TWI526887B - Current touch panel reading device - Google Patents

Description

Current touch panel reading device

The present invention relates to a touch device, and more particularly to a reading device for a current touch panel.

With the rapid development of electronic technology and the popularization of wireless communication and networks, various electronic devices have become an indispensable tool for life. However, common input/output (I/O) interfaces, such as keyboards or mice, have considerable operational difficulties. In contrast, the touch panel is an intuitive and simple input and output interface. Therefore, the touch panel is often applied as a human-machine interface between a person and an electronic device to perform control.

In general, the touch panel can be divided into a resistive touch panel, an optical touch panel, a capacitive touch panel, and the like. According to the readout means, it can be classified into a current type touch panel and a charge type touch panel. FIG. 1 illustrates a schematic diagram of a current touch panel and a conventional readout circuit. The plurality of scan lines of the touch panel 110 are driven by a gate driver 130 , and the plurality of sensor lines of the touch panel 110 are coupled to the read circuit 140 . The pixel layout of a conventional current touch panel is shown in FIG. Each of the pixels has a switch SW1 and a photo transistor PT.

When the bias voltage VBIAS is higher than the voltage of the node A, and the gate driver 130 turns on the switch SW1 via the scan line, since the photo transistor PT is in the forward bias state, a sense current Is is made. It will flow to the sensing line via the photo transistor PT and the switch SW1. Among them, the intensity of the received light of the photoelectric crystal PT affects the magnitude of the sensing current Is. That is to say, by using the reading circuit 140 to detect the magnitude and difference of the sensing current Is on each sensing line, it can be known whether there is a light shield at the corresponding position in the touch panel 110 (that is, whether there is a foreign object to touch the panel 110). The reading circuit 140 sends the detection result to the image processing circuit 150 in the form of a digital code. The image processing circuit 150 determines the touch position based on the digital code provided by all of the read circuits 140.

The conventional read circuit 140 converts the sense current Is into a corresponding voltage using an integrator (ie, the operational amplifier 141 and the feedback capacitor 142), and then is converted by an analog-to-digital converter (ADC) 143. The voltage is converted into a corresponding digital code, and finally the image processing circuit 150 determines the touch position based on the digital code. However, since the read operation of the touch panel 110 is performed using the integrator, if the sense current Is is too large, the output of the integrator may reach saturation. In order to prevent the output of the integrator from reaching saturation, the feedback capacitance (or integrating capacitance) 142 of the integrator must also increase the capacitance (ie, increase the area). Since each of the sensing lines of the touch panel 110 requires an integrator, the wafer area of the reading circuit 140 will be considerable.

The invention provides a reading device for a current touch panel, which comprises a current-to-voltage converter, a voltage gain unit and an analog-to-digital converter. The current to voltage conversion unit converts the sensing current of the current touch panel into a sensing voltage. An input end of the voltage gain unit is coupled to an output of the current to voltage conversion unit to receive the sensing voltage. The input of the analog to digital converter is coupled to the output of the voltage gain unit, and the analog to the output of the digital converter produces a digital code.

In an embodiment of the invention, the current to voltage conversion unit includes a resistor and a unity gain amplifier. The first end of the resistor receives the sense current, and the second end of the resistor is coupled to a reference voltage. The input end of the unity gain amplifier is coupled to the first end of the resistor, and the output end of the unity gain amplifier is coupled to the input end of the voltage gain unit.

In an embodiment of the invention, the current to voltage conversion unit includes a resistor and a current mirror. The first end of the resistor receives the first reference voltage, and the second end of the resistor is coupled to the input end of the voltage gain unit. The main current terminal of the current mirror receives the sensing current, and the current terminal of the current mirror is coupled to the second end of the resistor.

Based on the above, the present invention provides a reading device for a current touch panel, which uses a current-to-voltage conversion unit and a voltage gain unit (such as an inverting amplifier or a non-inverting amplifier) to read the sensing current of the touch panel, and thus can Avoid using integral capacitors to achieve the goal of reducing wafer area.

The above described features and advantages of the present invention will be more apparent from the following description.

