Charge Pump Frequency Selection in Touch Screen Sensor Interface System

• US 20120306801A1
• Filed: 05/31/2011
• Published: 12/06/2012
• Est. Priority Date: 05/31/2011
• Status: Active Grant

• Current Assignee: PixArt Imaging Incorporated
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Rai, Abhay Kumar, Souchkov, Vitali, Stone, Jeffrey
• Granted Patent: US 8,427,452 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04164 Connections between sensors and controllers, e.g. routing lines between electrodes and connection pads
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• 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 charge pump circuitry configured to generate output signals having first distortion signals superimposed thereon are disclosed. Demodulator input signals are also disclosed that have second distortion signals superimposed thereon. A synchronization signal is delivered to demodulator circuitry through at least first and second integer divider circuits and to charge pump circuitry through at least the first integer divider circuitry such that the first and second distortion signals have frequencies that are integer divisions of the synchronization frequency.

Claims

1. A capacitive touchscreen or touch panel system, comprising:

a touchscreen comprising a first plurality of electrically conductive drive electrodes configured in rows or columns, and a second plurality of electrically conductive sense electrodes configured 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 to locations where the first and second pluralities of electrodes intersect, the mutual capacitances changing in the presence of one or more fingers of a user or touch devices brought into proximity thereto;

drive circuitry operably connected to the first plurality of drive electrodes;

sense circuitry operably connected to the second plurality of sense is electrodes and configured to sense input signals therefrom;

demodulator circuitry having an input operably connected to the sense circuitry;

charge pump circuitry having an output operably connected to the drive circuitry, and

clock generator circuitry configured to output a synchronization signal having a clock generator frequency;

wherein the charge pump circuitry generates output signals having first distortion signals superimposed thereon, the demodulator input signals have second distortion signals superimposed thereon, the synchronization signal is delivered to the demodulator circuitry through at least first and second integer divider circuits and to the charge pump circuitry through at least the first integer divider circuitry, and the first and second distortion signals have frequencies that are integer divisions of the synchronization frequency.

2. The touchscreen or touch panel system of claim 1, wherein the integer divisions range between 1 and 1,000.

3. The touchscreen or touch panel system of claim 1, wherein the clock generator frequency ranges between about 1 MHz and about 50 MHz.

4. The touchscreen or touch panel system of claim 1, wherein there is a substantially constant phase shift between the first and second distortion signals.

5. The touchscreen or touch panel system of claim 1, further comprising a low pass filter circuit operably connected to an output of the demodulator circuitry.

6. The touchscreen or touch panel system of claim 3, further comprising an analog-to-digital converter (ADC) operably connected to an output of the low pass filter circuit.

7. The touchscreen or touch panel system of claim 6, further comprising a digital signal processor (DSP) operably connected to an output of the ADC.

8. The touchscreen or touch panel system of claim 7, wherein the DSP is operably connected to the clock generator circuitry to receive the synchronization signal therefrom.

9. The touchscreen or touch panel system of claim 8, wherein at least a third integer divider circuit is interposed between the clock generator and the DSP.

10. The touchscreen or touch panel system of claim 1, wherein the first and second distortion signals form ripples superimposed upon the charge pump output signal and the demodulator input signal, respectively.

11. The touchscreen or touch panel system of claim 1, wherein the first integer divider circuit comprises divide by N circuitry.

12. The touchscreen or touch panel system of claim 1, wherein the second integer divider circuit comprises divide by M circuitry.

13. The touchscreen or touch panel system of claim 1, wherein the charge is pump circuitry is incorporated into an integrated circuit.

14. The touchscreen or touch panel system of claim 1, further comprising at least one integrating amplifier having an input operably connected to the sense electrodes and an output operably connected to the demodulator circuitry.

15. A method of operating a capacitive touchscreen or touch panel system comprising a touchscreen comprising a first plurality of electrically conductive drive electrodes configured in rows or columns, and a second plurality of electrically conductive sense electrodes configured 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 of a user or touch devices brought into proximity thereto, drive circuitry operably connected to the first plurality of drive electrodes, sense circuitry operably connected to the second plurality of sense electrodes and configured to sense input signals therefrom, demodulator circuitry having an input operably connected to the sense circuitry, charge pump circuitry having an output operably connected to the drive circuitry, and clock generator circuitry configured to output a synchronization signal having a clock generator frequency, wherein the charge pump circuitry generates output signals having first distortion signals superimposed thereon, the demodulator input signals have second distortion signals superimposed thereon, the synchronization signal is delivered to the demodulator circuitry through at least first and second integer divider circuits and to the charge pump circuitry through at least the first integer divider circuitry, and the first and second distortion signals have frequencies that are integer divisions of the synchronization frequency, the method comprising:

operating the demodulator circuitry and the charge pump circuitry at integer divisions of the clock generator frequency.

16. The method of claim 15, wherein the integer divisions range between 1 and 1,000.

17. The method of claim 15, wherein the clock generator frequency ranges between about 1 MHz and about 50 MHz.

18. The method of claim 15, wherein there is a substantially constant phase shift between the first and second distortion signals.

19. The method of claim 15, further comprising operably connecting a low pass filter circuit to an output of the demodulator circuitry.

20. The method of claim 19, further comprising operably connecting an analog-to-digital converter (ADC) to an output of the low pass filter circuit.

21. The method of claim 20, further comprising operably connecting a digital signal processor (DSP) to an output of the ADC.

22. The method of claim 21, further comprising operably connecting the DSP to the clock generator circuitry to receive the synchronization signal therefrom.

23. The method of claim 22, further comprising interposing at least a third integer divider circuit between the clock generator circuitry and the DSP.

24. The method of claim 15, further comprising the first and second distortion signals forming ripples superimposed upon the charge pump output signal and the demodulator input signal, respectively.

25. The method of claim 15, further comprising providing the first integer divider circuit as divide by N circuitry.

26. The method of claim 15, further comprising providing the second integer divider circuit as divide by M circuitry.

27. The method of claim 15, further comprising incorporating the charge pump circuitry into an integrated circuit.

28. The method of claim 15, further comprising providing at least one integrating amplifier having an input operably connected to the sense electrodes and an output operably connected to the demodulator circuitry.