Patent Grant
8982162
1. Technical Field
The present invention relates to a technology capable of displaying gray scale by using a subfield driving scheme.
2. Related Art
According to the related art, there has been proposed a subfield driving scheme in which an on voltage or an off voltage is selectively applied to a display element (e.g., liquid crystal element) in each of a plurality of subfields obtained by dividing a field (for example, see JP-A-2003-114661). Further, JP-A-2008-241975 discloses a technology of storing a code (hereinafter, referred to as “driving code”), which indicate an on voltage or an off voltage in each subfield, in a storage circuit for each gray scale in a state in which the codes have been compressed.
The code (hereinafter, referred to as “compression code”) after compression in JP-A-2008-241975 includes a first portion, which designates the number of subfields in which an on voltage is applied and being continuous in a field, and a second portion which designates an on voltage or an off voltage in each of the remaining subfields in the field. Thus, as compared with a configuration of storing a driving code in a non-compression state, the capacity necessary for a storage circuit is reduced.
However, in JP-A-2008-241975, since the second portion of the compression code designates a voltage (on voltage/off voltage) in each subfield, if the total number of subfields in a field is increased to realize multilevel gray scale, the data amount of the second portion is increased proportionally to the total number of the subfields. Therefore, a case may occur in which the capacity necessary for the storage circuit cannot be sufficiently reduced.
An advantage of some aspects of the invention is to effectively reduce the data amount of a compression code obtained by compressing a driving code.
According to one aspect of the invention, there is provided a display device that displays a gray scale by applying a first voltage or a second voltage to a display element for each of a plurality of subfields obtained by dividing a field, the display apparatus including: a predetermined code storage unit that stores a predetermined code, in which indication values designating any one of the first voltage and the second voltage are arranged, for each identifier; a compression code storage unit that stores a compression code, which includes a first portion designating the number of the indication values (the number of subfields) and a second portion designating an identifier of the predetermined code, for each gray scale; a developing unit that generates a driving code according to a continuous code, in which indication values designating the first voltage are arranged by the number of the indication values designated by the first portion of the compression code, and a predetermined code corresponding to the identifier designated by the second portion of the compression code; and a driving circuit that applies any one of the first voltage and the second voltage to the display element for each subfield of the field based on the driving code generated by the developing unit with respect to a designated gray scale of the display element. The display device of the invention is used for various types of electronic apparatuses (e.g., personal computers or cell phones).
With such a configuration, since the compression code obtained by compressing the driving code is stored in the compression code storage unit, the capacity necessary for the compression code storage unit can be reduced, as compared with a configuration of storing the driving code in a non-compression state. Further, since the second portion of the compression code corresponds to the identifier of the predetermined code, it is advantageous in that the data amount of the compression code (in addition, the capacity necessary for the compression code storage unit) can be effectively reduced, as compared with the configuration of JP-A-2008-241975 in which the second portion of the compression code designates a voltage of each subfield. The above effect is particularly significant when the total number of the subfields in the field is increased to realize multilevel gray scale.
In addition, the compression code storage unit and the predetermined code storage unit are mounted as separate storage circuits. However, the compression code storage unit and the predetermined code storage unit may be provided as separate storage areas set in a single storage circuit. Further, the scope of the invention includes both a configuration (e.g., the first embodiment which will be described later) in which the developing unit sequentially develops a compression code corresponding to gray scale whenever the gray scale is designated (gray scale data is supplied), and a configuration (e.g., the second embodiment which will be described later) in which the developing unit develops in advance (before the display element starts to operate) a compression code corresponding to each gray scale.
