CN103123554A - Light sensing circuit and light sensing control method - Google Patents

Abstract

The invention discloses a light sensing circuit which comprises a capacitor, a light sensing unit, a reading transistor and a switch transistor. Wherein the capacitor stores an initial voltage; the reading transistor responds to a grid signal to be turned on so as to transmit the terminal voltage of the capacitor after discharging between the capacitor and the photosensitive unit; the photosensitive unit responds to the optical signal, so that the initial voltage of the capacitor is discharged between the capacitor and the photosensitive unit; the switch transistor responds to the control signal to control the initial voltage of the capacitor and the electrical conduction time of the photosensitive unit.

Description

Light sensing circuit and light sensing control method

【Technical field】

The present invention relates to a photo-sensing circuit, in particular to a photo-sensing circuit capable of controlling the electrical conduction time of the photo-sensing circuit and a control method thereof.

【Background technique】

In recent years, touch panels or touch screens have been widely used in various electronic products as auxiliary input devices, such as computers, smart phones, or digital flat-screen TVs. When a user wants to input a signal to an electronic device equipped with a touch panel, the user only needs to directly touch the touch panel with a finger or a stylus, and the input can be completed without a mouse or a keyboard.

Touch panels can be roughly classified into touch panels that can be classified into capacitive sensing type, resistive touch type, infrared beam sensing type, surface acoustic wave type, integral strain gauge type, piezoelectric effect type, or light sensing type. Wherein the light-sensing touch panel includes components such as photodiode or phototransistor, and the photodiode can be manufactured when manufacturing the driving circuit of the touch panel, and a current generated by sensing light incident on the photodiode is used to identify the light pen or The touch of a finger.

[FIG. 1] shows a photo-sensing circuit 10 in the prior art, which includes a capacitor Cst1, a phototransistor P, a read transistor M1, and an external circuit 11. The phototransistor P is used for receiving the light signal and generating corresponding photocurrent in response to the light signal. The first pulse signal Wn+1 is input to the gate of the phototransistor P, and the second pulse signal Sn+1 is input to the source of the phototransistor. The charge stored in the capacitor Cst1 is discharged through the path formed by the phototransistor P, and the magnitude of the discharge current is determined by the light intensity of the phototransistor P and the clamping voltage setting of the gate-source voltage (Vgs). The read transistor M1 is turned on in response to the gate signal Gn, so that the external circuit 11 can periodically detect the change of the voltage (Va) of the read capacitor Cst1. The external circuit 11 reads out the final capacitor voltage Va after a fixed period (frame) or fixed time discharge through the signal readout line RO and the readout transistor M1, and the external circuit 11 reads the final value of the capacitor voltage Va in the readout period And converted to the output voltage Vout, the system judges whether the phototransistor P receives a high-intensity light signal, so as to determine it as a touch state (touch input event).

[FIG. 2] is an operation timing diagram of the photo-sensing circuit 10 shown in [FIG. 1], which is an operation of one frame period (frame). Usually, one frame cycle includes two timing actions, and can be divided into three working cycles, which are read cycle, reset cycle (reset duration) and discharge cycle. The gate signal Gn is the reading period of the external circuit 11 , and the overlap of the first pulse signal Wn+1 and the second pulse signal Sn+1 is the reset period, and the potential of the capacitor is reset during the reset period. The period from the potential reset period to the next external circuit reading period is the capacitance voltage Va discharge period. This discharge period determines the change rate of the capacitance voltage Va potential according to the gate-source voltage difference (Vgs) and the intensity of light.

