CN1632857A - LED Display Panel and Its Digital/Analog Converter - Google Patents

Abstract

A light emitting diode display panel comprises a substrate, pixels and a digital/analog converter. The substrate has a first area and a second area, the thin film transistor formed in the first area has a first channel doping concentration, and the thin film transistor formed in the second area has a second channel doping concentration. The pixels are arranged in the second region. The digital/analog converter comprises a plurality of switch circuits and a plurality of current sources, wherein the switch circuits are selectively conducted according to the gray-scale values and are arranged in the second area. The plurality of current sources are respectively electrically connected with the plurality of corresponding switch circuits and respectively selectively output a current to generate a pixel current according to the conducting states of the plurality of corresponding switch circuits, and the pixel current is configured in the first area. The critical voltage offset of the thin film transistor in the first area is smaller than that of the thin film transistor in the second area.

Description

LED Display Panel and Its Digital/Analog Converter

technical field

The invention relates to a light-emitting diode display panel, and in particular to a digital/analog converter.

Background technique

The luminance of LED pixels is proportional to the pixel current flowing through them, so they are mostly driven by current. The driving circuit provides corresponding pixel currents according to different grayscale values, so that the light emitting diode pixels generate corresponding brightness according to the pixel currents. Therefore, the size of the pixel current directly affects the light-emitting brightness of the LED pixel. In general, there are many ways to generate pixel current. Most of them use thin film transistors as current sources. N current sources are set according to 2 ^N gray scale values and N currents are generated respectively. The sequence is (2 ⁰ )I, ( 2 ¹ )I, (2 ² )I...(2 ^N-1 )I, etc., N is a positive integer. During the display process, the corresponding current sources are turned on according to the gray scale value, and the currents output by the turned on current sources are summed up and output as the pixel current.

Please refer to FIG. 1 , which shows a schematic diagram of a circuit structure of a conventional digital/analog converter. Taking the digital/analog converter 100 for generating 8 types of pixel current IP as an example, it includes 9 thin film transistors QA1 - QA3 , QB1 - QB3 and QC1 - QC3 . The thin film transistors QA1 - QA3 are all used as current sources, and the ratios of channel width to length are W/L, 2W/L and 4W/L respectively, so as to generate currents I, 2I, 4I of different magnitudes respectively.

Suppose, when the gray scale value D is the data signal (D2 D2 D0) = (110) ₂ , the thin film transistor QB1 is not turned on, the current I goes to the ground voltage through the thin film transistors QC1, QA1, and the thin film transistors QB2, QB3 are caused by the data signal D2 and D1 are at a high potential to conduct, so the currents 2I and 4I respectively go through the thin film transistors QB2 , QB3 and QA2 , QA3 to the ground voltage, and become the pixel current IP. Therefore, the pixel current IP output by the digital/analog converter 100 will be 2I+4I=6I, and output to the corresponding pixel to display the brightness represented by the gray scale value D=(110) ₂ .

However, currently, the digital/analog converter 100 is mostly realized by low-temperature polysilicon process technology, so as to be integrated into the display panel of the LED display. The current source is realized by low-temperature polysilicon thin film transistors QA1 - QA3 , or other circuits composed of thin film transistors are used to realize the current source. However, no matter what the structure is, the threshold voltage (threshold voltage) and carrier mobility shift (Variation) of thin-film transistors produced by low-temperature polysilicon technology will vary due to the laser crystallization process, making each transistor as a current Source thin film transistors, such as QA1 to QA3, have different threshold voltages and carrier mobility offsets, so that the pixel current IP output by the digital/analog converter 100 will be equal to the gray scale value D Errors occur in the corresponding current, and the predetermined luminous brightness cannot be achieved.

