Display device and display device driving method
A display device includes: a luminance converter which converts input gradation value into a corresponding target luminance value; a luminance correction calculator which calculates output gradation value from the target luminance value using efficiency residual ratio representing a deterioration degree of a light-emitting element, and calculates a corrected luminance value therefrom; a current stress calculator which converts current stress amount on a light-emitting element calculated from the corrected luminance value into current stress amount when first reference current flows through the light-emitting element, and accumulates this to calculate an accumulated first stress amount; a CB stress calculator which converts CB stress amount on the light-emitting element into current stress amount when second reference current flows through the light-emitting element, and accumulates this to calculate an accumulated second stress amount; and an efficiency residual ratio calculator which updates the efficiency residual ratio, using the accumulated first and second stress amounts calculated.
1. A display device which includes a display screen in which pixels are arranged in a matrix, each of the pixels including a light-emitting element, the display device comprising:
a correction circuit which corrects an input gradation value indicated by a luminance signal included in a video signal, wherein
the correction circuit includes:
a luminance converter which converts the input gradation value into a target luminance value corresponding to the input gradation value;
a correction calculator which calculates an output gradation value from the target luminance value using an efficiency residual ratio which is an index representing a degree of deterioration of the light-emitting element, and calculates a corrected luminance value from the output gradation value, the output gradation value being obtained by correcting the input gradation value, the efficiency residual ratio indicating a residual ratio of light emission efficiency of the light-emitting element, the corrected luminance value being obtained by correcting the target luminance value;
a current stress calculator which converts a current stress amount on the light-emitting element that is calculated from the corrected luminance value into a first stress amount indicating a current stress amount when a first reference current flows through the light-emitting element, and calculates an accumulated first stress amount obtained by accumulating the first stress amount resulting from the conversion;
a carrier balance (CB) stress calculator which converts a CB stress amount, which is a stress amount due to carrier balance, on the light-emitting element into a second stress amount indicating a current stress amount when a second reference current flows through the light-emitting element or a second stress amount represented by an energizing time indicating a time for which current is supplied to the light-emitting element, and calculates an accumulated second stress amount obtained by accumulating the second stress amount resulting from the conversion; and
an efficiency residual ratio calculator which updates the efficiency residual ratio, using the accumulated first stress amount and the accumulated second stress amount that are calculated.
2. The display device according to claim 1 , wherein
the efficiency residual ratio is expressed by a ratio of a light emission luminance of the light-emitting element after deterioration to a light emission luminance of the light-emitting element at an initial stage of operation, and
the efficiency residual ratio calculator:
calculates, using a relationship between a luminance of the light-emitting element and an accumulated time for which the first reference current flows through the light-emitting element, a first efficiency residual ratio that is new and attributable to current stress, from the accumulated time which is calculated as the accumulated first stress amount;
calculates, using a relationship between the luminance of the light-emitting element and an accumulated time for which the second reference current flows through the light-emitting element or a relationship between the luminance of the light-emitting element and an accumulated time of the energizing time, a second efficiency residual ratio that is new and attributable to the carrier balance; and
updates the efficiency residual ratio by calculating the efficiency residual ratio from the first efficiency residual ratio and the second efficiency residual ratio.
3. The display device according to claim 1 , wherein
the current stress amount calculated from the corrected luminance value is a stress amount for a first current that flows through the light-emitting element when the light-emitting element is caused to emit light according to the corrected luminance value,
the stress amount for the first current is equivalent to a time for which the first current flows through the light-emitting element,
a stress amount for the first reference current is equivalent to a time for which the first reference current flows through the light-emitting element, and
the current stress calculator converts the current stress amount calculated from the corrected luminance value into the first stress amount by converting the time for which the first current flows through the light-emitting element into the time for which the first reference current flows through the light-emitting element.