According to a preferred embodiment of the invention, when the number of the indication values designated by the first portion of the compression code exceeds a predetermined value, the developing unit generates the driving code, which includes a predetermined number of indication values, by arranging the continuous code and a part of the predetermined code. Further, according to another preferred embodiment, when the number of the indication values designated by the first portion of the compression code is less than the predetermined value, the developing unit generates the driving code, which includes a predetermined number of indication values, by arranging the continuous code, the predetermined code, and at least one indication value designating the second voltage. According to the above embodiments, it is advantageous in that the driving code, which includes a desired number of indication values, can be generated while reducing the data amount of the compression code. In addition, it is preferred to employ a configuration in which the developing unit generates the driving code by disposing the indication value designating the second voltage between the continuous code and the predetermined code.
According to a preferred embodiment of the invention, each second portion of at least two compression codes stored in the compression code storage unit designates a common identifier. According to the above embodiment, since a common predetermined code is used for the generation of the driving code of at least two gray scales, the driving code can be generated using predetermined codes having a number smaller than the number of the gray scales. Thus, as compared with a configuration in which the predetermined code is necessary for each gray scale, it is advantageous in that the capacity necessary for the predetermined code storage unit is reduced.
According to a preferred embodiment of the invention, the compression code storage unit stores a plurality of first tables in which the compression code is set for each gray scale, the predetermined code storage unit stores a plurality of second tables in which the predetermined code is set for each identifier, a selecting unit is provided to select any one of the plurality of first tables and any one of the plurality of second tables, and the developing unit generates the driving code by using the first and second tables selected by the selecting unit. According to the above embodiment, since any one of the plurality of first tables and any one of the plurality of second tables are selected for the generation of the driving code, a relationship between a designated gray scale and the driving code can be appropriately changed. For example, after a temperature detection member, which detects the operation temperature (temperature of a display panel or peripheral temperature of the display panel) of the display panel, is provided, the selecting unit selects the first table and the second table according to the temperature detected by the temperature detection member.
The invention is also specified as a circuit (driving code generating circuit) which generates a driving code in which indication values designating any one of a first voltage and a second voltage applied to a display element are arranged for each subfield in a field. The driving code generating circuit of the invention includes: a predetermined code storage unit that stores a predetermined code, in which the indication values designating any one of the first voltage and the second voltage are arranged, for each identifier; a compression code storage unit that stores a compression code, which includes a first portion designating a number of the indication values and a second portion designating an identifier of the predetermined code, for each gray scale; and a developing unit that generates a driving code according to a continuous code, in which indication values designating the first voltage are arranged by the number of the indication values designated by the first portion of the compression code, and a predetermined code corresponding to the identifier designated by the second portion of the compression code. According to the above driving code generating circuit, the same effect as that obtained by the display device of the invention can be realized.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
The display panel 10 includes a pixel unit (display area) 20 in which a plurality of pixel circuits 22 are arranged, and a driving circuit 30 that drives each pixel circuit 22. In the pixel unit 20, M scanning lines 26 and N signal lines 28 extend in the direction in which they cross each other (M and N are natural numbers). The pixel circuits 22 are each disposed at positions corresponding to each crossing of the scanning lines 26 and the signal lines 28, and arranged in a matrix shape of (vertical M rows×horizontal N columns). Each pixel circuit 22 includes a liquid crystal element 24 in which the transmittance of liquid crystal varies depending on a voltage (a potential difference between a pixel electrode and an opposite electrode) between both ends thereof. The voltage between both ends of the liquid crystal element 24 is set according to the voltage of the signal line 28 when the scanning line 26 is selected.
