Gate driver on array (GOA) circuit and display device solving problem of electrical stress easily biasing threshold voltage of thin film transistor (TFT)

Abstract

Gate Driver on Array (GOA) circuit and display device solving problem of electrical stress easily biasing threshold voltage of thin film transistor (TFT), are provided. The GOA circuit including m cascaded GOA units, wherein an n.sup.th GOA unit includes a pull-up control unit, a pull-up unit, a compensation control unit, and a pull-down unit.

Claims

1. A Gate Driver On Array (GOA) circuit comprising m cascaded GOA units, wherein an n.sup.th GOA unit comprises: a pull-up control circuit, a pull-up circuit, a compensation control circuit, and a pull-down circuit; wherein m and n are positive integers and m≥n≥1; wherein the pull-up control circuit is connected to the compensation control circuit and the pull-up circuit respectively, the compensation control circuit is connected to the pull-up control circuit, the pull-up circuit, and the pull-down circuit respectively, the pull-up circuit is connected to the pull-up control circuit, the compensation control circuit, and the pull-down circuit respectively, and the pull-down circuit is connected to the pull-up circuit and the compensation control circuit respectively; wherein the pull-up control circuit comprises a first thin film transistor, the pull-up circuit comprises a second thin film transistor and a first capacitor, the pull-down circuit comprises a third thin film transistor, and the compensation control circuit comprises a fourth thin film transistor; a gate of the fourth transistor is connected to an n+1.sup.th stage row scanning signal Cout (n+1), a drain of the fourth thin film transistor is connected to a source of the first thin film transistor in the pull-up control circuit and a gate of the second thin film transistor in the pull-up circuit, a source of the fourth thin film transistor is connected to a drain of the third thin film transistor in the pull-down circuit, a source of the second thin film transistor in the pull-up circuit, and an n.sup.th stage row scanning signal Cout (n), and wherein the compensation control circuit is configured to control a threshold voltage of the second thin film transistor in the pull-up circuit to be stored in the first capacitor in the pull-up circuit; the pull-up control circuit is connected to an n−1.sup.th stage row scanning signal Cout (n−1), and is configured to raise a potential at a Q point; the pull-up circuit is configured to output the n.sup.th stage row scanning signal Cout (n) of a high potential; and the pull-down circuit is configured to pull the high potential of the n.sup.th stage row scanning signal Cout (n) to a low potential.

2. The GOA circuit according to claim 1, wherein a drain and a gate of the first thin film transistor are connected to the n−1.sup.th stage row scanning signal Cout (n−1) respectively, the source of the first thin film transistor is connected to the drain of the fourth thin film transistor and the pull-up circuit.

3. The GOA circuit according to claim 2, wherein a drain of the second thin film transistor is connected to a clock signal CK, the gate of the second thin film transistor is connected to the source of the first thin film transistor and the drain of the fourth thin film transistor, the source of the first thin film transistor is connected to the n.sup.th stage row scanning signal Cout (n) through the first capacitor, the source of the second thin film transistor is connected to the n.sup.th stage row scanning signal Cout (n) and the pull-down-circuit.

4. The GOA circuit according to claim 3, wherein the drain of the third thin film transistor is connected to the source of the second thin film transistor, the n.sup.th stage row scanning signal Cout (n), and the source of the fourth thin film transistor, a gate of the third thin film transistor is connected to an n+2.sup.th stage row scanning signal Cout (n+2), and a source of the third thin film transistor is connected to a ground.

5. The GOA circuit according to claim 4, wherein the source of the first thin film transistor and the drain of the fourth thin film transistor are connected through a second capacitor.

6. The GOA circuit according to claim 1, wherein the first thin film transistor, the second thin film transistor, the third thin film transistor, and the fourth thin film transistor are of an indium gallium zinc oxide (IGZO) thin film transistor.

7. A thin film transistor (TFT) substrate comprising the GOA circuit according to claim 1.

8. A display device comprising the TFT substrate according to claim 7.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) In order to describe clearly the embodiment in the present disclosure or the prior art, the following will introduce the drawings for the embodiment shortly. Obviously, the following description is only a few embodiments, for the common technical personnel in the field it is easy to acquire some other drawings without creative work.

(2) FIG. 1 is a schematic diagram of a horizontal scanning line of a liquid crystal display panel driven by an external integrated circuit.

(3) FIG. 2 is a schematic diagram of horizontal scanning lines of a liquid crystal display panel driven by gate driver on array (GOA).

(4) FIG. 3 is a GOA circuit and timing diagram according to the prior art.

(5) FIG. 4 is a schematic diagram of a GOA unit according to an embodiment of the present invention.

