC Class Codes: G06F 3/03543 Mice or pucks G06F3/03541 takes precedence
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

Capacitive proximity sensing is carried out by detecting a relative change in the capacitance of a “scoop” capacitor formed by a conductor and a surrounding ground plane. Charge is transferred between the “scoop” capacitor and a relatively large “bucket” capacitor, and a voltage of the bucket capacitor is applied to an input threshold switch. A state transition (e.g., from low to high, or high to low) of the input threshold switch is detected and a value (TouchVal) indicative of a number of cycles of charge transfer required to reach the state transition is determined. The presence or absence of an object or body portion in close proximity to or contact with a device can be determined by comparing TouchVal with a predetermined threshold value (TouchOff). In order to lessen the time required for detection, and/or improve the sensitivity thereof, the bucket capacitor may initially be charged to a repeatable non-zero reference level closer to the charge level that will cause a state transition. TouchOff can be adjusted to take into account environmentally induced (non-touch related) changes in the capacitance of the scoop capacitor. Power management may be provided in a user operated data input device utilizing the inventive proximity sensing.

Claims

1. A processor-readable storage medium having stored thereon instructions executable by the processor to perform steps of a method for sensing the presence of an object or body portion in contact with or close proximity to another object, the method comprising:

providing a first conductor capacitively coupled to a ground to thereby form a scoop capacitor having a capacitance which varies in relation to the proximity of said object or body portion to said conductor;

a pair of second and third conductors forming a bucket capacitor having a capacitance which is larger than a maximum capacitance of said scoop capacitor; and

an input threshold switch;

performing switching to selectively;

connect at least one of said scoop capacitor and said bucket capacitor to a voltage source to charge said at least one capacitor, set a charge of said bucket capacitor at a repeatable non-zero reference level, vary the charge of said bucket capacitor from said reference level in relation to a relative size of said scoop capacitor, and apply a voltage of said bucket capacitor to said input threshold switch;

detecting an input state of said input threshold switch;

determining a value (TouchVal) relating to a number of cycles of said varying of the bucket capacitor charge, corresponding to a detection of a transition of said input threshold switch; and

generating, based upon TouchVal, a signal indicative of an ON state wherein said object or body portion is in contact with or close proximity to said another object, and an OFF state wherein said object or body portion is not in contact with or close proximity to said object.

2. A processor-readable storage medium as recited in claim 1, wherein the at least one capacitor comprises said scoop capacitor and said varying of the charge of said bucket capacitor comprises transferring charge from said scoop capacitor to said bucket capacitor.

3. A processor-readable storage medium as recited in claim 2, wherein:

said first conductor of said scoop capacitor is commonly connected, together with a first one of said pair of conductors of said bucket capacitor, to a first terminal, the second of said pair of conductors of the bucket capacitor being connected to a second terminal, and said first one of said pair of conductors of said bucket capacitor is further connected to a third terminal;

said switching cyclically;

(a) clamps the first, second and third terminals to ground, to discharge the bucket capacitor;

(b) sets the first terminal to high impedance and drives the third terminal to thereby set the charge of said bucket capacitor to said reference level;

(c) sets the second and third terminals to be high impedance inputs and drives the first terminal to charge the scoop capacitor without charging the bucket capacitor, said input threshold switch being connected to one of said first terminal and said second terminal to receive a voltage therefrom when said one terminal is set to be said high impedance input; and

(d) sets the first terminal to be a high impedance input and drives the second terminal, to transfer charge of the scoop capacitor to the bucket capacitor; and

said detecting comprises sampling, in relation to the cycling through steps (a)–

(d), a state of said input threshold switch.

4. A processor-readable storage medium as recited in claim 1, wherein the at least one capacitor comprises said bucket capacitor, and said varying of the charge of said bucket capacitor comprises transferring charge from said bucket capacitor to said scoop capacitor.

