Patent Grant
8674910
The present invention contains subject matter related to Japanese Patent Application JP 2007-148697 filed in the Japan Patent Office on Jun. 5, 2007, and to Japanese Patent Application JP 2007-148698 filed in the Japan Patent Office on Jun. 5, 2007, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
This invention relates generally to a method for controlling the peak luminance level of a display panel, and more specifically to a display panel driving method, a display apparatus, a display panel driving apparatus and an electronic apparatus.
2. Description of the Related Art
In recent years, development of display apparatus of the self-luminous type wherein organic EL (Electro Luminescence) devices are arranged in a matrix has been and is advancing. A display panel which uses an organic EL device is simple and easy in reduction in weight and film thickness and besides is high in response speed, and therefore is superior in a moving picture display characteristic. A display panel which uses an organic EL device is hereinafter referred to also as organic EL panel.
Incidentally, as a driving method for an organic EL panel, a passive matrix driving method and an active matrix driving method are available. Recently, development of a display panel of the active matrix driving type wherein an active device in the form of a thin film transistor and a capacitor are disposed for each pixel circuit is being carried out energetically.
It is to be noted that a scanning line VSCAN1 in
Referring to
In the pixel circuit 11 shown in
Here, the operation state of the write control device T1 is controlled by the first scanning line VSCAN1 connected to the gate electrode of the write control device T1. When the write control device T1 is in an on state, a signal voltage corresponding to pixel data is written into the holding capacitor Cs through the signal line Vsig.
The signal voltage after being written is held in the holding capacitor Cs for a period of time of one field. The signal voltage held in the holding capacitor Cs corresponds to the gate-source voltage Vgs of the current driving device T2.
Accordingly, drain current Ids having a magnitude corresponding to the magnitude of the signal voltage held in the holding capacitor Cs flows to the current driving device T2. As the drain current Ids increases, the current flowing to the organic EL device OLED increases and the emitted light luminance increases.
It is to be noted, however, that supplying and stopping of the drain current Ids to the organic EL device OLED are controlled by the light emitting period control device T3. In particular, the organic EL device OLED emits light only within a period within which the light emitting period control device T3 is in an on state. The operation state of the light emitting period control device T3 is controlled by the second scanning line VSCAN2.
Also a pixel circuit having a circuit configuration shown in
In the pixel circuit 11 shown in
Incidentally,
As seen in
On the other hand, a period within which the first scanning line VSCAN1 has the H level and the second scanning line VSCAN2 has the L level corresponds to a writing period of the signal voltage.
Further, a period within which the first scanning line VSCAN1 has the L level and the second scanning line VSCAN2 has the H level corresponds to a light emitting period.
The reason why a variation function of the light emitting period is incorporated in the pixel circuit 11 in this manner is that such several advantages as described below are achieved.
One of the advantages is that, even if the amplitude of an input signal is not varied, the peak luminance level can be adjusted.
As a result, where the input signal is a digital signal, it is possible to adjust the peak luminance level without reducing the gradation number of the signal. On the other hand, where the input signal is an analog signal, since the signal amplitude does not decrease, the noise immunity can be raised. In this manner, variation control of the light emitting period length is effective to implement a pixel circuit which provides high picture quality and can easily adjust the peak luminance.
Further, the variation control of the light emitting period length has an advantage that, where the pixel circuit is of the current writing type, the writing current value can be increased to reduce the writing time.
Furthermore, the variation control of the light emitting period length is advantageous in that it improves the picture quality of moving pictures. It is to be noted that, in
As can be recognized from comparison of
On the other hand, where the light emitting period is sufficiently shorter than a one-field period as seen in
Where the light emitting period is 50% of a one-field period as seen in
Generally, it is known that, in the case of moving pictures wherein a one-field period is given by 60 Hz, if the light emitting period is set to 75% or more of a one-field period, then the moving picture characteristic is deteriorated significantly. Thus, it is estimated that preferably the light emitting period is suppressed to less than 50% of a one-field period.
It is to be noted that the light emitting period corresponding to the sth scanning line VSCAN2(s) can be given by an expression given below. However, it is assumed that a one-field period is given by m horizontal scanning periods, and writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and light emission is carried out simultaneously. Further, the ratio of the light emitting period occupying in a one-field period T is represented by DUTY.
