This application claims priority to Korean Patent Application No. 10-2008-0054328, filed on Jun. 10, 2008, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety are herein incorporated by reference.
1. Field of the Invention
The present invention relates to an analog-to-digital (“A/D”) converter, a display device including the A/D converter, and a driving method of the display device, and more particularly, to an A/D converter which can be easily implemented and can increase an input dynamic range, a display device including the A/D converter, and a driving method of the display device.
2. Description of the Related Art
A liquid crystal display (“LCD”) includes an LCD panel consisting of a first substrate having pixel electrodes, a second substrate having a common electrode, and a liquid crystal layer having dielectric anisotropy interposed between the first and second substrates. In the LCD, an electric field is created between the pixel electrode and the common electrode, and the intensity of the electric field is adjusted, thereby controlling the orientation of liquid crystal molecules in the liquid crystal layer to control the amount of light passing through the LCD panel, thereby obtaining desired images. The LCD is not a self-emitting device. Hence, it may require a light source to provide back light to the LCD panel.
Methods for adjusting the luminance of back light according to the ambient light that is externally supplied have recently been developed in order to reduce power consumption of a backlight unit. Meanwhile, in order to improve display quality, development is under way for adjusting the luminance of back light according to the image displayed on an LCD panel.
Such LCDs may include a photosensor for detecting the luminance of ambient light or back light. In addition, the LCDs may necessarily include an analog-to-digital converter for converting an output of the photosensor.
The present invention provides an exemplary embodiment of an analog-to-digital (“A/D”) converter which can be easily implemented and can increase an input dynamic range.
The present invention also provides an exemplary embodiment of a display device including an A/D converter which can be easily implemented and can increase an input dynamic range.
The present invention also provides an exemplary embodiment of a driving method of a display device including an A/D converter which can be easily implemented and can widen an input dynamic range.
The above and other aspects of the present invention will be described in, or will be apparent from, the following description of the exemplary embodiments.
According to one exemplary embodiment of the present invention, an A/D converter includes; a photocurrent integrator which integrates photocurrent and stores the integrated photocurrent in a feedback capacitor in the form of voltage, and a discharger which attenuates the voltage out from the photocurrent integrator in the form of an exponential function.
According to another exemplary embodiment of the present invention, a display device includes; an A/D converter which includes; a photocurrent integrator which integrates photocurrent and stores the integrated photocurrent in a feedback capacitor in the form of voltage, a discharger which attenuates the voltage out from the photocurrent integrator in the form of an exponential function, and a comparator which compares the voltage attenuated by the discharger with a reference voltage, a backlight unit which adjusts luminance of back light according to a time period wherein the attenuated voltage is greater than or equal to the reference voltage, and which outputs the same, and a display panel which receives the back light.
According to still another exemplary embodiment of the present invention, a driving method of a display device includes; integrating photocurrent and storing the integrated photocurrent in a feedback capacitor in the form of voltage, attenuating the voltage out from the photocurrent integrator in the form of an exponential function, and adjusting luminance of back light according to a time period wherein the attenuated voltage is equal to or greater than a reference voltage, and outputting the same.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.
It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including”, when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another elements as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Exemplary embodiments of the present invention are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present invention.
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
An exemplary embodiment of a display device and a driving method of the same according to the present invention will be described with reference to
Referring to
The display panel 300 includes a plurality of gate lines G1-Gk, a plurality of data lines D1-Dj, and a plurality of pixels PX. Each pixel PX is disposed at an intersection area of each of the gate lines G1-Gk and each of the plurality of data lines D1-Dj. Although not shown, the plurality of pixels PX may be divided into red subpixels, green subpixels, and blue subpixels, respectively.
Referring again to
The signal controller 700 receives first image signals R, G and B, external control signals Vsync, Hsync, Mclk, and DE, for controlling display of the first image signals R, G, and B, and the back light luminance level IL, and outputs a second image data signal IDAT, a data control signal CONT1, a gate control signal CONT2, and a light data signal LDAT.
