JP2003280585A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an optical element from being deteriorated. <P>SOLUTION: The display device has an interrupting circuit Tr3 which is provided between a current driven type optical element OLED (organic light emitting diode) 1 and a power source Vdd and a potential changing circuit C2 for pulling down the potential of one end nearer to the power source of the optical element OLED 1. The potential changing circuit C2 pulls down the potential of one end of the optical element 1 and applies a bias opposite to that at the time of performing light emission to the optical element 1 whilst the interval between the optical element 1 and the power source Vdd is interrupted by the interrupting circuit Tr3. Thus, the degradation of the optical elements is lowered. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a display device. The present invention particularly relates to an active matrix type display device.

[0002]

2. Description of the Related Art In recent years, organic ELs functioning as light emitting devices
(OLED: Organic Light Emitt
ing diode) display device is a CRT
It is drawing attention as a display device that replaces LCDs and LCDs. In particular, active research and development of an active matrix type display device in which a plurality of pixels are arranged in a matrix in the vertical and horizontal directions has been actively pursued. In an active matrix display device, a switching element is arranged in each pixel, and video data is sequentially written by the switching element for each scanning line.

The practical design of a display device using an organic EL element is in its infancy, and various pixel circuits have been proposed.
FIG. 11 shows an example of such a circuit.

This circuit is a thin film transistor (Thin).
Film Transistor: Hereinafter, simply TFT
That is, the transistor Tr10 and the transistor Tr20, and the capacitor C. Transistor Tr1
0 is for switching, transistor Tr20 is organic EL
It is for driving the element OLED10. In the transistor Tr10, the gate electrode is connected to the scan line 110, and the source electrode (or drain electrode) is the data line 1.
The drain electrode (or the source electrode) is connected to the gate electrode of the transistor Tr20 and one electrode of the capacitor C. The other electrode of the capacitor C is connected to the source electrode of the transistor Tr20. Data line 112
Is connected to a constant voltage source (not shown), and the organic EL element OLE
The brightness data that determines the current flowing through D10 is transmitted.

In the transistor Tr20, the source electrode is connected to the anode of the organic EL element OLED10,
The drain electrode is connected to the power supply line 114. Power line 11
Reference numeral 4 is connected to a power supply Vdd provided outside the pixel region, and a voltage for actually causing the organic EL element OLED10 to emit light is applied.

The organic EL element OLED10 includes a light emitting element layer sandwiched between an anode and a cathode. Organic EL
The anode of the element OLED10 is connected to the source electrode of the transistor Tr2, and the cathode is grounded.

The operation of the display device having the above configuration will be described. First, the scanning line 110 is set to high, and the transistor T
After turning on r10, a data potential is applied to the data line 112. At this time, the potential of the electrode of the capacitor C rises. At the same time, the potential of the gate electrode of the transistor Tr20 changes to the same as the potential of the electrode of the capacitor C.

When the potential of the gate electrode of the transistor Tr20 exceeds a predetermined value, a current corresponding to the voltage flows from the power source line 114 to the organic EL element OLED10, and the organic EL element.
The element OLED10 emits light. Even if the scanning line 110 is set to low, the gate potential of the transistor Tr20 is held by the capacitor C, so that the organic EL element OLED10 continues to emit light with the brightness according to the data potential applied to the gate electrode of the transistor Tr20.

[0009]

However, in a display device using an organic EL element, there is a problem in that element deterioration occurs due to aging, which causes variations in brightness. There is also a problem that the life of the device is shortened due to such deterioration. One of the causes of element deterioration,
Examples thereof include a carrier trap phenomenon that occurs in the interface between the organic layer and the inorganic layer in the organic EL element, the interface between the organic layer and the organic layer, or the bulk-shaped organic layer. According to this phenomenon, the carriers trapped in the organic EL element form an internal electric field, so that the electric field due to the voltage applied to the organic EL element is substantially reduced, and the luminance is reduced in the initial stage of driving. . Therefore, it is said that the decrease in brightness can be alleviated by applying an electric field in the opposite direction to release the trapped carriers (published by Junji Kido, "Organic EL Materials and Displays," CMC Corporation).