At this time, the light emitting period and the no-light emitting period are individually given by the following expressions:
Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY}·T
No-Light Emitting Period:
{[(s−1)/m]+DUTY}·T<t<{[(s−1)/m]+1}·T
where t satisfies a period given by the following expression:
[(s−1)/m]·T<t<{[(s−1)/m]+1}·T
Relating techniques are disclosed in JP-A-2002-514320, Japanese Patent Laid-Open No. 2005-027028 and Japanese Patent Laid-Open No. 2006-215213.
However, where a light emitting period and a no-light emitting period are provided in a one-field period, suppression of flickering becomes a new technical subject to be solved. Generally, in the case of moving pictures whose one-field period is given by 60 Hz, it is known that, if the light emitting period is set lower than 25% of a one-field period, then flickering is actualized, and it is considered desirable to set the light emitting period equal to or longer than 50% of a one-field period.
In particular, it is known that, in restriction to the light emitting period, two items of the picture quality of moving pictures and flickering have a tradeoff relationship, and the setting range of the light emitting period is restricted by the tradeoff relationship. However, the restriction to the setting range leads to restriction of the variation range of the peak luminance level.
Therefore, as a method of reducing flickering where the light emitting period is short, a method of dividing a light emitting period within a one-field period into a plurality of periods has been proposed.
Incidentally,
Incidentally,
Where a one-field period includes two light emitting periods, the light emitting period corresponding to the sth scanning line VSCAN2(s) can be given by an expression given below. It is to be noted, however, that a one-field period is given as m horizontal scanning periods, and writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and emission of light is started simultaneously. Further, the ratio of the light emitting period occupying in the one-field period T is represented by DUTY.
At this time, the light emitting period and the no-light emitting period are individually given by the following expressions:
Light Emitting Period in Former Half Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/2}·T
No-Light Emitting Period in Former Half Period:
{[(s−1)/m]+DUTY/2}·T<t<{[(s−1)/m]+½}T
Light Emitting Period in Latter Half Period:
[(s−1)/m+½]T<t<{[(s−1)/m]+(1+DUTY)/2}·T
No-Light Emitting Period in Latter Half Period:
{[(s−1)/m]+(1+DUTY)/2}·T<t<{[(s−1)/m]+1}·T
where t satisfies a period given by the following expression:
[(s−1)/m]·T<t<{[(s−1)/m]+1}·T
However, in the driving method wherein a one-field period is divided into a former half period and a latter half period, where the total light emitting period is 50% of a one-field period, light emission of 25%→no-light emission of 25%→light emission of 25%→no-light emission of 25% occurs repetitively.
According to this form of light emission, a movement of a line of sight same as that where the light emitting period is 75% of a one-field period occurs.
In other words, in the driving method wherein a one-field period is simply divided into a former half period and a latter half period, while flickering can be reduced, there is a technical subject to be solved in that motion artifact occurs and deteriorates the picture quality of moving pictures.
Therefore, it is demanded to provide a driving technique for a display panel wherein the peak luminance level can be adjusted over a wide range while suppression of both of appearance of motion artifact caused by increase of the ratio of the total light emitting period length occupying in a one-field period and appearance of flickering caused by decrease of the ratio of the light emitting period can be achieved simultaneously.
An embodiment according to the present invention proposes a method of and an apparatus for variably controlling, where the one-field period has N light emitting periods defined therein, N being equal to or greater than 2, the end timing of the ith light emitting period and the start timing of the i+1th light emitting period so as to satisfy the total light emitting period length within the one-field period, i being an odd number which satisfies 1≦i≦N−1 while i+1 satisfies 2≦i+1≦N.
In the method and apparatus, the end timing of an odd-numbered light emitting period and the start timing of an even-numbered light emitting period are varied to control the total light emitting period length. In other words, the total light emitting period length is controlled so as to narrow the gap (no-light emitting time) between a light emitting period and an adjacent light emitting period from the opposite directions.
By the driving technique, a driving method wherein the start timing of the first-time light emitting period and the end timing of the last-time light emitting period are fixed can be implemented. Accordingly, if the length from the start timing of the first-time light emitting period to the end timing of the last-timing light emitting period is set suitably, then it is possible to fix the movement width of the line of sight also upon display of moving images.
Also it is possible to vary the end timing of the last-time light emitting period in response to the total light emitting period length. However, also in this instance, since the controlling operation of the total light emitting period length is executed so as to narrow the gap (no-light emitting period) between adjacent ones of the light emitting periods from the opposite directions, increase of the movement width of the line of sight upon display of moving images can be suppressed.