The driving circuit 30 controls the transmittance (reflectivity) of each liquid crystal element 24 by driving the plurality of pixel circuits 22, respectively. The driving circuit 30 drives each pixel circuit 22 (each liquid crystal element 24) by using a subfield driving scheme. That is, as illustrated in
As illustrated in
The control circuit 40 of
The driving code generating circuit 50 converts the gray scale data G, which is sequentially supplied from the control circuit 40, into a driving code CDR. As illustrated in (A) to (E) of
The content of the driving code CDR is experimentally selected such that gray scale represented by the gray scale data G and the emission light amount (time-integrated value of transmittance) from the liquid crystal element 24 in one field F satisfy a desired relationship (gray scale-luminance characteristics). That is, after the emission light amount (time integrated value of transmittance) from the liquid crystal element 24 is sequentially measured in each of a plurality of cases of changing both the ratio of the number of the subfields SF, in which the on voltage is applied, in one field F and the number of the subfields SF in which the off voltage is applied, and the arrangement (hereinafter, referred to as “voltage applying pattern”) of the respective subfields SF, 256 types of voltage applying patterns, through which the emission light amount corresponding to each gray scale represented by the gray scale data G is obtained, are extracted from a plurality of voltage applying patterns, and then driving codes CDR (256 types of driving codes CDR corresponding to each gray scale which can be designated by the gray scale data G) corresponding to each voltage applying pattern after the extraction are determined.
In detail, in order that the ratio of the time for which the on voltage (or off voltage) is applied to the liquid crystal element 24 in one field F coincides with the ratio corresponding to the gray scale data G of each pixel circuit 22, each indication value X of the driving codes CDR is determined for each gray scale represented by the gray scale data G. For example, when the liquid crystal element 24 is set in a normally white mode, the driving codes CDR are determined such that, as the gray scale of the gray scale data G is high, the number of the subfields SF, in which the on voltage is applied to the liquid crystal element 24, is reduced (i.e., time length for which the transmittance of the liquid crystal element 24 is reduced by the applied on voltage is shortened). Meanwhile, when the liquid crystal element 24 is set in a normally black mode, the driving codes CDR are generated such that, as the gray scale designated by the gray scale data G is high, the number of the subfields SF, in which the on voltage is applied to the liquid crystal element 24, is increased.
Referring to
In the second section f2, the subfields SF in which the on voltage is applied to the liquid crystal element 24 and the subfields SF in which the off voltage is applied to the liquid crystal element 24 coexist with the ratio of the respective numbers of the subfields SF and the arrangement thereof corresponding to the gray scale data G. As illustrated in (A) to (C) of
In the third section f3, the subfield SF, in which the off voltage is applied to the liquid crystal element 24, continues immediately after the second section f2. As illustrated in (A) to (C) of
The driving circuit 30 of
As illustrated in
The signal line driving circuit 34 outputs a voltage (on voltage/off voltage) corresponding to each indication value X of the driving code CDR to each signal line 28 in synchronization with the selection of each scanning line 26 by the scanning line driving circuit 32. In detail, in a period in which the scanning line 26 of an ith row (i=1 to M) of one subfield SF is selected, the signal line driving circuit 34 outputs a voltage, which is represented by the indication value X of the subfield SF in the driving code CDR obtained by converting the gray scale data G of the pixel circuit 22 located at a jth column (j=1 to N) of the ith row, to the signal line 28 of the jth column. The voltage output to the signal line 28 of the jth column when the scanning line 26 of the ith row is selected is applied to the liquid crystal element 24 of the pixel circuit 22 located at the jth column of the ith row. Thus, the liquid crystal element 24 of each pixel circuit 22 is controlled according to gray scale (transmittance) corresponding to the gray scale data G in units of the field F.
As illustrated in
The predetermined code CB is a sequence of n2 indication values X for designating the on voltage and the off voltage with respect to each of the n2 subfields SF in the second section f2. As described above for the driving code CDR, each indication value X of the predetermined code CB is set to any one of the numerical value “1” for designating the on voltage and the numerical value “0” for designating the off voltage. Thus, the predetermined code CB can be formed with n2 bits (12 bits in the embodiment).
