TW201629935A - Light emitting diode pixel circuit and light emitting diode display - Google Patents

Abstract

A light emitting diode (LED) pixel circuit, disposed on an LED display is disclosed. The LED display includes a plurality of scan lines and a plurality of data lines. The LED pixel circuit includes a first transistor, including a gate coupled to a scan line of the plurality of scan lines, a first electrode coupled to a data line of the plurality of data lines, and a second electrode; a second transistor, including a gate and an electrode; a voltage control pulse width modulation module, coupled between the second electrode of the first transistor and the gate of the second transistor; and a lighting module, coupled to the electrode of the second transistor, the lighting module including an LED; and a constant current device, coupled to the LED, configured to drive the LED.

Description

Light-emitting diode pixel circuit and light-emitting diode display

The invention provides a light-emitting diode pixel circuit and a light-emitting diode display, in particular to a light-emitting diode pixel circuit and a light-emitting diode display which can produce uniform brightness and correctly display gray scale effects.

With the advancement of technology, various display products have been developed on the market, such as Liquid Crystal Display (LCD), Plasma Display Panel (PDP), and Light Emitting Diode (Light Emitting Diode). Display, LED display), etc. Among them, the light-emitting diode display has the advantages of high luminous efficiency, long life and low energy consumption, and has been widely applied to outdoor display cards and large outdoor billboards, and also exists in home television or computer displays.

In the prior art, the problem of uneven brightness is ubiquitous in a light-emitting diode display. Specifically, please refer to FIG. 1 , which is a schematic diagram of a conventional light-emitting diode pixel circuit 100 . The illuminating diode circuit 100 is coupled to a scan line SL1 and a data line DL1, and includes a first transistor Q1, a second transistor Q2, a storage capacitor C, and a light-emitting diode D1. When the scan line SL1 is selected and the first transistor Q1 is turned on, the second transistor Q2 drives a current ID1 according to a data line voltage Vdata1, and the current ID1 flows through the light-emitting diode D1 and is related to the brightness of the light-emitting diode D1. The light emitting diode pixel circuit 100 can display different gray level effects according to the data line voltage Vdata. However, the current ID1 is easily changed by the forward grading voltage Vf of one of the illuminating diodes D1, so that the illuminating diode pixel circuit 100 displays different brightness. The problem of uneven brightness. In detail, please continue to refer to FIG. 2 and FIG. 3, and FIG. 2 is a schematic diagram showing the relationship between the brightness of the light-emitting diode D1 and the current flowing through the light-emitting diode D1, and FIG. 3 is the light-emitting diode D1. A schematic diagram of the relationship between the current ID1 and the forward voltage Vf. As shown in Fig. 2, the luminance generated by the light-emitting diode D1 exhibits a linear relationship with the current flowing through the light-emitting diode D1. However, as shown in FIG. 3, the current ID1 flowing through the LED D1 exhibits a nonlinear relationship with the forward voltage Vf. Therefore, when the LED D1 is turned on, the forward biasing Vf slightly shifts. , the current ID1 flowing through the light-emitting diode D1 can be drastically changed. Among them, the forward voltage Vf is susceptible to the line impedance of the LED display, and the brightness of the LED D1 changes accordingly, so that the LED display exhibits uneven brightness.

In addition, the threshold voltage of the second transistor Q2 drifts due to process factors, thereby affecting the current ID1. In other words, even if the data line DL1 drives different pixel circuits with the same voltage, different pixels The circuit also generates different current outputs due to the inconsistent voltage of the second transistor Q2, so that the light-emitting diode D1 in each pixel circuit cannot correctly display the gray-scale effect, resulting in uneven brightness, which is serious. Affects the display quality of the entire screen.

Therefore, how to make each pixel circuit in the LED display display uniform brightness and correctly display the gray scale effect has become one of the goals of the industry.

Accordingly, it is a primary object of the present invention to provide a light emitting diode pixel circuit and a light emitting diode display that can display uniform brightness and correctly display gray scale effects.

The invention discloses a light-emitting diode pixel circuit, which is disposed on a light-emitting diode display, the light-emitting diode display comprises a plurality of scan lines and a plurality of data lines, and the light-emitting diode pixel circuit comprises a first The transistor includes a gate coupled to the scan of the plurality of scan lines a first electrode is coupled to one of the plurality of data lines and a second electrode; a second transistor includes a gate and an electrode; and a voltage controlled pulse modulation module coupled The second electrode of the first transistor and the gate of the second transistor; and a light emitting module coupled to the electrode of the second transistor, the light emitting module includes: a light emitting And a certain current device coupled to the light emitting diode for driving the light emitting diode.

