JP2008256827A - Driving method of pixel circuit, light emitting device, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct temperature characteristics of an OLED element while reducing power consumption. <P>SOLUTION: A power circuit 600 has a correcting circuit 610 having a correction table LUTr outputting a reference voltage Vref1 according to temperature and a source voltage supply circuit 620 having a voltage adjusting circuit 621. A second power supply potential Vssr is generated based upon the reference voltage Vref1. The second power supply potential Vssr is supplied to a cathode of the OLED element which emits light according to a drive current supplied from a drive transistor. The second power supply potential Vssr is set so that the operating point of the drive transistor is at the boundary between a linear area and a saturation area. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a driving method of a pixel circuit using a light emitting element such as an organic light emitting diode, a light emitting device, and an electronic apparatus.

As an image display device replacing a liquid crystal display device, an organic light emitting diode element (hereinafter referred to as OLED)
This is called an element. ) Is attracting attention. The OLED element electrically operates like a diode, and optically emits light at the time of forward bias, and the light emission luminance increases as the forward bias current increases.

In general, the luminance of the OLED element depends on the driving current corresponding to the supplied data. For example, in the pixel circuit shown in FIG. 13, a drive current corresponding to the voltage between the gate and source of the drive transistor Tr flows through the OLED element. The light emitting device includes a plurality of OLED elements.
In such a light emitting device, the temperature of the light emitting device rises due to the power consumed by the OLED element and the drive circuit that drives the OLED element. The OLED element has a property that the luminance increases as the temperature rises even when the driving current or the driving voltage is the same. As the problem, the display quality is deteriorated and wasteful power is consumed as heat. Furthermore, when the heat dissipation of the light emitting device is slower than the generated heat (not in time), in the worst case, the OLED element and the driving transistor may be damaged. Countermeasures include providing a heat radiating plate or a cooling mechanism. However, the provision of these mechanisms hinders miniaturization and thinning of the panel.
In addition, it is difficult to reduce the power consumption of the entire light emitting device.
Therefore, in order to correct the temperature characteristics of the OLED element, a technique is known in which the power supply potential Vdd is adjusted to control the magnitude of the drive voltage and drive current.

WO98 / 40871

By the way, since it is desirable for the driving transistor to have a constant driving current irrespective of the drain-source voltage, it is preferable to operate in the saturation region shown in FIG. However, since the operating points Q1 and Q2 change between when the temperature is high and when the temperature is low, in order to always operate in the saturation region, the drain-source voltage Vd is expected in consideration of a margin.
s must be set high. If it does so, there exists a problem that power consumption becomes high.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to reduce luminance fluctuation due to temperature rise while reducing power consumption.

In order to solve the above-described problem, a driving method of a pixel circuit according to the present invention includes a light emitting element that emits light with a light amount corresponding to a driving current flowing between a first electrode and a second electrode, and the driving current is supplied to the first electrode. 1
A method of driving a pixel circuit including a driving transistor supplied to an electrode, supplying a first potential to a source of the driving transistor, detecting a temperature of the light emitting element, and detecting the temperature of the light emitting element according to the detected temperature The second potential supplied to the second electrode is adjusted.

According to the present invention, since the potential supplied to the second electrode of the light emitting element is adjusted, the operating point of the driving transistor can be adjusted according to the temperature. Even when the light emitting element emits light with the same luminance, the voltage between the first electrode and the second electrode changes according to the temperature. On the other hand, when the light emitting element emits light with the same luminance, the light emitting element is driven even when the temperature changes. The magnitude of the current hardly changes. Therefore, while adjusting the operating point of the driving transistor by adjusting the second potential according to the temperature,
The light emission luminance can be corrected.

More specifically, it is preferable that the second potential is adjusted according to the detected temperature so that the voltage between the drain and source of the driving transistor becomes constant even when the temperature changes. In this case, since the voltage between the drain and source of the drive transistor can be kept constant, the power consumption of the drive transistor can be kept constant even when the temperature changes.

Further, the change amount according to the temperature of the second potential matches the change amount of the voltage between the first electrode and the second electrode of the light emitting element which changes according to the temperature when the driving current is constant. It is preferable to do. Since the drive current and the light emission luminance of the light emitting element are constant even when the temperature changes, the light emission luminance of the light emitting element that changes according to the temperature can be corrected by making the change constant.

