TW201420999A - Optical sensor circuit and control method for optical sensors - Google Patents

Abstract

An optical sensor circuit is provided. The optical sensor circuit includes a capacitor, a photo-sensing unit, a read transistor, and a switch transistor. The capacitor is charged with an initial voltage. The initial voltage of the capacitor discharges through the path between the capacitor and the photo-sensing unit. The read transistor turns on in response to a gate signal such that the voltage of the capacitor after discharging may be accessed by an external circuit. The switch transistor responds to a control signal to control the discharging time of the initial voltage of the capacitor.

Description

Light sensing circuit and light sensing control method

The invention relates to a light sensing circuit, in particular to a light sensing circuit capable of controlling an electrical conduction time of a light sensing circuit and a control method thereof.

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

The touch panel can be roughly classified into a touch panel, which can be classified into a capacitive sensing type, a resistive touch type, an infrared beam sensing type, a surface acoustic wave type, an overall strain gauge type, and a piezoelectric effect type. Or light sensing type. The light sensing type touch panel comprises a component such as a photodiode or a photoelectric transistor, and a photodiode can be fabricated when the driving circuit of the touch panel is manufactured, which senses light incident on the photodiode A current is generated to identify the touch of the stylus or finger.

The first embodiment shows a light sensing circuit 10 of the prior art, which includes a capacitor Cst1, an optoelectronic transistor P, a read transistor M1, and an external circuit 11. The photovoltaic transistor P is for receiving an optical signal and responding to the optical signal to generate a corresponding photocurrent. The first pulse signal Wn+1 is input to the gate of the photovoltaic transistor P, and the second pulse signal Sn+1 is input to the source of the photovoltaic transistor. The charge stored in the capacitor Cst1 is discharged through the path formed by the photovoltaic transistor P. The magnitude of the discharge current is determined by the illumination intensity of the photovoltaic transistor P and the gate-source voltage (Vgs) clamping setting. Reading transistor M1 is turned on in response to the gate signal Gn, so that the external circuit 11 can periodically detect the voltage (Va) change of the read capacitor Cst1. The external circuit 11 reads out the final capacitor voltage Va after being discharged through a fixed period (frame) or a fixed time via the signal readout line RO and the read transistor M1, and the external circuit 11 finalizes the capacitor voltage Va in the read cycle. The value is converted to the output voltage Vout, and the system determines whether the photovoltaic transistor P receives the high-intensity optical signal to determine the touch input event.

The "second diagram" is an operation timing chart of the optical sensing circuit 10 shown in "Fig. 1", which is an operation of one frame period. Usually, one picture period includes two timing actions, and can be divided into three duty cycles, which are a read cycle, a reset duration, and a discharge cycle. The gate signal Gn is a read period of the external circuit 11, and the first pulse signal Wn+1 overlaps with the second pulse signal Sn+1 as a reset period, and the capacitor is potential reset in the reset period. After the potential reset period to the next external circuit read cycle, the capacitor voltage Va discharge period determines the rate of change of the potential of the capacitor voltage Va according to the gate-source voltage difference (Vgs) and the illumination intensity.

The optical signal of the light pen and the ambient light have a large difference in light intensity, which causes different discharge rates on the photosensitive circuit, which will change in the capacitance voltage Va. The figure corresponds to two different curves, wherein the curve 21 is a matt pen contact ( In the case of a discharge in the case of Non-Touch), the curve 22 is a discharge condition in the case of a light pen touch. In general, in the non-contact state, the capacitor voltage Va has a capacitance voltage Va larger than the capacitor voltage Va in the light pen touch state (having a pressure difference ΔVa as shown). However, when the ambient light is increased or the like, the photocurrent generated by the photovoltaic transistor P may be greatly increased, thereby causing the capacitor Cst to pass through the photovoltaic transistor P. The discharge rate is accelerated, so the capacitor voltage Va in the non-contact state is lowered, as shown by the curve 23, causing the contact voltage Va and the light pen touch state in the non-contact state. The capacitor voltage Va is the same, and the voltage difference ΔVa=0 is caused as shown in the figure, which further causes misjudgment. Hereinafter, for convenience of discussion, the current generated in this case is referred to as an ambient current.

