CN101793370A - Light emitting module, driving method of diode and display device - Google Patents

Abstract

The invention discloses a light emitting module, a driving method of a diode and a display device. Wherein the light emitting module includes a light emitting diode, a driving circuit and a drain transistor. The cathode of the LED is electrically coupled to a first potential, and the anode thereof is electrically coupled to the driving circuit. Accordingly, the driving circuit can provide a driving current to the LED. In addition, the drain transistor includes a control terminal, a first access terminal and a second access terminal. Wherein, the first control terminal of the drainage transistor can control the degree of electrical conduction between the first access terminal and the second access terminal of the drainage transistor. The first channel end of the drain transistor is electrically coupled to the anode of the LED, and the second channel end of the drain transistor is electrically coupled to a second potential. In particular, both the above-mentioned first potential and the second potential are fixed potentials, and the first potential is different from the second potential.

Description

Light emitting module, driving method of diode and display device

technical field

The present invention relates to a pixel circuit of a display, and in particular to a pixel circuit of an active organic electroluminescent display.

Background technique

Organic Light Emitting Diode (OLED) displays have the advantages of high brightness, fast screen response, light and small size, full color, no viewing angle difference, no need for LCD-like backlight, and saving light source and power consumption. Therefore, organic light-emitting diodes have a tendency to replace twisted nematic (Twist Nematic; TN) and super twisted nematic (Super Twist Nematic; STN) liquid crystal displays, and further replace small-sized thin film transistor liquid crystal displays (TFT-LCD) , and become a display material commonly used in a new generation of portable information products, mobile phones, personal digital processors and portable computers.

Organic light emitting diode displays can be divided into passive organic light emitting diode (Passive Matrix OLED, PMOLED for short) display and active organic light emitting diode (Active Matrix OLED, AMOLED for short) display according to the driving method. Among them, the AMOLED display uses a thin film transistor (Thin Film Transistor, TFT) with a capacitor to store signals to control the brightness and grayscale performance of the OLED. Since the OLED does not need to be driven to a very high brightness in the active driving mode, it can achieve better life performance and high resolution requirements.

Generally speaking, the pixel operation of an AMOLED display can be divided into a discharge operation period, a write operation period and a light emission operation period. During the discharge operation period, the charge originally stored in the storage capacitor in the pixel of the AMOLED display is released, so that the potential of a new data signal is stored in the storage capacitor during the next data write operation period. Then, during the light-emitting operation period, the transistors in the pixels of the AMOLED display will generate a driving current according to the potential of the storage capacitor, and drive the OLED to emit light.

In the known AMOLED display, during the discharge operation period, the transistors in the pixels also generate a current due to the discharged charges, and this current may be referred to as a leakage current. The generation of leakage current will drive the OLED in the pixel to emit light when it should be in a dark state.

Contents of the invention

Therefore, the present invention provides a light-emitting module, a method for driving a light-emitting diode, and a display device, which can effectively block the leakage current during the discharge operation and solve the problem of false light emission.

The invention provides a light-emitting module, which includes a light-emitting diode, a driving circuit and a drain transistor. The cathode of the LED is electrically coupled to the first potential, and the anode thereof is electrically coupled to the driving circuit. In this way, the driving circuit can provide driving current to the LED. In addition, the drain transistor includes a control terminal, a first access terminal and a second access terminal. Wherein, the first control terminal of the drainage transistor can control the degree of electrical conduction between the first access terminal and the second access terminal of the drainage transistor. The first channel end of the drain transistor is electrically coupled to the anode of the LED, and the second channel end of the drain transistor is electrically coupled to a second potential. In particular, both the above-mentioned first potential and the second potential are fixed potentials, and the first potential is different from the second potential.

In an embodiment of the present invention, when the drain transistor is turned on, the sum of the absolute value of the voltage between the first access terminal and the second access terminal and the second potential will be smaller than the first potential and the start-up voltage of the light emitting diode ( on-voltage) and.

From another point of view, the present invention also provides a driving method of a light-emitting diode, including providing a driving circuit for electrically coupling to the anode of the light-emitting diode, so as to drive the light-emitting diode in due course, and the driving method of the present invention also The anode of the LED is electrically coupled to a fixed second potential through a switch. Wherein, the first potential is different from the second potential. In addition, during the operation of the driving circuit, the light emitting diode is in an off-state by turning on the switch for a part of the time period.