In the following embodiments, a photo current type touch panel 110 will be taken as an example to illustrate the application mode of the reading device of the present invention. However, the scope of application of the present invention should not be limited thereto. Any current touch panel can be applied in accordance with the teachings of this specification.

FIG. 2 is a schematic circuit diagram of a current touch panel reading device according to an embodiment of the invention. This reading device 200 includes a current to voltage conversion unit 210, a voltage gain unit 220, and an analog to digital converter 230. The current-to-voltage conversion unit 210 converts the sensing current Is of the current touch panel 110 into the sensing voltage Vs. The input end of the voltage gain unit 220 is coupled to the output of the current to voltage conversion unit 210 to receive the sensing voltage Vs. The voltage gain unit 220 outputs a corresponding gain voltage Vg to the analog converter 230 after gaining the sense voltage Vs. The aforementioned voltage gain unit 220 may be an inverting amplifier or a non-inverting amplifier, the details of which will be described later.

The analog to digital converter 230 has an input coupled to the output of the voltage gain unit 220. The analog to digital converter 230 converts the gain voltage Vg into a corresponding digital code Ds. The digital code Ds can be provided to a subsequent stage circuit (for example, the image processing circuit 150) for further data processing to determine the touch position in the touch panel 110.

3 is a circuit diagram of a current touch panel reading device according to a first embodiment of the present invention. Referring to FIG. 3, the aforementioned voltage gain unit 220 is implemented here as an inverting amplifier. The inverting amplifier includes a resistor 221, a resistor 222, and an operational amplifier 223. The first end of the resistor 221 is used as an input terminal of the inverting amplifier, and the second end of the resistor 221 is coupled to the first input end of the operational amplifier 223. The first end and the second end of the resistor 222 are respectively coupled to the first input end and the output end of the operational amplifier 223. The second input of the operational amplifier 223 receives the third reference voltage Vref, and the output of the operational amplifier 223 serves as the output of the inverting amplifier. In this embodiment, the first input terminal of the operational amplifier 223 is an inverting input, and the second input terminal of the operational amplifier 223 is a non-inverting input. In addition, the application of the embodiment can determine the level of the reference voltage Vref according to its design requirements. For example, the reference voltage Vref is set to the ground voltage (ie, 0V), or set to the band-gap voltage, or set to +5V, or set to other fixed voltages. This embodiment sets the reference voltage Vref to half of the system voltage VDDA level (ie, VDDA/2).

The current to voltage conversion unit 210 in FIG. 3 includes a resistor 211. The first end of the resistor 211 receives the sense current Is. The first end of the resistor 211 is coupled to the input end of the inverting amplifier (ie, the first end of the resistor 221), and the second end of the resistor 211 is coupled to a reference voltage (eg, a ground voltage). The sensing current Is provided by the touch panel 110 passes through the resistor 211, thus generating a sensing voltage Vs at the first end of the resistor 211. If the amount of change in the sense current Is is small, the resistance values of the resistors 211, 221, and 222 can be increased in order to be able to resolve the change in the gain voltage Vg. The resistors 211, 221, and 222 illustrated in FIG. 3 are fixed resistors. In order to respond to the different characteristics of different touch panels, the application of this embodiment can be implemented with "variable resistors" to implement the resistors 211, 221 and/or 222 depending on their design requirements.

4 is a circuit diagram showing a current type touch panel reading device according to a second embodiment of the present invention. This embodiment is similar to FIG. 3, so some of the contents will not be described again. The difference between the two is the current to voltage conversion unit 210. Referring to FIG. 4, the current to voltage conversion unit 210 includes a resistor 211 and a unity gain amplifier. Here, a unity gain amplifier is implemented with an operational amplifier 212. The first input end of the operational amplifier 212 is coupled to the first end of the resistor 211, the second input end of the operational amplifier 212 is coupled to the output end of the operational amplifier 212, and the output end of the operational amplifier 212 is coupled to the inverting amplifier. Input (ie the first end of the resistor 221). In the present embodiment, the first input of the operational amplifier 212 is a non-inverting input, and the second input of the operational amplifier 212 is an inverting input. Since the unity gain amplifier is configured in the current-to-voltage conversion unit 210, it is possible to avoid the load effect of the sensing voltage Vs.

