Capacitive touch sensing and light emitting diode drive matrix

• US 8,427,450 B2
• Filed: 12/18/2009
• Issued: 04/23/2013
• Est. Priority Date: 01/12/2009
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Microchip Technology Incorporated
• Inventors: Lin, Chien-Yi
• Primary Examiner(s): Chow, Van
• Application Number:
  US12/642,089
• Publication Number:
  US 20100177058A1
• Time in Patent Office: 1,222 Days
• Field of Search: None
• US Class Current: 345/174
• 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 system for sensing and indicating actuation of a capacitive touch sensor, 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 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;

a pulse generator coupled to the second terminal of the capacitive touch sensor, and

a light emitting diode (LED) coupled in parallel with the capacitive touch sensor wherein the LED is turned on by the pulse generator when the port switch completes a current path through the LED;

wherein when no object is in proximity to the capacitive touch sensor, a single voltage pulse from the pulse generator and through the capacitive touch sensor charges the sampling capacitor to a first voltage in proportion to a capacitance ratio of said capacitive touch sensor and a capacitance of said sampling capacitor,

wherein when an object having a capacitance is within a certain distance to the capacitive touch sensor, some of the voltage pulse through the capacitive touch sensor is diverted from the sampling capacitor, wherein the sampling capacitor is charged to a second voltage when the object is within said certain distance to the capacitive touch sensor, were the second voltage is less than the first voltage, and

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

2. The system according to claim 1, wherein the object is a finger.

3. The system according to claim 1, wherein the pulse generator is an output driver from the digital processor.

4. The system according to claim 1, wherein the digital processor stores in a memory thereof digital representations of voltages from the ADC, when at least one of the digital representations of voltages stored in memory is less than the others, a signal is generated indicating that the capacitive touch sensor was actuated.

5. The system according to claim 1, wherein the voltage on the sampling capacitor is sampled by the ADC and the LED is turned on during alternate time periods.

6. The system according to claim 1, wherein the sampling capacitor, ADC, pulse generator and digital device are fabricated in an integrated circuit device.

7. The system according to claim 6, wherein the integrated circuit device is a mixed signal microcontroller.

8. The system according to claim 1, wherein

the sampling switch is part of a multiplexer having an output coupled to the sampling capacitor;

and

the system comprises a plurality of combinations of capacitive touch sensors and associated LEDs coupled in parallel, each of the plurality of capacitive touch sensors is coupled to a respective input of the multiplexer;

wherein the pulse generator is coupled to selected ones of the plurality of capacitive touch sensors.

9. The system according to claim 8, wherein the plurality of capacitive touch sensor and LED combinations is arranged in a matrix having C column connections and R row connections.

10. The system according to claim 9, wherein the C column connections and R row connections are each coupled with a respective I/O port of the microcontroller and wherein the multiplexer is operable to couple each I/O port selectively with said ADC.

11. The system according to claim 10, wherein the microcontroller is programmed to subsequently:

set the row connections to logic low,

set the column connections to logic high,

determine and store whether and which row has been touched,

set the column connections to logic low,

set the row connections to logic high, and

determine and store whether and which column has been touched; and

to combine the results to determine which capacitive touch sensor (118a . . . l) has been touched.