JP2003043993A - Active matrix type display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a desired driving current to the light emitting element of each pixel constantly and correctly by eliminating dispersions in threshold voltages of active elements of insides of pixels and dispersions in driving currents due to an early effect of them. SOLUTION: A path over which a driving current which is to be generated from a voltage controlled current source to be controlled by a control voltage is made to flow is made changeable to a path which makes the driving current flow through a light emitting element and a path which makes the current flow through a data-side driving circuit and when respective pixels are scanned and selected and the driving current is made to flow through the data-side driving circuit, the control voltage is controlled by using the voltage comparator in the inside of the data-side driving circuit so that the driving current and the reference current of a luminance signal become equal based on the driving current and the control voltage at that time is held in a storage circuit and when the respective pixels are not scanned and selected, the driving current is supplied to the light emitting element based on the held control voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display provided with a light emitting element such as an organic electroluminescence (EL) whose luminance is controlled by a current in each pixel, and more specifically, to a display provided inside each pixel. The present invention relates to an active matrix type organic EL display that supplies a current to a light emitting element by an active element such as an insulated gate field effect transistor.

[0002]

2. Description of the Related Art In recent years, a display using an organic EL element has been developed, and its driving method includes a simple matrix method and an active matrix method. The former has a simple structure, but since it is difficult to realize a large-sized and high-definition display, active matrix methods have been actively developed.

When a large number of organic EL elements are used for driving by an active matrix circuit, each pixel has an insulated gate field effect transistor for controlling the supply of a driving current for driving the light emitting element, so-called thin film transistor (TFT).
Is connected, and by controlling this TFT, organic E
The light emitting operation of the L element is controlled.

(Conventional Example 1) FIG. 5 is a diagram of Japanese Patent Application Laid-Open No. 8-2346.
The equivalent circuit for one pixel shown in Japanese Patent No. 83 is shown.

The pixel circuit provided in the pixel is an organic EL element O
It is composed of an LED, a thin film transistor TFT1, a thin film transistor TFT2, and a capacitor C. Since an organic EL element generally has a rectifying characteristic, it may be called an organic light emitting diode (OLED).
The symbol of the diode is used. However, the light emitting element is not necessarily limited to the OLED, and may be any light emitting element whose brightness is controlled by the current flowing through the element, and the rectifying characteristic is not necessarily required. Figure 5
Then, the source of the p-type transistor TFT2 is connected to the power supply potential V
At dd, the drain is connected to the anode of the organic EL element OLED, and the cathode of the organic EL element OLED is connected to the ground potential. On the other hand, the gate of the p-type transistor TFT1 is the scanning line Scan and the source is the data line Data.
In addition, the drain is connected to the capacitor C and the gate of the TFT 2, and the other end of the capacitor is connected to the power supply potential Vdd.

In order to operate the pixel, first, the scanning line Sc
The TFT1 is turned on by an and the data line Data
When the data potential Vw representing the luminance information is applied to the capacitor C, the capacitor C is charged or discharged, and the gate potential of the TFT 2 matches the data potential Vw. T by scanning line Scan
When the FT1 is turned off, the gate potential of the TFT2 is held by the capacitor C, and the driving current corresponding to the gate-source voltage Vgs of the TFT2 is applied to the organic EL element OLE.
It is supplied to D and continues to emit light with a brightness according to the amount of current.

(Prior art example 2) FIG.
An equivalent circuit for one pixel shown in Japanese Patent No. 667 is shown.

The pixel circuit included in the pixel is an organic EL element O
An LED and a transistor TFT1 for converting a signal current into a voltage or supplying a current to the organic EL element OLED;
Transistor TFT2 that controls the operating state of transistor TFT1, and the state that takes in signal current or organic EL
It is composed of a transistor TFT3 and a transistor TFT4 which select a state in which a drive current is supplied to the element OLED, and a capacitor C which holds a voltage.