Further, when the brightness data set by the data potential is large, even if the brightness data is rewritten to set the small brightness data, the charges corresponding to the previous large brightness data remain without being discharged from the organic EL element. In some cases, there is a so-called afterimage phenomenon in which accurate luminance data cannot be set. In particular, when displaying a fast-moving moving image, the visibility may be reduced.

The present invention has been made in view of such circumstances, and an object thereof is to reduce deterioration of an optical element. Another object of the present invention is to eliminate variations in brightness by reducing deterioration of optical elements. Another object of the present invention is to extend the life of the optical element. Still another object of the present invention is to reduce the afterimage phenomenon.

[0012]

One aspect of the present invention relates to a display device. This device is provided between a current-driven optical element and a power supply, and has a potential fluctuation circuit that lowers the potential at one end of the optical element closer to the power supply. By pulling down, a bias reverse to that at the time of light emission is applied to the optical element.

Another aspect of the present invention also relates to a display device. This device has a cutoff circuit provided between a current-driven optical element and a power source, and a potential variation circuit that lowers the potential at one end of the optical element closer to the power source. While the optical circuit and the power supply are being cut off by the cutoff circuit, the potential at one end of the optical element is lowered, and a bias reverse to that at the time of light emission is applied to the optical element. Here, the one end of the optical element may be an anode of the optical element. By biasing the optical element in the opposite direction to that at the time of light emission, carriers trapped at the interface of the optical element can be released, and element deterioration can be reduced.

Another aspect of the present invention also relates to a display device. This device includes a cutoff transistor provided between a current-driven optical element and a power supply, and a potential fluctuation circuit that lowers the potential of one end of the optical element closer to the power supply. Is turned off and a signal for cutting off between the optical element and the power supply and a signal for lowering the potential are input at the same timing, and a bias reverse to that at the time of light emission is applied to the optical element. The signal for turning off the cutoff transistor and the signal for lowering the potential may be the same or may have an inversion relationship. As a result, the circuit configuration can be simplified and element deterioration can be reduced.

The potential fluctuation circuit may have a capacitance, and the potential at one end may be lowered via the capacitance. Through the capacitance, by reducing the potential of the electrode on the side far from the optical element of the capacitance by a predetermined potential difference, the potential difference of the electrode on the near side can also be reduced by the predetermined potential difference. The potential can be easily lowered.

The disconnection between the optical element and the power source and the reduction of the potential may be performed at a timing different from the timing for setting the luminance data to the optical element. By performing the brightness data setting timing, the disconnection between the optical element and the power supply, and the lowering of the potential at different timings, the luminance data can be set in a state where the potential at one end of the optical element is stable.

The potential variation circuit may have two transistors which are provided in parallel and which are turned on and off in a complementary manner, and by changing the transistor connected to the low potential source from off to on, of the two transistors. The potential may be lowered. According to this configuration, it is not necessary to provide a new signal line, and the circuit configuration can be simplified and the deterioration of the element can be reduced while keeping the circuit configuration simpler.

It is to be noted that any combination of the above constituent elements and the expression of the present invention converted between methods, devices, systems, etc. are also effective as an aspect of the present invention.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the following embodiments, an active matrix organic EL display is assumed as a display device.

(First Embodiment) FIG. 1 shows a configuration of a pixel circuit for two pixels of a display device according to the first embodiment. The pixel circuit 10 includes an (n-1) th pixel _Pn-1 and an nth pixel _Pn . Each pixel P _n-1 and P _n is
First transistor Tr1 and second transistor Tr
2, a third transistor Tr3, a first capacitor C1, a second capacitor C2, and an organic EL element OLED1. The first transistor Tr1 is for switching,
The second transistor Tr2 is for driving the organic EL element OLED1. The third transistor Tr3 is
It is for shutting off between the power supply Vdd and the organic EL element OLED1. In the present embodiment, the first transistor Tr1 is an n-channel type and the second transistor Tr2 is
Is a p-channel type, and the third transistor Tr3 is a p-channel type.

