CN101532874B - Optical sensor for display device - Google Patents

Abstract

A light sensor for a display device. The optical sensor comprises an optical receiver, a reset unit and a sampling unit. The optical receiver includes a first transistor, and a first conversion unit converting an output of the first transistor into a photo-voltage, the reset unit providing an initialized reference voltage in response to a reset signal, and includes a second transistor and a third transistor connected to each other. The control end of the second transistor is connected with the reset signal, and the control end of the third transistor is connected with the first conversion unit. The sampling unit outputs a photo voltage corresponding to the amount of light received in response to a sampling signal, and includes a fourth transistor responsive to the sampling signal and a second conversion unit converting an output of the fourth transistor into the photo voltage. The optical sensor can obtain a larger output light voltage variation range, and can effectively reduce the number of circuit elements and layout area to save cost. Moreover, the invention can effectively avoid the generation of threshold voltage deviation to improve the service life.

Description

A light sensor for a display device

technical field

The present invention relates to a light sensor, in particular to a light sensor arranged in a display device for sensing ambient light brightness. the

Background technique

An ambient light sensor is arranged on the display device to measure the intensity of the ambient lighting to adjust the brightness of the light source of the display device accordingly, so as to meet the requirements of providing good display effect and reducing power consumption at the same time. the

FIG. 1 is a circuit diagram showing a known light sensor 100 , and FIG. 2 is a timing diagram showing signals input to the light sensor 100 of FIG. 1 . Please refer to FIG. 1 and FIG. 2 at the same time. The light sensor 100 includes a sensing transistor Q1, a selection transistor Q2, a current generating transistor Q3, an output transistor Q4, and a capacitor C1. The light sensor 100 outputs a sensor current Iout, and the magnitude of the current Iout depends on the amount of light received. The sensing transistor Q1 is supplied with a first voltage VDD and a second voltage VGG. When the selection signal SELECT is at a high level, the selection transistor Q2 is turned on to electrically connect the sensing transistor Q1 and the capacitor C1 to the first voltage VDD. The sensing transistor Q1 does not generate photocurrent and the capacitor C1 is charged to have the first voltage VDD, and when the read signal READ is at a high level, the output transistor Q4 can be turned on to output the first voltage VDD. On the other hand, when the selection signal SELECT is at a low level, the selection transistor Q2 is turned off so that the sensing transistor Q1 and the capacitor C1 are both disconnected from the first voltage VDD. At this time, the capacitor C1 stores charges to generate light applied to the current generating transistor Q3 Voltage. Therefore, the magnitude of the sensor current Iout depends on the difference of the photovoltage relative to the first voltage VDD. Furthermore, when the read signal READ is at a high level, the output transistor Q4 can be turned on, so that the transistor Q4 can output a photovoltage Vout corresponding to the magnitude of the sensor current Iout. the

The disadvantage of the above design is that the current generating transistor Q3 will be damaged due to threshold voltage shift when it is negatively biased for a long time; on the other hand, according to the above design, because each reset When the (reset) circuit operates, the voltage of the node n1 will be set at the first voltage VDD, so the variation range of the difference between the reference voltage and the photovoltage will be very small. the

FIG. 3 is a circuit diagram showing another known light sensor 200 design. As shown in FIG. 3 , the light sensor 200 includes a sensing circuit 202 , a reference voltage generating circuit 204 , and a processing unit 206 . The sensing circuit 202 includes a sensing transistor Q1, a reset transistor Q2, a switching transistor Q3, and two capacitors C1, C2. The reference voltage generation circuit 204 includes a sensing transistor Q4, a reset transistor Q5, a switching transistor Q6, and two capacitors C3 and C4. The sensing transistor Q1 is supplied with a first voltage VDD and a second voltage VGG, and the capacitors C1 and C2 are connected with a third voltage VDC. The light sensor 200 is driven by a gate driver (not shown in the figure). When the reset transistor Q2 is turned on, the circuit performs a reset action. At this time, the switching transistor Q3 is turned on by the first stage output of the gate driver, so that the light sensor The switching transistor Q3 of 200 obtains a reference voltage ΔV1. After the sensing transistor Q1 is illuminated for a period of time, the switch transistor Q3 is turned on by the output of the last stage of the gate driver, and the switch transistor Q3 of the light sensor 200 obtains a changed photovoltage ΔV2. When the switch signal SWITCH is at a high level, the reference voltage ΔV1 or the changed photovoltage ΔV2 can be taken out. The advantage of this design lies in the circuit reset mechanism, so that the difference between the reference voltage and the changed photovoltage can be varied in a wide range. However, the disadvantage of this design is that two sets of circuits are required, that is, one set of sensing circuits 202 is used to generate the photovoltage and another set of reference voltage generating circuits 204 is used to generate the reference voltage, which will make the number of components of the light sensor 200 too many And increase the manufacturing cost. the