Please refer to "3A" and "3B", which is the relationship between the gate-source voltage difference (Vgs) and the output voltage (Vout) of the photo-electric crystal P, and the characteristic index of the photo-sensing circuit can be measured. The working window chart is used to judge that the upper solid line is the line connecting the light pen (Vgs) and the output voltage (Vout) under normal conditions, and the lower dotted line is the (Vgs) and output in the aforementioned ambient light state. Voltage (Vout) 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. The larger the voltage adjustment range indicates that the change in ambient light is greater. Adjustment margin. When the ambient light increases, the ambient current will cause the working window to shrink. In this case, the gate-source voltage difference (Vgs) of the light sensing circuit should be reduced to reduce the ambient current to maintain the system pair. Light pen recognition ability.

In view of the above problems, the present invention provides a light sensing circuit that solves the problems encountered in the prior art by controlling the length of discharge time of the photosensitive circuit when the ambient light intensity is increased to cause an increase in ambient current.

According to an embodiment of the present invention, a light sensing circuit includes a capacitor, a photosensitive unit, a reading transistor, and a switching transistor. The capacitor stores the initial voltage; the photosensitive unit changes its current level in response to the optical signal. 俾 causing the initial voltage of the capacitor to be discharged between the capacitor and the photosensitive unit, that is, the photosensitive unit responds to the optical signal to accelerate the discharge process between the capacitor and the photosensitive unit; the reading transistor is turned on in response to the gate signal to transmit the capacitor via The terminal voltage after discharge 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 method for controlling light sensing according to an embodiment of the invention includes responding to an optical signal, causing an initial voltage stored in a capacitor to be discharged between the capacitor and a photosensitive unit, and having a different discharge rate. Responding to a gate signal, the transmission capacitor is discharged via a voltage 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 discharge duration of the capacitor. When the ambient light intensity increases and the ambient current increases, the capacitor and the photosensitive unit are shortened. The discharge time between the cells is such that it maintains the total leakage current equivalent to the low ambient current through a longer discharge time, and the discharge rate caused by the light intensity of the light pen is very large, and the final capacitance potential is not affected, improving the conventional light sensing circuit. It is necessary to reduce the problem that the photo-sensing ability is lowered due to the gate-source voltage difference (Vgs).

The above description of the present invention and the following description of the embodiments of the present invention are intended to illustrate and explain the spirit and principles of the invention.

The detailed features and advantages of the present invention are described in detail below in the embodiments, which are sufficient to enable anyone skilled in the art to understand the technical contents of the present invention. The related objects and advantages of the present invention will be readily understood by those skilled in the art in light of this disclosure. The following examples are intended to describe the present invention in further detail, but are not intended to limit the scope of the invention.

Please refer to FIG. 4, which is a circuit diagram of the light sensing circuit 20 disclosed in the present invention. The light sensing circuit 20 includes a capacitor Cst2, a photosensitive unit P1, a read transistor M1, and a switching transistor S1. Among them, the photosensitive unit P1 can use a photoelectric transistor. In the case of using a photovoltaic transistor, the photovoltaic transistor has an energy level, and when the light intensity exceeds the energy level, a current is generated, wherein the photovoltaic transistor has a first end (ie, a 汲 extreme) and a second end (ie, a gate) Extreme) and the third end (ie the source end). The 汲 terminal of the photoelectric transistor is connected to the 汲 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 switching transistor S1 is 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. The photosensitive element P1 can be used in various embodiments and will be described in detail in the subsequent paragraphs. In this embodiment, the optical sensing circuit 20 may be provided with an external circuit 11 as shown in FIG. 1, but the description thereof is omitted here.