The n-1 th pixel P _n-1 and the n th pixel P _n
Have the same configuration, only the n-th pixel P _n will be described here. In the first transistor Tr1, the gate electrode is connected to the nth scan line 16, the source electrode (or drain electrode) is connected to the data line 20,
The drain electrode (or source electrode) is connected to the gate electrode of the second transistor Tr2 and one electrode of the first capacitor C1. The other electrode of the first capacitor C1 is grounded. The data line 20 is connected to a constant voltage source (not shown),
It transmits the brightness data that determines the current flowing through the organic EL element OLED1.

In the second transistor Tr2, the source electrode is connected to the drain electrode of the third transistor Tr3, and the drain electrode is connected to the anode of the organic EL element OLED1 and one electrode of the second capacitor C2.
The other electrode of the second capacitor C2 is connected to the (n-1) th inversion scanning line 14 to which the inversion signal of the signal propagated to the n-1th scanning line 12 is input.

In the third transistor Tr3, the gate electrode is connected to the (n-1) th scanning line 12 and the source electrode is connected to the power supply line 22. The power supply line 22 is connected to the power supply Vdd provided outside the pixel area, and the organic EL element O is actually connected.
A voltage is applied to cause the LED 1 to emit light.

The organic EL element OLED1 includes a light emitting element layer sandwiched between an anode and a cathode. The anode of the organic EL element OLED1 is connected to the drain electrode of the second transistor Tr2 and one electrode of the second capacitor C2, and the cathode is grounded.

FIG. 2 is a diagram showing the timing of signals in the (n-1) th scanning line 12, the (n-1) th inversion scanning line 14, the nth scanning line 16, and the nth inversion scanning line 18. First,
At the timing before point A, the (n-1) th scanning line 12
Both the scan line 16 and the nth scan line 16 are low. At the timing of point A, the n−1th scanning line 12 becomes high. At the timing of point B, the (n-1) th scanning line 12 becomes low and the nth scanning line 16 becomes high. Scanning line 1 at the timing of point C
6 is low. When the (n-1) th scan line 12 is low, the (n-1) th inversion scan line 14 is high, and when the nth scan line 16 is low, the nth inversion scan line 18 is high.

Next, the operation of the circuit in the nth pixel P _n will be described with reference to FIGS. When the (n-1) th scan line 12 is low (timing before point A), the third transistor Tr3 is in the on state. Therefore, the source electrode of the second transistor Tr2 is connected to the power supply Vdd. At this time, since the (n-1) th inversion scanning line 14 is high, the potential of the other electrode of the second capacitor C2 is high.

Next, when the (n-1) th scanning line 12 is made high (point A), the third transistor Tr3 is turned off, and the second transistor Tr2 and the power supply Vdd are cut off.
At this time, the n−1th inversion scanning line 14 becomes low,
The potential of the other electrode of the second capacitor C2 becomes a low potential, and the potential of the other electrode of the second capacitor C2 is lowered by the difference _Δhl between high and low. Along with this, the potential of one electrode of the second capacitor C2 is also lowered by Δ _hl . Since one electrode of the second capacitor C2 is connected to the anode of the organic EL element OLED1, the organic EL element OLED
The potential of the anode of No. 1 drops by Δ _hl . At this time, Δ _hl
Is set to be equal to or higher than the potential difference applied to the organic EL element OLED1, the potential of the anode of the organic EL element OLED1 becomes lower than the potential of the cathode, and the organic EL element OL
Reverse bias is applied to ED1.

Subsequently, the nth scanning line 16 is set to high and the nth scanning line 16
When the −1 scan line 12 is set low (point B), the third transistor Tr3 is turned on. At this time, the first transistor Tr1 is also turned on, the data potential applied to the data line 20 is written in the gate electrode of the second transistor Tr2, and the brightness data is set. Since the source electrode of the second transistor Tr2 is connected to the power supply Vdd via the third transistor Tr3, the organic EL element O
A current according to the data potential flows through the LED 1 and the organic EL
The element OLED1 emits light.