Contents of the invention

The purpose of the present invention is to provide a light sensor for a display device, which can obtain a wide sensing range with a small number of components, and can increase the working life of circuit components. the

According to an embodiment of the present invention, a light sensor for a display device includes a light receiver, a reset unit and a sampling unit. The light receiver receives external light and generates a photovoltage corresponding to the amount of received light, and includes a first transistor and a first conversion unit for converting the output of the first transistor into photovoltage. The reset unit responds to a reset signal to provide an initialized reference voltage, and includes a second transistor and a third transistor connected to each other, the control terminal of the second transistor is connected to the reset signal and the control terminal of the third transistor is connected to the first transistor. A conversion unit, and when the second transistor is turned on, the first conversion unit discharges through the third transistor to obtain an initialized reference voltage. The sampling unit responds to a sampling signal and outputs a photovoltage corresponding to the amount of received light, and includes a fourth transistor responding to the sampling signal, and a second conversion unit converting the output of the fourth transistor into a photovoltage. the

According to another embodiment of the present invention, a light sensor for a display device includes a sensing circuit, a reference voltage generating circuit and a processing unit. The sensing circuit includes a first light receiver, a first reset unit and a first read unit. The first photoreceiver receives external light and generates a photovoltage corresponding to the amount of received light. The first photoreceiver includes a first transistor and a first conversion unit for converting the output of the first transistor into photovoltage. The first reset unit responds to the first reset signal to provide an initialized photovoltage, the reset unit includes a second transistor and a third transistor electrically connected to each other, and the control terminal of the second transistor is connected to the first reset signal And the control end of the third transistor is connected to the first conversion unit, and when the second transistor is turned on, the first conversion unit discharges through the third transistor to obtain an initialized photovoltage. The first reading unit responds to the first reading signal to output a photovoltage corresponding to the amount of received light, the first reading unit includes a fourth transistor responding to the first reading signal, and a device for converting the output of the fourth transistor into a photovoltage a second conversion unit. The reference voltage generation circuit includes a second light receiver, a second reset unit and a second read unit. The second photoreceiver is shielded from external light to generate a reference voltage. The second photoreceiver includes a fifth transistor and a third conversion unit for converting the output of the fifth transistor into the reference voltage. The second reset unit responds to a second reset signal to provide an initialized reference voltage, the second reset unit includes a sixth transistor and a seventh transistor electrically connected to each other, and the control terminal of the sixth transistor is connected to the second reset The signal is set and the control terminal of the seventh transistor is connected to the third conversion unit, and when the sixth transistor is turned on, the third conversion unit discharges through the seventh transistor to obtain an initialized reference voltage. The second reading unit responds to a second reading signal to output a reference voltage, the second reading unit includes an eighth transistor that responds to the second reading signal, and a fourth transistor that converts the output of the eighth transistor into a reference voltage conversion unit. The processing unit receives the photovoltage and the reference voltage to generate an output signal corresponding to the difference between the photovoltage and the reference voltage. the

Through the design of various embodiments of the present invention, each time the photosensor performs a reset action, the storage capacitor voltage can be dropped to be equal to or close to the threshold of the third transistor through the auto-zero discharge action of the reset circuit. Voltage (reference voltage), and then gradually increase with the light, so that the light sensor can obtain a larger output photovoltage variation range relative to the reference voltage. Furthermore, since the output photovoltage and the reference voltage are taken out by the same circuit, the number of circuit components and layout area can be effectively reduced to save cost. On the other hand, since the photo-sensing transistor is subjected to positive bias (positive gate voltage VGH) and negative bias (light voltage) in turn, it can effectively avoid threshold voltage shift and improve working life. the

