JP2007240694A - LIGHT EMITTING DEVICE, ELECTRONIC DEVICE, AND METHOD FOR DETERMINING CORRECTION VALUE - Google Patents

Abstract

A correction value that precisely reflects the characteristics of a light emitting element is determined according to a current flowing through the light emitting element.
A unit circuit U includes a light emitting element E that emits light according to a current IEL supplied from a power supply line 17 and a drive transistor Tdr that controls the current IEL according to a gate voltage. The voltage control unit 52 sets the power supply voltage VEL of the feeder line 17 to the voltage value V1 during the driving period and sets the voltage value V2 during the setting period. The voltage value V1 is a voltage for operating the driving transistor Tdr in the saturation region, and the voltage value V2 is a voltage for operating in the non-saturation region. The current measuring unit 53 measures the current value Q flowing from the power supply line 17 to the light emitting element E during the set period. The data generation unit 54 and the correction value determination unit 421 determine the correction value A according to the current value Q. In the drive period, each light emitting element E is driven by applying a voltage according to the gradation data G2 and the correction value A to the gate of the drive transistor Tdr.
[Selection] Figure 2

Description

  The present invention relates to a technique for correcting the luminance (light quantity) of a light emitting element such as an organic light emitting diode element.

  Conventionally, a light emitting device using a transistor (hereinafter referred to as “driving transistor”) for controlling the light emitting element has been proposed. The drive transistor is interposed, for example, between the power supply line and the light emitting element. The current supplied from the power supply line to the light emitting element is controlled according to the gate voltage of the driving transistor.

  By the way, there are various characteristics such as voltage-current characteristics (a relation between a voltage applied to the light-emitting element and a current flowing through the light-emitting element) and current-luminance characteristics (a relation between a current flowing through the light-emitting element and the luminance of the light-emitting element). There may be an error in the characteristics initially or over time. In order to reduce the influence of this error, a technique for correcting the luminance of each light emitting element has been conventionally proposed.

For example, Patent Document 1 discloses a technique for measuring a current flowing through each light emitting element when the driving transistor is in a conductive state, and determining a correction value for each light emitting element based on the result of the measurement. When the light emitting device is actually used, a voltage corresponding to gradation data designating the gradation (luminance) of the light emitting element and a predetermined correction value is supplied to the gate of the driving transistor.
JP 2002-278513 A

  However, the current measured when determining the correction value under the technique of Patent Document 1 is actually determined predominantly according to the gate voltage of the driving transistor, and the characteristics of each light emitting element (particularly, voltage-current). The characteristic) has little effect on this current. Therefore, the above technique has a problem that it is difficult to detect an error in the characteristics of the light emitting element with high sensitivity, and it is difficult to realize correction reflecting the characteristics of each light emitting element with high accuracy. In view of such circumstances, an object of the present invention is to solve the problem of determining a correction value that accurately reflects the characteristics of a light emitting element in accordance with a current flowing through the light emitting element.

  In order to solve the above-described problems, the light-emitting device according to the present invention uses a first voltage (for example, a voltage value in each mode) in a first period (for example, a driving period in each mode described below). V1) and voltage control means (for example, voltage control in FIG. 2) that sets the second voltage (for example, voltage value V2 in each mode) lower than the first voltage in the second period (for example, set period in each mode). Unit 52), a light emitting element that emits light in accordance with a current supplied via a power supply line, and a current path that is arranged on a path of a current supplied to the light emitting element via a power supply line. A drive transistor controlled according to the current, current measuring means for measuring the current flowing through the light emitting element via the feeder in the second period (for example, the current measuring unit 53 in FIG. 2), and current measured by the current measuring means Depending on The correction value determining means to be determined (for example, the data generation unit 54 and the correction value determining unit 421 in FIG. 2), and the voltage corresponding to the gradation data and the correction value determined by the correction value determining means are set to drive transistors in the first period. Drive means (for example, the data line drive circuit 25) for supplying to the gates of the first and second gates.

  In the above configuration, when the current measuring unit measures the current value that is the basis for determining the correction value, the voltage of the feeder is in the first period (that is, the period in which the luminance of the light emitting element is corrected according to the correction value). ) Is set to a second voltage lower than the first voltage. Therefore, since the voltage-current characteristics (hereinafter referred to as “IV characteristics”) of the light emitting element significantly affect the current measured by the current measuring means, it is possible to determine a correction value that accurately reflects the characteristics of the light emitting element. It becomes.

  In a preferred aspect of the present invention, the first voltage is a voltage for operating the driving transistor in a saturation region, and the second voltage is a voltage for operating the driving transistor in a non-saturation region (linear region). According to this aspect, since the driving transistor operates in the saturation region in the first period, the current supplied to the light emitting element is controlled with high accuracy according to the voltage of the gate of the driving transistor. On the other hand, since the driving transistor operates in the non-saturated region in the second period for determining the correction value, it is possible to significantly reflect the characteristics (particularly IV characteristics) of the light emitting element in the current measured by the current measuring means. Become.

In the present invention, a configuration (for example, a first embodiment described later) in which a common correction value is determined for a plurality of light emitting elements is employed. However, in order to correct the difference in characteristics for each light emitting element, a configuration in which a correction value is individually determined for each light emitting element is preferable. In this configuration, for example, the correction value is determined according to the result of measuring the current flowing through one light emitting element. However, since the current flowing through one light-emitting element is extremely weak, there is a problem that high-performance current detection means is required to detect this, and the manufacturing cost of the light-emitting device increases.
Therefore, a light emitting device according to a preferred embodiment of the present invention includes a plurality of unit circuits each including a light emitting element and a driving transistor, and the current measuring means includes an element group (for example, as shown in FIG. 7). For each of the light emitting elements E belonging to the region B0), a current flowing through a predetermined number of light emitting elements belonging to the element group (for example, a plurality of light emitting elements E belonging to the region B1 in FIG. 7) is measured, and correction value determining means Determines a correction value (for example, a correction value indicated by a white circle in part (b) of FIG. 7) for each element group according to each current measured by the current measuring means, and each light emitting element is interpolated by each correction value. (For example, a correction value indicated by a black circle in part (b) of FIG. 7) is determined. In addition, the specific example of the above aspect is later mentioned as 2nd Embodiment.
According to this aspect, the correction value of each light emitting element is determined by interpolating the correction value of each element group according to the result of measuring the current flowing through the predetermined number of light emitting elements. Therefore, the current measuring means is not required to have a performance for detecting a weak current flowing in one light emitting element. Therefore, there is an advantage that the correction value of each light emitting element can be determined while reducing the manufacturing cost of the light emitting element.