Next, when the nth scan line 16 is set to low (C
Point), the first transistor Tr1 is turned off. At this time, since the (n−1) th scanning line 12 is also low, the third transistor Tr3 is kept on and the second transistor Tr3 is turned on.
The second source electrode is connected to the power supply Vdd. Since the data potential is held by the first capacitor C1 at the gate electrode of the second transistor Tr2, the organic EL element OLE
D1 continues to emit light with a brightness according to the data potential.

As described above, in the present embodiment, the reverse bias is applied to the organic EL element OLED1 prior to the setting of the luminance data, so that the carriers trapped at the interface or the like in the organic EL element OLED1 are released. Therefore, element deterioration of the organic EL element OLED1 can be reduced. As a result, it is possible to mitigate the decrease in brightness of the organic EL element OLED1, and it is also possible to prevent brightness variations in the display device. In addition, the organic EL element OLE
The life of D1 can be extended. Further, since the reverse bias can be applied using the existing scanning signal or its inverted signal, the circuit configuration can be simplified and the advantage of the reverse bias can be obtained.

(Second Embodiment) FIG. 3 shows a configuration of a pixel circuit for two pixels of a display device according to a second embodiment of the present invention. The pixel circuit 30 according to the present embodiment is
In addition to the configuration of the pixel circuit 10 shown in FIG. 1, it differs from the first embodiment in that it includes a fourth transistor Tr4 and a fifth transistor Tr5. Fourth transistor T
The r4 is a p-channel type and the fifth transistor Tr5 is an n-channel type. In the present embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

The gate electrodes of the fourth transistor Tr4 and the fifth transistor Tr5 are the n-1th scanning line 12
Connected to. In the fourth transistor Tr4, the source electrode is grounded and the drain electrode is connected to the other electrode of the second capacitor C2. In the fifth transistor Tr5, the source electrode is connected to the (n + 1) th scanning line 32,
The drain electrode is connected to the other electrode of the second capacitor C2.

FIG. 4 is a diagram showing signal timings in the (n-1) th scan line 12, the nth scan line 16, and the (n + 1) th scan line 32. First, at the timing before point A, the (n-1) th scanning line 12, the nth scanning line 16, and the (n + th) scanning line
All one scan line 32 is low. At the timing of point A, the n−1th scanning line 12 becomes high. At the timing of point B, the (n-1) th scanning line 12 becomes low and the nth scanning line 16 becomes high. At the timing of point C, the nth scanning line 16 becomes low and the (n + 1) th scanning line 32 becomes high. The n + 1th scanning line 32 becomes low at the timing of point D.

Next, with reference to FIGS. 3 and 4, the operation of the circuit in the nth pixel P _n will be described. When the (n-1) th scan line 12, the nth scan line 16, and the (n + 1) th scan line 32 are low (timing before point A), the third transistor Tr3 is on. At this time, the source electrode of the second transistor Tr2 is connected to the power supply Vdd. At this time, the fourth transistor Tr4 is in the ON state, and the potential of the other electrode of the second capacitor C2 becomes the ground potential.

Next, when the (n-1) th scanning line 12 is made high (point A), the third transistor Tr3 is turned off, and the second transistor Tr2 and the power supply Vdd are cut off.
At this time, the fourth transistor Tr4 is turned off and the fifth transistor Tr5 is turned on. Here, since the (n + 1) th scanning line 32 is low, the potential of the other electrode of the second capacitor C2 is low. If the low potential is set lower than the ground potential, the potential of the other electrode of the second capacitor C2 is lowered by the difference Δ _0l between the ground potential and the low. Along with this, the potential of one electrode of the second capacitor C2 is also lowered by Δ _0l . Therefore, the organic EL element OL
The potential of the anode of ED1 also decreases by Δ _0l . At this time, Δ
_{If 0l} is set to be _equal to or higher than the potential difference applied to the organic EL element OLED1, the potential of the anode of the organic EL element OLED1 becomes lower than the potential of the cathode, and the organic EL element OLED1 is reverse biased.

