JP2003108069A - Driving circuit of light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit of a light emitting element in which current that flows into light emitting elements is more accurately controlled, a power supply voltage is suppressed to a lower level as much as possible and a stable operation is made possible. SOLUTION: The driving circuit is provided with a current supplying circuit (1) and a driving control circuit (2a). In the circuits (1) and (2a), a current (Is) having a same value of a current (Ir), which flows from a supply transistor (M5) that supplies a current to drive a light emitting element (EL), is led to the circuit (2a) through a reference transistor (M4) and a control is made so that the current (Is) becomes closer to a desired set current value (Idrv) and each of source/drain voltage information (Vs and Vr) becomes equal employing the current (Is), based on source/drain voltage information (Vs) of the transistor (M4) and source/drain voltage information (Vr and Vdrv) of the transistor (M5).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control type light emitting element drive circuit in which emission brightness is controlled by a current flowing through the element.

[0002]

2. Description of the Related Art In recent years, a self-luminous display using a light emitting element has been attracting attention, and an organic electroluminescence element (organic EL) which is a current control type light emitting element whose emission brightness is controlled by a current flowing through the element. The active development of applied devices is being carried out, and many proposals have been made for their drive circuits. In this drive circuit, it is necessary to accurately supply a desired current to the light emitting element, and this applies not only to the organic electroluminescence element but also to current drive type light emitting element drive circuits in general.

FIG. 12 is a conceptual diagram of a single-color image display panel in which light emitting elements are arranged on a two-dimensional plane and applied to an image display section. In the image display unit 4, (x) × (y) current supply circuits 1 including light emitting elements are arranged. Therefore, the number of horizontal pixels is x and the number of vertical pixels is y. The column drive control circuits 2i to 2x are connected to a current supply circuit (column) in charge thereof, and the connected column drive signals Ai to Ax set an injection current for controlling a desired light emission amount in each current supply circuit 1. It is a thing. The row selection signal generators 3i to 3y set the injection currents in the column drive control circuits 2i to 2x so that the setting operation is always performed in one pixel, so that the current supply circuit 1 of the corresponding row to which the output signal is connected. The selection signals Bi to By for controlling the selection circuit included in the above are output. The drive signals Ai to Ax and the row selection signals Bi to By may be one and a plurality of signals, respectively.

(Conventional Example 1 of Current Supply Circuit 1) FIG. 9 shows a current supply circuit 1a which is an example of a current supply circuit included in a conventional drive circuit for a light emitting element. The power supply VCC is connected to the source terminal of the P-type transistor M5 (M5 _S , the source terminal is represented by the subscript _S in this specification) as a supply transistor for supplying current, and the gate terminal (M5 S5).
_A capacitor C1 is connected between G (the gate terminal is represented by _G in this specification) and the power supply VCC.
The drain terminal of the P-type transistor M5 (M5 _D , the drain terminal is denoted by _D in this specification) is connected to the first terminal of the light emitting element, and the second terminal of the light emitting element is grounded (GND). ing. M5 _G is connected to the drain terminal (M1 _D ) of the transistor M1 as a control switch for controlling the gate terminal voltage, and is connected to the source terminal (M1 _D ).
1 _S ) receives the control voltage Vd for setting the current value of the transistor M5, and the gate terminal (M1 _G ) receives the selection signal S1. In the case of FIG. 12, the drive signals Ai to
Ax corresponds to the control voltage Vd, and the selection signals Bi to By are S
Equivalent to 1. When the selection signal S1 = L, M1 = ON, the control voltage Vd charges the capacitor C1, and the M5 injects a current according to the gate terminal voltage Vg (= Vd) into the light emitting element to emit light. When S1 = H, M1 = OFF and M
5 _G is held at the gate terminal voltage Vg, and the light emitting element continues to emit light at the gate terminal voltage Vg. The transistors M5 and M1 are thin film transistors (TF).
T) and the capacitor C1 is also made by a thin film process. The capacitor C1 may be composed of parasitic capacitances of M5 and M1.