From another point of view, the present invention further provides a display device, including a power supply device and a light source. The power supply device can provide power to the light emitting source, and the light emitting source includes at least one light emitting module. The light emitting module includes a light emitting diode, a driving circuit and a drain transistor. The cathode of the LED is electrically coupled to a first potential, and the anode thereof is electrically coupled to the driving circuit. Accordingly, the driving circuit can provide a driving current to the LED. In addition, the drain transistor includes a control terminal, a first access terminal and a second access terminal. Wherein, the first control terminal of the drainage transistor can control the degree of electrical conduction between the first access terminal and the second access terminal of the drainage transistor. The first channel end of the drain transistor is electrically coupled to the anode of the LED, and the second channel end of the drain transistor is electrically coupled to a second potential. In particular, both the above-mentioned first potential and the second potential are fixed potentials, and the first potential is different from the second potential.

Since the present invention electrically couples the anode of the light emitting diode to a drain transistor, it can effectively block the influence of the leakage current on the light emitting diode, thereby avoiding false lighting.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments are described in detail together with the accompanying drawings.

Description of drawings

FIG. 1 is a system block diagram of a display device according to a preferred embodiment of the present invention;

FIG. 2 is a circuit block diagram of a preferred lighting module according to the present invention;

FIG. 3 is a flow chart illustrating the steps of an operation method of a light emitting diode according to a preferred embodiment of the present invention;

FIG. 4 is a circuit diagram of a light emitting module according to the first embodiment of the present invention;

FIG. 5 is a timing diagram of a control signal according to the first embodiment of the present invention;

FIG. 6 is a circuit diagram of a light emitting module according to a second embodiment of the present invention;

FIG. 7 is a timing diagram of a control signal according to a second embodiment of the present invention.

Among them, reference signs

100: Display device 102: Power supply device

104: Light source 110: Light module

112: LED 202: Drive circuit

204: switch 402, 404, 406, 408, 410, 422: transistor

412: capacitor P1: discharge operation cycle

P2, P3: Write operation cycle P4: Lighting operation cycle

PA1: path V_Data: data signal

VN1, VN2, VEM: Control signal Vref1, Vref2, VDD, VSS: Operating voltage

S302, S304, S306, S308: Step flow of the operation method of the light emitting diode

Detailed ways

The main spirit of the present invention is to provide a drainage channel during the discharge operation period of the display to divert the leakage current caused by the discharge charge to other places instead of passing through the LED. In this way, the problem of false light emission can be solved.

FIG. 1 is a system block diagram of a display device according to a preferred embodiment of the present invention. Referring to FIG. 1 , a display device 100 provided in this embodiment includes a power supply device 102 and a light source 104 . Wherein, the power supply device 102 is electrically coupled to the light emitting source 104 to supply the required power, such as operating voltages Vref1 , Vref2 , VDD and VSS.

Please continue to refer to FIG. 1 , the light emitting source 104 has at least one light emitting module, and in this embodiment, the light emitting source 104 has a plurality of light emitting modules 110 , and these light emitting modules 110 are arranged in an array. In essence, each light emitting module 110 in the light emitting source 104 is a pixel respectively. In addition, each light emitting module 110 has a light emitting diode 112 respectively. When each LED 112 is driven by the corresponding driving current, it will be lighted up respectively. The gray scale of each pixel is related to the magnitude of the driving current driving each light emitting diode. In some embodiments, these light emitting diodes 112 can be implemented using organic light emitting diodes.

FIG. 2 is a circuit block diagram of a preferred light-emitting module according to the present invention; FIG. 3 is a flow chart showing the steps of an operation method of a light-emitting diode according to a preferred embodiment of the present invention. Please refer to FIG. 2 and FIG. 3 together. In the light emitting module 110 , as described in step S302 , a driving circuit 202 may be provided, which may be electrically coupled to the anode of the light emitting diode 112 and may drive it timely. In this embodiment, the driving circuit can receive the power output by the power supply device 102 in FIG. 1 , such as the working voltage Vref1 . In addition, the driving circuit 202 can also receive a data signal V_Data, and can receive multiple control signals, such as control signals VN1 , VN2 and VEM.