In detail, the signal controller 700 may convert the first image signal R, G, B into a second image signal IDAT and output the same. In addition, the signal controller 700 may receive the back light luminance level IL, which is supplied from the light-emitting unit LB, compensate the light data signal LDAT according to the received back light luminance level IL and supply the compensated light data signal LDAT to the backlight driver 800.
In one exemplary embodiment, the signal controller 700 may be functionally divided into an image signal control unit 600_1 and a light data signal control unit 600_2. The image signal control unit 600_1 controls the image displayed on the display panel 300, while the light data signal control unit 600_2 controls the operation of the backlight driver 800. In one exemplary embodiment, the image signal control unit 600_1 and the light data signal control unit 600_2 may be physically separated from each other.
In detail, the image signal control unit 600_1 receives a first image signal R, G, B and outputs a second image signal IDAT corresponding to the received first image signal R, G, B. In one exemplary embodiment, the image signal control unit 600_1 may also receive external control signals Vsync, Hsync, Mclk, and DE, and generate a data control signal CONT1 and a gate control signal CONT2. Examples of the external control signals Vsync, Hsync, Mclk, and DE include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a main clock signal MCLK, and a data enable signal DE. In the present exemplary embodiment, the data control signal CONT1 is used to control the operation of the data driver 500, and the gate control signal CONT2 is used to control the operation of the gate driver 400.
In addition, the image signal control unit 600_1 may receive the first R, G, and B image signal R, G, B, output a representative image signal R_DB, and supply the same to the light data signal control unit 600_2. The image signal control unit 600_1 will be described below in more detail with reference to
The light data signal control unit 600_2 may receive the representative image signal R_DB and the back light luminance level IL and supply a light data signal LDAT to the backlight driver 800. The light data signal control unit 600_2 will be described below in more detail with reference to
The gate driver 400, provided with the gate control signal CONT2 from the image signal control unit 600_1, applies a gate signal to the gate lines G1-Gk. Here, the gate signal is composed of a combination of a gate-on voltage Von and a gate-off voltage Voff, which may be generated from a gate on/off voltage generator (not shown). The gate control signal CONT2 for controlling the operation of the gate driver 400 includes a vertical synchronization start signal instructing start of the operation of the gate driver 400, a gate clock signal controlling an output timing of the gate-on signal, an output enable signal that determines a pulse width of the gate-on voltage Von, etc. Although not shown in the drawing, alternative exemplary embodiments include configurations wherein the gate driver 400 may include a plurality of gate driving chips.
The data driver 500 receives the data control signal CONT1 from the image signal control unit 600_1 and applies a voltage corresponding to the second image signal IDAT to the data lines D1-Dj. In one exemplary embodiment, the voltage corresponding to the second image signal IDAT may be a voltage supplied from a gray voltage generator (not shown) according to grayscales of the second image signal IDAT. That is to say, the voltage may be obtained by dividing a driving voltage of the gray voltage generator according to the grayscales of the second image signal IDAT. The data control signal CONT1 includes signals for controlling the operation of the data driver 500. The signals for controlling the operation of the data driver 500 include a horizontal synchronization start signal for starting the operation of the data driver 500, an output enable signal that determining the output of an image data voltage, etc. Although not shown in the drawing, alternative exemplary embodiments include configurations wherein the data driver 500 may include a plurality of data driving chips.
The backlight driver 800 adjusts luminance of back light supplied from a light-emitting block LB in response to a light data signal LDAT. The luminance of back light supplied from the light-emitting block LB may vary according to a duty ratio of the light data signal LDAT. The internal structure and operation of the backlight driver 800 will later be described in more detail with reference to
The light-emitting block LB may include at least one light source and provides back light to the display panel 300. In one exemplary embodiment, the light-emitting block LB may include a light-emitting diode (“LED”), e.g., a point light source, as shown. However, alternative exemplary embodiments include configurations wherein the light source may be a line light source, or a surface light source. The luminance of back light supplied from the light-emitting block LB may be controlled by the backlight driver 800 connected to the light-emitting block LB.