Description of drawings

Fig. 1 is a circuit diagram showing a known photosensor, and Fig. 2 is a timing diagram showing signals input to the photosensor of Fig. 1;

Figure 3 is a circuit diagram showing another known photosensor design;

Fig. 4 is the circuit diagram of the light sensor according to an embodiment of the present invention, and Fig. 5 is the timing diagram of the signal of inputting the light sensor of Fig. 4;

Fig. 6 is a schematic diagram illustrating the potential change of the first capacitor;

Fig. 7 is a schematic diagram of a processing unit according to an embodiment of the present invention;

Figure 8 is a circuit diagram of an optical sensor according to another embodiment of the present invention, and Figure 9 is a timing diagram of a signal input to the optical sensor of Figure 8;

FIG. 10 is a circuit diagram of a light sensor according to another embodiment of the present invention. the

Reference number

10, 20, 30 light sensors 12 processing units

14 Amplifiers 16 Analog-to-Digital Converters

32 sensing circuit 34 reference voltage generation circuit

36 processing units 100, 200 light sensors

202 sensing circuit 204 reference voltage generation circuit

206 processing unit BM shading element

C1-C4 capacitor n1 node

Q1-Q6 Transistor T1-T8 Transistor

ΔV1 reference voltage ΔV2 photovoltage

VDD first voltage VGG second voltage

VDC third voltage VGH positive gate voltage

VGL negative gate voltage Vref reference voltage

Vout output light voltage READ reading signal

RESET reset signal SELECT selection signal

STV scan start signal SWITCH switch signal

SAMPLE sampling signal

Detailed ways

The design of the light sensor according to the preferred embodiment of the present invention will be described below with reference to the related drawings, wherein the same components will be described with the same reference numerals. the

Fig. 4 is a circuit diagram of the light sensor 10 according to an embodiment of the present invention, and Fig. 5 is a timing diagram of signals input to the light sensor 10 of Fig. 4, according to the design of this embodiment, because the light sensor 10 is arranged on a display device ( (not shown) to sense ambient light brightness, so the voltage source of the light sensor 10 can be, for example, a gate driver IC (gate driver IC) that provides the scanning voltage of the display device. As shown in Figure 4, the light sensor 10 includes a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4, a fifth transistor T5, a first capacitor C1, a second capacitor C2 and a third capacitor C3. The gate of the first transistor T1 is connected to a scan start signal STV, its drain is connected to a first voltage, and its source is connected to a second voltage and the first capacitor C1. The first and second voltages can be, for example, respectively A positive gate voltage VGH and a negative gate voltage VGL of a gate driver IC. The gate of the second transistor T2 is connected to a reset signal RESET, and the drain thereof is connected to the source of the first transistor T1. The drain of the third transistor T3 is connected to the source of the second transistor T2, the source is connected to the negative gate voltage VGL, and the gate is connected to the source of the first transistor T1 and the first capacitor C1. A gate of the fourth transistor T4 is connected to a sampling signal SAMPLE, a drain thereof is connected to the first capacitor C1 , and a source thereof is connected to the second capacitor C2 . The gate of the fifth transistor T5 is connected to a read signal READ, the drain is connected to the source of the first transistor T1 and the first capacitor C1 , and the source is connected to the third capacitor C3 . the