Next, as described in step S304 , the cathode of the LED can be electrically coupled to the working voltage VSS. In this embodiment, the voltage signal VSS has a fixed first potential. On the other hand, the anode of the LED 112 can also be electrically coupled to the working voltage Vref2 through a switch 204 as described in step S306 . Wherein, the working voltage Vref2 has a fixed second potential, and the second potential is different from the first potential. In particular, the sum of the absolute value of the voltage at both ends of the switch and the second potential is smaller than the sum of the first potential and the start-up voltage of the light emitting diode.

In addition, the operation of the switch 204 can be as described in step S308 , during the operation of the driving circuit 202 , during a part of the period, such as the discharge operation period, the switch 204 is turned on to make the LED 112 turn off. In this way, during the discharge operation period, if the driving circuit 202 generates leakage current, the leakage current can pass through the LED 112 due to the conduction of the switch 204 .

first embodiment

FIG. 4 is a circuit diagram of a light emitting module according to an embodiment of the present invention. Referring to FIG. 4 , in this embodiment, the driving circuit 202 includes a first transistor 402 , a second transistor 404 , a third transistor 406 , a fourth transistor 408 , a fifth transistor 410 and a capacitor 412 . The first channel terminal of the first transistor 402 is electrically coupled to the data signal V_Data, and its control terminal is controlled by the first control signal VN1. In addition, the second pass terminal of the first transistor 402 is electrically coupled to the control terminal of the second transistor 404 through the capacitor 412 , and the second pass terminal of the first transistor 402 is also electrically coupled to the control terminal of the fourth transistor 408 first access end. The second channel end and the control end of the fourth transistor 408 are respectively electrically coupled to the operating voltage Vref1 and the third control signal VEM.

A first pass terminal of the second transistor 404 is electrically coupled to the working voltage VDD, and a second pass terminal thereof is electrically coupled to first pass terminals of the third transistor 406 and the fifth transistor 410 . Wherein, the control terminal of the third transistor is electrically connected to the second control signal VN2 , and its second pass terminal is electrically coupled to the control terminal of the second transistor 404 . On the other hand, the control terminal of the fifth transistor 410 is electrically coupled to the control signal VEM, and the second channel terminal thereof is electrically coupled to the anode of the light emitting diode 112 .

Please continue to refer to FIG. 4 , the switch 204 can also be implemented by a drain transistor 422 . The first channel end of the drain transistor 422 is electrically coupled to the anode of the LED 112 , and the control end and the second channel end of the drain transistor are respectively electrically coupled to the second control signal VN2 and the operating voltage Vref2 . In this way, the conduction degree of the first channel terminal and the second channel terminal of the drain transistor 422 is determined by the potential of the control terminal of the drain transistor 422 . In particular, when the drain transistor 422 is turned on, the sum of the absolute value of the voltage between the first pass terminal and the second pass terminal of the drain transistor and the second potential of the working voltage Vref2 will be smaller than the first potential of the working voltage Vref1 and the sum of the start-up voltage of the LED 112.

In this embodiment, the transistors 402, 404, 406, 408, 410 and 422 may all be PMOS transistors. Taking the PMOS transistor as an example, the timing sequence of the control signal in FIG. 4 will be described below.

FIG. 5 is a timing diagram of a control signal according to the first embodiment of the present invention. Please refer to FIG. 4 and FIG. 5 together. During the discharge operation period P1, the first control signal VN1 is in a high state, while the second control signal VN2 and the third control signal VEM are both in a low state, thus causing the first transistor 402 to be turned off. And the third transistor 406 , the fourth transistor 408 , the fifth transistor 410 and the drain transistor 422 are all turned on. At this time, the charge originally stored in the capacitor 412 will be released along the path PA1 from the third transistor 406 to the fifth transistor 410 , thus generating a current on the path PA1 . At this time, since the sum of the absolute value of the voltage between the first and second access terminals of the drain transistor 422 and the second potential of the operating voltage Vref2 is smaller than the sum of the first potential of the operating voltage Vref1 and the start-up voltage of the light emitting diode And, therefore, the LED 112 is not turned on. In other words, the current generated on the path PA1 will pass through the LED 112 and flow through the drain transistor 422 at this moment. Therefore, the situation of erroneous light emission does not occur.