  In addition, the characteristics of the light-emitting element vary depending on the temperature. Therefore, in a preferred aspect of the present invention, a temperature measuring means for measuring the ambient temperature of the light emitting device is further arranged, and the correction value determining means includes the current measured by the current measuring means and the temperature measured by the temperature measuring means. The correction value is determined according to. According to this aspect, it is possible to realize an optimal correction according to the temperature of the light emitting element. A specific example of the above aspect will be described later as a fourth embodiment.

  The light emitting device according to the present invention is used in various electronic devices. A typical example of this electronic device is a device using a light emitting device as a display device. Examples of this type of electronic device include a personal computer and a mobile phone. However, the use of the light emitting device according to the present invention is not limited to image display. For example, an exposure device (exposure head) for forming a latent image on an image carrier such as a photosensitive drum by irradiation of light, a device (backlight) that is arranged on the back side of the liquid crystal device and illuminates it, or The light emitting device of the present invention can be applied to various uses such as various illumination devices such as a device that illuminates a document by being mounted on an image reading device such as a scanner.

  The present invention is also specified as a method for determining a luminance correction value of a light emitting element. A light-emitting device using the method according to the present invention includes a light-emitting element that emits light according to a current supplied via a power supply line, and a drive transistor disposed on a current path. In this device, the light emitting element is controlled by setting the gate of the driving transistor to a voltage corresponding to the gradation data and the correction value in a period during which one voltage is supplied. The correction value is determined by setting the second voltage in the voltage control process by setting the power supply line to a second voltage lower than the first voltage and by controlling the drive transistor in a conductive state. A current supply process for supplying current to the light emitting element via the feeder line, a current measurement process for measuring the current flowing to the light emitting element in the current supply process, and a correction value according to the current measured in the current measurement process. And a correction value determination process for determining. According to the above method, for the same reason as the light emitting device according to the present invention, it is possible to determine a correction value that accurately reflects the characteristics of the light emitting element according to the current flowing through the light emitting element.

  For a light-emitting device that includes a plurality of unit circuits each including a light-emitting element and a drive transistor, in a current measurement process, a predetermined number belonging to the element group for each of a plurality of element groups into which the plurality of light-emitting elements are divided. In the correction value determination process, a correction value is determined for each element group according to each current measured in the current measurement process, and correction of each light emitting element is performed by interpolation of each correction value. It is desirable to determine the value. According to this method, it is possible to determine the correction value for each light emitting element while suppressing the accuracy required for measuring the current of the light emitting element. A specific example of this aspect will be described later as a second embodiment.

  In a preferred embodiment of the method according to the present invention, a temperature measurement process for measuring the ambient temperature of the light emitting device is executed, and in the correction value determination process, the current measured in the current measurement process and the temperature measurement process are used. The correction value is determined according to the measured temperature. According to this aspect, it is possible to realize an optimal correction according to the temperature of the light emitting element. A specific example of the above aspect will be described later as a fourth embodiment.

<A: First Embodiment>
FIG. 1 is a block diagram showing a specific form of a light emitting device used in various electronic devices as means for displaying an image. As shown in the figure, the light emitting device D generates a display panel 10 that displays an image, a control circuit 40 that controls each part of the light emitting device D, a power supply voltage VEL and a ground voltage Gnd, and supplies them to the display panel 10. Power supply circuit 50.

  The display panel 10 includes an element array unit 11 in which a plurality of unit circuits (pixel circuits) U are arranged, a scanning line driving circuit 22 that controls each unit circuit U under the control of the control circuit 40, and a light emission control circuit 23. And a data line driving circuit 25. Each unit circuit U includes a light emitting element E that emits light by supplying electric energy. Each light emitting element E emits light in any of a plurality of light emission colors (red, green, and blue). The three light-emitting elements E that emit red, green, and blue constitute a pixel that is the minimum unit of an image.

  The element array unit 11 includes m scanning lines 12 extending in the X direction, m light emission control lines 13 extending in the X direction in pairs with the scanning lines 12, and orthogonal to the X direction. N data lines 15 extending in the Y direction are formed (each of m and n is a natural number of 2 or more). Each unit circuit U is arranged at a position corresponding to each intersection of a pair of scanning line 12 and light emission control line 13 and data line 15. Accordingly, these unit circuits U are arranged in a matrix of m rows × n columns. In the element array section 11, a power supply line 17 extending from the power supply circuit 50 to each unit circuit U is formed. The power supply voltage VEL output from the power supply circuit 50 is supplied to each unit circuit U via the feeder line 17.

  The control circuit 40 defines the operation timing of each part of the light emitting device D by supplying various control signals such as a clock signal and a synchronization signal. The control circuit 40 of the present embodiment includes a correction circuit 42 that generates gradation data G2 by correcting the gradation data G1. The gradation data G1 is data that designates the gradation (luminance) of each light emitting element E, and is serially supplied to the correction circuit 42 from various host devices such as a CPU of an electronic device in which the light emitting device D is mounted. The

  The period during which the light emitting device D operates is divided into a setting period and a driving period. The set period is a period for determining a numerical value (hereinafter referred to as “correction value”) applied to correction by the correction circuit 42 according to the characteristics of each light emitting element E. The driving period is a period for driving each light emitting element E according to the correction value determined in the setting period and the gradation data G1 supplied from the host device (according to the gradation data G2 generated by the correction circuit 42). It is a period during which the light emitting element E of each unit circuit U is driven). In other words, the drive period is a period during which an image designated by the host device is actually displayed on the element array unit 11.

  The set period in the present embodiment is a period immediately after the light emitting device D is turned on, and the drive period is a period after the set period has elapsed. The control circuit 40 outputs to the power supply circuit 50 a control signal Sc (for example, a signal whose logic level changes between the setting period and the driving period) designating either the setting period or the driving period. In addition, the timing and the frequency | count of a setting period are arbitrary. For example, the operation for determining the correction value may be executed periodically (for example, every predetermined number of frame periods) a plurality of times.