In FIG. 6, the source of the TFT1 is the power supply potential V
The gate is connected to the source of the TFT 2 and the capacitor C. The other end of the capacitor C is connected to the power supply potential Vdd. The drain of TFT1 is TFT
It is connected to the drain of the TFT 2, the drain of the TFT 3, and the drain of the TFT 4. The source of the TFT4 is connected to the anode of the organic EL element OLED,
The cathode of is connected to ground potential. The source of the TFT3 is connected to the data signal line Data, and the TFT2, T
The gates of FT3 and TFT4 are all connected to the scanning line Scan.

In order to operate the pixel, first, the scanning line Sc
TFT2 and TFT3 are turned on by an and TFT4
When is turned off, the signal current Iw is taken into the TFT1, a gate-source voltage Vgs necessary for flowing the signal current Iw is generated in the TFT1, and the voltage Vgs is held in the capacitor C. TFT by scanning line Scan
2. When the TFT3 is turned off and the TFT4 is turned on, the TFT1 continues to flow a drive current to the organic EL element OLED based on the voltage held in the capacitor C, and the organic EL element OLED has a brightness corresponding to the current amount. Keeps emitting light.

(Prior art example 3) FIG.
An equivalent circuit for one pixel shown in Japanese Patent No. 7659 is shown.

A pixel circuit included in a pixel connects or disconnects a pixel circuit and a data line by a conversion transistor TFT1 for converting a signal current into a voltage, a transistor TFT2 for controlling a drive current flowing in a light emitting element, and a scanning line ScanA. Transistor TFT3 for scanning, scanning line S
A switching transistor T that short-circuits the gate and drain of the TFT1 during writing of luminance information by canB.
It is composed of an FT4, a capacitor C that holds the gate-source voltage of the TFT1 even after writing the brightness information, and an organic EL element OLED.

In FIG. 7, the sources of TFT1 and TFT2 are connected to the power supply potential Vdd, and the gate of TFT1 is TFT.
2 is connected to the gate, the capacitor C, and the drain of the TFT 4. The other end of the capacitor C is connected to the power supply potential Vdd. The drain of the TFT2 is an organic EL element OL
It is connected to the anode of the ED and the cathode of the organic EL element OLED is connected to the ground potential. The drain of TFT1 is connected to the source of TFT4 and the drain of TFT3. The source of the TFT 3 is connected to the data signal line Data. The gates of the TFT3 are scan lines ScanA and TF.
The gate of T4 is connected to the scan line ScanB.

In order to operate the pixel, first, the scanning line Sc
When the TFT3 and the TFT4 are turned on by anA and ScanB, the TFT1 and the TFT2 have a current mirror structure, the signal current Iw is taken into the TFT1, and the TFT2 causes a current to flow to the organic EL element OLED according to the current mirror ratio. The voltage generated at the gate of the TFT1 is held in the capacitor C. Scan line ScanA,
When the TFT 3 and the TFT 4 are turned off by ScanB, the current mirror structure of the TFT 1 and the TFT 2 is released, and the TFT 2 according to the voltage held in the capacitor C.
Keeps flowing a current through the organic EL element OLED, and the light emitting element keeps emitting light with a brightness corresponding to the amount of the current.

[0015]

In the active matrix type display, the thin film transistor which is an active element is generally formed on one glass substrate at the same time by using amorphous silicon or polysilicon. However, it is known that the TFT formed using amorphous silicon or polysilicon has poor crystallinity and poor controllability of the conduction mechanism as compared with single crystal silicon, and thus its characteristics vary widely.

Therefore, even in a TFT formed on the same substrate, the threshold voltage Vth thereof is several hundred meters depending on each pixel.
It is not uncommon for V, in some cases, to vary by 1 V or more. In this case, for example, even if the same signal potential Vw is written to different pixels, since Vth varies depending on the pixel, the current flowing through the light emitting element is different, and desired luminance cannot be obtained, and high image quality cannot be expected as a display.

