Touch sensing circuit and a signal demodulating method

A touch sensing circuit including a plurality of touch sensing channels is provided. Each of the touch sensing channels includes at least one operational amplifier circuit and a demodulating circuit. The operational amplifier circuit is configured to receive a touch sensing signal, and amplify the touch sensing signal. The operational amplifier circuit includes an operational amplifier. The operational amplifier has an inverting end, and the inverting end is coupled to a direct-current voltage. The demodulating circuit is coupled to the operational amplifier circuit. The demodulating circuit is configured to demodulate the amplified touch sensing signal by mixing the amplified touch sensing signal with a demodulating signal. A waveform of the demodulating signal includes a flat region. In addition, a signal demodulating method is also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to an electrical circuit and a signal processing method, in particular, to a touch sensing circuit and a signal demodulating method.

2. Description of Related Art

As the technology of touch panel develops, touch panels become widely used as the screens of electronic devices, such as mobile phones, laptop computers, and tablet computers. Touch panels allow the user to input or operate the electronic devices more conveniently and make the interface more user-friendly and convenient.

Generally speaking, the electrode structure of a capacitive touch panel includes multiple scanning electrodes and multiple sensing electrodes. In terms of actual application, the scanning electrodes are used to receive the driving signals inputted by a panel controller/driver, so as to drive the touch panel to sense the touch of the user. The sensing electrodes are used to generate touch sensing signals corresponding to the user's touch. In the conventional technology, AFE (analog front-end) hardware modules are used as interface sensors of many kinds to digital systems, providing hardware modularity. For touch sensing circuits, AFE circuits are also configured to compensate the touch sensing signals by using a compensation capacitor. However, the compensation capacitor may occupy large circuit area, so as to increase manufacturing costs. In addition, the touch sensing circuit demodulates the touch sensing signals with a sine wave signal. Accordingly, a high-bit multiplier for signal demodulation is necessary, thereby increasing the complexity of the touch sensing circuit, and reducing circuit performance.

Hence, how to design a touch sensing circuit that has simplified circuit structure and satisfactory circuit performance without increasing the manufacturing costs is one of the most important topics in the pertinent field.

SUMMARY OF THE INVENTION

Accordingly, the invention is directed to a touch sensing circuit and a signal demodulating method, capable of simplifying circuit structure and enhancing circuit performance.

The invention provides a touch sensing circuit includes a plurality of touch sensing channels. Each of the touch sensing channels includes at least one operational amplifier circuit and a demodulating circuit. The operational amplifier circuit is configured to receive a touch sensing signal, and amplify the touch sensing signal. The operational amplifier circuit includes an operational amplifier. The operational amplifier has an inverting end, and the inverting end is coupled to a direct-current voltage. The demodulating circuit is coupled to the operational amplifier circuit. The demodulating circuit is configured to demodulate the amplified touch sensing signal by mixing the amplified touch sensing signal with a demodulating signal. A waveform of the demodulating signal includes a flat region.

In an exemplary embodiment of the invention, the at least one operational amplifier circuit includes a plurality of operational amplifier circuits. Each of the touch sensing channels includes a multiplexer circuit. The multiplexer circuit is coupled between the operational amplifier circuits and the demodulating circuit. The multiplexer circuit is configured to sequentially select one of the operational amplifier circuits, and pass the amplified touch sensing signal to the demodulating circuit.

In an exemplary embodiment of the invention, the unselected operational amplifier circuits are disabled to stop working.

In an exemplary embodiment of the invention, the amplified touch sensing signal is a periodical signal having a period. The demodulating circuit demodulates the amplified touch sensing signal to extract a carrier signal from the amplified touch sensing signal during a part time interval of the period.

In an exemplary embodiment of the invention, the operational amplifier further has a non-inverting end and an output end. The non-inverting end is coupled to a ground voltage. The operational amplifier circuit further includes an impedance device. The impedance device is coupled between the inverting end and the output end.