4. The display device according to claim 1 , wherein
when converting the CB stress amount into the second stress amount indicating the current stress amount when the second reference current flows through the light-emitting element:
the CB stress amount is calculated using the corrected luminance value or a time for which current is supplied to the light-emitting element in order to cause the light-emitting element to emit light;
the CB stress amount is equivalent to a time for which a second current flows through the light-emitting element when the light-emitting element is caused to emit light according to the corrected luminance value;
a stress amount for the second reference current is equivalent to a time for which the second reference current flows through the light-emitting element; and
the current stress calculator converts the CB stress amount into the second stress amount by converting the time for which the second current flows through the light-emitting element into the time for which the second reference current flows through the light-emitting element.
5. A method of driving a display device which includes a display screen in which pixels are arranged in a matrix, each of the pixels including a light-emitting element, the method comprising:
correcting an input gradation value indicated by a luminance signal included in a video signal, wherein
the correcting includes:
converting the input gradation value into a target luminance value corresponding to the input gradation value;
calculating an output gradation value from the target luminance value using an efficiency residual ratio which is an index representing a degree of deterioration of the light-emitting element, and calculating a corrected luminance value from the output gradation value, the output gradation value being obtained by correcting the input gradation value, the efficiency residual ratio indicating a residual ratio of light emission efficiency of the light-emitting element, the corrected luminance value being obtained by correcting the target luminance value;
converting a current stress amount on the light-emitting element that is calculated from the corrected luminance value into a first stress amount indicating a current stress amount when a first reference current flows through the light-emitting element, and calculating an accumulated first stress amount obtained by accumulating the first stress amount resulting from the conversion;
converting a CB stress amount, which is a stress amount due to carrier balance, on the light-emitting element into a second stress amount indicating a current stress amount when a second reference current flows through the light-emitting element, and calculating an accumulated second stress amount obtained by accumulating the second stress amount resulting from the conversion; and
updating the efficiency residual ratio, using the accumulated first stress amount and the accumulated second stress amount that were calculated.
6. The method according to claim 5 , wherein
the efficiency residual ratio is expressed by a ratio of a light emission luminance of the light-emitting element after deterioration to a light emission luminance of the light-emitting element at an initial stage of operation, and
the updating of the efficiency residual ratio includes:
calculating, using a relationship between a luminance of the light-emitting element and an accumulated time for which the first reference current flows through the light-emitting element, a first efficiency residual ratio that is new and attributable to current stress, from the accumulated time which is calculated as the accumulated first stress amount;
calculating, using a relationship between the luminance of the light-emitting element and an accumulated time for which the second reference current flows through the light-emitting element or a relationship between the luminance of the light-emitting element and an accumulated time of the energizing time, a second efficiency residual ratio that is new and attributable to the carrier balance; and
updating the efficiency residual ratio by calculating the efficiency residual ratio from the first efficiency residual ratio and the second efficiency residual ratio.
7. The method according to claim 5 , wherein
the current stress amount calculated from the corrected luminance value is a stress amount for a first current that flows through the light-emitting element when the light-emitting element is caused to emit light according to the corrected luminance value,
the stress amount for the first current is equivalent to a time for which the first current flows through the light-emitting element,
a stress amount for the first reference current is equivalent to a time for which the first reference current flows through the light-emitting element, and
the converting of the current stress includes converting the current stress amount calculated from the corrected luminance value into the first stress amount by converting the time for which the first current flows through the light-emitting element into the time for which the first reference current flows through the light-emitting element.
8. The method according to claim 5 , wherein
when converting the CB stress amount into the second stress amount indicating the current stress amount when the second reference current flows through the light-emitting element:
the CB stress amount is calculated using the corrected luminance value or a time for which current is supplied to the light-emitting element in order to cause the light-emitting element to emit light;
the CB stress amount is equivalent to a time for which a second current flows through the light-emitting element when the light-emitting element is caused to emit light according to the corrected luminance value;
a stress amount for the second reference current is equivalent to a time for which the second reference current flows through the light-emitting element; and
the converting of the CB stress amount includes converting the CB stress amount into the second stress amount by converting the time for which the second current flows through the light-emitting element into the time for which the second reference current flows through the light-emitting element.