The control signal generator 610 receives the external control signals Vsync, Hsync, Mclk, and DE and outputs the data control signal CONT1 and the gate control signal CONT2. In detail, exemplary embodiments of the control signal generator 610 may generate various signals, such as a vertical start signal STV for starting the operation of the gate driver 400 shown in
The image signal processor 620 may receive first image signals R, G and B and output second image signals IDAT corresponding to the received first image signals R, G and B. The second image signals IDAT may be signals converted from the first image signals R, G and B for improving display quality, for example, the first image signal R, G and B may be converted by overdriving. Overdriving and other methods for improving display quality would be well-known to one of ordinary skill in the art, and a detailed explanation about their operation will not be given herein.
The representative value determiner 630 determines a representative image signal R_DB displayed on the display panel 300. For example, the representative value determiner 630 may receive the first image signals R, G, and B and determine the representative image signal R_DB. In one exemplary embodiment, the representative image signal R_DB may be an average luminance value of the first image signals R, G, and B. Thus, the representative image signal R_DB may indicate an average luminance value of the image displayed on the display panel 300.
The luminance determiner 640 receives the representative image signal R_DB, determines a luminance R_LB of back light corresponding to the representative image signal R_DB, and outputs the luminance R_LB of back light to the luminance compensator 650. In one exemplary embodiment, the luminance determiner 640 may determine the luminance R_LB of back light using, a look-up table (not shown). Alternative exemplary embodiments include configurations wherein the luminance determiner 640 determines luminance R_LB of back light using alternative methods, as would be apparent to one of ordinary skill in the art.
The luminance compensator 650 receives the native luminance R_LB and the back light luminance level IL, and supplies compensated luminance R′_LB to the light data signal output portion 660. The luminance compensator 650 provides the light data signal output portion 660 with the compensated luminance R′_LB, which is compensated according to the luminance of ambient light. Here, the back light luminance level IL may be a value obtained by measuring the luminance of ambient light. In detail, in one exemplary embodiment, if the luminance of ambient light is low, the back light luminance level IL is a small value, while if the luminance of ambient light is high, the back light luminance level IL is a large value.
The luminance of back light can be adjusted depending on the luminance of ambient light by compensating the luminance R_LB using the back light luminance level IL, which varies according to the luminance of ambient light, e.g., light coming from external to the display 10. That is to say, if the luminance of ambient light is low, the luminance of back light is reduced, and if the luminance of ambient light is high, the luminance of back light is increased. In such a manner, the display quality can be improved and power consumption can be reduced.
Alternatively, the luminance compensator 650 provides the light data signal output portion 660 with the compensated luminance R′_LB, which is compensated according to the measured luminance of back light, e.g., light coming from the light-emitting block LB. In this exemplary embodiment, the back light luminance level IL may correspond to the measured luminance of back light. In detail, in one exemplary embodiment, if the measured luminance of back light is smaller than a desired value, the back light luminance level IL may be a large value, while if the measured luminance of back light is greater than a desired value, the back light luminance level IL may be a small value.
For example, in an exemplary embodiment where a light-emitting device including the light-emitting unit LB deteriorates over time, the luminance of back light supplied from the light-emitting unit LB may be lower than a desired luminance value even though the same driving signals are applied thereto. In this case, compensation can be made to achieve a desired level of back light supplied from the light-emitting unit LB by increasing the back light luminance level IL and compensating for the luminance R_LB using the increased back light luminance level.
As described above, the measured luminance of back light is compared with a desired luminance level, and the luminance R_LB of back light is compensated using the adjusted back light luminance level IL, thereby controlling the luminance of back light to reach a desired level to improve display quality and reduce power consumption.
The light data signal output portion 660 outputs the light data signal LDAT according to the compensated luminance R′_LB provided from the luminance compensator 650. The light data signal LDAT corresponding to the compensated luminance R′_LB is supplied to the backlight driver 800, thereby adjusting the luminance of back light supplied from the light-emitting unit LB.