The invention further discloses a light emitting diode display comprising a plurality of scan lines; a plurality of data lines perpendicular to the plurality of scan lines; and a plurality of light emitting diode pixel circuits, each of the light emitting diode pixels The circuit is coupled to the scan line of the plurality of scan lines and the data line of the plurality of data lines. Each of the LED pixels includes a first transistor, and a gate is coupled to the scan. a first electrode is coupled to the data line and a second electrode; a second transistor includes a gate and an electrode; and a voltage-controlled pulse wave modulation module coupled to the first electrode The second electrode of the crystal and the gate of the second transistor; and a light emitting module coupled to the electrode of the second transistor, the light emitting module includes a light emitting diode; and a current device The light emitting diode is coupled to the light emitting diode for driving the light emitting diode.

100, 400, 500, 600, 700‧‧‧Lighting diode circuit

402, 602‧‧‧Light Module

T1, T2, Q1, Q2‧‧‧ transistors

D, D1‧‧‧Lighting diode

VCP‧‧‧Variable Pulse Modulation Module

CC‧‧‧ constant current device

SL, SL1‧‧‧ scan line

DL, DL1‧‧‧ data line

Vdata‧‧‧ data line voltage

V _DD ‧‧‧positive voltage

Vf‧‧‧ 顺 压

C _S , C‧‧‧ storage capacitor

ID1, ID4, ID5, ID6, ID7‧‧‧ Current

Figure 1 is a schematic diagram of a conventional light-emitting diode pixel circuit.

Figure 2 is a schematic diagram showing the relationship between luminance and current of a light-emitting diode.

Figure 3 is a schematic diagram of the relationship between the current and the forward voltage of the light-emitting diode.

4A is a schematic view of a light emitting diode display according to an embodiment of the present invention.

Figure 4B is a schematic diagram of a light-emitting diode pixel circuit of Figure 4A.

FIG. 5 is a schematic diagram of a light emitting diode pixel circuit according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of a light emitting diode pixel circuit according to an embodiment of the present invention.

FIG. 7 is a schematic diagram of a light-emitting diode pixel circuit according to an embodiment of the present invention.

Please refer to FIG. 4A and FIG. 4B , FIG. 4A is a schematic diagram of a light-emitting diode display 40 according to an embodiment of the present invention, and FIG. 4B is a schematic diagram of a light-emitting diode pixel circuit 400 of the light-emitting diode display 40 . . The LED display 40 is provided with a plurality of LED pixels 400, a plurality of data lines DL, and a plurality of scan lines SL perpendicular to the data lines DL. The intersections of the data lines DL and the scan lines SL are connected. There is a light emitting diode pixel circuit 400. For convenience of description, only one light-emitting diode pixel circuit 400 is shown in FIG. 4A. Actually, a light-emitting diode painting is disposed at the intersection of each of the data lines DL and the scanning lines SL in the light-emitting diode display 40. The pixel circuit 400 is coupled to the corresponding data line DL and the scan line SL, that is, the light-emitting diode pixel circuit 400 is distributed on the LED display 40 in a matrix form. The LED device 400 includes a first transistor T1, a second transistor T2, a storage capacitor C _S , a voltage-controlled pulse modulation module VCP, and a light-emitting module 402. A gate of the first transistor T1 is coupled to the scan line SL, and one electrode of the first transistor T1 is coupled to the data line DL, and the other electrode of the first transistor T1 is coupled to the voltage-controlled pulse modulation mode. The group VCP is coupled to the storage capacitor C _S , and the voltage-controlled pulse modulation module VCP is coupled to one of the gates of the second transistor T2 . The light emitting module 402 is coupled between a drain of the second transistor T2 and a positive voltage V _DD . The light emitting module 402 includes a light emitting diode D and a constant current device CC. The constant current device CC is a constant current source, which can generate a fixed current ID4 to drive the light-emitting diode D. When the second transistor T2 is turned on, the light-emitting diode D generates a fixed brightness LI.