(Conventional Example 2 of Current Supply Circuit 1) FIG.
Example of current supply circuit included in conventional light emitting element drive circuit
Is the current supply circuit 1b. Current supply circuit 1
The difference from a will be described. M5 _GIn the tragedy
P-type transistor M with the same current drive characteristics as the M5
13 gate terminal (M13_G) Is connected, M13_SIs electric
Connected to source VCC, M13 _DAnd M14_SIs connected and M
14_DIs M13_GConnected to the M14_GIs the selection signal S4
It is connected. In addition M13_SM1_DIs connected,
M1_SA control current Id for setting the light emission amount is input to
M1_GThe selection signal S1 is input to. In the case of FIG.
The drive signals Ai to Ax correspond to Id, and the selection signals Bi to B
y corresponds to the selection signals S4 and S1. S1 = L and S4
= L, M1 = ON and M14 = ON
In the current mirror circuit consisting of transistors M13 and M5
Become. At this time, when the control current Id is supplied, the power is supplied to M13.
The current Id flows and the current drive characteristic of M13 causes M13 to flow._G
Capacitor C1 is charged until this voltage is reached.
Then, a current related to the control current Id flows to M5 and the light emitting element
This current is injected into the child and the light emitting element emits light. S1 = H
And S4 = H, M1 = OFF and M14 = OF
When it becomes F, the charging voltage of the capacitor C1 is held.
Then, the current related to the control current Id flows to M5,
The light emitting element continues to emit light in the set state. Transi
The transistors M5, M1, M13 and M14 are thin film transistors.
(TFT), capacitor C1 is also a thin film process
Created in. The capacitor C1 includes M5, M13 and M
It may be composed of 14 parasitic capacitances.

(Conventional Example 3 of Current Supply Circuit 1) FIG. 11 shows a current supply circuit 1c which is an example of a current supply circuit included in a conventional drive circuit for a light emitting element. Differences from the current supply circuit 1b will be described. M5 _G is connected to M14 _D , M
5 _D is connected to M14 _S, and the selection signal S4 is input to M14 _G. M5 _D is connected to M15 _S , M15 _D is connected to the first terminal of the light emitting element, and the selection signal S is connected to M15 _G.
5 is input. In the case of FIG. 12, the drive signals Ai to Ax correspond to Id, and the selection signals Bi to By are the selection signals S1 and S.
4, corresponding to S5. When S1 = L, S4 = L, S5 = H, M1 = ON, M14 = ON, M15 = OFF and M5 becomes a bias voltage circuit for receiving the control current Id, and the light emitting element is turned off. The capacitor C1 is charged until the M5 _G voltage becomes a voltage determined by the current driving characteristic of M5. When S1 = H, S4 = H, S5 = L, M1
= OFF, M14 = OFF, M15 = ON and M5 _G
The voltage is held at the charging voltage of the capacitor C1, and at this time, a current related to the control current Id continues to flow in M5 to cause the light emitting element to emit light. Transistors M1, M5,
M14 and M15 are composed of thin film transistors (TFTs), and the capacitor C1 is also formed by a thin film process. The capacitor C1 may be composed of parasitic capacitances of M1, M5 and M14.

In the conventional example described above, the transistors M1, M14, and M15 are configured by selecting signals S1, S4,
The configuration does not matter as long as S5 can be appropriately input and the switch operation can be performed. In addition, P-type transistors M5 and M13
Can be easily configured with an N-type transistor by changing the connection with the light emitting element, power supply VCC, GND, and the like.

[0008]

However, the conventional current supply circuits 1a to 1c have the following problems.

First, in Conventional Example 1, for example, in each current supply circuit 1a of the image display section in which TFTs are arranged in a large area, the amount of light emission in each current supply circuit 1a varies due to the variation in the current driving characteristics mainly with Vth of the transistor M5. A stable image cannot be reproduced on the display panel.