Please refer to FIG. 2 , which is a schematic diagram of traditional current source distribution. The traditional solution is to distribute the current sources that generate currents I, 2I, 4I, and 8I evenly in space, that is, each current source ideally generates a fixed current I. For example, two current sources are used in proportion to generate 2I, and four One current source produces 4I, eight current sources produce 8I, etc., and so on. Please refer to Figure 2, the average distribution in space means that when the pixel current IP corresponding to the grayscale value D is 8I, eight current sources are used to generate 8I, and the eight current sources are A, B, C, D, E, F, G, H, and the eight current sources A, B, C, D, E, F, G, H are scattered on the left and right sides, and this will generate a current source of 8I in Spatially evenly distributed to reduce the difference between each pixel current IP. However, this method will greatly increase the area of the digital/analog converter 100 . Therefore, in order to solve the problem that the threshold voltage and carrier mobility of thin film transistors will vary due to the laser crystallization process, resulting in different offsets between the threshold voltage and carrier mobility of each thin film transistor, resulting in uneven images. , is one of the issues that the industry urgently needs to solve.

Contents of the invention

In view of this, the object of the present invention is to provide a light-emitting diode display panel and its digital/analog converter, so as to solve the problem that the threshold voltage offsets of each current source implemented by a thin film transistor are different from each other, to improve picture quality.

According to the object of the present invention, a digital/analog converter is provided for a light emitting diode display panel. The LED display panel has a substrate and at least one pixel. The substrate has a first area and a second area. The pixel at least includes a first thin film transistor and a light emitting diode. The first thin film transistor is used to drive the light emitting diode according to the pixel current. The first thin film transistor is arranged in the second area. The digital/analog converter includes multiple switching circuits and multiple current sources. A plurality of switch circuits are respectively realized by at least one second thin film transistor and are selectively turned on according to a gray scale value. A plurality of switch circuits are arranged in the second area. The plurality of current sources are respectively realized by at least one third thin film transistor and are respectively electrically connected to the corresponding plurality of switch circuits, and each selectively outputs a current according to the conduction state of the corresponding plurality of switch circuits to generate pixel current. Multiple current sources are arranged in the first area.

Wherein, the thin film transistors formed in the first region have a first channel doping concentration, and the thin film transistors formed in the second region have a second channel doping concentration. Under the low-temperature polysilicon process, the threshold voltage (Threshold Voltage) deviation (variation) of the thin film transistor in the first region is the first deviation, and the threshold voltage deviation of the thin film transistor in the second region is the second deviation amount, the first offset is less than the second offset.

According to another object of the present invention, a light emitting diode display panel is provided, which includes a substrate, pixels and a digital/analog converter. The substrate has a first area and a second area. The pixel at least includes a first thin film transistor and a light emitting diode. The first thin film transistor is used to drive the light emitting diode according to the pixel current and is arranged in the second area. The digital/analog converter outputs the pixel current according to the grayscale value, which includes a plurality of switch circuits and a plurality of current sources. A plurality of switch circuits are respectively realized by at least one second thin film transistor and are selectively turned on according to the gray scale value. A plurality of switch circuits are arranged in the second area. The plurality of current sources are realized by at least one third thin film transistor respectively. The plurality of current sources are respectively electrically connected to the corresponding plurality of switch circuits and selectively output a current according to the conduction states of the corresponding plurality of switch circuits to generate the pixel current. Multiple currents are configured in the first area.

Wherein, the thin film transistors formed in the first region have a first channel doping concentration, and the thin film transistors formed in the second region have a second channel doping concentration. Under the low-temperature polysilicon process, the threshold voltage (Threshold Voltage) deviation (variation) of the thin film transistor in the first region is the first deviation, and the threshold voltage deviation of the thin film transistor in the second region is the second deviation amount, the first offset is less than the second offset.

In order to make the above-mentioned purpose, features, and advantages of the present invention more comprehensible, a preferred embodiment will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of a circuit architecture of a conventional digital/analog converter.

Fig. 2 is a schematic diagram of traditional current source distribution.

FIG. 3 is an experimental result diagram of doping dose and threshold voltage of a low-temperature polysilicon thin film transistor.

FIG. 4 is a schematic diagram of an electroluminescence display panel according to a preferred embodiment of the present invention.

FIG. 5A is a schematic circuit diagram of an example of a thin film transistor as a current source.

FIG. 5B is a schematic circuit diagram of another example using a thin film transistor as a current source.

FIG. 6 is a schematic diagram of the circuit structure of the digital/analog converter 408 ( 1 ) as an example.