The capacitor Cst2 stores an initial voltage. When the optical signal is irradiated on the photosensitive unit P1, the photosensitive unit P1 responds to the optical signal to generate different photocurrents, so that the initial voltage stored in the capacitor Cst2 is discharged through the photosensitive unit P1, and the optical signal referred to here can be from the optical pen. The light signal or the light signal from 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 for reading the transistor, so that the reading circuit reads the terminal voltage of the capacitor Cst2 discharged through the photosensitive unit. The terminal voltage read is the final potential of a particular period.

The switching 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 total amount of ambient current is 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 photo-sensing mechanism (leakage mechanism) of the photo-sensing circuit is determined by the I _DS and the discharge duration of the photo-electric crystal. Therefore, as long as the product is fixed, the judgment of the external circuit on the change of the ambient light can be ensured. Therefore, when the current is sensed to increase, that is, the time of the discharge is adjusted so that the I _DS and the discharge duration remain approximately fixed, and the function of the switching transistor S1 is to control this electrical conduction time.

Please refer to FIG. 5 for the operation timing diagram of the optical sensing circuit 20 disclosed in the present invention. The timing of the overlap of the first pulse signal Wn+1 timing and the second pulse signal Sn+1 is a reset period (reset duration). 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 pressure difference between the first pulse signal Wn+1 and the second pulse signal Sn+1 to make the capacitor Cst2 The potential of the terminal is reset to the initial potential, and 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. 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 switching 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. The curve 24 is a discharge situation after the light sensing circuit disclosed in the present invention is used, and is also a discharge condition in which a light pen is touched to cause discharge, and a curve 25 is a discharge condition in a light pen touch. Therefore, when the ambient light increases to generate an ambient current, there is no connection. The capacitor voltage Va in the (Non-Touch) state is turned off by the switching transistor S1 to end the discharge to maintain a certain value without falling, and the capacitive voltage in the non-contact state is in contact with the light pen (Light Pen) The capacitance voltage Va in the Touch state is different and does 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 yet another embodiment, an external circuit independent of a sensing circuit of the present invention can be used to reset the terminal potential of the capacitor to an initial potential.

Hereinafter, various embodiments of the photosensitive element P1 will be described. Please refer to FIG. 6 , which is another embodiment of the present invention, wherein the photosensitive unit P1 includes a photovoltaic transistor Q, wherein the photovoltaic transistor Q has a first end (ie, a 汲 extreme) and a second end (ie the gate extreme) and the third end (ie the source extreme). The first end (ie, the 汲 terminal) is connected to the 汲 terminal of the switching transistor S1, and the second end (ie, the gate terminal) is connected to the third end (ie, the source terminal) and is controlled by the first pulse signal Wn+1. . As can be seen from the above, when it is no longer necessary to adjust the gate-source voltage difference (Vgs) of the photovoltaic transistor, a simplified design of a fixed gate-source voltage difference (Vgs) = 0 can be used, that is, a gate-source Very direct connection, the photosensitive element P1 is connected in a gate-source short circuit manner, which can reduce a set of external power supply, and the adjustment of the electrical conduction time is determined by the width of the control signal SC. The operation mode of gate-source voltage difference (Vgs)=0 is less likely to cause I-V characteristic shift due to long-time operation, which is 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 photovoltaic transistor Q1 and a second photovoltaic transistor Q2, and the first end of the first photovoltaic transistor Q1 ( That is, the extreme pole) is connected to the drain of the switching transistor S1 The second end of the first optoelectronic transistor Q1 (ie, the gate terminal) is connected to the third end of the second optoelectronic transistor Q2 (ie, the source terminal), and the third end of the first optoelectronic transistor Q1 (ie, The source terminal is connected to the first end of the second photovoltaic transistor Q2 (ie, the 汲 terminal), wherein the second end of the second photovoltaic transistor Q2 (ie, the gate terminal) is controlled by the first pulse signal Wn+1, The third end (ie, the source terminal) of the second photovoltaic transistor Q2 is controlled by the second pulse signal Sn+1. The first photovoltaic transistor Q1 and the second photovoltaic transistor Q2 of the circuit are designed in series to reduce the problem of environmental current increase caused by long-term operation or deterioration of environmental conditions. The control signal SC can amplify its adjustment range.