Specifically, when the scan line SL is selected, the first transistor T1 is turned on and a data line voltage Vdata is transmitted to the voltage-controlled pulse wave modulation module VCP, and the voltage-controlled pulse wave modulation module VCP is one. Voltage-Controlled Pulse Width Modulator, voltage-controlled pulse width modulator converts input signals into pulse signals of different duty ratios, voltage control pulse width modulation The transformers are well known in the art and the details of their operation are not described herein. Specifically, the voltage-controlled pulse wave modulation module VCP generates a pulse wave signal corresponding to the voltage Vdata according to the voltage Vdata, and transmits the pulse wave signal to the gate of the second transistor T2, thereby controlling the second transistor. The conduction state of T2 is to adjust the gray scale effect of the LED pixel circuit 400. In detail, the voltage Vdata is related to the input voltage Vin of one of the voltage-controlled pulse wave modulation modules VCP, assuming that the minimum value of the input voltage Vin is 0V and the maximum value is V _M , when the voltage-controlled pulse wave modulation module VCP When an input voltage is 0.1V _M , the VCP output of the voltage-controlled pulse modulation module has a pulse signal with a 10% empty ratio. When the input voltage of the VCP of the voltage-controlled pulse modulation module is 0.9V _M , The VCP output of the voltage-controlled pulse wave modulation module has a 90% pulse signal, and so on. The VCP pulse-modulation module VCP can generate a pulse with a voltage ratio corresponding to the voltage Vdata according to the voltage Vdata. Wave signal.

After the pulse signal is output to the gate of the second transistor T2, the pulse signal can control the conduction state of the second transistor T2. For example, when the pulse wave signal with 20% empty ratio is transmitted to the gate of the second transistor T2 when the pulse ratio of 20% is transmitted, only 20% of the pulse wave is in one pulse period. The second transistor T2 is turned on, and the second transistor T2 is turned off in the remaining 80% of the pulse period. In other words, only 20% of the pulse period LEDs are bright (ie, the light is two) The polar body D conducts and produces a fixed brightness LI), and the remaining 80% of the pulse period is dark (ie, the light-emitting diode D is off). When the pulse wave period is less than a specific period (ie, the pulse wave frequency is greater than a specific frequency), the human eye cannot detect the transition between the light and dark diodes D, and the brightness is approximately perceived by the human eye at this time. It is 20% of the brightness LI. Similarly, when the pulse signal of 80% of the air ratio is transmitted to the gate of the second transistor T2, the brightness perceived by the human eye is about 80% of the brightness LI. In other words, the gray scale effect of the LED pixel circuit 400 may depend on the space ratio of the pulse signal outputted by the voltage controlled pulse modulation module VCP, so that the LED is illuminated. The circuit 400 can generate a pulse wave signal having a space ratio corresponding to the voltage Vdata by using the voltage-controlled pulse wave modulation module VCP according to the voltage Vdata of the data line DL, and control the conduction of the second transistor T2 and the light-emitting diode D. The state is to adjust the gray scale effect of the LED pixel circuit 400.

In the prior art, as in the light-emitting diode pixel circuit 100 of FIG. 1, the light-emitting diode pixel circuit 100 controls the second transistor Q2 according to the data line voltage Vdata1, and the second transistor Q2 drives the light-emitting diode 2 The current ID1 of the polar body D1 is used to display different gray scale effects. However, the light-emitting diode D1 is liable to cause a change in the current ID1 flowing through the light-emitting diode D1 due to line impedance or process factors, thereby causing the light-emitting diode to be changed. D1 displays different brightness, causing the LED display to display uneven brightness. In contrast, the present invention uses a constant current device to generate a fixed current to drive the light emitting diode, so that the light emitting diode displays uniform brightness, and then uses the voltage controlled pulse wave modulation module to convert the data line voltage into different air gaps. The pulse signal of the ratio is adjusted to adjust the gray scale effect of the LED pixel circuit, so that the LED display can display uniform brightness and correctly display the gray scale effect.

It is to be noted that the foregoing embodiments are intended to illustrate the concept of the present invention, and those skilled in the art can make various modifications without limitation thereto. For example, please refer to FIG. 5. FIG. 5 is a schematic diagram of a light emitting diode pixel circuit 500 according to an embodiment of the present invention. The light-emitting diode pixel circuit 500 is similar in structure to the light-emitting diode pixel circuit 400, so the same elements follow the same symbols. The light-emitting module 402 is coupled between a source of the second transistor T2 and a ground, and the constant current device CC in the light-emitting module 402 can still generate a light-emitting module 402. Fixing the current ID5 to drive the light-emitting diode D to produce a fixed brightness of the light-emitting diode D also meets the requirements of the present invention.

