KR20090071401A - Display Devices with Amibient Light Sensing - Google Patents

Abstract

A display device with ambient light sensing is provided to change the brightness of a black light by controlling a pulse width and a pulse period of the output of the lighting source. A first signal based on the surrounding optical level under a first lighting source driving condition by using an optical sensor. A second signal based on the surrounding optical level under a second light source driving condition is generated by using the optical sensor(30) arrangement. The difference of the optical sensor is compensated by processing a first and a second signal when they are operated under the first and the second light source driving condition.

Description

Display devices with Amibient Light Sensing

The present invention relates to a display device for modulating light therefrom using an illumination light source. This application claims the priority of US patent application Ser. No. 61 / 016,605, filed December 26, 2007, which states that all of the content is incorporated in this application.

Liquid crystal displays are the most common example of this type of modulating display device, and typically include an active plate and a passive plate with a liquid crystal material interposed therebetween. The active plate includes an array of transistor switching devices, usually one-to-one associated with this transistor and the pixels of the display. Each pixel is also associated with a pixel electrode on an active plate, to which the pixel electrode is applied a signal that controls the brightness of the individual pixel.

The level of ambient light greatly affects the performance of the display device used to modulate the light source.

As is known, information from light sensors can be used to alter the behavior of the display to improve the performance of the display. For example, you can adjust the display's backlight intensity based on information from an optical sensor that can detect the characteristics of the ambient light to reduce the power consumption of the display at low ambient light levels, while maintaining high quality at high ambient light levels. It can produce output.

The optical sensors required for this can be formed as part of an active plate using thin film technology, which is a convenient way to add optical sensor functionality without the need for additional processes or separate components. Examples of photosensitive devices may be thin film transistors, thin film diodes, lateral diodes or photoresist.

However, if the display device uses an illumination light source (which can be a backlight or a front light), it can be difficult to optically isolate the light sensor from this light source.

Referring to FIG. 1 showing this problem, the display system has a display 10, a backlight 12, an optical sensor 14 and a control circuit 16 for driving the display and the backlight. The signal may be supplied from the photosensor 14 to the control circuit 16 to vary the operation of the display and backlight according to the change in illumination detected by the control circuit.

There are two contributions to the output signal of the sensor 14, the light component 20 generated in the ambient light 18 and the backlight 12 in front of the display. In order to properly adjust the behavior of the display and backlight, it is necessary to distinguish the light from these two sources.

WO 20007/069107 discloses a system which enables the measurement of both ambient light level and backlight output level using a light sensor.

2 briefly illustrates how the optical sensor can be integrated into a display. In this example, the display consists of a liquid crystal layer 28 sandwiched between two glass substrates 24, 26. In this example, the photosensors are arranged in an array of photosensor elements 30, made on the lower substrate 26 closest to the backlight 42 or backlight light guide of the display. The optical sensor may be a thin film diode, thin film transistor or other photosensitive device. Ambient light from the front of the display may pass through the upper substrate 24 and the liquid crystal layer 28 to reach the photosensor 30.

The sensor may also receive ambient light modulated by the display pixels after passing through the display as shown by the illustrated optical path 31. The sensor may also receive light that has passed through the lower substrate 26, starting from the backlight of the display, as represented by light paths 32 and 34.

When measuring ambient lighting, the components added from the ambient light and backlight modulated to the output signal are undesirable and should be minimized and ideally eliminated.

Blocking the straight light path from the backlight to the light sensor is possible by providing an opaque layer to the base of the thin film layers forming the light sensor, for example. However, light starting from the backlight will be reflected or induced in the substrates of the display and eventually reach the sensor through indirect paths. This indirect path 32 and direct path 34 are also shown.

For the sake of completeness, the photomask layer 36 is shown in FIG. 2. It is known to use a black mask layer to shield areas of the active plate through which unmodulated light can pass, and also to shield transistors because of their light dependent operating characteristics. Top and bottom polarizers 38 and 40 are also shown. The black mask layer has openings that allow ambient light to reach the sensor 30.

The photosensors may be integrated into the display pixels or provided with a few photosensor devices at the edge of the pixel array.

