Patent ID: 12223918

DETAILED DESCRIPTION

Specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, however, the embodiments described are not intended to limit the present invention and it is not intended for the description of operation to limit the order of implementation. Moreover, any device with equivalent functions that is produced from a structure formed by a recombination of elements shall fall within the scope of the present invention. Additionally, the drawings are only illustrative and are not drawn to actual size.

The using of “first”, “second”, “third”, etc. in the specification should be understood for identifying units or data described by the same terminology, but are not referred to particular order or sequence.

FIG.1is a schematic diagram of a current calibration system in accordance with an embodiment. Referring toFIG.1, a current calibration system100includes an electrical device110and a display device120. The electrical device110may be a personal computer, a server, or any electrical device with computation capability. The display device120includes a circuit130, a backlight module140, and a display panel150. The circuit130includes a time controller131and a microcontroller unit (MCU)132. The microcontroller unit132may be replaced with a field programmable gate array (FPGA) which is not limited in the disclosure. The backlight module140includes multiple light emitting units such as light-emitting diodes which are driven by currents of the backlight module140to serve as a backlight source. The display panel150is, for example, a liquid crystal display panel.FIG.2is a schematic diagram of regions of the display panel and the corresponding light emitting units in accordance with an embodiment. In the embodiment ofFIG.2, the display panel150includes 15 regions (e.g. regions151-153), and each region corresponds to the multiple light emitting units (e.g. light emitting units141-142). The brightness level of each light emitting unit can be controlled by the amplitude of the current flowing through the corresponding light emitting unit for increasing the contrast ratio of a frame. For example, if a portion of the frame in a particular region is relatively dark, the brightness levels of the corresponding light emitting units are decreased; and if a portion of the frame in that particular region is relatively bright, the brightness levels of the corresponding light emitting units are increased. When the frame is to be rendered, the time controller131calculates a setting value of each region of the display panel150. The setting value indicates the required brightness level. In some embodiments, each light emitting unit is controlled by a switch (not shown), and a current flows through the light emitting unit when the switched is turned on, and there is no current flowing through the light emitting unit when the switch is turned off. The amplitude of the current flowing through the light emitting unit is determined by a duty cycle of the switch.FIG.2is merely an example, and the number of the regions in the display panel150and the number of the light emitting units corresponding to one region are not limited in the disclosure.

Referring toFIG.1, the microcontroller unit132includes multiple calibration lookup tables. Each calibration lookup table corresponds to one of the multiple light emitting units and records at least one parameter and multiple duty cycles. The parameter is, for example, a current amplitude or other parameters for controlling the current value. The magnitude of the current flowing through the light emitting unit is determined according to the parameter and the duty cycles so as to determine the brightness level of the light emitting unit. In the embodiment, the current amplitude (mA) is multiplied with the duty cycle (%) to determine a current value (mA) of the light emitting unit. How the parameter and the duty cycles are determined will be described below.

FIG.3is a diagram illustrating a brightness-duty-cycle response curve of the light emitting unit in accordance with an embodiment. Referring toFIG.3, a straight line310represents a linear relationship between the brightness levels and the duty cycles. The maximum duty cycle Dt(e.g. 100%) corresponds to a brightness level Btwhich is pre-determined (e.g. based on the specification of the product). A curve320represents the real response curve of the light emitting unit. When the parameter (i.e. current amplitude) Atand the maximum duty cycle Dtare used to drive a light emitting unit, this light emitting unit only provides a brightness level Bnwhich is less than the predetermined brightness level Bt. Therefore, the brightness level corresponding to the maximum duty cycle has to be calibrated first.

In detail, when driving the light emitting unit according to the parameter Atand the duty cycle Dt, the electrical device110can measure the brightness level Bnthrough a luminance meter or other suitable meters and determine if the brightness level Bnis less than the predetermined brightness level Bt. If the brightness level Bnis less than the predetermined brightness level Bt, then the parameter Atis adjusted such that the adjusted parameter Atcan drive the light emitting unit to provide a brightness level which meets the predetermined brightness level Bt(i.e. the difference is within a predetermined range). An_caldenotes the adjusted parameter which is recorded in the calibration lookup table. In some embodiments, the parameter An_calmay be calculated according to the parameter Atand the brightness level Bnas the following Equation 1.