(6) FIG. 5 is a GOA unit level transmission relationship and a signal timing according to an embodiment of the present invention.

(7) FIG. 6 is an equivalent circuit diagram of a thin film transistor.

(8) FIG. 7 is a circuit diagram of a GOA unit according to an embodiment of the present invention.

(9) FIG. 8 is a schematic diagram of a signal source required by a GOA unit according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(10) The technical solution of a gate driver on array (GOA) circuit, a TFT substrate, a display device, and an electronic equipment provided by the present invention is clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work fall into the protection scope of the present invention.

(11) In the description of the present invention, it is understood that the orientation or position relationship indicated by the terms such as “center”, “portrait”, “landscape”, “length”, “width”, “thickness”, “up”, “low”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, etc. are based on the orientation or position relationship shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, construction and operation in a specific orientation. Therefore, it cannot be understood as a limitation to the present invention. In addition, the terms “first”, “second”, “third”, etc. are used for descriptive purposes only, and should not be interpreted as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as “first”, “second”, and “third” may explicitly or implicitly include one or more features. In the description of the present invention, the meaning of “plurality” is two or more, unless specifically defined otherwise.

(12) In the present invention, the terms “installation”, “connected”, “connection”, “fixed” and the like shall be understood in a broad sense unless otherwise specified and defined, For example, they can be a fixed connection, a detachable connection, or an integral unit; they can be mechanical or electrical connection; they can be directly connected or indirectly connected through an intermediate medium, they can be the internal connection of the two elements or the interaction relationship between the two elements, unless explicitly defined otherwise. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

(13) In the present invention, the term “exemplary” is used to mean “serving as an example, illustration, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. In order to enable any person skilled in the art to implement and use the present invention, the following description is given. In the following description, the invention is set forth in detail for the purpose of explanation. It should be understood by those of ordinary skill in the art that the present invention can be implemented even without using these specific details. In other instances, well-known structures and procedures will not be described in detail in order to avoid unnecessary details from obscuring the description of the present invention. Therefore, the present invention is not intended to be limited to the illustrated embodiments, but should be consistent with the widest scope consistent with the principles and features disclosed by the present invention.

(14) In the prior art, a forward bias stress of IGZO-TFT is not ideal, long-term forward bias stress will cause a threshold voltage (Vth) of the TFT to drift forward. An opening speed of the IGZO-TFT device becomes slower, which in turn has a serious impact on the gate drive circuit. The embodiments of the present invention provide a GOA circuit which can be used for LCD displays or OLED displays. The GOA circuit can be included in products or components with display functions, such as LCD TVs, mobile phones, digital cameras, tablet computers, computers, electronic paper, navigators, and the like.

(15) It should be noted that the technical features involved in different embodiments of the present invention described below can be combined as long as they do not conflict with each other.

(16) The pixel circuit of the AMOLED panel uses thin-film transistors to form a current source to light the panel. When IGZO-TFT is subjected to stress, Vth is likely to shift, so the pixel circuit needs to use a compensation circuit to compensate for Vth. FIG. 4 is a schematic diagram of a GOA unit according to an embodiment of the present invention, please refer to FIG. 4, a GOA circuit is provided, the GOA circuit includes m cascaded GOA units, and an n.sup.th GOA unit includes: a pull-up control unit 101, a pull-up unit 102, a compensation control unit 104, and a pull-down unit 103, wherein m and n are positive integers, and m≥n≥1.

(17) The pull-up control unit 101 is connected to the compensation control unit 104 and the pull-up unit 102, the compensation control unit 104 is connected to the pull-up control unit 101, the pull-up unit 102, and the pull-down unit 103. The pull-up unit 102 is connected to the pull-up control unit 101, the compensation control unit 104, and the pull-down unit 103. The pull-down unit 103 is connected to the pull-up unit 102 and the compensation control unit 104. The pull-up control unit 101 is an effective method to reduce the leakage current at Q point. The pull-up control unit 101 can reduce the leakage current at point Q to a certain extent. The ability to maintain the potential at point Q is the key to ensuring the stable output of the GOA circuit.

(18) The pull-up control unit 101 is connected to an n−1.sup.th stage row scanning signal Cout (n−1) to raise the potential of Q point, and the pull-up unit 102 is used to output the n.sup.th stage row scanning signal Cout (n) of a high potential. The compensation control unit 104 is used to cause a thin film transistor in the pull-up control unit 102 to form a diode connection structure. Threshold voltage of thin film transistors in the control pull-up unit 102 is stored in the capacitor in the pull-up unit 102. The pull-down unit 103 is used to pull down the potential of the n.sup.th stage row scanning signal Cout (n) to a low potential.