Another problem faced when integrating the ambient light sensor into the display substrate is that the ambient light level varies so widely that it exceeds 100,000 lux in direct sunlight and only a few lux at night or in a dark room. In low light level measurements, the leakage current (dark current) of a photodiode or phototransistor is a source of serious error. In the case of LCDs, at low and medium levels of light, the light from the backlight or front light can significantly alter the output signal of the sensor, preventing ambient light level measurements.

This can be avoided by turning off the backlight or front light during the measurement, but at high levels of ambient light, the light source should be operated continuously to maximize display brightness.

Under these different conditions, measuring ambient light levels requires a change in the measurement method. This creates a discontinuity in the output of the measurement when the measurement type changes.

According to the present invention, there is provided a method of controlling a display device comprising a display modulator for modulating light provided by an illumination light source, said method using ambient light in a first illumination light source driving condition using an array of photosensors. Generating a first signal based on the level; Generating a second signal based on the ambient light level in a second illumination light source driving condition different from the first illumination light source driving condition using the photosensor heat; Compensation for covering the first and second illumination light source driving conditions by processing the first and second signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. Inducing thermal sensor thermal characteristics; And controlling the display device using the detected light level based on the light level detected by the light sensor row based on the compensated light sensor thermal characteristic.

In this method, light sensors are used to measure ambient light, and the measurement is performed with two or more types of measurement under different illumination light source driving conditions. For example, these types make it dependent on the intensity of the ambient light. Compensated optical sensor characteristics (ie, one model of the transfer function) are generated to ensure continuity in the measurement output when moving from one type of measurement to another. To achieve this, compare the results measured using the types and add the correction by the difference.

The control of the display device preferably includes the step of controlling the illumination light source, and a number of known control techniques can be applied according to the accurate determination of the ambient light level.

The first illumination light source driving condition may include an on state of the illumination light source, and then the second illumination light source driving condition may include an off state of the illumination light source.

Preferably, generating the signal in the first and second driving conditions comprises (in each case) detecting the light level with a first optical sensor exposed to ambient light at the output position of the display; Detecting an optical level with a second optical sensor more shielded from ambient light than the first optical sensor; And inducing ambient light levels by processing signals generated by the first and second photosensors.

Thus, each photosensor signal already compensates for the unwanted illumination reaching the sensor. This is possible because the relative contributions of unwanted illumination are made similar for the two sensors while the desired ambient light component to be measured has a large difference. Thus, this processing involves subtracting the signal generated by the second sensor from the signal generated by the first sensor to derive an ambient light level.

The compensation procedure includes linearly shifting the optical sensor thermal response characteristic in one of the plurality of illumination light source driving conditions to remove discontinuities between the optical sensor thermal response characteristics for the two illumination light source driving conditions. This creates a single continuous linear relationship.

In a preferred embodiment, the method of controlling the display device further comprises: generating a third signal based on a second ambient light level in the first illumination light source driving condition using the photosensor heat; Generating a fourth signal based on the second ambient light level under the second illumination light source driving condition using the photosensor heat; And processing the first to fourth signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions to cover the first and second illumination light source driving conditions. Inducing a compensated optical sensor thermal characteristic.

In this case, additional sensor measurement means that the compensation procedure linearly shifts and changes the slope of the optical sensor thermal response characteristic in one of the illumination light source driving conditions, thereby reducing the It may include the step of removing the discontinuity and the gradient change between the optical sensor thermal response characteristics.

The present invention also provides a computer program comprising computer program code means adapted to perform this method.

The present invention also provides a display device comprising an illumination light source, a display modulator, an optical sensor array, and a processor.

The display modulator modulates the light provided by the illumination light source. The light sensor train generates a signal based on the ambient light level and the illumination light source. The processor is configured to generate a first signal based on an ambient light level in a first illumination light source driving condition using the photosensor row; Generate a second signal based on the ambient light level at a second illumination light source driving condition different from the first driving condition using the photosensor row; Compensation for covering the first and second illumination light source driving conditions by processing the first and second signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. Induce thermal sensor thermal characteristics; Based on the compensated optical sensor thermal characteristic, the display device is controlled using the detected optical level based on the optical level detected by the optical sensor thermal.

The following description is an aspect considered to be optimal for practicing the present invention. This description is intended to explain the general principles of the invention and should not be construed in a limiting sense. The scope of the invention may best be determined by reference to the claims.

