METHODS AND SYSTEMS FOR SIGMA DELTA CAPACITANCE MEASURING USING SHARED COMPONENTS

• US 20110001494A1
• Filed: 08/16/2010
• Published: 01/06/2011
• Est. Priority Date: 06/03/2005
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: HARGREAVES, Kirk, REYNOLDS, Joseph Kurth
• Granted Patent: US 7,977,954 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 3/04166 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 sigma-delta 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. A switch or IO controlling the charge sharing and/or charge changing can also be shared 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 a plurality of measurable capacitances, the system comprising:

at least one passive network coupled to the plurality of measurable capacitances;

at least one charge changing circuit coupled to the at least one passive network; and

a controller, the controller including a plurality of digital outputs coupled to the plurality of measurable capacitances, wherein the controller is configured to perform, for each of the plurality of measurable capacitances, a charge transfer measurement process comprising;

repeatedly applying an associated voltage to the measurable capacitance using an associated digital output in the plurality of digital outputs,

accumulating charge on an associated passive network of the at least one passive network by repeatedly sharing charge between the measurable capacitance and the associated passive network,

generating quantized values by repeatedly measuring a voltage on the associated passive network using a quantizer having at least one threshold,

repeatedly changing charge on the associated passive network by a quantized amount of charge using an associated charge changing circuit of the at least one charge changing circuit, the quantized amount of charge based on the quantized values, and

digitally filtering the quantized values.

2. The system of claim 1 wherein the at least one passive network comprises a passive network with at least two integrating capacitances, wherein the at least two integrating capacitances are coupled to power supply voltages and provide a conditioned voltage that varies with the at least one threshold of the quantizer.

3. The system of claim 1, further comprising a plurality of sensor electrodes configured to provide the plurality of measurable capacitances, wherein each of the plurality of measurable capacitances comprises a capacitance measured between a sensor electrode in the plurality of sensor electrodes and a proximate external object.

4. The system of claim 1, further comprising a plurality of sensor electrodes configured to provide the plurality of measurable capacitances, wherein each of the plurality of measurable capacitances comprises a transcapacitance measured between sensor electrodes in the plurality of sensor electrodes.

5. The system of claim 1 wherein at least two of the plurality of measurable capacitances are associated with the same associated charge changing circuit.

6. The system of claim 1 wherein at least two of the plurality of measurable capacitances are associated with different associated charge changing circuits.

7. The system of claim 1 wherein at least two of the plurality of measurable capacitances are associated with the same associated passive network.

8. The system of claim 1, wherein the controller is configured to measure multiple measurable capacitances of the plurality of measurable capacitances concurrently by accumulating charge from different ones of the multiple measurable capacitances on different associated passive networks.

9. The system of claim 1 wherein each of the plurality of measurable capacitances comprises a transcapacitance measured between sensor electrodes in a plurality of sensor electrodes, and wherein the controller is configured to apply different associated voltages to multiple measureable capacitances of the plurality of measurable capacitances concurrently.

10. The system of claim 1 further comprising a voltage conditioning circuit configured to provide a variable reference voltage to an associated passive network of at least one measurable capacitance of the plurality of measurable capacitances, the variable reference voltage varying with the at least one threshold of the quantizer.

11. The system of claim 10 wherein the 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 divider node.

12. The system of claim 1 wherein the controller is configured, for at least one measurable capacitance of the plurality of measurable capacitances, to change the charge on the associated passive network by:

allowing charge on the associated passive network to pass through a resistance of the associated charge changing circuit.

13. The system of claim 12, wherein the quantizer comprises a comparator.

14. A controller comprising:

a plurality of digital outputs; and

a memory, the memory including executable instructions to perform, for each of a plurality of measureable capacitances, a charge transfer measurement process comprising;

repeatedly applying an associated voltage to the measurable capacitance using a digital output in the plurality of digital outputs;

accumulating charge on an associated passive network by repeatedly sharing charge from the measurable capacitance;

generating quantized values by repeatedly measuring a voltage on the associated passive network using a quantizer having at least one threshold;

repeatedly changing a charge on the associated passive network by a quantized amount of charge, the quantized amount of charge based on the quantized values; and

digitally filtering the quantized values to determine a measure of the measurable capacitance.

15. The controller of claim 14 wherein, for at least two of the plurality of measureable capacitances, the repeatedly changing a charge comprises:

using a same charge changing circuit.

16. The controller of claim 14 wherein, for at least one measurable capacitance of the plurality of measurable capacitances, the repeatedly changing the charge on the associated passive network comprises:

repeatedly allowing charge on the associated passive network to pass through a resistance.

17. The controller of claim 14 wherein at least two measureable capacitances of the plurality of measureable capacitances are associated with the same associated passive network.

18. The controller of claim 14 wherein at least two measureable capacitances of the plurality of measureable capacitances are associated with different associated passive networks, and wherein the charge transfer measurement process is performed concurrently for the at least two measurable capacitances.

19. The controller of claim 14 wherein at least two measurable capacitances of the plurality of measurable capacitances are associated with different associated voltages, and wherein the charge transfer measurement process is performed concurrently for the at least two measurable capacitances.

20. The controller of claim 14 wherein the memory further includes executable instructions for providing a guarding voltage to a guarding electrode configured to electrically guard the plurality of measurable capacitances.

21. A method of measuring a plurality of measurable capacitances, the method comprising:

repeatedly applying a first voltage to a first measurable capacitance using a first switch;

accumulating charge on a passive network by repeatedly sharing charge between the first measurable capacitance and the passive network;

generating first quantized values by repeatedly measuring a voltage on the passive network using a quantizer having at least one threshold;

repeatedly changing charge in the passive network by a quantized amount of charge based on the first quantized values;

digitally filtering the first quantized values;

repeatedly applying a second voltage to a second measurable capacitance using a second switch;

accumulating charge on the passive network by repeatedly sharing charge between the second measurable capacitance and the passive network;

generating second quantized values by repeatedly measuring a voltage on the second passive network using at least one of the quantizer and a second quantizer,

repeatedly changing charge in the second passive network by a second quantized amount of charge based on the second quantized values; and

digitally filtering the second quantized values.