Sync signal generator for a capacitive sensor

• US 8,525,532 B2
• Filed: 12/23/2010
• Issued: 09/03/2013
• Est. Priority Date: 12/23/2010
• Status: Active Grant

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: Ningrat, Kusuma Adi
• Primary Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US12/978,101
• Publication Number:
  US 20120161794A1
• Time in Patent Office: 985 Days
• Field of Search: 324/672, 324/667, 324/678, 324/681, 324/679
• US Class Current: 324/679
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G09G 2330/06 Handling electromagnetic interferences [EMI], covering emitted as well as received electromagnetic radiation
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors

Abstract

A sync signal generator for a capacitive sensor includes a charge amplifier having an input for coupling to an inactive receive line in the capacitive sensor, a first comparator having a first input for receiving a first threshold voltage, a second input coupled to an output of the charge amplifier, and an output for providing a first sync signal, and a second comparator having a first input for receiving a second threshold voltage, a second input coupled to the output of the charge amplifier, and an output for providing a second sync signal. The charge amplifier includes an operational amplifier having a feedback circuit including a capacitor and a switch. The first threshold voltage is provided by a first digital-to-analog converter, and the second threshold voltage is provided by a second digital-to-analog converter.

Claims

1. A sync signal generator for a capacitive sensor comprising:

a charge amplifier having an input coupled to an inactive receive line in the capacitive sensor;

a first comparator having a first input for receiving a first threshold voltage, a second input coupled to an output of the charge amplifier, and an output for providing a first sync signal; and

a second comparator having a first input for receiving a second threshold voltage, a second input coupled to the output of the charge amplifier, and an output for providing a second sync signal.

2. The sync signal generator of claim 1 wherein the charge amplifier comprises an operational amplifier.

3. The sync signal generator of claim 2 wherein the operational amplifier further comprises a feedback circuit.

4. The sync signal generator of claim 3 wherein the feedback circuit comprises a capacitor.

5. The sync signal generator of claim 3 wherein the feedback circuit comprises a switch.

6. The sync signal generator of claim 1 wherein the first threshold voltage is provided by a first digital-to-analog converter.

7. The sync signal generator of claim 1 wherein the second threshold voltage is provided by a second digital-to-analog converter.

8. A touch-screen system comprising:

a sensor panel and LCD display;

an LCD driver in communication with the sensor panel and LCD display, the LCD driver having an output for providing a periodic signal; and

a sync signal generator in communication with a touch sensor for the sensor panel, the sync signal generator comprising;

a charge amplifier having an input coupled to an inactive receive line in the sensor panel;

a first comparator having a first input for receiving a first threshold voltage, a second input coupled to an output of the charge amplifier, and an output for providing a first sync signal to the touch sensor; and

a second comparator having a first input for receiving a second threshold voltage, a second input coupled to the output of the charge amplifier, and an output for providing a second sync signal to the touch sensor.

9. The sync signal generator of claim 8 wherein the charge amplifier comprises an operational amplifier.

10. The sync signal generator of claim 9 wherein the operational amplifier further comprises a feedback circuit.

11. The sync signal generator of claim 10 wherein the feedback circuit comprises a capacitor.

12. The sync signal generator of claim 10 wherein the feedback circuit comprises a switch.

13. The sync signal generator of claim 8 wherein the first threshold voltage is provided by a first digital-to-analog converter.

14. The sync signal generator of claim 8 wherein the second threshold voltage is provided by a second digital-to-analog converter.

15. A method of generating a sync signal for use in a touch sensor circuit comprising:

converting the charge on an inactive receive line of a capacitive sensor into an output voltage;

comparing the output voltage to a first threshold voltage to provide a first sync signal for use in the touch sensor circuit; and

comparing the output voltage to a second threshold voltage to provide a second sync signal for use in the touch sensor circuit.

16. The method of claim 15, wherein the charge on the inactive receive line is converted into an output voltage using a charge amplifier.

17. The method of claim 15, wherein the output voltage is compared to a first threshold voltage using a comparator.

18. The method of claim 15, wherein the output voltage is compared to a second threshold voltage using a comparator.

19. The method of claim 15, wherein the first threshold voltage is provided by a first digital-to-analog converter.

20. The method of claim 15, wherein the second threshold voltage is provided by a second digital-to-analog converter.