Ancal=BtBn×At[Equation⁢1]

Next, a brightness-duty-cycle response curve330is defined by the predetermined brightness level Bt, the adjusted parameter An_caland the duty cycle Dt. The brightness-duty-cycle response curve330is estimated by measuring multiple brightness levels (also referred to as candidate brightness levels) when applying multiple duty cycles (also referred to as candidate duty cycles). The more the candidate brightness levels are measured, the more precise the brightness-duty-cycle response curve330is.FIG.4is a diagram of estimating a turning point of the brightness-duty-cycle response curve in accordance with an embodiment. Referring toFIG.4, multiple candidate duty cycles D1-D7are first set. The light emitting unit is driven according to the candidate duty cycles D1-D7to obtain candidate brightness levels B1-B7. Each candidate duty cycle and the corresponding candidate brightness level constitute a coordinate such as (D1, B1) which is a point on the brightness-duty-cycle response curve330. Accordingly, the brightness-duty-cycle response curve330is determined based on the coordinates whether the curve330is linear or non-linear. To be specific, segments401-408are defined by the candidate duty cycles D1-D7and the candidate brightness levels B1-B7. For example, the coordinate (D1, B1) and the coordinate (D2, B2) define the segment402, and so on. Next, a slope of each of the segments401-408is calculated. For example, the slope of the segment402is calculated as the following Equation 2, and so on for the slops of the other segments.

B2-B1D2-D1[Equation⁢2]

If a difference between a maximum slope and a minimum slope along the segments401-408is greater than a threshold, then it is determined that the brightness-duty-cycle response curve330is non-linear, otherwise it is linear.

One or more turning points are also estimated in some embodiments. In detail, an initial duty cycle is set to be 0, and the corresponding brightness level is also set to be 0. A coordinate (0, 0) is a start point of the brightness-duty-cycle response curve330. Next, the maximum slope and the minimum slope are initialized by, for example, setting the maximum slope to be 0, and setting the minimum slope to be a large number. Next, the candidate duty cycles D1-D7are selected in ascending order. A slope is calculated according to the selected candidate duty cycle and the initial duty cycle. For example, the duty cycle D1is selected first, and the corresponding slope is B1/D1. If this slope is less than the minimum slope, then the minimum slope is set to be B1/D1. If this slope is greater than the maximum slope, then the maximum slope is set to be B1/D1. The next candidate duty cycle D2is then selected, and the corresponding slope is B2/D2. If the slope B2/D2is less than the minimum slope, then the minimum slope is set to be B2/D2. If the slope B2/D2is greater than the maximum slope, then the maximum slope is set to be B2/D2. Next, judging by whether or not the difference between the maximum slope and the minimum slope is greater than the threshold, and if yes, the currently selected candidate duty cycle D2and the corresponding candidate brightness level B2are set to be a new turning point represented as the coordinate (D2, B2). After finding a new turning point, the maximum slope and the minimum slope are reset, and the new turning point (D2, B2) is taken as a new initial point, the candidate duty cycle D3is selected, the corresponding slope (B3−B2)/(D3−D2) is calculated to update maximum slope and the minimum slope, and so on for all the candidate duty cycles.