The second potential is determined so that the operating point of the driving transistor is near the boundary between the linear region and the saturation region when the light emitting element emits light at the maximum brightness at the detected temperature. Is preferred. In this case, since the margin for operating the drive transistor in the saturation region can be greatly reduced, the power consumption of the drive transistor can be reduced.

Next, a light-emitting device according to the present invention includes a light-emitting element that emits light with a light amount corresponding to a drive current flowing between a first electrode and a second electrode, a drive transistor that supplies the drive current to the first electrode, A plurality of pixel circuits including a temperature detecting means for detecting a temperature of the light emitting element; a first potential supplied to a source of the driving transistor; and a second potential applied to the second electrode. Power supply means for supplying and adjusting the second potential in accordance with the detected temperature.

According to the present invention, since the potential supplied to the second electrode of the light emitting element is adjusted, the operating point of the driving transistor can be adjusted according to the temperature. Even when the light emitting element emits light with the same luminance, the voltage between the first electrode and the second electrode changes according to the temperature. On the other hand, when the light emitting element emits light with the same luminance, the light emitting element is driven even when the temperature changes. The magnitude of the current hardly changes. Therefore, while adjusting the operating point of the driving transistor by adjusting the second potential according to the temperature,
The light emission luminance can be corrected.

In the light-emitting device described above, the light-emitting element has a plurality of types of light-emitting colors, and the power supply unit individually generates the second potential according to the light-emitting color of the light-emitting element, and corresponding light-emitting colors. It supplies to the light emitting element of this. The light emitting element emits light with a predetermined emission color according to the light emission characteristics of the light emitting material. Therefore, if the luminescent color is different, the temperature characteristics of the luminescent material are also different.
According to the present invention, since the second potential is individually set when a plurality of types of light emitting elements are used,
As a whole light-emitting device, it is possible to reduce luminance fluctuation due to temperature rise while reducing power consumption. The light emitting element may be an element that emits light with a single emission color, and the second electrode may be provided in common to the plurality of light emitting elements. In this way, since it is not necessary to provide the second electrodes individually, the structure can be simplified.

Further, the power supply means includes adjustment means for adjusting the second potential according to the detected temperature so that the voltage between the drain and source of the driving transistor is constant even when the temperature changes. It is preferable. In this case, since the voltage between the drain and source of the drive transistor can be kept constant, the power consumption of the drive transistor can be kept constant even when the temperature changes.

Further, the power supply means changes between the first electrode and the second electrode of the light emitting element, which changes according to the temperature when the driving current is constant, with the change corresponding to the temperature of the second potential being constant. It is preferable that an adjustment unit that adjusts the second potential so as to coincide with a change in voltage is provided.
Since the drive current and the light emission luminance of the light emitting element are constant even when the temperature changes, the light emission luminance of the light emitting element that changes according to the temperature can be corrected by making the change constant.

The power supply means may be configured to cause the operating point of the driving transistor to be in the vicinity of the boundary between the linear region and the saturation region when the light emitting element emits light at the maximum brightness at the detected temperature. An adjusting means for adjusting two potentials is provided. In this case,
Since the margin for operating the drive transistor in the saturation region can be greatly reduced, the power consumption of the drive transistor can be reduced.

The adjustment unit includes a storage unit that stores the temperature and correction data for correcting the second potential in association with each other, reads the correction data corresponding to the detected temperature with reference to the storage unit, It is preferable to adjust the second potential based on the read correction data. In this case, since the correction data can be acquired by referring to the storage means, the processing load can be reduced as compared with the case where the correction data is generated by calculation. However, when there is a margin in processing capacity, correction data may be calculated by calculation. In this case, the storage means becomes unnecessary, so that the storage capacity can be reduced.

In the light emitting device described above, it is preferable that the second potential is set lower than the ground potential. In this case, compared with the case where the second potential is set to the ground potential, the potential supplied to the gate of the driving transistor and the first potential can be lowered.
The power consumption can be further reduced.
Furthermore, the light emitting element is preferably an organic light emitting diode.

Next, an electronic apparatus according to the present invention includes the light emitting device described above. Such electronic devices include personal computers, mobile phones, personal digital assistants, monitors, digital still cameras, viewfinders, and the like. A printer as an electronic apparatus (image forming apparatus) may be provided with the above-described light emitting device. Here, the light emitting device may be provided by forming an electrostatic latent image on an image carrier such as a photosensitive drum, and may be formed by arranging a plurality of light emitting elements in an array in the main scanning direction. .