In the case of the configuration of the conventional example 1 (Japanese Patent Laid-Open No. 8-234683), this influence is directly exerted. Further, although the conventional example 2 (Japanese Patent Laid-Open No. 2001-56667) solves the problem of the variation in the threshold voltage, the source / drain voltage Vds of the TFT 1 and the organic EL element OLED when converting the signal current into a voltage are used. T when supplying drive current
Since the source-drain voltage Vds of the FT1 is different, an accurate drive current based on the data signal cannot flow through the light emitting element due to the Early effect of the transistor. Further, in the conventional example 3 (Japanese Patent Laid-Open No. 2001-147659), the problem regarding the variation in the threshold voltage is solved by the TFT1 and the TFT2.
Although the error level of the current mirror configured by is reduced, it does not fundamentally solve the dispersion problem. Further, the source-drain voltage Vds1 of the TFT1 and the TF
Since the source / drain voltage Vds2 of T2 is different,
As in the second conventional example, an accurate drive current cannot flow through the light emitting element due to the Early effect of the transistor.

An object of the present invention is to solve the problem of dispersion of the drive current supplied to the light emitting element due to the dispersion of the threshold voltage, which has existed in the above-mentioned prior art, and to provide an active matrix type display having higher performance than the conventional one. To do.

[0019]

According to the present invention for solving the above-mentioned problems, a plurality of pixels each having a pixel circuit including at least a light emitting element are arranged in a matrix, and a scanning side for controlling the pixel circuit. An active matrix type display having at least a drive circuit and a data side drive circuit, wherein the light emitting element is a current control type light emitting element whose brightness changes according to a current flowing in the light emitting element, and the pixel circuit is A light emitting element, a voltage controlled current source, a first switch circuit, and a second switch circuit, wherein the voltage controlled current source stores an active element controlled by a control voltage and the control voltage. A memory circuit capable of generating a drive current based on the control voltage, and the first switch circuit includes:
The second switch circuit has a function of switching the voltage controlled current source between a voltage controllable state and a control voltage holding state, and the second switch circuit causes a path through which the drive current flows to the light emitting element and a data side drive. The scanning-side drive circuit is connected to at least the first switch circuit and the second switch circuit, and has a function of switching to a circuit flow path. It has a function of performing control for holding a control voltage, and control for setting a path through which the drive current flows into the path through which the light emitting element flows or a path through which the data side drive circuit flows. , Connected to the voltage controlled current source via the first switch circuit and connected to the second switch circuit, and the voltage controlled current source is in a voltage controllable state When the path through which the drive current flows is a path through which the data-side drive circuit flows, the drive current is controlled by controlling the control voltage of the voltage-controlled current source, and the voltage control is further performed based on the drive current. It is characterized by having a function of controlling the control voltage of the current source to bring the drive current closer to a current value corresponding to desired luminance information.

