Capacitive touch sensing and light emitting diode drive matrix

• US 8,780,068 B2
• Filed: 04/19/2013
• Issued: 07/15/2014
• Est. Priority Date: 01/12/2009
• Status: Expired due to Fees

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Microchip Technology Incorporated
• Inventors: Lin, Chien-Yi
• Primary Examiner(s): Chow, Van
• Application Number:
  US13/866,700
• Publication Number:
  US 20130229385A1
• Time in Patent Office: 452 Days
• Field of Search: 345173-179
• US Class Current: 345/173
• 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
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/96073 Amplitude comparison
• CPC Class Codes: H03K 2217/960785 with illumination

Abstract

A pulse is applied through a capacitive touch key sensor to a sampling capacitor of an analog-to-digital converter (ADC). The voltage charge arriving at the sampling capacitor will be maximum when there is substantially no shunt capacitance between the capacitive touch key sensor and the sampling capacitor. However, a object such as an operator'"'"'s finger when in close proximity to the capacitive touch key sensor will create a shunt to ground capacitance that diverts some of the charge that is supposed to go to the sampling capacitor and thereby reducing the voltage charge on the sampling capacitor. This change in charge voltage when the capacitive touch key sensor is activated (touched) may be easily detected with the ADC. In addition, light emitting diode (LED) displays may be integrated with the capacitive touch key sensors and use the same connections on an integrated circuit device in a time division multiplexed manor.

Claims

1. A method for sensing actuation of a capacitive touch sensor and indicating such actuation, in a system comprising:

a sampling capacitor having a first terminal connected to a reference potential and a second terminal;

an analog-to-digital converter (ADC) connected to the second terminal of the sampling capacitor;

a capacitive touch sensor having a first terminal connected to the sampling capacitor through a sampling switch and through a port switch with the reference potential and having a second terminal; and

a light emitting diode (LED) coupled in parallel with the capacitive touch sensor;

wherein the capacitive touch sensor and the LED use common connections;

wherein the method comprises;

generating a single voltage pulse and charging through the capacitive touch sensor the sampling capacitor to a first voltage in proportion to a capacitance ratio thereof, wherein when an object having a capacitance is in close proximity to the capacitive touch sensor some of the voltage pulse through the capacitive touch sensor is diverted from the sampling capacitor, and wherein the sampling capacitor is charged to a second voltage when the object is in close proximity to the capacitive touch sensor, wherein the second voltage is less than the first voltage, and

determining said voltage on said sampling capacitor; and

controlling the port switch and a voltage at said second terminal of the capacitive touch sensor to turn on said LED.

2. The method according to claim 1, wherein the system further comprises:

a multiplexer;

a plurality of capacitive touch sensors arranged in a matrix of C columns and R rows, wherein each capacitive touch sensor having a first terminal coupled to the sampling capacitor through said multiplexer and through respective port switches with the reference potential and a second terminal; and

a plurality of light emitting diodes (LED) each coupled in parallel with one of the capacitive touch sensors;

wherein each combination of capacitive touch sensor and LED use common connections;

wherein the method further comprises;

setting row and column connections of said matrix to logic low,

set ports connected to the rows to an analog input mode;

setting column connections of said matrix to logic high,

determining and storing whether a row is at a lower voltage than other rows to determine which row has been touched,

setting the row and column connections to logic low,

set ports connected to the columns to an analog input mode;

setting the row connections to logic high, and

determining and storing whether a column is at a lower voltage than other columns to determine which column has been touched;

combining the results to determine which capacitive touch sensor has been touched; and

controlling said multiplexer, port switches and a voltage at said second terminal of a respective capacitive touch sensor using time division multiplexing to turn on said associated LED.

3. The method according to claim 1, wherein a plurality of capacitive touch sensors are arranged in Cx columns and Ry rows, said method comprising the steps of:

connecting each Cx column and Ry row to a port of a microcontroller;

setting Cx columns and Ry rows to a logic low;

setting the Ry rows to an input mode for determining analog voltage values of the Ry rows by said microcontroller;

setting the Cx columns to a logic high;

scanning the Ry rows to determine which one of the Ry rows is at a lower analog voltage value than the other Ry rows;

setting the Cx columns and the Ry rows to a logic low;

setting the Cx columns to the input mode for determining analog voltage values of the Cx columns;

setting the Ry rows to a logic high;

scanning the Cx columns to determine which one of the Cx columns is at a lower analog voltage value than the other Cx columns; and

determining from an intersection of the Cx column and the Ry row having the lower analog voltage values which one of the plurality of capacitive touch sensors was touched.

4. The method according to claim 3, wherein the steps of determining the analog voltage values of the Cx columns and Ry rows are done with an analog-to-digital converter (ADC) of said microcontroller.