<1. Embodiment>
FIG. 1 is a block diagram showing a schematic configuration of a light emitting device according to an embodiment of the present invention. The light emitting device 1 includes a light emitting panel AA and an external circuit. In the light emitting panel AA, a display area A, a scanning line driving circuit 100, a data line driving circuit 200, and a temperature sensor 300 are formed. Among these, in the display area A, m scanning lines 101 are formed in parallel with the X direction. In addition, n data lines 103 are formed in parallel with the Y direction orthogonal to the X direction. A pixel circuit 400 </ b> A is provided corresponding to each intersection of the scanning line 101 and the data line 103. The pixel circuit 400A includes an OLED element. The symbols “R”, “G”, and “B” shown in the figure mean “red”, “green”, and “blue”, respectively, and indicate the emission color of the OLED element.
In this example, pixel circuits 400 </ b> A for each color are arranged along the data line 103.

Among the pixel circuits 400A, the pixel circuit 400A corresponding to the R color is connected to the power supply line LR, and the pixel circuit 400A corresponding to the G color is connected to the power supply line LG, and corresponds to the B color. The pixel circuit 400A is connected to the power supply line LB. The power supply circuit 600 supplies the first power supply potential Vdd and the second power supply potential Vss to the pixel circuit 400A. First power supply potential Vdd
Is a potential supplied to the source of the driving transistor 401 described later, and in this example, is a higher potential than the second power supply potential Vss, and is common to all the pixel circuits 400A. The first power supply potential Vdd may be set according to the emission color of the OLED element 420. On the other hand, the second power supply potential Vss differs depending on the emission color of the OLED element 420. The second power supply potential Vssr corresponds to the R color, the second power supply potential Vssg corresponds to the G color, and the second power supply potential Vssb corresponds to the B color.

The power supply circuit 600 includes a correction circuit 610 that generates reference power supply voltages Vref1, Vref2, and Vref3, and a power supply voltage supply circuit 620 that outputs second power supply potentials Vssr, Vssg, and Vssb. The reference power supply voltage Vref1 is R color and the reference power supply voltage Vre
f2 corresponds to the G color, and the reference power supply voltage Vref3 corresponds to the B color. Power supply voltage supply circuit 620
Generates a second power supply potential Vssr, Vssg, and Vssb by subjecting the reference power supply voltages Vref1, Vref2, and Vref3 to correction processing in consideration of the temperature characteristics of the OLED element. The second power supply potentials Vssr, Vssg, and Vssb are supplied to the pixel circuit 400A corresponding to each color of RGB via the power supply lines LR, LG, and LB. The reason why the power supply lines LR, LG, and LB are provided for each color in this manner is that the light emission characteristics of the OLED elements are different for each color.
This is because it is necessary to supply power to the battery.

The scanning line driving circuit 100 scans signals Y1 and Y for sequentially selecting a plurality of scanning lines 101.
2, Y3,..., Ym are generated. The scanning signal Y1 is a pulse having a width corresponding to one horizontal scanning period (1H) from the first timing of one vertical scanning period (1F).
01 is supplied. Thereafter, the pulses are sequentially shifted to scan line 1 in the 2nd, 3rd,..., Mth rows.
01 are supplied as scanning signals Y2, Y3,..., Ym. Generally i (i is 1 ≦ i
When the scanning signal Yi supplied to the scanning line 101 in the row reaches an H level,
It indicates that the scanning line 101 is selected.

The data line driving circuit 200 supplies supply gradation signals X1, X2, X3,..., Xn to each of the pixel circuits 400A located on the selected scanning line 101 based on the gradation data D. In this example, the supply gradation signals X1 to Xn are given as voltage signals indicating gradation luminance.

The temperature sensor 300 detects the temperature of the light emitting panel AA and outputs a temperature signal TS. The temperature sensor 300 can be configured by, for example, a diode, wiring, or the like. When wiring is used as the temperature sensor, the temperature can be detected by a change in the resistance value.
The wiring may be formed of the same layer and the same material as the gate electrode, the source electrode, and the drain electrode of a transistor used in the pixel circuit 400A, the data line driving circuit 200, the scanning line driving circuit 100, or the like. It may be formed of the same layer and the same material as the wiring such as the data line 103. Alternatively, the same OLED element as the OLED element included in the pixel circuit 400A may be formed in the same process and used as the temperature sensor 300. .