If the amount of change in the sense current Is is small, in order to enable the change of the gain voltage Vg to be resolved, in addition to increasing the resistance values of the resistors 211, 221 and 222 in FIGS. 3 and 4, multiple strings may be included in the voltage gain unit 220. Several inverting amplifiers are used to make the gain ratio of the voltage gain unit 220 higher. For example, FIG. 5 is a circuit diagram illustrating the voltage gain unit 220 of FIG. 2 in accordance with a third embodiment of the present invention.

Referring to FIG. 5, the inverting amplifier (voltage gain unit 220) includes n inverting amplifying circuits 510-1 to 510-n. These inverting amplifying circuits 510-1 to 510-n are connected in series to each other to form an amplifier string. An input end of the first inverting amplifying circuit 510-1 of the amplifier string is coupled to an output of the current to voltage converting unit 210 to receive the sensing voltage Vs, and a last inverting amplifying circuit 510 of the amplifier string The output of the -n is coupled to the analog to the input of the digital converter 230. For the implementation of the above-described inverting amplifying circuits 510-1 to 510-n, reference may be made to the related description of the "inverting amplifier" in FIG. 3, and thus the details are not described herein. Since a plurality of inverting amplifiers (i.e., inverting amplifying circuits 510-1 to 510-n) are connected in series in the voltage gain unit 220, the gain multiplying factor of the voltage gain unit 220 is improved.

FIG. 6 is a circuit diagram showing a current type touch panel reading device according to a fourth embodiment of the present invention. This embodiment is similar to FIG. 3, so some of the contents will not be described again. The difference between the two is that FIG. 6 implements the aforementioned voltage gain unit 220 with a non-inverting amplifier. This non-inverting amplifier includes an operational amplifier 224, a resistor 225, and a resistor 226. The first input of the operational amplifier 224 is coupled to the output of the current to voltage conversion unit 210 to receive the sense voltage Vs, and the output of the operational amplifier 224 outputs the gain voltage Vg to the input of the digital converter 230. The first end of the resistor 226 is coupled to the second input of the operational amplifier 224, and the second end of the resistor 226 receives a reference voltage (eg, a ground voltage). The first end and the second end of the resistor 225 are respectively coupled to the second input end and the output end of the operational amplifier 224. In the present embodiment, the first input of the operational amplifier 224 is a non-inverting input, and the second input of the operational amplifier 224 is an inverting input. In another embodiment, one or more inverters (not shown) may be configured between the voltage gain unit 220 and the analog-to-digital converter 230 illustrated in FIG. 6 according to design requirements.

Application The present inventors can implement the current to voltage conversion unit 210 of FIG. 6 in any manner depending on their design requirements. For example, in addition to the implementation of the current to voltage conversion unit 210 shown in FIGS. 3 and 4, the current to voltage conversion unit 210 can also be implemented using a resistor and a current mirror. In another embodiment, the non-inverting amplifier internal to voltage gain unit 220 includes a plurality of non-inverting amplifying circuits. These non-inverting amplifying circuits are connected in series to each other to form an amplifier string. An input of the first non-inverting amplifying circuit of the amplifier string is coupled to an output of the current to voltage converting unit 210 to receive the sensing voltage Vs. An output of the last non-inverting amplifying circuit of the amplifier string is coupled to an analog to the input of the digital converter 230. For the implementation of the above amplifier string, reference may be made to FIG. 5, that is, the inverting amplifying circuits 510-1~510-n of FIG. 5 may be replaced by a non-inverting amplifying circuit.

FIG. 7 is a circuit diagram showing the current-to-voltage conversion unit 210 of FIG. 2 in accordance with a fifth embodiment of the present invention. The current to voltage conversion unit 210 includes a resistor 710 and a current mirror 720. The first end of the resistor 710 receives the first reference voltage (eg, the system voltage VDDA), and the second end of the resistor 710 is coupled to the input of the voltage gain unit 220. Here, the resistor 710 is implemented with a P-channel gold-oxygen half (PMOS) transistor 711 to reduce the area of the wafer occupied by the resistor 710. A first end (eg, a source) of the transistor 711 receives a system voltage VDDA, and a second end (eg, a drain) of the transistor 711 is coupled to a control terminal (eg, a gate) to an input of the voltage gain unit 220.

