Touch screen controller

• US 6,738,048 B1
• Filed: 10/27/2000
• Issued: 05/18/2004
• Est. Priority Date: 10/29/1999
• Status: Active Grant

• Current Assignee: Texas Instruments Tucson Corp. (Texas Instruments, Inc.)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Rundel, Bernd M.
• Primary Examiner(s): Nguyen, Chanh
• Assistant Examiner(s): Anyaso, Uchendu O.
• Application Number:
  US09/698,848
• Time in Patent Office: 1,299 Days
• Field of Search: 345/173, 345/174, 345/175, 345/176, 345/177, 345/179, 345/180, 345/178, 345/533, 178/18.05, 178/18.06, 178/18.07, 178/18.02, 178/18.03, 178/18.04, 340/562, 714/48, 341/155
• US Class Current: 345/173
• CPC Class Codes: G06F 1/3215 Monitoring of peripheral devices
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: G06F 3/0488 using a touch-screen or digitiser, e.g. input of commands through traced gestures

Abstract

An improved touch screen controller including a comparator and an analog-to-digital converter. The comparator of the touch screen controller detects a touch of the touch screen while the analog-to-digital converter is powered down. The Data Out (DOUT) line of the touch screen controller is used to signal the microprocessor that a touch has occurred. The unique structure of the improved touch screen controller and the fast switching edges of the comparator output signal provide for a faster touch screen controller that consumes little power without requiring a dedicated pin for the touch signal.

Claims

1. A touch screen controller for controlling a touch screen and for detecting a screen touch of the touch screen, the touch screen controller comprising:

a comparator having a first input and a second input, wherein the comparator is configured to produce an output that is a function of a comparison of the first input and the second input;

a digital multiplexer electrically connected to the comparator, wherein the digital multiplexer is configured to receive the output of the comparator and output a first digital signal representative of the output, wherein the first digital signal is indicative of whether the screen touch is occurring, wherein the first digital signal is a LOW digital signal when the screen touch is not occurring, and wherein the first digital signal is a HIGH digital signal when the screen touch is occurring;

an analog-to-digital portion for converting a voltage produced by the touch screen into a second digital signal, wherein the second digital signal is indicative of an x,y position of the screen touch;

a control logic component electrically connected to the digital multiplexer, wherein the control logic component is configured to receive the first digital signal of the digital multiplexer and the second digital signal of the analog-to-digital portion; and

a plurality of pins electrically connected to the control logic component, wherein one of the plurality of pins comprises a data output pin, wherein the data output pin is configured to output both the first digital signal and the second digital signal received from the control logic component, wherein the first digital signal is output as the HIGH digital signal to indicate that the screen touch is occurring before the second digital signal is output.

2. The touch screen controller of claim 1 wherein the first input of the comparator is representative of a voltage of the touch screen and the second input of the comparator is representative of a reference voltage.

3. The touch screen controller of claim 1, wherein the analog-to-digital portion comprises:

an analog multiplexer;

a capacitor digital-to-analog converter electrically connected to the analog multiplexer;

a successive approximation register electrically connected to the digital-to-analog converter; and

a second comparator electrically connected to the successive approximation register.

4. A touch screen system comprising:

resistive touch screen;

a touch screen controller electrically connected to the resistive touch screen, wherein the touch screen controller comprises;

a comparator having a first input connected to the touch screen and a second input connected to reference voltage, wherein the comparator is configured to produce an output that is a function of a comparison of the first input and the second input;

a digital multiplexer electrically connected to the comparator, wherein the digital multiplexer is configured to receive the output of the comparator and output a first digital signal representative of the output, wherein the first digital signal is indicative of whether a screen touch is occurring, wherein the first digital signal is a LOW digital signal when the screen touch is not occurring, and wherein the first digital signal is a HIGH digital signal when the screen touch is occurring;

an analog-to-digital portion for converging a voltage produced by the touch screen into a second digital signal, wherein the second digital signal is indicative of an x,y position of the screen touch;

a control logic component electrically connected to the digital multiplexer, wherein the control logic component is configured to receive the first digital signal of the digital multiplexer and the second digital signal of the analog-to-digital portion; and

a plurality of pins electrically connected to the control logic component, wherein one of the plurality of pins comprises a data output pin, wherein the data output pin is configured to output both the first digital signal and the second digital signal received from the control logic component, wherein the first digital signal is output as the HIGH digital signal to indicate that the screen touch is occurring before the second digital signal is output; and

a microprocessor electrically connected to the control logic component of the touch screen controller, wherein the microprocessor is configured to receive the first and second digital signals of the touch screen controller.