The timing generation circuit 700 generates various control signals and outputs them to the scanning line driving circuit 10.
0 and output to the data line driving circuit 200. Further, the image processing circuit 800 generates gradation data D subjected to image processing such as gamma correction, and outputs it to the data line driving circuit 200. In addition,
In this example, the power supply circuit 600, the timing generation circuit 700, and the image processing circuit 800 are provided outside the light emitting panel AA. However, some or all of these components are disposed in the light emitting panel A.
You may import it into A. Furthermore, some of the components provided in the light emitting panel AA may be provided as an external circuit. For example, the temperature sensor 300 may be provided outside the light emitting panel AA.
However, it is preferable to arrange the pixel circuit 400A within a detectable range.

Next, the pixel circuit 400A will be described. FIG. 2 shows a circuit diagram of the pixel circuit 400A. The pixel circuit 400A shown in the figure corresponds to the R color of the i-th row, and the second power supply potential V
ssr is supplied. The pixel circuit 400A corresponding to the other colors has the same configuration except that the second power supply potential Vssg (G color) or the second power supply potential Vssb (B color) is supplied instead of the second power supply potential Vssr. Has been. The pixel circuit 400A includes two thin film transistors (TF
T: abbreviated as thin film transistors) 401 and 402, capacitive element 410, and OLED
And an element 420. Among these, the source electrode of the P-channel TFT 401 is connected to a node to which the first power supply potential Vdd is supplied, while its drain electrode is connected to the OLED element 42.
Each is connected to zero anode 420a (first electrode).

One end of the capacitive element 410 is connected to the source electrode of the TFT 401, while the other end is connected to the T
The gate electrode of FT 401 and one electrode of TFT 402 are connected to each other. TFT
The gate electrode 402 is connected to the scanning line 101, and the other electrode is connected to the data line 103. The cathode 420b of the OLED element 420 is connected to the power supply line LR and supplied with the second power supply potential Vssr. A light emitting layer is sandwiched between the anode 420a and the cathode 420b, and emits light with luminance according to the forward current.

In such a configuration, when the scanning signal Yi becomes H level, the N-channel TFT 4
Since 02 is turned on, the data signal Vdata is written to the gate electrode of the TFT 401, and the potential is held by the capacitor 410. Here, the current Ioled flowing through the OLED element 420 is determined by the gate-source voltage of the TFT 401.

3 to 5 show temperature characteristics of the OLED element 420. FIG. 3 and 4, even if the voltage Voled between the first electrode 420a and the second electrode 420b of the OLED element 420 is the same, the light emission luminance L and the current Ioled vary depending on the temperature. Further, it can be seen from FIG. 5 that the relationship between the current Ioled and the light emission luminance L hardly changes depending on the temperature. That is, the OLED element 420 depends on the temperature.
If the voltage Voled between the two electrodes is adjusted, it is most effective in reducing the fluctuation of the luminance L.

Here, two modes are conceivable for adjusting the voltage Voled. The first mode is a method of adjusting the gate potential (data amplitude) of the drive transistor 401 and the first power supply potential Vdd. The second mode is a method of adjusting the second power supply potential Vss of the cathode 420b of the OLED element 420. When the P-channel type is adopted as the driving transistor 401 as in this embodiment, it is preferable to adjust only the second power supply potential Vss because the driving current Ioled depends on the gate-source voltage Vgs. In the first aspect, since it is necessary to adjust both the gate potential (data amplitude) of the drive transistor 401 and the first power supply potential Vdd to the same extent, the configuration becomes complicated and it is not suitable for downsizing of the light emitting device 1. .

Therefore, in the present embodiment, the second aspect is adopted. In this case, the second power supply potential Vss is
First, the drain-source voltage Vds of the driving transistor 401 is set to be constant even when the temperature changes. As a result, the power consumption of the drive transistor 401 becomes constant regardless of the temperature change. Second, the amount of change according to the temperature of the second power supply potential Vss is a voltage between the first electrode 420a and the second electrode 420b of the OLED element 420 that changes according to the temperature when the drive current Ioled is constant. Set to match the change in Voled. Third, second
The power supply potential Vss is determined so that the operating point of the drive transistor 401 is in the vicinity of the boundary between the linear region and the saturation region when the OLED element 420 emits light with the maximum luminance at the detected temperature. Thereby, the power consumption of the drive transistor 401 can be reduced.