The main current terminal of the current mirror 720 receives the sensing current Is, and the current terminal of the current mirror 720 is coupled to the second end of the resistor 710. By setting the current magnification of both the main current terminal and the servant current terminal of the current mirror 720, the current mirror 720 can amplify the weak sensing current Is. This amplified sense current is converted to the sense voltage Vs via the resistor 710. Thus, under the condition that the strong light and the weak light illuminate the photoelectric crystal PT, the variation range of the obtained sensing voltage Vs can be increased, so that the recognition degree of the sensing voltage Vs can be increased. The sensing voltage Vs is further amplified by an inverting amplifier/non-inverting amplifier (ie, voltage gain unit 220) to obtain a gain voltage Vg to facilitate subsequent processing.

The current mirror 720 here includes a first transistor 721 and a second transistor 722. This embodiment implements transistors 721 and 722 in an N-channel gold-oxygen half (NMOS) transistor. The first end (eg, the drain) of the transistor 721 serves as the main current terminal of the current mirror 720, and the second end (eg, the source) of the transistor 721 receives the second reference voltage (eg, the ground voltage), and the control of the transistor 721 An end (eg, a gate) is coupled to the first end of the transistor 721. The first end of the transistor 722 serves as the servant current terminal of the current mirror 720, the second end of the transistor 722 receives the second reference voltage (ground voltage), and the control end of the transistor 722 is coupled to the control terminal of the transistor 721. By determining the appearance ratio of the transistors 721 and 722, the current magnification of both the main current terminal and the current terminal of the current mirror 720 can be set.

FIG. 8 is a circuit diagram showing the current-to-voltage conversion unit 210 of FIG. 2 in accordance with a sixth embodiment of the present invention. This embodiment is similar to that of FIG. 7, and thus some of the contents will not be described again. The difference between the two is that FIG. 8 uses a current mirror 730 instead of the aforementioned current mirror 720. The current mirror 730 includes a first transistor 731, a second transistor 732, a third transistor 733, and a fourth transistor 734. A first end (e.g., a drain) of the transistor 731 serves as a main current terminal of the current mirror 730, and a control terminal (e.g., a gate) of the transistor 731 is coupled to the first end of the transistor 731. A first end (e.g., a drain) of the transistor 732 serves as a servant current terminal of the current mirror 730, and a control terminal (e.g., a gate) of the transistor 732 is coupled to the control terminal of the transistor 731. A first end (eg, a drain) of the transistor 733 is coupled to a second end (eg, a source) of the transistor 731, and a second end (eg, a source) of the transistor 733 receives a reference voltage (eg, a ground voltage), and A control terminal (eg, a gate) of the transistor 733 is coupled to the first end of the transistor 733. A first end (eg, a drain) of the transistor 734 is coupled to a second end (eg, a source) of the transistor 732, and a second end (eg, a source) of the transistor 734 receives a reference voltage (ground voltage), and the A control terminal (eg, a gate) of the crystal 734 is coupled to the control terminal of the transistor 733.

In summary, when the switch SW1 of the touch panel 110 is off, the sense current Is is not sensed on the sense line, so the gain voltage Vg is the lowest at this time. At this point the system can fetch the first digit value of the gain voltage Vg via the analog to digital converter 230. When the switch SW1 of the touch panel 110 is turned on, the sensing current Is appears on the sensing line, and the gain voltage Vg is raised. At this time, the system can amplify and convert the sensing current Is into a gain voltage Vg through the current-to-voltage conversion unit 210 and the inverting amplifier (or non-inverting amplifier), and then pass the gain voltage Vg via the analog-to-digital converter 230. The binary digit value is taken out. The system can calculate the difference between the second digit value and the first digit value. Since the sensing current Is generated by the strong light and the weak light illuminating the photoelectric crystal PT is different, the aforementioned difference may also be different, so that the position of the touch can be located.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