5. A system for sensing actuation of a capacitive touch sensor and indicating such actuation, comprising:

a sampling capacitor having a first terminal connected to a reference potential and a second terminal;

an analog-to-digital converter (ADC) connected to the second terminal of the sampling capacitor;

a capacitive touch sensor having a first terminal connected to the sampling capacitor through a sampling switch and through a port switch with the reference potential and having a second terminal; and

a light emitting diode (LED) coupled in parallel with the capacitive touch sensor;

wherein the capacitive touch sensor and the LED use common connections;

and a digital processor configured

to generate a single voltage pulse and to charge through the capacitive touch sensor the sampling capacitor to a first voltage in proportion to a capacitance ratio thereof, wherein when an object having a capacitance is in close proximity to the capacitive touch sensor some of the voltage pulse through the capacitive touch sensor is diverted from the sampling capacitor, and wherein the sampling capacitor is charged to a second voltage when the object is in close proximity to the capacitive touch sensor, wherein the second voltage is less than the first voltage, and

to determine said voltage on said sampling capacitor through said ADC; and

to control the port switch and a voltage at said second terminal of the capacitive touch sensor to turn on said LED.

6. The system according to claim 5, wherein a plurality of capacitive touch sensors are arranged in Cx columns and Ry rows, and said digital processor is further operable:

to connect each Cx column and Ry row to a port;

to set Cx columns and Ry rows to a logic low;

to set the Ry rows to an input mode for determining analog voltage values of the Ry rows;

to set the Cx columns to a logic high;

to scan the Ry rows to determine which one of the Ry rows is at a lower analog voltage value than the other Ry rows;

to set the Cx columns and the Ry rows to a logic low;

to set the Cx columns to the input mode for determining analog voltage values of the Cx columns;

to set the Ry rows to a logic high;

to scan the Cx columns to determine which one of the Cx columns is at a lower analog voltage value than the other Cx columns; and

to determine from an intersection of the Cx column and the Ry row having the lower analog voltage values which one of the plurality of capacitive touch sensors was touched.

7. The system according to claim 6, wherein the digital processor controls the analog-to-digital converter (ADC) to determine the analog voltage values of the Cx columns and Ry rows.

8. The system according to claim 5, wherein the system further comprises:

a multiplexer;

a plurality of capacitive touch sensors arranged in a matrix of C columns and R rows, wherein each capacitive touch sensor having a first terminal coupled to the sampling capacitor through said multiplexer and through respective port switches with the reference potential and a second terminal; and

a plurality of light emitting diodes (LED) each coupled in parallel with one of the capacitive touch sensors;

wherein each combination of capacitive touch sensor and LED use common connections;

wherein the digital processor is further configured;

to set row and column connections of said matrix to logic low,

to set ports connected to the rows to an analog input mode;

to set column connections of said matrix to logic high,

to determine and store whether a row is at a lower voltage than other rows to determine which row has been touched,

to set the row and column connections to logic low,

to set ports connected to the columns to an analog input mode;

to set the row connections to logic high, and

to determine and store whether a column is at a lower voltage than other columns to determine which column has been touched;

to combine the results to determine which capacitive touch sensor has been touched; and

to control said multiplexer, port switches and a voltage at said second terminal of a respective capacitive touch sensor using time division multiplexing to turn on said associated LED.

9. A system for sensing actuation of one or more of a plurality of capacitive touch sensors, said system comprising:

a sampling capacitor having a first terminal connected to a reference potential and a second terminal;

an analog-to-digital converter (ADC) connected to the second terminal of the sampling capacitor, the ADC converting an analog voltage on the sampling capacitor to a digital representation thereof;

a digital processor coupled to a digital output of the ADC;

a capacitive touch sensor and a light emitting diode (LED) coupled in parallel with the capacitive touch sensor, wherein the capacitive touch sensor has a first terminal connected to the sampling capacitor through a sampling switch and through a port switch with the reference potential and having a second terminal,

a pulse generator controlled by said digital processor, wherein the digital processor is configured to control the pulse generator to feed a voltage pulse through the capacitive touch sensor to charge the sampling capacitor to a first voltage in proportion to a capacitance ration thereof, wherein when an object is in close proximity to the capacitive touch sensor some of the voltage pulse through the capacitive touch sensor is diverted from the sampling capacitor, and whereby the sampling capacitor is charged to a second voltage when the object is in close proximity to the capacitive touch sensor, wherein the second voltage is less than the first voltage; and

wherein the digital processor is operable to control the port switch and a voltage at said second terminal of the capacitive touch sensor to turn on said LED.

10. The system according to claim 9, wherein the object is a finger.

11. The system according to claim 9, wherein the digital processor stores in a memory thereof digital representations of voltages from the ADC for said capacitive touch sensor, wherein when a digital representation of a voltage sampled by the ADC is less then a respective one of the stored voltage representations in memory, a signal is generated indicating that the capacitive touch sensors was actuated.

12. The system according to claim 9, wherein the voltage on the sampling capacitor is sampled by the ADC and the LED is turned on during alternate time periods.

13. The system according to claim 9, wherein the sampling capacitor, ADC, I/O ports, and digital processor are fabricated in an integrated circuit device.

14. The system according to claim 13, wherein the integrated circuit device is a mixed signal microcontroller.