FIG. 6 shows a configuration of a main part of the power supply circuit 600. The power supply circuit 600 includes a correction circuit 610 and a power supply voltage supply circuit 620. The correction circuit 610 includes an AD converter 510 that converts the temperature signal TS from an analog signal to a digital signal and outputs temperature data. The temperature data is supplied to correction tables LUTr, LUTg, and LUTb corresponding to RGB colors.
In the correction table LUTr, the temperature and the reference voltage Vref1 are stored in association with each other, and when the correction data is supplied, the corresponding reference voltage Vref1 is output. The same applies to the correction tables LUTr and LUTb.

The power supply voltage supply circuit 620 includes voltage adjustment circuits 621 to 623 corresponding to RGB colors. The voltage adjustment circuit 621 includes a positive input terminal to which the reference voltage Vref1 is supplied, an operational amplifier having a resistor R2 between the output terminal and the negative input terminal, and a resistor R1 provided between the power supply Vx and the negative input terminal. With. The second power supply potential Vssr is given by the following equation.
Vssr = Vref1 + R2 (Vref1-Vx) / R1
Here, since the reference voltage Vref1 is a voltage according to the temperature, the second power supply potential Vssr
Can be adjusted according to the temperature. Note that at least one of the resistors R1 and R2 may be configured by an electronic volume, and the value thereof may be adjusted according to the temperature.

FIG. 7 is an explanatory diagram illustrating a method for setting the operating point of the driving transistor. The operating point of the driving transistor 401 is set as follows. First, the gate-source voltage Vgs of the drive transistor 401 is set according to the highest luminance of the OLED element 420. Second,
At the lowest temperature in the temperature range for operating the OLED element 420, the drive transistor 4
The second power supply potential Vss is set so that the operating point 01 becomes the boundary between the linear region and the saturation region (Vds> Vgs−Vth). Third, the correction table L according to the temperature characteristics of the OLED element 420
UT (LUTr to LUTb) is created.

Thus, when the driving transistor 401 is configured as a P-channel type, the gate-source voltage Vgs can be determined only by the gate potential (data voltage Vdata) and the source voltage (first power supply potential Vdd) of the driving transistor 401. Therefore, when the second power supply potential Vss is adjusted according to the temperature characteristics, only the voltage Voled between the two electrodes of the OLED element 420 can be changed, and the magnitude of the drive current Ioled does not change. Therefore, it is the most effective method for reducing luminance fluctuation due to temperature while reducing power consumption.

By the way, the voltage at which the drive transistor 401 starts to saturate. That is, when the voltage at the boundary between the saturation region and the linear region is Vp, the current I _{dsat at the} voltage Vp is given by the following equation. I _dsat = 1/2 ・ W / L ・ μ ・ C _ox・ Vp ²
Where W is the gate width, L is the gate length, μ is the mobility, and C _ox is the gate capacitance. When designing with a margin, it is necessary to reduce the voltage Vp. On the contrary,
When I _dsat is constant (to ensure the same drive current), (W / L) can be reduced when Vp can be increased without providing a margin as in this embodiment. . Accordingly, the gate width W of the driving transistor 401 can be reduced, so that high definition can be easily achieved. If the driving transistor 401 and the OLED element 420 do not overlap (for example, a bottom emission structure), the area of the OLED element 420 can be increased and the aperture ratio can be improved.

Furthermore, it is preferable to set the second power supply potential Vss below the ground potential. This point is shown in FIG.
Will be described with reference to FIG. First, as shown in FIG. 5A, the second power supply potential Vss is set to 0 V from the beginning.
In the case of (ground potential), for example, the gate potential (data amplitude) of the drive transistor 401
Is 3V to 13V, and the high potential power supply VHH of the scanning line driving circuit 100 needs to be 15V or more, and is generally set to 17V that is + 2V. By increasing the drive voltage, TF
It is necessary to increase the breakdown voltage of T. As a result, the reliability of the circuit is impaired and a malfunction may occur. The higher the drive voltage, the greater the power consumption. Furthermore, there is a problem that the response speed of the circuit becomes slow.

