JP2003140613A - Active matrix type display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix type display realizing a high quality display by solving the problem of variation of current supplied to light emitting elements caused by variation of threshold voltage of transistors and the problem of an influence by an early effect. SOLUTION: A light emitting element (OLED), a voltage control current source (T1) for supplying a driving current to the light emitting element (OLED), and a current-voltage conversion element (T2) for detecting the driving current are arranged, and the voltage control current source (T1) is controlled based on a current value of the driving current detected by the current-voltage conversion element (T2). Moreover, a high-speed response can be realized by arranging a reference voltage source (Vs) for resetting the voltage between the terminals of the light emitting element (OLED).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display in which each pixel is provided with a light emitting element such as an organic electroluminescence element (organic EL element) whose brightness is controlled by a current flowing through the element. ,
The present invention relates to an active matrix type 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 and driven by an active matrix circuit, an insulated gate field effect transistor, so-called thin film transistor (TFT), for controlling current supply to the light emitting element is connected to each pixel. The light emitting operation of the organic EL element is controlled by controlling the TFT.

(Prior art example 1) FIG.
An equivalent circuit for one pixel shown in Japanese Patent No. 683 is shown.

Pixels include a light emitting element OLED, a first thin film transistor TFT1, and a second thin film transistor TFT.
2 and a capacitor C. Since an organic EL element generally has a rectifying characteristic, it may be called an OLED (organic light emitting diode), and the symbol of diode is used in the drawing. 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.

In FIG. 15, the source of the p-type transistor TFT1 is at the power supply potential Vdd, and the drain is the light emitting element OLE.
It is connected to the anode of D and the cathode of the light emitting element OLED is connected to the GND potential. On the other hand, the gate of the p-type transistor TFT2 is connected to the scanning line Scan, the source is connected to the data line Data, the drain is connected to the capacitor C and the gate of the TFT1, and the other end of the capacitor is the power supply potential Vdd.
It is connected to the.

In order to operate the pixel, first, the scanning line Sc
The TFT2 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 1 matches the data potential Vw. T by scanning line Scan
When the FT2 is turned off, the gate potential of the TFT1 is held by the capacitor C, a current corresponding to the gate-source voltage Vgs of the TFT1 is supplied to the light emitting element OLED, and light emission is continued with a brightness according to the amount of the current.

(Prior art example 2) FIG.
An equivalent circuit for one pixel shown in Japanese Patent No. 6667 is shown.

The pixel includes a light emitting element OLED, a first transistor TFT1 for converting a signal current into a voltage or supplying a current to the light emitting element OLED, and a second transistor TFT2 for controlling the operating state of the first transistor. ,
It is composed of a third transistor TFT3 and a fourth transistor TFT4 for selecting a state of taking in a signal current or supplying a current to the light emitting element OLED, and a capacitor C for holding a voltage.

In FIG. 16, the source of the TFT1 is connected to the power supply potential Vdd, and the gate is connected to the source of the TFT2 and the capacitor C. The other end of the capacitor C is connected to the power supply potential Vdd. The drain of TFT1 is TF
It is connected to the drain of T2, the drain of TFT3, and the drain of TFT4. The source of the TFT4 is the light emitting element O
It is connected to the anode of the LED and the cathode of the light emitting element is G
It is connected to the ND potential. The source of the TFT3 is connected to the data signal line Data, and TFT2, TFT3, TF
The gates of T4 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
Is turned off, a signal current Iw is taken into the TFT1, and a gate-source voltage Vgs necessary for flowing the signal current Iw is generated in the gate of the TFT1. This voltage Vg
Hold s in capacitor C. When the scanning line Scan turns off the TFT2 and TFT3 and turns on the TFT4, the TFT1 continues to flow a current to the light emitting element based on the voltage held in the capacitor C, and the light emitting element has a brightness corresponding to the current amount. It keeps emitting light.

(Prior art example 3) FIG.
An equivalent circuit for one pixel shown in Japanese Patent No. 47659 is shown.

The pixel includes a first transistor TFT1 for controlling a drive current flowing through the light emitting element, a second transistor TFT2 for conversion for converting a signal current into a voltage, and a scanning line S.
a third transistor TFT3 for connection that connects or disconnects the pixel circuit and the data line with canA; a fourth transistor TFT4 for switching that short-circuits the gate and drain of the TFT2 during writing of luminance information by the scanning line ScanB; It is composed of a capacitor C which holds the gate-source voltage of the TFT 1 even after the writing of the luminance information and a light emitting element OLED.

In FIG. 17, the sources of TFT1 and TFT2 are connected to the power supply potential Vdd, and the gate of TFT1 is TF.
It is connected to the gate of T2, the capacitor C, and the drain of TFT4. The other end of the capacitor C is connected to the power supply potential Vdd. The drain of the TFT1 is a light emitting element OLE.
It is connected to the anode of D and the cathode of the light emitting element OLED is connected to the GND potential. The drain of TFT2 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 gate of the TFT3 has a scanning line ScanA and a TFT4.
The gate of 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 TFT2, and the TFT1 causes the current to flow to the light emitting element OLED according to the current mirror ratio. The voltage generated at the gate of the TFT 1 is held in the capacitor C. Scan line ScanA,
When the TFT3 and the TFT4 are turned off by the ScanB, the current mirror structure of the TFT1 and the TFT2 is released, and the TFT1 according to the voltage held by the capacitor C is released.
Keeps flowing the current to the light emitting element OLED, and the light emitting element continues to emit light with the brightness corresponding to the amount of the current.

[0016]

In the active matrix type display, the thin film transistor which is an active element is usually formed on one glass substrate at the same time by using amorphous silicon or polysilicon.

However, a 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 it is known that its characteristics vary widely. ing. Therefore, even in a TFT formed on the same substrate, it is not uncommon for the threshold voltage Vth thereof to vary by several hundred mV depending on the pixel, or 1 V or more in some cases. In this case, even if the same signal potential Vw is written to different pixels, for example, Vth varies depending on the pixel, and
If the current flowing through D is different, desired brightness cannot be obtained and high image quality cannot be expected as a display.

In the case of the structure of the conventional example 1 (Japanese Patent Laid-Open No. 8-234683), this problem is likely to be noticeable. Further, the conventional example 2 (Japanese Patent Laid-Open No. 2001-56667) is
Although the problem of threshold voltage variation is solved, the source / drain voltage Vds of the TFT 1 when converting the signal current into a voltage is different from the source / drain voltage Vds when supplying the current to the OLED. Due to the Early effect of the transistor, the signal current cannot be accurately passed through the light emitting element. In addition, the conventional example 3 (Japanese Patent Laid-Open No. 2001-147)
Japanese Patent No. 659) reduces the problem regarding the variation of the threshold voltage to the error level of the current mirror formed by the TFT1 and the TFT2, but does not fundamentally solve the variation problem. Further, the source-drain voltage Vds1 of the TFT1 and the source-drain voltage Vds of the TFT2
Since ds2 is different, the signal current cannot accurately flow to the light emitting element due to the Early effect of the transistor, as in the second conventional example. Furthermore, as a light emitting element, an organic EL
When an element is used, the operating voltage of the light emitting element increases due to the deterioration of the organic EL element over time, and the source / drain voltage of the TFT 1 cannot be sufficiently secured. The current largely deviated from is supplied to the light emitting element.

The present invention provides an active matrix type display which solves the problem of the variation of the current supplied to the light emitting element due to the variation of the threshold voltage Vth and the problem of the influence of the Early effect and realizes a high quality display. Especially.

[0020]

According to a first aspect of the 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 the pixel circuit is controlled. An active matrix type display having at least a scanning side driving circuit and a data side driving circuit, wherein the pixel circuit includes the light emitting element,
At least a first voltage control current source, a first switch circuit, a drive current voltage conversion element, a second voltage control current source, a second switch circuit, and a third switch circuit, The scan side drive circuit is connected to at least the first switch circuit, the second switch circuit, and the third switch circuit, and the first switch circuit, the second switch circuit, and the second switch circuit. 3 has a function of controlling each of the switch circuits into a conductive state or a non-conductive state,
The data side drive circuit, a control circuit, a reference voltage source,
And a selection switch circuit. (1-a) In the pixel circuit, (1) the light emitting element is a current control type light emitting element whose brightness changes according to a drive current flowing in the light emitting element, (2) The first voltage controlled current source includes at least an active element controlled by a control voltage and a storage circuit capable of storing the control voltage, and has a function of generating the drive current based on the control voltage. And a control terminal for inputting the control voltage of the active element is connected to the data side drive circuit via the first switch circuit, and (3) the drive current / voltage conversion element outputs the drive current. Connected in series to a flowing current path and having a function of converting the drive current into a voltage, (4) the second
Has a function of generating a monitor current correlated with the drive current based on the output voltage of the drive current / voltage conversion element, and the output terminal for outputting the monitor current has the second switch circuit. (5) The third switch circuit is connected between a reference voltage source provided in the data side drive circuit and the light emitting element, and (1-) b) In the data side drive circuit, (1) the control circuit sets the first drive circuit so that the drive current supplied to the light emitting element based on the monitor current has a current value necessary for obtaining a desired brightness. (2) the reference voltage source has a function of controlling a voltage controlled current source,
(3) The selection switch circuit has a function of outputting a reset potential for setting a voltage between terminals of the light emitting element to a predetermined voltage value, and (3) the selection switch circuit outputs one of the control circuit and the reference voltage source. Is output to the pixel circuit, both the first switch circuit and the second switch circuit are in a conductive state, and the third switch circuit is in a non-conductive state. A function of controlling the first voltage-controlled current source by the control circuit based on the monitor current when the output of the control circuit is selected by the switch circuit, and at least the first voltage control current source immediately before the control period. A device for controlling the inter-terminal voltage of the light emitting element to a predetermined voltage value when the switch circuit of No. 3 is conductive and the output of the reference voltage source is selected by the selection switch circuit. Characterized in that it has and.