If no turning point is found, it means the brightness-duty-cycle response curve330is a linear function. If there are turning points, each time a turning point is found, the brightness-duty-cycle response curve330is divided into a new linear segment (i.e. linear function). That is, the brightness-duty-cycle response curve330will be a piecewise linear function consisting of (or approximated by) multiple linear functions. The piecewise linear function is defined by the candidate duty cycles and the candidate brightness levels. From another aspect, each linear function includes a slope and a group of duty cycles. For example, the linear function of the segment402includes the corresponding slope and a group of duty cycles D1and D2. The slopes of the linear functions of any two groups of duty cycles are difference from the each other. For example, the duty cycles D5and D6are referred to as a first group of duty cycles, and the duty cycles D3and D4are referred to as a second group of duty cycles. The minimum value D5of the first group of duty cycles is greater than the maximum value D4of the second group of duty cycles. The slope of the linear function (i.e. segment406) of the first group of duty cycles is greater than the slope of the linear function (i.e. segment404) of the second group of duty cycles. For another example, the duty cycles D5and D6are referred to as a first group of duty cycles, and the duty cycle D4and D5are referred to as a second group of duty cycles. The minimum value D5of the first group of duty cycles is equal to the maximum value D5of the second group of duty cycles. The slope of the linear function (i.e. segment406) of the first group of duty cycles is greater than the slope of the linear function (i.e. segment405) of the second group of duty cycles. The slopes of the linear functions in embodiment ofFIG.4are increasing. That is, the slopes of the linear functions increase as the brightness level increases. Accordingly, the backlight module140has more scales when the brightness level is low. Note that the brightness levels B1-B5are less than 50% of the maximum brightness levels for fine-tuning. In addition, the backlight module140has fewer scales when the brightness level is high. Note that the brightness levels B6and B7are greater than 50% of the maximum brightness level for sharp adjustment. Therefore, this is in favor of fine-tuning brightness when the frame is dark. The slopes of the linear functions may be decreasing based on the character of the light emitting unit. For example, referring toFIG.5, a brightness-duty-cycle response curve510is also a piecewise linear function consisting of (or approximated by) linear functions corresponding to segments501-505. The slopes of the segments501-505are decreasing. For example, the duty cycles D3and D4are referred to as a first group of duty cycles, and the duty cycles D1and D2are referred to as a second group of duty cycles. The minimum value D3of the first group of duty cycles is greater than the maximum value D2of the second group of duty cycles. The slope of the linear function (i.e. segment504) corresponding to the first group of duty cycles is less than the slope of the linear function (i.e. segment502) corresponding to the second group of duty cycles. For another example, the duty cycles D3and D4are referred to as a first group of duty cycles, and the duty cycle D2and D3are referred to as a second group of duty cycles. The minimum value D3of the first group of duty cycles is equal to the maximum value D3of the second group of duty cycles. The slope of the linear function (i.e. segment504) corresponding to the first group of duty cycles is less than the slope of the linear function (i.e. segment503) corresponding to the second group of duty cycles. That is, the slopes of the linear functions decreased while the brightness increases. In the embodiment, the backlight module140has more scales for the duty cycles when the brightness level is high. Note that the brightness levels B2, B3and B4corresponding to the duty cycles D2, D3and D4are higher than 50% of the maximum brightness level for fined-tuning. In contrast, the backlight module140has fewer scales for the duty cycles when the brightness level is low. Note that only the brightness level B1corresponding to the duty cycle D1is lower than 50% of the maximum brightness level for sharp adjustment. This is in favor of the brightness adjustment for high environment brightness (e.g. in the harsh sunlight or in a backlight status where the brightness of the display is not sufficient).

In the embodiment ofFIG.3, the brightness level Bnis measured based on the duty cycle Dtand the preset parameter Atand is less than the predetermined brightness level Bt. Therefore, the updated parameter should be recorded in the calibration lookup table. If the measured brightness level is greater than or equal to the predetermined brightness level, then the parameter is directly recorded in the calibration lookup table without adjustment. For example,FIG.6is a diagram illustrating a brightness-duty-cycle response curve610in accordance with an embodiment. In the embodiment ofFIG.6, after the light-emitting diode is driven based on the preset parameter Atand the duty cycle Dt, the measured brightness level Bnis greater than the predetermined brightness level Bt. Therefore, the parameter Atis recorded in the corresponding calibration lookup table without adjustment. Next, the brightness-duty-cycle response curve610is defined by the predetermined brightness level Bt, the parameter Atand the duty cycle Dmwhich is the value for driving the light emitting unit to produce the predetermined brightness level Bt. When the predetermined brightness level Btis required, the light emitting diode is driven based on the parameter Atand the duty cycle Dm. When a lower brightness level is required, only the duty cycle will be adjusted to be lower accordingly.