Please refer to FIG. 8 , which is another embodiment of the present invention, wherein the photosensitive unit P1 includes a photodiode D having a cathode end and an anode end, the cathode end is connected to the switching transistor S1, and the anode end is received. The first pulse signal controls Wn+1.

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

Please refer to FIG. 11 , which is a flowchart of a method for controlling a light sensing circuit disclosed in the present invention. First, the reading transistor periodically isolates the electrical conduction state between the external circuit and the photosensitive circuit in the panel, and responds to the optical signal, so that the initial voltage stored by the capacitor is discharged between the switching transistor and the photosensitive unit due to different illumination intensity. There are different discharge rates (step S1). In response to the switch transistor control signal, the switch transistor is turned on to electrically connect the capacitor to the photosensitive element (step S2). The initial voltage of the capacitor is reset by the photosensitive element or other circuit, and then the capacitor voltage (Va) is switched via the switching transistor and the photosensitive element according to the voltage and the illumination condition of the photosensitive element (step S3). When the switch transistor is set to be off, the capacitor is separated from the photosensitive element, and the capacitor potential can be maintained at a fixed level because there is no other significant discharge path (step S4). The read transistor is periodically turned on, and an external circuit is used to detect the residual potential of the capacitor (step S5). The control signal is generated after the gate signal is completed. After the control signal is over, the discharge of the initial voltage of the capacitor is terminated. 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. 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, the switching transistor is added between the photosensitive unit and the capacitor to control the duration of discharge of the capacitor by the photosensitive unit, and when the ambient light intensity increases, the ambient current increases, which reduces the large ambient current. The action time is to maintain the leakage current similar to the low (general) environmental turbulence for a long period of time, and to improve the traditional photo-sensing circuit to reduce the sensitivity of the gate-source voltage difference (Vgs). .

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

P‧‧‧Photosensitive unit

Cst1‧‧‧ capacitor

10‧‧‧Light sensing circuit

11‧‧‧External circuit

20‧‧‧Light sensing circuit

21‧‧‧ Curve

22‧‧‧ Curve

23‧‧‧ Curve

24‧‧‧ Curve

25‧‧‧ Curve

Cst2‧‧‧ capacitor

P1‧‧‧Photosensitive unit

M1‧‧‧Reading transistor

S1‧‧‧Switching transistor

Gn‧‧‧ gate signal

SC‧‧‧Control signal

Wn+1‧‧‧ first pulse signal

Sn+1‧‧‧ second pulse signal

RO‧‧‧ signal readout line

Va‧‧‧capacitor voltage

Q‧‧‧Photoelectric crystal

Q1‧‧‧First Photoelectric Crystal

Q2‧‧‧Second Photoelectric Crystal

D‧‧‧Photoelectric diode

D1‧‧‧first photodiode

D2‧‧‧Second Photodiode

101‧‧‧rich oxide layer components

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

Fig. 2 is an operation timing chart of a light sensing circuit of the prior art.

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

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

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

Figure 5 is a timing chart showing the operation of the light sensing circuit disclosed in the present invention.