The backlight driver 800 operates as follows. When the light data signal LDAT is activated to a high level, the switching element BLQ of the backlight driver 800 is turned on and a power supply voltage Vin is supplied to the light-emitting block LB. Accordingly, current flows through the light-emitting block LB and an inductor L. Here, the inductor L stores the energy derived from the current. When the light data signal LDAT is activated to a low level, the switching element BLQ is turned off, creating a closed circuit constituted by the light-emitting block LB, the inductor L, and a diode D, so that current flows therethrough. As the energy stored in the inductor L is discharged, the quantity of current is reduced. Since a time taken for the switching element BLQ to be turned on is adjusted according to the duty ratio of the light data signal LDAT, the luminance of the light-emitting block LB can be controlled.
The light measuring unit 900 illustrated in
Referring to
The photocurrent integrator 920 integrates photocurrent Iph and stores the integrated photocurrent in the feedback capacitor in the form of voltage. The photocurrent integrator 920 includes an operational amplifier “amp” having a first input node connected to the photoelectric conversion element PD through which the photocurrent Iph flows, and a second input node to which a bias voltage “Vbias” is applied; and a feedback capacitor connected between the first input node and the output node of the operational amplifier amp. In one exemplary embodiment, the photocurrent integrator 920 may be, for example, a photodiode, as illustrated in
A voltage “Vph” output from the photocurrent integrator 920 is applied to a node of the discharger 930. The discharger 930 attenuates the voltage Vph output from the photocurrent integrator 920 in the form of an exponential function. As shown in
The comparator cpr receives a voltage “Vph” attenuated by the discharger 930 and a reference voltage “Vref”, compares the received voltages with each other, and outputs a comparison result. For example, the comparator cpr may output a signal in a high level for a time period in which the voltage Vph attenuated by the discharger 930 reaches the reference voltage Vref. That is to say, in one exemplary embodiment, the voltage “Vout” output from the comparator cpr may be a digital signal composed of a combination of a high level and a low level.
The reset switch is connected between the first input node and the output node of the operational amplifier amp. The reset switch is turned on in response to a reset signal Φ rst, and resets the voltage Vph output from the photocurrent integrator 920 to a bias voltage Vbias.
The operation of the A/D converter 910 illustrated in
Next, in an integration period, when Φ1 and Φ2 signals are activated to high levels, a feedback capacitor, e.g., a first capacitor C1, is charged with photocurrent Iph for a time period tsp1 corresponding to the high-level period, and the voltage Vph output from the photocurrent integrator 920 increases with a predetermined slope. If the voltage Vph output from the photocurrent integrator 920 reaches a value of Vph0 at a timing point at which the Φ1 and Φ2 signals go low, the value of Vph0 can be expressed as:
(Vph0−Vbias)*C1=Iph*tsp1 Equation (1):
Next, in an attenuation period, if Φ1 and Φ2 signals are maintained at low levels, the voltage Vph output from the photocurrent integrator 920 is attenuated with a time constant τ of the discharger 930. That is to say, the voltage Vph output from the photocurrent integrator 920 is attenuated with the time constant τ in the form of an exponential function, which can be expressed as τ=RL*CL.
Assuming that a timing point at which the voltage Vph output from the photocurrent integrator 920 reaches Vph0 is set to be t=0, Vph(t) at an arbitrary time t can be expressed as:
{Vph(t)−Vbias}=(Vph0−Vbias)*exp(−t/τ) Equation (2):
Assuming that t1 denotes a time taken for the voltage Vph output from the photocurrent integrator 920 to reach the reference voltage Vref by attenuation, the following equation can be produced from Equation (2):
(Vref−Vbias)=(Vph0−Vbias)*exp(−t1/τ) Equation (3):
In Equation (1), the equation (Vph0−Vbias)=(Iph*tsp1)/C1 is applied to Equation (3), producing Equation (4):
(Vref−Vbias)=(Iph*tsp1)/C1*exp(−t1/τ) Equation (4):
Taking the natural logs and rearranging for t1:
t1=τ[ln(Iph)−ln{(Vref−Vbias)*C1/tsp1}] Equation (5):
Converting the natural log of the right side of Equation (5) into a log having a base of 10:
t1=(τ/loge)*[log(Iph)−log{(Vref−Vbias)*C1/tsp1}] Equation (6):
In Equation (6), since τ, Vref, Vbias, C1, and tsp1 are all constants, Equation (6) can be rewritten as:
t1=A*log(Iph)+B Equation (7):
where A=τ/loge, B=−τ*ln{(Vref−Vbias)*Cf/tsp1}.