Like reference symbols in the various drawings indicate like elements, and repeated descriptions are omitted.

The present invention provides a display device in which light measurement is performed using two or more measurement types that differ in illumination light source driving conditions. The processing of the optical sensor signal is done in such a way that the compensated optical sensor characteristics (ie, one model of the transfer function) ensure the continuity of the output of the measurement when moving from one type of measurement to another.

As described above, when measuring ambient light, additional components from the modulated ambient light and backlight should be eliminated.

One way to do this is to introduce a second sensor that has a sensitivity different from the ambient light level but similar to the unwanted component of the light.

Such an arrangement is shown in FIG. 3. The arrangement of sensors 30 includes a first sensor A that is exposed to ambient light while the second sensor B is below the liquid crystal layer rather than the top of the light masking layer 36 (in this example, FIG. 2 in this example). Visible) and its output contains much less contribution from ambient light as compared to the first sensor (A).

It is advantageous to match the sensor characteristics well so that the sensors can be arranged in the Common Centroid Layout of FIG. 3. The second sensor B has the same area as the first sensor A but is divided into two equivalent parts B1 and B2 located on both sides of the first sensor A. FIG.

Output signals of the sensor A and the sensor B can be described by Equations 1 and 2, respectively.

S ₁ = k ₁₁ L _A + k ₁₂ k _M L _A + k ₁₃ L _B + k ₁₄ L _D

S ₂ = k ₂₁ L _A + k ₂₂ k _M L _A + k ₂₃ L _B + k ₂₄ L _D

L _A is the ambient light level.

k ₁₁ and k ₂₁ represents a sensitivity to ambient light of the first and second sensors, and calculates the efficiency of converting the amount of ambient light reaching the sensor and the light reaching the sensor to generate an output signal.

k ₁₂ k ₂₂ represents the sensitivity of the two sensors to modulated ambient light.

k _M represents the modulation of the ambient light by the display pixels and varies with the displayed image.

L _B is the backlight brightness.

k ₁₃ and k ₂₃ represents the sensitivity of the two sensors to the backlight.

L _D is a numerical value expressing the background signal of the sensor, for example, the dark current of the photodiode, with a corresponding luminous intensity.

k ₁₄ k ₂₄ converts the background signal intensity value into the influence on the sensor signal output.

When measuring the ambient light level, L _A represents the desired signal and k _M L _A , L _B and L _D are factors in the unwanted components of the sensor output. When designing two sensors, their output contains a causative component that is significantly different from the desired signal and a causal component similar to the unwanted signal component, thereby subtracting the output of one sensor from the other to produce The difference value can be made large.

Equation 3 that can represent this shows the difference between the output signal of the sensor 1 and the sensor 2.

S ₁ -S ₂ = (k ₁₁ -k ₂₁ ) L _A + (k ₁₂ -k ₂₂ ) k _M L _A + (k ₁₃ -k ₂₃ ) L _B + (k ₁₄ -k ₂₄ ) L _D

In the design of the sensor

If k ₁₁ is made much larger than k ₂₁ , k ₁₂ is approximately equal to k ₂₂ , k ₁₃ is approximately equal to k ₂₃ , and k ₁₄ is approximately equal to k ₂₄ , the desired component of the resulting signal is increased relative to the unwanted component. Can be. In an ideal case, when k ₁₂ equals k ₂₂ , k ₁₃ equals k ₂₃ , and k ₁₄ equals k ₂₄ , the unwanted components are removed and result in equation (4).

S ₁ -S ₂ = (k ₁₁ -k ₂₁ ) L _A

Subtracting unwanted signals in this way is effective, provided that the unwanted signal components are not too large for the ambient light components. If the ambient light level is low or medium, for example 5000 lux below, L _B is L _A Can be much larger than In practical situations, k ₁₃ is unlikely to be the same as k ₂₃ , so the measurement of ambient light can be significantly affected by the backlight.

This problem can be overcome by measuring the ambient light with the backlight off. This has a good effect on low level ambient light, since pulse width modulation is usually used to control the brightness of the backlight so that ambient light measurements can be made in one of the backlight off periods. However, at high levels of ambient light, the backlight should be operated at 100% operating rate to provide the highest brightness. Under these circumstances, ambient light level measurements should be made with the backlight on.

