TWI409761B - Light emitting diode driving circuit and driving method therefor, and display device - Google Patents

Abstract

The present invention relates to a light emitting diode (LED) driving circuit including a first through third transistors, a unidirectional conduction device and a capacitor. A control terminal of the first transistor is subjected to the control of a first signal for determining the on/off states of the first transistor. The second transistor is electrically coupled between a power source potential and a LED element and a control terminal of which is for receiving a data signal delivered by the first transistor being on state. A control terminal of the third transistor is subjected to the control of a second signal for determining whether to deliver the power source potential to a first terminal of the capacitor. A second terminal of the capacitor is electrically coupled to the control terminal of the second transistor. The unidirectional conduction device is electrically coupled between the first terminal of the capacitor and a reference signal. The unidirectional conduction device would be disabled in a certain time period resulting from the unidirectional conduction device being reverse-biased caused by the reference signal.

Description

Light-emitting diode driving circuit, driving method thereof and display device

The present invention relates to the field of display technology, and in particular to a light emitting diode driving circuit, a driving method thereof, and a display device.

The light of a light emitting diode (LED) display device generally uses a transistor with a storage capacitor to store a charge to control the brightness performance of the light emitting diode; wherein the light emitting diode system is a current driving component, which is based on The current flowing through is different in magnitude and produces varying degrees of light. Please refer to FIG. 1 , which is a schematic diagram of a single pixel circuit of a conventional LED display device. The pixel circuit 10 includes a light emitting diode driving circuit 12 and an organic light emitting diode 16; the light emitting diode driving circuit 12 controls the brightness performance of the organic light emitting diode 16 and is two A transistor-capacitor (2T1C) architecture. Specifically, the LED driving circuit 12 includes a transistor M1, a transistor M2, and a capacitor C1. The gate of the transistor M1 receives the data signal Vdata due to the electrical coupling relationship, and the gate of the transistor M1 receives the control signal SCAN. Controlling to determine whether to transmit the data signal Vdata to the source of the transistor M1; the gate of the transistor M2 is electrically coupled to the source of the transistor M1, and the source of the transistor M2 is electrically coupled to the power supply potential OVDD The anode of the transistor M2 is electrically coupled to the anode of the organic light-emitting diode 16, and the cathode of the organic light-emitting diode 16 is electrically coupled to another power supply potential OVSS; the two ends of the capacitor C1 are connected across the transistor. Between the gate and source of M2.

However, since the OVDD power lines of the respective pixel circuits of the light-emitting diode display device are connected together, when the organic light-emitting diode 16 emits light, a current flows through the OVDD power supply line. However, since the OVDD power supply line has a metal impedance, a power supply voltage drop (ie, IR Drop) is generated, which causes a difference in the power supply potential OVDD of each pixel circuit. Since the luminance of the organic light-emitting diode 16 is proportional to the magnitude of the current flowing through, and the power supply potential OVDD of each pixel circuit is different, a difference in current between the pixel circuit and the pixel circuit is generated, which is generated. The brightness will be different, which will cause the panel to display unevenly. In addition, due to the influence of the process, the threshold voltages of the transistors of the respective pixel circuits are not completely the same, so that even if the same data signal is given, the current generated by different pixel circuits is still different, which may result in uneven display of the panel. .

It is an object of the present invention to provide a light emitting diode driving circuit to improve the problem of panel display unevenness in the prior art.

It is still another object of the present invention to provide a method of driving a light emitting diode to improve the problem of uneven display of panels in the prior art.

It is still another object of the present invention to provide a display device to improve the problem of uneven display of panels in the prior art.