The light signal of the light pen and the light signal of the ambient light are greatly different in light intensity, resulting in different discharge rates on the photosensitive circuit, which will cause changes in the capacitor voltage Va. The figure corresponds to two different curves, of which curve 21 is the contact of the non-light pen ( The discharge situation during Non-Touch), and the curve 22 is the discharge situation when the light pen touches (Light PenTouch). Generally speaking, the capacitor voltage Va in the Non-Touch state is greater than the capacitor voltage Va in the Light Pen Touch state (there is a voltage difference ΔVa as shown in the figure). However, when the ambient light increases and other similar factors may cause a substantial increase in the photocurrent generated by the phototransistor P, the discharge rate of the capacitor Cst through the phototransistor P is accelerated, so the capacitor voltage Va in the non-contact (Non-Touch) state decreases , as shown in the curve 23, it will cause the capacitor voltage Va in the non-contact (Non-Touch) state to be the same as the capacitor voltage Va in the light pen touch (Light Pen Touch) state, resulting in a voltage difference ΔVa=0 as shown in the figure, and further misjudgment. In the following, for the convenience of discussion, the current generated in this situation is referred to as ambient current.

Please refer to "Figure 3A" and "Figure 3B", which are the relationship diagrams between the gate-source voltage difference (Vgs) and the output voltage (Vout) of the phototransistor P, and the characteristic indicators of the light sensing circuit can be measured from the working range chart ( working window chart), the upper solid line is the relationship between the light pen contact (Vgs) and the output voltage (Vout) under normal conditions, and the lower dotted line is the relationship between (Vgs) and the output voltage (Vout) under the aforementioned ambient light sensing conditions ) relationship line. There is a gate-source voltage difference (Vgs) interval corresponding to the output voltage (Vout) potential difference between the two curves, which is defined as the working window W (working window). The larger the voltage adjustment range, the more effective it is for changes in ambient light. Large adjustment margin. When the ambient light increases, ambient current will be generated, which will reduce the working window W (working window) of the system. At this time, it is necessary to reduce the gate-source voltage difference (Vgs) of the light sensing circuit to reduce the ambient current, so as to maintain the system’s Light pen recognition ability.

【Content of invention】

In view of the above problems, the present invention proposes a light sensing circuit, so that when the ambient light intensity increases and the ambient current increases, the discharge time of the light sensing circuit is controlled to solve the problems encountered in the prior art.

According to a photo-sensing circuit disclosed in an embodiment of the present invention, the photo-sensing circuit includes a capacitor, a photo-sensing unit, a reading transistor and a switching transistor. The capacitor stores the initial voltage; the photosensitive unit changes its current in response to the light signal, so that the initial voltage of the capacitor is discharged between the capacitor and the photosensitive unit, that is, the photosensitive unit responds to the light signal and accelerates the discharge between the capacitor and the photosensitive unit process; the read transistor is turned on in response to the gate signal to transfer the terminal voltage after the capacitor is discharged between the capacitor and the photosensitive unit; and the switching transistor responds to the control signal to control the electrical conduction time of the capacitor and the photosensitive unit.

A light sensing control method disclosed according to an embodiment of the present invention includes responding to a light signal so that an initial voltage stored in a capacitor is discharged through a gap between the capacitor and a photosensitive unit to have different discharge rates. Respond to a gate signal to transmit the voltage at one end of the capacitor after being discharged between the capacitor and the photosensitive unit. Responding to a control signal to control the electrical conduction time of the capacitor and the photosensitive unit.

According to the light sensing circuit of the present invention, a switching transistor is added between a photosensitive unit and a capacitor to control the length of the capacitor discharge duration. When the ambient light intensity increases and the ambient current increases, it shortens the capacitor and the photosensitive unit. The discharge time between the discharge time, so that it maintains a total leakage equivalent to the low ambient current through a long discharge time, and the discharge rate caused by the light intensity of the light pen is very large, and the final capacitance potential will not be affected. It is necessary to improve the traditional light sensing circuit. The problem of reduced photosensitivity caused by reducing the gate-source voltage difference (Vgs).

The above description of the content of the present invention and the following description of the implementation are used to demonstrate and explain the spirit and principle of the present invention, and to provide further explanation of the patent application scope of the present invention.

【Description of drawings】

FIG. 1 is a circuit diagram of a light sensing circuit in the prior art.

FIG. 2 is an operation timing diagram of a light sensing circuit in the prior art.