The first transistor T1 has a photosensitive layer (not shown), which generates charge carriers when it receives a certain amount of ambient light, and the charge carriers move due to the voltage difference between the drain and source of the first transistor T1 to generate The photocurrent I, the magnitude of the photocurrent I depends on the amount of light received. Please refer to FIG. 4 and FIG. 5 at the same time. When the scan start signal STV is at a high level, the first transistor T1 is turned on. At this time, the positive gate voltage VGH is charged to the first capacitor C1 through the first transistor T1 . Then when the reset signal RESET is at a high level, the second transistor T2 is turned on, and at this time the third transistor T3 is also turned on so that the electric quantity stored in the first capacitor C1 is discharged through the third transistor T3, so that the potential of the first capacitor C1 will be down to be equal or almost equal to the threshold voltage of the third transistor T3. Then when the read signal READ is at a high level, the fifth transistor T5 is turned on and the output of the fifth transistor T5 is converted into the potential difference of the third capacitor C3, so the reference voltage Vref can be taken out by the third capacitor C3, at this time the reference voltage Vref That is, the threshold voltage of the third transistor T3. Because the threshold voltage of different transistors T3 may be slightly different, the design of using the threshold voltage of the third transistor T3 as the reference voltage Vref can obtain the most suitable adjustment for the characteristics of each transistor T3. The reference voltage Vref is used for the effect of the light sensor 10 . On the other hand, when the reset signal RESET is at a low level, the second transistor T2 is turned off, so at this time the potential of the first capacitor C1 gradually rises as the photocurrent I flows to the first capacitor C1 to charge the first capacitor C1, and at this time The reference voltage Vref remains fixed. Therefore, when the sampling signal SAMPLE is at a high level, the fourth transistor T4 is turned on at this time and the output of the fourth transistor T4 is converted into the potential difference of the second capacitor C2, so the second capacitor C2 can take out the potential difference after being irradiated by ambient light. The photovoltage Vout, at this time, the photovoltage Vout is the potential of the first capacitor C1 after being charged and changed by the photocurrent I. the

The potential change of the first capacitor C1 is shown in Figure 6. It can be clearly seen from Figure 6 that through the coordinated auto-zero discharge action of the second transistor T2 and the third transistor T3, the potential of the first capacitor C1 can be determined by The positive gate voltage VGH drops to be equal to or close to the threshold voltage of the third transistor T3, and the threshold voltage can be output as a fixed reference voltage Vref. Afterwards, the potential of the first capacitor C1 gradually rises with ambient light irradiation, and the finally sampled output photovoltage Vout and the reference voltage Vref have a potential difference ΔV. As shown in FIG. 7 , the processing unit 12 receives the output photovoltage Vout and the reference voltage Vref to generate an output signal corresponding to the difference between the photovoltage and the reference voltage. In detail, the processing unit 12 includes an amplifier 14 and an analog-to-digital converter (ADC) 16. The difference ΔV between the sampled and measured output photovoltage Vout and the reference voltage Vref is amplified by the amplifier 14, and is then amplified by the analog-to-digital converter. 16 is converted into a digital luminance control signal, and then the backlight luminance is adjusted according to the value of the luminance control signal, so as to meet the requirements of providing a good display effect and reducing power consumption at the same time. the

Through the design of the above-mentioned embodiment, each time the photosensor 10 performs a reset action, the storage capacitor voltage can drop to the threshold voltage of the third transistor T3 through the auto-zero discharge action of the reset circuit. (reference voltage), and then increase gradually with the light, so that the light sensor 10 can obtain a larger output photovoltage variation range relative to the reference voltage. Furthermore, since the output photovoltage and the reference voltage are taken out by the same circuit, the number of circuit components and layout area can be effectively reduced to save cost. On the other hand, the light-sensing transistor (the first transistor T1) generally operates in the negative voltage range, because the current characteristics in this range are better, but under the condition of negative bias for a long time, there will be obvious threshold The phenomenon of voltage shift (threshold voltage shift) is easy to cause damage. Therefore, in this embodiment, the gate bias signal is designed to be triggered once in a frame period, so that the first transistor T1 is subjected to positive bias (positive gate voltage VGH) and negative bias (lighting voltage) in turn, so that It can effectively avoid the generation of threshold voltage shift. the

FIG. 8 is a circuit diagram of a light sensor 20 according to another embodiment of the present invention, and FIG. 9 is a timing diagram of signals input to the light sensor 20 of FIG. 8 . Please refer to FIG. 8 and FIG. 9 at the same time. In this embodiment, the gate of the fifth transistor T5 and the source of the third transistor T3 are simultaneously connected by the read signal READ, so that the third transistor can be activated when the read signal READ is at a high level. T3 is turned off. the