According to the above method, the calibration lookup table records the adjusted or the preset parameter and multiple duty cycles. For example, the content of an exemplary calibration lookup table is shown in the following Table 1.

TABLE 1For nthlight emitting unitDimmingDutylevelParametercycle0An_calD01D1. . .. . .mDm

Table 1 corresponds to nthlight emitting unit. The first column records dimming levels (or brightness levels in other embodiments); the second column records the parameter which is an adjusted parameter An_calin this example; and the third column records the corresponding duty cycles. If the corresponding brightness-duty-cycle response curve is linear, then the calibration lookup table records at least two duty cycles including a duty cycle (e.g. 0%) corresponding to the minimum dimming level and a duty cycle (e.g. Dr ofFIG.3or DmofFIG.6) for producing the predetermined brightness level. If the corresponding brightness-duty-cycle response curve is non-linear, then the calibration lookup table additionally records the duty cycle and the dimming level of at least one turning point.

The duty cycles for the nthlight emitting unit may be applied to other light emitting units because the brightness-duty-cycle response curves for different light emitting units should be similar under the same process. Although the same duty cycles are adopted, the brightness levels and the parameter can be estimated again. In detail, another light emitting unit (also referred to as a second light emitting unit) is driven based on the predetermined parameter, the brightness level of the second light emitting unit is measured, and then the parameter may be adjusted such that the brightness level of the second light emitting unit meets the predetermined brightness level. The adjusted parameter is recorded in the calibration lookup table (also referred to as a second calibration lookup table) corresponding to the second light emitting unit. Next, the turning point (i.e. duty cycles) of Table 1 is added into the second calibration lookup table, and the brightness levels of these duty cycles are measured. The second calibration lookup table also records the measured brightness level or the corresponding dimming levels. In this way, there is no need to re-find the turning point of the brightness-duty-cycle response curve of the second light emitting unit.

Referring toFIG.1, the established calibration lookup table is stored in the microcontroller unit132. When a frame is to be rendered, the time controller131performs a local dimming algorithm to calculate a setting value which could be a dimming level or a brightness level. The microcontroller unit132receives a signal indicating the setting value from the time controller131so as to access the corresponding calibration lookup table according to the setting value. An output duty cycle is determined according to the duty cycles in the calibration lookup table. Next, a current value of the light emitting unit is determined based on the output duty cycle and the parameter, and the current value is used to drive the light emitting unit. Since the output current of each region of the display panel is calibrated, uniform brightness is achieved to avoid a situation of uneven brightness across the regions. This method can corporate with local dimming technology so that each region can produce expected brightness. Embodiments will be provided to describe the calculation of the output duty cycle.

First, if the brightness-duty-cycle response curve is linear, then the circuit130obtains an adjusted duty cycle according to the brightness level of the brightness-duty-cycle response curve as the output duty cycle. That is, the circuit130interpolates the output duty cycle according to the linear function and the dimming level (or brightness level) to be rendered. For example, a calibration lookup table recodes an adjusted parameter An_cal, a duty cycle (herein represented as Dn) corresponding to the minimum dimming level and the duty cycle (herein represented as Dmwhich is not necessarily 100%) corresponding to the maximum dimming level. The calculation of the following Equation 3 is performed according to the brightness level (or dimming level) to be rendered.

