Readout circuit for touch panel

• US 7,863,966 B1
• Filed: 09/17/2009
• Issued: 01/04/2011
• Est. Priority Date: 09/17/2009
• Status: Expired due to Fees

• Current Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated)
• Original Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated)
• Inventors: Lee, Guo-Ming, Chuang, Kai-Lan
• Primary Examiner(s): ZWEIZIG, JEFFERY SHAWN
• Application Number:
  US12/561,857
• Time in Patent Office: 474 Days
• Field of Search: 327/509, 327/517
• US Class Current: 327/517
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/042 by opto-electronic means

Abstract

A readout circuit for touch panel includes first and second switches, an operational amplifier (OP-AMP), a feedback capacitor, a comparison unit, and a counter. A first input terminal and an output terminal of the OP-AMP are respectively coupled to a second terminal of the first switch and an input terminal of the comparison unit. A second input terminal of the OP-AMP receives a reference voltage. Two terminals of the feedback capacitor and the second switch are respectively coupled to the first input terminal and the output terminal of the OP-AMP. The comparison unit selects first or second threshold voltages to compare with an output of the OP-AMP according to a output of the comparison unit. An input terminal of the counter receives the output of the comparison unit.

Claims

1. A readout circuit for a touch panel comprising:

a first switch having a first terminal serving as an input terminal of the readout circuit;

an operational amplifier (OP-AMP) having a first input terminal coupled to a second terminal of the first switch, having a second input terminal receiving a reference voltage;

a feedback capacitor having a first terminal coupled to the first input terminal of the OP-AMP, having a second terminal coupled to an output terminal of the OP-AMP;

a second switch having a first terminal couple to the first input terminal of the OP-AMP, having a second terminal coupled to the output terminal of the OP-AMP;

a comparison unit having an input terminal coupled to the output terminal of the OP-AMP;

a controller for controlling the comparison unit, the first switch and the second switch in accordance with an output of the comparison unit, wherein the controller controls the comparison unit for comparing the output of the OP-AMP with a first threshold voltage if the output of the comparison unit is a first logic value, and the controller controls the comparison unit for comparing the output of the OP-AMP with a second threshold voltage if the output of the comparison unit is a second logic value; and

a counter having an input terminal receiving the output of the comparison unit, having an output terminal serving as an output terminal of the readout circuit.

2. The readout circuit of claim 1, wherein during a power-on period, the controller turns on the first switch and the second switch, and the controller controls the comparison unit for comparing the output of the OP-AMP with the first threshold voltage.

3. The readout circuit of claim 1, wherein during a reset period, the controller turns on the first switch and the second switch, and the controller controls the comparison unit for comparing the output of the OP-AMP with the first threshold voltage.

4. The readout circuit of claim 1, wherein when the output of the comparison unit is the first logic value, the controller turns on the first switch and turns off the second switch.

5. The readout circuit of claim 1, wherein when the output of the comparison unit is the second logic value, the controller turns off the first switch and turns on the second switch.

6. The readout circuit of claim 1, wherein the first input terminal of the OP-AMP is an inverting input terminal, and the second input terminal of the OP-AMP is a non-inverting input terminal.

7. The readout circuit of claim 1, wherein the comparison unit comprises:

a selector, wherein if the output of the comparison unit is the first logic value, the selector outputs the first threshold voltage, and if the output of the comparison unit is the second logic value, the selector outputs the second threshold voltage; and

a comparator having a first input terminal coupled to the output terminal of the OP-AMP, having a second input terminal receiving the output of the selector.

8. The readout circuit of claim 7, wherein the first input terminal of the comparator is a non-inverting input terminal, and the second input terminal of the comparator is an inverting input terminal.

9. The readout circuit of claim 1, wherein the first threshold voltage is greater than the second threshold voltage.

10. The readout circuit of claim 1, wherein the second threshold voltage is greater than the reference voltage.

11. The readout circuit of claim 1, wherein the first threshold voltage is smaller than a system voltage.

12. The readout circuit of claim 1, wherein the counter counts a rising edge of the output of the comparison unit.