After that, when the nth scanning line 16 is made high and the n-1th scanning line 12 is made low (point B), the third transistor Tr3 is turned on again. At this time, the fourth transistor Tr4 is turned on and the fifth transistor Tr5 is turned off. In addition, the first transistor Tr1 is also turned on, and the data potential applied to the data line 20 is written in the gate electrode of the second transistor Tr2. Since the source electrode of the second transistor Tr2 is connected to the power supply Vdd via the third transistor Tr3, a current according to the data potential flows through the organic EL element OLED1 and the organic EL element OLED1 emits light.

At subsequent timings, as in the first embodiment, the organic E is used until the next cycle.
The L element OLED1 continues to emit light with a brightness according to the data potential.

In the present embodiment, since it is not necessary to use the inversion signal of the scanning signal propagated to the (n-1) th scanning line 12 and the nth scanning line 16, only the existing signal line is used and the first signal line is used. It is possible to obtain the same advantages as those of the embodiment. This keeps the circuit configuration simpler,
It is possible to mitigate the decrease in brightness of the organic EL element OLED1 and prevent variations in brightness in the display device.

(Third Embodiment) FIG. 5 shows a configuration of a pixel circuit for two pixels of a display device according to a third embodiment of the present invention. The pixel circuit 40 according to the present embodiment is
This is different from the second embodiment in that the source electrode of the fourth transistor Tr4 is connected to the power supply and the source electrode of the fifth transistor Tr5 is grounded. In the present embodiment, the same components as those in the second embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

In the present embodiment, the (n-1) th scan line 1
The scanning timings of the 2nd and nth scanning lines 16 are the same as those shown in FIG. When the (n-1) th scan line 12 is low (before the point A), the fourth transistor Tr4 is turned on and the fifth transistor Tr5 is turned off. At this time, the potential of the other electrode of the second capacitor C2 is the power source potential. Next, when the (n-1) th scan line 12 becomes high (A
Point), the fourth transistor Tr4 is turned off and the fifth transistor Tr5 is turned on. At this time, the potential of the other electrode of the second capacitor C2 becomes the ground potential. Therefore, the potential of the second of the other electrode of the capacitor C2 is pulled by the difference delta _Vdd of the power supply potential and the ground potential. Accordingly, the potential of one electrode of the second capacitor C2 also pulled by delta _Vdd. As a result, the potential of the anode of the organic EL element OLED1 becomes lower than the potential of the cathode,
Reverse bias is applied to the L element OLED1. The subsequent timings are the same as in the second embodiment.

In this embodiment, similarly to the second embodiment, the organic EL element OLED1 can be reverse-biased by using only the existing signal line. Also,
By switching the signal to the (n-1) th scan line 12, the potential of the second capacitor C2 is lowered by delta _Vdd, organic E
It is possible to reliably apply the reverse bias to the L element OLED1. As a result, it is possible to mitigate the decrease in brightness of the organic EL element OLED1, and it is also possible to prevent brightness variations in the display device.

(Fourth Embodiment) FIG. 6 shows the configuration of a pixel circuit for one pixel of a display device according to a fourth embodiment of the present invention. The pixel circuit 50 according to the present embodiment is
In the first embodiment, the second transistor Tr2 is an n-channel type, and one electrode of the second capacitor C2 is connected between the second transistor Tr2 and the third transistor Tr3. Different from Also, the second capacitance C2
The other electrode of is connected to the nth inversion scanning line 18. The gate electrode of the third transistor Tr3 is the nth scanning line 16
Connected to. The other electrode of the first capacitor C1 is kept at a predetermined potential V, but may be grounded as in the first embodiment. In the present embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

FIG. 7 is a diagram showing the timing of signals in the nth scanning line 16 and the nth inversion scanning line 18. The operation of the circuit in the nth pixel P _n will be described with reference to FIGS. 6 and 7. First, the nth scan line 16 is low,
When the inversion scanning line 18 is high (timing before the point B), the third transistor Tr3 is in the on state. At this time, the drain electrode of the second transistor Tr2 is connected to the power supply Vdd. At this time, the potential of the other electrode of the second capacitor C2 becomes high potential.

