Sync signal generator for a capacitive sensor
View Patent ↗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.
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.