According to the first aspect of the present invention, in the first voltage-controlled current source, the active element is an insulated gate field effect transistor, and the control terminal of the active element is an insulated gate field effect transistor. A gate terminal of a transistor, wherein the storage circuit comprises a capacitor, a first terminal of the insulated gate field effect transistor is connected to a first terminal of the light emitting element and the third switch circuit, and A second terminal is connected to a common potential for all pixels, a second terminal of the insulated gate field effect transistor is connected to the drive current / voltage conversion element, and a gate terminal of the insulated gate field effect transistor is the first of the capacitor. Connected to a terminal and the first switch circuit,
The second terminal of the capacitor is connected to a common potential for all pixels "," the other terminal of the third switch circuit connected to the first terminal of the insulated gate field effect transistor is the insulated gate Connected to the gate terminal of the field effect transistor ”is included as a preferable mode.

A second invention for solving the above problems is as follows.
An active matrix display in which a plurality of pixels each including 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. The pixel circuit includes at least the light emitting element, a first voltage control current source, a first switch circuit, a drive current / voltage conversion element, a second voltage control current source, and a second switch circuit. The scanning side drive circuit is connected to at least the first switch circuit and the second switch circuit, and includes the first switch circuit and the second switch circuit.
(2a), the data side drive circuit includes at least a control circuit having a sample hold circuit and an input / output changeover switch. In the pixel circuit, (1) the light emitting element is a current control type light emitting element whose brightness changes according to a drive current flowing in the light emitting element, and (2) the first voltage control current source is a control circuit. For inputting the control voltage of the active element, including at least an active element controlled by a voltage and a memory circuit capable of storing the control voltage, having a function of generating the drive current based on the control voltage The control terminal is connected to the data side drive circuit via the first switch circuit, and (3)
The drive current-voltage conversion element is connected in series with a current path through which the drive current flows, and has a function of converting the drive current into a voltage. (4) The second voltage-controlled current source, It has a function of generating a monitor current correlated with the drive current based on the output voltage of the drive current / voltage conversion element, and an output terminal for outputting the monitor current has the data side drive circuit via the second switch circuit. Connected to the
(5) The terminals of the first switch circuit and the second switch circuit on the side connected to the data side drive circuit are short-circuited, (2-b) in the data side drive circuit,
(1) The control circuit including the sample hold circuit is
A signal having a correlation with the monitor current is sampled and held, and based on the held signal, the drive current supplied to the light emitting element has a current value necessary for obtaining a desired brightness. (2) The input / output change-over switch is connected between the control circuit and the pixel circuit, and has a function of controlling a voltage-controlled current source, and includes the first switch circuit and the second switch circuit. It has a function of performing a synchronous operation to switch between an input state in which a monitor current is input from the pixel circuit and an output state in which a control voltage is output to the pixel circuit, and the first switch circuit is in a non-conductive state and When the second switch circuit is in the conductive state, the input / output changeover switch is set to the input state, the monitor current is input, and a signal having a correlation with the monitor current is sampled and held. And the second switch circuit is in the non-conductive state, the input / output changeover switch is in the output state, and the sample / hold circuit is in the hold state. It has a function of controlling the first voltage-controlled current source based on the signal held by the hold circuit.

In the present invention according to the second aspect, "sampling in the sample-hold circuit and control of the first voltage-controlled current source based on a signal held in the sample-hold circuit are time-divided. Alternating with control "," in the first voltage controlled current source,
The active element is an insulated gate field effect transistor, the control terminal of the active element is a gate terminal of the insulated gate field effect transistor, the memory circuit is composed of a capacitor, One terminal is connected to the first terminal of the light emitting element, the second terminal of the light emitting element is connected to a common potential for all pixels, and the second terminal of the insulated gate field effect transistor is connected to the drive current / voltage conversion element. And a gate terminal of the insulated gate field effect transistor is a first gate of the capacitor.
A terminal and the first switch circuit, and the second terminal of the capacitor is connected to the common potential of all pixels ”.

A third invention for solving the above problems is as follows.
An active matrix display in which a plurality of pixels each including 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. The pixel circuit includes the light emitting element, a first voltage control current source, a first switch circuit, a drive current / voltage conversion element, a second voltage control current source, a second switch circuit, and a third switch circuit. The switch circuit is connected to at least the first switch circuit, the second switch circuit and the third switch circuit, the first switch circuit, The data-side drive circuit has a function of controlling each of the second switch circuit and the third switch circuit into a conductive state or a non-conductive state, and At least a control circuit including a hold circuit, a reference voltage source, a selection switch circuit, and an input / output changeover switch are included. (3-a) In the pixel circuit, (1) the light emitting element is the light emitting element. Is a current-controlled light-emitting element whose brightness changes according to a drive current flowing through the device. (2) The first voltage-controlled current source is an active element controlled by a control voltage and a memory circuit capable of storing the control voltage. And a control terminal for inputting the control voltage of the active element, the control terminal having the function of generating the drive current based on the control voltage.
Is connected to the data side drive circuit via the switch circuit of (3), and (3) the drive current / voltage conversion element is connected in series to a current path through which the drive current flows, and has a function of converting the drive current into a voltage. (4) The second voltage controlled current source has a function of generating a monitor current correlated with the drive current based on the output voltage of the drive current / voltage conversion element, and outputs the monitor current. And an output terminal connected to the data side drive circuit via the second switch circuit, and (5) the third switch circuit includes a reference voltage source and the light emitting element provided in the data side drive circuit. And (6) the terminals of the first switch circuit and the second switch circuit on the side connected to the data side drive circuit are short-circuited, and (3-b) the data side drive circuit. At (( ) A control circuit including the sample hold circuit samples and holds a signal correlated with the monitor current, and a drive current flowing through the light emitting element based on the held signal obtains a desired brightness. The reference voltage source has a function of controlling the first voltage controlled current source so as to have a necessary current value, and (2) the reference voltage source resets the terminal voltage of the light emitting element to a predetermined voltage value. (3) the selection switch circuit has a function of selecting which of the control circuit and the reference voltage source to output to the pixel circuit, ) The input / output changeover switch is connected between the control circuit and the pixel circuit, and operates in synchronization with the first switch circuit, the second switch circuit and the third switch circuit, circuit Has a function of switching between an input state in which the monitor current is input and an output state in which a control voltage or a reset potential is output to the pixel circuit, the second switch circuit is in a non-conductive state, and the third switch Selecting the output of the reference voltage source by the selection switch circuit when the circuit is in a conducting state,
The reset potential is output to the pixel circuit to control the inter-terminal voltage of the light emitting element to a predetermined voltage value, the second switch circuit is in a conductive state, and the first switch circuit and the third switch circuit are in a conductive state. When the switch circuits are both in the non-conducting state, the input / output switch is set to the input state,
The monitor current is input, a signal correlated with the monitor current is sampled by the sample hold circuit, the first switch circuit is in a conductive state, and the second switch circuit and the third switch circuit are The signal held by the sample-hold circuit when the input / output changeover switch is in the output state and the output of the control circuit is selected by the selection switch circuit when both are in the non-conduction state and the sample-hold circuit is in the hold state. It has a function of controlling the first voltage controlled current source based on the above.

In the third aspect of the present invention, "the sampling in the sample-hold circuit and the control of the first voltage-controlled current source based on the signal held in the sample-hold circuit are time-divided. Alternately performing control "" In the first voltage controlled current source, the active element is an insulated gate field effect transistor, and the control terminal of the active element is a gate terminal of the insulated gate field effect transistor. The memory circuit is composed of a capacitor, the first terminal of the insulated gate field effect transistor is connected to the first terminal of the light emitting element and the third switch circuit, and the second terminal of the light emitting element is common to all pixels. A second terminal of the insulated gate field effect transistor is connected to the drive current / voltage conversion element, and the insulated gate field effect transistor is connected to the insulated gate field effect transistor. The gate terminal of the field effect transistor is connected to the first terminal of the capacitor and the first switch circuit, and the second terminal of the capacitor is connected to the common potential of all pixels. The third transistor connected to the first terminal of the effect transistor
The other terminal of the switch circuit is connected to the gate terminal of the insulated gate field effect transistor ”.