According to the present invention, in the above-mentioned invention, "the data side driving circuit includes a reference current source having luminance information,
A voltage comparator that outputs a voltage for setting the control voltage by inputting the voltage at the output end of the reference current source and the reference voltage, and the output end of the reference current source is also connected to the second switch circuit; When the voltage control current source is in the voltage controllable state and the path through which the drive current flows is the path through which the data side drive circuit flows, the drive current is input to the output terminal of the reference current source having the brightness information. , Having a function of controlling the control voltage of the voltage controlled current source by the voltage comparator so that the current value of the drive current becomes equal to the output current value of the reference current source having the brightness information.
"Setting the reference voltage input to the voltage comparator near the voltage between the terminals during operation of the light emitting element", "the data side drive circuit further includes a precharge circuit, and the precharge circuit includes: Is connected to at least the input side of the two inputs of the voltage comparator to which the output end of the reference current source is connected, and the output end of the reference current source is connected to the voltage comparator. Has a function of precharging the voltage to a predetermined preparatory voltage. "" The data side drive circuit is capable of performing the precharge operation when the voltage controlled current source is in the control voltage holding state. "There is", "the data side drive circuit is capable of performing control to perform the precharge operation immediately before the voltage controlled current source is in the voltage controllable state", "the predetermined preparation voltage is Be the same voltage value as the reference voltage "," the storage circuit is a capacitor,
The active element, the first switch circuit, and the second switch circuit are composed of insulated gate field effect transistors, and the second switch circuit is a differential switch ”,“ the pixel circuit Further includes a reset circuit, and the reset circuit is connected to at least the light emitting element and has a function of resetting a voltage between terminals of the light emitting element to a predetermined value or less. It is connected to the scanning side drive circuit by a wiring common to the first switch circuit, and the reset operation is possible at the same time when the voltage controlled current source is in a voltage controllable state. "," The storage circuit is a capacitor And the active element, the first switch circuit, the second switch circuit, and the reset circuit are insulated gate field effect transistors. Consists of a register, the second
The switch circuit is a differential switch "," the voltage-controlled current source includes a first transistor and a capacitor, and the gate of the first transistor is connected to one end of the capacitor and the first switch circuit. " The source of the first transistor and the other end of the capacitor are connected to the power supply potential, the drain of the first transistor serves as an output, and the drain is connected to the second switch circuit. And the first switch circuit is
A second transistor, the drain of the second transistor is connected to the voltage controlled current source, the source of the second transistor is connected to the data side drive circuit, and the gate of the second transistor is connected to the gate of the second transistor. The scanning side drive circuit is connected, and the second switch circuit is composed of third and fourth transistors.
The sources of the transistors are connected together to the voltage controlled current source to form a differential switch circuit, the drain of the third transistor is connected to the data side drive circuit, and the drain of the fourth transistor is The reset circuit is connected to the light emitting element and the reset circuit, and the reset circuit is composed of a fifth transistor, and the drain of the fifth transistor is connected to the second switch circuit and the light emitting element. The source of the transistor No. 5 is connected to the reset potential, and the gate of the fifth transistor is connected to the scanning side drive circuit by a wiring common to the first switch circuit. "," The insulated gate The field-effect transistor is a thin film transistor ”.

Here, the voltage controlled current source means a means for regulating the current to flow based on the voltage, and the voltage comparator means
The means for not only comparing the voltages but outputting the voltages based on the comparison is shown.

The voltage controllable state means a state in which control can be performed by changing the control voltage, and the control voltage holding state means that the control voltage recorded in the memory circuit is not changed from the outside. It shows the state of holding.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention in which an organic electroluminescence element (organic EL element) is used as a light emitting element will be described below, but the present invention is not limited to these and the light emitting element is not limited thereto. The present invention is effective in an active matrix type display using a current control type light emitting element whose brightness is controlled by a driving current flowing in the matrix.

(Embodiment 1) FIG. 1 is a configuration diagram showing a first embodiment of an active matrix type display of the present invention. In FIG. 1, the pixel circuit shows only one pixel.

First, the structure will be described.

The pixel circuit inside the pixel is an organic EL element OL.
ED, 1 p-type thin film transistor corresponding to an active element that constitutes a voltage control current source that generates a drive current based on a control voltage, 1 capacitor corresponding to a memory circuit, and voltage control current source can be voltage controlled One n-type transistor corresponding to the first switch circuit having a function of switching between the state and the control voltage holding state, and the path through which the drive current flows are switched between the path through the light emitting element and the path through the data side drive circuit. Two p-type transistors corresponding to the second switch circuit having a function, and an n-type transistor 1 corresponding to the reset circuit connected to the light emitting element and having a function of resetting the terminal voltage of the light emitting element to a predetermined value or less. It consists of individual pieces. In this embodiment, the second switch circuit is a differential switch.

The configuration will be described in more detail.

