Capacitance measurement system and method

• US 8,368,409 B2
• Filed: 06/02/2011
• Issued: 02/05/2013
• Est. Priority Date: 03/16/2009
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Mueck, Michael, Cormier, Ronald F. Jr.
• Primary Examiner(s): Velez, Roberto
• Application Number:
  US13/151,712
• Publication Number:
  US 20110234534A1
• Time in Patent Office: 614 Days
• Field of Search: None
• US Class Current: 324/678
• CPC Class Codes: G01D 1/00 Measuring arrangements giving results other than momentary value of variable, of general application G01D3/00 takes precedence; in tariff metering apparatus G01D4/00; transducers not specially adapted for a specific variable G01D5/00
• CPC Class Codes: G01D 15/00 Component parts of recorders for measuring arrangements not specially adapted for a specific variable
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A capacitance measurement system precharges first terminals (21-0 . . . 21-k . . . 21-n) of a plurality of capacitors (25-0 . . . 25-k . . . 25), respectively, of a CDAC (capacitor digital-to-analog converter) (23) included in a SAR (successive approximation register) converter (17) to a first voltage (V_DD) and pre-charges a first terminal (3-j) of a capacitor (C_SENj) to a second voltage (GND). The first terminals are coupled to the first terminal of the capacitor to redistribute charges therebetween so as to generate a first voltage on the first terminals and the first terminal of the capacitor, the first voltage being representative of a capacitance of the first capacitor (C_SENj). A SAR converter converts the first voltage to a digital representation (DATA) of the capacitor. The capacitance can be a touch screen capacitance.

Claims

1. An apparatus comprising:

a capacitive touch screen panel; and

a touch screen panel controller having a precharge phase, a measurement conversion phase, wherein the touch screen panel controller includes;

a capacitor bank that includes a plurality of weighted capacitors that are coupled in parallel with one another to a node;

a first switching circuit that is coupled to the capacitive touch screen panel, wherein the first switching circuit is configured to precharge at least a portion of the capacitive touch screen panel during the precharge mode, and wherein the first switching circuit is configured to couple the portion of the touch screen panel to the capacitor bank during the measurement phase;

a comparator that is coupled to the node;

successive approximation register (SAR) logic that is coupled to the comparator; and

a second switching circuit that is coupled to the first switching circuit and the capacitor bank, wherein the second switching circuit is controlled by the SAR logic during the conversion phase, and wherein at least a portion of the second switching circuit is activated during the precharge phase.

2. The apparatus of claim 1, wherein the node further comprises a first node, and wherein the capacitive touch screen panel further comprises a plurality of sensing capacitors that are arranged in an array having a plurality of rows and a plurality of columns, wherein each column is associated with at least one of a plurality of second nodes, and wherein each sensing capacitor for each column is coupled to its associated second node.

3. The apparatus of claim 2, wherein the first switching circuit further comprises:

a first set of switches, wherein each switch from the first set of switches being coupled to at least one of the plurality of second nodes, and wherein each switch from the second set of switches is configured to be closed during the precharge phase; and

a second set of switches, wherein each switch from the second set of switches is coupled between the touch screen panel and at least one of weighted capacitors, wherein each switch from the second set of switches is configured to be closed during the measurement phase.

4. The apparatus of claim 3, and wherein the second switching circuit further comprises:

a third set of switches, wherein each switch from the third set of switches is coupled to at least one of the weighted capacitors and at least one of the switches from the second set of switches, and wherein each switch from the third set of switches is configured to be closed during the precharge phase;

a fourth set of switches, wherein each switch from the third set of switches is coupled to at least one of the weighted capacitors and at least one of the switches from the second set of switches, and wherein each switch from the third and fourth sets of switches are controlled by the SAR logic during the conversion phase.

5. The apparatus of claim 4, wherein the touch screen panel controller further comprises a maintaining switch that is coupled to each weighted capacitor, wherein the maintaining switch is configured to be closed during the precharge phase and the measurement phase.

6. The apparatus of claim 4, wherein each switch from the second set of switches is coupled to a third node, and wherein the first switching circuit further comprises a fifth set of switches, wherein each switch from the fifth set of switches is coupled to the third node and at least of the second nodes.

7. The apparatus of claim 6, wherein the the touch screen panel controller further comprises a charge pump that is coupled to the third node.

8. An apparatus comprising:

a capacitive touch screen panel having;

a plurality of row electrodes; and

a plurality of column electrodes, wherein the plurality of row electrodes and the plurality of column electrodes are arranged to form an array of sensing capacitors; and

a touch screen panel controller having a precharge phase, a measurement phase, and a conversion phase, wherein the touch screen panel controller includes;

a first switch that is coupled to each row electrode and that is configured to receive a first voltage, wherein the first switch is configured to be closed during the precharge phase;

a second switch that is coupled to each row electrode and that is configured to receive a second voltage, wherein the second switch is configured to be closed during the measurement phase;

a first set of switches, wherein each switch from the second set of switches is coupled to at least one column electrode, and wherein each switch from the second set of switches is configured to be closed during the precharge phase;

a second set of switches, wherein each switch from the second set of switches is coupled to the touch screen panel, wherein each switch from the second set of switches is configured to be closed during the measurement phase;

a plurality of capacitors, wherein each capacitor coupled to at least one of the switches from the second set of switches;

a third set of switches, wherein each switch from the third set of switches is configured to receive the first voltage, and wherein each switch from the third set of switches is coupled to at least one of the capacitors, and wherein each switch from the third set of switches is configured to be closed during the precharge phase; and

a fourth set of switches, wherein each switch from the fourth set of switches is coupled to at least one of the capacitors;

a comparator that is coupled to each of the capacitors; and

SAR logic that is coupled to the comparator and that is configured to control each switch from the third and fourth sets of switches during the conversion phase.

9. The apparatus of claim 8, wherein the touch screen panel controller further comprises a third switch that is coupled to each capacitor and that is configured to receive a third voltage.

10. The apparatus of claim 9, wherein each switch from the second set of switches is coupled to a node, wherein the touch screen panel controller further comprises a fifth set of switches, wherein each switch from the fifth set of switches is coupled to at least one of the column electrodes and to the node, and wherein each switch from the fifth set of switches is configured to be closed during the measurement phase.

11. The apparatus of claim 10, wherein the touch screen panel controller further comprises a charge pump that is coupled to the node.

12. The apparatus of claim 10, wherein the first voltage is a supply voltage, and wherein the second voltage is ground.