In the present invention, in the above-mentioned first to third inventions, "the drive current-voltage conversion element and the second voltage-controlled current source are current mirror structures composed of insulated gate field effect transistors. And "the insulated gate field effect transistor is a thin film transistor formed on the same substrate".

An organic EL element (OLED) which is a light emitting element preferably used in the present invention is considered to be a capacitive element having a self-discharge circuit in an equivalent circuit. Figure 1
It is the part 7 surrounded by the dotted line of 2. The portion 6 is a self-discharge circuit.

Therefore, for example, if the pixel size is 100 μm
X300 μm, the capacitance value of an OLED per pixel is 60 pF, and the voltage-current characteristics are shown in FIG. 13 ((A) represents vertical axis (current) in real number, (B) represents vertical axis (current)). Is expressed as a logarithm), FIG.
In the experimental circuit shown in, the drive current I0 is set to 10 μA and SW
A simulation was performed with respect to a voltage change at the anode end of the OLED when SW1 was turned off after injecting a current of 10 μA in the ON state for 1 and becoming a stable state. FIG. 14 shows the result. The horizontal axis of FIG. 14 is the time axis,
The vertical axis indicates the voltage change (anode-cathode voltage) when SW1 changes to OFF at time 0 sec.
This result indicates that when the maximum brightness level changes to the minimum brightness level, the control may not completely converge within the drive current setting control time (within the scanning time). Such a problem can be solved by promptly discharging the charge stored in the OLED by the reference voltage source as in the present invention.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a first terminal and a second terminal of a transistor represent two terminals other than a gate terminal, that is, a source terminal and a drain terminal. Direction, P-type of transistor, N
Depending on conditions such as type, which of the first terminal and the second terminal is the source terminal or the drain terminal is different, but for convenience of description, in each of the following embodiments, the current direction is assumed to be one, Two terminals that are either the source or the drain are fixed and shown as the source and the drain.

The first and second terminals of the light emitting element,
The first terminal and the second terminal of the capacitor respectively represent either one of the two terminals, and the polarity and the like are appropriately selected according to the specific circuit configuration as in the description of the transistor.

Furthermore, as a light emitting element, an organic EL element (OL) having advantages such as large area and easy full colorization is obtained.
Although a preferable mode using ED) is shown, 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 does not necessarily require rectification characteristics. .

(Embodiment 1) FIG. 1 is a configuration diagram showing a circuit configuration included in Embodiment 1 of an active matrix type display of the present invention.

First, the configuration of this embodiment will be described.

In the pixel circuit 1, the anode of the OLED is connected to the source of the first n-type thin film transistor T1 and constitutes a source follower. Further, one end of the capacitor C and the drain of the second n-type thin film transistor T4 are connected to the gate of T1, and the drain and gate of the first p-type thin film transistor T2 and the second p-type thin film transistor are connected to the drain of T1. The gate of T3 is connected. The cathode of the OLED and the other end of the capacitor are G
It is connected to ND. The sources of T2 and T3 are connected to the power supply potential Vdd. The drain of T3 is connected to the drain of the third n-type thin film transistor T5, and the monitor current Im is output from the source of T5. The source of T4 becomes the control voltage input terminal. It should be noted that T4 and T5 perform a switch operation that brings them into an electrically conducting state or a non-conducting state. A control signal ScanA output from a scanning side drive circuit (not shown in the drawing) installed outside the pixel region is input to the gate of T5, and output from the scanning side drive circuit to the gate of T4. Control signal Scan
B has been entered. In the structure described in this embodiment, T2 and T3 can be said to be a current mirror structure.

In addition to the above structure, the drain of the fourth n-type thin film transistor T6 is connected to the anode end of the OLED, and the source of T6 is connected to the gate of T1. T6
The control signal ScanC output from the scanning side drive circuit is input to the gate of the. T6 operates as a switch. The source of T6 may be connected to the source side of T4, but as in the present embodiment,
It is preferably connected to the gate and the source of one. As a result, the voltage between the gate and the source of T1 becomes 0 during the reset period, and the drive current does not flow, so that unnecessary light emission of the light emitting element can be prevented.

In the constituent elements of these pixel circuits, in the present embodiment and the following third embodiment, the thin film transistor T1 and the capacitor C serve as the first voltage controlled current source,
The thin film transistor T2 serves as a drive current / voltage conversion element, the thin film transistor T3 serves as a second voltage control current source, the thin film transistor T4 serves as a first switch circuit, the thin film transistor T5 serves as a second switch circuit, and the thin film transistor T6.
Correspond to the third switch circuits, respectively.

The data side drive circuit 2 causes a reference current Ir having luminance information to flow through the resistor R1 to generate a voltage Vr, and causes a monitor current Im output from the pixel circuit 1 to flow through the resistor R2 and a voltage (monitor voltage) Vm. Generate and generate voltage comparison circuit AM
Vr is input to the positive input terminal of P1 and Vm is input to the negative input terminal of P1, and the output of AMP1 is the first nMOS transistor M.
1 connected to the source. The drain of M1 is connected to the drain of the second nMOS transistor M2 and the source of T4 of the pixel circuit 1 via the signal line Vw. M2
The reference voltage source Vs is connected to the source of the. The reference voltage source Vs is made with the GND potential as a reference, and the voltage Vs is a fixed voltage equal to or lower than the light emission threshold voltage of the voltage between the terminals of the OLED, or the drive current thereof according to the brightness information. Average OLED operating voltage Von corresponding to
It is desirable to apply a voltage equal to By rapidly discharging the electric charge stored in the OLED by using this reference voltage source, the brightness can be changed promptly and the high speed performance is improved.

In the components of these data side drive circuits, in the present embodiment and the following third embodiment, the voltage comparison circuit AMP1, the resistors R1 and R2, and the reference current source Ir are provided in the control circuit, and the MOS transistor M1 is provided. , M2 correspond to the selection switch circuits, respectively.

Next, the operation of this embodiment will be described.

First, before the drive current setting control for causing the pixel to emit light with a desired brightness, the anode end of the OLED is subjected to control initial voltage setting control.

In the OLED initial voltage setting control, first, the control signal S1 in the data side drive circuit is set to low level, M1 is turned off, the control signal S2 is set to high level, and M2 is turned on. Next, after the scanning signal ScanB is set to the high level to turn on T4, the scanning signal ScanC is set to the high level to turn on T6. T in this state
The gate voltage of 1 and the anode voltage of the OLED can be set to Vs. Since the gate-source voltage of T1 is 0V, the current flowing between the source and drain of T1 is 0A. When the OLED initial voltage setting control ends, the scanning signal ScanC is set to the low level and T6 is turned off, and then the control signal S2 is set to the low level and M2 is turned off.

Then, the drive current setting control is performed while T4 is in the ON state.

In the drive current setting control, a control voltage (gate voltage of T1) that determines the drive current is set.

To start this control, first, the scanning signal ScanA is set to the high level to turn on T5, and then the control signal S1 is set to the high level to turn on M1 to set the controllable state. The control voltage determined by this control is the operating voltage Von when the OLED emits light, which is equal to T1.
It is a voltage obtained by adding the gate-source voltage Vgs.

Once in the controllable state, the current Id flowing through the OLED when the output voltage Vw of the AMP1 in the data side drive circuit 2 is applied to the gate of T1 via T4.
Is detected by a current mirror composed of T2 and T3 installed on the source side of T1, and the detected current is passed to the data side drive circuit 2 as a monitor current Im. In the data side drive circuit 2, the reference current Id having the brightness information is applied to the resistor R1.
Is converted into a voltage Vr by the resistor R2, and the monitor current Im is converted into a voltage Vm by the resistor R2, and the output voltage Vw of the AMP1 is controlled so that Vr and Vm become equal. V
When r and Vm become equal, the current I flowing through the OLED
d is a drive current required to obtain a desired brightness. The output voltage Vw of the AMP1 is written in the gate of T1 and at the same time, the voltage Vw is also written in the capacitor C connected thereto.

If the drive current is set, the scan signal S
After setting canB to the low level and turning T4 to the OFF state (non-conduction state), the scanning signal ScanA is set to the low level and T
5 is turned off (non-communication state). In this state,
The drive current setting control from the data side drive circuit 2 is not performed, the voltage Vw recorded in the capacitor C of the pixel circuit 1 is held, and the gate voltage of T1 is controlled by this held voltage Vw to drive the drive current Id. Will continue to be supplied.

In order to accurately write the control voltage to the capacitor C, the scan signals ScanA and Sc at the end of the control.
It is desirable that the changes in anB are not performed simultaneously, but in the order described above.