  The scanning line driving circuit 22 generates scanning signals Y 1 to Ym for selecting each of the m scanning lines 12 and outputs the scanning signals Y 1 to Ym to each scanning line 12. In the driving period, each of the scanning signals Y1 to Ym sequentially transitions to a high level. That is, the scanning signal Yi output to the scanning line 12 in the i-th row (i is an integer satisfying 1 ≦ i ≦ m) is at a high level in the i-th horizontal scanning period in the frame period (that is, the first line). The i-th scanning line 12 is selected), and the low level is maintained in other periods.

  The light emission control circuit 23 generates light emission control signals C1 to Cm that define a period during which the light emitting element E of each unit circuit U actually emits light, and outputs it to each light emission control line 13. In the drive period, the light emission control signal Ci supplied to the light emission control line 13 in the i-th row transitions to a low level during a horizontal scanning period when the scanning signal Yi is at a high level, and is at a high level in other periods. To maintain. Therefore, a signal obtained by inverting the logic level of the scanning signal Yi is used as the light emission control signal Ci. In FIG. 1, the light emission control circuit 23 and the scanning line drive circuit 22 are illustrated as separate circuits, but the light emission control circuit 23 and the scanning line drive circuit 22 are mounted on a single IC chip. Is also adopted.

  The data line driving circuit 25 outputs data signals X1 to Xn to each data line 15. The data signals X1 to Xn are voltage signals that specify the luminance of the light emitting element E of each unit circuit U. In the horizontal scanning period in which the scanning signal Yi maintains a high level in the driving period, the data signal Xj supplied to the data line 15 in the j-th column (j is an integer satisfying 1 ≦ j ≦ n) The voltage Vdata corresponds to the luminance specified for the light emitting element E of the unit circuit U in the j-th column belonging to. The luminance of each light emitting element E (the voltage Vdata of the data signal Xj) is specified by the gradation data G2 supplied from the control circuit 40 to the data line driving circuit 25.

  FIG. 2 is a block diagram showing a specific configuration of the power supply circuit 50 and the correction circuit 42. In the figure, the illustration of the control circuit 40 other than the correction circuit 42 is omitted. As shown in FIG. 2, the correction circuit 42 includes a correction value determination unit 421 and a separation unit 422, and three correction units 423 (423r, 423g, and 423b) each corresponding to a different light emission color. The correction value determination unit 421 is means for determining a correction value A (Ar · Ag · Ab) for each emission color based on the actual characteristics of each light emitting element E. In the present embodiment, a common correction value A is determined for each light emitting element E having a common emission color. A specific example of the operation for determining the correction value A will be described later.

  In the driving period, the gradation data G1 is serially supplied from the host device to the separation unit 422. The separation unit 422 separates the gradation data G1 into separate lines of gradation data (G1 [r] · G1 [g] · G1 [b]) for each emission color. The gradation data G1 [r] corresponding to the red light emitting element E is supplied from the separation unit 422 to the correction unit 423r. Similarly, the gradation data G1 [g] corresponding to green is supplied to the correction unit 423g, and the gradation data G1 [b] corresponding to blue is supplied to the correction unit 423b.

  Each correction unit 423 generates gradation data G2 by calculation (for example, addition or multiplication) of the gradation data G1 supplied from the separation unit 422 and the correction value A supplied from the correction value determination unit 421 in the driving period. It is means to do. For example, the correction unit 423r generates and outputs the gradation data G2 [r] by calculating the gradation data G1 [r] and the correction value Ar. Similarly, the correction unit 423g generates gradation data G2 [g] from the gradation data G1 [g] and the correction value Ag, and the correction unit 423b uses the gradation data G1 [b] and the correction value Ab. Tone data G2 [b] is generated. Three systems of gradation data G2 (G2 [r], G2 [g], G2 [b]) output from each correction unit 423 are input to the data line driving circuit 25 and used to generate the data signal Xj. . Therefore, the voltage Vdata of the data signal Xj output from the data line driving circuit 25 during the driving period is the correction value A (Ar · Ag · Ab) and the gradation data G1 (G1 [r] · G1 [g] · G1 [b ]).

  Next, the configuration of each unit circuit U will be described with reference to FIG. In the figure, only one unit circuit U in the j-th column belonging to the i-th row is shown, but all unit circuits U in the element array section 11 have the same configuration. As shown in FIG. 3, the unit circuit U includes a light emitting element E disposed on a path from the power supply line 17 to the ground line (ground voltage Gnd). The light emitting element E of the present embodiment is an organic light emitting diode (OLED) element in which a light emitting layer made of an organic EL (ElectroLuminescent) material is interposed between an anode and a cathode. The light emitting layer emits light with luminance (luminance) corresponding to the current value of the current IEL supplied from the feeder line 17. The cathode of the light emitting element E is grounded (ground voltage Gnd).

  A p-channel transistor (hereinafter referred to as “driving transistor”) Tdr is disposed on the path of the current IEL (between the feeder line 17 and the light emitting element E). The drive transistor Tdr is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) that controls the current value of the current IEL in accordance with the gate voltage. The source of the driving transistor Tdr is electrically connected to the feeder line 17. A capacitive element C is interposed between the gate and source (feed line 17) of the drive transistor Tdr.

  Between the drain of the drive transistor Tdr and the anode of the light-emitting element E, an n-channel transistor (hereinafter referred to as “light-emission control transistor”) Tel that controls electrical connection (conduction / non-conduction) between the two is interposed. . The gates of the light emission control transistors Tel in the unit circuits U in the i-th row are connected in common to the light-emission control line 13 in the i-th row. In addition, an n-channel transistor (hereinafter referred to as “selection transistor”) Tsl for controlling electrical connection between the gate and the data line 15 of the driving transistor Tdr is interposed. The gates of the selection transistors Tsl in the unit circuits U in the i-th row are commonly connected to the scanning line 12 in the i-th row.

  Next, the operation of the unit circuit U during the driving period will be described. When the scanning signal Yi changes to the high level and the selection transistor Tsl changes to the ON state in the i-th horizontal scanning period in each frame period, the voltage of the data signal Xj supplied to the data line 15 at that time Vdata is applied to the gate of the drive transistor Tdr. Further, during the period in which the scanning signal Yi is at the high level, the light emission control signal Ci is at the low level, and the light emission control transistor Tel is maintained in the off state.