The predetermined code CB is used as a part corresponding to each subfield SF in the second section f2 of the driving code CDR. For example, the predetermined code CB of
As illustrated in the driving code CDR of
Further, in the second table L2, the number of indication values X having the numerical value “1” is in common, but a plurality of predetermined codes CB, in which the positions (positions of subfields SF in which the on voltage is applied) of the indication values X are different from each other, are included. For example, in relation to the predetermined codes CB having identifiers D set to 1 to 3 as illustrated in
The developing unit 54 of
As illustrated in
When the number n1 of the subfields SF designated by the first portion S1 of the compression code C0 is less than the threshold value Nth (Nth=47−n2), the synthesizing unit 68 interposes the indication value X of the numerical value “0”, which corresponds to the boundary subfield SF, between the sequence code CA and the predetermined code CB, and adds (48−n1−1−n2) indication values X of the numerical value “0” immediately after the predetermined code CB, thereby generating the driving code CDR including 48 indication values X. The indication values X of the numerical value “0” added immediately after the predetermined code CB indicate application of the off voltage in each subfield SF of the third section f3.
For example, as illustrated in
Meanwhile, when the number n1 of the subfields SF designated by the first portion S1 of the compression code C0 exceeds the threshold value Nth, the synthesizing unit 68 interposes the indication value X of the numerical value “0”, which corresponds to the boundary subfield SF, between the sequence code CA and the predetermined code CB, and destroys (n1+1+n2−48) indication values X of the rear side of the predetermined code CB, thereby generating the driving code CDR including 48 indication values X. That is, the driving code CDR when the number n1 of the subfields SF exceeds the threshold value Nth does not include an indication value X corresponding to the third section f3.
For example, as illustrated in
When the number n1 of the subfields SF exceeds the threshold value Nth as described above, since the predetermined code CB is partially destroyed, the content of a part destroyed from the predetermined code CB is arbitrary. For example, since 9 indication values X of the rear side of the predetermined code CB are destroyed when the number n1 of the subfields SF is 44 as illustrated in
In addition, when the number n1 of the subfields SF designated by the first portion S1 of the compression code C0 coincides with the threshold value Nth, that is, when (n1+1+n2=48) is established, the synthesizing unit 68 interposes the indication value X of the numerical value “0” between the sequence code CA generated by the first processing unit 64 and the predetermined code CB generated by the second processing unit 66, thereby generating the driving code CDR including 48 indication values X. That is, addition of indication values X (numerical value is “0”) consecutive to the predetermined code CB or partial destruction of the predetermined code CB is not performed.
According to the above-described embodiment, since the compression code C0 obtained by compressing the driving code CDR is stored in the storage circuit 52, it is advantageous in that the capacity necessary for the storage circuit 52 can be reduced, as compared with the configuration in which the driving code CDR in a non-compression state is stored in the storage circuit 52 and is used for the conversion of the gray scale data G. In addition, since the second portion S2 of the compression code C0 corresponds to the identifier D of the predetermined code CB, it is advantageous in that the data amount (moreover, the capacity necessary for the storage circuit 52) of the compression code C0 can be reduced, as compared with the configuration of JP-A-2008-241975 in which the second portion S2 of the compression code C0 designates the voltage applying pattern in the second section f2. The effect of the reduction in the data amount of the compression code C0 becomes significant as the number of the subfields SF constituting the second section f2 is increased. Since it is necessary to increase the number of the subfields SF in the second section f2 in order to increase the number of gray scales by reducing the width of gray scale, the first embodiment is advantageous in that multilevel gray scale can be effectively realized while reducing the capacity necessary for the storage circuit 52.
Further, addition of the indication values X of the numerical value “0” is performed when the number n1 of the subfields SF is less than the threshold value Nth, and the partial destruction (ignition) of the predetermined code CB is performed when the number n1 of the subfields SF exceeds the threshold value Nth, so that it is not necessary to regulate the addition of the numerical value “0” or the partial destruction of the predetermined code CB by the compression code C0. Thus, as compared with the configuration in which the addition of the numerical value “0” or the partial destruction of the predetermined code CB is designated by the compression code C0, the data amount of the compression code C0 can be reduced. In addition, the indication value X of the numerical value “0” corresponding to the boundary subfield SF is automatically added between the sequence code CA and the predetermined code CB, so that the data amount of the compression code C0 can be reduced, as compared with the configuration in which the voltage of the boundary subfield SF is designated by the compression code C0.