As a result, by suitably setting the length from the start timing of the first-time light emitting period to the end timing of the last-time light emitting period, the peak luminance level can be adjusted over a wide range while appearance of flickering and motion artifact is suppressed.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.
In the following, an organic EL panel of the active matrix driving type to which embodiments according to the present invention are applied is described.
It is to be noted that, to those matters which are not disclosed in the present specification and the accompanying drawings, techniques which are known in the technical field to which an embodiment according to the present invention belongs are applied.
Referring to
The light emitting timing determination section 23 is a component unique to the organic EL panel 21. A ratio DUTY of a light emitting period occupying within a one-field period T is provided to the light emitting timing determination section 23. The light emitting timing determination section 23 determines an arrangement of light emitting periods so as to satisfy the ratio DUTY provided thereto. Here, the arrangement of the light emitting periods is determined for each second scanning line VSCAN2. The light emitting timing determination section 23 and the second scanning line driving section 7 correspond to a “display panel driving section”.
Although a particular determination method of light emitting periods is hereinafter described, the light emitting timing determination section 23 determines start timings and end timings of light emitting periods such that a period between two adjacent ones of light emitting periods, that is, a no-light emitting period, is narrowed from the opposite directions.
It is to be noted that, in order to reduce flickering and motion artifact to improve the picture quality, it is desirable to determine timings such that the period length from a start timing of the first-time light emitting period to an end timing of the last-time light emitting period becomes equal to or longer than 25% of a one-field period but equal to or shorter than 75% of a one-field period.
The light emitting timing determination section 23 operates to supply a start pulse DSST for providing a start timing of each light emitting period and an end pulse DSET for providing an end timing of each light emitting period to the second scanning line driving section 7 together with a clock DSCK.
Here, a driving example where the start timing of the first-time light emitting period and the end timing of the last-time light emitting period are fixed and the start timings and the end timings of each light emitting periods are determined so as to satisfy the ratio DUTY is described.
Incidentally, while it is represented in
At this time, the light emitting timing determination section 23 determines the light emitting period corresponding to the sth scanning line VSCAN2(s) in accordance with the expression given below.
However, the following calculation expressions are represented such that a one-field period is given by m horizontal scanning periods. Further, the sth scanning line VSCAN2(s) is represented such that writing operation is carried out within the sth horizontal scanning period and emission of light is started simultaneously. Further, the ratio of the total light emitting period occupying within a one-field period T is represented by DUTY. It is to be noted that, if a result of the calculation does not become an integral value, then the corresponding timing is adjusted in a unit of a clock.
At this time, the light emitting period and the no-light emitting period are given by the following expressions:
First-Time Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/2}·T
First-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/2}·T<t<{[(s−1)/m]+0.6−DUTY/2}·T
Second-Time Light Emitting Period:
{[(s−1)/m]+0.6−DUTY/2}·T<t<{[(s−1)/m]+0.6}·T
Second-Time No-Light Emitting Period:
{[(s−1)/m]+0.6}·T<t<{[(s−1)/m]+1}·T
where t is a period which satisfies the following expression:
[(s−1)/m]·T<t<{[(s−1)/m]+1}·T
In the case of the present driving example, the total light emitting period can be variably controlled within the range of 0% to 60% of the one-field period T.
Besides, where the present driving example is viewed from the point of view of motion artifact and flickering, this is equivalent to a case wherein the light emitting period is set to 0% to 60% of a one-field period. Accordingly, deterioration of the picture quality can be suppressed from the point of view of both of flickering and motion artifact. As a result, even if the peak luminance level is adjusted over a wide range, a method which does not involve deterioration of the picture quality can be implemented.
Incidentally, in the case of the driving example 1, it is necessary to vary the first-time light emitting period and the second-time light emitting period simultaneously by an equal adjustment amount as seen in
Therefore, when compared with an alternative case wherein a one-field period includes one light emitting period, the adjustment amount of the light emitting periods decreases to ½. In other words, when compared with the alternative case wherein a one-field period includes one light emitting period, the minimum adjustment width of the light emission luminance becomes doubled.
Such a characteristic as just described is not preferable from a point of view that the light emission luminance is adjusted smoothly.
Therefore, in the present driving example, the display panel incorporates a function of varying, upon variation of the ratio DUTY by a minimum adjustment width, only one of the end timing of the first-time light emitting period and the start timing of the second-time light emitting period alternately by the minimum adjustment width.