In an exemplary embodiment of the invention, the demodulating circuit includes a mixer circuit, a filter circuit and a gain amplifier circuit. The mixer circuit is coupled to at least one operational amplifier circuit. The mixer circuit is configured to receive and mix the amplified touch sensing signal and the demodulating signal to generate the demodulated touch sensing signal. The filter circuit is coupled to the mixer circuit. The filter circuit is configured to receive the demodulated touch sensing signal, and reduce noise of the demodulated touch sensing signal. The gain amplifier circuit is coupled to the filter circuit. The gain amplifier circuit is configured to receive and amplify the demodulated touch sensing signal that the noise is reduced.

In an exemplary embodiment of the invention, the demodulating circuit further includes an analog-to-digital converter circuit. The analog-to-digital converter circuit is coupled to the mixer circuit and located before the mixer circuit or after the mixer circuit. The analog-to-digital converter circuit is configured to convert the touch sensing signal of an analog format to the touch sensing signal of a digital format.

The invention provides a signal demodulating method adapted to a touch sensing circuit. The signal demodulating method includes: receiving at least one touch sensing signal, and amplify the touch sensing signal by compensating the received at least one touch sensing signal via a direct-current voltage; and demodulating the amplified touch sensing signal by mixing the amplified touch sensing signal with a demodulating signal. A waveform of the demodulating signal includes a flat region.

In an exemplary embodiment of the invention, the at least one touch sensing signal includes a plurality of touch sensing signals. The signal demodulating method further includes: sequentially selecting one of the amplified touch sensing signals to be demodulated.

In an exemplary embodiment of the invention, the amplified touch sensing signal is a periodical signal having a period. In the step of demodulating the amplified touch sensing signal by mixing the amplified touch sensing signal with the demodulating signal, the amplified touch sensing signal is demodulated to extract a carrier signal from the amplified touch sensing signal during a part time interval of the period.

In an exemplary embodiment of the invention, the step of demodulating the amplified touch sensing signal by mixing the amplified touch sensing signal with the demodulating signal includes: mixing the amplified touch sensing signal and the demodulating signal to generate the demodulated touch sensing signal; reducing noise of the demodulated touch sensing signal; and amplifying the demodulated touch sensing signal that the noise is reduced.

In an exemplary embodiment of the invention, the step of demodulating the amplified touch sensing signal by mixing the amplified touch sensing signal with the demodulating signal further includes: converting the touch sensing signal of an analog format to the touch sensing signal of a digital format before or after the step of mixing the amplified touch sensing signal and the demodulating signal to generate the demodulated touch sensing signal.

According to the above descriptions, in the exemplary embodiments of the invention, the operational amplifier circuit compensates the received touch sensing signal via a direct-current voltage, and the demodulating circuit demodulates the amplified touch sensing signal with a demodulating signal that the waveform includes a flat region, such that circuit structure is simplified and circuit performance is enhanced.

DESCRIPTION OF THE EMBODIMENTS

The term “coupling/coupled” used in this specification (including claims) of the disclosure may refer to any direct or indirect connection means. For example, “a first device is coupled to a second device” should be interpreted as “the first device is directly connected to the second device” or “the first device is indirectly connected to the second device through other devices or connection means.” In addition, the term “signal” can refer to a current, a voltage, a charge, a temperature, data, electromagnetic wave or any one or multiple signals.

FIG. 1andFIG. 2respectively illustrate a capacitive touch sensing scheme and an equivalent circuit thereof according to an embodiment of the invention. Referring toFIG. 1andFIG. 2, a capacitive touch panel100of the present embodiment includes a plurality of touch electrodes arranged in an array. The touch electrodes are categorized into scanning electrodes110and sensing electrodes120. A touch controller/driver may output driving signals112to the scanning electrodes110, so as to drive the sensing electrodes120to sense a gesture200. The gesture200performs on the capacitive touch panel100and changes surface capacitances of the areas between the scanning electrodes110and the sensing electrodes120that the gesture200touches. The sensing electrodes120senses capacitance variations thereof, and transmits touch sensing signals114to a touch sensing circuit300. The information related to the gesture200are carried on the touch sensing signals114. In an embodiment of the invention, the touch sensing circuit300may include a plurality of touch sensing channels to process the touch sensing signals114transmitted from the sensing electrodes120of different rows or columns.