The result of this is shown in FIG. This shows the degree to which the difference signals between the two sensors S ₁ -S ₂ depend on the ambient light level. Plot 50 occurs when the measurement is taken with the backlight off at low level ambient light. Plot 52 appears with backlight on at high level ambient light.

When the backlight is off, L _B is 0, so the measured output signal may be approximated by Equation 4 above. However, when the backlight is on, the output component caused by the backlight is large L _B. Because of the value, it cannot be ignored and therefore the signal is represented by Equation 5 below.

S ₁ -S ₂ = (k ₁₁ -k ₂₁ ) L _A + (k ₁₃ -k ₂₃ ) L _B

This difference in output signal depending on which type of measurement is used may cause problems when the output signal controls the operating area of the display, for example, the brightness of the backlight. In the manufacture of a display, calibration parameters can be measured and stored in the display module, but over time the light output of the backlight changes and therefore the calibration parameters must be periodically remeasured.

The present invention provides an automatic calibration of the optical sensor upon switching the measurement type. There is a range of ambient light levels in which both types of measurements are available at the time of measurement as shown in FIG. This is area 54. By using the value of one measurement at the backlight off and comparing it with the value of the measurement at the backlight on, it is possible to calculate the calibration parameters required to remove the output signal components resulting from the backlight.

For example, as shown in FIG. 5, the measurement values D _M1 and D _M2 obtained under the same ambient light conditions can be used for calculation of calibration parameters. The output signal of the sensors is linearly dependent on the ambient light level. In the simplest case, it can be estimated that linear dependence produces an offset in the sensor's output signal characteristic when measured at backlight on, but the characteristic slope will not change.

Dotted line 60 shows a plot of the measurements made with backlight on after the calibration was made.

The calibration parameter k _O can be defined as one that can be added to the results of one measurement at the backlight on, to provide a result consistent with the measurement at the backlight off. This is shown in equations (6) and (7).

k _O = D _M1 -D _M2

Post-Calibration = Pre-Calibration + k _O

Although the procedure for calculating these calibration parameters has been described in the form of individual measurements, in practice it is highly likely that processing or filtering the sensor output will reduce the noise impact on the sensor output signal. Thus, the measurements D _M1 and D _M2 can also be regarded as the results generated by the processing group of samples of the sensor output obtained over substantially the same time.

If the slope of the sensor characteristic changes when the ambient light measurement type is switched, more complicated calibration is required. This may be the case when different sensors are used for the measurement at different high level ambient light, for example when smaller sensors are used for the higher level ambient light measurement.

In this case, there must be at least four measurement results to know the slope ratio k _S of the characteristics for the two measurement types. This calculation is shown in Equation 8:

Measurements should be made at two different ambient light level values that fall within the range in which both types of measurement are available. The need for two measurements is needed to determine the difference k _O at the offsets of the two measurements, as shown in Equation 9:

k _O = D _M1A -k _S D _M2A

Measurements made with the backlight on measurement type can now be calibrated according to equation (10).

Measurement after calibration = k _S x Measurement before calibration + k ₀

Calibration parameters can be stored and changed when the display is operated in various ambient light conditions that require a change in measurement type over time. When the display is not in use, the current average of the calibration parameters is established and stored so that the parameters are ready until the next time the display is turned on. If the calibration parameters were not stored at display off, they can be incorporated into the display's startup sequence to make the necessary measurements in the backlight off and on states to determine the calibration parameters when the display is turned on.

Specific examples of measurement types have been described when the display backlight is off or on. However, other types of measurement may be implemented in the present invention that require correction upon switching from one type to another to generate an ambient light level indication signal without discontinuities.

7 illustrates the method of the present invention as a flow of processing steps.

In step 70, the backlight is on. In step 72 a first set signal is obtained from the photosensor column in the region of ambient light levels which takes the signal on and back light on and off both on and off.

In step 74, in the backlight off, step 76, a second set signal is obtained from the photosensor row for the same ambient light level (i.e., when the ambient light has not changed since it is close enough in time) with the backlight off.

In step 78, the first and second set signals are processed and corrected optical sensor thermal characteristics are derived to cover the first and second illumination light source driving conditions.

In step 80, the display device is controlled using the measured detection light level. The corrected characteristic can be updated regularly, for example whenever the ambient light level is within the correct range.