A light emitting diode driving circuit according to an embodiment of the invention is suitable for driving a light emitting diode. The light emitting diode driving circuit has a plurality of transistors, and each of the transistors includes a control end, a first path end and a second path end. Specifically, the LED driving circuit includes a first transistor, a second transistor, a third transistor, a unidirectional component, and a capacitor. The control end of the first transistor is controlled by the first signal to determine an electrical conduction state between the first path end and the second path end of the first transistor, and the first path end of the first transistor is electrically Receiving a data signal; the control end of the second transistor is electrically coupled to the second path end of the first transistor, and the first path end of the second transistor is electrically coupled to the preset potential, The second path end of the second transistor is electrically coupled to the light emitting diode; the control end of the third transistor is controlled by the second signal to determine between the first path end and the second path end of the third transistor In an electrically conductive state, the first path end of the third transistor is electrically coupled to the predetermined potential; one end of the unidirectional conduction element is electrically coupled to the second path end of the third transistor, and the other end is electrically And receiving the reference signal; the capacitor is electrically coupled between the second path end of the third transistor and the control end of the second transistor. Furthermore, the reference signal will cause the unidirectional conduction element to be non-conducting due to reverse bias during a certain period of time.

In an embodiment of the invention, the unidirectional conduction element is a diode.

In an embodiment of the invention, the unidirectional conduction element is a fourth transistor, and the control end of the fourth transistor receives the reference signal simultaneously with the first path end due to the electrical coupling relationship, and the fourth transistor The second path end is electrically coupled to the second path end of the third transistor.

A method for driving a light-emitting diode according to an embodiment of the present invention is applicable to the above-mentioned light-emitting diode driving circuit. Specifically, the LED driving method includes the steps of: (1) adjusting the first signal, the second signal, and the reference signal to turn on the first transistor and the unidirectional conduction element in the first period, and to enable the third transistor And being unable to conduct; and (2) adjusting the first signal, the second signal, and the reference signal to turn on the third transistor in the second period after the first period of time, and to make the first transistor and the one-way element incapable of being turned on. Among them, in the second period, the unidirectional conduction element is unable to conduct due to the reverse bias.

In an embodiment of the invention, the first signal and the second signal are inverted, and the reference signal is in phase with the second signal.

A display device according to an embodiment of the invention includes a power supply device and a light source. The power supply device is configured to provide power; the light source is electrically coupled to the power supply device to receive power. Specifically, the light source includes at least one light emitting module, and the light emitting module includes a light emitting diode and a light emitting diode driving circuit. The LED driving circuit has a plurality of transistors, each of which includes a control end, a first path end and a second path end. More specifically, the LED driving circuit includes a first transistor, a second transistor, a third transistor, a unidirectional conduction component, and a capacitor; and a control end of the first transistor is controlled by the first signal to determine the first An electrical conduction state between the first path end and the second path end of the transistor, the first path end of the first transistor receives the data signal due to the electrical coupling relationship; the control end of the second transistor is electrically coupled Connected to the second path end of the first transistor, the first path end of the second transistor is electrically coupled to the preset potential provided by the power supply device, and the second path end of the second transistor is electrically coupled to a light-emitting diode; the control end of the third transistor is controlled by the second signal to determine an electrical conduction state between the first path end and the second path end of the third transistor, the first path of the third transistor The terminal is electrically coupled to the preset potential; one end of the unidirectional conduction component is electrically coupled to the second path end of the third transistor, and the other end receives the reference signal due to the electrical coupling relationship; the capacitor is electrically coupled Connected to the second path end and the second of the third transistor Between the control terminal of the crystal. Furthermore, the reference signal will cause the unidirectional conduction element to be non-conducting due to reverse bias during a certain period of time.

In an embodiment of the invention, the unidirectional conduction element of the display device is a diode.

In an embodiment of the invention, the unidirectional conduction component of the display device is a fourth transistor, and the control end of the fourth transistor receives the reference signal simultaneously with the first path end due to the electrical coupling relationship, and the fourth The second via end of the transistor is electrically coupled to the second via end of the third transistor.