(19) In a specific optional embodiment, the capacitor is a bootstrap capacitor. The bootstrap capacitor uses the characteristic that the voltage across the capacitor cannot be abrupt. When a certain voltage is maintained across the capacitor, increase the negative voltage of the capacitor, the positive voltage still maintains the original voltage difference with the negative terminal, and the voltage equal to the positive terminal is lifted by the negative terminal. In an alternative embodiment, one end of the bootstrap capacitor is electrically connected to one end of the pull-up control unit 101 outputting the pull-up control signal Q (N), the other end of the bootstrap capacitor is electrically connected to one end of the n.sup.th stage row scanning signal G (n) of the current row array circuit row drive circuit unit output by the pull-up unit 102. The bootstrap capacitor is mainly used to raise potential, and is used to generate a high level scan signal of the current stage. The voltage between a gate and a source of the thin film transistor in the pull-up unit 102 is maintained to stabilize the output of the thin film transistor, that is, the output of the n.sup.th stage row scanning signal G (n).

(20) The GOA circuit includes m cascaded GOA units, please refer to FIG. 5, FIG. 5 is a GOA cell level transmission relationship and signal timing according to an embodiment of the present invention. The GOA circuit contains m cascaded GOA units, each level of GOA unit correspondingly drives a raw scanning line. The structure of all single-stage GOA units is almost the same, and there are only slight differences in the first and last stages. These differences are not related to this application, so they will not be described in detail here. When the n.sup.th stage GOA unit is driven, the n.sup.th stage GOA unit outputs a high-level n.sup.th row scan signal G (n) and an n.sup.th stage transfer signal ST (n). Among them, the n.sup.th row scanning signal G (n) is used to turn on a TFT switch of each pixel in a row in the panel and charge a pixel electrode in each pixel. The n.sup.th stage transmission signal ST (n) is used to provide a stage transmission signal for a next level during forward scanning, and is used to provide a stage transmission signal for a last level during backward scanning.

(21) The GOA circuit provided in this embodiment is consistent with the working principle of the above-mentioned GOA unit embodiment. For the specific structural relationship and working principle, refer to the above-mentioned GOA unit embodiment, which will not be repeated here.

(22) The GOA circuit according to embodiments of the present invention may include a plurality of thin film transistors. FIG. 6 is an equivalent circuit diagram of a thin film transistor. Three electrodes of the thin film transistor are called a gate, a source, and a drain. Correspondingly, voltages loaded on the respective electrodes can be marked as Vg, Vs and Vd, respectively. Here, the source and the drain are actually indistinguishable, but for convenience of description, in the exemplary embodiment, the lower end is generally called the source, and the higher end is called the drain. Therefore, voltage Vgs=Vg−Vs that determines the state of the thin film transistor. When Vgs>0, the thin film transistor is turned on, and the current flows from the drain to the source. When Vgs=0, the thin film transistor is in a micro-conduction state, and current flows from the drain to the source. When Vgs<0, the device is off. Alternatively, in other exemplary embodiments, the lower voltage end may be referred to as the drain, and the higher voltage end may be referred to as the source, that is, when the thin film transistor is in the on state, current flows from the source to the drain.

(23) The Q point in the GOA circuit is the gate point of the thin film transistor that controls the high level of the output signal. When the Q point is at a high potential, the thin film transistor is turned on, and the output signal remains at a high potential. Voltage VGL+Vth of the above-mentioned GOA circuit will always be stored at the Q point, thereby solving the problem that the GOA circuit buffer TFT in the prior art is subjected to the stress of the CK signal Vds, and the Vth of the TFT is prone to positive deviation, resulting in serious distortion of the output signal. To a large extent, the stability of the gate drive circuit is improved, which is beneficial to the improvement of the display effect of the liquid crystal display panel.

(24) In an alternative embodiment, the GOA unit may be manufactured based on IGZO-TFT.

(25) FIG. 7 is a circuit diagram of a GOA unit according to an embodiment of the present invention. Referring to FIG. 7, the pull-up control unit 101 includes a first thin film transistor T1, a drain and a gate of the first thin film transistor T1 are connected to the n−1.sup.th stage row scanning signal Cout (n−1), a source of the first thin film transistor T1 is connected to the compensation control unit 104 and the pull-up unit 102. Specifically, the source of the first thin film transistor T1 is connected to a drain of the fourth thin film transistor T4 in the compensation control unit 104, the source of the first thin film transistor T1 is connected to a gate of the second thin film transistor T2 in the pull-up unit 102.