When the configuration of the present embodiment described above is used, a voltage obtained by adding the operating voltage Von at the time of light emission of the OLED and the Vgs of the drive current generating transistor so that a current value for obtaining a desired light amount flows in the light emitting element. Control
Threshold voltage Vth and O of drive current generating transistor
Even if the operating voltage Von of the LEDs varies, the problem that the brightness of each pixel changes does not occur. In addition, since there is no change in the path through which the drive current flows when the drive current is set and when it is held, the Early effect of the drive current generation transistor is completely unrelated.

Further, the source-drain voltage of the transistor for generating the drive current, the anode-cathode end voltage (ON voltage) at the time of the light emitting operation of the OLED greatly changes depending on the brightness, or the ON-voltage becomes large due to deterioration over time. Even if the temperature rises and the operation state in the triode region is not obtained enough, the drive current is stable and accurate.
Can be supplied to.

Further, when the monitor current Im is small with respect to the parasitic capacitance of the wiring and there is a risk that control cannot be performed stably, the mirror ratio of the current mirrors of T2 and T3 is appropriately designed, and accordingly, The resistance value in the data side drive circuit may be changed.

Further, in the description of the present embodiment, the luminance information is given to the reference current Ir, but the present invention is not limited to this, and the reference current Ir is made constant, and the resistance value of the resistor R1 is changed, whereby the luminance information is changed. It is also possible to control the light emission luminance according to the above, or it is possible to control the light emission luminance by keeping the resistance value of the reference current Ir and the resistance R1 constant and varying the resistance value of the resistor R2.

Further, the T of the pixel circuit in the present embodiment is
Although 4 and T5 are n-type thin film transistors, these transistors operate as switches as described above, and p-type thin film transistors may be used. However, when a p-type thin film transistor is used,
The inverted control signal must be input to the gate.

In the present embodiment, the insulated gate type thin film transistor using amorphous silicon or polysilicon has been described in mind, but the invention is not limited to the use of a transistor made of a silicon material, but a compound semiconductor or an organic semiconductor. The type of transistor used in the present invention is not limited as long as the same effect can be obtained with a transistor formed by the above method.

(Embodiment 2) This embodiment shows the overall structure of an active matrix type display having the circuit structure shown in Embodiment 1. Figure 10
11 is a configuration diagram thereof, and FIG. 11 is a timing chart for explaining the operation of the active matrix type display of the present embodiment.

FIG. 10 shows a part of a display having M × N pixels. Vw terminals of pixel circuits arranged in the data line direction (pixel circuits arranged in the vertical direction in FIG. 10) are all connected, and similarly, all Vm terminals are also connected and connected to the data side drive circuit. Further, ScanA and ScanB of the pixel circuits arranged in the scanning line direction (pixel circuits arranged in the horizontal direction in FIG. 10) are all connected to ScanA and ScanB of the scanning side drive circuit. In addition,
Since the scanning side driving circuit and the data side driving circuit need to operate in synchronization with each other, a signal supply circuit 5 for controlling timing is provided. Luminance information data (Data)
First, the clock (Ck) is input to the signal supply circuit 5, Data is output to the data side drive circuit 2, and Ck is output to the data side drive circuit 2 and the scan side drive circuit 3.

The operation of this embodiment will be described.

First, when the scanning of the first line is started, the scanning signal ScanA first becomes high level, and at the same time, the reference current source in the data side drive circuit sets the current value based on the image information. Next, the scanning signal ScanB becomes high level, and the drive current setting control is started for each selected pixel circuit.

The drive current setting control for the first line is completed within the specified time, and then the control for the second line is performed. To end the control, first, the scanning signal ScanB is set to low level, and then the scanning signal ScanA is set to low level. At the same time, the operation of the second line is started. Until the driving current setting control ends and the next scanning, the driving current is supplied to the OLED based on the voltage held in the capacitor in the pixel circuit, and the OLED continues to emit light.

It is desirable that the timings of the control signals in this embodiment have the relationship shown in FIG.

A detailed description of the light emitting operation of each pixel has been given in the first embodiment, and will not be repeated here.

Although the active matrix type display having the circuit configuration shown in the first embodiment is shown in the present embodiment, the same applies to the circuits having the configurations shown in the following third to seventh embodiments. Thus, an active matrix type display can be manufactured and operated.

(Third Embodiment) FIG. 2 is a configuration diagram showing a circuit configuration included in a third embodiment of an active matrix type display of the present invention.

The difference between this embodiment and the first embodiment is that
That is, the OLED is arranged on the power supply potential side. First, the configuration of the present embodiment will be described.

In the pixel circuit 1, the cathode of the OLED is connected to the source of the first p-type thin film transistor T1 and constitutes a source follower. Further, one end of the capacitor C and the drain of the first n-type thin film transistor T4 are connected to the gate of T1, and the drain and gate of the second n-type thin film transistor T2 and the third n-type thin film transistor are connected to the drain of T1. The gate of T3 is connected. The anode of the OLED and the other end of the capacitor are connected to the power supply potential Vdd. The sources of T2 and T3 are connected to GND. The drain of T3 is connected to the source of the fourth n-type thin film transistor T5, and the monitor current Im is output from the drain of T5. The source of T4 becomes the control voltage input terminal. It should be noted that T4 and T5 perform a switch operation that brings them into an electrically conducting state or a non-conducting state. A control signal ScanA output from a scanning side drive circuit (not shown in the drawing) installed outside the pixel region is input to the gate of T5, and output from the scanning side drive circuit to the gate of T4. Control signal Scan
B has been entered. In the structure shown in this embodiment, T2 and T3 can be said to have a current mirror structure.

In addition to the above structure, the drain of the fifth n-type thin film transistor T6 is connected to the cathode of the OLED, and the source of T6 is connected to the gate of T1. T
The scanning signal ScanC output from the scanning-side drive circuit is input to the gate of 6. T6 operates as a switch.

The data side driving circuit 2 causes the reference current Ir having the luminance information to flow through the resistor R1 to generate the voltage Vr, and causes the monitor current Im output from the pixel circuit 1 to flow through the resistor R2 to generate the voltage (monitor voltage) Vm. Generate and generate voltage comparison circuit AM
Vr is input to the positive input terminal of P1 and Vm is input to the negative input terminal of P1, and the output of AMP1 is the first nMOS transistor M.
1 connected to the source. The drain of M1 is connected to the drain of the second nMOS transistor M2 and the source of T4 of the pixel circuit 1 via the signal line Vw. M2
The reference voltage source Vs is connected to the source of the. This reference voltage source Vs is made with reference to the power supply potential Vdd,
The voltage Vs is a fixed voltage equal to or lower than the light emission threshold voltage of the OLED, or an average operating voltage Vo of the OLED corresponding to the drive current according to the brightness information.
It is desirable to provide a voltage equal to n.

The operation of the present embodiment can be performed by the same method as the operation method of the first embodiment if attention is paid to the change in polarity, and therefore the description thereof will be omitted.

By using the structure of the present embodiment shown above, the same effect as that of the first embodiment can be obtained.

As for the case where the monitor current is small, the current mirror ratio may be appropriately designed as in the first embodiment.

Although the reference current Ir is provided in the reference current Ir also in the description of the present embodiment, the present invention is not limited to this, and the resistor may be provided as described in the first embodiment.

Further, in the present embodiment, the pixel circuits T4 and T4 are
5, T6, and M1 and M2 in the data side drive circuit are n
Although it is a p-type transistor, as described above, this transistor operates as a switch.
Type transistor may be used. However, when a p-type transistor is used, an inverted control signal must be input to the gate.

The type of transistor used is the same as in the first embodiment.

(Embodiment 4) Considering the size per pixel of a single color of a color display, it is about 300 μm.
It becomes about (vertical) × about 100 μm (horizontal), and considering this, it is desirable that the number of scanning lines and data lines is as small as possible. The present embodiment is a concrete embodiment of the present invention in consideration of this.

FIG. 3 is a configuration diagram showing a circuit configuration included in the fourth embodiment of the active matrix type display of the present invention.

First, the configuration of the pixel circuit 1 of the present embodiment will be described.

In the pixel circuit 1, the anode of the OLED is connected to the source of the first n-type thin film transistor T1 and constitutes a source follower. Further, one end of the capacitor C and the drain of the second n-type thin film transistor T4 are connected to the gate of T1, and the drain and gate of the first p-type thin film transistor T2 and the second p-type thin film transistor are connected to the drain of T1. The gate of T3 is connected. The cathode of the OLED and the other end of the capacitor are G
It is connected to ND. The sources of T2 and T3 are connected to the power supply potential Vdd. The drain of T3 is connected to the drain of the third n-type thin film transistor T5. T
The source of 4 and the source of T5 are short-circuited, and the pixel circuit 1
There is only one signal line output from the
Let be c. It should be noted that T4 and T5 perform a switch operation that brings them into an electrically conducting state or a non-conducting state. T5
A control signal Sc output from a scanning side drive circuit (not shown in the figure) installed outside the pixel region is applied to the gate of
anA is input, and the control signal ScanB output from the scanning side drive circuit is input to the gate of T4. In the structure shown in this embodiment mode, T2 and T3
Can be said to have a current mirror structure.