In the embodiment of the present invention, the structure of the LED driving circuit is designed such that the LED driving circuit includes a plurality of transistors, and a single-conducting element, such as a diode connected by a diode, through each of the transistors. The specific connection mode and control mode between the transistors and the process based on the adjacent transistor are small and negligible. Before the light-emitting diode, the current flowing through the light-emitting diode and the threshold voltage of the transistor are raised. And the preset potential level is basically irrelevant, so the influence of the process factor and the power supply voltage drop on the current can be suppressed, and the better compensation effect can be achieved, thereby effectively improving the problem of uneven display of the panel in the prior art.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

Referring to FIG. 2, a schematic structural view of a display device related to an embodiment of the present invention is shown. As shown in FIG. 2, the display device 20 includes a power supply device 21 and a light source 23. The power supply device 21 is configured to supply power such as the power supply potentials OVDD and OVSS. The illumination source 23 is electrically coupled to the power supply device 21 to receive the power supply potentials OVDD and OVSS. Specifically, the illumination source 23 includes at least one illumination module 230. This embodiment shows two examples by way of example and not limitation.

Each of the light emitting modules 230 includes a light emitting diode such as an organic light emitting diode 232 and a light emitting diode driving circuit 234. The LED driving circuit 234 includes a plurality of transistors M1, M2, M3, M4 and a capacitor C. In this embodiment, the transistors M1, M2, M3 and M4 are used as switches, and the gate, the drain and the source of each of the transistors M1, M2, M3 and M4 are respectively the control end of the switch and the first path. And a second path end; and the transistors M1, M2, M3 and M4 form a switch module for determining whether current is allowed to flow through the organic light emitting diode 232; further, the transistor M4 is connected by a diode The mode (that is, the gate of the transistor M4 is electrically connected to the source) is provided in the LED driver circuit 234 as a unidirectional conduction element. In addition, the transistors M1 and M3 are N-type transistors, and the transistors M2 and M4 are P-type transistors, but the invention is not limited thereto.

More specifically, the gate of the transistor M1 is controlled by the control signal SCAN to electrically conduct between the drain and the source of the transistor M1, and the drain of the transistor M1 receives the data signal due to the electrical coupling relationship. Vdata. The gate of the transistor M2 is electrically coupled to the source of the transistor M1. The source of the transistor M2 is electrically coupled to the power supply potential OVDD provided by the power supply device 21, and the gate of the transistor M2 is electrically coupled. The anode of the organic light-emitting diode 232 is electrically coupled to another power supply potential OVSS provided by the power supply device 21, where OVDD is greater than OVSS. The gate of the transistor M3 is controlled by the control signal EM to determine the electrical conduction state between the drain and the source of the transistor M3, and the drain of the transistor M3 is electrically coupled to the power supply potential OVDD. The gate of the transistor M4 is electrically coupled to the source of the transistor M3. The gate and the source of the transistor M4 receive the reference signal Vref due to the electrical coupling relationship. The capacitor C is electrically coupled between the source of the transistor M3 and the gate of the transistor M2. Here, the electrical connection point between the capacitor C and the transistor M3 is denoted as node A, and the capacitance of the capacitor C and the transistor M2. The sexual connection point is indicated as node G.

It should be noted that the control signals SCAN, EM, data signal Vdata and reference signal Vref received by the respective illumination modules 230 in FIG. 2 are denoted by the same component symbols, but are not used to limit: at the same time, each illumination mode The control signals SCAN, EM, data signal Vdata and reference signal Vref of group 230 must have the same value.

The specific operation process of any of the LED driving circuits 234 will be described in detail below with reference to FIG. 2 and FIG. 3. FIG. 3 illustrates a plurality of signals SCAN, EM, Vdata, and Vref related to the LED driving circuit 234. Timing diagram.

Specifically, in the T1 period, the control signal SCAN is adjusted to a high level, the control signal EM and the reference signal Vref are both adjusted to a low level and the reference signal Vref is taken as a value V1, and the transistor M1 is in an on state, The crystal M4 (here, the unidirectional conduction element) is also in an on state, and the transistor M3 is in an off state; at this time, the potential at the node A is (V1+Vth4), and the potential at the node G is Vdata, wherein Vth4 is the threshold voltage of the transistor M4.