  During the period in which the scanning signal Yi is maintained at the high level, charges corresponding to the voltage Vdata are accumulated in the capacitor C. Therefore, even if the scanning signal Yi transits to the low level and the selection transistor Tsl changes to the off state, The gate of the drive transistor Tdr is maintained at the voltage Vdata. On the other hand, when the light emission control signal Ci transits to a high level, the light emission control transistor Tel changes to the on state, and the path of the current IEL is established. Therefore, the current IEL corresponding to the voltage Vdata of the gate of the drive transistor Tdr is supplied to the light emitting element E. By supplying the current IEL, the light emitting element E emits light with a luminance corresponding to the voltage Vdata. Since the voltage Vdata is generated according to the gradation data G1 and the correction value A, it can be said that the luminance of the light emitting element E is corrected according to the correction value A in the present embodiment.

  The power supply voltage VEL supplied from the power supply circuit 50 to each unit circuit U is set to the voltage value V1 during the driving period. The voltage value V1 is a level at which the drive transistor Tdr is operated in the saturation region when applied to the source (feed line 17) of the drive transistor Tdr. That is, the voltage value V1 is set so that the gate-source voltage VGS, the drain-source voltage VDS, and the threshold voltage Vth of the drive transistor Tdr satisfy the condition of “VGS−Vth> VDS”. As described above, since the driving transistor Tdr operates in the saturation region during the driving period, the influence of the drain-source voltage VDS on the current IEL is different from the configuration in which the driving transistor Tdr is in the non-saturation region during the driving period. (Ideally the current IEL does not depend on the voltage VDS). Therefore, the current value of the current IEL and the luminance of the light emitting element E corresponding to the current value can be set with high accuracy according to the gate-source voltage VGS (voltage Vdata of the data signal Xj).

  Next, a specific configuration of the power supply circuit 50 will be described with reference to FIG. As shown in the figure, the power supply circuit 50 includes a control unit 51, a voltage control unit 52, a current measurement unit 53, and a data generation unit 54. The control unit 51 controls each unit of the power supply circuit 50 according to the control signal Sc supplied from the control circuit 40.

  The current measuring unit 53 detects the current that actually flows through the light emitting element E of the element array unit 11 (current that flows through the feeder line 17) in the set period. The current measurement unit 53 of the present embodiment is a DAC (Digital to Analog Converter) that outputs the current value Q of the current flowing through the feeder line 17 as digital data. On the other hand, the data generation unit 54 functions as a unit for determining the correction value A (Ar · Ag · Ab) based on the current value Q output from the current measurement unit 53 together with the correction value determination unit 421 of the correction circuit 42. . As described above, in the present embodiment, the correction value A is determined based on the result of detecting the current that actually flows through the light emitting element E. The control unit 51 operates the current measurement unit 53 and the data generation unit 54 when the control signal Sc designates a set period, and the current measurement unit 53 and the data generation unit when the control signal Sc designates a drive period. The operation of 54 is stopped.

  Here, part (a) of FIG. 4 is a graph showing the relationship between the gate voltage (voltage Vdata of the data signal Xj) of the driving transistor Tdr operating in the saturation region and the current IEL flowing through the light emitting element E. A curve Fa1 in the figure shows characteristics at an initial stage where the light emitting element E is not deteriorated (that is, immediately after manufacture), and a curve Fa2 shows characteristics at a stage where the light emitting element E deteriorates with time. As can be understood from the fact that the curve Fa1 and the curve Fa2 almost coincide with each other, the current IEL flowing through the light emitting element E in a state where the drive transistor Tdr operates in the saturation region is equal to the voltage Vdata of the gate of the drive transistor Tdr. Accordingly, the characteristic of each light emitting element E is hardly reflected in the current IEL. Therefore, if the current measuring unit 53 measures the current value Q when the driving transistor Tdr is operating in the saturation region, the change in the characteristics of the light emitting element E is not detected with high sensitivity, and each of the light emitting elements E There is a problem that the correction value A that accurately reflects the characteristics cannot be set (the accuracy of correcting the luminance of the light emitting element E is limited). Even when the drive transistor Tdr operates in the saturation region, if the gate voltage Vdata is sufficiently reduced, the change in the current IEL accompanying the deterioration of the characteristics of the light emitting element E (curve Fa1 and curve Fa2). The difference is increased to the extent that an effective correction value can be selected. However, in this case, as shown in part (a) of FIG. 4, an excessive current exceeding a predetermined allowable value flows through the light emitting element E, so that the light emitting element E may be electrically destroyed.

  In view of the above circumstances, in the present embodiment, the operating point of the drive transistor Tdr in the set period is set in the non-saturated region. Part (b) of FIG. 4 is a graph showing the relationship between the voltage Vdata of the gate of the driving transistor Tdr operating in the non-saturation region and the current IEL flowing through the light emitting element E. A curve Fb1 in the figure shows a characteristic at a stage where the light emitting element E is not deteriorated (the same stage as the characteristic Fa1 of the part (a)), and a curve Fb2 shows a stage where the light emitting element E deteriorates with time (part ( The characteristic at the same stage as the curve Fa2 in b) is shown.

  The drain-source voltage VDS of the driving transistor Tdr varies depending on the characteristics of the light emitting element E (more specifically, the voltage dividing ratio of the power supply voltage VEL corresponding to the characteristics of the light emitting element E). The current IEL flowing through the drive transistor Tdr operating in the non-saturation region varies depending on the drain-source voltage VDS. Therefore, as shown in part (b) of FIG. 4, when the driving transistor Tdr is operated in the non-saturated region, the current IEL flowing through the light emitting element E and the characteristics of the light emitting element E are deteriorated at the initial stage. The difference from the current flowing in the current increases as compared with the case where the drive transistor Tdr operates in the saturation region. Moreover, the current flowing through the light emitting element E is suppressed to a current value lower than the allowable value even when the voltage Vdata is sufficiently low (for example, when the data voltage is zero (Gnd)). In other words, the current measuring unit 53 can detect the current value Q reflecting the influence of the change of each light emitting element E with high sensitivity while suppressing the supply of overcurrent to the light emitting element E.