Subsequently, when the nth scanning line 16 is set to high and the nth inversion scanning line 18 is set to low (point B), the third transistor Tr3 is turned off, and the second transistor Tr2 and the power supply Vdd are separated from each other. Be cut off. At this time, the second capacitance C
The potential of the other electrode of 2 becomes a low potential, and the potential of the other electrode of the second capacitor C2 is lowered by the difference _Δhl between high and low. Along with this, the potential of one electrode of the second capacitor C2 and the potential of the drain electrode of the second transistor Tr2 are also lowered by Δ _hl . As shown in FIG. 7, the potentials at the positions a and b in FIG. 6 are lowered at the timing of point B, and the potential gradually rises.

Where Δ _hl is the second transistor Tr
2 and the potential difference applied to the organic EL element OLED1 or more, the potential of the drain electrode of the second transistor Tr2 becomes lower than the potential of the cathode of the organic EL element OLED1. Therefore, the drain electrode and the source electrode of the second transistor Tr2 are replaced with each other, and the electric charge remaining in the anode of the organic EL element OLED1 escapes from the second capacitor C2 via the second transistor Tr2. As a result, a reverse bias is applied to the organic EL element OLED1.

Since the data potential is applied to the second transistor Tr2 via the first transistor Tr1 while the nth scanning line 16 is high, the data potential itself is set correctly. When the nth scan line 16 becomes low (C
Point), the third transistor Tr3 is turned on, and the organic E
A current according to the data potential flows through the L element OLED1,
The organic EL element OLED1 emits light. As shown in FIG. 7, the potentials at the positions a and b in FIG. 6 return to the original potential again at the timing of point C.

As described above, in the present embodiment, the organic EL element OLED1 is reverse-biased before setting the brightness data by using the scanning signal propagated to the nth scanning line 16 and its inverted signal. You can As a result, it is possible to mitigate the decrease in brightness of the organic EL element OLED1, and it is also possible to prevent brightness variations in the display device.

(Fifth Embodiment) FIG. 8 shows the configuration of a pixel circuit for one pixel of a display device according to a fifth embodiment of the present invention. The pixel circuit 60 according to the present embodiment is
The third transistor Tr3 is an n-channel type, and the gate electrode of the third transistor Tr3 and the second capacitor C
This is different from the fourth embodiment in that the other electrode of No. 2 is connected to the control signal line 62. In the present embodiment, the same components as those in the fourth embodiment are designated by the same reference numerals,
Description is omitted as appropriate.

FIG. 9 is a diagram showing the timing of signals on the nth scan line 16 and the control signal line 62. The operation of the circuit in the nth pixel P _n will be described with reference to FIGS. 8 and 9. First, when the n-th scanning line 16 is set low and the control signal line 62 is set high (timing before point A), the third transistor Tr3 is turned on. At this time, the drain electrode of the second transistor Tr2 is connected to the power supply Vdd. At this time, the potential of the other electrode of the second capacitor C2 becomes high potential.

Then, when the control signal line 62 is set low (point A), the third transistor Tr3 is turned off, and the second transistor Tr2 and the power supply Vdd are cut off. At this time, the potential of the other electrode of the second capacitor C2 becomes a low potential, and the potential of the other electrode of the second capacitor C2 is lowered by the difference _Δhl between high and low. Along with this, the potential of one electrode of the second capacitor C2 and the potential of the drain electrode of the second transistor Tr2 are also lowered by Δ _hl . As shown in FIG. 9, the potentials at the positions c and d in FIG. 8 are lowered at the timing of point B,
The potential gradually rises.

Here, as in the fourth embodiment, Δ
_hl is the second transistor Tr2 and the organic EL element O
By setting the potential difference applied to the LED1 or more, the organic EL element OLED1 can be reverse-biased.