The gate of the first transistor T1 is connected to the drains of the capacitor C and the second transistor T2 (the electrode of T2 (the electrode serving as the drain here) when charging and discharging the capacitor C is also the source). However, for simplification of description, in the present specification, regarding T2, the side of the two electrodes serving as the source or the drain of the thin film transistor, which is connected to the capacitor C, is referred to as the drain). The drain of T1 is connected to the source of the third transistor T3 and the source of the fourth transistor T4. The scanning lines are connected to the gates of T3 and T4, the control signal SA is input to the gate of T3, and the control signal SB is input to the gate of T4. The control signals SA and SB are differential signals. The drain of T4 is connected to the drain of the fifth transistor T5 and the anode of the OLED. The source of T5 is connected to the reset potential Vcom. The gates of T2 and T5 are connected to a common scanning line,
The control signal SC is input to the gates of T2 and T5. T
The source of 1 and the other end of the capacitor C have a power supply potential Vdd
In addition, the cathode of the OLED is connected to ground potential.

The control signals SA, SB and SC are controlled by a scanning side drive circuit (not shown in FIG. 1) provided outside the pixel area.

The source of T2 is connected to the output of the voltage comparator AMP1 inside the data side drive circuit installed outside the pixel region, and the drain of T3 is the reference current source Id having the brightness information inside the data side drive circuit. Of the AMP1 and the positive terminal of the AMP1. AMP
The reference voltage Vr is input to the negative electrode terminal of 1.

The reset potential Vcom is a potential for resetting the terminal voltage of the OLED, and is a ground potential or OL.
It is desirable to set the light emission threshold voltage of the ED or less. From the viewpoint of power consumption, a voltage slightly lower than the light emitting threshold voltage of the OLED is desirable. Further, for ease of manufacturing, it is preferable to connect the reset potential commonly to all pixels.

When the drive current setting control is performed with T3 in the ON state and T4 in the OFF state, the drain voltage of T1 becomes the reference voltage Vr in the control stable state, and
When T3 is in the OFF state and T4 is in the ON state and the current generated in T1 is supplied to the OLED to perform the light emitting operation,
The drain voltage of T1 becomes the voltage Von between the terminals generated when the OLED operates (lights up). Therefore, in order to eliminate the influence of the Early effect due to the change in the drain-source voltage of the T1 transistor due to the circuit operating state, the reference voltage Vr in the data side driving circuit is set to the OLED operating voltage Von.
It is desirable to make it near.

Next, the operation will be described.

First, the gate voltage of T1, which generates the drive current to be supplied to the OLED, that is, the control voltage, is set in order to cause the pixel to emit light with a desired brightness. In order to perform this operation, first, the differential switch constituted by T3 and T4 is turned on by T3 and turned off by T4 by the control signals SA and SB, and a driving current flowing path is passed to the data side driving circuit. Use as a route. Next, T2 is turned on by the control signal SC, and the voltage controlled current source is set to the voltage controllable state. At this time, the drive current output from T1 (input as Im to the data side drive circuit) and the reference current source Id in the data side drive circuit form the voltage comparator A in the data side drive circuit.
Capacitance (not shown in the figure) parasitic on the positive terminal of MP1 is charged or discharged, and the gate voltage of T1 is controlled so that the positive terminal voltage of AMP1 becomes equal to the reference voltage Vr. It approaches the current value corresponding to the desired brightness information. Then, when the drive current generated by T1 and the current generated by the reference current source Id having the luminance information are equal to each other, this control becomes stable. The controlled gate voltage of T1 is held in the capacitor C connected to it. At the same time, T5 is in the ON state at the same time, so that it is short-circuited to the reset potential Vcom and the inter-terminal voltage of the OLED is reset to a predetermined value or less. This is organic E
This is an effective means for extending the life of the L element.

Next, when the gate voltage is set, T2 and T5 are turned off by the control signal SC to bring the voltage controlled current source to the control voltage holding state, and the reset operation of the reset circuit is stopped. Next, the differential switch composed of T3 and T4 is controlled by the control signals SA and SB, and T3 is turned off.
In the F state, T4 is turned on, and the path through which the drive current flows is the path through which the OLED flows. In this state, control from the data side driving circuit outside the pixel is not performed, and the gate-source voltage Vgs of T1 is given by the control voltage held in the capacitor C inside the pixel, and the driving corresponding to this voltage is performed. Current is supplied to the OLED.

