Capacitive touchscreen signal acquisition without panel reset

• US 8,274,491 B2
• Filed: 12/01/2010
• Issued: 09/25/2012
• Est. Priority Date: 06/21/2010
• Status: Active Grant

• Current Assignee: PixArt Imaging Incorporated
• Original Assignee: PixArt Imaging Incorporated
• Inventors: Souchkov, Vitali
• Primary Examiner(s): Boddie, William
• Assistant Examiner(s): Said, Mansour M
• Application Number:
  US12/957,489
• Publication Number:
  US 20110310054A1
• Time in Patent Office: 664 Days
• Field of Search: 345 87-100, 345156-174, 345204-205, 345/207, 345211-214, 324/658, 382/124, 200/19.06, 200/43.01, 200/43.06, 178/18.01
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

Various embodiments of readout circuits are disclosed where no touchscreen or touch panel recharge is required, and the amount of time available for signal acquisition is twice that relative to prior art touchscreen or touch panel readout circuits. Voltage offsets of the integrating amplifiers may be compensated for by notch filtering signals stored in readout circuit capacitors. Some embodiments of readout circuits disclosed herein permit large dynamic range capacitive touchscreen or touch panel signals to be processed, and do not require panel reset. Readout circuits are disclosed that permit doubling of the signal acquisition rate and pre-filtering of acquired touch panel signals for improved immunity from harmonic EMI. Signal acquisition and temporary storage may be carried out using the same capacitors in such readout circuits.

Claims

1. A capacitive touchscreen system, comprising:

a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, the mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, stray capacitances being associated with each of the second plurality of electrodes;

one or more drive circuits operably connected to the first plurality of drive electrodes, and

a plurality of sense circuits, each of the plurality of sense circuits being operably connected to a corresponding one of the second plurality of sense electrodes, each sense circuit comprising a gain capacitor having first and second terminals, a first switch, a second switch, a third switch, and an operational amplifier having positive and negative input terminals and an output terminal, the first terminal of the gain capacitor being connected to the corresponding sense electrode, the second terminal of the gain capacitor being operably connected to the first and second switches, the positive input terminal being connected to ground, the first switch being located between the second terminal of the gain capacitor and ground, the second switch being located between the second terminals of the gain capacitor and the negative input terminal of the operational amplifier, the third switch being located in a feedback loop of the operational amplifier between the negative input and output terminals thereof, the feedback capacitor being arranged in parallel with respect to the third switch in the feedback loop;

wherein during a first stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first switch is closed, the second switch is open, the third switch is closed, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the first stage is transferred to the feedback capacitor during a second stage when the first switch is open, the second switch is closed, the third switch is open, and the drive signal is low.

2. The touchscreen system of claim 1, wherein the operational amplifier is a transconductance amplifier.

3. The touchscreen system of claim 1, wherein operation of the first, second and third switches is controlled by a processor operably connected to the sense circuit.

4. The touchscreen system of claim 3, wherein the processor is configured to provide first digital control signals to the first and third switches that are in a logical high state over at least portions of time when the drive signal is high and that are in a logical low state when the drive signal is low.

5. The touchscreen system of claim 4, wherein the processor is further configured to provide first digital control signals to the first and third switches that are in logical low state near leading and trailing edges of each high drive signal.

6. The touchscreen system of claim 3, wherein the processor is configured to provide a second digital control signal to the second switch that is in a logical high state over at least portions of time when the drive signal is low and that is in a logical low state when the drive signal is high.

7. The touchscreen system of claim 6, wherein the processor is further configured to provide a second digital control signal to the second switch that is in a logical high state after trailing edges of one high drive signal and before leading edges of a following high drive signal.

8. A capacitive touchscreen system, comprising:

a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, the mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, stray capacitances being associated with each of the second plurality of electrodes;

one or more drive circuits operably connected to the first plurality of drive electrodes, and

a plurality of sense circuits, each of the plurality of sense circuits being operably connected to a corresponding one of the second plurality of sense electrodes, each sense circuit comprising a gain capacitor having first and second terminals, a first switch, a second switch, a third switch, a fourth, and an operational amplifier having positive and negative input terminals and an output terminal, the first terminal of the gain capacitor being connected to the corresponding sense electrode, the second terminal of the gain capacitor being operably connected to the first switch, the positive input terminal being connected to ground, the first switch being located between the gain capacitor and the negative input terminal of the operational amplifier, the second switch being located in a first feedback loop of the operational amplifier between the negative input and output terminals thereof, a feedback capacitor having a first terminal connected to the negative input of the amplifier and a first terminal of the second switch, a second terminal of the feedback capacitor being connected to the third switch and the fourth switch, the third switch being located between the second terminal of the feedback capacitor and ground, the fourth switch being located between the second terminal of the feedback capacitor and the output terminal of the operational amplifier;

wherein during a first stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first, second and third switches are closed, the fourth switch is open, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the first stage is transferred to the feedback capacitor during a second stage when the second and third switches are open, the first and fourth switches are closed, and the drive signal is low, the first switch being open momentarily between the first and second stages.