Next, when the nth scanning line 16 is set to high and the control signal line 62 is set to high (point B), the first transistor Tr1 and the third transistor Tr3 are turned on, and the second transistor Tr2 is turned on. A data potential is written in the gate electrode, a current corresponding to the data potential flows through the organic EL element OLED1, and the organic EL element OLED1 emits light. As shown in FIG. 9, the potentials at the positions c and d in FIG. 8 return to their original potentials at the timing of point B. After that, the nth scan line 16 is set to low (C
Point), the current corresponding to the data potential continues to flow in the organic EL element OLED1, and the organic EL element OLED1 emits light.

In the present embodiment, the control signal line 62 may be supplied with the inverted signal of the scanning line in the ( _{n−1) th} pixel P _n−1 pixel in the previous stage. Also, the first capacitance C1
The other electrode of may be connected to the anode of the organic EL element OLED1.

In this embodiment, since the organic EL element OLED1 is reverse-biased prior to the timing of setting the luminance data, the luminance data can be set in a state where the potential on the anode side of the organic EL element OLED1 is stable. it can. Therefore, the other end of the first capacitor C1 is connected to the organic EL.
Even if it is connected to the anode of the element OLED1, the luminance data is held stably.

(Sixth Embodiment) FIG. 10 shows the structure of a pixel circuit for two pixels of a display device according to a sixth embodiment of the present invention. Pixel circuit 70 according to the present embodiment
Differs from the first embodiment in that the third transistor Tr3 is not provided. The drain electrode of the second transistor Tr2 is connected to the power supply line 22. In the present embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

In the present embodiment, the (n-1) th scan line 1
The scanning timings of 2, the (n-1) th inversion scanning line 14, the nth scanning line 16, and the nth inversion scanning line 18 are the same as those shown in FIG. As described in the first embodiment, at the timing of point A, the potential of the other electrode of the second capacitor C2 is lowered by the difference _Δhl between the high potential and the low potential. Along with this, the potential of one electrode of the second capacitor C2 is also lowered by Δ _hl . As a result, the potential of the anode of the organic EL element OLED1 becomes lower than the potential of the cathode, and the organic EL element OLED1 is reverse biased.

In another example, the other electrode of the second capacitor C2 is a signal that is controlled independently of the scanning line, such as the control signal line 62 described in the fifth embodiment. It may be connected to a wire. In this case, the signal line
At the timing of point A shown in FIG. 2, the organic EL element OLE
A signal is propagated that causes a potential difference in the second capacitor C2 that is sufficient to apply a reverse bias to D1.

In the present embodiment, the second capacitor C2
Power supply Vdd and organic EL element OLED1 when the potential of
Since there is no disconnection between the
Reverse bias can be applied to the L element OLED1.
As a result, it is possible to mitigate the decrease in brightness of the organic EL element OLED1, and it is also possible to prevent brightness variations in the display device.

The present invention has been described above based on the embodiments. It is understood by those skilled in the art that these embodiments are mere examples, and that various modifications can be made to the combinations of the respective constituent elements and the respective processing processes, and such modifications are also within the scope of the present invention. By the way. Hereinafter, such an example will be described.

For example, although the third transistor Tr3 is a p-channel type in the first embodiment, the third transistor Tr3 is an n-channel type and the gate electrode of the third transistor Tr3 is the n-1th. Reverse scan line 14
The same effect can be obtained by connecting to. Similarly, the n-channel type and the p-channel type may be reversed in the fourth and fifth embodiments. In that case, the third transistor Tr3 may be turned off at the timing of lowering the potential of the second capacitor C2.

Further, in the first embodiment, the second embodiment and the third embodiment, the second transistor Tr2 is of p-channel type, but it may be of n-channel type. .

As in the case of the sixth embodiment, the pixel circuits of the second to fifth embodiments may not have the third transistor Tr3 for shutting off.

Two or more switching transistors for setting data in the driving transistor may be arranged in series. At that time, the characteristics of these transistors such as the current amplification factor may be different. For example, if the current amplification factor of the transistor close to the driving transistor is set to be low, the effect of reducing the leakage current is great.

Further, the characteristics of the switching transistor and the driving transistor may be changed. For example, if the current amplification factor of the driving transistor is reduced, the range of setting data corresponding to the same brightness range will expand,
The brightness can be easily controlled.