Description of reference symbols

100: Digital/Analog Converter

400: LED display panel

402: Substrate

404: Data drive circuit

406: pixel array

408: Digital/Analog Converter

410: Scan driving circuit

Transistors: QA1, QA2, QA3, QB1, QB2, QB3, QC1, QC2, QC3, Q1, Q2, Q3

Detailed ways

During the manufacturing process of low-temperature polysilicon thin film transistors, the thin film transistors manufactured under different channel doping concentrations have different variations in the threshold voltage. Please refer to FIG. 3 , which shows the experimental results of the doping dose and the threshold voltage of the low-temperature polysilicon thin film transistor using the XeCl laser at an energy of 350 mJ/cm ² . The horizontal axis represents the doping dosage (doping dosage) of the channel doping concentration, in cm ⁻² . The vertical axis represents the threshold voltage Vt in units of volts. Curve N is a relationship curve between the dopant dose of NMOS and its threshold voltage offset, and curve P is a relationship curve between the dopant dose of PMOS and its threshold voltage offset. Under different doping doses, different channel doping concentrations are formed, so that thin film transistors will have different threshold voltage shifts, and the error bar E is used to represent the threshold voltage shift (Variation) size. For example, when the doping dose is 1.0E+13cm ⁻² , the threshold voltage variation (Variation) of the NMOS corresponds to the length of the error node E. The longer the error node line E, the larger the offset, that is, the larger the difference of the threshold voltage of the NMOS. Therefore, it can be seen that in the curve N, the maximum threshold voltage shift of the NMOS is when the doping dose is 1.0E+13cm ⁻² .

Using this relationship, find out the doping concentration of the formed channel under a certain doping dose, and the manufactured thin film transistor has the smallest threshold voltage shift, that is, the shortest error node line. For example, change the channel doping concentration (channel doping) of PMOS by doping boron (Boron), and find out the channel doping concentration when the threshold voltage shift (Variation) of PMOS is the smallest, such as point A in Figure 3 , when the dopant dose is 8.0E+12cm ^-2 , the threshold voltage shift (Variation) of PMOS is the smallest. Therefore, when the thin film transistor manufactured with this dopant dose of 8.0E+12cm ^-2 is used as a current source, the difference between the current output by each current source and the ideal value will be the smallest, so that the digital/analog conversion Lu The output pixel current is closer to the ideal value.

Please refer to FIG. 4 , which is a schematic diagram of an electroluminescence display panel according to a preferred embodiment of the present invention. The electroluminescent display panel includes a substrate 402 , a data driving circuit 404 , a scanning driving circuit 410 and a pixel array 406 . The substrate 402 is, for example, an electroluminescence display substrate, which has a first region L1 and a second region L2. The pixel array 406 is composed of a plurality of pixels, and each pixel includes at least one thin film transistor Q1 and an electroluminescent body, such as an organic light emitting diode (Organic Light Emitting Diode) or a polymer organic light emitting diode (Polymer Light Emitting Diode). Emitting Diode) (thin film transistor Q1 and electroluminescent body are not shown in FIG. 4). Therefore, the electroluminescence display panel is, for example, a light emitting diode display panel. The TFT Q1 is used to drive the LED according to the pixel current. The thin film transistor Q1 is disposed in the second region L2. The scanning driving circuit 410 sequentially outputs scanning signals to the pixel array 406 so that each pixel receives the corresponding pixel current IP'(1)~IP'(X), X is a positive integer, and the scanning driving circuit 410 is configured in the second Second area L2.

The data driving circuit 404 outputs pixel currents IP′(1)˜IP′(X) according to grayscale values and includes a plurality of digital/analog converters 408(1)˜408(X). Each of the digital/analog converters 408(1)˜408(X) includes a plurality of switch circuits and a plurality of current sources (the plurality of switch circuits and the plurality of current sources are not shown in FIG. 4 ). A plurality of switch circuits are realized by at least one thin film transistor Q2 respectively. A plurality of switch circuits are selectively turned on according to the gray scale value, and are arranged in the second area L2. The plurality of current sources are respectively implemented by at least one thin film transistor Q3 and are electrically connected to the corresponding switch circuits, so as to selectively output a current according to the conduction state of the corresponding switch circuits to generate the pixel current IP . A plurality of current sources are disposed in the first area L1. Wherein, the thin film transistors formed in the first region L1, such as the thin film transistor Q3, have the first channel doping concentration, and the thin film transistors formed in the second region L2, such as the thin film transistors Q1 and Q2, have the second channel doping concentration. Concentration, under the low-temperature polysilicon process, the threshold voltage (Variation) of the thin film transistor Q3 in the first region L1 is a first deviation, and the threshold voltage of the thin film transistors Q1 and Q2 in the second region L2 The voltage offset is the second offset, and the first offset is smaller than the second offset.