FIG. 10 is a circuit diagram of an optical sensor 30 according to another embodiment of the present invention. The timing diagram of signals input to the optical sensor 30 in FIG. 10 may be similar to that in FIG. 9 . As shown in FIG. 10 , the light sensor 30 includes a sensing circuit 32 , a reference voltage generating circuit 34 and a processing unit 36 . The sensing circuit 32 includes a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4, a first capacitor C1 and a second capacitor C2. An input terminal of the first transistor T1 is connected to the positive gate voltage VGH, a control terminal thereof is connected to a scan start signal STV, and an output terminal thereof is connected to the first capacitor C1. The input end of the second transistor T2 is connected to the output end of the first transistor T1, and the control end of the second transistor T2 is connected to a reset signal RESET. The input end of the third transistor T3 is connected to the output end of the second transistor T2, the control end of the third transistor T3 is connected to the first capacitor C1, and the output end of the third transistor is connected to the negative gate voltage VGL. The input end of the fourth transistor T4 is connected to the first capacitor C1, the control end thereof is connected to the read signal READ, and the output end thereof is connected to the second capacitor C2. The reference voltage generating circuit 34 includes a fifth transistor T5, a sixth transistor T6, a seventh transistor T7, an eighth transistor T8, a third capacitor C3 and a fourth capacitor C4. The circuit connection relationship of the reference voltage generating circuit 34 is similar to that of the sensor circuit 32, so it will not be described again here. The main difference between the two is that the reference voltage generating circuit 34 is additionally provided with a light blocking member (light blocking member) BM to shield the first The five-transistor T5 protects it from external light. On the contrary, the first transistor T1 of the sensing circuit 32 is irradiated by external light and generates a photovoltage corresponding to the amount of received light. Therefore, the sensing circuit 32 can output the photovoltage Vout corresponding to the amount of received light, the reference voltage generating circuit 34 can output a fixed reference voltage Vref, and the processing unit 36 receives the photovoltage Vout and the reference voltage Vref to generate a difference corresponding to the two. An output signal of value. The processing unit 36 may, for example, include an amplifier 14 and an analog-to-digital converter (ADC) 16 as shown in FIG. 7 . In this embodiment, the second transistor T2 and the third transistor T3 of the sensing circuit 32 also respond to the reset signal RESET to perform the aforementioned auto-zero discharge operation to provide an initial photovoltage, and refer to The sixth transistor T6 and the seventh transistor T7 of the voltage generating circuit 34 also respond to the reset signal RESET to perform an automatic zero-return discharge operation to provide an initialization reference voltage. the

The above descriptions are illustrative only, not restrictive. Anyone skilled in the art can make equivalent modifications based on the above-mentioned embodiments of the present invention without departing from its spirit and scope. Therefore, any equivalent modification or change without departing from the spirit and scope of the present invention shall be included in the appended claims. the

Claims (15)

