Methods and systems for detecting a capacitance using sigma-delta measurement techniques

• US 7,948,245 B2
• Filed: 02/18/2010
• Issued: 05/24/2011
• Est. Priority Date: 06/03/2005
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Reynolds, Joseph Kurth, Hargreaves, Kirk, Ely, David, Haines, Julian
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US12/708,339
• Publication Number:
  US 20100148806A1
• Time in Patent Office: 460 Days
• Field of Search: 324/679, 324/686
• US Class Current: 324/686
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

Methods, systems and devices are described for detecting a measurable capacitance using sigma-delta measurement techniques. According to various embodiments, a voltage is applied to the measurable capacitance using a first switch. The measurable capacitance is allowed to share charge with a passive network. If the charge on the passive network is past a threshold value, then the charge on the passive network is changed by a known amount for a sufficient number of repetitions until the measurable capacitance can be detected. 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 a button, slider, touchpad or other input sensor.

Claims

1. A program product comprising:

a) a proximity sensor program configured to determine a capacitance value of a measurable capacitance by;

repeatedly applying a predetermined voltage to the measurable capacitance;

repeatedly sharing charge between the measurable capacitance and an integrating capacitance to accumulate charge on the integrating capacitance;

repeatedly measuring voltage on the integrating capacitance and generating quantized values responsive to the repeated measurings;

repeatedly changing charge on the integrating capacitance based on the quantized values; and

determining the capacitance value of the measurable capacitance from the quantized values; and

b) computer readable media bearing the proximity sensor program.

2. The program product of claim 1 wherein the proximity sensor program is configured to change the charge on the integrating capacitance by passing charge on the integrating capacitance through a resistor for a period of time.

3. The program product of claim 2 wherein the period of time is determined at least in part by the quantized values.

4. The program product of claim 1 wherein the repeatedly measuring voltage on the integrating capacitance and generating quantized values responsive to the repeated measurings comprises comparings using a comparator to generate the quantized values.

5. The program product of claim 4 wherein the proximity sensor program further comprises providing the quantized values to a latch, wherein the latch includes a latch output, and wherein the latch output is used in the repeatedly changing charge on the integrating capacitance based on the quantized values.

6. The program product of claim 1 wherein the determining the capacitance value of the measurable capacitance from the quantized values comprises filtering the quantized values.

7. The program product of claim 1 wherein the repeatedly changing charge on the integrating capacitance based on the quantized values maintains the voltage on the integrating capacitance near a threshold.

8. The program product of claim 1 wherein the determining the capacitance value of the measurable capacitance from the quantized values comprises counting the quantized values within a period of time to determine the capacitance value of the measurable capacitance from the quantized values.

9. A program product comprising:

a) a proximity sensor program configured to determine a capacitance value of a first capacitance by performing the steps of;

applying a voltage to the first capacitance;

allowing the first capacitance to share charge with a second capacitance;

outputting a quantized value reflective of whether a voltage on the second capacitance is past a threshold;

changing a charge on the second capacitance by an amount of charge responsive to the voltage on the second capacitance being past the threshold, wherein the amount of charge is determined at least in part as a function of the quantized value;

repeating each of the applying step, the allowing step, the outputting, and the changing step at least once to generate at least one additional quantized value, such that the quantized value and the at least one additional quantized value form a plurality of quantized values; and

determining the capacitance value using the plurality of quantized values; and

b) computer readable media bearing the proximity sensor program.

10. The program product of claim 9 wherein the step of changing the charge on the second capacitance by the amount of charge comprises passing charge on the second capacitance through a resistor for a period of time, where the period of time is determined at least in part from the quantized value.

11. The program product of claim 9 wherein the step of outputting the quantized value comprises outputting from a comparator.

12. The program product of claim 9 wherein the step of determining the capacitance value using the plurality of quantized values comprises filtering the plurality of the quantized values.

13. The program product of claim 9 wherein the step of determining the capacitance value using the plurality of quantized values comprises counting the plurality of quantized values generated within a period of time by the repeating step.

14. The program product of claim 9 wherein the step of repeating of the applying step, the allowing step, and the changing step maintains the voltage on the second capacitance near the threshold.

15. A controller including a memory, the memory including executable instructions for determining a capacitance value of a first capacitance by performing the steps of:

repeatedly applying a predetermined voltage to the first capacitance;

repeatedly sharing charge between the first capacitance and a second capacitance to accumulate charge on the second capacitance;

repeatedly measuring voltage on the second capacitance using an input of the controller and generating quantized values responsive to the repeated measurings;

repeatedly changing charge on the second capacitance based on the quantized values; and

determining the capacitance value of the first capacitance using the quantized values.

16. The controller of claim 15 wherein the controller is configured to repeatedly change charge on the second capacitance based on the quantized values using a charge on a delta capacitance.

17. The system of claim 15 wherein the memory further including executable instructions for determining a capacitance value of a third capacitance by performing the steps of:

repeatedly applying a second predetermined voltage to the third capacitance;

repeatedly sharing charge between the third capacitance and a fourth capacitance to accumulate charge on the fourth capacitance;

repeatedly measuring voltage on the fourth capacitance using a second input of the controller and generating second quantized values responsive to the repeated measurings of voltage on the fourth capacitance;

repeatedly changing charge on the fourth capacitance based on the second quantized values; and

determining the capacitance value of the third capacitance using the second quantized values.

18. The system of claim 15 wherein the memory further including executable instructions for determining a capacitance value of a third capacitance by performing the steps of:

repeatedly applying a second predetermined voltage to the third capacitance;

repeatedly sharing charge between the third capacitance and a fourth capacitance to accumulate charge on the fourth capacitance;

repeatedly measuring voltage on the fourth capacitance using the input of the controller and generating second quantized values responsive to the repeated measurings of voltage on the fourth capacitance;

repeatedly changing charge on the fourth capacitance based on the second quantized values; and

determining the capacitance value of the third capacitance from the second quantized values.

19. The system of claim 15 wherein the memory further including executable instructions for determining a capacitance value of a third capacitance by performing the steps of:

repeatedly applying a second predetermined voltage to the third capacitance;

repeatedly sharing charge between the third capacitance and the second capacitance to accumulate charge on the second capacitance;

repeatedly measuring voltage on the second capacitance using the input of the controller and generating second quantized values responsive to the repeated measurings of voltage on the second capacitance;

repeatedly changing charge on the second capacitance based on the second quantized values; and

determining the capacitance value of the third capacitance from the second quantized values.