JP2003316320A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the luminance degradation of an organic EL display panel and also to reduce the power consumption of EL power source circuits. <P>SOLUTION: A first EL power source circuit 2 outputs a positive power source voltage PVdd which is to be supplied to respective organic EL elements existing in an organic EL display panel 1 on a first power source line 3 and a second power source circuit 4 outputs a negative power source voltage CV which is to be supplied to the respective organic EL elements existing in the panel 1 on a second power source line 5. Moreover, a current detecting circuit 6 for detecting a current flowing through the second power source line 5 is provided between the power source circuit 2 and the display panel 1. An amplitude limiting circuit 10 which is incorporated in a controller IC 9 limits the amplitude of a video signal VS1 when an current detection output voltage Vdet which is outputted from the current detecting circuit 6 becomes equal to or larger than a reference level Vref and it outputs a video signal VS2' whose amplitude is limited to the display panel 1. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a display device including a plurality of organic EL elements and performing display by lighting the organic EL elements according to a video signal.

[0002]

2. Description of the Related Art In recent years, electroluminescence (Elec
tro Luminescence: An EL display device using an element (hereinafter, abbreviated as “EL”) is drawing attention as a display device that replaces a CRT or LCD. In particular, a thin film transistor (Thin Film) is used as a switching element for driving the EL element.
Transistor: E provided with "TFT")
L display devices have been developed.

FIG. 4 shows the structure of an organic EL display device.
Reference numeral 40 denotes an organic EL display panel, which includes a plurality of pixels including a plurality of organic EL elements and arranged in a matrix. Reference numeral 41 denotes a controller IC, which performs signal processing and timing adjustment based on a video signal Vs1 and a synchronization signal Vsync input from the outside to create a video signal Vs2 and various timing signals Ts, and the organic EL display panel 40. Is being supplied to.

Reference numeral 42 denotes an EL power supply circuit, which is an organic E
The positive power supply voltage PVdd supplied to each organic EL element in the L display panel 40 is output to the first power supply line 43, and the negative power supply voltage CV supplied to each organic EL element is output to the second power supply line 44. There is.

FIG. 5 shows an equivalent circuit diagram of one pixel in the organic EL display panel 50. The gate signal line 50 that supplies the gate signal Gn and the drain signal, that is, the drain signal line 60 that supplies the video signal Dm intersect with each other. The video signal Dm is created by sampling the above video signal Vs2 with a sampling signal. The gate signal Gn is created based on the timing signal Ts.

An organic EL element 120, a TFT 100 for driving the organic EL element 120, and a TFT 110 for selecting a pixel are arranged near the intersection of these signal lines.

A positive power supply voltage PVdd is supplied from the first power supply line 43 of FIG. 4 to the drain 110d of the TFT 100 for driving the organic EL element. Also, the source 11
0s is connected to the anode 121 of the organic EL element 120.

Further, the gate signal Gn is supplied by connecting the gate signal line 50 to the gate 110g of the pixel selecting TFT 110, and the drain signal line 60 is connected to the drain 110d.
m is supplied. The source 110s of the TFT 110 is connected to the gate 100g of the TFT 100. Here, the gate signal Gn is output from a gate driver circuit (not shown). The video signal Dm is output from a drain driver circuit (not shown).

The organic EL element 120 is composed of the anode 1
21, a cathode 122, and a light emitting element layer 123 formed between the anode 121 and the cathode 122. The negative power supply voltage CV from the second power supply line 44 of FIG. 4 is supplied to the cathode 122.

A storage capacitor 130 is connected to the gate 100g of the TFT 100. That is, one electrode of the storage capacitor 130 is connected to the gate 100g, and the other electrode is connected to the storage capacitor electrode 131. The storage capacitor 130 is provided to hold a video signal of a display pixel for one field period by holding a charge according to the video signal Dm.

The operation of the EL display device having the above configuration will be described below. When the gate signal Gn becomes high level for one horizontal period, the TFT 110 is turned on. Then, the video signal Dm is transmitted from the drain signal line 60 to the TFT.
It is applied to the gate 100 g of the TFT 100 through 110. Then, the conductance of the TFT 100 changes according to the video signal Dm supplied to the gate 100g, and a corresponding drive current is supplied to the organic EL element 120 through the TFT 100, and the organic EL element 120 lights up.

[0012]

When the amplitude of the video signal Dm increases, the change in the conductance of the TFT 100 also increases, the driving current flowing through the organic EL element 120 increases, and the brightness of the organic EL element 120 also increases.