In the case of the driving example 1 described hereinabove, the start timing of the first-time light emitting period and the end timing of the second-time light emitting period are fixed for the maximum variation range (0% to 60% of the total light emitting period) of the peak luminance level.
However, another method may be adopted wherein the start timing of the first-time light emitting period and the end timing of the second-time light emitting period are fixed only within part of the variation range and, when the part of the variation range is exceeded, one light emitting period is provided and the end timing is gradually prolonged. For example, such a method may be adopted that, within a range shorter than 40% of a one-field period, the light emitting period is divided into two periods, but within a range of 40% to 60% of a one-field period, one light emitting period is provided and the period length is gradually extended.
It is to be noted that the
Further,
Incidentally, also in the cases of
At this time, the light emitting timing determination section 23 determines the light emitting period corresponding to the sth scanning line VSCAN2(s) in accordance with an expression given below.
However, also in the case of the calculation expression given below, it is assumed that a one-field period is given by m horizontal scanning periods. Also it is assumed that a writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and light emission is carried out simultaneously.
Further, the ratio of the light emitting period occupying in a one-field period T is represented by DUTY. It is to be noted that, if a result of the calculation does not become an integral value, then the corresponding timing is adjusted in a unit of a clock.
At this time, the light emitting period and the no-light emitting period are given by the following expressions:
where 0<DUTY<0.4,
First-Time Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/2}·T
First-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/2}·T<t<{[(s−1)/m]+0.4−DUTY/2}·T
Second-Time Light Emitting Period:
{[(s−1)/m]+0.4−DUTY/2}·T<t<{[(s−1)/m]+0.4}·T
Second-Time No-Light Emitting Period:
{[(s−1)/m]+0.4}·T<t<{[(s−1)/m]+1}·T
where 0.4<DUTY<0.6,
Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY}·T
No-Light Emitting Period:
{[(s−1)/m]+DUTY}·T<t<{[(s−1)/m]+1}·T
In the present driving example, where the total light emitting period length (ratio DUTY) occupying in a one-field period T is less than 40% of the one-field period T, the light emitting period is divided into two periods for driving. Consequently, the apparent ratio of the light emitting period can be made equal to 40%, and deterioration of the picture quality by flickering can be minimized as much.
On the other hand, where the total light emitting period length (ratio DUTY) occupying in a one-field period T is equal to or longer than 40% but equal to or shorter than 60%, one light emitting period is used for driving. Consequently, from the point of view of both of flickering and motion artifact, the peak luminance level can be adjusted over a wide range while deterioration of the picture quality is suppressed.
Naturally, also in this instance, a driving method similar to that of the driving example 2 may be adopted. In particular, where the total light emitting period length (ratio DUTY) occupying in a one-field period T is shorter than 40% of the one-field period T, only one of the end timing of the first-time light emitting period and the start timing of the second-time light emitting period may be varied by a minimum adjustment amount.
In the case of the driving example 1 described hereinabove, the start timing of the first-time light emitting period and the end timing of the second-time light emitting period are fixed for the maximum variation range (0% to 60% of the total light emitting period) of the peak luminance level.
On the other hand, in the case of the driving example 3 described hereinabove, the start timing of the first-time light emitting period and the end timing of the second-time light emitting period are fixed for only part of the maximum variation range of the peak luminance level, and where the part of the range is exceeded, only one light emitting period is used and the light emitting period length is extended simply.
However, for the second-time (last-time) light emitting period, a method of variably controlling also the end timing of the light emitting period in response to the ratio DUTY of the light emitting period may be used in combination with the driving example 1.
However, since the end timing of the second-time (last-time) light emitting period is prolonged, if the total light emitting period exceeds 75% of a one-field period, then deterioration of the picture quality by motion artifact becomes conspicuous. Accordingly, it is demanded to determine a reference point for the second-time light emitting period so that a maximum variation range of the peak luminance level is satisfied.
Here, a case is described wherein the position of two thirds of an estimated maximum variation range is determined as a base point of the second-time light emitting period. In particular, two light emitting periods are determined preceding to the base point, and the end timing of the second-time light emitting period is determined at a point later than the base point.
For example, where the estimated maximum variation range is given by 0% to 60% of a one-field period, the base point for the second-time light emitting period is determined at the position of 40% from the top of the one-field period.
It can be considered that this is similar to that where 60% which are the maximum variation range are virtually divided into three light emitting periods of 20% to carry out control. In this instance, it may be considered that the end timing of the second-time light emitting period and the start timing of the third-time light emitting period are fixed to 40%.