Next, the second embodiment of the invention will be descried. In the first embodiment, the developing unit 76 sequentially develops the gray scale data G, which is output from the control circuit 40 during the operation of the display panel 10, to the driving code CDR. In the second embodiment, the driving code CDR of each gray scale is developed before the display panel 10 starts to operate (e.g., immediately after the display device 100 is powered on). In addition, in the following embodiment, modified examples and application, the same reference numerals are used to designate elements having operations and functions identical to those of the first embodiment, and detailed description thereof will be omitted in order to avoid redundancy.
The second embodiment employs a driving code generating circuit 70 of
As illustrated in
Since movement of the liquid crystal element 24 is dependent on the temperature T, the voltage applying pattern (the driving code CDR), in which each gray scale of the gray scale data G and the emission light amount from the liquid crystal element 24 satisfy a desired relationship, varies depending on the temperature T. The first table L1 and the second table L2 of the table L corresponding to the specific temperature T are set such that the 256 types of driving codes CDR determined under the temperature T can be generated. Thus, the contents of the first table L1 and the second table L2 are different from each other for each table L (i.e., each temperature T).
Before the display panel 10 starts to operate (e.g., immediately after power is supplied thereto), the selecting unit 74 of
The storage unit 82 stores the 256 types of driving codes CDR obtained after the compression codes C0 are developed by the developing unit 76. That is, a table L3, in which the driving codes CDR are arranged for each gray scale, that is, a look-up table L3, in which the gray scale data G corresponds to the driving codes CDR, is generated in the storage unit 82 before the display panel 10 starts to operate. After the display panel 10 starts to operate, the converting unit 84 converts the gray scale data G, which is sequentially supplied from the control circuit 40, into the driving codes CDR. That is, the converting unit 84 searches for the driving codes CDR, which correspond to the gray scale data G, from the table L3 of the storage unit 82, and sequentially outputs the driving codes CDR to the signal line driving circuit 34.
According to the above configuration, since only a table L, which correspond to the actual temperature T, is developed among the plurality of tables L corresponding to different temperatures T, it is advantageous in that the capacity necessary for the storage circuit 72 can be reduced, as compared with the configuration in which each of the plurality of tables L stores the driving codes CDR of each gray scale in a non-compression state. In addition, since the second portion S2 of the compression code C0 corresponds to the identifier D of the predetermined code CB, similarly to the first embodiment, it is advantageous in that the data amount of the compression code C0 can be effectively reduced. According to the second embodiment, since the plurality of tables L are stored in the storage circuit 72, the effect of the reduction in the data amount of the compression code C0 is particularly significant.
The previous embodiments are modified in various types. Detailed modified examples for the previous embodiments are exemplified as follows. In addition, two or more modified examples arbitrarily selected from the following examples can be appropriately combined.
The order (in addition, order of the sequence code CA and the predetermined code CB) of the first section f1, the second section f2 and the third section f3 according to the previous embodiments may be appropriately changed. For example, it may be possible to employ a configuration in which the third section f3 is located prior to the second section f2 and the second section f2 is located prior to the first section f1. The developing units 54 and 76 add the indication value X of “0” corresponding to the boundary subfield SF just prior to the sequence code CA, connect the predetermined code CB just prior to the indication value X, and add the indication value X (indication value X corresponding to the third section f3) of “0” just prior to the predetermined code CB, thereby generating the driving codes CDR including 48 indication values X. Further, in the configuration in which the third section f3 is interposed between the first section f1 and the second section f2, an appropriate number of numerical values “0s” are disposed between the sequence code CA and the predetermined code CB.