FIG. 3A is a graph showing the relationship between the gate-source voltage difference (Vgs) and the output voltage (Vout) of the light sensing circuit in the prior art.

3B is a graph showing the relationship between the gate-source voltage difference (Vgs) and the output voltage (Vout) of the light sensing circuit in the prior art.

FIG. 4 is a circuit diagram of the light sensing circuit disclosed in the present invention.

FIG. 5 is an operation timing diagram of the light sensing circuit disclosed in the present invention.

FIG. 6 is an embodiment of the light sensing circuit disclosed in the present invention.

FIG. 7 is an embodiment of the light sensing circuit disclosed in the present invention.

FIG. 8 is an embodiment of the light sensing circuit disclosed in the present invention.

FIG. 9 is an embodiment of the light sensing circuit disclosed in the present invention.

FIG. 10 is an embodiment of the light sensing circuit disclosed in the present invention.

FIG. 11 is a flow chart of the control method of the light sensing circuit disclosed in the present invention.

[Description of main component symbols]

P.........photosensitive unit

Cst1...Capacitance

10..........Light sensing circuit

11.......External circuit

20........... Light sensing circuit

21... Curve

22... Curve

23.......curve

24..........Curve

25.......curve

Cst2...Capacitance

P1.......photosensitive unit

M1.......Read Transistor

S1.......Switching transistor

Gn.......Gate signal

SC........Control signal

Wn+1 first pulse signal

Sn+1...the second pulse signal

RO........Signal readout line

Va......Capacitor voltage

Q.........Phototransistor

Q1.......First phototransistor

Q2..........Second phototransistor

D.........Photodiode

D1.......First photodiode

D2.......Second Photodiode

101.......Silicon-rich oxide layer components

【Detailed ways】

The detailed features and advantages of the present invention are described in detail below in the embodiments, the content of which is sufficient to enable any person familiar with the relevant art to understand the technical content of the present invention and implement it accordingly, and according to the content disclosed in this specification, the scope of the patent application and the drawings , anyone skilled in the relevant art can easily understand the related objects and advantages of the present invention. The following examples are to further describe the viewpoints of the present invention in detail, but not to limit the scope of the present invention in any respect.

Please refer to "FIG. 4", which is a circuit diagram of the light sensing circuit 20 disclosed in the present invention. The photo-sensing circuit 20 includes a capacitor Cst2, a photo-sensing unit P1, a reading transistor M1 and a switching transistor S1. The photosensitive unit P1 can use a phototransistor. In the case of using a phototransistor, the phototransistor has an energy level that generates a current when the light intensity exceeds the energy level, wherein the phototransistor has a first terminal (ie, the drain terminal), a second terminal (ie, the gate terminal) and The third end (that is, the source end). The drain terminal of the phototransistor is connected to the drain terminal of the switching transistor S1, and the gate terminal and the source terminal are respectively controlled by the first pulse signal Wn+1 and the second pulse signal Sn+1. The switch transistor S1 is then electrically coupled to the capacitor Cst2 and the read transistor M1, and finally electrically connected to the signal readout line RO to read the signal. Various embodiments can be used for the photosensitive element P1, which will be described in detail in the following paragraphs. In this embodiment, the light sensing circuit 20 can also be provided with an external circuit 11 as shown in FIG. 1 , but its description is omitted here.

The capacitor Cst2 stores an initial voltage. When a light signal is irradiated on the photosensitive unit P1, the photosensitive unit P1 will respond to the light signal and generate photocurrents of different sizes, so that the initial voltage stored in the capacitor Cst2 is discharged through the photosensitive unit P1. The light signal referred to here can come from a light pen The light signal from the light source or the light signal from the ambient light. Next, the reading transistor M1 is turned on in response to the gate signal Gn, wherein the gate signal Gn is a control signal of the reading transistor for the reading circuit to read the terminal voltage of the capacitor Cst2 discharged through the photosensitive unit. The terminal voltage is taken as the final potential for a specific period.

