Control device and method with compensation of coordinate calculating for a capacitive touch panel

• US 20070291011A1
• Filed: 09/12/2006
• Published: 12/20/2007
• Est. Priority Date: 06/20/2006
• Status: Active Grant

• Current Assignee: eGalax_eMPIA Technology Inc.
• Original Assignee: eGalax_eMPIA Technology Inc.
• Inventors: Chang, Chin-Fu
• Granted Patent: US 7,839,393 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A control device for a capacitive touch panel has multiple voltage driving/current detecting circuits respectively connected to four corners of a top conductive layer of the touch panel. An auxiliary voltage driving/current detecting circuit is connected to a bottom conductive layer of the touch panel. When the touch panel is pressed, all voltage driving/current detecting circuits detect first current values at four corners of the top conductive layer. The auxiliary voltage driving/current detecting circuit also detects a second current value from the bottom conductive layer. The second current value is used to compensate all first current values so that the coordinate information of the position being pressed can be exactly calculated.

Claims

1. A control method for a capacitive touch panel that has a substrate, a top conductive layer and a bottom conductive layer, the method comprising the steps of:

applying AC signals with the same amplitude to corners of the top conductive layer respectively;

detecting first current values of the corners of the top conductive layer;

detecting a second current value of the bottom conductive layer;

compensating each detected first current value based on the second current value; and

calculating coordinate data of a position being touched on the touch panel according to the compensated first current values.

2. The control method as claimed in claim 1, wherein in the step of compensating, a part of the second current value is subtracted from each of the first current values.

3. The control method as claimed in claim 2, a quarter of the second current value is subtracted from each of the first current values.

7. The control device as claimed in claim 3, each voltage driving/current detecting unit comprising an operational amplifier with a positive input terminal, a negative input terminal and an output terminals, the positive input terminal connected to the AC signal producing unit, the negative input terminal connected to the output terminal through a feedback resistor and to be connected to the top conductive layer, wherein the first current value of the top conductive layer is measured using the feedback resistor.

9. The control device as claimed in claim 7, the auxiliary voltage driving/current detecting circuit comprising an operational amplifier with a positive input terminal, a negative input terminal and an output terminals, the negative input terminal connected to the output terminal through a feedback resistor, the output terminal connected to the compensating circuit, wherein the second current value of the bottom conductive layer is measured using the feedback resistor.

11. The control device as claimed in claim 9, the positive input terminal of the operational amplifier of the auxiliary voltage driving/current detecting circuit connected to either a signal ground or a constant DC level.

4. A control device for capacitive touch panel that has a top conductive layer and a bottom conductive layer, the control device comprising:

an alternate current (AC) signal producing unit, which generates an AC signal with a constant amplitude;

multiple voltage driving/current detecting units, which receive the AC signal and are respectively connected to corners of the top conductive layer to output the AC signal to the corners, and respectively detect a first current value at each corner;

an auxiliary voltage driving/current detecting unit connected to the bottom conductive layer to detect a second current value of the bottom conductive layer;

multiple signal processing units respectively connected to the multiple voltage driving/current detecting units, each signal processing unit comprising;

a compensating circuit connected to an output terminal of a respective voltage driving/current detecting unit to compensate the first current value by using the second current value;

a filtering circuit connected to an output terminal of the compensating circuit;

a sampling circuit connected to an output terminal of the filtering circuit;

an integrating amplifier connected to an output terminal of the sampling circuit; and

an analog to digital (A/D) converting circuit connected to the output terminal of the sampling circuit;

a central control unit connected to the AC signal producing unit and the signal processing units to receive output data of each signal processing unit to calculate coordinate of a point being touched on the touch panel.

5. The control device as claimed in claim 4, wherein the compensating circuit is a subtracter with two input terminals respectively connecting to one voltage driving/current detecting unit and the auxiliary voltage driving/current detecting unit.

6. The control device as claimed in claim 4, the central control unit comprising:

a sampling control unit connected to the sampling circuit to control sampling frequency and time;

an integrating control circuit connected to the integrating amplifier to control a gain of the integrating amplifier;

an arithmetic circuit connected to the sampling control circuit, the integrating control circuit, the AC signal producing unit and the A/D converting circuit to control their operations, the arithmetic circuit further adapted to connect to a host.

8. The control device as claimed in claim 6, the auxiliary voltage driving/current detecting circuit comprising an operational amplifier with a positive input terminal, a negative input terminal and an output terminals, the negative input terminal connected to the output terminal through a feedback resistor, the output terminal connected to the compensating circuit, wherein the second current value of the bottom conductive layer is measured using the feedback resistor.

10. The control device as claimed in claim 8, the positive input terminal of the operational amplifier of the auxiliary voltage driving/current detecting circuit connected to either a signal ground or a constant DC level.