According to the previous embodiments, when the number n1 of the subfields SF exceeds the threshold value Nth, the predetermined code CB is partially destroyed. However, it may be possible to employ a configuration of storing the predetermined code CB, which includes (48−n1−1) indication values X corresponding to the number n1 of the subfields SF exceeding the threshold value Nth, in the second table L2 and using the predetermined code CB for the generation of the driving code CDR, that is, a configuration of storing a plurality of predetermined codes CB which have a different number of indication values X. Further, according to the previous embodiments, when the number n1 of the subfields SF is less than the threshold value Nth, the indication values X of the numerical value “0” are compensated such that the number of the indication values X is 48. However, it may be possible to employ a configuration in which a shortage (the number of the compensated 0s) of the indication values X is designated by the compression code C0.
According to the second embodiment, the table L is selected according to the temperature T. However, a criterion for selecting the table L is not limited to the temperature T. For example, it may be possible to employ a configuration of selecting any one of a plurality of tables L according to peripheral illumination of the display panel 10. Further, it may be possible to employ a configuration in which the first table L1 and the second table L2 are prepared for each display color (e.g., each color of RGB) of the liquid crystal element 24, or a configuration in which pseudo contour is controlled by selectively using a plurality of tables L3, which are generated from the tables L different from each other, for generation of the driving codes CDR. According to the above configurations, since it is necessary to store the plurality of tables in the storage circuits 52 and 72, the effect of the invention, that is, the reduction in the data amount of the driving code C0, is particularly effective.
According to the previous embodiments, the first portion S1 of the driving code C0 designates the number n1 of the subfields SF in which the on voltage is applied. However, it may be possible to employ a configuration in which the first portion S1 designates the number of the subfields SF in which the off voltage is applied.
The display element used for the display of an image is not limited to the liquid crystal element 24. In relation to a display element applied to the display device of the invention, a self-emission type display element, which emits light by itself, is not distinguished from a non-emission type display element (e.g., the liquid crystal element 24) which changes transmittance or reflectivity of external light, or a current driving type display element, which is driven by the supply of electric current, is not distinguished from a voltage driving type display element which is driven by the application of an electric field (voltage). For example, the invention can be applied to a display device using various display elements such as organic EL elements, inorganic EL elements, FE (Field-Emission) elements, SE (Surface conduction Electron emitter) elements, BS (Ballistic electron Emitting) elements, LED (Light Emitting Diode) elements, electrophoresis elements or electrochromic elements. That is, the display element includes an electro-optic element having optical properties (gray scale) changed in response to an electrical action (supply of electric current or application of voltage).
Next, an electronic apparatus using the display device 100 according to the previous embodiments will be described.
In addition to the apparatuses exemplified in
The entire disclosure of Japanese Patent Application No. 2009-053054, filed Mar. 6, 2009 is expressly incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-053054 | Mar 2009 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5389922 | Seroussi et al. | Feb 1995 | A |
| 5396595 | Standley | Mar 1995 | A |
| 5684865 | Mohtashemi et al. | Nov 1997 | A |
| 7084861 | Iisaka | Aug 2006 | B2 |
| 7088349 | Iisaka | Aug 2006 | B2 |
| 8531369 | Toyooka | Sep 2013 | B2 |
| 20020158857 | Iisaka | Oct 2002 | A1 |
| 20030072466 | Eisenbraun | Apr 2003 | A1 |
| 20030184809 | Clouthier et al. | Oct 2003 | A1 |
| 20070262889 | Kuo et al. | Nov 2007 | A1 |
| 20080231587 | Takahashi | Sep 2008 | A1 |
| 20090060047 | Schneider | Mar 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 2003-114661 | Apr 2003 | JP |
| 2008-241975 | Oct 2008 | JP |
| 2008-241975 | Oct 2008 | JP |
| 2008241975 | Oct 2008 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20100225675 A1 | Sep 2010 | US |