In the conventional examples 2 and 3, by driving the supply transistor by the gate terminal voltage obtained by actually flowing the control current Id, the above-mentioned problem of variation is solved, but the current caused by the control current Id is improved. Since Vds at the time of setting and Vds at the time of light emission hold (for example, in 1b, Vds of the transistor M13 at current setting and Vds of the transistor M5 at light emission hold) are different,
It cannot be guaranteed that the same current as Id flows through the transistor M5 due to the Early effect.

Further, the voltage value of the power supply VCC must be set with a large margin for the following reason, and it is affected by the fluctuation of the power supply voltage VCC (longer than the frame period), and stable image reproduction is possible. Is not guaranteed.

(Reason 1) In order to avoid the triode region in which the current driving characteristic of the transistor M5 is greatly deteriorated, the operation region is set in the triode characteristic region [Vds <(Vgs <Vgs where the current driving characteristic varies depending on the drain-source voltage Vds). -Vt
h)] must be avoided for operation. That is, at least the pentode characteristic region [Vds> (Vgs-Vth)] must be operated. Therefore, the Vds of the transistor M5 is limited, and the power supply VCC needs to be set higher than the operating voltage of the light emitting element.

(Reason 2) Even if the transistor M5 is operated in the pentode characteristic region, the transistor M5 requires a larger Vds to avoid the Early effect in which the current driving characteristic varies depending on the Vds value, and the power supply VCC is larger. Need to take.

(Reason 3) The organic EL element has a deterioration characteristic related to the integrated light emission value, the light emitting operation voltage tends to increase, and the power supply VCC needs to be further increased.

Further, since the power supply voltage VCC must be set to be considerably higher than the operating voltage of the light emitting element, the TFT
The amount of heat generated by the power consumption of the circuit section is propagated to the light emitting elements arranged close to each other (up and down or left and right).
In particular, the deterioration of the organic EL element, which is vulnerable to heat, is also promoted.

The present invention has been made in view of the above problems, and it is possible to control the current flowing through the light emitting element more accurately, and further, to drive the light emitting element capable of stable operation by suppressing the power supply voltage as low as possible. The purpose is to provide a circuit.

[0017]

SUMMARY OF THE INVENTION An invention for solving the above problems is to supply a current to at least the light emitting element in a current control type light emitting element drive circuit in which the emission brightness is controlled by the current flowing through the element. A current supply circuit; and a drive control circuit for controlling the current supply circuit, wherein the current supply circuit comprises a supply transistor, a reference transistor,
A first reference switch, a second reference switch, a control switch,
At least a capacitor is formed, the supply transistor and the reference transistor are formed to have the same electrical characteristics, the first terminal of the supply transistor is connected to the first power supply, and the second terminal of the supply transistor is the light emission. Connected to the first terminal of the element and connected to the drive control circuit via the second reference switch, the second terminal of the light emitting element is connected to the second power supply, and the gate terminal of the supply transistor is the reference transistor. Connected to the gate terminal of the capacitor and to the drive control circuit via the control switch and to the first terminal of the capacitor, the second terminal of the capacitor being the first terminal of the supply transistor.
A first terminal of the reference transistor is connected to the first power supply, and a second terminal of the reference transistor is connected to the drive control circuit via the first reference switch. A reference current having the same current value as the injection current supplied to the light emitting element via the supply transistor can be input to the drive control circuit via the reference transistor, and the voltage of the second terminal of the reference transistor can be used. A certain reference terminal voltage can be input to the drive control circuit via the first reference switch, and a supply terminal voltage that is the voltage of the second terminal of the supply transistor is input to the drive control circuit via the second reference switch. The reference current and the reference terminal voltage input via the first reference switch and the second reference switch can be input. Based on the supply terminal voltage that is input by the gate of the supply transistor via the control switch so that the reference current approaches the desired set current value and the reference terminal voltage approaches the supply terminal voltage. It is characterized by having a function of controlling a terminal voltage.