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

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

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

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

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

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

20‧‧‧Light sensing circuit

Cst2‧‧‧ capacitor

P1‧‧‧Photosensitive unit

M1‧‧‧Reading transistor

Gn‧‧‧ gate signal

SC‧‧‧Control signal

S1‧‧‧Switching transistor

Wn+1‧‧‧ first pulse signal

Sn+1‧‧‧ second pulse signal

RO‧‧‧ signal readout line

Va‧‧‧capacitor voltage

Claims (16)

A light sensing circuit includes: a capacitor for storing an initial voltage; a photosensitive unit that is turned on in response to an optical signal, wherein the initial voltage of the capacitor is discharged between the photosensitive unit and the photosensitive unit; The crystal is turned on in response to a gate signal to transmit a voltage of the capacitor after being discharged between the capacitor and the photosensitive unit; and a switching transistor is responsive to a control signal to control the electrical property of the capacitor and the photosensitive unit On time. The light sensing circuit of claim 1, wherein the control signal is generated after the gate signal ends. The optical sensing circuit of claim 1, wherein after the control signal ends, the capacitor forms an electrical open circuit with the photosensitive unit, and the discharging of the photosensitive unit terminates. The light sensing circuit of claim 1, wherein the photosensitive unit is controlled by a first pulse signal and a second pulse signal, and the photosensitive unit returns the first pulse signal and the second pulse signal to provide a current The capacitor is charged to exceed the initial voltage. The optical sensing circuit of claim 4, wherein the period of the second pulse signal is greater than the period of the first pulse signal. The photo sensing circuit of claim 4, wherein the photosensitive unit comprises a photovoltaic transistor, wherein the photovoltaic transistor has a first end, a second end and a third end, the first end being connected to the Switching the transistor, the second end receives the first pulse Signal control, the third end is controlled by the second pulse signal. The photo sensing circuit of claim 4, wherein the photosensitive unit comprises a photovoltaic transistor, wherein the photovoltaic transistor has a first end, a second end and a third end, the first end being connected to the The switch transistor is connected to the third end and controlled by the first pulse signal. The photo sensing circuit of claim 4, wherein the photosensitive unit comprises a first optoelectronic transistor and a second optoelectronic transistor, the first end of the first optoelectronic transistor being connected to the switching transistor, a second end of the first optoelectronic transistor is connected to the third end of the second optoelectronic transistor, and a third end of the first optoelectronic transistor is connected to the first end of the second optoelectronic transistor, wherein the second optoelectronic The second end of the transistor is controlled by the first pulse signal, and the third end of the second optoelectronic transistor is controlled by the second pulse signal. The photo sensing circuit of claim 4, wherein the photosensitive unit comprises a photodiode having a cathode end and an anode end, the cathode end being connected to the switching transistor, wherein the anode end receives the first pulse signal control. The photo sensing circuit of claim 4, wherein the photosensitive unit comprises a first photodiode and a second photodiode, a cathode end of the first photodiode and the second photodiode The anode end of the body is connected and connected to the switch transistor. The anode end of the first photodiode is connected to the cathode end of the second photodiode and is controlled by the first pulse signal. The photo sensing circuit of claim 4, wherein the photosensitive unit comprises a silicon-rich oxide (SRO) element having a first end and a second end, the first end being connected to the switch a transistor, the second end receives the first pulse signal control. A method for controlling light sensing includes: responding to an optical signal, causing an initial voltage stored in a capacitor to be discharged between the photosensitive unit and the photosensitive unit, and having a different discharge rate; responding to a gate signal to Transmitting the capacitance through a voltage between the capacitor and the photosensitive unit; and responding to a control signal to change the electrical conduction time of the capacitor and the photosensitive unit. The method of controlling light sensing according to claim 12, wherein the control signal is generated after the gate signal ends. The method of controlling light sensing according to claim 12, wherein the discharge of the capacitor is terminated after the control signal ends. The method of controlling light sensing according to claim 12, wherein the photosensitive unit is controlled by a first pulse signal and a second pulse signal, and the photosensitive unit returns the first pulse signal and the second pulse signal to provide a Current is charged to the capacitor beyond the initial voltage. The method of controlling light sensing according to claim 15, wherein the period of the second pulse signal is greater than the period of the first pulse signal.