In the T2 period, the control signal SCAN is adjusted to a low level, the control signal EM and the reference signal Vref are both adjusted to a high level and the reference signal Vref is taken as a value V2 (here, V2 is greater than V1), the transistor M3 In the on state, the transistor M1 is in the off state, and the transistor M4 cannot be turned on due to the reverse bias; at this time, the potential at the node A is OVDD, and the potential at the node G is [Vdata+OVDD-(V1+Vth4). ], the transistor M2 is turned on, and the current flowing through the organic light-emitting diode 232 is Ids=k(Vsg−Vth) ² =k[(V1-Vdata)+(Vth4-Vth)] ² , where k is a constant and Vth is The threshold voltage of the transistor M2. Here, for the transistor M2 and the transistor M4 in the same light-emitting module 230, the process difference based on the adjacent transistor is negligible and can be considered as Vth4=Vth, so Ids=k(V1-Vdata) ² . It can be seen that the current Ids flowing when the organic light-emitting diode 232 is in the light-emitting phase is independent of the threshold voltage of the transistor and the power supply voltage OVDD, and the influence of the process factor and the power supply voltage drop on the current can be eliminated, and the compensation effect is achieved. Further, the problem of display unevenness in the prior art can be effectively improved.

In addition, it can be seen from FIG. 3 that during the operation of the LED driver circuit 234, the control signal SCAN is inverted from the control signal EM, and the reference signal Vref is in phase with the control signal EM.

4(a) and 4(b) are respectively a simulation diagram of the threshold voltage offset compensation effect of the LED driving circuit 12 of FIG. 1 and the LED driver circuit 234 of FIG. 4(a) and 4(b) show the Ids vs. Vdata characteristic curves for the case where the threshold voltage of the transistor M2 is Vth, negative drift to (Vth-0.3), and positive drift to (Vth+0.3). 4(a) and 4(b), the LED driving circuit 234 of the embodiment of the present invention has a better threshold voltage offset compensation effect.

5(a) and 5(b) are respectively a simulation diagram of the power supply voltage drop compensation effect of the LED driving circuit 12 of FIG. 1 and the LED driver circuit 234 of FIG. Figures 5(a) and 5(b) show the Ids vs. Vdata characteristic curves for the power supply potential values of OVDD, 5% change in OVDD, and 10% change in OVDD. It can be seen from FIGS. 5(a) and 5(b) that the LED driving circuit 234 of the embodiment of the present invention has a better power supply voltage drop compensation effect.

In summary, the embodiment of the present invention is designed by arranging the structure of the LED driving circuit so that the LED driving circuit includes a plurality of transistors and a single-conducting element, for example, connected in a diode manner. The transistor, the specific connection mode and the control mode between the respective transistors, and the process based on the adjacent transistor are small, negligible, and the current flowing through the light-emitting diode during the light-emitting phase of the light-emitting diode The threshold voltage of the transistor and the magnitude of the power supply potential are basically independent, so that the influence of the process factor and the power supply voltage drop on the current can be suppressed, and the effect of better compensation can be achieved, thereby effectively improving the problem of uneven display of the panel in the prior art.

In addition, any person skilled in the art can appropriately change the LED driving circuit and the driving method according to the above embodiments of the present invention, for example, changing the transistor M4 in the LED driving circuit 234 to a diode, The anode of the polar body is electrically coupled to the node A, and the cathode of the diode receives the reference signal Vref due to the electrical coupling relationship; the type of the transistor is appropriately changed (P type or N type); and/or each electric power is used The electrical connection between the source and the drain of the crystal is interchanged and the like.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

10. . . Pixel circuit

12. . . Light-emitting diode driving circuit

16. . . Organic light-emitting diode

Vdata. . . Data signal

SCAN. . . Control signal

OVDD, OVSS. . . Power supply potential

M1, M2. . . Transistor

C1. . . capacitance

20. . . Display device

twenty one. . . Power supply unit

twenty three. . . Light source

230. . . Light module

232. . . Organic light-emitting diode

234. . . Light-emitting diode driving circuit

EM. . . Control signal

Vref. . . Reference signal

M3, M4. . . Transistor

C. . . capacitance

A, G. . . node

V1, V2. . . Reference signal value

T1, T2. . . Time slot

1 is a schematic diagram of a single pixel circuit of a conventional light emitting diode display device.

2 is a schematic structural view of a display device related to an embodiment of the present invention.

FIG. 3 is a timing diagram showing a plurality of signals related to the LED driving circuit shown in FIG.