  As described above, the driving transistor Tdr operates in the saturation region during the driving period and operates in the non-saturation region during the setting period. The voltage control unit 52 in FIG. 2 is means for determining the operating point of the drive transistor Tdr by controlling the voltage value of the power supply voltage VEL supplied to the feeder line 17. That is, the voltage control unit 52 sets the power supply voltage VEL to either the voltage value V1 or the voltage value V2.

  The voltage value V1 is a level at which the drive transistor Tdr is operated in the saturation region as already described. On the other hand, the voltage value V2 is set lower than the voltage value V1 so that the driving transistor Tdr operates in the non-saturated region when applied to the source. More specifically, the voltage value V2 is set so that the gate-source voltage VGS, the drain-source voltage VDS, and the threshold voltage Vth of the drive transistor Tdr satisfy the condition “VGS−Vth <VDS”. The

  The control unit 51 instructs the voltage control unit 52 to specify the voltage value V1 when the control signal Sc specifies the drive period, and the voltage control unit 52 sets the voltage value V2 when the control signal Sc specifies the set period. Instruct. Therefore, the voltage control unit 52 sets the power supply voltage VEL to the voltage value V1 during the driving period and operates the driving transistor Tdr in the saturation region, while setting the power supply voltage VEL to the voltage value V2 during the setting period. The drive transistor Tdr is operated in the non-saturation region.

  Next, the operation of the light emitting device D (operation for determining the correction value A) during the set period will be described. In the setting period, the operating point of the driving transistor Tdr is set in the non-saturated region by setting the power supply voltage VEL to the voltage value V2 by the voltage controller 52. Further, the control circuit 40 turns on the light emission control transistor Tel and the selection transistor Tsl of each unit circuit U corresponding to one light emission color (hereinafter referred to as “measurement target color”) of red, green, and blue. The scanning line driving circuit 22 and the light emission control circuit 23 are controlled. Further, the control circuit 40 controls the data line driving circuit 25 so that the voltage Vdata of each data signal X1 to Xn becomes the ground voltage Gnd.

  With the above operation, the drive transistor Tdr in the unit circuit U for the color to be measured is turned on in the non-saturated region by supplying the ground voltage Gnd (voltage Vdata) to the gate. Therefore, a current IEL (current value I1 in part (b) of FIG. 4) reflecting the characteristics of the light emitting element E flows through each light emitting element E of the measurement target color. At this time, the current measuring unit 53 detects the current flowing through the feeder line 17 (that is, the sum of the currents IEL flowing through all the light emitting elements E of the measurement target color) and specifies the current value Q.

  In the present embodiment, the correction value A is determined for each emission color based on the relationship between the current supplied to the light emitting element E and the luminance of the light emitting element E at the time of supply (hereinafter referred to as “IL characteristic”). On the other hand, the current value Q is a numerical value that reflects the relationship (IV characteristics) between the voltage applied to the light emitting element E and the current that flows during the application. Since there is a correlation between the change in the IV characteristic and the IL characteristic due to the deterioration of the light emitting element E, in this embodiment, first, the average IV characteristic of each light emitting element E of the color to be measured is the current. Second, the IL characteristic is specified from the IV characteristic based on the correlation between the IV characteristic and the IL characteristic, and the correction value A is determined based on the IL characteristic. The above procedure will be described in detail as follows.

  Since the voltage applied to the light emitting element E when the current measuring unit 53 measures the current value Q varies depending on the characteristics of the drive transistor Tdr (voltage division ratio of the power supply voltage VEL (voltage value V2)), the current value Q emits light. There is a case where the numerical value does not reflect only the IV characteristic of the element E (the influence of the characteristic of the driving transistor Tdr). 2 calculates a numerical value R (hereinafter referred to as “IV characteristic value”) R reflecting only the IV characteristic of each light emitting element E from the current value Q. The IV characteristic value R is a numerical value that is an index of the ease of current flow in the light emitting element E (current that flows when a predetermined voltage is applied between the anode and the cathode of the light emitting element E).

  FIG. 5 is a graph showing the relationship between the current value Q and the IV characteristic value R. The characteristics shown in the figure are determined experimentally or statistically in consideration of the electrical characteristics of the drive transistor Tdr. The data generation unit 54 specifies the IV characteristic value R so that the relationship of FIG. 5 is established with the current value Q measured by the current measurement unit 53. For example, as illustrated in FIG. 5, if the current value Q is “Q1”, the data generation unit 54 specifies the IV characteristic value R as “R1”. The data generation unit 54 is realized by a table that associates the current value Q and the IV characteristic value R (a table that outputs the IV characteristic value R corresponding to the current value Q supplied from the current measurement unit 53). Alternatively, the data generation unit 54 may calculate the IV characteristic value R by multiplying a coefficient (for example, the slope of the graph of FIG. 5) reflecting the characteristic of FIG.

  Next, the correction value determination unit 421 determines a numerical value (hereinafter referred to as “IL characteristic value”) S corresponding to the IL characteristic of the light emitting element E from the IV characteristic value R specified by the data generation unit 54. The IL characteristic value S is, for example, the luminous efficiency (that is, the slope of the graph indicating the current-luminance relationship) that is the amount of change in luminance of the light emitting element E when the current supplied to the light emitting element E changes by a unit amount. It is a numerical value that serves as an index.

  FIG. 6 is a graph showing the correlation between the IV characteristic value R and the IL characteristic value S. In the figure, the correlation between the IV characteristic value R and the IL characteristic value S is shown for each of red (Fr), green (Fg), and blue (Fb). Each correlation illustrated in FIG. 6 is determined experimentally or statistically. Note that “Sr0” in FIG. 6 is an initial IL characteristic value S of the red light emitting element E (an IL characteristic value S at a stage where the light emitting element E has not deteriorated). Similarly, “Sg0” is an initial value of the green IL characteristic value S, and “Sb0” is an initial value of the blue IL characteristic value S. As shown in FIG. 6, between the IV characteristic value R and the IL characteristic value S, both numerical values decrease with the deterioration of the light emitting element E over time (the characteristics of the light emitting element E deteriorate as the light emitting element E deteriorates). Is changed along the arrow in the figure).