Therefore, on a bright screen (screen when the amplitude of the video signal Dm is large), there is a problem that the current supplied from the EL power supply circuit 42 increases and power consumption increases.

Further, when a current is passed through the organic EL element 120, the luminance thereof deteriorates, that is, a so-called luminance deterioration characteristic is exhibited. If the current flowing through the organic EL element 120 increases and the screen becomes too bright, the organic EL display panel 40
However, there was a problem that the decrease in the luminance was large.

Therefore, it is an object of the present invention to reduce the power consumption of the EL power supply circuit and to suppress the deterioration of the brightness of the organic EL display panel.

[0016]

The display device of the present invention includes a plurality of organic EL elements, and an organic EL display panel which performs display by applying a current to the plurality of organic EL elements in response to a video signal and lighting them. A power supply line that supplies power to the organic EL element, a current detection circuit that detects a current flowing in the power supply line, and an amplitude limiter that limits the amplitude of the video signal according to the detection output of the current detection circuit. And a circuit.

According to the present invention, since the function of detecting the current flowing in the power supply line and limiting the amplitude of the video signal is added, the luminance of the organic EL display panel is lowered and the luminance is deteriorated at a predetermined current level or more. It becomes possible to suppress.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a display device according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an organic EL display panel, which includes a plurality of pixels including a plurality of organic EL elements and arranged in a matrix. 2 is the first EL
Power supply circuit, each organic EL in the organic EL display panel 1
The positive power supply voltage PVdd supplied to the element is output to the first power supply line 3. 4 is a second EL power supply circuit,
The negative power supply voltage CV supplied to each organic EL element in the organic EL display panel 1 is output to the second power supply line 5.

A current detection circuit 6 for detecting a current flowing through the second power supply line 5 is provided in the current path of the second power supply line 5. Current detection circuit 6
Is composed of, for example, a resistor 7 provided in the current path of the second power supply line 5 and a differential amplifier 8 for amplifying a difference voltage generated across the resistor 7 due to a current i flowing through the resistor 7. The differential amplifier 8 outputs the current detection output voltage Vdet.

Reference numeral 9 denotes a controller IC, which is based on a video signal Vs1 and a synchronization signal Vsync input from the outside.
Video processing Vs
2 ', various timing signals Ts are created and supplied to the organic EL display panel 1. The controller IC9 has
The amplitude limiting circuit 10 is built in. Amplitude limiting circuit 10
When the current detection output voltage Vdet from the current detection circuit 6 becomes equal to or higher than the reference level Vref, the amplitude of the video signal Vs1 is limited, and the amplitude-limited video signal Vs2 'is output.

Since the structure of the organic EL display panel 1 is exactly the same as that described with reference to FIG. 5, the description thereof will be omitted.

With the above configuration, the current detection output voltage Vdet
Is higher than the reference level Vref, the video signal Vs2 '
Is limited in amplitude, so that the luminance of the organic EL display panel 1 is suppressed and the luminance deterioration is suppressed. Further, the currents supplied by the first EL power supply circuit 2 and the second EL power supply circuit 4 are also reduced, so that the power consumption is reduced.

FIG. 2 is a diagram showing an example of the amplitude limiting circuit 10 incorporated in the controller IC 9. The current detection output voltage Vdet input from the terminal 11 is converted into a digital value by the analog / digital converter 12. The output of the analog / digital converter 12 is the reference level Vref.
It is input to the variable gain amplifier 13 together with the (digital value).

The variable gain amplifier 13 sets the gain G to 1 when the current detection output voltage Vdet is lower than the reference level Vref, and sets the gain to less than 1 (when the current detection output voltage Vdet is higher than the reference level Vref ( For example, the arithmetic processing is performed so as to be changed to 0.5).

The amplitude limiting circuit 10 is not limited to the digital arithmetic circuit as described above, but may be composed of, for example, an analog variable gain amplifier. In this case, the analog / digital converter 12 is unnecessary, and the reference level Vref also becomes an analog value.

Also, a video signal Vs1 input from the outside
May be a digital signal or an analog signal. In the case of a digital signal, it is applied to the variable gain amplifier 13 after being converted into an analog signal by D / A conversion.

Further, the current detection circuit 6 has a negative power supply voltage CV.
However, it may be provided in the first power supply line 3 to which the positive power supply voltage PVdd is supplied. However, in the latter case, since the positive power supply voltage PVdd for driving the organic EL element may become unstable due to the provision of the current detection circuit 6, the current detection circuit 6 outputs the negative power supply voltage CV. It is desirable to provide the second power supply line 5 to be supplied.

