METHODS AND SYSTEMS FOR SWITCHED CHARGE TRANSFER CAPACITANCE MEASURING USING SHARED COMPONENTS

• US 20080116904A1
• Filed: 10/26/2007
• Published: 05/22/2008
• 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
• Granted Patent: US 7,902,842 B2
• Time in Patent Office: Days
• US Class Current: 324/678
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• 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: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

Methods, systems and devices are described for detecting a measurable capacitance using charge transfer techniques that can be implemented with many standard microcontrollers, and can share components to reduce device complexity and improve performance. In the various implementations of this embodiment, the passive network used to accumulate charge can be shared between multiple measurable capacitances. Likewise, in various implementations a voltage conditioning circuit configured to provide a variable reference voltage can be shared between multiple measurable capacitances. Finally, in various implementations a guarding electrode configured to guard the measurable capacitances can be shared between multiple measurable capacitances. In each of these cases, sharing components can reduce device complexity and improve performance.

Claims

1. A system for measuring each of a plurality of measurable capacitances, the system comprising:

a passive network, the passive network comprising at least one integrating capacitance and an isolating impedance statically coupled to the plurality of measurable capacitances, the at least one integrating capacitance configured to accumulate charge received from the plurality of measurable capacitances through the isolating impedance; and

a controller, the controller including a plurality of digital outputs, each of the plurality of digital outputs coupled to a measurable capacitance in the plurality of measurable capacitances, the controller configured to measure each of the plurality of measurable capacitances by performing, for each selected measurable capacitance in the plurality of measurable capacitances, a charge transfer process for a number of times equal to at least two and a measuring process for a second number of times equal to at least one, wherein the charge transfer process comprises applying a pre-determined voltage to the selected measurable capacitance in the plurality of measurable capacitance with at least one of the plurality of digital outputs and then allowing the selected measurable capacitance to share charge with the passive network such that charge from multiple charge transfer processes accumulates on the at least one integrating capacitance of the passive network, and wherein the measuring process comprises quantizing a representation of a charge on the passive network to measure the selected measurable capacitance.

2. The system of claim 1 wherein the at least one integrating capacitance includes two integrating capacitances, and wherein the two integrating capacitances are coupled to a power supply voltage and provide a conditioned voltage.

3. The system of claim 1 further comprising a charge changing circuit coupled to the at least one integrating capacitance in the passive network.

4. The system of claim 1 wherein each of the plurality of measurable capacitances comprises a capacitance measured between a sensor electrode and a proximate external object.

5. The system of claim 1 wherein each of the plurality of measurable capacitances comprises a transcapacitance measured between sensor electrodes.

6. The system of claim 1 wherein the controller is further configured to reset the charge on the at least one integrating capacitance before the performing of the first charge transfer process.

7. A system for measuring each of a plurality of measurable capacitances, the system comprising:

at least one passive network, each passive network in the at least one passive network including at least one integrating capacitance and at least one isolating impedance, each of the at least one integrating capacitance and the at least one isolating impedance statically coupled to at least one of the plurality of measurable capacitances, the at least one integrating capacitance configured to accumulate charge received from the at least one of the plurality of measurable capacitances through the at least one isolating impedance;

a controller, the controller including a plurality of digital outputs, each of the plurality of digital outputs coupled to a measurable capacitance in the plurality of measurable capacitances, the controller configured to measure each of the plurality of measurable capacitances by performing, for each selected measurable capacitance in the plurality of measurable capacitances, a charge transfer process for a number of times equal to at least two and a measuring process for a second number of times equal to at least one, wherein the charge transfer process comprises applying a pre-determined voltage to the selected measurable capacitance in the plurality of measurable capacitances with at least one of the plurality of digital outputs and then allowing the selected measurable capacitance to share charge with the at least one passive network such that charge from multiple charge transfer processes accumulates on the at least one integrating capacitance of the at least one passive network; and

wherein the measuring process comprises quantizing relative to a threshold voltage a representation of a charge on the at least one passive network to measure the selected measurable capacitance.

a voltage conditioning circuit coupled to the at least one passive network, the voltage conditioning circuit adapted to provide a variable reference voltage that varies with the threshold voltage.