  The correction value determination unit 421 specifies the IL characteristic value S so that the relationship corresponding to the measurement target color in FIG. 6 is established with the IV characteristic value R specified by the data generation unit 54. For example, when the measurement target color is red (characteristic Fr), if the IV characteristic value R is “R1”, the correction value determination unit 421 specifies the IL characteristic value S as “S1”. The correction value determination unit 421 is realized by a table that associates the IV characteristic value R and the IL characteristic value S (a table that outputs the IL characteristic value S corresponding to the IV characteristic value R supplied from the data generation unit 54). Alternatively, the correction value determination unit 421 may calculate the IL characteristic value S by multiplying a coefficient reflecting each characteristic in FIG. 6 (for example, the slope of each graph in FIG. 6) and the IV characteristic value R. Then, the correction value determining unit 421 corrects the measurement target color so that the IL characteristic value S specified according to the IV characteristic value R becomes the initial IL characteristic value (Sr0 · Sg0 · Sb0) of the light emitting element E. The value A is determined. The correction value A (Ar · Ag · Ab) for each emission color is determined by executing the above process for all emission colors.

  As described above, in the present embodiment, when the current value Q is measured, the driving transistor Tdr operates in the non-saturated region, so that a correction value that faithfully reflects a slight change in the characteristics of the light emitting element E is determined. be able to. Therefore, the characteristics of the light emitting element E can be brought close to the initial state with high accuracy.

<B: Second Embodiment>
Next, a second embodiment of the present invention will be described. In the first embodiment, the configuration in which the correction value is determined for each emission color is exemplified. On the other hand, in the present embodiment, the correction value is determined for each of a plurality of regions into which the element array unit 11 is divided. In addition, about the element which an effect | action and function are common in 1st Embodiment among each form shown below, the same code | symbol as FIG. 1 thru | or FIG. 3 is attached | subjected, and the detailed description is abbreviate | omitted suitably.

  Part (a) of FIG. 7 is a conceptual diagram showing a partial arrangement of the unit circuits U in the element array unit 11. As shown in the figure, the element array section 11 is divided into a plurality of regions B0. Each region B0 includes a plurality of unit circuits U (light emitting elements E). Further, in each area B0, an area (a hatched area in part (a) of FIG. 7) B1 including a predetermined number of unit circuits U is defined.

  In the present embodiment, correction values are determined for each of the plurality of regions B1 in the same procedure as in the first embodiment. That is, the drive transistor Tdr of each unit circuit U belonging to one region B1 is turned on in the non-saturated region, and the sum of currents flowing through the light emitting elements E in the region B1 is specified as the current value Q. A correction value A is determined based on the current value Q.

  Part (b) of FIG. 7 is a graph showing the relationship between the position (horizontal axis) of each unit circuit U and the correction value (vertical axis). The white circles shown in the figure indicate the correction value A determined for each region B1. A configuration in which the correction value A determined for each region B1 as described above is applied to correction of the luminance of all the light emitting elements E in the region B0 including the region B1 is also conceivable. However, in this configuration, the difference in luminance between the light emitting elements E adjacent to each other across the boundary of the region B0 may be noticeable and clearly perceived by the user. Therefore, in the present embodiment, as indicated by a black circle in part (b) of FIG. 7, the correction values A for all the unit circuits U are interpolated with the correction values A determined for the region B1. Is determined. According to this configuration, it is possible to eliminate the discontinuity in luminance of the light emitting elements E adjacent to each other across the boundary of each region B0. Various known techniques are applied as a method of calculating the correction value A by interpolation. For example, the correction value of each unit circuit U may be determined by approximating the variation of the correction value along the X direction or Y direction of each region B1 with a straight line, or the variation of the correction value may be approximated with a curve. The correction value of the unit circuit U may be determined.

  In the above embodiment, the configuration in which the correction value A is calculated for each unit circuit U in the region B1, which is the portion of the region B0, is exemplified. However, the correction is performed for all unit circuits U belonging to the region B0. The value A may be calculated. Further, the method of defining the region B0 and the region B1 (the shape of each region and the number of unit circuits U) is arbitrarily changed.

<C: Third Embodiment>
Next, a third embodiment of the present invention will be described. In the first embodiment, the configuration in which the luminance of each light emitting element E is corrected by the calculation of the correction value A and the gradation data G1 is exemplified. However, the configuration for reflecting the correction value A on the luminance of each light emitting element E. Are appropriately changed as illustrated below.

  The control circuit 40 of this embodiment outputs the gradation data G1 supplied from the host device as it is to the data line driving circuit 25 as the gradation data G2. The data line driving circuit 25 includes a voltage output type DAC that generates data signals X1 to Xn of the voltage Vdata corresponding to the gradation data G2 based on a predetermined voltage (hereinafter referred to as “reference voltage”). The control circuit 40 changes the reference voltage according to the correction value A determined by the correction value determination unit 421. For example, the light emission efficiency of the light emitting element E decreases due to deterioration. Therefore, as the deterioration of the light emitting element E with time progresses (that is, as the IV characteristic value R and the IL characteristic value S decrease), the range of the voltage Vdata of the data signal Xj is expanded (more specifically, The control circuit 40 corrects the reference voltage based on the correction value A so that the minimum value of the voltage Vdata decreases. According to this configuration, since the maximum value of the current supplied to the light emitting element E is increased, the luminance can be maintained at a predetermined value (for example, an initial value) regardless of the degree of deterioration of the light emitting element E. Further, the reference voltage of the data line driving circuit 25 may be corrected so that the relative ratio of the luminance of the light emitting elements E of the respective emission colors is maintained. As described above, the calculation of the gradation data G1 and the correction value A is not essential in the present invention.

  Note that, as the light emitting element E deteriorates with time, the IV characteristic value R decreases and current does not easily flow through the light emitting element E. In the above, the configuration in which the luminance of the light emitting element E is maintained by adjusting the voltage Vdata is exemplified. However, the configuration in which the luminance of the light emitting element E is maintained at a predetermined value by adjusting the voltage value V1 of the power supply voltage VEL in the driving period. Adopted. That is, the control circuit 40 may control the power supply circuit 50 (voltage control unit 52) based on the correction value so that the voltage value V1 becomes higher as the deterioration of the light emitting element E with time progresses. As described above, in the light emitting device D, a configuration in which the correction value is reflected on the luminance of the light emitting element E is sufficient, and a specific configuration or method for correcting the luminance is arbitrary.