The switch transistor S1 responds to the control signal SC to control the electrical conduction time of the capacitor Cst2 and the photosensitive unit P1.

Since the power of the entire ambient current is the magnitude of the ambient current multiplied by the ambient current time (Q=I*T), when the ambient light intensity increases and the ambient current increases, the switching transistor S1 is turned off to control the length of the electrical conduction time. The light-sensing mechanism (leakage mechanism) of the light-sensing circuit is determined by the I _DS of the phototransistor and the discharge duration, so as long as the product of the two is fixed, the external circuit can ensure that the judgment of the ambient light change remains unchanged. Therefore, when the current increase is sensed, the discharge time is adjusted so that the I _DS and the discharge duration remain approximately constant, and the function of the switching transistor S1 is to control the electrical conduction time.

Please refer to "Fig. 5" which is an operation timing diagram of the light sensing circuit 20 disclosed in the present invention, where the overlap of the timing of the first pulse signal Wn+1 and the timing of the second pulse signal Sn+1 is the reset period (resetduration) , the photosensitive unit P1 is controlled by the first pulse signal Wn+1 and the second pulse signal Sn+1, and the photosensitive unit P1 responds to the relative voltage difference between the first pulse signal Wn+1 and the second pulse signal Sn+1, so that the capacitor Cst2 The terminal potential is reset to the initial potential, the high level period of the two pulse signals determines the initial voltage of the capacitor, and the low level period determines the discharge condition. Wherein the period of the second pulse signal Sn+1 is greater than the period of the first pulse signal Wn+1. The control signal SC is generated after the gate signal Gn ends, and the switch transistor S1 responds to the control signal SC to control the discharge time of the capacitor. When the control signal SC ends, the discharge behavior of the capacitor Cst2 is terminated. Curve 24 is the discharge situation after using the light sensing circuit disclosed in the present invention, which is also the discharge situation caused by no light pen touch, and curve 25 is the discharge situation when the light pen touch (Light Pen Touch). Therefore, when the ambient light increases and the ambient current is generated, the capacitor voltage Va in the non-contact (Non-Touch) state, the switching transistor S1 is turned off and the discharge is completed to maintain a certain value without falling, and the non-contact (Non-Touch) The capacitor voltage in the state is different from the capacitor voltage Va in the state of light pen touch (Light Pen Touch), which will not cause misjudgment.

In this embodiment, the terminal potential Va of the capacitor Cst2 is reset to the initial potential by the first pulse signal Wn+1 and the second pulse signal Sn+1. In another embodiment, an external circuit independent of the sensing circuit of the present invention may also be used to reset the terminal potential of the capacitor to the initial potential.

Various implementations of the photosensitive element P1 are listed below. Please refer to "Fig. 6", which is another embodiment of the present invention, wherein the photosensitive unit P1 includes a phototransistor Q, wherein the phototransistor Q has a first terminal (ie, the drain terminal), a second terminal (ie Gate terminal) and the third terminal (that is, the source terminal). The first terminal (ie, the drain terminal) is connected to the drain terminal of the switching transistor S1, and the second terminal (ie, the gate terminal) is connected to the third terminal (ie, the source terminal) and is controlled by the first pulse signal Wn+1. As mentioned above, when it is no longer necessary to adjust the gate-source voltage difference (Vgs) of the phototransistor, a simplified design with a fixed gate-source voltage difference (Vgs) = 0 can be used, that is, the gate-source Directly connected, the photosensitive element P1 is connected in a gate-source short circuit mode, which can reduce a set of external power supplies, and the adjustment of the electrical conduction time is determined by the width of the control signal SC. The operation mode in which the gate-source voltage difference (Vgs)=0 is less likely to cause I-V characteristic deviation due to long-term operation, and will be more conducive to long-term operation.