5. A processor-readable storage medium as recited in claim 4, wherein:

said first conductor of said scoop capacitor is commonly connected, together with a first one of said pair of conductors of said bucket capacitor, to a first terminal, the second of said pair of conductors of the bucket capacitor being connected to a second terminal, and said first one of said pair of conductors of said bucket capacitor is further connected to a third terminal;

said switching cyclically;

(a) drives the first terminal high, drives the second terminal low and sets the third terminal to high impedance, to charge the bucket capacitor;

(b) sets the first terminal to high impedance and drives the third terminal low to thereby drop the charge of said bucket capacitor to said reference level;

(c) sets the second and third terminals to be high impedance inputs and drives the first terminal low, to discharge the scoop capacitor without discharging the bucket capacitor; and

(d) sets said first terminal to be a high impedance input and drives the second terminal, to transfer charge from the bucket capacitor to the scoop capacitor, said input threshold switch being connected to one of said first terminal and said second terminal to receive a voltage therefrom when said one terminal is set to be said high impedance input; and

said detecting comprises sampling, in relation to the cycling through steps (a)–

(d), a state of said input threshold switch.

6. A processor-readable storage medium as recited in claim 1, wherein the at least one capacitor comprises said scoop capacitor and said bucket capacitor connected in series, and said varying of the charge of said bucket capacitor comprises charging said bucket capacitor with said voltage source, as regulated by said scoop capacitor.

7. A processor-readable storage medium as recited in claim 6, wherein:

said first conductor of said scoop capacitor is commonly connected, together with a first one of said pair of conductors of said bucket capacitor, to a first terminal, the second of said pair of conductors of the bucket capacitor being connected to a second terminal, said first one of said pair of conductors of said bucket capacitor further being connected to a third terminal;

said switching cyclically;

(a) drives the first, second and third terminals low, to discharge the bucket capacitor and scoop capacitor;

(b) sets the second terminal to high impedance and drives the third terminal high to thereby set said reference level charge of said bucket capacitor;

(c) sets the first terminal to be a high impedance input and drives the second terminal high, to place the bucket capacitor and scoop capacitor in series; and

(d) sets said second terminal to be a high impedance input and drives the first terminal low, to discharge the scoop capacitor without discharging the bucket capacitor, said input threshold switch being connected to one of said first terminal and said second terminal to receive a voltage therefrom when said one terminal is set to be said high impedance input; and

said detecting comprises sampling, in relation to the cycling through steps (a)–

(d), a state of said input threshold switch.

8. A processor-readable storage medium as recited in claim 1 including further instructions for performing steps comprising:

comparing TouchVal, or a number derived from TouchVal, with a predetermined threshold value (TouchOff), or a number derived from TouchOff; and

wherein said signal generating generates said ON and OFF state indicating signals based upon an output of said comparing.

9. A processor-readable storage medium as recited in claim 8 including further instructions for performing steps comprising:

dynamically adjusting the value of TouchOff in accordance with a relative decrease in the capacitance of said scoop capacitor occurring during said OFF state.

10. A processor-readable storage medium as recited in claim 9 including further instructions for performing steps comprising:

deriving a value (TouchAvg) from TouchVal, wherein said comparing compares TouchAvg with TouchOff during said ON state.

11. A processor-readable storage medium as recited in claim 10, wherein TouchAvg is initially set to equal TouchVal upon a transition from the OFF state to the ON state, and the value of TouchAvg is incremented upon TouchVal exceeding TouchAvg for a predetermined interval.

12. A processor-readable storage medium as recited in claim 11, wherein said decrease in the capacitance of said scoop capacitor is determined from the occurrence of an increase in TouchVal during said OFF state.

13. A processor-readable storage medium as recited in claim 12, wherein said decrease in the capacitance of said scoop capacitor is determined from TouchVal remaining above TouchOff for a predetermined interval.

14. A processor-readable storage medium as recited in claim 8 including further instructions for performing steps comprising:

deriving a value (TouchAvg) from TouchVal, wherein said comparing compares TouchAvg with TouchOff during said ON state.

15. A processor-readable storage medium as recited in claim 8, wherein in said signal generating, a transition from said OFF state to said ON state occurs upon TouchVal decreasing below TouchOff by a predetermined amount.

16. A processor-readable storage medium as recited in claim 8, wherein TouchOff is decremented upon TouchVal remaining below TouchOff for a predetermined interval.

17. A processor-readable storage medium as recited in claim 1, wherein TouchVal for a control cycle n is a moving average value.