FIG. 3illustrates a schematic block diagram of a touch sensing channel according to an embodiment of the invention. Referring toFIG. 3, the touch sensing channel310of the present embodiment may serve as an analog front-end (AFE) circuit for processing the received touch sensing signal114, and further output the processed touch sensing signal116to a circuit of the next-stage. In an embodiment of the invention, the touch sensing channel310may include a set of analog signal conditioning circuitry that uses operational amplifiers, filters, and sometimes application-specific integrated circuits for sensors and other circuits to provide a configurable and flexible electronics functional block, needed to interface a variety of sensors to an analog-to-digital converter or in some cases to a microcontroller.

In the present embodiment, the touch sensing channel310includes an operational amplifier circuit312and a demodulating circuit314. The operational amplifier circuit312receives and amplifies the touch sensing signal114, and outputs the amplified touch sensing signal Vs to the demodulating circuit314. The demodulating circuit314is coupled to the operational amplifier circuit312. The demodulating circuit314demodulates the amplified touch sensing signal Vs by mixing the amplified touch sensing signal Vs with a demodulating signal Vde. In the present embodiment, a waveform of the demodulating signal Vde includes a flat region. In a preferable embodiment, the demodulating signal Vde may be a square wave, but the invention is not limited thereto. Any signal that a waveform includes a flat region may be adopted for the demodulating signal.

FIG. 4toFIG. 8respectively illustrate schematic waveform is of demodulating signals according to a plurality of embodiments of the invention. Referring toFIG. 4toFIG. 8, each of the demodulating signals includes a flat region in the exemplary embodiments. For example, the demodulating signal Vde0illustrated inFIG. 4is a square wave having a relatively wide flat region FR0. The demodulating signal Vde1illustrated inFIG. 5includes a flat region FR1, and has two edges that slopes gradually change. The demodulating signal Vde2illustrated inFIG. 6includes a flat region FR2, and has two edges with constant slopes. The demodulating signal Vde3illustrated inFIG. 7includes a flat region FR3, and has a left edge with a constant slope and a right edge that the slope gradually changes. The demodulating signal Vde4illustrated inFIG. 8includes a flat region FR4, and has a left edge that the slope gradually changes and a right edge with a constant slope. However, the foregoing waveforms are not intended to limit the invention but may be adjusted according to the design.

FIG. 9illustrates a schematic circuit diagram of a touch sensing channel according to an embodiment of the invention. Referring toFIG. 9, the operational amplifier circuit412of the present embodiment includes an operational amplifier411and an impedance device413. The operational amplifier411has an inverting end, a non-inverting end, and an output end. The inverting end is coupled to a direct-current voltage VDC. The non-inverting end is coupled to a ground voltage. The impedance device413is coupled between the inverting end and the output end. In the present embodiment, the inverting end is coupled to the direct-current voltage VDC for signal compensation, and thus a compensation capacitor is unnecessary. The circuit structure of the operational amplifier circuit412is further simplified.

In the present embodiment, the operational amplifier circuit412amplifies the touch sensing signal114, and outputs the amplified touch sensing signal Vs to the demodulating circuit414. In the present embodiment, the demodulating circuit414includes a mixer circuit415, a filter circuit417and a gain amplifier circuit419. The mixer circuit415is coupled to the operational amplifier circuit412. The mixer circuit415receives and mixes the amplified touch sensing signal Vs and the demodulating signal Vde to generate the demodulated touch sensing signal Vs′. The filter circuit417is coupled to the mixer circuit415. The filter circuit417receives the demodulated touch sensing signal Vs′, and reduces noise of the demodulated touch sensing signal Vs′. The gain amplifier circuit419is coupled to the filter circuit417. The gain amplifier circuit419receives and amplifies the demodulated touch sensing signal Vs′ that the noise is reduced. The gain amplifier circuit419outputs the processed touch sensing signal116to the circuit of the next-stage.