[0065]

According to the present invention, the deterioration of the optical element can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a pixel circuit for two pixels of a display device according to a first embodiment.

FIG. 2 is a diagram showing timings at which a signal on each signal line becomes high and low, respectively.

FIG. 3 is a diagram showing a configuration of a pixel circuit for two pixels of a display device according to a second embodiment.

FIG. 4 is a diagram showing timings at which a signal on each signal line becomes high and low, respectively.

FIG. 5 is a diagram showing a configuration of a pixel circuit for two pixels of a display device according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a pixel circuit for one pixel of a display device according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing timings at which a signal on each signal line becomes high and low, respectively.

FIG. 8 is a diagram showing a configuration of a pixel circuit for one pixel of a display device according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing timings at which a signal on each signal line becomes high and low, respectively.

FIG. 10 is a diagram showing a configuration of a pixel circuit for two pixels of a display device according to a sixth embodiment of the present invention.

FIG. 11 is a diagram showing a configuration of a pixel circuit for one pixel of a conventional display device.

[Explanation of symbols]

10 pixel circuits, 12 n-1 scan lines, 14 n-1 inverted scan lines, 16 n scan lines, 18 n scan lines
Inversion scan line, 20 data line, 22 power line, T
r1 first transistor, Tr2 second transistor, Tr3 third transistor, Tr4 fourth transistor, Tr5 fifth transistor, C1
1st capacity, C2 2nd capacity, OLED1 1st organic EL element, Vdd power supply

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 670 G09G 3/20 670K H05B 33/14 H05B 33/14 A (72) Inventor Eiji Taguchi Osaka Moriguchi City 2-5-5 Keihan Hondori Sanyo Electric Co., Ltd. (72) Inventor Yukihiro Noguchi Osaka Prefecture Moriguchi City 2-5-5 Keihan Hondori Sanyo Electric Co., Ltd. (72) Koichi Yamada Osaka Prefecture 2-5-5 Keihan Hondori, Moriguchi Sanyo Electric Co., Ltd. (72) Inventor Yoshiyuki Ishizuka 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. F-term (reference) 3K007 AB02 AB11 AB17 BB07 DB03 GA02 GA04 5C080 AA06 BB05 DD05 DD22 DD29 EE19 EE29 FF11 HH09 JJ03 JJ04 5C094 AA03 AA07 AA13 AA31 AA53 AA54 BA03 BA27 CA19 CA25 DB01 DB04 EA04 EA07 FB01 FB20 GA10

Claims (6)

[Claims] 1. A potential variation circuit provided between a current-driven optical element and a power source for lowering the potential at one end of the optical element closer to the power source, wherein the potential variation circuit is the optical element. By lowering the potential of the one end, a bias reverse to that at the time of light emission is applied to the optical element. 2. A potential cutoff circuit provided between a current-driven optical element and a power supply; and a potential fluctuation circuit that lowers the potential at one end of the optical element closer to the power supply, the potential The fluctuation circuit pulls down the potential of the one end of the optical element while the optical element and the power supply are cut off by the cutoff circuit, and applies a reverse bias to the light emitting element to the optical element. A display device characterized by being provided. 3. A cut-off transistor provided between a current-driven optical element and a power supply; and a potential fluctuation circuit that lowers the potential at one end of the optical element closer to the power supply, A signal for turning off the shutoff transistor to shut off between the optical element and the power source and a signal for lowering the potential are input at the same timing, and the signal opposite to that at the time of light emission is input to the optical element. A display device characterized by being biased. 4. The display device according to claim 1, wherein the potential change circuit has a capacitance, and the potential at the one end is lowered via the capacitance. 5. The disconnection between the optical element and the power source and the reduction of the potential are performed at a timing different from the timing of setting the luminance data to the optical element. The display device according to claim 1. 6. The potential change circuit is provided in parallel,
2. The device according to claim 1, further comprising two transistors that are turned on and off in a complementary manner, and the potential connected to the low potential source is changed from off to on to lower the potential. 5. The display device according to any one of 5.