On the other hand, when the second power supply potential Vss is less than the ground potential as shown in FIG. 5B, the above-described problems can be solved by lowering the drive voltage. For example, the second power supply potential Vss
Is set to -2V, 15V is sufficient for the high potential power supply VHH. As a result, the power consumption of the entire light emitting device 1 can be further reduced. The problem of luminance fluctuation due to temperature rise depends on the gradation to be displayed. That is, when displaying white data for all the pixel circuits 400A,
Power consumption is highest and temperature rises. By reducing the amplitude of the data signal Vdata, it is possible to suppress power consumption and make it difficult for the temperature to rise from the beginning. Further, as shown in FIG. 5B, the potential of the first power supply potential Vdd can be lowered, so that power consumption can be suppressed.

As described above, according to the present embodiment, the brightness change due to the temperature change is reflected and adjusted in the second power supply potential Vss, so that the brightness change can be canceled and the power consumption can be reduced. At the same time, the temperature of the light emitting panel AA can be prevented from rising unilaterally, and since no heat sink or cooling mechanism is required, the light emitting panel AA can be made smaller and thinner.
Manufacturing costs can be reduced. Furthermore, the burn-in of the OLED element 420 can be prevented and the life of the light emitting panel AA can be extended. In addition, since it is not necessary to design a margin in consideration of the temperature characteristics of the OLED element 420, the power consumption of the drive transistor 401 can be significantly reduced.

In the above-described embodiment, the P-channel type is used as the driving transistor 401.
An N-channel driving transistor 401 may be used. In this case, the pixel circuit 400B illustrated in FIG. 9 is employed. In this example, the second power supply potential is Vddr, and the first power supply potential is VC.
T. That is, the second power supply potential Vddr on the high potential side is varied according to the temperature.
In the above-described embodiment, the second power supply potential Vss is made different according to the emission color of the OLED element 420, and the correction tables LUTr, LUTg, and LUT are changed for each emission color as shown in FIG.
b and the voltage adjustment circuit 621 are provided, but the second power supply potential Vss may be commonly supplied regardless of the emission color, and the correction table and the voltage adjustment circuit 621 may be provided in common. By doing in this way, the structure of the cathode 420b of the OLED element 420 and the power supply circuit 600 can be simplified.
For example, if a plurality of OLED elements 420 that emit white or blue light are provided and a plurality of colors such as blue, red, and green are obtained by a color filter or a fluorescence conversion film, the temperature characteristics of the OLED elements 420 are common. Therefore, the second power supply potential Vss is set to a plurality of OLED elements 420.
Preferably, one correction table and one voltage adjustment circuit 621 are provided.
In the above-described embodiment, the OLED element 420 emits light of three colors of RGB. However, the OLE emits light of three colors different from the three colors of single color, two colors, four colors, or RGB.
A D element 420 may be used.

<2. Application example>
Next, an electronic apparatus to which the light emitting device 1 according to the above-described embodiment is applied will be described. FIG.
0 shows the configuration of a mobile personal computer to which the light emitting device 1 is applied. The personal computer 2000 includes a light emitting device 1 as a display unit and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the light-emitting device 1 uses the OLED element 420, it is possible to display an easy-to-see screen with a wide viewing angle.

FIG. 11 shows a configuration of a mobile phone to which the light emitting device 1 is applied. The cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and the light emitting device 1 as a display unit. By operating the scroll button 3002, the screen displayed on the light emitting device 1 is scrolled.

FIG. 12 shows a portable information terminal (PDA: Personal Digital Assistant) to which the light emitting device 1 is applied.
The structure of s) is shown. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and the light emitting device 1 as a display unit. 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 1.

Electronic devices to which the light emitting device 1 is applied include those shown in FIGS. 10 to 12, a digital still camera, a liquid crystal television, a viewfinder type, a monitor direct view type video tape recorder, a car navigation device, a pager, and an electronic notebook. , Calculators, word processors, workstations, videophones, POS terminals, devices equipped with touch panels, and the like. And the light-emitting device 1 mentioned above is applicable as a display part of these various electronic devices. Note that a printer may be used as the electronic apparatus (image forming apparatus) to which the light emitting device 1 is applied. Here, the light-emitting device 1 is provided to form an electrostatic latent image on an image carrier such as a photosensitive drum, and may be formed by arranging a plurality of OLED elements in an array in the main scanning direction. Good.