In the present embodiment, the demodulating signal Vde is generated via a signal generator circuit500. The signal generator circuit500may be embedded inside the demodulating circuit414or arranged outside of the demodulating circuit414. The invention is not limited thereto. In addition, the demodulating signal Vde of the present embodiment may be a square wave, and the waveform thereof includes a flat region. Therefore, the mixer circuit415for mixing the amplified touch sensing signal Vs and the demodulating signal Vde may include a low-bit multiplier for signal demodulation.

In the present embodiment, the mixer circuit415, the filter circuit417, the gain amplifier circuit419and the signal generator circuit500may be implemented by using any adaptive mixer circuit, filter circuit, gain amplifier circuit and signal generator circuit in the related art, which are not particularly limited by the invention. Therefore, enough teaching, suggestion, and implementation illustration for internal circuit structures and implementations of the mixer circuit415, the filter circuit417, the gain amplifier circuit419and the signal generator circuit500may be obtained with reference to common knowledge in the related art, which are not repeated hereinafter.

FIG. 10toFIG. 11respectively illustrate schematic diagrams of signal demodulation according to a plurality of embodiments of the invention. Referring toFIG. 10toFIG. 11, the amplified touch sensing signal Vs may be a periodical signal Vs10or Vs11having a period T in the exemplary embodiments. In the present embodiment, by using the demodulating signal Vde1, the demodulating circuit414demodulates the amplified touch sensing signal Vs10or Vs11to extract a carrier signal that includes the information related to the gesture200from the amplified touch sensing signal Vs10or Vs11during a part time interval t1or t2of the period T. Taking the signal demodulation illustrated inFIG. 10for example, the part time interval t1that the carrier signal is extracted substantially locates in a middle region of the high level, and thus the issue of time jitter is reduced in the present embodiment. Demodulating the amplified touch sensing signal Vs10or Vs11by using other demodulating signals Vde0and Vde2to Vde4may be deduced by analogy, and it is not further described herein.

FIG. 12illustrates a schematic circuit diagram of a touch sensing channel according to another embodiment of the invention. Referring toFIG. 12, the touch sensing channel510of the present embodiment is similar to the touch sensing channel410illustrated inFIG. 9, and the main difference therebetween, for example, lies in that the demodulating circuit514further includes an analog-to-digital converter circuit516. The analog-to-digital converter circuit516is located before the mixer circuit515, and connected between the operational amplifier511and the mixer circuit515. The analog-to-digital converter circuit516converts the touch sensing signal Vs of an analog format to the touch sensing signal Vs of a digital format. In another embodiment of the invention, the analog-to-digital converter circuit may also be located after the mixer circuit.

FIG. 13illustrates a schematic circuit diagram of a touch sensing channel according to another embodiment of the invention. Referring toFIG. 13, the touch sensing channel610of the present embodiment is similar to the touch sensing channel410illustrated inFIG. 9, and the main difference therebetween, for example, lies in that the demodulating circuit614further includes an analog-to-digital converter circuit616. The analog-to-digital converter circuit616is located after the mixer circuit615, and connected between the mixer circuit615and the filter circuit617. The analog-to-digital converter circuit616converts the demodulated touch sensing signal Vs′ of an analog format to the demodulated touch sensing signal Vs′ of a digital format.

FIG. 14illustrates a schematic block diagram of a touch sensing channel according to another embodiment of the invention. Referring toFIG. 14, the touch sensing channel710of the present embodiment is similar to the touch sensing channel310illustrated inFIG. 3, and the main difference therebetween, for example, lies in that the touch sensing channel710includes a plurality of operational amplifier circuits712_1to712_4and further includes a multiplexer circuit716.