In the constituent elements of these pixel circuits, in the present embodiment and the following fifth embodiment, the thin film transistor T1 and the capacitor C serve as the first voltage controlled current source,
The thin film transistor T2 corresponds to the drive current / voltage conversion element, the thin film transistor T3 corresponds to the second voltage controlled current source, the thin film transistor T4 corresponds to the first switch circuit, and the thin film transistor T5 corresponds to the second switch circuit.

The structure of the data side drive circuit 2 will be described.

Signal line Vc connected to pixel circuit 1
Is the drain of the first nMOS transistor M1 and the second
Connected to the drain of the nMOS transistor M2. The control signal S1 is input to the gate of M1, and the control signal S2 is input to the gate of M2. The source of M1 is connected to the resistor R2 and the sample hold circuit 4, and the other end of the resistor R2 is connected to GND. The control signal SH is input to the sample hold circuit 4. The output of the sample hold circuit 4 is connected to the negative input terminal of the voltage comparison circuit AMP1. The output of AMP1 is connected to the source of M2. The reference current Ir having the brightness information is connected to the positive input terminals of the resistors R1 and AMP1, and the other end of the resistor R1 is connected to GND. AMP1 is a MOS
It is desirable that it is composed of a transistor and that the output end has a charge pump configuration. In the configuration of this embodiment, M1 and M2 operate as a switch circuit.

In the components of these data side drive circuits, in the present embodiment and the following fifth embodiment, the voltage comparison circuit AMP1, the sample hold circuit 4 and the resistor R are provided.
1, R2 and the reference current source Ir correspond to the control circuit, and the MOS transistors M1 and M2 correspond to the input / output changeover switch.

The structure of the sample hold circuit 4 in the data side drive circuit described above can be realized by the structure shown in FIG. 6, for example.

The sample hold circuit shown in FIG. 6 will be described.

Vin serving as an input terminal is the first nMOS transistor.
Langista T_SIt is input to the gate of 1. T_SSeo of 1
Is the second nMOS transistor T_SSource 2 and No. 2
NMOS transistor T of 3_SConnected to the drain of 3
ing. T_SThe source of 3 is connected to GND, T_SDo of 3
T so that the desired constant current can be generated in the rain_SGame of 3
The voltage V1 is input to the switch. T_SThe drain of 1
First pMOS transistor T_S4 drain and gate
And the second pMOS transistor T_SConnect to gate 5
Has been done. T_S4, T_SThe source of 5 is the power supply potential Vdd
It is connected. T _S2 drain is T_S2 gates and
T_STo the drain of 5 and the fourth nMOS transistor T_S
It is connected to the drain of 6. T_S6 source is
Indexer C_SIs connected and this end becomes the output. T_S
A control signal S3 is input to the gate of 6.

With this structure, a voltage equal to the input voltage Vin is output to the gate of T _S 2. When T _S 6 is in the ON state by the control signal S3, a voltage equal to the input voltage Vin is output to the output terminal, and at the same time, the voltage is also written in the capacitor C _S. T _S 6 is the control signal S
In the OFF state by 3, the voltage of the capacitor C _S is held at the voltage written immediately before.

Next, an example of the operation of this embodiment is shown in FIG.
This will be described with reference to the timing chart shown in FIG.

The time tc is the scan selection time, that is, the drive current setting controllable time. Within this time, the brightness information conversion time ts and the drive current setting control time tn (n =
1 to 5), and the time tn (n = 1 to 5) is composed of the monitor current sampling time tan (n = 1 to 5) and the control voltage writing time tbn (n = 1 to 5). In the present embodiment, n = 1 to 5, but it is not limited to this, and may be repeated as many times as the time permits.

First, at the time of ts, the reference current Ir changes according to the brightness information, and the voltage Vr also changes accordingly.

Next, at time ta1, ScanA = high level → T5 = ON ScanB = low level → T4 = OFF S1 = high level → M1 = ON S2 = low level → M2 = OFF SH = high level → sampling state . In this state, the monitor current Im from the pixel circuit is converted into the monitor voltage Vm0 in the data side drive circuit, and the sampling voltage Vm0 is applied to the negative input terminal of the voltage comparison circuit AMP1.
m is input. At this point, the voltage information written in the capacitor in the pixel has not changed from the previous information, so there is a large potential difference between Vm and Vr. Based on this potential difference, the voltage comparator AMP1 generates a strong control command so that Vm becomes equal to Vr. That is, A
If the output end of MP1 had a charge pump configuration, the output of AMP1 would be the difference current between the two current sources that make up the charge pump, and a strong control command means that the difference current is maximum.

Subsequently, at time tb1, ScanA = low level → T5 = OFF ScanB = high level → T4 = ON S1 = low level → M1 = OFF S2 = high level → M2 = ON SH = low level → hold state, and AMP1 The output signal (control signal) is written to the gate and capacitor of T1 of the pixel circuit, and the drive current Id changes accordingly. The writing time is given by tx, and the control gain is determined by the size of this time.

Subsequently, at the time of ta2, like the time of ta1, ScanA = high level → T5 = ON ScanB = low level → T4 = OFF S1 = high level → M1 = ON S2 = low level → M2 = OFF SH = high Level → becomes the sampling state, the monitor current Im is converted to the monitor voltage Vm,
The monitor voltage Vm is sampled. At this time, tb
Since the voltage of the capacitor of the pixel circuit is rewritten in the time of 1, the potential difference between Vm and Vr is smaller than that in the time of ta1, so the output of AMP1 generates a weaker control command than before. ing.

Subsequently, at the time of tb2, again like tb1, ScanA = low level → T5 = OFF ScanB = high level → T4 = ON S1 = low level → M1 = OFF S2 = high level → M2 = ON SH = low level → hold It becomes the state and AM is connected to the gate and capacitor of T1 of the pixel circuit
Write the output signal of P1. However, since the output signal (control command) of AMP1 is weaker than that at tb1, the amount of change in drive current that can be changed at the same time tx is small.

Similarly, the control is sequentially repeated in the order of ta3 → tb3 → ta4 → tb4 to converge to the target value.

As shown in FIG. 5 showing the present embodiment, for example, if it is determined that Vm and Vr become equal at the time of ta5, the control output from AMP1 holds the previous control voltage at tb5. It becomes a state.

If the structure of the present embodiment described above is used, as in the case of the first embodiment, a stable and accurate drive current can be obtained without being affected by the Early effect.
Can be supplied to.

Further, the detection of the monitor current output from the pixel circuit and the control of the drive current setting voltage are sequentially and repeatedly performed by using the sampling and holding circuit to set the drive current necessary for obtaining the desired brightness. can do. Then, by this, the number of signal lines connecting the pixel circuit and the data side drive circuit can be made one.

In order to accurately write the control signal to the capacitor C, it is desirable to perform the switch operation in the order shown in FIG.

Further, in this embodiment, the pixel circuits T4 and T4 are
5 and M1 and M2 in the data side drive circuit are n-type transistors, but as described above, this transistor operates as a switch, and a p-type transistor may be used. However, when a p-type transistor is used, an inverted control signal must be input to the gate.

The current mirror ratio may be appropriately designed as in the first embodiment to cope with the case where the monitor current is small.

Although the reference current Ir is provided in the reference current Ir also in the description of the present embodiment, the present invention is not limited to this, and the resistor may be provided as described in the first embodiment.

The types of transistors used are the same as those in the first embodiment.

(Fifth Embodiment) FIG. 4 is a configuration diagram showing a circuit configuration included in a fifth embodiment of an active matrix type display of the present invention.

The difference between this embodiment and the fourth embodiment is that
That is, the OLED is arranged on the power supply potential side. Since the operation concept is the same as that of the fourth embodiment, only the configuration of the present embodiment will be described.

In the pixel circuit 1, the cathode of the OLED is connected to the source of the first p-type thin film transistor T1 to form a source follower. Further, one end of the capacitor C and the drain of the first n-type thin film transistor T4 are connected to the gate of T1, and the drain and gate of the second n-type thin film transistor T2 and the third n-type thin film transistor are connected to the drain of T1. The gate of T3 is connected. The anode of the OLED and the other end of the capacitor are connected to the power supply potential Vdd. The sources of T2 and T3 are connected to GND. The drain of T3 is connected to the source of the fourth n-type thin film transistor T5.
The source of T4 and the drain of T5 are short-circuited, the number of signal lines output from the pixel circuit 1 is one, and the signal line name is Vc. It should be noted that T4 and T5 perform a switch operation that brings them into an electrically conducting state or a non-conducting state.
A control signal ScanA output from a scanning side drive circuit (not shown in the drawing) installed outside the pixel region is input to the gate of T5, and output from the scanning side drive circuit to the gate of T4. The control signal ScanB is input. In the structure described in this embodiment, T2 and T3 can be said to be a current mirror structure.