It is to be noted that
While, also in the cases of
At this time, the light emitting timing determination section 23 determines the light emitting periods corresponding to the sth scanning line VSCAN2(s) in accordance with an expression given below.
However, also in the case of the calculation expression given below, it is assumed that a one-field period is given by m horizontal scanning periods. Also it is assumed that a writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and light emission is carried out simultaneously.
Further, the ratio of the light emitting period occupying in a one-field period T is represented by DUTY. It is to be noted that, if a result of the calculation does not become an integral value, then the corresponding timing is adjusted in a unit of a clock.
At this time, the light emitting period and the no-light emitting period are given by the following expressions:
where 0<DUTY<0.6,
First-Time Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/3}·T
First-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/3}·T<t<{[(s−1)/m]+0.4−DUTY/3}·T
Second-Time Light Emitting Period:
{[(s−1)/m]+0.4−DUTY/3}·T<t<{[(s−1)/m]+0.4+DUTY/3}·T
Second-Time No-Light Emitting Period:
{[(s−1)/m]+0.4+DUTY/3}·T<t<{[(s−1)/m]+1}·T
In the present driving example, the total light emitting period length (ratio DUTY) occupying in a one-field period T can be controlled within the range of 0% to 60%. Simultaneously, from the point of view of flickering and motion artifact, effects similar to those of the variation control based on the light emission period of 40% to 60% can be implemented.
In particular, in the present driving example, although the end timing of the second-time light emitting period is not fixed, since the start timing of the second-time light emitting period increases or moves forwardly together with increase of the light emitting period, deterioration of the picture quality by flickering and motion artifact can be minimized similarly as in the driving examples described hereinabove.
Here, an example of driving wherein the end timing of light emitting periods is variably determined such that a given total light emitting period length (ratio DUTY) is satisfied in a state wherein the distance between start timings of each adjacent ones of the light emitting periods is defined so as to be shorter than a length obtained by dividing a one-field period by the number N (≧2) of the light emitting periods.
Incidentally, also in the cases of
At this time, the light emitting timing determination section 23 determines the light emitting period corresponding to the sth scanning line VSCAN2(s) in accordance with an expression given below.
However, also in the case of the calculation expression given below, it is assumed that a one-field period is given by m horizontal scanning periods. Also it is assumed that a writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and light emission is carried out simultaneously. Further, the ratio of the light emitting period occupying in a one-field period T is represented by DUTY. It is to be noted that, if a result of the calculation does not become an integral value, then the corresponding timing is adjusted in a unit of a clock.
At this time, the light emitting period and the no-light emitting period are given by the following expressions:
First-Time Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/2}·T
First-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/2}·T<t<{[(s−1)/m]+0.3}·T
Second-Time Light Emitting Period:
{[(s−1)/m]+0.3}·T<t<{[(s−1)/m]+DUTY/2}·T
Second-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/2}·T<t<{[(s−1)/m]+1}·T
where t is a period which satisfies the following expression:
[(s−1)/m]·T<t<{[(s−1)/m]+1}·T
In the present driving example, the distance between the start timings of adjacent light emitting periods is 30%. Accordingly, even if the total light emitting period length is close to 0%, from the point of view of flickering and motion artifact, a visual effect equal to that within a light emitting period which is 30% of a one-field period can be obtained.
Also where the total light emitting period length gradually increases from 0%, the increasing amount is allocated uniformly to the two light emitting periods.
Therefore, even at a point of time at which the total light emitting period length approaches 60%, from the point of view of flickering and motion artifact, a visual effect equal to that within a light emitting period which is 60% of a one-field period can be obtained.
It is to be noted that, with the method in related art, even where the total light emitting period length is 60% similarly, from the point of view of flickering and motion artifact, a visual effect equal to that where the light emitting period is 80% of a one-field period is provided.
In this manner, according to the driving method of the present driving example, even if the peak luminance level is adjusted over a wide range, for example, over a range from 0% to 60%, the adjustment range on the visual sensation from 25% or more to 75% or less of a one-field period can be satisfied. In other words, the driving method implements reduction of deterioration of the picture quality even if the peak luminance level is adjusted over the wide range.
Incidentally, in the case of the driving example 5, it is necessary to vary the first-time light emitting period and the second-time light emitting period simultaneously by an equal adjustment amount as seen in
Therefore, when compared with an alternative case wherein a one-field period includes one light emitting period, the adjustment amount of the peak luminance level decreases to ½. In other words, when compared with the alternative case wherein a one-field period includes one light emitting period, the minimum adjustment width of the peak luminance level becomes doubled.