Further, the difference between this embodiment and the conventional ones is that in the traditional method, the entire driving circuit, such as the data driving circuit or the scanning driving circuit, is fabricated on the same substrate 402 as the pixel array with the same channel doping concentration, and the channel The doping concentration is, for example, the second channel doping concentration. Under the second channel doping concentration, the absolute values of the threshold voltages of PMOS and NMOS are similar to facilitate circuit design. However, at this channel doping concentration, the threshold voltage shift of the thin film transistor is relatively large. For example, when the doping dose is 2.0E+12cm ^-2 in FIG. 3, the threshold voltages of PMOS and NMOS are nearly symmetrical (in FIG. point B and C). However, at this time, the error node line E′ of the PMOS is larger than that of other dopant dosages, so the threshold voltage shift of the PMOS is larger at this dopant dosage (2.0E+12cm ⁻² ). In this embodiment, in each digital/analog converter 408 , a plurality of current sources are realized by thin film transistors having a first channel doping concentration, such as thin film transistor Q3 . With the spirit of this embodiment, the dopant dose that minimizes the offset of the threshold voltage is found through experiments, and the channel doping concentration generated by the doping dose is used as the first channel doping concentration, and the first channel doping concentration is used as the first channel doping concentration. The thin film transistor Q3 formed under the channel doping concentration is disposed in the first region L1 of the substrate 402 . In this way, the thin film transistor Q3 with the smallest threshold voltage shift can be obtained, so as to reduce the element difference between the multiple current sources realized by the thin film transistor Q3, so that the magnitude of the current generated by the multiple current sources can be close to the ideal value .

There are many ways to implement a current source with thin film transistors. Please refer to FIG. 5A and FIG. 5B. FIG. 5A is a schematic circuit diagram of an example of using a thin film transistor as a current source, and FIG. 5B is another example of using a thin film transistor as a current source. The schematic diagram of the circuit. In FIG. 5A and FIG. 5B , the thin film transistor Q3 uses different W/L ratios to set the magnitude of the current when the thin film transistor Q3 is turned on, so as to achieve the output current (2 ⁰ )I, (2 ¹ )I...( 2 ^N-1 )I. Alternatively, a current source can be realized by means of a current mirror. Therefore, no matter what kind of thin film transistors are used to form the current source structure, it is realized by the thin film transistor Q3 having the first channel doping concentration. In this way, the magnitude of each stage of current output by the multiple current sources in each digital/analog converter 408 will become more uniform.

Please refer to FIG. 6 , which shows a schematic circuit structure diagram of the digital/analog converter 408 ( 1 ) as an example. Thin film transistors Q3 ( 1 ) to Q3 (N) serving as current sources are disposed in the first region L1 . Since the critical voltage offset is the minimum, the difference between the output currents (2 ⁰ )I, (2 ¹ )I...(2 ^N-1 )I of each stage of current source will be greatly reduced, and A plurality of switch circuits are realized by thin film transistors Q2(0)˜Q2(N−1) and Q2(0′)˜Q2(N−1′), and are disposed in the second region L2. In this way, the difference between the pixel current IP'(1) generated by the D/A converter 408(1) and the pixel current IP'(X) generated by the D/A converter 408(X) will be smaller. When all the digital/analog converters 408(1)-408(K) receive the same gray scale value D, the pixel current IP'( 1)~IP'(K) will be smaller than the traditional ones, and will be closer to the current corresponding to the gray scale value D, so that the entire display screen will display the same brightness and be more uniform than the traditional one.

