Methods and systems for detecting a capacitance using switched charge transfer techniques

• US 7,750,649 B2
• Filed: 03/13/2009
• Issued: 07/06/2010
• Est. Priority Date: 06/03/2005
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Routley, Paul, Hargreaves, Kirk, Reynolds, Joseph Kurth, Ely, David, Haines, Julian
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US12/404,123
• Publication Number:
  US 20090174416A1
• Time in Patent Office: 480 Days
• Field of Search: 324/678, 324/688
• US Class Current: 324/678
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device
• 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 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: H03J 9/00 Remote-control of tuned circuits; Combined remote-control of tuning and other functions, e.g. brightness, amplification mechanical remote-control arrangements H03J1/00 ; using a microprocessor H03J1/0025; constructional details of remote control switching devices H01H9/0235
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

Methods, systems and devices are described for detecting a measurable capacitance using charge transfer techniques. According to various embodiments, a charge transfer process is performed for two or more times. During the charge transfer process, a pre-determined voltage is applied to the measurable capacitance, and the measurable capacitance is then allowed to share charge with a filter capacitance through a passive impedance that remains coupled to both the measurable capacitance and to the filter capacitance throughout the charge transfer process. The value of the measurable capacitance can then be determined as a function of a representation of a charge on the filter capacitance and the number of times that the charge transfer process was performed. Such a detection scheme may be readily implemented using conventional components, and can be particularly useful in sensing the position of a finger, stylus or other object with respect to an input sensor.

Claims

1. A program-product comprising:

A) a computer program adapted to configure a controller to measure a measurable capacitance by executing the steps of;

performing a charge transfer process at least twice, wherein the charge transfer process comprises the steps of applying a voltage to the measurable capacitance and allowing the measurable capacitance to share charge with a filter capacitance through a passive impedance that remains coupled to both the measurable capacitance and to the filter capacitance during the applying and allowing steps; and

determining a value of the measurable capacitance based on a voltage on the filter capacitance and a quantity of times that the charge transfer process was performed; and

B) computer-readable media bearing the computer program.

2. The program-product of claim 1 wherein the computer program is further adapted to configure the controller to execute the step of resetting voltage on the filter capacitance in response to detecting the voltage on the filter capacitance being past a threshold.

3. The program-product of claim 2 wherein the computer program is adapted to configure the controller to determine the value of the measurable capacitance based on the voltage on the filter capacitance and the quantity of times that the charge transfer process was performed by:

determining the measurable capacitance based on a number of times the charge transfer process is performed before the voltage on the filter capacitance is detected to pass the threshold.

4. The program-product of claim 1 wherein the computer program is further adapted to configure the controller to execute the step of performing a second charge transfer process at least once, wherein the second charge transfer process comprises the steps of applying an opposing voltage to the measurable capacitance and allowing the measurable capacitance to share charge with the filter capacitance through the passive impedance, and wherein the voltage transfers charge in a first direction, and the opposing voltage transfers charge in a second direction opposite the first direction.

5. The program-product of claim 4 wherein the computer program is further adapted to configure the controller to execute the step of setting the voltage on the filter capacitance to a first value after the performing of the charge transfer process at least twice and setting the voltage on the filter capacitance to a second value after the performing of the second charge transfer process for at least once.

6. The program-product of claim 4 wherein the computer program is adapted to configure the controller to determine the value of the measurable capacitance based on the voltage on the filter capacitance and the quantity of times that the charge transfer process was performed by:

ascertaining a number of performances of the first charge transfer process needed for the voltage on the filter capacitance to cross a first threshold and a number of performances of the second charge transfer processes needed for the voltage on the filter capacitance to cross a second threshold.

7. The program-product of claim 1 wherein the computer program is adapted to configure the controller to apply the voltage to the measurable capacitance by:

applying a predetermined voltage with a digital output of the controller.

8. The program-product of claim 1 wherein the computer program is adapted to configure the controller to determine the voltage on the filter capacitance by:

comparing the voltage to a threshold voltage.

9. The program-product of claim 1 wherein the computer program is adapted to configure the controller to determine the voltage on the filter capacitance by:

comparing the voltage to a threshold voltage of a digital input of the controller.

