Capacitive voltage divider touch sensor

• US 9,367,179 B2
• Filed: 05/27/2008
• Issued: 06/14/2016
• Est. Priority Date: 05/27/2008
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Irkliy, Alex
• Primary Examiner(s): Vazquez, Arleen M
• Assistant Examiner(s): ALLGOOD, ALESA M
• Application Number:
  US12/127,558
• Publication Number:
  US 20090295409A1
• Time in Patent Office: 2,940 Days
• Field of Search: 324/658, 324/678, 345/173, 345/174, 178/18.06, 178/19.03
• US Class Current: 1/1
• 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 3/04166 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

A system for measuring capacitance has a measurement circuit with a first reference capacitor connected to a first node and to a second node. Each of the nodes is connected to a unit operable to apply a reference voltage or ground to one of the nodes. Each node has a first pad connected to the first node and a unit operable to measure voltage between the first node and second node.

Claims

1. A system for measuring capacitance, comprising:

a microcontroller comprising a measurement circuit and a plurality of external pins;

a reference capacitor coupled to a first pin and to a second pin of the microcontroller;

the first pin connected to a first switching unit of the microcontroller configured to apply or remove a reference voltage or ground to said first pin;

the second pin connected to a second switching unit of the microcontroller configured to apply or remove a reference voltage or ground to said second pin;

a pad connected to the first pin wherein the second pin is connected to the reference capacitor; and

an analog to digital converter in said microcontroller operable to measure a voltage between the first pin and second pin,

wherein the microcontroller is configured to control the first and second switching units to apply in a first state the reference voltage simultaneously to said first and said second pin from which state the reference voltage is removed from the first pin, and the second pin is switched from the reference voltage to ground and after a predetermined settling time, said analog to digital converter is controlled to measure a first voltage between the first pin and the second pin, and thereafter to control the first and second switching units to apply in a second state the reference voltage simultaneously to said first and said second pin from which state said reference voltage is removed from said second pin and first pin is switched from the reference voltage to ground and after a predetermined settling time, said analog to digital converter is controlled to measure a second voltage between the first pin and the second pin.

2. The system of claim 1, wherein the first and second switching units operable for applying reference voltages and ground to the first and second pins, respectively, each comprising:

a first switch connected to one of the first and second pins and to the reference voltage; and

a second switch connected to the one of the first or second pins and to ground.

3. The system of claim 1, wherein the microcontroller comprises firmware to control the first and second switching unit.

4. The system of claim 1, wherein the system forms a proximity sensor.

5. The system of claim 1, wherein the microcontroller is further configured to determine a capacitance of the pad from said first and second voltage.

6. The system of claim 5, further comprising:

a plurality of first and second pin pairs, a plurality of pads connected with each first pin, a plurality of reference capacitors connected with each first and second pin, and a plurality of first and second switching units operable to apply a reference voltage or ground to each pin of said first and second pin pairs;

each said reference capacitor connected to one of said first and second pin pairs;

each said first and second pin pairs connected to a respective one of said first and second switching units;

each said pad connected to a respective first pin.

7. The system of claim 1, wherein the first and second switching units operable for applying reference voltages and ground to said first and second pins can be enabled through configuration of the microcontroller.

8. The system of claim 7, wherein the analog to digital converter operable for measuring voltage between the first pin and second pin can be enabled through configuration of said chip.

9. A method of measuring capacitance of a pad comprising:

coupling the pad and a first terminal of a reference capacitor to a first I/O port of a microcontroller;

coupling a second I/O port of the microcontroller to a second terminal of the reference capacitor;

simultaneously applying a voltage to the pad and to both terminals of the reference capacitor and thereafter removing the voltage from the first terminal and the pad and switching the second terminal of the reference capacitor from the voltage to ground,

after a predetermined settling time, measuring a resulting first voltage across the reference capacitor,

thereafter simultaneously applying the voltage to the pad and to both terminals of the reference capacitor and thereafter removing the voltage from the second terminal and switching the first terminal of the reference capacitor and the pad from the voltage to ground,

after a predetermined settling time, measuring a resulting second voltage across the reference capacitor, and

determining a capacitance value of said pad from the measured first and measured second voltages.

10. The method of claim 9, wherein the action of applying voltage across said pad is automated by the microcontroller through firmware.

11. The method of claim 9, wherein the action of applying voltage across said reference capacitor is automated by a microcontroller.

12. The method of claim 9, wherein the action of grounding said reference capacitor is automated by a microcontroller through firmware.

13. The method of claim 9, wherein the second voltage is compared with the first voltage.

14. The method of claim 9 applied to the measurement of capacitance of a plurality of pads.

15. A method of calculating the capacitance of two pads connected across a reference capacitor, comprising:

coupling a first pad and a first terminal of a reference capacitor to a first I/O port of a microcontroller;

coupling a second pad and a second terminal of the reference capacitor to a second I/O port of the microcontroller;

performing steps in the following order;

applying a reference voltage to the first I/O port and the second I/O port in a first state;

directly from said first state, grounding one terminal of said reference capacitor not connected to the first pad while removing the reference voltage from the respective other terminal to create a circuit comprising said reference capacitor coupled in series with said first pad; and

measuring a first resulting voltage across said reference capacitor, said first resulting voltage corresponding to the capacitance value of said first pad;

and thereafter the method further comprises steps in the following order;

applying the reference voltage to the first I/O port and the second I/O port;

grounding one terminal of said reference capacitor not connected to the second pad while removing the reference voltage from the respective other terminal to create a circuit comprising said reference capacitor coupled in series with said second pad; and

measuring a second resulting voltage across said reference capacitor, said second resulting voltage corresponding to the capacitance value of said second pad.

16. A system for measuring capacitance, comprising:

a reference capacitor connected to a first node and to a second node, wherein first and second nodes are external I/O pins of a microcontroller;

each said node connected to a first and second switching unit of the microcontroller operable to apply or remove a reference voltage or ground to one of said nodes;

a first pad connected to the first node;

a second pad connected to the second node; and

an analog to digital converter of the microcontroller operable to measure a voltage between the first node and second node,

wherein for measuring a capacitance of the first and second pad, the first and second switching units are controlled to apply the reference voltage simultaneously to said first and said second node in a first state and directly from said first state to remove the reference voltage from said first node and to apply ground to said second node and after a predetermined settling time, to control said analog to digital converter to measure a first voltage at the first node, and

thereafter said first and second switching units are controlled to apply the reference voltage to said first and said second node and subsequently to remove the reference voltage from said second node and to apply ground to said first node and after a predetermined settling time, to control said analog to digital converter to measure a second voltage at the second node, wherein the microcontroller determines the capacitance of the first pad from said first voltage and the capacitance of the second pad form said second voltage.

17. The system of claim 16, wherein the first and second switching units operable for applying reference voltages and ground to the nodes each comprising:

a first switch connected to the node and to the reference voltage; and

a second switch connected to the node and to ground.

18. The system of claim 16, further comprising:

a plurality of first and second node pairs, a plurality of first pads, a plurality of second pads, a plurality of reference impedances, and a plurality of first and second switching units operable to apply a reference voltage or ground to each node of said first and second node pairs;

each said reference impedance is connected to one of said first and second node pairs;

each said first and second node pairs are connected to a respective one of said first units;

each said first pad connected to a respective first node; and

each said second pad connected to a respective second node.