On the other hand, please refer to FIG. 6. FIG. 6 is a schematic diagram of a light emitting diode pixel circuit 600 according to an embodiment of the present invention. The light-emitting diode pixel circuit 600 is similar in structure to the light-emitting diode pixel circuit 400, so the same elements follow the same symbols. Different from the LED pixel circuit 400, the LED device 600 includes a light-emitting module 602 coupled between the drain of the second transistor T2 and the positive voltage V _DD , and the constant current device CC is a constant current sink, which can draw a fixed current ID6 from the light-emitting diode D to drive the light-emitting diode D, so that the light-emitting diode D produces a fixed brightness, which is also in accordance with the requirements of the present invention. Similarly, the light-emitting module 602 can also be coupled between the source and the ground of the second transistor T2. As shown in FIG. 7, the constant current device CC draws a fixed current ID7 to drive the LED D. It is also in accordance with the requirements of the present invention to produce a fixed brightness of the light-emitting diode D.

In summary, the light-emitting diode pixel circuit of the present invention uses a constant current device to generate a fixed current to drive the light-emitting diode, so that the light-emitting diode displays uniform brightness, and then uses the voltage-controlled pulse wave modulation module to data. The line voltage is converted into pulse wave signals with different space ratios to adjust the gray scale effect of the light emitting diode pixel circuit, so that the light emitting diode display can display uniform brightness and correctly display the gray scale effect.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

400‧‧‧Light Diode Pixel Circuit

402‧‧‧Lighting module

T1, T2‧‧‧ transistor

D‧‧‧Lighting diode

VCP‧‧‧Variable Pulse Modulation Module

CC‧‧‧ constant current device

SL‧‧‧ scan line

DL‧‧‧ data line

Vdata‧‧‧ data line voltage

V _DD ‧‧‧positive voltage

C _S ‧‧‧ storage capacitor

ID4‧‧‧ current

Claims (8)

A light-emitting diode pixel circuit is disposed on a light-emitting diode display, the light-emitting diode display comprises a plurality of scan lines and a plurality of data lines, and the light-emitting diode pixel circuit comprises: a first electricity The crystal includes a gate coupled to the scan line of the plurality of scan lines, a first electrode coupled to the data line of the plurality of data lines, and a second electrode; and a second transistor including a gate and an electrode; a voltage-controlled pulse wave modulation module coupled to the second electrode of the first transistor and the gate of the second transistor; and a light emitting module coupled to the gate The illuminating module includes: a illuminating diode; and a current device coupled to the illuminating diode for driving the illuminating diode. The illuminating diode pixel circuit of claim 1, wherein the constant current device generates a fixed current when the second transistor is turned on, and the illuminating diode generates a fixed brightness. The illuminating diode chip circuit of claim 1, wherein the voltage-controlled pulse wave modulation module generates a pulse signal according to a data voltage of the data line, and outputs the pulse signal to the second The gate of the transistor controls the on state of the second transistor to adjust the gray scale effect of the LED pixel circuit. The illuminating diode pixel circuit of claim 1, further comprising a storage capacitor coupled to the second electrode of the first transistor. A light emitting diode display comprising: a plurality of scan lines; a plurality of data lines perpendicular to the plurality of scan lines; and a plurality of light emitting diode pixel circuits, each of the light emitting diode pixel circuits being coupled to one of the plurality of scan lines and the plurality of data lines a light-emitting diode circuit comprising: a first transistor, a gate coupled to the scan line, a first electrode coupled to the data line, and a first a second electrode, a second transistor, including a gate and an electrode; a voltage-controlled pulse wave modulation module coupled to the second electrode of the first transistor and the gate of the second transistor And a light-emitting module coupled to the electrode of the second transistor, the light-emitting module includes: a light-emitting diode; and a current device coupled to the light-emitting diode for driving the light-emitting diode Light-emitting diode. The illuminating diode display of claim 5, wherein the constant current device generates a fixed current when the second transistor is turned on, and the illuminating diode generates a fixed brightness. The LED display of claim 5, wherein the voltage-controlled pulse modulation module generates a pulse signal according to a data voltage of the data line, and outputs the pulse signal to the second transistor. The gate is configured to control a conduction state of the second transistor to adjust a gray scale effect of each of the LED pixels. The illuminating diode display of claim 5, further comprising a storage capacitor coupled to the second electrode of the first transistor.