For the plurality of switching circuits and other circuits included in each digital/analog converter 408, other circuits such as the scan driving circuit 410, the pixel array 406 and the data driving circuit 404, for the threshold voltage offset of the thin film transistor, and It will not have much impact on its operation. Therefore, except for a plurality of current sources in the data driving circuit 404 , other circuits are all disposed in the second region L2 of the substrate 402 . In the second region L2 using the second channel doping concentration, the absolute values of the threshold voltages of PMOS and NMOS are similar, which is convenient for circuit design. Alternatively, when the scan driving circuit 410 is to be integrated on the display panel, it is also disposed in the second area L2 of the substrate 402 .

In the light-emitting diode display panel and its digital/analog converter disclosed in the above-mentioned embodiments of the present invention, by finding the channel doping concentration at which the threshold voltage shift is the smallest, the thin film transistors manufactured with the channel doping concentration are obtained. The critical voltage offset is the smallest, and multiple current sources in the digital/analog converter are implemented with the thin film transistors, so that the current magnitude of each stage of the current source will be closer to the ideal value.

In summary, although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. Anyone skilled in this art can make various modifications without departing from the spirit and scope of the present invention. Changes and modifications, so the protection scope of the present invention shall prevail as defined by the appended claims.

Claims (14)

1. digital/analog converter, be used for a LED display panel, this LED display panel has a substrate and at least one pixel, this substrate is to have a first area and a second area, this pixel comprises a first film transistor and a light emitting diode at least, this the first film transistor be in order to according to a pixel current to drive this light emitting diode, this first film transistor is to be disposed at this second area, this digital/analog converter comprises:

A plurality of on-off circuits are to reach with at least one second thin film transistor (TFT) respectively, and described on-off circuit is that described on-off circuit is to be configured in this second area according to an optionally conducting of GTG value; And

A plurality of current sources, be to reach with at least one the 3rd thin film transistor (TFT) respectively, described current source is to electrically connect with corresponding described on-off circuit respectively, and the conducting state of the pairing described on-off circuit of foundation, optionally to export an electric current separately to produce this pixel current, described current source is to be configured in this first area;

Wherein, the thin film transistor (TFT) that is formed on this first area is to have a first passage doping content, the thin film transistor (TFT) that is formed on this second area is to have a second channel doping content, under the low temperature polycrystalline silicon processing procedure, the critical voltage side-play amount of the thin film transistor (TFT) of this first area is one first side-play amount, the critical voltage side-play amount of the thin film transistor (TFT) in this second area is one second side-play amount, and this first side-play amount is less than this second side-play amount.

2. digital/analog converter as claimed in claim 1 wherein, in this digital/analog converter, has only described current source to be configured in this first area.

3. LED display panel comprises:

One substrate has a first area and a second area;

One pixel comprises a first film transistor and a light emitting diode at least, and this first film transistor is in order to driving this light emitting diode according to a pixel current, and this first film transistor is to be configured in this second area; And

One digital/analog converter, to export this pixel current, this digital/analog converter comprises according to a GTG value for it:

A plurality of on-off circuits are to reach with at least one second thin film transistor (TFT) respectively, and described on-off circuit is that described on-off circuit is to be configured in this second area according to an optionally conducting of GTG value; And

A plurality of current sources, be to reach with at least one the 3rd thin film transistor (TFT) respectively, described current source is to electrically connect with corresponding described on-off circuit respectively, and the conducting state of the pairing described on-off circuit of foundation, optionally to export an electric current separately to produce this pixel current, described current source is to be configured in this first area;

Wherein, the thin film transistor (TFT) that is formed on this first area is to have a first passage doping content, the thin film transistor (TFT) that is formed at this second area is to have a second channel doping content, under the low temperature polycrystalline silicon processing procedure, the critical voltage side-play amount of the thin film transistor (TFT) of this first area is one first side-play amount, the critical voltage side-play amount of the thin film transistor (TFT) in this second area is one second side-play amount, and this first side-play amount is less than this second side-play amount.

4. display panel as claimed in claim 3 wherein, in this digital/analog converter, has only described current source to be arranged on this first area.