In the present embodiment, the multiplexer circuit716is coupled between the operational amplifier circuits712_1to712_4and the demodulating circuit714. The multiplexer circuit714sequentially selects one of the operational amplifier circuits712_1to712_4, and pass the amplified touch sensing signal Vs1, Vs2, Vs3or Vs4to the demodulating circuit714for signal demodulation. In the present embodiment, the touch sensing channel710demodulates the amplified touch sensing signals Vs1to Vs4in a manner of time-division multiplexing (TDM). The multiplexer circuit714may sequentially or randomly demodulate the amplified touch sensing signals Vs1to Vs4to output the processed touch sensing signal.

For example, the multiplexer circuit714may select the operational amplifier circuit712_1. The operational amplifier circuits712_2to712_4are disabled. The operational amplifier circuit712_1transmits the amplified touch sensing signal Vs1to the multiplexer circuit714, and the multiplexer circuit714passes the amplified touch sensing signal Vs1to the demodulating circuit714for signal demodulation. In the meanwhile, the operational amplifier circuits712_2to712_4may be disable to stop working, and thus the operational amplifier circuits712_2to712_4do not transmit the amplified touch sensing signals Vs2to Vs4to the multiplexer circuit714. Next, the multiplexer circuit714may select the operational amplifier circuit712_2. The operational amplifier circuits712_1,712_3and712_4are disabled. The operational amplifier circuit712_2transmits the amplified touch sensing signal Vs2to the multiplexer circuit714, and the multiplexer circuit714passes the amplified touch sensing signal Vs2to the demodulating circuit714for signal demodulation. The operation of the operational amplifier circuits712_3and712_4can be deduced by analogy, and it is not further described herein.

In the present embodiment, if one of the operational amplifier circuits712_1to712_4is enabled, the other operational amplifier circuits are disabled. By adopting the manner of time-division multiplexing for signal demodulation, the filter circuit of the demodulating circuit714is further simplified. For example, a ROM table thereof is relatively small.

In the present embodiment, the operational amplifier circuits712_1to712_4, the multiplexer circuit716, and the demodulating circuit714may be implemented by using any adaptive operational amplifier circuit, multiplexer circuit, and demodulating circuit in the related art, which are not particularly limited by the invention. In one embodiment, the operational amplifier circuits712_1to712_4and the demodulating circuit714may be implemented by using the operational amplifier circuit and the demodulating circuit illustrated inFIG. 9,FIG. 12orFIG. 13. Therefore, enough teaching, suggestion, and implementation illustration for internal circuit structures and implementations of the operational amplifier circuits712_1to712_4, the multiplexer circuit716, and the demodulating circuit714may be obtained with reference to common knowledge in the related art, which are not repeated hereinafter.

FIG. 15is a flowchart illustrating steps of a signal demodulating method in an embodiment of the invention. Referring toFIG. 9andFIG. 15, the signal demodulating method is at least adapted to the touch sensing channel410inFIG. 9, but the invention is not limited thereto. The signal demodulating method at least includes the following steps. In step S500, the touch sensing channel410receives the touch sensing signal114, and amplifies the touch sensing signal114by compensating the received the touch sensing signal114via the direct-current voltage VDS. In step S510, the touch sensing channel410demodulates the amplified touch sensing signal Vs by mixing the amplified touch sensing signal Vs′ with the demodulating signal Vde that the waveform includes a flat region, so as to output the processed touch sensing signal116.

Besides, the signal demodulating method described in the present embodiment of the invention is sufficiently taught, suggested, and embodied in the embodiments illustrated inFIG. 1toFIG. 14, and therefore no further description is provided herein.

In summary, in the exemplary embodiments of the invention, the operational amplifier circuit compensates the received touch sensing signal via a direct-current voltage, and thus a compensation capacitor is unnecessary. The circuit structure of the operational amplifier circuit is further simplified. The demodulating circuit demodulates the amplified touch sensing signal with a demodulating signal that the waveform includes a flat region by a low-bit multiplier. Accordingly, the circuit performance is enhanced.