During the previous write operation period P2, the first control signal VN1 is switched to a low state; the second control signal VN2 is maintained at a low state; and the third control signal VEM is switched to a high state. Therefore, the first transistor 402, the third transistor 406, and the drain transistor 422 are all turned on, while the fourth transistor 408 and the fifth transistor 410 are turned off. At this time, the data signal V_Data is input to the light emitting module 110 from the first channel end of the first transistor 402 , and the capacitor 412 stores the potential of the data signal V_Data from the second channel end of the first transistor 402 .

Next, during the subsequent write operation period P3, the first control signal VN1 and the third control signal VEM will maintain their original states, while the second control signal VN2 will switch from a low state to a high state, thus causing the third transistor 406 and drain transistor 422 will be turned off. This makes the potential stored in the capacitor 412 be locked at the potential of the data signal V_Data.

During the light-emitting operation period P4, the first control signal VN1 and the third control signal VEM are respectively switched to a high state and a low state, while the second control signal VN2 is maintained at a high state. Therefore, the first transistor 402 , the third transistor 406 and the drain transistor 422 are turned off, while the fourth transistor 408 and the fifth transistor 410 are turned on. At this time, the second transistor 404 generates a driving current due to the charge stored in the capacitor 412 , and the driving current passes through the fifth transistor 410 to drive the LED 112 to emit light.

It can be found from FIG. 5 that the first control signal VN1 and the third control signal VEM are opposite to each other. Therefore, utilizing this characteristic, the first control signal VN1 and the third control signal VEM can replace each other. The following discloses another embodiment to illustrate how to use fewer control signals to control the driving circuit 202 .

second embodiment

FIG. 6 is a circuit diagram of a light emitting module according to a second embodiment of the present invention. Please refer to FIG. 6, the difference between this embodiment and the first embodiment is that the fourth transistor 408 and the fifth transistor 410 can be realized by using NMOS transistors, and the first transistor 402, the second transistor 406, the third transistor 408 and The drain transistor 422 is also implemented by a PMOS transistor. In this way, the first control signal VN1 can replace the third control signal VEM in the first embodiment and be sent to the control terminals of the fourth transistor 408 and the fifth transistor 410 to control their states.

FIG. 7 is a timing diagram of a control signal according to a second embodiment of the present invention. Please refer to FIG. 7 , those skilled in the art can deduce the operation steps of the light emitting module 110 in FIG. 6 from the content of the first embodiment according to the timing sequence of the control signal shown in FIG. 7 , so no more details are given.

third embodiment

Please continue to refer to FIG. 6 and FIG. 7. In the third embodiment, the first transistor 402, the third transistor 406, and the drain transistor 422 in the driving circuit 202 can be realized by using NMOS transistors, while the second transistor 404 and the fourth transistor 408 and the fifth transistor 410 can be realized by using PMOS transistors. In this way, those skilled in the art can apply to the driving circuit 202 in the third embodiment only by inverting the timing of the control signal in FIG. 7 .

To sum up, in the present invention, the anode of the LED 112 is coupled to the fixed second potential through a switch, and the switch is turned on during the discharge operation period. Therefore, the present invention can make the leakage current flow along the path where the switch is turned on, and pass through the LED 112, so as to solve the problem of false lighting.

Certainly, the present invention also can have other multiple embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding Changes and deformations should belong to the scope of protection of the appended claims of the present invention.

Claims (10)

1. a light emitting module is characterized in that, comprising:

One light emitting diode, the negative electrode of this light emitting diode are electrically coupled to one first current potential;

One drive circuit, the anode that is electrically coupled to this light emitting diode is to provide a drive current to this light emitting diode; And

One drainage transistor, comprise control end, first path terminal and alternate path end, transistorized first control end of this drainage is controlled the degree that electrically conducts between transistorized first path terminal of this drainage and the alternate path end, transistorized first path terminal of this drainage is electrically coupled to the anode of this light emitting diode, the transistorized alternate path end of this drainage is electrically coupled to one second current potential

Wherein, this first current potential and this second current potential are all fixed potential, and this first current potential is different with this second current potential.