Please refer to "Fig. 7", which is another embodiment of the present invention, wherein the photosensitive unit P1 includes a first phototransistor Q1 and a second phototransistor Q2, and the first terminal (ie, the drain terminal) of the first phototransistor Q1 ) is connected to the drain terminal of the switching transistor S1, the second terminal (that is, the gate terminal) of the first phototransistor Q1 is connected to the third terminal (that is, the source terminal) of the second phototransistor Q2, and the first phototransistor Q1 is connected to the third terminal (that is, the source terminal). The three terminals (that is, the source terminal) are connected to the first terminal (that is, the drain terminal) of the second phototransistor Q2, wherein the second terminal (that is, the gate terminal) of the second phototransistor Q2 receives the first pulse signal Wn+1 control, the third terminal (ie source terminal) of the second phototransistor Q2 is controlled by the second pulse signal Sn+1. The first phototransistor Q1 and the second phototransistor Q2 of this circuit are designed in series, which is beneficial to reduce the problem of increased environmental current caused by long-term operation or deteriorating environmental conditions. The control signal SC can expand its adjustment range.

Please refer to "Figure 8", which is another embodiment of the present invention, wherein the photosensitive unit P1 includes a photodiode D with a cathode terminal and an anode terminal, the cathode terminal is connected to the switching transistor S1, and the anode terminal receives the first pulse signal Control Wn+1.

Please refer to "Figure 9", wherein the photosensitive unit P1 includes a first photodiode D1 and a second photodiode D2, the cathode terminal of the first photodiode D1 is connected to the anode terminal of the second photodiode D2, and is connected to the switching transistor S1 , the anode terminal of the first photodiode D1 is connected to the cathode terminal of the second photodiode D2, and is controlled by the first pulse signal Wn+1.

Please refer to "FIG. 10", wherein the photosensitive unit P1 includes a silicon-rich oxide (SRO) element 101 with a first end and a second end, the first end is connected to the switching transistor S1, and the second end is received by the second end. A pulse signal Wn+1 control.

Please refer to "FIG. 11", which is a flow chart of the control method of the light sensing circuit disclosed in the present invention. First, the reading transistor periodically isolates the electrical conduction state of the external circuit and the photosensitive circuit in the panel, and responds to the light signal, so that the initial voltage stored in the capacitor is discharged through the switching transistor to the photosensitive unit due to different light intensities. There are different discharge rates (step S1). In response to the switch transistor control signal, the switch transistor is set to be turned on, so that the capacitor and the photosensitive element are electrically connected (step S2). The initial voltage of the capacitor is reset by the photosensitive element or other circuits, and then according to the voltage of the photosensitive element and the lighting conditions, the capacitor voltage (Va) passes through the switching transistor and the photosensitive element to start the discharge process (step S3). When the switching transistor is set to be off, the capacitor is separated from the photosensitive element, and since there is no other obvious discharge path, the potential of the capacitor can be maintained at a fixed level (step S4). The read transistor is turned on periodically, and the external circuit is used to detect the residual potential of the capacitor (step S5). The control signal is generated after the gate signal ends. After the control signal ends, the discharge behavior of the initial voltage of the capacitor is terminated. Wherein the photosensitive unit is controlled by at least one pulse signal, and the photosensitive unit responds to the first pulse signal and the second pulse signal to provide a current to charge the capacitor to exceed the initial voltage. Wherein the period of the second pulse signal is greater than the period of the first pulse signal.

According to the light sensing circuit of the present invention, a switch transistor is added between the photosensitive unit and the capacitor to control the duration of the capacitor being discharged from the photosensitive unit. When the ambient light intensity increases and the ambient current increases, it reduces the effect of the large ambient current Time, to maintain leakage similar to low (general) environmental overcurrent for a long time, to improve the traditional photo-sensing circuit needs to reduce the gate-source voltage difference (Vgs) to reduce the photosensitive ability.

Although the present invention is disclosed by the aforementioned embodiments, they are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, all changes and modifications made belong to the scope of patent protection of the present invention. For the scope of protection defined by the present invention, please refer to the attached scope of patent application.

