Scanning control device for a capacitive touch panel

• US 20070291012A1
• Filed: 09/12/2006
• Published: 12/20/2007
• Est. Priority Date: 06/20/2006
• Status: Abandoned Application

• Current Assignee: eGalax_eMPIA Technology Inc.
• Original Assignee: eGalax_eMPIA Technology Inc.
• Inventors: Chang, Chin-Fu
• Application Number:
  US11/519,094
• Publication Number:
  US 20070291012A1
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer

Abstract

A scanning control device for a capacitive touch panel uses voltage driving/current detecting circuits to connect to a top conductive layer of the touch panel. Output terminals of all voltage driving/current detecting units are connected to a signal processing unit through a switching unit. Output data of the signal processing unit are output to a central control unit. If the touch panel is pressed, all voltage driving/current detecting circuits detect current values at four corners of the top conductive layer and sequentially output the current values to the signal processing unit. The processed data output from the signal processing unit are transmitted to the central control unit. Based on the received data, the central control unit calculates coordinate of a pressed point on the touch panel.

Claims

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

an alternate current (AC) signal producing unit to generate an AC signal with a constant voltage amplitude;

multiple voltage driving/current detecting units respectively connected to corners of the top conductive layer to provide the AC signal to the corners, and respectively detecting a current value at each corner;

a switching unit connected to the multiple voltage driving/current detecting units to sequentially output the current values of the multiple voltage driving/current detecting units;

a signal processing unit connected to the switching unit to receive and process the current values output from the switching unit; and

a central control unit connected to the AC signal producing unit, the switching unit and the signal processing unit to receive output data of the signal processing unit and calculate coordinate of a pressed point on the touch panel based on the data.

2. The scanning control device for capacitive touch panel as claimed in claim 1, wherein the switching unit is a multiplexer with a set of output terminals and multiple input terminals connected to the voltage driving/current detecting units, and is controlled by the central control unit.

3. The scanning control device for capacitive touch panel as claimed in claim 2, wherein the signal processing unit comprises a filtering circuit, a sampling circuit, an integrating amplifier and an analog to digital (AID) converting circuit, and the central control unit comprises:

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.

4. The scanning control device for capacitive touch panel 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 current values of the top conductive layer are measured using the feedback resistors.

5. The scanning control device for capacitive touch panel as claimed in claim 3 further comprising:

an auxiliary voltage driving/current detecting circuit connected to the bottom conductive layer of the capacitive touch panel; and

the signal processing unit further comprising a compensating circuit with input terminals connected to the auxiliary voltage driving/current detecting circuit and the switching unit, wherein the compensating circuit has output terminals connected to the filtering circuit.

6. The scanning control device for capacitive touch panel as claimed in claim 5, 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.

7. The scanning control device for capacitive touch panel as claimed in claim 6, the positive input terminal of the operational amplifier of the auxiliary voltage driving/current detecting circuit connected to a DC ground.

8. The scanning control device for capacitive touch panel as claimed in claim 5, the compensating circuit comprising a buffer and a subtracter.