Such a characteristic as just described is not preferable from a point of view that the light emission luminance is adjusted smoothly.
Therefore, in the present driving example, the display panel incorporates a function of varying, upon variation of the peak luminance level (ratio DUTY) by a minimum adjustment width, only one of the end timing of the first-time light emitting period and the start timing of the second-time light emitting period alternately by the minimum adjustment width.
C-3. Driving Example 7 of the Display Panel
In the case of the driving example 5 described hereinabove, two light emitting periods are disposed in a one-field period except the maximum value (60%) of the variation range of the peak luminance level.
However, another method may be adopted wherein a light emitting period within a one-field period is divided into two periods only within part of the variation range, and after the part of the variation range is exceeded, only the end timing of the one light emitting period which is a combination of the two light emitting periods is gradually prolonged.
In the following description, it is assumed that, only where the total light emitting period length (ratio DUTY) which provides an adjustment amount for the peak luminance level is given by 40% or less of a one-field period, a driving method which presupposes disposition of two light emitting periods is applied, but where the total light emitting period length (ratio DUTY) exceeds 40% of a one-field period, another driving method which presupposes disposition of one light emitting period is applied.
Also it is assumed that the maximum variation range of the total light emitting period length (ratio DUTY) is given by 0% to 60%.
It is to be noted that the
More specifically,
However, where the total light emitting period length is proximate to 0%, from the point of view of flickering and motion artifact, a visual effect equal to that within a light emitting period which is 20% of a one-field period may be obtained, and there is the possibility that the visual effect may become lower than that where the lighting emitting period is 25% of a one-field period with which good picture quality can be obtained.
However, the light emitting period on the visual effect becomes lower than 25% of a one-field period only where the ratio DUTY is lower than 10% of the total light emitting period length. Besides, the light emitting period on the visual effect can be 20% of a one-field period at the lowest. Accordingly, when compared with the technique in related art, deterioration of the picture quality by flickering can be reduced significantly.
Incidentally, also in the cases of
At this time, the light emitting timing determination section 23 determines the light emitting period corresponding to the sth scanning line VSCAN2(s) in accordance with an expression given below.
However, also in the case of the calculation expression given below, it is assumed that a one-field period is given by m horizontal scanning periods. Also it is assumed that writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and light emission is carried out simultaneously.
Further, the ratio of the light emitting period occupying in a one-field period T is represented by DUTY. It is to be noted that, if a result of the calculation does not become an integral value, then the corresponding timing is adjusted in a unit of a clock.
At this time, the light emitting period and the no-light emitting period are given by the following expressions:
where 0<DUTY<0.4,
First-Time Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/2}·T
First-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/2}·T<t<{[(s−1)/m]+0.2}·T
Second-Time Light Emitting Period:
{[(s−1)/m]+0.2}·T<t<{[(s−1)/m]+(0.2+DUTY/2}·T
Second-Time No-Light Emitting Period:
{([(s−1)/m]+(0.2+DUTY/2}·T<t<{[(s−1)/m]+1}·T
where 0.4<DUTY<0.6,
Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY}·T
No-Light Emitting Period:
{[(s−1)/m]+DUTY}−T<t<{[(s−1)/m]+1}·T
In the present driving example, where the total light emitting period length (ratio DUTY) occupying in a one-field period T is less than 40% of the one-field period T, the light emitting period is divided into two periods for driving. Consequently, the apparent ratio of the light emitting period can be increased from 20% to 40%. By this, deterioration of the picture quality by flickering can be minimized.
On the other hand, where the total light emitting period length (ratio DUTY) occupying in a one-field period T is equal to or longer than 40% but equal to or shorter than 60%, one light emitting period is used for driving. Consequently, from the point of view of flickering and motion artifact, deterioration of the picture quality can be suppressed.
In this manner, the peak luminance level can be adjusted over a wide range while deterioration of the picture quality is suppressed.
It is to be noted that, also in this instance, a driving method similar to that of the driving example 6 may be adopted. In particular, where the total light emitting period length (ratio DUTY) occupying in a one-field period T is shorter than 40% of the one-field period T, only one of the end timing of the first-time light emitting period and the end timing of the second-time light emitting period may be varied by a minimum adjustment amount.
