CAPACITIVE TOUCH SENSING SYSTEM

• US 20150153868A1
• Filed: 12/03/2013
• Published: 06/04/2015
• Est. Priority Date: 12/03/2013
• Status: Active Grant

• Current Assignee: PixArt Imaging Incorporated
• Original Assignee: PixArt Imaging Incorporated
• Inventors: TIEW, KEI-TEE
• Granted Patent: US 9,886,142 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

There is provided a capacitive touch sensing system including a touch panel, a plurality of amplification units, an analog signal processing unit and an AD converter. The touch panel includes a plurality of driving electrodes intersecting with a plurality of sensing electrodes. Each of the amplification units is coupled to one of the sensing electrodes so as to output an amplified sensing signal. The analog signal processing unit demodulates a differential signal of the amplified sensing signals outputted by two adjacent amplification units or demodulates the amplified sensing signal outputted by the amplification units to generate a dc signal. The AD converter converts the dc signal to a digital signal.

Claims

1. A capacitive touch sensing system, comprising:

a touch panel comprising a plurality of driving electrodes intersecting with a plurality of sensing electrodes;

a differential unit calculating a difference between sensing signals outputted by two adjacent sensing electrodes to output a differential signal;

a downconversion unit configured to demodulate the differential signal to generate a dc signal and to accumulate the dc signal; and

an AD converter configured to convert the accumulated dc signal to a digital signal.

2. The capacitive touch sensing system as claimed in claim 1, wherein the differential unit is integrated in the downconversion unit.

3. The capacitive touch sensing system as claimed in claim 1, wherein the downconversion unit comprises a demodulation unit and an accumulation unit;

the demodulation unit demodulates the differential signal with two orthogonal signals and the accumulation unit accumulates a predetermined times of the dc signal.

4. The capacitive touch sensing system as claimed in claim 3, wherein the downconversion unit demodulates the differential signal with two signal arrays [1 0−

1 0] and ±

[0−

1 0 1] respectively.

5. The capacitive touch sensing system as claimed in claim 1, further comprising a multiplexer coupled between the downconversion unit and the AD converter.

6. The capacitive touch sensing system as claimed in claim 1, further comprising a plurality of amplification units respectively coupled to the sensing electrodes for amplifying the sensing signals outputted by the sensing electrodes.

7. The capacitive touch sensing system as claimed in claim 6, further comprising a common mode rejection connected between two adjacent amplification units for limiting input common mode voltages of the two adjacent amplification units.

8. The capacitive touch sensing system as claimed in claim 6, further comprising a common mode feedback connected between two adjacent amplification units for maintaining common mode levels of output voltages of the two adjacent amplification units.

9. The capacitive touch sensing system as claimed in claim 1, further comprising a digital back end configured to identify a touch position according to the digital signal.

10. The capacitive touch sensing system as claimed in claim 9, wherein the downconversion unit demodulates the differential signal with two orthogonal signals to generate two dc signals and the AD converter outputs two digital signals;

and the digital back end calculates a vector norm of the two digital signals to accordingly identify the touch position.

11. A capacitive touch sensing system, comprising:

a touch panel comprising a plurality of driving electrodes intersecting with a plurality of sensing electrodes;

a driving circuit sequentially inputting a driving signal having a driving frequency to the driving electrodes;

a downconversion unit configured to demodulate sensing signals outputted by each of the sensing electrodes with an operating frequency of 4 times of the driving frequency to generate a dc signal and to accumulate the dc signal; and

an AD converter configured to convert the accumulated dc signal to a digital signal.

12. The capacitive touch sensing system as claimed in claim 11, wherein the downconversion unit demodulates the sensing signals with two signal arrays [10−

1 0] and ±

[0−

1 0 1] respectively.

13. The capacitive touch sensing system as claimed in claim 11, further comprising a multiplexer coupled between the downconversion unit and the AD converter.

14. The capacitive touch sensing system as claimed in claim 11, further comprising a plurality of amplification units respectively coupled to the sensing electrodes for amplifying the sensing signals outputted by the sensing electrodes.

15. The capacitive touch sensing system as claimed in claim 11, wherein the downconversion unit demodulates the sensing signals with two orthogonal signals to generate two dc signals and the AD converter outputs two digital signals associated with each of the sensing electrodes.

16. A capacitive touch sensing system, comprising:

a touch panel comprising a plurality of driving electrodes intersecting with a plurality of sensing electrodes;

a plurality of amplification units respectively coupled to the sensing electrodes for amplifying sensing signals outputted by the sensing electrodes;

a differential unit calculating a difference between amplified sensing signals outputted by two adjacent amplification units to output a differential signal; and

an AD converter configured to convert the differential signal to a digital signal.

17. The capacitive touch sensing system as claimed in claim 16, further comprising a common mode rejection connected between two adjacent amplification units for limiting input common mode voltages of the two adjacent amplification units.

18. The capacitive touch sensing system as claimed in claim 16, further comprising a common mode feedback connected between two adjacent amplification units for maintaining common mode levels of output voltages of the two adjacent amplification units.

19. The capacitive touch sensing system as claimed in claim 16, further comprising a multiplexer coupled between the differential unit and the AD converter.

20. The capacitive touch sensing system as claimed in claim 16, wherein the differential unit sequentially calculates the difference between the amplified sensing signals of a first group of two adjacent amplification units and a second group of two adjacent amplification units;

when the differential unit is calculating the difference between the amplified sensing signals of the first group of two adjacent amplification units, the AD converter is configured to convert the differential signals associated with the second group of two adjacent amplification units to digital signals whereas when the differential unit is calculating the difference between the amplified sensing signals of the second group of two adjacent amplification units, the AD converter is configured to convert the differential signals associated with the first group of two adjacent amplification units to digital signals.