According to the present invention, in the above invention, the drive control circuit allows the first reference switch, the second reference switch, and the control switch to pass through the first reference switch during a period in which all three switches are conductive. Based on the reference current and the reference terminal voltage input via the second reference switch and the supply terminal voltage input via the second reference switch, the reference terminal voltage and the supply terminal are set so that the reference current approaches a desired set current value. As a preferable aspect, it has a function of controlling the gate terminal voltage of the supply transistor via the control switch so that the voltage approaches.

Further, the present invention includes a light emitting system characterized in that at least a plurality of drive circuits for the light emitting element of the present invention are provided.

[0020]

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 the mold, which of the first terminal and the second terminal is the source terminal or the drain terminal is different, but one of the modes will be described below. In addition, the first terminal and the second terminal of the light emitting element and the first terminal and the second terminal of the capacitor respectively represent any one of the two terminals. The polarity and the like may be appropriately selected depending on the circuit configuration.

As the combination of the first power supply and the second power supply, for example, the power supply potential and the ground potential may be used, or both may be the power supply potential, and these may be appropriately selected depending on the design.

[Embodiment 1] FIG. 1 is a circuit diagram of an embodiment of a current supply circuit included in a drive circuit for a light emitting element of the present invention, and FIG. 2 is included in a drive circuit for a light emitting element of the present invention. It is a circuit diagram of a drive control circuit 2a which is an embodiment of a drive control circuit. The display panel system of FIG. 12 is configured using the current supply circuit 1 and the drive control circuit 2a.

(Construction of Current Supply Circuit) In the P-type transistor M5, the source terminal (M5 _S ) is connected to the power supply VCC, and the drain terminal (M5 _D ) is connected to the current injection terminal of the light emitting element whose other terminal is grounded. Gate terminal (M5 _G )
A capacitor C1 having the other end connected to the power supply VCC is connected to the. M5 _G is connected to M4 _{G which} is a P-type transistor whose current drive characteristic is the same as that of M5, and M4 _S is a power supply V
Connected to CC. M5 _G and M4 _G are connected to M1 _D , the control voltage Vd is input to M1 _S , and the selection signal S1 is input to M1 _G. M4 _D is connected to M2a _S
The selection signal S2 is input to 4 _G , and the signal Vs is output to M2a _D. The current injection terminal of the light emitting element and M5 _D are M2
connected to b _D , the selection signal S3 is input to M2b _G ,
The signal Vr is output to M2b _D. Note that M1 and M2b
Although the direction of the current flowing through is not constant, here, for simplicity, the two electrodes serving as the source terminal and the drain terminal are represented as above.

(Structure of Drive Control Circuit) Signal Vr and Signal V
s is input to M7 _G and M9 _G , respectively, and M7 _S and M9 _S are connected, and a current source having twice the set current Idrv for setting the light emission amount of the light emitting element is connected to the connection point. M7 _D is connected to the power supply VDD, and M9 _D is connected to the transistor M8 whose drain and gate are connected. M8 _G and M8 _D are connected to M11 _G , and M11 _S is connected to the power supply VDD. M11 _D is connected to the transistor M12 whose drain and gate are connected, and M12 _S is grounded. M
M10 _G is connected to the 12 _G, M10 _D is connected signal Vs is input to the M9 _G. M12 _G is input to M6 _G ,
M12 _S is connected to VEE, and M12 _D has a set current Id.
rv is connected, and this connection point is a differential voltage amplifier AMP1.
Connected to the negative electrode terminal of. The reference voltage VREF of (1/2) VDD, for example, is input to the positive electrode side of the differential voltage amplifier AMP1, and the control voltage Vd is output to the output terminal. To simplify the explanation here, M7⇔M9, M8⇔M1
Each of the transistor pairs 1 and M6⇔M10⇔M12 has the same current driving characteristic.