1. A light sensor for a display device, characterized in that the light sensor comprises: A photoreceiver which receives external light and generates a photovoltage corresponding to the amount of received light, the photoreceiver comprising a first transistor having a photosensitive layer, and a device for converting the output of the first transistor into said photovoltage a first conversion unit; A reset unit, which responds to a reset signal to provide an initialized reference voltage, the reset unit includes a second transistor and a third transistor connected to each other, the control terminal of the second transistor is connected to the reset signal and the control end of the third transistor is connected to the first conversion unit, and when the second transistor is turned on, the first conversion unit discharges through the third transistor to obtain the initialization reference voltage; and A sampling unit, which responds to a sampling signal to output the photovoltage corresponding to the received light amount, the sampling unit includes a fourth transistor that responds to the sampling signal, and a fourth transistor that converts the output of the fourth transistor into the photovoltage the second conversion unit, Wherein the input end of the first transistor is connected to a positive gate voltage, the control end of the first transistor is connected to a scan start signal, and the output end of the first transistor is connected to the first switching unit; the input end of the second transistor is connected to the output end of the first transistor, the input end of the third transistor is connected to the output end of the second transistor; the input end of the fourth transistor The terminal is connected to the first conversion unit, the control terminal of the fourth transistor is connected to the sampling signal, and the output terminal of the fourth transistor is connected to the second conversion unit. 2. The light sensor according to claim 1, wherein the first and the second conversion units are respectively a capacitor. 3. The light sensor according to claim 1, wherein the output terminal of the third transistor is connected to a negative gate voltage. 4. The light sensor as claimed in claim 1, wherein the reference voltage is substantially a threshold voltage of the third transistor. 5. The optical sensor according to claim 1, wherein the optical sensor further comprises a reference voltage output unit, the reference voltage output unit responds to a read signal to output the reference voltage, and includes a response to the read signal a fifth transistor and a third conversion unit for converting the output of the fifth transistor into the reference voltage. 6. The light sensor according to claim 5, wherein the third converting unit is a capacitor. 7. The light sensor according to claim 5, wherein the input end of the fifth transistor is connected to the first conversion unit and the output end of the first transistor, and the fifth transistor The control end of the fifth transistor is connected to the read signal, and the output end of the fifth transistor is connected to the third conversion unit. 8. The light sensor according to claim 5, wherein the read signal is connected to the output terminal of the third transistor. 9. The optical sensor according to claim 1, wherein the optical sensor further comprises a processing unit, and the processing unit receives the photovoltage and the reference voltage to generate a corresponding An output signal of the difference between the photovoltage and the reference voltage. 10. A light sensor for a display device, characterized in that the light sensor comprises: A sensing circuit, the sensing circuit includes: A first photoreceiver which receives external light and generates a photovoltage corresponding to the amount of received light, the first photoreceiver includes a first transistor having a photosensitive layer, and converts the output of the first transistor into the A first conversion unit of the photovoltage; A first reset unit, which responds to a first reset signal to provide an initialized photovoltage, the reset unit includes a second transistor and a third transistor electrically connected to each other, the second transistor The control terminal is connected to the first reset signal and the control terminal of the third transistor is connected to the first conversion unit, and when the second transistor is turned on, the first conversion unit passes through the Discharging the third transistor to obtain the initialized photovoltage; and A first reading unit, which responds to a first reading signal to output the photovoltage corresponding to the amount of received light, the first reading unit includes a fourth transistor responding to the first reading signal, and the The output of the fourth transistor is converted into a second conversion unit of the photovoltage; A reference voltage generation circuit, the circuit includes: A second photoreceiver, which is shielded from external light to generate a reference voltage, the second photoreceiver includes a fifth transistor, and a third transistor that converts the output of the fifth transistor into the reference voltage conversion unit; A second reset unit, which responds to a second reset signal to provide an initialized reference voltage, the second reset unit includes a sixth transistor and a seventh transistor electrically connected to each other, the sixth The control end of the transistor is connected to the second reset signal and the control end of the seventh transistor is connected to the third conversion unit, and when the sixth transistor is turned on, the third conversion unit passes through the seventh Discharging the transistor to obtain the initialized reference voltage; and A second reading unit, which responds to a second reading signal to output the reference voltage, the second reading unit includes an eighth transistor responding to the second reading signal, and the eighth transistor a fourth conversion unit whose output is converted into the reference voltage; and a processing unit, receiving the photovoltage and the reference voltage to generate an output signal corresponding to the difference between the photovoltage and the reference voltage, Wherein the input end of the first transistor is connected to a positive gate voltage, the control end of the first transistor is connected to a scan start signal, and the output end of the first transistor is connected to the first conversion unit; The input end of the second transistor is connected to the output end of the first transistor, the input end of the third transistor is connected to the output end of the second transistor; the input end of the fourth transistor is connected to the first conversion unit, the control end of the fourth transistor is connected to the read signal, and the output end of the fourth transistor is connected to the second converting unit. 11. The light sensor as claimed in claim 10, wherein the reference voltage generating circuit further comprises a light-shielding element to shield the fifth transistor from external light. 12. The light sensor according to claim 10, wherein the first, second, third and fourth converting units are respectively a capacitor. 13. The light sensor as claimed in claim 10, wherein the output terminal of the third transistor is connected to a negative gate voltage. 14. The light sensor according to claim 10, wherein the input end of the fifth transistor is connected to a positive gate voltage, the control end of the fifth transistor is connected to a scan start signal, and the The output terminal of the fifth transistor is connected to the third conversion unit; the input terminal of the sixth transistor is connected to the output terminal of the fifth transistor, and the input terminal of the seventh transistor is connected to the The output terminal of the sixth transistor, and the output terminal of the seventh transistor is connected to a negative gate voltage; the input terminal of the eighth transistor is connected to the third conversion unit, and the control of the eighth transistor The terminal is connected to the read signal, and the output terminal of the eighth transistor is connected to the fourth conversion unit. 15. The light sensor according to claim 10, wherein the processing unit comprises an amplifier for amplifying the voltage difference and an analog for converting the voltage difference into a digital brightness control signal digitizer.

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