The structure of the data side drive circuit 2 will be described.

The signal line Vc connected to the pixel is the first
Source of the nMOS transistor M1 and the second nMOS
It is connected to the drain of the transistor M2. The control signal S1 is input to the gate of M1, and the control signal S2 is input to the gate of M2. The drain of M1 is connected to the resistor R2 and the sample hold circuit 4, and the other end of the resistor R2 is connected to the power supply potential Vdd. The control signal SH is input to the sample hold circuit 4. The output of the sample hold circuit 4 is connected to the negative input terminal of the voltage comparison circuit AMP1. The output of AMP1 is connected to the source of M2. Further, the reference current Ir having the brightness information is connected to the positive input terminals of the resistors R1 and AMP1, and the other end of the resistor R1 is connected to the power supply potential Vdd. In addition, AMP1
Is preferably a MOS transistor, and the output end is preferably of a charge pump configuration. In the configuration of this embodiment, M1 and M2 operate as a switch circuit.

The structure of the sample hold circuit 4 can be realized, for example, by the structure shown in FIG. 6 as in the fourth embodiment.

Also in this embodiment, the same effect as in the fourth embodiment can be obtained.

Further, regarding the change of the configuration, the fourth embodiment is also adopted.
Is possible as well.

(Sixth Embodiment) FIG. 7 is a configuration diagram showing a circuit configuration included in a sixth embodiment of an active matrix type display of the present invention.

First, the structure of the pixel circuit 1 of the present embodiment will be described.

In the pixel circuit 1, the anode of the OLED is connected to the source of the first n-type thin film transistor T1 and constitutes a source follower. Further, one end of the capacitor C and the drain of the second n-type thin film transistor T4 are connected to the gate of T1, and the drain and gate of the first p-type thin film transistor T2 and the second p-type thin film transistor are connected to the drain of T1. The gate of T3 is connected. The cathode of the OLED and the other end of the capacitor are G
It is connected to ND. The sources of T2 and T3 are connected to the power supply potential Vdd. The drain of T3 is connected to the drain of the third n-type thin film transistor T5. T
The source of 4 and the source of T5 are short-circuited, and the pixel circuit 1
There is only one signal line output from the
Let be c. It should be noted that T4 and T5 perform a switch operation that brings them into an electrically conducting state or a non-conducting state. T5
A control signal Sc output from a scanning side drive circuit (not shown in the figure) installed outside the pixel region is applied to the gate of
anA is input, and the control signal ScanB output from the scanning side drive circuit is input to the gate of T4.

The configuration up to this point is similar to that of the fourth embodiment. The present embodiment has a configuration in which the fourth n
The drain of the thin film transistor T6 is connected to the anode end of the OLED, and the source of T6 is connected to the gate of T1. The control signal ScanC output from the scanning side drive circuit is input to the gate of T6. T6 operates as a switch. It should be noted that in the structure shown in this embodiment, T2 and T3 can be said to be a current mirror structure.

In the constituent elements of these pixel circuits, in the present embodiment and the following seventh embodiment, the thin film transistor T1 and the capacitor C serve as the first voltage controlled current source,
The thin film transistor T2 serves as a drive current / voltage conversion element, the thin film transistor T3 serves as a second voltage control current source, the thin film transistor T4 serves as a first switch circuit, the thin film transistor T5 serves as a second switch circuit, and the thin film transistor T6.
Correspond to the third switch circuits, respectively.

The data side drive circuit 2 installed outside the pixel region will be described.

Signal line Vc connected to pixel circuit 1
Is the drain of the first nMOS transistor M1, the drain of the second nMOS transistor M2, and the third nMOS transistor M2.
It is connected to the drain of the MOS transistor M3.
The control signal S1 is input to the gate of M1, the control signal S2 is input to the gate of M2, and the control signal S3 is input to the gate of M3. The source of M1 is connected to the resistor R2 and the sample hold circuit 4, and the other end of R2 is connected to GND. The control signal SH is input to the sample hold circuit 4. The output of the sample hold circuit 4 is connected to the negative input terminal of the voltage comparison circuit AMP1. The output of AMP1 is connected to the source of M2. The reference current Ir having the brightness information is connected to the positive input terminals of the resistors R1 and AMP1, and the other end of the resistor R1 is connected to GND. AMP1 is composed of MOS transistors,
It is desirable that the output end has a charge pump configuration. A reference voltage source Vs is connected to the source of M3. The reference voltage source Vs is made with the GND potential as a reference, and the voltage Vs is set to a fixed voltage equal to or lower than the light emission threshold voltage of the OLED, or an average value corresponding to the drive current according to the brightness information. It is desirable to provide a voltage equal to the operating voltage Von of the OLED.

The sample hold circuit 4 is, for example, as shown in FIG.
The structure shown in may be used.

In the components of these data side drive circuits, in the present embodiment and the following seventh embodiment, the voltage comparison circuit AMP1, the sample hold circuit 4 and the resistor R are provided.
1, R2 and the reference current source Ir in the control circuit, the MOS transistors M1 and M2 in the input / output switch, and MO.
The S transistors M2 and M3 correspond to the selection switch circuits, respectively. That is, in the present embodiment and the following seventh embodiment, M2 has a configuration that also serves as a constituent element of two switches.

Next, an example of the operation of this embodiment is shown in FIG.
This will be described with reference to the timing chart shown in FIG.

The time tc is the scan selection time, that is, the drive current setting controllable time. Within this time, brightness information conversion and OLED anode end voltage setting time ts
And the drive current setting control time tn (n = 1 to 5), and the time tn is the monitor current sampling time tan (n = 1 to 1).
5) and the control voltage writing time tbn (n = 1 to 5). In the present embodiment, n = 1 to 5, but it is not limited to this, and may be repeated as many times as the time permits.

First, at time ts, ScanA = low level → T5 = OFF ScanB = high level → T4 = ON ScanC = high level → T6 = ON S1 = low level → M1 = OFF S2 = low level → M2 = OFF S3 = high Level → M3 = ON SH = Low level → Hold state, the reference current Ir changes in the data side drive circuit, and the voltage Vr also changes accordingly. At the same time, O
Control for setting the anode end voltage of the LED to the voltage Vs is performed.

Then, at time ta1, ScanA = high level → T5 = ON ScanB = low level → T4 = OFF ScanC = low level → T6 = OFF S1 = high level → M1 = ON S2 = low level → M2 = OFF S3 = Low level → M3 = OFF SH = High level → Sampling state. In this state, the monitor current Im from the pixel circuit is converted into the monitor voltage Vm0 in the data side drive circuit, and the sampling voltage Vm0 is applied to the negative input terminal of the voltage comparison circuit AMP1.
m is input. At this time, the voltage information written in the capacitor in the pixel has not changed from the previous information, and thus there is a large potential difference between Vm and Vr.

Based on this potential difference, the voltage comparator AMP1
Generates a strong control command so that Vm becomes equal to Vr. That is, if the output end of the AMP1 has a charge pump structure, the output of the AMP1 becomes a difference current between two current sources forming the charge pump, and a strong control command means that the difference current is large.

Subsequently, at time tb1, ScanA = low level → T5 = OFF ScanB = high level → T4 = ON ScanC = low level → T6 = OFF S1 = low level → M1 = OFF S2 = high level → M2 = ON S3 = low level → M3 = OFF SH = low level → Hold state, the output signal (control signal) of AMP1 is written to the gate and capacitor of T1 of the pixel circuit, and the drive current Id changes accordingly. The writing time is given by tx, and the control gain is determined by the size of this time.

Subsequently, at the time of ta2, like the time of ta1, ScanA = high level → T5 = ON ScanB = low level → T4 = OFF ScanC = low level → T6 = OFF S1 = high level → M1 = ON S2 = low level → M2 = OFF S3 = Low level → M3 = OFF SH = High level → Sampling state, monitor current Im is converted to monitor voltage Vm,
The monitor voltage Vm is sampled. At this time, tb
Since the voltage of the capacitor of the pixel circuit is rewritten in the time of 1, the potential difference between Vm and Vr is smaller than that in the time of ta1, so the output of AMP1 generates a weaker control command than before. ing.

Then, at the time of tb2, again like tb1, ScanA = low level → T5 = OFF ScanB = high level → T4 = ON ScanC = low level → T6 = OFF S1 = low level → M1 = OFF S2 = high level → M2 = ON S3 = Low level → M3 = OFF SH = Low level → Hold state, AM in the gate and capacitor of T1 of the pixel circuit
Write the output signal of P1. However, since the output signal (control command) of AMP1 is weaker than that at tb1, the amount of change in drive current that can be changed at the same time tx is small.

Similarly, ta3 → tb3 → ta4 → tb4 is sequentially repeated to converge to the target value.