In the present embodiment, the current generated inside the pixel is connected to the data side drive circuit outside the pixel to control and determine the desired current value. Therefore, the threshold of the transistor that determines the drive current of each pixel is determined. There is no problem even if the value current varies, and T3 and T4 are differential switches.
The drive current setting control and the drive current supply operation are switched by appropriately providing the voltage levels of the differential signals of SA and SB, so that the drain-source voltage of T1 that determines the drive current does not change and the transistor early The current fluctuation due to the effect is prevented, and high-definition image display is possible.

It is preferable to use a widely used insulated gate field effect transistor as the transistor, and it is more preferable to use the thin film transistor from the viewpoint of downsizing of the active matrix display.

(Second Embodiment) FIG. 4 is a constitutional view showing a second embodiment of the active matrix display of the present invention. In FIG. 4, the pixel circuit shows only one pixel.

First, the structure will be described. Since the configuration of the pixel circuit is the same as that of the first embodiment, the description will be omitted.

In the configuration of the first embodiment or the like, when there is a large parasitic capacitance in the wiring through which the drive current generated by the voltage control current source is present during the drive current setting control, the drive current setting control becomes unstable. There is a possibility of falling. In the present embodiment, in order to prevent control instability due to a delayed response of control, the positive terminal voltage of the voltage comparator in the data side drive circuit is set to a predetermined value when the voltage controlled current source is in the control voltage holding state. A precharge circuit for precharging to the preparation voltage is added in the data side drive circuit. Preferably, the precharge operation is performed immediately before the voltage controlled current source enters the voltage controllable state, and more preferably, the predetermined preparation voltage and the reference voltage Vr input to the negative terminal of the voltage comparator. It is to make the same voltage value. Thereby, the operation time of the drive current setting control can be shortened. This is because the control convergence voltage of the drive current setting control (voltage when the control is stable) becomes the positive terminal voltage Vr of the AMP1.

First, the structure will be described.

The output of the voltage buffer AMP2 is connected to the positive terminal of the voltage comparator AMP1 via the switch circuit SW1. The same voltage Vr as the reference voltage input to the positive terminal of the voltage comparator AMP1 is input to the positive terminal of the voltage buffer APM2. Voltage buffer AMP2
The negative terminal of is short-circuited with the output of the voltage buffer AMP2. The switch SW1 is turned on by the control signal SD
/ OFF operation is controlled.

Next, the operation will be described.

When the inside of the pixel is brought into the drive current setting control preparation state by the control signals SA and SB, the switch SW1 is turned on by the control signal SD and the voltage comparator AMP1.
Is rapidly precharged to the voltage Vr. Then, the precharge operation is completed before the voltage control current source becomes the voltage controllable state, and thereafter the drive current control is performed. Since other operations are the same as those in the first embodiment, the description thereof will be omitted.

(Embodiment 3) This embodiment shows the overall structure of an active matrix type display including the structures shown in the above embodiments. In particular, here, description will be made assuming the case of having the configuration of the first embodiment, but the case of having the configuration of the second embodiment can be similarly performed.

FIG. 2 is a configuration diagram showing a third embodiment of the active matrix type display of the present invention, and FIG. 3 is a timing chart of control signals in the configuration of the present embodiment.

FIG. 2 shows a part of an active matrix type display having M × N pixels.
All the Vw terminals of the pixels lined up in the data line direction (pixels lined up in the vertical direction in FIG. 2) are connected, and similarly, all the Im terminals are also connected, and are connected to the data side drive circuit installed outside the pixel region. ing. Further, the SA terminals, SB terminals, and SC terminals of pixels arranged in the scanning line direction (pixels arranged in the horizontal direction in FIG. 2) are all connected to the scanning side drive circuit. Although not shown in the figure, since the scanning side driving circuit and the data side driving circuit need to operate in synchronization, timing information is exchanged.