2. light emitting module according to claim 1, it is characterized in that, absolute value of voltage between transistorized first path terminal of this drainage during this drainage transistor turns and the alternate path end and this second current potential and, less than the starting resistor of this first current potential and this light emitting diode with.

3. light emitting module according to claim 1 is characterized in that, a plurality of transistors are arranged in this drive circuit, and each these transistor comprises control end, first path terminal and alternate path end separately, and this drive circuit comprises:

One the first transistor, the control end of this first transistor is subjected to the control of one first control signal, and first path terminal of this first transistor is electrically coupled to a data-signal;

One transistor seconds, first path terminal of this transistor seconds is electrically coupled to an operating potential;

One the 3rd transistor, the 3rd transistorized control end is subjected to the control of one second control signal, the 3rd transistorized first path terminal is electrically coupled to the alternate path end of transistor seconds, and the 3rd transistorized alternate path end is electrically coupled to the control end of this transistor seconds;

One the 4th transistor, the 4th transistorized control end is subjected to the control of one the 3rd control signal, the 4th transistorized first path terminal is electrically coupled to the alternate path end of this first transistor, and the 4th transistorized alternate path end is electrically coupled to one the 3rd current potential;

One the 5th transistor, the 5th transistorized control end is subjected to the control of the 3rd control signal, the 5th transistorized first path terminal is electrically coupled to the alternate path end of this transistor seconds, and the 5th transistorized alternate path end is electrically coupled to the anode of this light emitting diode; And

One electric capacity, first end of this electric capacity are electrically coupled to the 4th transistorized first path terminal, and second end of this electric capacity is electrically coupled to the control end of this transistor seconds.

4. light emitting module according to claim 3 is characterized in that, this first transistor, this transistor seconds, the 3rd transistor, the 4th transistor, this drainage transistor of the 5th transistor AND gate are all the P transistor npn npn.

5. light emitting module according to claim 3 is characterized in that, this first transistor, this transistor seconds, this drainage transistor of the 3rd transistor AND gate are the P transistor npn npn, and the 4th transistor AND gate the 5th transistor is the N transistor npn npn.

6. light emitting module according to claim 3 is characterized in that, this first transistor, this drainage transistor of the 3rd transistor AND gate are the N transistor npn npn, and this transistor seconds, the 4th transistor AND gate the 5th transistor are the P transistor npn npn.

7. a LED driving method is applicable to drive a light emitting diode, it is characterized in that this LED driving method comprises:

Provide anode that one drive circuit is electrically coupled to this light emitting diode with this light emitting diode of in good time driving;

Make the negative electrode of this light emitting diode be electrically coupled to one first fixing current potential;

Make the anode of this light emitting diode be electrically coupled to one second fixing current potential by a switch, this first current potential is different with this second current potential; And

In this drive circuit operating period, make this light emitting diode present closed condition by this switch of conducting in the period in part.

8. LED driving method according to claim 7 is characterized in that, the absolute value of voltage of this switch ends and this second current potential and, less than the starting resistor of this first current potential and this light emitting diode with.

9. a display unit is characterized in that, comprising:

One power supply device is in order to provide electric power; And

One light emitting source is electrically coupled to this power supply device to accept electric power, and this light emitting source comprises at least one light emitting module, and this light emitting module comprises:

One light emitting diode, the negative electrode of this light emitting diode are electrically coupled to one first current potential;

One drive circuit, the anode that is electrically coupled to this light emitting diode is to provide a drive current to this light emitting diode; And

One drainage transistor, comprise control end, first path terminal and alternate path end, transistorized first control end of this drainage is controlled the degree that electrically conducts between transistorized first path terminal of this drainage and the alternate path end, transistorized first path terminal of this drainage is electrically coupled to the anode of this light emitting diode, and the transistorized alternate path end of this drainage is electrically coupled to one second current potential

Wherein, this first current potential and this second current potential are all fixed potential, and this first current potential is different with this second current potential.

10. display unit according to claim 9, it is characterized in that, absolute value of voltage between transistorized first path terminal of this drainage during this drainage transistor turns and the alternate path end and this second current potential and, less than the starting resistor of this first current potential and this light emitting diode with.

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