10. The program-product of claim 1 wherein the computer program is adapted to configure the controller to determine the voltage on the filter capacitance by:

making an analog-to-digital conversion of the voltage.

11. A proximity sensor device comprising:

a measurable capacitance;

a filter capacitance coupled to the measurable capacitance through a passive impedance;

a controller, the controller coupled to the measurable capacitance, the controller configured to;

perform a charge transfer process at least twice, wherein the charge transfer process comprises the steps of applying a voltage to the measurable capacitance and allowing the measurable capacitance to share charge with the filter capacitance through the passive impedance, wherein the passive impedance remains coupled to both the measurable capacitance and to the filter capacitance during the applying and allowing steps;

determine a value of the measurable capacitance based on a voltage on the filter capacitance and a quantity of times that the charge transfer process was performed; and

determine positional information for an object in a sensing region using the value of the measurable capacitance.

12. proximity sensor device of claim 11 wherein the controller is further adapted to reset the voltage on the filter capacitance in response to detecting the voltage on the filter capacitance being past a threshold.

13. The proximity sensor device of claim 12 wherein the controller is adapted to determine the value of the measurable capacitance based on the voltage on the filter capacitance and the quantity of times that the charge transfer process was performed by

determining a number of times the charge transfer process is performed before the voltage on the filter capacitance is detected to pass the threshold.

14. The proximity sensor device of claim 11 wherein the controller is further adapted to execute a second charge transfer process at least once, wherein the second charge transfer process comprises the steps of applying an opposing voltage to the measurable capacitance and allowing the measurable capacitance to share charge with the filter capacitance through the passive impedance, wherein the voltage transfers charge in a first direction, and the opposing voltage transfers charge in a second direction opposite the first direction.

15. The proximity sensor device of claim 14 wherein the controller is further adapted to set the voltage on the filter capacitance to a first value after the performing of the charge transfer process at least twice and to set the voltage on the filter capacitance to a second value after the performing of the second charge transfer process at least once.

16. The proximity sensor device of claim 14 wherein the controller is adapted to determine the value of the measurable capacitance based on the voltage on the filter capacitance and the quantity of times that the charge transfer process was performed by:

ascertaining a number of performances of the first charge transfer process needed for the voltage on the filter capacitance to cross a first threshold and a number of performances of the second charge transfer processes needed for the voltage on the filter capacitance to cross a second threshold.

17. The proximity sensor device of claim 11 wherein the controller is adapted to apply the voltage to the measurable capacitance by:

applying a predetermined voltage with a digital output of a controller.

18. The proximity sensor device of claim 11 wherein the controller is adapted to determine the voltage on the filter capacitance by:

comparing the voltage to a threshold voltage.

19. The proximity sensor device of claim 11 wherein the controller is adapted to determine the voltage on the filter capacitance by:

comparing the voltage to a threshold voltage of a digital input of the controller.

20. A program-product comprising:

A) a user interface program configured to execute the steps of;

repeatedly performing a charge transfer process, where the charge transfer process comprises applying a voltage to a sensor electrode and allowing the sensor electrode to share charge with a filter capacitance through a passive impedance;

determining a voltage of the filter capacitance;

determining a number of times the charge transfer process was performed;

determining a value of a capacitance associated with the sensor electrode based on the voltage of the filter capacitance and the number of times of the charge transfer process was performed; and

determining positional information for an object in a sensing region using the value of the capacitance; and

indicating a user interface function in response to the determined positional information; and

B) computer-readable media bearing the user interface program

21. A method of responding to positional information about at least one object in a sensing region of a sensor, the method comprising:

performing a charge transfer process at least twice, wherein the charge transfer process comprises;

applying a voltage to a measurable capacitance;

allowing the measurable capacitance to share charge with a filter capacitance through a passive impedance that remains coupled to both the measurable capacitance and to the filter capacitance during both the applying and the allowing;

determining a value of the measurable capacitance based on a voltage on the filter capacitance and a quantity of times that the charge transfer process was performed;

determining positional information about the at least one object in the sensing region using the value of the measurable capacitance; and

indicating a user interface function in response to the positional information.