The operation of this embodiment will be described.

When the scanning of the first line is started, first, the control signal SA is set to the Low level and the control signal SB is set to the High level, the selected pixels are in the drive current setting control preparation state, and the reference current in the data side drive circuit is set. The source sets the current value of the reference current source based on the image information, and the control signal SC becomes H
At the high level, the voltage-controlled current source of each pixel enters the voltage controllable state.

When the control signal SC goes low, the drive current setting control ends, and the voltage Vw is held as a control voltage in the capacitor which is the memory circuit of the voltage controlled current source. Then, when the control signal SA becomes High level and the control signal SB becomes Low level, the drive current determined based on the control voltage held in the capacitor is supplied to the light emitting element, and the light emitting element emits light until the next scanning time. At the same time, the scanning of the second line is started. Two
The operation of the first line is the same as that of the first line, so the description is omitted.

[0051]

As described above, when the present invention is used, the driving current can be stably and accurately obtained without being affected by the variation in the threshold voltage of the transistor constituting the driving current source installed in each pixel. It can be supplied to the light emitting device. In addition, since a drive current can be stably and accurately supplied to the light emitting element without being affected by the Early effect, high-definition image display is possible. Furthermore, since the voltage between the terminals of the light emitting element is reset by the reset potential inside the pixel, the life of the light emitting element can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an active matrix type display of the present invention.

FIG. 2 is a configuration diagram showing a third embodiment of an active matrix type display of the present invention.

FIG. 3 is a timing chart of control signals in the configuration of the third embodiment.

FIG. 4 is a configuration diagram showing a second embodiment of an active matrix type display of the present invention.

FIG. 5 is a configuration diagram showing an active matrix display of Conventional Example 1.

FIG. 6 is a configuration diagram showing an active matrix display of Conventional Example 2.

FIG. 7 is a configuration diagram showing an active matrix display of Conventional Example 3.

[Explanation of symbols]

OLED Organic EL element TFT1 to TFT4, T1 to T5 thin film transistor C capacitor R, R1, R2 resistance Iw, Id Reference current source Vr, Vd Reference voltage source AMP1 voltage comparator

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 641 G09G 3/20 641D H05B 33/14 H05B 33/14 AF term (reference) 3K007 AB02 AB11 AB17 BA06 CA01 CB01 DA01 DB03 EB00 GA04 5C080 AA06 BB05 DD03 DD29 EE28 FF11 JJ03 5C094 AA07 AA31 AA55 BA03 BA27 CA19 CA25 DA09 DA13 DB01 DB04 EA04 EA05 EA07 FB01 FB12 FB14 FB15 FB20 GA10

Claims (13)