In the above description, for the sake of clarity, the illuminating light source is illustrated as a backlight, but there is also a front-illumination display system and the invention is of course applied to such a display.

The present invention can be implemented using the display design shown in Figs. 1 and 2, and provides one other method for processing signals of a plurality of optical sensors, which method comprises a control circuit for backlight control and calculation processing (16). ).

The optical sensor is preferably an integrated thin film device formed using a thin film layer, such as for the manufacture of display pixel arrays, the arrangement of the optical sensors being an array of optical sensor elements, wherein the optical sensor elements are integrated one-to-one with the display pixels or Can be arranged along the perimeter.

The invention can be used in the implementation of LCDs or other light modulating displays with back or front illumination, and through the control of the illumination source there is a smooth transition between the response of the photosensor heat, especially between types of operation such as backlight on and backlight off. can do.

The information obtained about the ambient light can be used in a known manner to adjust the backlight (or other light source) output to realize electrical saving in dark ambient light conditions and to ensure good image visibility in bright ambient light conditions.

In the above example, the computational output may be used to control the illumination light source of the display but instead or additionally the output may be controlled in other parts of the display operation, such as the brightness, contrast or gamma setting of the display, or the refresh frequency. Can be used to change the

One way to perform the calculations needed to process the light sensor signal is by computer program, but the same method can be implemented in analog or digital circuits.

In the simplest case, the averaging of the measurement output can be achieved by integrating the output obtained at the photosensitive device for some predetermined number of measurements. This integration can be done in the optical sensor circuit, for example by integrating the photodiode's output current into a capacitor during the selected measurement period. Each capacitor can be used for different driving conditions of the illumination light source. For example, when the backlight is on and off, individual capacitors can be used to integrate the photodiode current during each measurement.

The voltages established at the two capacitors then represent the sum of the measurements corresponding to each aspect of the backlight.

Also available are complex calculations that take as input a sequence or set of measurements sampled over time with different illumination light source driving conditions. 5 and 6 are therefore only possible examples of processing schemes that may be implemented. Moreover, the relationship between the light sensor output and the brightness level has been shown to be completely straight. It is not necessary to do this and the invention applies to other transfer functions. Always the best match occurs in the overlap between two transfer functions, providing a single transfer function that is actually combined.

If the duration of the measurements differs by type, the output of the two measurements can be scaled to account for different integration periods and the equations can be changed accordingly.

As described above, the brightness of the backlight can be changed by adjusting the pulse width or the pulse period for a given pulse width of the illumination light source output with pulses.

The invention can be applied to many other types of displays with illumination light sources, such as transflective displays.

Various modifications will be apparent to those skilled in the art.

Although the present invention has been described as a preferred embodiment by way of example, it should be construed that the present invention is not limited to the disclosed embodiment. On the contrary, the intention is to cover all of the various modifications and similar arrangements apparent to those skilled in the art. Accordingly, the scope of the claims should be interpreted quite broadly to encompass all such variations and similar arrangements.

1 is known to control the backlight output level using photodetection, a plan view of a display that can be controlled to implement the method of the present invention,

2 is a cross sectional view of a known active matrix LCD which may be used in the display device of the present invention, using integrated optical sensors,

3 is a cross-sectional view of an active matrix LCD using a plurality of integrated optical sensors proposed in the present invention;

4 is a first graph showing the appearance of discontinuities in different sensing types,

5 is a second graph used to describe the first example of the optical sensor control method of the present invention;

6 is a third graph used to describe a second example of the optical sensor control method of the present invention;

7 is an illustration of the method of the present invention.