In the case of the driving example 5 described hereinabove, where the peak luminance level is controlled by control of the length of two light emitting periods, the distance between the start timings of the two light emitting periods is set shorter than the period length (50%) which is one half of a one-field period. More particularly, the distance between the start timings of two adjacent light emitting periods is set to 30%.
However, control based on the total light emitting period length can be implemented also by control of each of three or more divisional light emitting periods.
Here, a driving example where four light emitting periods are set within a one-field period is described. Naturally, the distance between the start timings of adjacent light emitting periods is set shorter than a period length (25%) where a one-field period is equally divided into four periods.
It is to be noted that
Also in the cases of
At this time, the light emitting timing determination section 23 determines the light emitting period corresponding to the sth scanning line VSCAN2(s) in accordance with an expression given below.
However, also in the case of the calculation expression given below, it is assumed that a one-field period is given by m horizontal scanning periods. Also it is assumed that a writing operation into the sth scanning line VSCAN2(s) is carried out within the sth horizontal scanning period and light emission is carried out simultaneously.
Further, the ratio of the light emitting period occupying in a one-field period T is represented by DUTY. It is to be noted that, if a result of the calculation does not become an integral value, then the corresponding timing is adjusted in a unit of a clock.
At this time, the light emitting period and the no-light emitting period are given by the following expressions:
where 0<DUTY<0.6,
First-Time Light Emitting Period:
[(s−1)/m]·T<t<{[(s−1)/m]+DUTY/4}·T
First-Time No-Light Emitting Period:
{[(s−1)/m]+DUTY/4}·T<t<{[(s−1)/m]+0.15}·T
Second-Time Light Emitting Period:
{[(s−1)/m]+0.15}·T<t<{[(s−1)/m]+0.15+DUTY/4}·T
Second-Time No-Light Emitting Period:
{[(s−1)/m]+0.15+DUTY/4}·T<t<{[(s−1)/m]+0.3}·T
Third-Time Light Emitting Period:
{[(s−1)/m]+0.3}·T<t<{[(s−1)/m]+0.3+DUTY/4}·T
Third-Time No-Light Emitting Period:
{[(s−1)/m]+0.3+DUTY/4}·T<t<{[(s−1)/m]+0.45}·T
Fourth-Time Light Emitting Period:
{[(s−1)/m]+0.45}·T<t<{[(s−1)/m]+0.45+DUTY/4}·T
Fourth-Time No-Light Emitting Period:
{[(s−1)/m]+0.45+DUTY/4}·T<t<{[(s−1)/m]+1}·T
In the present driving example, the total light emitting period length (ratio DUTY) occupying in a one-field period T can be variably controlled within the range of 0% to 60%. Simultaneously, from the point of view of flickering and motion artifact, effects similar to those of the variation control based on the light emission period of 45% to 60% can be implemented.
In particular, in the present driving example, although the end timing of each of the light emitting periods is not fixed, since the distance between the start timings of adjacent light emitting periods is shorter than one fourth of the total light emitting period length the expansion of the movement width of the line of sight can positively be suppressed. Further, since the number of light emitting periods increases to four, even where the ratio DUTY of the light emitting period occupying in a one-field period T has a value proximate to zero, the light emission width on the visual sensation can be increased so that flickering can be perceived more readily.
In other words, deterioration of the picture quality by flickering and motion artifact can be minimized.
Further, the driving example 8 and the driving example 7 described hereinabove may be combined. In particular, four light emitting periods may be used only within part of a variation range such that, if this range is exceeded, then only one light emitting period is used for control.
In the driving example 8 described above, the distances of the start timings of adjacent ones of light emitting periods are equal to each other (15%).
However, only some of the distances between the start timings between adjacent light emitting periods may be set as short as less than one over the number of light emitting periods within a one-field period. For example, in the case of the driving example 8, the distance between the start timings of the first- and second-time light emitting periods may be set to 15% while the distance between the start timings between the second- and third-light emitting periods and the distance between the start timings of the third- and fourth-light emitting periods are set to 25%.
Also in such a case as just described, the movement width of the line of sight can be suppressed when compared with an alternative case wherein a one-field period is equally divided by the number of light emitting periods. Consequently, a deterioration compensation effect of the picture quality involved in variation control of the peak luminance level can be expected. However, in order to avoid significant deterioration of the picture quality, preferably the variation range of the total light emitting period length is set so as to be included in the range from 25% to 75% of a one-field period.