<D: Fourth Embodiment>
The IV characteristic value R and the IL characteristic value S of the light emitting element E change depending on the temperature of the light emitting element E in addition to the degree of deterioration of the light emitting element E over time. Since the aspect of change according to temperature differs between the IV characteristic value R and the IL characteristic value S, the correlation between the IV characteristic value R and the IL characteristic value S illustrated in FIG. 4 differs depending on the temperature of the light emitting element E. To do. In consideration of the above circumstances, in the present embodiment, the correction value A is determined according to the current value Q detected by the current measuring unit 53 and the ambient temperature of the light emitting device D (ideally, the temperature of the light emitting element E). Is determined.

  FIG. 8 is a block diagram showing the configuration of the light emitting device D according to this embodiment. As shown in the figure, the light emitting device D includes a temperature sensor 60 in addition to the elements of the first embodiment. The temperature sensor 60 is a means for measuring the temperature of the light emitting device D or its surroundings. A temperature T (hereinafter simply referred to as “measured temperature”) T measured by the temperature sensor 60 is output to the correction value determination unit 421 of the correction circuit 42.

  FIG. 9 is a graph showing the relationship between the IV characteristic value R and the IL characteristic value S (a graph corresponding to FIG. 4). A curve Fc1 in the figure shows a characteristic when the measured temperature T is “T1”, and a curve Fc2 shows a characteristic when the measured temperature T is “T2 (T2> T1)”. As shown in FIG. 9, the correlation between the IV characteristic value R and the IL characteristic value S changes according to the temperature of the light emitting device D. For example, the IV characteristic value R and the IL characteristic value S at the stage where the light emitting element E is not deteriorated are numerical values at the point P1 when the measured temperature T is “T1”, whereas the measured temperature T is “T2”. If so, the value of the point P2 is obtained. Note that a curve CL passing through the points P1 and P2 shows how the relationship between the IV characteristic value R and the IL characteristic value S of the light emitting element E that has not yet deteriorated changes according to a change in temperature. .

  When the temperature T measured by the temperature sensor 60 is “T1,” the correction value determination unit 421 sets the IL characteristic value S so as to satisfy the relationship of the characteristic Fc1 with the IV characteristic value R specified by the data generation unit 54. If the temperature measured by the temperature sensor 60 is “T2”, the IL characteristic value S is specified so as to satisfy the relationship of the characteristic Fc2 with the IV characteristic value R. For example, when the IV characteristic value R is “R1”, the correction value determination unit 421 specifies “Sa” as the IL characteristic value S if the measured temperature T is “T1”, and the measured temperature T is “T2”. If so, “Sb” is specified as the IL characteristic value S. Then, the correction value determination unit 421 determines the correction value A corresponding to the IL characteristic value S as in the first embodiment. Therefore, the correction value A applied to the correction of the gradation data G1 differs depending on the measured temperature T.

  The correction value determination unit 421 is realized by setting a table that associates the IV characteristic value R and the IL characteristic value S for each numerical value (range) of the measured temperature T. That is, the correction value determination unit 421 selects a table corresponding to the measured temperature T notified from the temperature sensor 60 from among a plurality of tables, and the IL characteristic value corresponding to the IV characteristic value R specified by the data generation unit 54. S is specified from the selected table and output. Alternatively, the coefficient reflecting the characteristics of FIG. 6 is held for each range of the measured temperature T, and the coefficient corresponding to the measured temperature T notified from the temperature sensor 60 and the IV characteristic value R among these coefficients (for example, The IL characteristic value S may be calculated by multiplication.

  As described above, according to the present embodiment, since the correction value A is determined according to the current value Q and the measured temperature T, the luminance of each light emitting element E regardless of the current value Q or the measured temperature T. Can be adjusted to a predetermined value. Although the configuration of the present embodiment has been described above based on the first embodiment, the configuration for determining the correction value A according to the measured temperature T as in the present embodiment is the second embodiment or the third embodiment. The form is similarly adopted.

<E: Modification>
Various modifications can be made to each of the above embodiments. An example of a specific modification is as follows. In addition, you may combine each following aspect suitably.

(1) Modification 1
In each of the above embodiments, the configuration in which the correction value A is determined through the determination of the IV characteristic value R and the IL characteristic value S from the measurement of the current value Q is illustrated. However, the correction value A corresponding to the current value Q is determined. The specific procedure for doing so is changed as appropriate. For example, a correlation between the current value Q and the correction value A may be set in advance, and the correction value A may be determined directly from the current value Q based on this correlation. This configuration is realized by, for example, a table in which the current value Q and the correction value A are associated (a table that outputs the correction value A corresponding to the current value Q supplied from the current measurement unit 53). Alternatively, the correction value A may be calculated by calculating the current value Q based on an arithmetic expression indicating the correlation between the current value Q and the correction value A.

(2) Modification 2
The configuration of each unit circuit U is changed as appropriate. For example, a configuration in which the light emission control transistor Tel in FIG. 3 is omitted (a configuration in which the drain of the driving transistor Tdr is directly connected to the light emitting element E) may be employed. For example, as a line head (optical head) for exposing a photosensitive drum in an image forming apparatus, a light emitting device D in which a plurality of unit circuits U are arranged in only one direction and a data line 15 is formed for each unit circuit U. Is used. The light emitting device D may have a configuration in which the selection transistor Tsl is omitted (a configuration in which the gate of the driving transistor Tdr is directly connected to the data line 15). Further, the conductivity type of each transistor constituting the unit circuit U is arbitrarily changed.

(3) Modification 3
In each of the above embodiments, an organic light emitting diode element is exemplified as the light emitting element E. However, the present invention is also applied to a light emitting device using other light emitting elements. For example, light-emitting elements and light-emitting diode elements including light-emitting layers made of inorganic EL materials, field emission (FE) elements, surface-conduction electron-emitter (SE) elements, ballistic electron emission (BS) Various light emitting elements such as a ballistic electron surface emitting element can be used in the light emitting device of the present invention.

<F: Application example>
Next, an electronic apparatus using the light emitting device according to the present invention will be described. 10 to 12 show a form of an electronic apparatus that employs the light-emitting device D according to any one of the above forms as a display device.