It is a block diagram which shows the structure of the light-emitting device which concerns on embodiment of this invention. It is a circuit diagram which shows the structure of the pixel circuit in the same apparatus. It is a graph which shows the temperature characteristic of the OLED element used for the pixel circuit. It is a graph which shows the temperature characteristic of the OLED element used for the pixel circuit. It is a graph which shows the temperature characteristic of the OLED element used for the pixel circuit. It is a block diagram which shows the structure of the principal part of the power circuit in the apparatus. It is a graph for demonstrating the operating point of a drive transistor. It is explanatory drawing which shows the relationship of an electric potential. It is a circuit diagram of a pixel circuit according to a modification. It is a perspective view which shows the structure of the mobile type personal computer to which the same apparatus is applied. It is a perspective view which shows the structure of the mobile telephone to which the same apparatus is applied. It is a perspective view which shows the structure of the portable information terminal to which the same apparatus is applied. It is explanatory drawing for demonstrating the operating point of the drive transistor in the conventional light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light-emitting device, 420 ... Organic light emitting diode, 400A, 400B ... Pixel circuit, 300 ...
Temperature sensor (temperature detection means), 600 ... power supply circuit, 610 ... correction circuit, 620 ... power supply voltage supply circuit, TS ... temperature signal, LUTr, LUTg, LUTb ... correction table, Vssr,
Vssg, Vssb ... second power supply potential, Vref1, Vref2, Vref3 ... reference voltage.

Claims (13)

A driving method of a pixel circuit comprising: a light emitting element that emits light with a light amount corresponding to a driving current flowing between a first electrode and a second electrode; and a driving transistor that supplies the driving current to the first electrode. ,
Supplying a first potential to a source of the driving transistor;
Detecting the temperature of the light emitting element;
Adjusting the second potential supplied to the second electrode according to the detected temperature;
A driving method of a pixel circuit. 2. The pixel according to claim 1, wherein the second potential is adjusted according to the detected temperature so that a voltage between a drain and a source of the driving transistor becomes constant even when the temperature changes. Circuit driving method. The amount of change in accordance with the temperature of the second potential matches the amount of change in voltage between the first electrode and the second electrode of the light emitting element that changes in accordance with temperature when the driving current is constant. The pixel circuit driving method according to claim 1, wherein: The second potential is determined so that the operating point of the driving transistor is in the vicinity of the boundary between the linear region and the saturation region when the light emitting element emits light with the maximum luminance at the detected temperature. The method for driving a pixel circuit according to claim 1, wherein: Light emission in which a plurality of pixel circuits each including a light emitting element that emits light with a light amount corresponding to a drive current flowing between the first electrode and the second electrode and a drive transistor that supplies the drive current to the first electrode are arranged A device,
Temperature detecting means for detecting the temperature of the light emitting element;
Power supply means for supplying a first potential to the source of the driving transistor and supplying a second potential to the second electrode, and adjusting the second potential in accordance with the detected temperature;
A light emitting device characterized by that. The light emitting element has a plurality of types of emission colors,
The power supply means generates the second potential individually according to the emission color of the light emitting element and supplies the second potential to the corresponding light emitting element.
The light emitting device according to claim 5. The power supply means includes adjustment means for adjusting the second potential in accordance with the detected temperature so that the voltage between the drain and source of the driving transistor is constant even when the temperature changes. The light emitting device according to claim 5, wherein the light emitting device is a light emitting device. The power supply means changes the voltage corresponding to the temperature of the second potential with the voltage between the first electrode and the second electrode of the light emitting element, which changes according to the temperature when the driving current is constant. The light-emitting device according to claim 5, further comprising an adjusting unit that adjusts the second potential so as to coincide with a change amount. When the light emitting element emits light at the maximum brightness at the detected temperature, the power supply means causes the second potential so that the operating point of the driving transistor is near the boundary between the linear region and the saturation region. The light-emitting device according to claim 5, further comprising adjusting means for adjusting the light intensity. The adjustment unit includes a storage unit that stores the temperature and correction data for correcting the second potential in association with each other, reads the correction data corresponding to the detected temperature with reference to the storage unit, The light emitting device according to claim 6, wherein the second potential is adjusted based on the read correction data. The light emitting device according to claim 6, wherein the second potential is set lower than a ground potential. The light emitting device according to claim 6, wherein the light emitting element is an organic light emitting diode. An electronic apparatus comprising the light-emitting device according to any one of claims 6 to 12.

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