(Explanation of Operation) The operation of causing the light emitting element to emit light by using the current supply circuit 1 and the drive control circuit 2a is shown in FIG.
This will be described with reference to FIGS. 7 and 8. Here, as an example, a case where the selection signals S1 to S3 are all the same will be described. In the period T1 (n) in FIG. 8A, the selection signal S (n) on the nth row of the image display unit 4 becomes L level, and the current supply circuit 1 (i to x) on the nth row is set to the drive current setting mode. Then, the light emission continuation mode is set in a period other than the period T1 (n). In the period T1 (n + 1) in FIG. 8B, the selection signal S (n + 1) on the (n + 1) th row of the image display unit 4 becomes L level, and the current supply circuit 1 (i on the (n + 1) th row is supplied.
To x) are in the drive current setting mode, and the period T1 (n +
In the period other than 1), the emission continuation mode is set. Period T
1 and the period (T1 + T2) are generally the same for the corresponding row. The row transition period T2 does not have to be provided if there is no problem in operation. In the period T1, the selection signal S (S1 to S
3) goes to L level, so transistors M1 and M2
All of a and M2b are turned on. At this time, the corresponding current supply circuit 1 and drive control circuit 2a are equivalent to the circuit as shown in FIG. At this time, the set current Idrv is equal to the injection current I that determines the light emission amount of the light emitting element of the corresponding current supply circuit 1.
Set a set current Idrv related to r. First, the control voltage Vd is output so that the current flowing through M6 becomes the set current Idrv regardless of the difference between the voltage Vr and the voltage Vs. Next, the sample voltage Vs, which is the drain voltage of the transistor M4 through which the current Is is flowing, operates so as to be substantially equal to the voltage Vr which is the operating voltage Vdrv of the light emitting element, and the transistor M10 with respect to the current Is flowing through the transistor M4. The current flows through M10 so that the currents flowing through the same become equal. The current of M6 changed by this operation is controlled to become the current Idrv again, and the current of M10 that is equal to the current of M6 is the set current Idrv.
It becomes equal to drv. When all the above operations converge,
The current Is becomes equal to the set current Idrv, and the voltage Vs becomes equal to the voltage Vr which is the operating voltage Vdrv of the light emitting element. At this time, since the transistors M4 and M5 operating at the same gate voltage Vg are in the same operating state, the injection current Ir into the light emitting element is equal to the current Is and therefore equal to the set current Idrv. The above operation is the power supply voltage VD
It holds even if D is not equal to the power supply voltage VCC. Further, the transistors M4 and M5 have a pentode region (Vds> Vgs−).
Vth) and the triode region (Vds <Vgs-Vth) are also irrelevant to the operation, and therefore the power supply voltage VCC can be applied to the operating voltage of the light emitting element against the deterioration variation and the variation between the current supply circuits 1. May be kept to a minimum.
The states of the injection current Ir and the operating voltage Vdrv of the light emitting element in the period T1 are shown in FIGS.

Next, when the period T1 ends, the current supply circuit 1 of the corresponding row changes the selection signal S (S1 to S3) from L to H level (FIGS. 8a and 8b).
2a and M2b are all turned off. Therefore, the connection of the drive control circuit 2 is cut off, and the circuit becomes equivalent to the circuit shown in FIG. M
The gate terminal voltage Vg of 4 _G and M5 _G is held, and the current Ir and the current Is are continuously applied to the transistors M5 and M4.
And the light emitting element continues to emit the set light emission. However, M
Since 4 _D is open, M4 _D continues to rise and the transistor M4 enters the resistance region (Vds≈0 v) from the triode region, and the transistor current drive capability disappears, so that M4 _D becomes the power supply VCC and the current Is is reached. Disappears, resulting in the circuit state shown in FIG.

[Second Embodiment] FIG. 3 is a circuit diagram of a drive control circuit 2b which is an embodiment of a drive control circuit included in the drive circuit for a light emitting element of the present invention. Using the drive control circuit of this embodiment, a display panel system similar to that shown in Embodiment 1 can be constructed. The feature of this embodiment is that the voltage Vr is supplied to the differential voltage amplifier AMP via the voltage buffer BUFF1.
1 is input to the positive electrode terminal. With this configuration, when the drive control circuit 2 completes the current setting operation, the transistor M6 and the transistor M10 have the same operating condition, so that the current Is becomes closer to the set current Idrv.
Therefore, the injection current Ir of the light emitting element is also set by the set current Id.
A desired light emission operation can be obtained by approaching rv.