[Claims] 1. An active matrix display in which a plurality of pixels each having a pixel circuit including at least a light-emitting element are arranged in a matrix and at least a scanning side driving circuit and a data side driving circuit for controlling the pixel circuit are provided. Wherein the light emitting element is a current control type light emitting element whose brightness changes according to a current flowing through the light emitting element, and the pixel circuit includes the light emitting element, a voltage controlled current source,
The voltage control current source includes at least a first switch circuit and a second switch circuit, and the voltage controlled current source includes at least an active element controlled by a control voltage and a memory circuit capable of storing the control voltage. The second switch circuit has a function of generating a drive current based on the second switch circuit, and the first switch circuit has a function of switching the voltage controlled current source between a voltage controllable state and a control voltage holding state. A function of switching the path through which the drive current flows into a path through which the light emitting element flows and a path through which the data side drive circuit flows, and the scanning side drive circuit includes at least the first switch circuit and the first switch circuit. 2 is connected to the switch circuit to control the voltage controlled current source to be in the voltage controllable state or the control voltage holding state, and to flow the drive current to the light emitting element. A path or a control for setting a path to flow to the data side drive circuit, the data side drive circuit is connected to the voltage controlled current source through at least the first switch circuit, and When the voltage control current source is connected to the second switch circuit, the voltage control current source is in the voltage controllable state, and the path through which the drive current flows is the path through which the data side drive circuit flows, the current value of the drive current is desired. An active matrix type display characterized in that the control voltage of the voltage controlled current source is controlled so that the current value corresponds to the brightness information. 2. The data side drive circuit receives a reference current source having luminance information, and a voltage comparator which outputs a voltage for setting the control voltage with the voltage at the output end of the reference current source and the reference voltage as inputs. An output end of the reference current source is also connected to the second switch circuit, the voltage control current source is in a voltage controllable state, and the path through which the drive current flows is a path through which the data side drive circuit flows. Sometimes, the drive current is input to the output terminal of the reference current source having the brightness information, and the voltage is adjusted so that the current value of the drive current becomes equal to the output current value of the reference current source having the brightness information. 2. The comparator has a function of controlling the control voltage of the voltage controlled current source.
Active matrix type display described in. 3. The active matrix type display according to claim 2, wherein the reference voltage input to the voltage comparator is set near a voltage between terminals when the light emitting element is operating. 4. The data side drive circuit further includes a precharge circuit, and the precharge circuit has at least one of the two inputs of the voltage comparator to which the output end of the reference current source is connected. It has the function to precharge the voltage of the point connected to the side and connecting the output terminal of the reference current source and the voltage comparator to a predetermined preparation voltage. Active matrix display. 5. The active matrix according to claim 4, wherein the data side driving circuit is capable of performing the precharge operation when the voltage controlled current source is in a control voltage holding state. Type display. 6. The active matrix according to claim 5, wherein the data side driving circuit is capable of performing the precharge operation immediately before the voltage controlled current source enters a voltage controllable state. Type display. 7. The active matrix type display according to claim 4, wherein the predetermined preparation voltage has the same voltage value as the reference voltage. 8. The storage circuit is composed of a capacitor, and the active element, the first switch circuit, and the second switch circuit are composed of insulated gate field effect transistors, and the second The active matrix type display according to any one of claims 1 to 7, wherein the switch circuit is a differential switch. 9. The pixel circuit further includes a reset circuit, the reset circuit being at least connected to the light emitting element and having a function of resetting a terminal voltage of the light emitting element to a predetermined value or less. 9. An active matrix display according to any one of claims 1-8. 10. The reset circuit is connected to the scanning side drive circuit by a wiring common to the first switch circuit, and the reset operation is possible at the same time when the voltage controlled current source is in a voltage controllable state. The active matrix type display according to claim 9, wherein: 11. The storage circuit is composed of a capacitor, and the active element, the first switch circuit, the second switch circuit, and the reset circuit are composed of insulated gate field effect transistors. The active matrix display according to claim 9, wherein the second switch circuit is a differential switch. 12. The active matrix type display according to claim 11, wherein the voltage-controlled current source comprises a first transistor and a capacitor, and a gate of the first transistor is connected to one end of the capacitor and the first transistor. Connected to the switch circuit of
The source of the first transistor and the other end of the capacitor are connected to a power supply potential, the drain of the first transistor serves as an output, and the drain is connected to the second switch circuit, The first switch circuit includes a second transistor, the drain of the second transistor is connected to the voltage controlled current source, the source of the second transistor is connected to the data side drive circuit, and The scanning-side drive circuit is connected to the gate of a second transistor, the second switch circuit includes third and fourth transistors, and the sources of the third and fourth transistors are both the above-mentioned. A differential switch circuit connected to a voltage controlled current source, wherein the drain of the third transistor is connected to the data side drive circuit, A drain of a fourth transistor is connected to the light emitting element and the reset circuit, the reset circuit includes a fifth transistor, and a drain of the fifth transistor has the second switch circuit and the light emitting element. The source of the fifth transistor is connected to the reset potential, and the gate of the fifth transistor is connected to the scanning side drive circuit through a wiring common to the first switch circuit. An active matrix type display characterized in that. 13. The active matrix type display according to claim 8, wherein the insulated gate field effect transistor is a thin film transistor.