<Description of Symbols for Main Parts of Drawings>

10: display 12: backlight

14: optical sensor 16: control circuit

18: ambient light 20: light component

24, 26: glass substrate 28: liquid crystal layer

30: array of optical sensor elements 31: optical path

32: indirect path 34: direct path

36: photomask layer 38, 40: polarizer

42: backlight

Claims (10)

A method of controlling a display device comprising a display modulator for modulating light provided by an illumination light source, the method comprising: Generating a first signal based on an ambient light level at a first illumination light source driving condition using an array of photosensors; Generating a second signal based on the ambient light level in a second illumination light source driving condition different from the first illumination light source driving condition using the photosensor heat; Cover the first and second illumination light source driving conditions by processing the first and second signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. Inducing a compensated optical sensor thermal characteristic; And Controlling the display device using the detected light level based on the light level detected by the light sensor train based on the compensated light sensor thermal characteristic. Control method of a display device comprising. The method of claim 1, Controlling the display device comprises controlling the illumination light source, The first illumination light source driving condition includes an on state of the illumination light source, The second illumination light source driving condition is to turn off the illumination light source Control method of a display device comprising. The method of claim 1, The first illumination light source driving condition includes an on state of the illumination light source, The second illumination light source driving condition is to turn off the illumination light source Control method of a display device comprising. The method of claim 1, The generating of the signal in the first driving condition may include: Detecting a light level with a first optical sensor exposed to ambient light at an output position of the display; Detecting an optical level with a second optical sensor more shielded from ambient light than the first optical sensor; And Processing the signals generated by the first and second photosensors to derive ambient light levels, wherein the signals generated by the second sensors are subtracted from the signals generated by the first sensors to derive ambient light levels Steps to Control method of a display device comprising. The method of claim 1, The generating of the signal in the second driving condition may include: Detecting a light level with a first optical sensor exposed to ambient light at an output position of the display; Detecting an optical level with a second optical sensor more shielded from ambient light than the first optical sensor; And Processing the signals generated by the first and second optical sensors to derive ambient light levels, wherein the signals generated by the second sensor are subtracted from the signals generated by the first sensor to derive ambient light levels Steps Control method of a display device comprising. The method of claim 1, Processing the first and second signals may linearly shift the photosensor thermal response characteristic in one of the illumination light source driving conditions to cause the photosensor thermal response characteristics for the two illumination light source driving conditions. The optical sensor thermal response characteristics for the two illumination light source driving conditions by linearly shifting and changing the slope of the optical sensor thermal response characteristic in one of the illumination light source driving conditions by removing discontinuities therebetween. Steps to eliminate discontinuities and gradient changes between Control method of a display device comprising. The method of claim 1, Generating a third signal based on a second ambient light level in the first illumination light source driving condition using the photosensor heat; Generating a fourth signal based on the second ambient light level under the second illumination light source driving condition using the photosensor heat; And Cover the first and second illumination light source driving conditions by processing the first to fourth signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. Inducing a compensated optical sensor thermal characteristic The control method of the display device further comprising. The method of claim 1, And wherein said illumination light source is controlled to provide a desired output level using pulse width modulation control. A computer program comprising computer program code means, embodied in a computer readable medium, and when the program is run on a computer, Executing a method of controlling a display device comprising a display modulator for modulating light provided by an illumination light source, The control method of the display device, Generating a first signal based on an ambient light level at a first illumination light source driving condition using an array of photosensors; Generating a second signal based on the ambient light level in a second illumination light source driving condition different from the first illumination light source driving condition using the photosensor heat; Cover the first and second illumination light source driving conditions by processing the first and second signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. Inducing a compensated optical sensor thermal characteristic; And Controlling the display device using the detected light level based on the light level detected by the light sensor train based on the compensated light sensor thermal characteristic. Computer program included. As a display device, Illumination light source; A display modulator for modulating light provided by the illumination light source; An array of photosensors for generating signals based on ambient light levels and the illumination light sources; And A processor for processing signals received from the photosensor row Including, The processor, Generate a first signal based on an ambient light level in a first illumination light source driving condition using the photosensor heat; Generate a second signal based on the ambient light level at a second illumination light source driving condition different from the first driving condition using the photosensor row; Cover the first and second illumination light source driving conditions by processing the first and second signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. Derive the compensated optical sensor thermal characteristics; Control the display device using the detected light level based on the light level detected by the light sensor row based on the compensated light sensor thermal characteristic; The processor is further Generate a third signal based on a second ambient light level at the first illumination light source driving condition using the photosensor heat; Generate a fourth signal based on the second ambient light level in the second illumination light source driving condition using the photosensor heat; Cover the first and second illumination light source driving conditions by processing the first to fourth signals to compensate for the difference between the photosensor thermal response characteristics when operating in the first and second illumination light source driving conditions. A display device for inducing a compensated optical sensor thermal characteristic.

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