[Third Embodiment] FIG. 4 shows a light emitting device of the present invention.
2 is an embodiment of a drive control circuit included in the drive circuit of FIG.
It is a circuit diagram of a drive control circuit 2c. Drive control circuit of this embodiment
Display panel similar to that shown in the first embodiment
System can be configured. The feature of this form is Transis
Where M16, M17, M18 and M19 are added
Is. M19 is set twice by the setting bias VB
The current Idrv is configured to flow, and M17
Is configured so that the set current Idrv flows. M17_D
And M6_DThe gate and drain are connected to
Have the same current drive characteristics that are connected to the power supply VDD.
Transistors M16 and M18 are connected. Also M
17 _DAnd M6_DIs the positive electrode of the differential voltage amplifier AMP1
It is connected to the terminal and the negative electrode terminal. With this configuration
Conversion of a loop that sets the current of the transistor M6 to Idrv
The gain is mainly determined only by the gain of the differential voltage amplifier AMP1.
Operation of the drive control circuit 2 in the current setting operation
Is guaranteed to be stable.

[Fourth Embodiment] FIG. 5 is a circuit diagram of a drive control circuit 2d which is an embodiment of a drive control circuit included in the drive circuit for a light emitting element of the present invention. Using the drive control circuit of this embodiment, a display panel system similar to that shown in Embodiment 1 can be constructed. The feature of this embodiment is that the configuration is simplified by adding a current mirror by the transistors M20 and M21 and excluding the differential voltage amplifier AMP1.

In the operation described above, M8⇔M11
Each of the transistor pairs of M6⇔M10⇔M12 may have a current driving characteristic of an appropriate ratio.
Further, the transistors M1, M2a and M of the current supply circuit 1
2b only needs to be switched, so the selection signal S
The circuit configuration is not limited as long as 1 to S3 are appropriately input.
The P-type transistors M5 and M4 are N if the connection terminals of the light emitting element are changed and the drive control circuit 2 is configured accordingly.
It is clear that a type transistor can also be used.

[0031]

As described above, when the current supply circuit and the drive control circuit using the light emitting device of the present invention are used in an image display panel or the like, the following effects are obtained.

(Effect 1) The light emitting element of each current supply circuit can perform a stable light emitting operation by the set injection current without being affected by the characteristic value of the TFT of each current supply circuit and the characteristic value variation.

(Effect 2) The light emitting element can perform a stable light emitting operation by the set injection current even with respect to the fluctuation of the driving voltage depending on the operating state of the light emitting element and the variation of the operating voltage between the light emitting elements.

(Effect 3) As a result, the current driving capability of the TFT for driving the light emitting element has a margin as compared with the conventional one, and therefore the transistor size can be remarkably reduced. Can be made smaller.

(Effect 4) Since the power supply voltage for driving the light emitting element can be minimized, the power consumed by the TFT circuit can be suppressed, and the power consumption of the display panel can be saved.

(Effect 5) In addition, by suppressing the electric power consumed by the TFT circuit, heat propagation to the light emitting element is reduced, which is very advantageous in the light emitting element having a characteristic weak against heat.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a current supply circuit included in a drive circuit for a light emitting device of the present invention.

FIG. 2 is a circuit diagram of an embodiment of a drive control circuit included in a drive circuit for a light emitting device of the present invention.

FIG. 3 is a circuit diagram of an embodiment of a drive control circuit included in a drive circuit for a light emitting device of the present invention.

FIG. 4 is a circuit diagram of an embodiment of a drive control circuit included in a drive circuit for a light emitting device of the present invention.