  FIG. 10 is a perspective view showing a configuration of a mobile personal computer employing the light emitting device D. As shown in FIG. The personal computer 2000 includes a light emitting device D that displays various images, and a main body 2010 on which a power switch 2001 and a keyboard 2002 are installed. Since the light emitting device D uses an organic light emitting diode element as the light emitting element E, it is possible to display an easy-to-see screen with a wide viewing angle.

  FIG. 11 is a perspective view illustrating a configuration of a mobile phone to which the light emitting device D is applied. The cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and a light emitting device D that displays various images. By operating the scroll button 3002, the screen displayed on the light emitting device D is scrolled.

  FIG. 12 is a perspective view illustrating a configuration of a personal digital assistant (PDA) to which the light emitting device D is applied. The portable information terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and a light emitting device D that displays various images. When the power switch 4002 is operated, various kinds of information such as an address book and a schedule book are displayed on the light emitting device D.

  In addition, as an electronic device to which the light emitting device according to the present invention is applied, in addition to the devices shown in FIGS. 10 to 12, a digital still camera, a television, a video camera, a car navigation device, a pager, an electronic notebook, electronic paper, Examples include calculators, word processors, workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices equipped with touch panels, and the like. Further, the use of the light emitting device according to the present invention is not limited to the display of images. For example, in an image forming apparatus such as an optical writing type printer or an electronic copying machine, an optical head (writing head) that exposes a photosensitive member according to an image to be formed on a recording material such as paper is used. The light-emitting device of the present invention is also used as this type of optical head.

It is a block diagram which shows the structure of the light-emitting device which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of a power supply circuit and a correction circuit. It is a block diagram which shows the structure of a unit circuit. It is a graph which shows the relationship between the voltage of the gate of a drive transistor, and the current which flows into a light emitting element about each of a drive period and a setting period. 4 is a graph showing a relationship between a current value Q and an IV characteristic value R. 4 is a graph showing a relationship between an IV characteristic value R and an IL characteristic value S. It is a conceptual diagram explaining the method to determine a correction value in 2nd Embodiment. It is a block diagram which shows the structure of the light-emitting device which concerns on 4th Embodiment. It is a graph which shows a mode that the correlation of IV characteristic value R and IL characteristic value S changes according to temperature. It is a perspective view which shows the form (personal computer) of the electronic device which concerns on this invention. It is a perspective view which shows the form (cellular phone) of the electronic device which concerns on this invention. It is a perspective view which shows the form (mobile information terminal) of the electronic device which concerns on this invention.

Explanation of symbols

D: Light emitting device, 10: Display panel, 11: Element array unit, U: Unit circuit, E: Light emitting element, 12: Scan line, 13: Light emission control line, 15: Data line, DESCRIPTION OF SYMBOLS 17 ... Feed line, 22 ... Scan line drive circuit, 23 ... Light emission control circuit, 25 ... Data line drive circuit, 40 ... Control circuit, 42 ... Correction circuit, 421 ... Correction value determination part, 422 ...... Separation unit, 423 (423r, 423g, 423b) ... Correction unit, 50 ... Power supply circuit, 51 ... Control unit, 52 ... Voltage control unit, 53 ... Current measurement unit, 54 ... Data generation unit , 60... Temperature sensor, Tdr... Drive transistor, Tel... Light emission control transistor, Tsl.

Claims (9)

Voltage control means for controlling the voltage supplied to the feeder line to the first voltage in the first period and setting the second voltage lower than the first voltage in the second period;
A light emitting element that emits light in response to a current supplied via the feeder line;
A driving transistor disposed on a path of a current supplied to the light emitting element via the feeder line and controlling the current according to a gate voltage;
Current measuring means for measuring a current flowing through the light emitting element via the feeder line in the second period;
Correction value determining means for determining a correction value according to the current measured by the current measuring means;
And a driving unit that supplies a voltage corresponding to the gradation data and the correction value determined by the correction value determination unit to the gate of the driving transistor in the first period. 2. The light emitting device according to claim 1, wherein the first voltage is a voltage for operating the driving transistor in a saturation region, and the second voltage is a voltage for operating the driving transistor in a non-saturation region. A plurality of unit circuits each including a light emitting element and a driving transistor;
The current measuring means measures, for each of the element groups obtained by dividing the plurality of light emitting elements, a current flowing through a predetermined number of light emitting elements belonging to the element group,
The correction value determining means determines a correction value for each of the element groups according to each current measured by the current measuring means, and determines a correction value for each light emitting element by interpolation of each correction value. Or the light-emitting device of Claim 2. Comprising temperature measuring means for measuring the ambient temperature of the light emitting device,
The light emitting device according to any one of claims 1 to 3, wherein the correction value determining unit determines a correction value according to the current measured by the current measuring unit and the temperature measured by the temperature measuring unit.   The electronic device which comprises the light-emitting device in any one of Claims 1-4. A light-emitting element that emits light in response to a current supplied through a power supply line; and a drive transistor disposed on the current path, wherein the driving is performed during a period in which a first voltage is supplied to the power supply line. A method of determining the correction value for a light-emitting device in which the light-emitting element is controlled by setting a gate of a transistor to a voltage according to gradation data and a correction value,
A voltage control process for setting the feeder line to a second voltage lower than the first voltage;
By controlling the drive transistor to be in a conductive state, a current supply process for passing a current to the light emitting element via the feeder line set to the second voltage in the voltage control process;
A current measurement process for measuring a current flowing through the light emitting device in the current supply process;
A correction value determination method, comprising: a correction value determination process for determining the correction value according to the current measured in the current measurement process. The correction value according to claim 6, wherein the first voltage is a voltage for operating the driving transistor in a saturation region, and the second voltage is a voltage for operating the driving transistor in a non-saturation region. Method. The light emitting device includes a plurality of unit circuits each including a light emitting element and a driving transistor,
In the current measurement process, for each of a plurality of element groups dividing the plurality of light emitting elements, a current flowing through a predetermined number of light emitting elements belonging to the element group is measured,
In the correction value determination process, a correction value is determined for each element group according to each current measured in the current measurement process, and a correction value for each light emitting element is determined by interpolation of the correction values. The correction value determination method according to claim 6 or 7. Including a temperature measurement process for measuring the ambient temperature of the light emitting device,
9. The correction value is determined according to the current measured in the current measurement process and the temperature measured in the temperature measurement process in the correction value determination process. How to determine the correction value.

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