4(a) and 4(b) are respectively a simulation diagram of the threshold voltage offset compensation effect of the LED driving circuit shown in FIG. 1 and the LED driving circuit shown in FIG.

5(a) and 5(b) are respectively a simulation diagram of the power supply voltage drop compensation effect of the LED driving circuit shown in FIG. 1 and the LED driving circuit shown in FIG.

20. . . Display device

twenty one. . . Power supply unit

twenty three. . . Light source

230. . . Light module

232. . . Organic light-emitting diode

234. . . Light-emitting diode driving circuit

M1, M2, M3, M4. . . Transistor

C. . . capacitance

Vdata. . . Data signal

SCAN, EM. . . Control signal

Vref. . . Reference signal

OVDD, OVSS. . . Power supply potential

A, G. . . node

Claims (4)

An LED driving circuit is adapted to drive a light emitting diode. The LED driving circuit has a plurality of transistors. Each of the transistors includes a control end, a first path end and a second path. The LED driving circuit includes: a first transistor, the control end of the first transistor is controlled by a first signal to determine the first path end and the second side of the first transistor An electrical conduction state between the path ends, the first path end of the first transistor receives a data signal due to an electrical coupling relationship; and a second transistor, the control end of the second transistor The first path end of the second transistor is electrically coupled to a predetermined potential, and the second path end of the second transistor is electrically coupled to the second path end of the second transistor. Connected to the light-emitting diode; a third transistor, the control end of the third transistor is controlled by a second signal to determine the first path end and the second path end of the third transistor Electrically conductive state, the first path end of the third transistor is electrically coupled a predetermined potential; a single-conducting component, one end electrically coupled to the second path end of the third transistor, the other end receiving a reference signal due to the electrical coupling relationship; and a capacitor, electrical coupling Connected between the second path end of the third transistor and the control end of the second transistor, wherein the reference signal causes the unidirectional element to be reverse biased during a certain period of time Turning on; wherein the one-way conducting component is a diode. A method for driving a light-emitting diode, which is suitable for use in a light-emitting diode driving circuit according to claim 1, wherein the light-emitting diode driving method package The first signal, the second signal and the reference signal are adjusted to turn on the first transistor and the unidirectional conduction element, and the third transistor is not conductive; and Adjusting the first signal, the second signal, and the reference signal to turn on the third transistor in a second period after the first period, and the first transistor and the unidirectional element are incapable of being turned on, wherein In the second period, the one-way conducting component is incapable of conducting due to reverse bias; wherein the one-way conducting component is a diode. The method of driving the LED according to the second aspect of the invention, wherein the first signal is inverted from the second signal, and the reference signal is in phase with the second signal. A display device includes: a power supply device for providing power; and a light source electrically coupled to the power supply device for receiving power, the light source comprising at least one light emitting module, the light emitting module comprising: a light-emitting diode; and a light-emitting diode driving circuit, wherein the light-emitting diode driving circuit has a plurality of transistors, each of the plurality of transistors respectively including a control end, a first path end and a second path end, The LED driving circuit includes: a first transistor, the control end of the first transistor is controlled by a first signal to determine the first path end and the second path end of the first transistor An electrical conduction state, the first path end of the first transistor receives a data signal due to an electrical coupling relationship; and a second transistor, the control end of the second transistor is electrically coupled To the second pass end of the first transistor, the first of the second transistor The second end of the second transistor is electrically coupled to the light emitting diode; the third transistor is electrically connected to the light emitting diode; the third transistor is electrically coupled to the light emitting diode; The control end of the transistor is controlled by a second signal to determine an electrical conduction state between the first path end and the second path end of the third transistor, the first path of the third transistor The terminal is electrically coupled to the predetermined potential; a single-conducting component is electrically coupled to the second path end of the third transistor, and the other end receives a reference signal due to the electrical coupling relationship; a capacitor electrically coupled between the second path end of the third transistor and the control end of the second transistor, wherein the reference signal causes the one-way element to be in a certain period of time Reverse biased without conduction; wherein the unidirectional conduction element is a diode.