8. The system of claim 7 wherein the threshold voltage is a threshold voltage of a digital input of the controller.

9. The system of claim 7 further comprising a charge changing circuit coupled to the at least one integrating capacitance in a passive network of the at least one passive network.

10. The system of claim 7 wherein each of the plurality of measurable capacitances comprises a capacitance measured between a sensor electrode and a proximate external object.

11. The system of claim 7 wherein each of the plurality of measurable capacitances comprises a transcapacitance measured between sensor electrodes.

12. The system of claim 7 wherein the a voltage conditioning circuit includes a voltage divider having a first divider impedance and a second divider impedance, the first divider impedance and the second divider impedance coupled at a divider node, and wherein the voltage conditioning circuit is configured to couple a power supply voltage to the at least one passive network through the voltage divider node.

13. The system of claim 12 wherein the first divider impedance comprises a first divider capacitance and wherein the second divider impedance comprises a second divider capacitance.

14. The system of claim 13 further comprising a resistance coupled to the power supply voltage and the divider node in parallel with the first divider capacitance.

15. The system of claim 12 wherein the first divider impedance comprises a first divider resistance and wherein the second divider impedance comprises a second divider resistance.

16. A system for measuring each of a plurality of measurable capacitances, the system comprising:

at least one passive network, each passive network in the at least one passive network including at least one integrating capacitance and at least one isolating impedance, each of the at least one integrating capacitance and the at least one isolating impedance statically coupled to at least one of the plurality of measurable capacitances, the at least one integrating capacitance configured to accumulate charge received from the at least one of the plurality of measurable capacitances through the at least one isolating impedance;

a guarding electrode, the guarding electrode proximate each of the plurality of measurable capacitances; and

a controller, the controller including a plurality of digital outputs, each of the plurality of digital outputs coupled to a measurable capacitance in the plurality of measurable capacitances, the controller configured to measure each selected measurable capacitance in the measurable capacitances by performing, for each of the measurable capacitances, a charge transfer process for a number of times equal to at least two and a measuring process for a second number of times equal to at least one, wherein the charge transfer process comprises applying a pre-determined voltage to the selected measurable capacitance in the plurality of measurable capacitances with at least one of the plurality of digital outputs and then allowing the selected measurable capacitance to share charge with the at least one passive network such that charge from multiple charge transfer processes accumulates on the at least one integrating capacitance of the at least one passive network; and

wherein the measuring process comprises quantizing a representation of a charge on the at least one integrating capacitance of the at least one passive network, the controller further configured to provide a guard signal to the guarding electrode using an output to guard the plurality of measurable capacitances during at least a portion of time in which the predetermined voltage is applied to the selected measurable capacitance and during at least a portion of the time in which the selected measurable capacitance shares charge with the at least one passive network.

17. The system of claim 16 further comprising a charge changing circuit coupled to the at least one integrating capacitance in a passive network of the at least one passive network.

18. The system of claim 16 wherein each of the plurality of measurable capacitances comprises a capacitance measured between a sensor electrode and a proximate external object.

19. The system of claim 16 wherein each of the plurality of measurable capacitances comprises a transcapacitance measured between sensor electrodes.

20. The system of claim 16 wherein the guarding electrode is coupled to the output through a guarding network, and wherein the guarding network comprises a voltage divider.

21. The system of claim 16 wherein the controller is further configured to apply the guard signal by switching the output between a first reference voltage and a second reference voltage.

22. The system of claim 16 wherein the controller is further configured to apply the guard signal by switching the output between a first reference voltage and an open circuit condition.

23. The system of claim 16 wherein the guarding electrode is coupled to the output through a guarding network, and wherein the guarding network comprises a voltage divider.

24. The system of claim 16 further comprising a guarding network coupling the guarding electrode and the output, wherein the guarding network comprises a first guard capacitance and a second guard capacitance substantially greater than the first guard capacitance, wherein the controller is further configured to apply the guard signal by switching the output between a first reference voltage and an open circuit condition and accumulating charge on the second guard capacitance.

25. The system of claim 16 wherein the output to guard the plurality of measurable capacitances comprises an output of the controller.