That is to say, the time t1 taken for the voltage attenuated by the discharger 930 to reach the reference voltage Vref is linearly proportional to the log value of photocurrent Iph.
Referring to
The A/D converter 910 receives the photocurrent Iph output from the photoelectric conversion element PD and outputs the output voltage Vout, as described with reference to
The counter 940 receives the output voltage Vout from the A/D converter 910 and outputs the output voltage Vout at a high level for a time period t1 as illustrated in
The luminance level output portion 950 receives the length of the time period t1 from the counter 940 and outputs a back light luminance level IL corresponding thereto. Here, in one exemplary embodiment, the corresponding relationship between the time period t1 and the back light luminance level IL may be stored in a lookup table LUT. The luminance level output portion 950 may output the back light luminance level IL corresponding to the time period t1 using the LUT.
As described above with reference to
In such a manner, the luminance of back light can be adjusted using the back light luminance level IL varying depending on the luminance of ambient light. That is to say, if the ambient light is low, the luminance of back light may be reduced, while if the ambient light is high, the luminance of back light may be increased.
Alternatively, as described above with reference to
Meanwhile, in one exemplary embodiment, the A/D converter 910, the counter 940 and the luminance level output portion 950 of the light measuring unit 900 may be mounted on the display panel 300, as illustrated in
Another exemplary embodiment of a display device and a driving method of the same according to the present invention will be described with reference to
Referring to
The operation of the A/D converter 911 will now be described in more detail. A photocurrent integrator 921 may include a first capacitor C1, a second capacitor C2 having capacitance smaller than that of the first capacitor C1, and a third capacitor C3 having capacitance larger than that of the first capacitor C1. In one exemplary embodiment, the capacitance of the second capacitor C2 may be ( 1/10)n times that of the first capacitor C1, and the capacitance of the third capacitor C3 may be 10 n times that of the first capacitor C1, wherein “n” is a positive real number.
In addition, the photocurrent integrator 921 may include a first selection switch SEL1 limiting current flow toward the first capacitor C1, a second selection switch SEL2 limiting current flow toward the second capacitor C2, and a third selection switch SEL3 limiting current flow toward the third capacitor C3.
The operation of the photocurrent integrator 921 will now be described in more detail. Depending on the magnitude of photocurrent Iph, one among the first capacitor C1, the second capacitor C2, and the third capacitor C3 may function as a feedback capacitor.
In detail, when the first selection switch SEL1 is closed so that the first capacitor C1 functions as a feedback capacitor, if t1, e.g., a time taken for an attenuated voltage to reach a reference voltage, is shorter than a predetermined time, the first selection switch SEL1 is opened and the second selection switch SEL2 may be closed. Accordingly, the second capacitor C2 may then function as a feedback capacitor.
Alternatively, when the first selection switch SEL1 is closed so that the first capacitor C1 functions as a feedback capacitor, if the photocurrent Iph value is greater than a saturation value of the operational amplifier amp, the first selection switch SEL1 may be opened and the third switch SEL3 may also be closed. Accordingly, the third capacitor C3 may function as a feedback capacitor.
Conditions for selecting one among first to third feedback capacitors C1, C2, and C3 in the circuit illustrated in
Referring to
Referring to
Conversely, referring to
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. It is therefore desired that the present embodiments be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than the foregoing description to indicate the scope of the invention.
Number | Date | Country | Kind |
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10-2008-0054328 | Jun 2008 | KR | national |