9. The touchscreen system of claim 8, wherein the operational amplifier is a transconductance amplifier.

10. The touchscreen system of claim 8, wherein operation of the first, second, third, and fourth switches is controlled by a processor operably connected to the sense circuit.

11. The touchscreen system of claim 10, wherein the processor is configured to provide first digital control signals to the first, second and third switches that are in a high logical state over at least portions of time when the drive signal is high and that are in a low logical state when the drive signal is low.

12. The touchscreen system of claim 11, wherein the processor is further configured to provide first digital control signals to the first, second and third switches that are in a low logical state near leading and trailing edges of each high drive signal.

13. The touchscreen system of claim 10, wherein the processor is configured to provide a second digital control signal to the fourth switch that is in a high logical state over at least portions of time when the drive signal is low and that is in a low logical state when the drive signal is high.

14. The touchscreen system of claim 13, wherein the processor is further configured to provide the second digital control signal to the fourth switch that is in a high logical state after trailing edges of one high drive signal and before leading edges of a following high drive signal.

15. A capacitive touchscreen system, comprising:

a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, the mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, stray capacitances being associated with each of the second plurality of electrodes;

one or more drive circuits operably connected to the first plurality of drive electrodes, and

a plurality of sense circuits, each of the plurality of sense circuits being operably connected to a corresponding one of the second plurality of sense electrodes, each sense circuit comprising a gain capacitor having first and second terminals, first, second, third, fourth, fifth and sixth switches, an operational amplifier having positive and negative input terminals and an output terminal, and first and second feedback capacitors, the first terminal of the gain capacitor being connected to the corresponding sense electrode, the second terminal of the gain capacitor being operably connected to the first switch, the positive input terminal being connected to ground, the first switch being located between the gain capacitor and the negative input terminal of the operational amplifier, the second switch being located in a feedback loop of the operational amplifier between the negative input and output terminals thereof, the first feedback capacitor having a first terminal connected to the negative input of the amplifier and a first terminal of the second feedback capacitor, the sixth switch being connected between a second terminal of the second feedback capacitor and the output of the operational amplifier, a second terminal of the first feedback capacitor being connected to the third and fourth switches, the third switch being located between the second terminal of the first feedback capacitor and ground, the fourth switch being located between the second terminal of the first feedback capacitor and the output terminal of the operational amplifier, the fifth switch being located between the second terminal of the second feedback capacitor and ground;

wherein during a first stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first, second and third switches are closed, the fourth, fifth and sixth switches are open, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the first stage is transferred to the first feedback capacitor during a second stage when the second, third, fifth and sixth switches are open, the first and fourth switches are closed, and the drive signal is low, the first switch being open momentarily between the first and second stages, during a third stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first, second and fifth switches are closed, the third, fourth and sixth switches are open, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the third stage is transferred to the second feedback capacitor during a fourth stage when the second, third, fourth and fifth switches are open, the first and sixth switches are closed, and the drive signal is low, the first switch being open momentarily between the third and fourth stages.

16. The touchscreen system of claim 15, wherein the operational amplifier is a transconductance amplifier.

17. The touchscreen system of claim 15, wherein operation of the first, second, third, fourth, fifth and sixth switches is controlled by a processor operably connected to the sense circuit.

18. The touchscreen system of claim 17, wherein the processor is configured to provide first digital control signals to the first, second and third switches that are in a high logical state over at least portions of time when the drive signal is high and that are in a low logical state when the drive signal is low.

19. The touchscreen system of claim 18, wherein the processor is further configured to provide first digital control signals to the first, second and third switches that are in a low logical state after trailing edges of one high drive signal and before leading edges of a following high drive signal.

20. The touchscreen system of claim 17, wherein the processor is configured to provide a second digital control signal to the fifth switch that is in a high logical state over at least portions of time when the drive signal is low and that is in a low logical state when the drive signal is high.

21. The touchscreen system of claim 20, wherein the processor is further configured to provide the second digital control signal to the fourth switch that is in a high logical state after trailing edges of one high drive signal and before leading edges of a following high drive signal.

22. The touchscreen system of claim 21, wherein the processor is configured to provide third digital control signals to the first, second and fifth switches that are in a high logical state over at least portions of time when the drive signal is low and that are in a low logical state when the drive signal is high.

23. The touchscreen system of claim 22, wherein the processor is configured to provide fourth digital control signals to the first and sixth switches that are in a high logical state over at least portions of time when the drive signal is low and that are in a low logical state when the drive signal is high.