Dk=Dn+Dm-Dnm-n×(k-n)[Equation⁢3]

Dkdenotes the output duty cycle. m denotes the maximum dimming level (or maximum brightness level). n denotes the minimum dimming level (or minimum brightness level). k denotes the dimming level (or brightness level) of the setting value. Dmdenotes the duty cycle corresponding to the maximum dimming level (or maximum brightness level). Dndenotes the duty cycle corresponding to the minimum dimming level (or minimum brightness level). The microcontroller unit132receives a signal from the time controller131to access the corresponding calibration lookup table according to the received brightness level (or dimming level), and determines the output duty cycle Dkaccording to the duty cycles stored in the calibration lookup table and the Equation 3. Next, a current value of the corresponding light emitting unit is determined to drive the light emitting unit according to the output duty cycle Dkand the parameter An_calrecorded in the calibration lookup table.

On the other hand, if the brightness-duty-cycle response curve is non-linear, then the brightness-duty-cycle response curve contains at least one turning point. Each turning point includes a turning-point brightness level (or turning-point dimming level) and a turning-point duty cycle that are stored in the calibration lookup table. The circuit130interpolate the output duty cycle according to the setting value, the turning-point brightness level, and the turning-point duty cycle. For example,FIG.7is a diagram of interpolating the output duty cycle in accordance with an embodiment. Referring toFIG.7, Bkdenotes the brightness level of the setting value. Two turning-point brightness levels Biand Bi+1closest to the brightness level Bkare found in the calibration lookup table. The brightness level Bkis greater than the turning-point brightness level Biand less than the turning-point brightness level Bi+1. Two turning-point duty cycles Diand Di+1are read from the calibration lookup table according to the turning-point brightness levels Biand Bi+1. Next, the output duty cycle Dkis interpolated according to the following Equation 4.

Dk=Di+(Di+1-Di)(Bi+1-Bi)×(Bk-Bi)[Equation⁢4]

In detail, the microcontroller unit132receives a signal from the time controller131, accesses the calibration lookup table according to the received brightness level (or dimming level), and determines the output duty cycle Dkaccording to the duty cycles of the calibration lookup table and the Equation 4. Note that if the brightness level Bkis equal to one of the turning-point brightness level Biin the calibration lookup table, then the turning-point duty cycle Diis outputted as Dk. No matter which case happens, after the output duty cycle Dkis obtained, a current value is determined to drive the corresponding light emitting unit according to the output duty cycle Dkand the parameter An_calin the calibration lookup table. An expected brightness level is achieved through the above method.

FIG.8is a flow chart of a calibration method of a display device in accordance with an embodiment. The calibration method is performed by the electrical device110and the display device120in cooperation. Referring toFIG.8, in step801, a first light emitting unit is driven to produce a first brightness level by a current according to a parameter and a first duty cycle, and the first brightness level of the first light emitting unit is measured. In step802, it is determined if the first brightness level is less than a predetermined brightness level. If the result of the step802is “yes”, in step803, the parameter is adjusted such that the first brightness level of the first light emitting unit meets the predetermined brightness level, and the adjusted parameter is recorded in a calibration lookup table corresponding to the first light emitting unit. If the result of the step802is “no”, the parameter is not adjusted. In step804, the parameter is directly recorded in the calibration lookup table corresponding to the first light emitting unit. In step805, a brightness-duty-cycle response curve is defined. In step806, it is determined if the brightness-duty-cycle response curve is linear. If the result of step806is “yes”, in step807, an adjusted duty cycle is obtained according to a brightness level on the brightness-duty-cycle response curve as an output duty cycle. If the result of step806is “no” (i.e. non-linear), the brightness-duty-cycle response curve contains at least one turning point. In step808, an adjusted duty cycle is interpolated according to a turning-point brightness level and a turning-point duty cycle of the turning point as the output duty cycle. In step809, a current value is determined to drive the first light emitting unit according to the output duty cycle and the parameter in the calibration lookup table. However, all the steps inFIG.8have been described in detail above, and therefore the description will not be repeated. Note that the steps inFIG.8can be implemented as program codes or circuits, and the disclosure is not limited thereto. In addition, the method inFIG.8can be performed with the aforementioned embodiments, or can be performed independently. In other words, other steps may be inserted between the steps of theFIG.8.

Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.