110. . . Touch panel

130. . . Gate driver

140, 200. . . Read circuit

141, 212, 223, 224. . . Operational Amplifier

142. . . Feedback capacitor

143, 230. . . Analog to digital converter

150. . . Image processing circuit

210. . . Current to voltage conversion unit

220. . . Voltage gain unit

211, 221, 222, 225, 226, 710. . . resistance

510-1, 510-n. . . Inverting amplifier circuit

711. . . P-channel MOS semi-transistor

720, 730. . . Current mirror

721~722, 731~734. . . N-channel MOS semi-transistor

Ds. . . Digital code

Is. . . Sense current

PT. . . Photoelectric crystal

SW1. . . switch

VBIAS. . . Bias voltage

Vg. . . Gain voltage

Vs. . . Sense voltage

FIG. 1 illustrates a schematic diagram of a current touch panel and a conventional readout circuit.

FIG. 2 is a schematic circuit diagram of a current touch panel reading device according to an embodiment of the invention.

3 is a circuit diagram of a current touch panel reading device according to a first embodiment of the present invention.

4 is a circuit diagram showing a current type touch panel reading device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing the voltage gain unit of FIG. 2 according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a current type touch panel reading device according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing the current-to-voltage conversion unit of FIG. 2 according to a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram showing the current-to-voltage conversion unit of FIG. 2 according to a sixth embodiment of the present invention.

110. . . Touch panel

130. . . Gate driver

200. . . Read circuit

210. . . Current to voltage conversion unit

220. . . Voltage gain unit

230. . . Analog to digital converter

Ds. . . Digital code

Is. . . Sense current

PT. . . Photoelectric crystal

SW1. . . switch

VBIAS. . . Bias voltage

Vg. . . Gain voltage

Vs. . . Sense voltage

Claims (8)

A reading device for a current touch panel includes: a current to voltage conversion unit for converting a sensing current output by a current touch panel into a sensing voltage, wherein the sensing current reflects the a touch of a current touch panel; a voltage gain unit having an input coupled to the current to the output of the voltage conversion unit to receive the sense voltage; and an analog to digital converter having an input coupled to the input At the output of the voltage gain unit, the analog to the output of the digital converter produces a digital code. The reading device of the current touch panel of claim 1, wherein the current to voltage conversion unit comprises: a resistor, the first end of which receives the sensing current, wherein the first end of the resistor is coupled To the input of the voltage gain unit, the second end of the resistor is coupled to a reference voltage. The reading device of the current touch panel of claim 1, wherein the current to voltage conversion unit comprises: a resistor, the first end of which receives the sensing current, and the second end of the resistor is coupled And a unit gain amplifier having an input coupled to the first end of the resistor and an output of the unity gain amplifier coupled to the input of the voltage gain unit. The reading device of the current touch panel of claim 3, wherein the unity gain amplifier comprises an operational amplifier, and the first input end of the operational amplifier is an input end of the unity gain amplifier, the operational amplifier a second input coupled to the output of the operational amplifier The output of the operational amplifier acts as the output of the unity gain amplifier. The reading device of the current touch panel of claim 1, wherein the current to voltage conversion unit comprises: a resistor, the first end of which receives a first reference voltage, and the second end of the resistor is coupled To the input end of the voltage gain unit; and a current mirror, the main current end receives the sensing current, and the current end of the current mirror is coupled to the second end of the resistor. The reading device of the current touch panel of claim 5, wherein the resistor is a transistor, the first end of the transistor receives the first reference voltage, and the second end of the transistor is controlled The terminal is coupled to the input of the voltage gain unit. The reading device of the current touch panel of claim 5, wherein the current mirror comprises: a first transistor having a first end serving as a main current terminal of the current mirror, the first transistor The second end receives a second reference voltage, and the control end of the first transistor is coupled to the first end of the first transistor; and a second transistor has a first end serving as a current of the current mirror The second end of the second transistor receives the second reference voltage, and the control end of the second transistor is coupled to the control end of the first transistor. The reading device of the current touch panel of claim 7, wherein the first reference voltage is a system voltage, and the second reference voltage is a ground voltage.