5. display panel as claimed in claim 3, wherein, this display panel more comprises scan driving circuit, so that this pixel receives this pixel current, this scan drive circuit is arranged on this second area to this scan drive circuit output one scan signal to this pixel.

6. LED display panel is to comprise:

One substrate has a first area and a second area, and the thin film transistor (TFT) that is formed at this first area has a first passage doping content, and the thin film transistor (TFT) that is formed at this second area has a second channel doping content;

One pixel comprises a first film transistor and an Organic Light Emitting Diode at least, and this first film transistor is in order to driving this Organic Light Emitting Diode according to a pixel current, and this first film transistor is this second area of configuration;

Scan driving circuit, be output one scan signal to this pixel so that this pixel receives this pixel current, this scan drive circuit is to be disposed at this second area; And

One data drive circuit, to export this pixel current, this data drive circuit comprises a digital/analog converter according to a GTG value, this digital/analog converter comprises:

A plurality of on-off circuits are to be arranged at this second area and to be reached by the thin film transistor (TFT) of this second area, and described on-off circuit is according to this optionally conducting of GTG value; And

A plurality of current sources, be arranged on this first area and reached by the thin film transistor (TFT) of this first area, described current source is to electrically connect with corresponding described on-off circuit respectively, and the conducting state of the pairing described on-off circuit of foundation, optionally export an electric current separately to produce this pixel current;

Wherein, the critical voltage side-play amount of the thin film transistor (TFT) of this first area is one first side-play amount, and the critical voltage side-play amount of the thin film transistor (TFT) in this second area is one second side-play amount, and this first side-play amount is less than this second side-play amount.

7. electroluminescence body display panel is to comprise:

One pixel comprises a first film transistor and an electroluminescence body, this first film transistor be in order to according to a pixel current to drive this electroluminescence body;

A plurality of on-off circuits are that each is reached with one second thin film transistor (TFT) with a second channel doping content at least, and described on-off circuit is according to an optionally conducting of GTG value; And

A plurality of current sources, be that each is reached with one the 3rd thin film transistor (TFT) with a first passage doping content at least, described current source is to electrically connect with corresponding described on-off circuit respectively, and the conducting state of the pairing described on-off circuit of foundation, optionally to export an electric current separately to produce this pixel current;

Wherein, this first passage doping content is different with this second channel doping content.

8. electroluminescence body display panel as claimed in claim 7, wherein, the critical voltage side-play amount that the critical voltage side-play amount that described the 3rd thin film transistor (TFT) is had is had less than described second thin film transistor (TFT).

9. electroluminescence body display panel as claimed in claim 7, wherein, the critical voltage side-play amount that this first passage doping content is described the 3rd thin film transistor (TFT) is hour pairing doping content.

10. electroluminescence body display panel as claimed in claim 7, wherein, this second thin film transistor (TFT) and the 3rd thin film transistor (TFT) are low-temperature polysilicon film transistors.

11. an electroluminescence body display base plate comprises:

A plurality of electroluminescence bodies;

A plurality of current sources are reached by a plurality of thin film transistor (TFT)s with a first passage doping content; And

A plurality of on-off circuits, reached by a plurality of thin film transistor (TFT)s with a second channel doping content, these a plurality of current sources are to electrically connect with a plurality of on-off circuits of corresponding this respectively, and according to the conducting state of pairing this a plurality of on-off circuits to drive these a plurality of electroluminescence bodies of correspondence;

Wherein, this first passage doping content is different with this second channel doping content.

12. electroluminescence body display base plate as claimed in claim 11, wherein, this first passage doping content is the critical voltage side-play amount hour pairing doping content of these a plurality of thin film transistor (TFT)s with this first passage doping content.

13. electroluminescence body display base plate as claimed in claim 11, wherein, the critical voltage side-play amount of these a plurality of thin film transistor (TFT)s with this first passage doping content is less than these a plurality of critical voltage side-play amounts with thin film transistor (TFT) of this second channel doping content.

14. electroluminescence body display base plate as claimed in claim 11, wherein, these a plurality of thin film transistor (TFT)s with this first passage doping content are low-temperature polysilicon film transistors with these a plurality of thin film transistor (TFT)s with this second channel doping content.

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