As shown in FIG. 5 showing the present embodiment, for example, if it is determined that Vm and Vr become equal at the time of ta5, the control output from AMP1 holds the previous control voltage at tb5. It becomes a state.

According to this embodiment, both the effects of the first embodiment and the effects of the fourth embodiment can be obtained.

Further, regarding the change of the configuration, the first embodiment is also adopted.
It is possible in the same manner as in the case of 4 and 4.

(Embodiment 7) FIG. 8 is a configuration diagram showing a circuit configuration included in Embodiment 7 of an active matrix type display of the present invention.

The difference between this embodiment and the sixth embodiment is that
That is, the OLED is arranged on the power supply potential side. Since the operation concept is the same as that of the sixth embodiment, only the configuration of the present embodiment will be described.

In the configuration of the pixel circuit 1, the cathode of the OLED is connected to the source of the first p-type thin film transistor T1 to form a source follower. Further, one end of the capacitor C and the drain of the first n-type thin film transistor T4 are connected to the gate of T1, and the drain and gate of the second n-type thin film transistor T2 and the third n-type thin film transistor are connected to the drain of T1. The gate of T3 is connected. The anode of the OLED and the other end of the capacitor are connected to the power supply potential Vdd. The sources of T2 and T3 are connected to GND. The drain of T3 is connected to the source of the fourth n-type thin film transistor T5.
The source of T4 and the drain of T5 are short-circuited, the number of signal lines output from the pixel circuit 1 is one, and the signal line name is Vc. It should be noted that T4 and T5 perform a switch operation that brings them into an electrically conducting state or a non-conducting state.
A control signal ScanA output from a scanning side drive circuit (not shown in the figure) installed outside the pixel region is input to the gate of T5, and output from the scanning side drive circuit to the gate of T4. The control signal ScanB is input.

The configuration up to this point is the same as that of the fifth embodiment. In the present embodiment, in addition to this structure, the fifth n
The drain of the thin film transistor T6 is connected to the cathode end of the OLED, and the source of T6 is connected to the gate of T1. The control signal ScanC output from the scanning side drive circuit is input to the gate of T6. T6 operates as a switch. It should be noted that in the structure shown in this embodiment, T2 and T3 can be said to be a current mirror structure.

The data side drive circuit 2 installed outside the pixel area will be described.

Signal line Vc connected to pixel circuit 1
Is the source of the first nMOS transistor M1 and the second
Drain of the nMOS transistor M2 and the third nM
It is connected to the drain of the OS transistor M3. M
The control signal S1 is input to the gate of 1, the control signal S2 is input to the gate of M2, and the control signal S3 is input to the gate of M3. The drain of M1 is connected to the resistor R2 and the sample hold circuit 4, and the other end of R2 is connected to the power supply potential Vdd. The sample hold circuit 4 has a control signal SH
Has been entered. The output of the sample hold circuit 4 is connected to the negative input terminal of the voltage comparison circuit AMP1. A
The output of MP1 is connected to the source of M2. Also,
The reference current Ir having luminance information is connected to the positive input terminals of the resistor R1 and AMP1, and the other end of the resistor R1 has the power supply potential Vdd.
It is connected to the. It is desirable that the AMP1 is composed of a MOS transistor and that the output terminal has a charge pump structure. A reference voltage source Vs is connected to the source of M3. This reference voltage source Vs has a power supply potential Vdd.
The voltage Vs is set to a fixed voltage equal to or lower than the light emitting threshold voltage of the OLED, or equal to the average operating voltage Von of the OLED corresponding to the drive current according to the brightness information. It is desirable to apply a voltage.

The sample hold circuit 4 is, for example, as shown in FIG.
The structure shown in may be used.

According to this embodiment, both the effects of the third embodiment and the effects of the fifth embodiment can be obtained.

In addition, regarding the change of the configuration, the third embodiment is also applicable.
It is possible in the same manner as in step 5 and step 5.

[0139]

As described above, according to the present invention, stable and accurate supply to the current light emitting element is not affected by the variation in the threshold voltage of the transistor constituting the drive current source installed in each pixel circuit. it can.

Further, at the stage of shifting from the period for controlling the control voltage of the driving current source to the period for continuously supplying a constant current to the light emitting element based on the set control voltage, the voltage between the input and output terminals of the driving current source is changed. Since it can be prevented from changing, it is completely free from the influence of the Early effect, which has been a problem when an insulated gate field effect transistor is used as a drive current source. Even if the source / drain voltage of the transistor that generates the drive current cannot be sufficiently secured due to the large change in the anode / cathode voltage and the operating region becomes the triode region, the drive current is emitted stably and accurately. Since it can be supplied to the device, high-definition image display is possible.

[Brief description of drawings]

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

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

FIG. 3 is a configuration diagram showing a circuit configuration included in an embodiment of an active matrix type display of the present invention.

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

FIG. 5 is a timing chart for explaining the operation of the embodiment of the active matrix display of the present invention.

FIG. 6 is a sample hold circuit used in one embodiment of the active matrix display of the present invention.

FIG. 7 is a configuration diagram showing a circuit configuration included in an embodiment of an active matrix type display of the present invention.

FIG. 8 is a configuration diagram showing a circuit configuration included in an embodiment of an active matrix type display of the present invention.

FIG. 9 is a timing chart for explaining the operation of the embodiment of the active matrix display of the present invention.

FIG. 10 is a configuration diagram showing an embodiment of an active matrix type display of the present invention.

FIG. 11 is a timing chart for explaining the operation of the embodiment of the active matrix display of the present invention.

FIG. 12 is a simulation circuit diagram for examining discharge characteristics of an OLED model.

FIG. 13 is a voltage-current characteristic of the created OLED model.

FIG. 14 is a result of OLED discharge characteristic simulation.

FIG. 15 is a configuration diagram showing a circuit configuration included in an active matrix display of Conventional Example 1.

16 is a configuration diagram showing a circuit configuration included in an active matrix display of Conventional Example 2. FIG.

FIG. 17 is a configuration diagram showing a circuit configuration included in an active matrix display of Conventional Example 3.

[Explanation of symbols]

OLED light emitting element TFT1 to TFT4, T1 to T6 thin film transistor M1 to M3 MOS transistors C capacitor R, R1, R2 resistance Ir reference current source Vs reference voltage source AMP1 voltage comparison circuit 1 pixel circuit 2 Data side drive circuit 3 Scanning side drive circuit 4 sample and hold circuit 5 Signal supply circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 641 G09G 3/20 641D 642 642A H01L 29/786 H05B 33/14 A H05B 33/14 H01L 29 / 78 614 F term (reference) 3K007 AB17 BA06 BB07 DA01 DB03 EB00 GA04 5C080 AA06 BB05 DD04 DD05 EE28 FF11 JJ02 JJ03 JJ04 JJ06 5F110 AA30 BB01 GG02 GG04 GG05 GG13 GG15 NN71

Claims (12)