Claims (16)

1. A light sensing circuit, comprising: A capacitor for storing an initial voltage; a photosensitive unit, which is turned on in response to a light signal, so that the initial voltage of the capacitor is discharged through the gap between the capacitor and the photosensitive unit; a read transistor, which is turned on in response to a gate signal, so as to transmit a terminal voltage of the capacitor after being discharged between the capacitor and the photosensitive unit; and A switch transistor responds to a control signal to control the electrical conduction time between the capacitor and the photosensitive unit. 2. The light sensing circuit according to claim 1, wherein the control signal is generated after the gate signal ends. 3 . The light sensing circuit according to claim 1 , wherein after the control signal ends, the capacitor forms an electrical open circuit with the photosensitive unit, and the capacitor discharges to the photosensitive unit. 4 . 4. The light sensing circuit according to claim 1, wherein the photosensitive unit is controlled by a first pulse signal and a second pulse signal, and the photosensitive unit responds to the first pulse signal and the second pulse signal To provide a current to charge the capacitor to exceed the initial voltage. 5. The photo-sensing circuit according to claim 4, wherein the period of the second pulse signal is greater than the period of the first pulse signal. 6. The photo-sensing circuit according to claim 4, wherein the photo-sensing unit comprises a phototransistor, wherein the phototransistor has a first terminal, a second terminal and a third terminal, the first terminal Connected to the switching transistor, the second terminal is controlled by the first pulse signal, and the third terminal is controlled by the second pulse signal. 7. The photo-sensing circuit according to claim 4, wherein the photo-sensing unit comprises a phototransistor, wherein the phototransistor has a first terminal, a second terminal and a third terminal, the first terminal connected to the switching transistor, the second terminal is connected to the third terminal and controlled by the first pulse signal. 8. The light sensing circuit according to claim 4, wherein the light sensing unit comprises a first phototransistor and a second phototransistor, the first end of the first phototransistor is connected to the switching transistor, The second terminal of the first phototransistor is connected to the third terminal of the second phototransistor, the third terminal of the first phototransistor is connected to the first terminal of the second phototransistor, wherein the second phototransistor of the second phototransistor The second terminal is controlled by the first pulse signal, and the third terminal of the second phototransistor is controlled by the second pulse signal. 9. The photo-sensing circuit according to claim 4, wherein the photo-sensing unit comprises a photodiode having a cathode terminal and an anode terminal, the cathode terminal is connected to the switching transistor, and the anode terminal is received by the first A pulse signal control. 10. The light sensing circuit according to claim 4, wherein the photosensitive unit comprises a first photodiode and a second photodiode, the cathode terminal of the first photodiode is connected to the anode of the second photodiode The terminal is connected to the switching transistor, the anode terminal of the first photodiode is connected to the cathode terminal of the second photodiode, and is controlled by the first pulse signal. 11. The photo-sensing circuit according to claim 4, the photo-sensing unit comprises a silicon-rich oxide (SRO) element, having a first end and a second end, the first end is connected to The second end of the switching transistor is controlled by the first pulse signal. 12. A control method for light sensing, comprising: Responding to a light signal, so that an initial voltage stored in a capacitor is discharged between the capacitor and a photosensitive unit, so that there are different discharge rates; Responding to a gate signal to transmit the voltage at one terminal of the capacitor after being discharged between the capacitor and the photosensitive unit; and Responding to a control signal to change the electrical conduction time between the capacitor and the photosensitive unit. 13. The light sensing control method according to claim 12, wherein the control signal is generated after the gate signal ends. 14. The light sensing control method according to claim 12, wherein the discharge of the capacitor is terminated after the control signal ends. 15. The light sensing control method according to claim 12, wherein the photosensitive unit is controlled by a first pulse signal and a second pulse signal, and the photosensitive unit responds to the first pulse signal and the second pulse signal The pulse signal provides a current to charge the capacitor beyond the initial voltage. 16 . The light sensing control method according to claim 15 , wherein the period of the second pulse signal is greater than the period of the first pulse signal.

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