5. The touch screen system of claim 4 wherein the first input of the comparator is representative of a voltage of the touch screen and the second input of the comparator is representative of a reference voltage.

6. The touch screen system of claim 4 wherein the analog-to-digital portion comprises:

an analog multiplexer;

a capacitor digital-to-analog converter electrically connected to the analog multiplexer;

a successive approximation register electrically connected to the digital-to-analog converter; and

a second comparator electrically connected to the successive approximation register.

7. A method for detecting a touch of a touch screen by using a touch screen controller, the method comprising the steps of:

powering down the touch screen controller;

outputting a first digital signal on a pin of the touch screen controller, wherein the first digital signal is representative that the touch is not occurring and the pin of the touch screen controller is shared for a data out signal, wherein the first digital signal comprises a LOW digital signal;

comparing a voltage from the touch screen to reference voltage and producing a comparison signal based on the result of the comparison, wherein the touch screen voltage is the analog equivalent of a coordinate position of the touch;

outputting a second digital signal on the pin of the touch screen controller, wherein the second digital signal is generated from the comparison signal and the second digital signal is representative that the touch is occurring, wherein the second digital signal comprises a HIGH digital signal;

converting the voltage from the touch screen to a digital data; and

outputting the digital data in the form of the data out signal on the pin of the touch screen controller, wherein the digital data comprises x,y coordinate information for the touch, wherein the second digital signal is output before the data out signal.

8. A driver for a touch screen of a device for controlling a touch screen, the driver comprising:

a control logic component, wherein the control logic component is configured to receive a first digital signal and a second digital signal, wherein the first digital signal is indicative of whether a screen touch is occurring, wherein the first digital signal is a LOW digital signal when the screen touch is not occurring, and wherein the first digital signal is a HIGH digital signal when the screen touch is occurring, and wherein the second digital signal is indicative of an x,y position of the screen touch, wherein the first digital signal is output as the HIGH digital signal to indicate that the screen touch is occurring before the second digital signal is output; and

a plurality of pins electrically connected to the control logic component, wherein one of the plurality of pins comprises a data output pin, wherein the data output pin is configured to output both the first digital signal and the second digital signal received from the control logic component.

9. The driver according to claim 8, further comprising:

a comparator having a first input and a second input, wherein the comparator is configured to produce an output that is a function of a comparison of the first input and the second input; and

a digital multiplexer electrically connected to the comparator, wherein the digital multiplexer is configured to receive the output of the comparator and output the first digital signal representative of the output of the comparator.

10. The driver according to claim 8, further comprising an analog-to-digital portion for converting a voltage produced by the touch screen into the second digital signal.

11. The driver according to claim 8, wherein the data output pin is configured to output both the first digital signal and the second digital signal to a microprocessor.

12. The driver according to claim 8, wherein the device is a personal digital assistant.

13. The driver according to claim 8, wherein the device is a point of sale terminal.

14. The driver according to claim 8, wherein the touch screen is a 5-wire resistive touch screen.

15. The driver according to claim 8, wherein the touch screen is a 4-wire resistive touch screen.

16. A device for detecting a screen touch of a touch screen, the device comprising:

a control logic, wherein the control logic component is configured to receive a first digital signal and a second digital signal, wherein the first digital signal is indicative of whether the screen touch is occurring, wherein the first digital signal is a LOW digital signal when the screen touch is not occurring and the first digital signal is a HIGH digital signal when the screen touch is occurring, and wherein the second digital signal is indicative of an x,y position of the screen touch; and

a plurality of pins electrically connected to the control logic component, wherein one of the plurality of pins comprises a data output pin, wherein the data output pin is configured to output both the first digital signal and the second digital signal received from the control logic component, wherein the first digital signal is output as the HIGH digital signal to indicative that the screen touch is occurring before the second digital signal is output.