[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 pixel circuit includes the light emitting element, a first voltage controlled current source, a first switch circuit, a drive current / voltage conversion element, a second voltage controlled current source, and a second switch. Circuit,
At least a third switch circuit, wherein the scan side drive circuit is connected to at least the first switch circuit, the second switch circuit and the third switch circuit, and the first switch Circuit, said second
A switch circuit and a third switch circuit, each of which has a function of controlling a conductive state or a non-conductive state, the data side drive circuit, a control circuit, a reference voltage source,
A selection switch circuit, and (1-a) in the pixel circuit, (1) the light emitting element is a current control type light emitting element whose brightness changes according to a drive current flowing in the light emitting element, (2) The first voltage controlled current source includes at least an active element controlled by a control voltage and a storage circuit capable of storing the control voltage, and has a function of generating the drive current based on the control voltage. And a control terminal for inputting the control voltage of the active element is connected to the data side drive circuit via the first switch circuit, (3) the drive current / voltage conversion element outputs the drive current. It is connected in series to a flowing current path and has a function of converting the drive current into a voltage. (4) The second voltage control current source is based on an output voltage of the drive current / voltage conversion element. The output terminal for outputting a monitor current having a function of generating a monitor current correlated with the drive current is connected to the data side drive circuit via the second switch circuit, and (5) the third The switch circuit is connected between a reference voltage source provided in the data side drive circuit and the light emitting element, (1-b) in the data side drive circuit, (1) the control circuit is the monitor. (2) the reference voltage source, which has a function of controlling the first voltage-controlled current source so that the drive current flowing through the light-emitting element based on the current has a current value required to obtain a desired brightness. Has a function of outputting a reset potential for setting a voltage between terminals of the light emitting element to a predetermined voltage value, (3) the selection switch circuit is one of the control circuit and the reference voltage source. Output to the pixel circuit The selection switch circuit has a function of selecting whether to output, the first switch circuit and the second switch circuit are both in a conductive state, and the third switch circuit is in a non-conductive state. A function of controlling the first voltage controlled current source by the control circuit based on the monitor current when the output of the circuit is selected; and at least the third switch circuit immediately before the control period. An active matrix type having a function of controlling the terminal voltage of the light emitting element to a predetermined voltage value when the output of the reference voltage source is selected by the selection switch circuit in the conductive state. display. 2. The first voltage controlled current source, wherein the active element is an insulated gate field effect transistor, and the control terminal of the active element is a gate terminal of the insulated gate field effect transistor. The circuit includes a capacitor, a first terminal of the insulated gate field effect transistor is connected to the first terminal of the light emitting element and the third switch circuit, and a second terminal of the light emitting element is connected to a common potential for all pixels. A second portion of the insulated gate field effect transistor
A terminal is connected to the drive current / voltage conversion element, a gate terminal of the insulated gate field effect transistor is connected to the first terminal of the capacitor and the first switch circuit, and a second terminal of the capacitor is common to all pixels. The active matrix type display according to claim 1, wherein the active matrix type display is connected to a potential. 3. The other terminal of the third switch circuit connected to the first terminal of the insulated gate field effect transistor is connected to the gate terminal of the insulated gate field effect transistor. The active matrix type display according to claim 2. 4. 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 drive circuit and a data side drive circuit for controlling the pixel circuit are provided. Wherein the pixel circuit includes the light emitting element, a first voltage controlled current source, a first switch circuit, a drive current / voltage conversion element, a second voltage controlled current source, and a second switch. Circuit,
The scan side drive circuit is connected to at least the first switch circuit and the second switch circuit, and the first switch circuit and the second switch circuit are in a conductive state or a non-conductive state. And a control circuit having a sample hold circuit, and an input / output changeover switch. (2-a) In the pixel circuit, (1) The above The light emitting element is a current control type light emitting element whose brightness changes according to a drive current flowing through the light emitting element, and (2) the first voltage controlled current source is an active element controlled by a control voltage, and A storage circuit capable of storing a control voltage, having a function of generating the drive current based on the control voltage, for inputting the control voltage of the active element The control terminal is connected to the data side drive circuit via the first switch circuit, (3) the drive current / voltage conversion element is connected in series to a current path through which the drive current flows, and (4) The second voltage controlled current source has a function of generating a monitor current correlated with the drive current based on the output voltage of the drive current / voltage conversion element. An output terminal for outputting the monitor current is connected to the data side drive circuit via the second switch circuit, (5) the data side drive circuit of the first switch circuit and the second switch circuit The terminal on the side connected to is short-circuited, (2-b) in the data side drive circuit, (1) the control circuit including the sample hold circuit is:
A signal having a correlation with the monitor current is sampled and held, and based on the held signal, the drive current supplied to the light emitting element has a current value necessary for obtaining a desired brightness. (2) The input / output changeover switch is connected between the control circuit and the pixel circuit, and has a function of controlling a voltage-controlled current source, and the first switch circuit and the second switch circuit. It has a function of performing a synchronous operation to switch between an input state in which a monitor current is input from the pixel circuit and an output state in which a control voltage is output to the pixel circuit, wherein the first switch circuit is in a non-conducting state, and When the second switch circuit is in the conducting state, the input / output changeover switch is set to the input state, the monitor current is input, and the signal having the correlation with the monitor current is sample-held. Sampled at road, the first switch circuit is in the conducting state and the second
The input / output changeover switch is set to the output state when the switch circuit is off, and the sample / hold circuit is set to the hold state based on the signal held by the sample / hold circuit. An active matrix type display characterized by having a function of controlling a display. 5. Sampling in the sample and hold circuit and control of the first voltage controlled current source based on the signal held in the sample and hold circuit,
The active matrix display according to claim 4, wherein the display is alternately performed by time division control. 6. In the first voltage controlled current source, the active element is an insulated gate field effect transistor, and the control terminal of the active element is a gate terminal of the insulated gate field effect transistor. The circuit includes a capacitor, a first terminal of the insulated gate field effect transistor is connected to a first terminal of the light emitting element, a second terminal of the light emitting element is connected to a common potential for all pixels, and the insulated gate field effect transistor is connected. The second terminal of the effect transistor is connected to the drive current / voltage conversion element, and the gate terminal of the insulated gate field effect transistor is the first terminal of the capacitor.
The active matrix type display according to claim 4 or 5, wherein a terminal and the first switch circuit are connected, and a second terminal of the capacitor is connected to a common potential for all pixels. 7. 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 pixel circuit includes the light emitting element, a first voltage controlled current source, a first switch circuit, a drive current / voltage conversion element, a second voltage controlled current source, and a second switch. Circuit,
At least a third switch circuit, the scan side drive circuit is connected to at least the first switch circuit, the second switch circuit and the third switch circuit, the first switch A circuit, a second switch circuit, and a third switch circuit, each of which has a function of controlling a conductive state or a non-conductive state, the data-side drive circuit, a control circuit including a sample hold circuit, and a reference At least a voltage source, a selection switch circuit, and an input / output changeover switch;
a) In the pixel circuit, (1) the light emitting element is a current control type light emitting element whose luminance changes according to a drive current flowing in the light emitting element, and (2) the first voltage control current source is And including at least an active element controlled by a control voltage and a storage circuit capable of storing the control voltage, having a function of generating the drive current based on the control voltage, and inputting the control voltage of the active element. Is connected to the data side drive circuit via the first switch circuit, and (3) the drive current / voltage conversion element is connected in series to a current path through which the drive current flows, A function of converting a drive current into a voltage, and (4) the second voltage-controlled current source generates a monitor current correlated with the drive current based on the output voltage of the drive current-voltage conversion element. And an output terminal for outputting the monitor current is connected to the data side drive circuit via the second switch circuit, and (5) the third switch circuit is provided in the data side drive circuit. Connected between a provided reference voltage source and the light emitting element, (6) terminals of the first switch circuit and the second switch circuit on the side connected to the data side drive circuit are short-circuited, (3-b) In the data side drive circuit, (1) the control circuit including the sample hold circuit is
A signal having a correlation with the monitor current is sampled and held, and based on the held signal, the drive current supplied to the light emitting element has a current value necessary for obtaining a desired brightness. (2) The reference voltage source has a function of applying a reset potential for setting a voltage between terminals of the light emitting element to a predetermined voltage value, and (3) the reference voltage source has a function of controlling a voltage controlled current source. The selection switch circuit has a function of selecting which output of the control circuit and the reference voltage source is to be output to the pixel circuit, (4) the input / output switch is the control circuit and An input state connected between the pixel circuit and the first switch circuit, the second switch circuit, and the third switch circuit in synchronization with each other to input the monitor current from the pixel circuit; Pixel A selection switch circuit having a function of switching to an output state of outputting a control voltage or a reset potential to a path, when the second switch circuit is in a non-conducting state and the third switch circuit is in a conducting state. The output of the reference voltage source is selected to output the reset potential to the pixel circuit to control the terminal voltage of the light emitting element to a predetermined voltage value, and the second switch circuit is in a conductive state. And the first
When both the switch circuit and the third switch circuit are in the non-conducting state, the input / output changeover switch is set to the input state, the monitor current is input, and a signal having a correlation with the monitor current is input to the sample hold circuit. Sampling, the first switch circuit is in a conducting state and the second switch circuit is in a conductive state.
When both the switch circuit and the third switch circuit are in the non-conducting state, the input / output changeover switch is set to the output state, the output of the control circuit is selected by the selection switch circuit, and the sample hold circuit is held. An active matrix type display having a function of controlling the first voltage controlled current source based on a signal held by the sample hold circuit. 8. Sampling in the sample and hold circuit and control of the first voltage controlled current source based on a signal held in the sample and hold circuit,
The active matrix display according to claim 7, wherein the display is alternately performed by time division control. 9. In the first voltage controlled current source, the active element is an insulated gate field effect transistor, and the control terminal of the active element is a gate terminal of the insulated gate field effect transistor, The circuit includes a capacitor, a first terminal of the insulated gate field effect transistor is connected to the first terminal of the light emitting element and the third switch circuit, and a second terminal of the light emitting element is connected to a common potential for all pixels. A second portion of the insulated gate field effect transistor
A terminal is connected to the drive current / voltage conversion element, a gate terminal of the insulated gate field effect transistor is connected to the first terminal of the capacitor and the first switch circuit, and a second terminal of the capacitor is common to all pixels. 9. The active matrix type display according to claim 7, which is connected to a potential. 10. The other terminal of the third switch circuit connected to the first terminal of the insulated gate field effect transistor is connected to the gate terminal of the insulated gate field effect transistor. Claim 9
Active matrix type display described in. 11. The drive current-voltage conversion element and the second
11. The active matrix type display according to claim 1, wherein the voltage controlled current source has a current mirror structure composed of an insulated gate field effect transistor. 12. The active matrix type display according to claim 1, wherein the insulated gate field effect transistors are thin film transistors formed on the same substrate. Type display.