FIG. 5 is a circuit diagram of an embodiment of a drive control circuit included in a drive circuit for a light emitting device of the present invention.

FIG. 6 is a circuit diagram for explaining a continuous light emission operation of the drive circuit for the light emitting element of the present invention.

FIG. 7 is an operation circuit diagram for explaining a light emission continuation operation of a current supply circuit included in a drive circuit for a light emitting element of the present invention.

FIG. 8 is a time chart for explaining the operation of the drive circuit of the light emitting device of the present invention in the form shown in FIG.

FIG. 9 is an example of a current supply circuit included in a conventional drive circuit for a light emitting element.

FIG. 10 is an example of a current supply circuit included in a conventional drive circuit for a light emitting element.

FIG. 11 is an example of a current supply circuit included in a conventional drive circuit for a light emitting element.

FIG. 12 is a conceptual diagram of an image display panel.

[Explanation of symbols]

1 Current supply circuit 2, 2a to 2c, 2i to 2x drive control circuit 3i to 3y row selection circuit 4 Image display section C1 capacitor EL light emitting element Idrv set current Ir injection current Is reference current M1 control switch M2a first reference switch M2b Second reference switch M4 reference transistor M5 supply transistor VCC power supply Vd control voltage Vdrv operating voltage Vg Gate terminal voltage Vs sample voltage GND ground

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 641 G09G 3/20 641D 642 642A H05B 33/14 H05B 33/14 A F term (reference) 3K007 AB02 AB06 AB17 BA06 DA01 DB03 EB00 GA04 5C080 AA06 BB05 DD05 DD22 DD26 EE28 FF11 JJ02 JJ03 JJ04

Claims (3)

[Claims] 1. A drive circuit for a current-controlled light-emitting element, the emission luminance of which is controlled by a current flowing through the element, wherein a current supply circuit for supplying a current to at least the light-emitting element and a drive control for controlling the current supply circuit. A circuit, the current supply circuit includes at least a supply transistor, a reference transistor, a first reference switch, a second reference switch, a control switch, and a capacitor, and the supply transistor and the reference transistor have uniform electrical characteristics. The first terminal of the supply transistor is connected to a first power supply, the second terminal of the supply transistor is connected to the first terminal of the light emitting element, and the drive control is performed via the second reference switch. A second terminal of the light emitting device is connected to a second power source, and a gate terminal of the supply transistor is connected to a circuit. Connected to the gate terminal of the reference transistor and connected to the drive control circuit via the control switch and to the first terminal of the capacitor, the second terminal of the capacitor connected to the first terminal of the supply transistor And the first terminal of the reference transistor is the first terminal
And a second terminal of the reference transistor connected to the drive control circuit via the first reference switch, and an injection current supplied from the first power supply to the light emitting element via the supply transistor. A reference current having the same current value can be input to the drive control circuit via the reference transistor, and a reference terminal voltage, which is a voltage of a second terminal of the reference transistor, can be drive-controlled via the first reference switch. A supply terminal voltage, which is the voltage of the second terminal of the supply transistor, can be input to the drive control circuit via the second reference switch, and the drive control circuit includes the first reference switch. Based on the reference current and the reference terminal voltage input via the second reference switch and the supply terminal voltage input via the second reference switch,
It has a function of controlling the gate terminal voltage of the supply transistor via the control switch so that the reference current approaches a desired set current value and the reference terminal voltage approaches the supply terminal voltage. Light emitting element drive circuit. 2. The drive control circuit includes a reference current input via the first reference switch during a period in which all of the three switches, the first reference switch, the second reference switch, and the control switch are conductive. And based on the reference terminal voltage and the supply terminal voltage input via the second reference switch, the reference current approaches the desired set current value and the reference terminal voltage approaches the supply terminal voltage. The drive circuit for the light emitting element according to claim 1, having a function of controlling a gate terminal voltage of the supply transistor via the control switch. 3. A light emitting system comprising at least a plurality of drive circuits for the light emitting element according to claim 1.