As described above, the present invention detects the current flowing through the first EL power supply line 3 or the second EL power supply line 5 and feeds back the detected output to the controller IC 9 to display the organic EL display panel 1 To control the amplitude (contrast) of the video signal Vs1 sent to the
ontrast limiter) function is added.

FIG. 3 shows how the signal amplitude of the video signal Vs2 'changes. In one horizontal period, for example, when the amplitude of the video signal Vs2 ′ gradually increases as shown in FIG. 3, or when there is no ACL function, it increases as it is.
When the ACL function is provided, the video signal Vs1 has a predetermined A
The amplitude is limited when the voltage exceeds the CL start voltage. Therefore, the contrast is lowered and the luminance is lowered. The ACL start voltage VACL can be arbitrarily set according to the reference level Vref.

[0031]

According to the present invention, the current flowing through the power supply line for supplying power to the organic EL element is detected, and the amplitude of the video signal is limited according to the detected output. When the value is equal to or more than the predetermined value, the brightness of the organic EL display panel is reduced, and the deterioration of the brightness of the organic EL display panel can be suppressed.

Further, as a result of limiting the amplitude of the video signal in accordance with the above detection output, the current supplied by the power supply circuit to the power supply line is also reduced, so that the power consumption can be suppressed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a display device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an amplitude limiting circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing how the signal amplitude of a video signal Vs2 ′ changes.

FIG. 4 is a circuit diagram of a display device according to a conventional example.

FIG. 5 is an equivalent circuit diagram of one pixel of an EL display device.

[Explanation of symbols]

1 Organic EL display panel 2 First EL power supply circuit 3 First power line 4 Second EL power supply circuit 5 Second power line 6 Current detection circuit 7 resistance 8 differential amplifier 9 Controller IC 10 Amplitude limiting circuit 11 terminals 12 Analog-to-digital converter 13 variable gain amplifier

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 642 G09G 3/20 642E 642P 670 670K H05B 33/14 H05B 33/14 A

Claims (8)

[Claims] 1. An organic EL display panel including a plurality of organic EL elements, wherein a current is applied to the plurality of organic EL elements in response to a video signal to illuminate the organic EL display panel, and power is supplied to the organic EL elements. A display comprising: a power supply line; a current detection circuit that detects a current flowing through the power supply line; and an amplitude limiting circuit that limits the amplitude of the video signal according to a detection output of the current detection circuit. apparatus. 2. The display device according to claim 1, wherein the amplitude limiting circuit limits the amplitude of the video signal when the detection output of the current detecting circuit is equal to or more than a predetermined value. 3. The amplitude limiting circuit includes an amplifier that amplifies the amplitude of the video signal, and sets the gain of the amplifier to 1 when the detection output of the current detection circuit is less than a predetermined value.
The display device according to claim 1, wherein the gain of the amplifier is limited to less than 1 when the detection output of the current detection circuit is equal to or more than a predetermined value. 4. An organic EL display panel comprising a plurality of organic EL elements, wherein an organic EL display panel performs display by applying a current to the organic EL elements in response to a video signal and lighting the organic EL elements.
A first power supply line for supplying a positive power supply voltage to the anode of the L element, a second power supply line for supplying a negative power supply voltage to the cathode of the organic EL element, and a current of the first power supply line or the second power supply line. A display device comprising: a current detection circuit for detecting; and an amplitude limiting circuit for limiting the amplitude of the video signal according to a detection output of the current detecting circuit. 5. The current detection circuit includes a resistor provided in a current path of the first power supply line or the second power supply line, and an operational amplifier for amplifying a voltage generated in the resistance.
5. The display device according to claim 4, further comprising: an output of the operational amplifier as a detection output. 6. The display device according to claim 4, wherein the current detection circuit is inserted in a current path of the second power supply line. 7. The current detection circuit includes a resistor inserted in a current path of the second power supply line and an operational amplifier for amplifying a voltage generated in the resistance, and uses an output of the operational amplifier as a detection output. The display device according to claim 6, wherein: 8. The amplitude limiting circuit includes an amplifier for amplifying the amplitude of the video signal, and when the detection output of the current detecting circuit is less than a predetermined value, the gain of the amplifier is set to 1
5. The display device according to claim 4, wherein the gain of the amplifier is limited to 1 or less when the detection output of the current detection circuit is a predetermined value or more.