In the driving example 6 described above, where the number of light emitting periods to be disposed in a one-field period is two, when the peak luminance level is varied by a minimum variation unit, the light emitting period length is controlled to increase or decrease by the minimum unit only for one of the two light emitting periods.
This driving method can be applied similarly also where the number of light emitting periods to be disposed in a one-field period is three or more. It is to be noted that, where the number of light emitting periods to be disposed in a one-field period is N, the number of those light emitting periods whose light emitting period length should be varied should be equal to or less than N−1. Naturally, as the number of N−1 decreases, the peak luminance level can be adjusted with increased smoothness.
In particular, most preferably the number of those light emitting periods whose light emitting period length should be varied with the minimum variation amount of the peak luminance level is only one from among the N light emitting periods. It is to be noted that the position of the light emitting period or periods whose light emitting period length should be varied is any number.
In the foregoing description, a pixel array section and a driving circuit are formed on one panel.
However, it is possible to produce and distribute the pixel array section 3 and the driving sections 5, 7, 9, 23 or the like separately from each other. For example, it is possible to fabricate the driving sections 5, 7, 9, 23 or the like as an independent drive IC (integrated circuit) and distribute the same independently of a panel on which the pixel array section 3 is formed.
The organic EL panel 21 in the embodiment described above may be distributed in the form of a display module 31 having an appearance configuration shown in
The display module 31 has a structure wherein an opposing section 33 adhered to the surface of a support board 35. The opposing section 33 includes a substrate formed from a transparent member of glass or the like and has a color filter, a protective film, a light blocking film and so forth disposed on the surface thereof.
It is to be noted that a flexible printed circuit (FPC) 37 for inputting and outputting a signal from the outside to the support board 35 and vice versa and other necessary elements may be provided on the display module 31.
The organic EL panel in the embodiments described hereinabove is circulated also in the form of a commodity wherein the organic EL panel is incorporated in an electronic apparatus.
It is to be noted that the electronic apparatus 41 is not restricted to apparatus of a particular field only if it incorporates a function of displaying an image produced in the electronic apparatus 41 or inputted from the outside.
The electronic apparatus 41 of the type described may be, for example, a television receiver. An example of an appearance of a television receiver 51 is shown in
A display screen 57 formed from a front panel 53, a filter glass plate 55 and so forth is disposed on the front face of a housing of the television receiver 51. The display screen 57 corresponds to the organic EL panel described hereinabove in connection with the embodiment.
Or, the electronic apparatus 41 may be, for example, a digital camera. An example of an appearance of a digital camera 61 is shown in
The digital camera 61 includes an image pickup lens not shown disposed on the rear face side of a protective cover 63 which is in a closed state in
Or else, the electronic apparatus 41 may be, for example, a video camera.
Referring to
Or otherwise, the electronic apparatus 41 may be, for example, a portable terminal apparatus.
The portable telephone set 91 includes an upper side housing 93, a lower side housing 95, a connection portion 97 in the form of a hinge, a display screen 99, an auxiliary display screen 101, a picture light 103 and an image pickup lens 105. The display screen 99 and the auxiliary display screen 101 correspond to the organic EL panel described hereinabove in connection with the embodiment.
Furthermore, the electronic apparatus 41 may be, for example, a computer.
The notebook type computer 111 includes a lower side housing 113, an upper side housing 115, a keyboard 117 and a display screen 119. The display screen 119 corresponds to the organic EL panel described hereinabove in connection with the embodiment.
The electronic apparatus 41 may further be formed as an audio reproduction apparatus, a game machine, an electronic book, an electronic dictionary or the like.
The driving methods described hereinabove may be applied also to other apparatus than organic EL panels. For example, the driving methods may be applied, for example, to inorganic EL panels, display panels on which LEDs (light emitting diode) are arrayed, plasma display panels and display panels of the self-luminous type wherein light emitting elements having other diode structures are arrayed on the surface.
Further, the driving methods described hereinabove may be applied also to display panels of the non-self-luminous type such as liquid crystal display panels.
While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-148697 | Jun 2007 | JP | national |
| 2007-148698 | Jun 2007 | JP | national |
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| Japanese Office Action issued Mar. 6, 2012 for corresponding Japanese Application No. 2007-148697. |
| Japanese Office Action issued Mar. 6, 2012 for corresponding Japanese Application No. 2007-148698. |
| Number | Date | Country | |
|---|---|---|---|
| 20080303847 A1 | Dec 2008 | US |