(26) The pull-up unit 102 includes a second thin film transistor T2 and a first capacitor Cbt1, the drain of the second thin film transistor T2 is connected to the clock signal CK, the gate of the second thin film transistor T2 is connected to the source of the first thin film transistor T1, the source of the first thin film transistor T1 is connected to the n.sup.th stage row scanning signal Cout (n) through the first capacitor Cbt1, a source of the second thin film transistor T2 is connected to the n.sup.th stage row scanning signal Cout (n) and the pull-down unit 103, respectively. Specifically, the source of the second thin film transistor T2 is connected to a drain of the third thin film transistor T3 in the pull-down unit 103.

(27) The pull-down unit 103 includes a third thin film transistor T3, the drain of the third thin film transistor T3 is connected to the source of the second thin film transistor T2, the n.sup.th stage row scanning signal Cout (n) and the compensation control unit 104. Specifically, the drain of the third thin-film transistor T3 is connected to a source of the fourth thin-film transistor T4 in the compensation control unit 104, and the gate of the third thin-film transistor T3 is connected to the n+2.sup.th stage row scanning signal Cout (n+2). A source of the third thin film transistor T3 is connected to VGL.

(28) The compensation control unit 104 includes a fourth thin film transistor T4, a gate of the fourth thin film transistor T4 is connected to the n+1.sup.th stage row scanning signal Cout (n+1), a drain of the fourth thin film transistor T4 is connected to the source of the first thin film transistor T1, and a source of the fourth thin film transistor T4 is connected to the drain of the third thin film transistor T3 and the n.sup.th stage row scanning signal Cout (n).

(29) In an alternative embodiment, the source of the first thin film transistor and the drain of the fourth thin film transistor are connected by a second capacitor. Please refer to FIG. 8, in S1 stage, the potential of Q point is VGL+Vth. In the S2 stage, the n−1.sup.th stage row scanning signal Cout (n−1) becomes high potential. According to the principle of capacitive coupling, the high potential of VGH is written to point Q, the potential at point Q will be VGL+Vth+VGH.

(30) FIG. 8 is a schematic diagram of a signal source required by a GOA unit according to an embodiment of the present invention. The working principle of the GOA unit according to an embodiment of the present invention is described below in conjunction with FIG. 8.

(31) S1 stage: the potential at the point Q is VGL+Vth, and then the n−1.sup.th stage row scanning signal Cout (n−1) rises to a high potential, the potential at point M rises from VGL to VGH, and point Q is theoretically coupled to (VGH−VGL).Math.Cbt2/(Cbt1+Cbt2)+VGL+Vth, the second thin film transistor T2 is turned on, and the n.sup.th stage row scanning signal Cout (n) remains low.

(32) S2 stage: the n−1.sup.th stage row scanning signal Cout (n−1) drops to low potential, the first thin film transistor T1 is turned off, and the second thin film transistor T2 remains on. The Cout (n) potential rises from VGL to VGH, and the point Q potential is theoretically (VGH−VGL)Cbt1/(Cbt1+Cbt2)+(VGH−VGL) Cbt2/(Cbt1+Cbt2)+VGL+Vth=VGH+Vth, the potential of the second thin film transistor T2 is Vgs-Vth=VGH. Therefore, the current of the second thin film transistor T2 is independent of Vth, and the output waveform of the GOA is not affected by the Vth shift of the second thin film transistor T2.

(33) S3 stage: the n+1.sup.th stage row scanning signal Cout (n+1) rises to a high potential, the fourth thin film transistor T4 turns on, the clock signal CK drops from a high potential to a low potential, and the gate and drain of the second thin film transistor T2 are connected to each other to form a diode structure. The second thin film transistor T2 will generate a current discharge, the voltage of the gate and the drain will decrease at the same time, when it drops to VGL+Vth, the gate voltage (VGL+Vth) minus the source voltage (VGL) is exactly equal to Vth. Therefore, the second thin film transistor T2 will be turned off and the gate voltage will not continue to decrease. Due to the existence of the storage capacitor Cbt1, the voltage of VGL+Vth will always be stored at the Q point.

(34) Stage S4: the n+2.sup.th stage row scanning signal Cout (n+2) rises to a high potential, the third thin film transistor T3 is turned on, and the n.sup.th stage row scanning signal Cout (n) potential is reset to VGL.

(35) In an optional embodiment, the transistor used in the embodiment of the present invention may be a thin film transistor, a field effect transistor, or other devices with the same characteristics. For example, the thin film transistor is an IGZO thin film transistor. According to the function in the circuit, the transistor used in the embodiment of the present invention is mainly a switching transistor. Since the source and drain of the switching transistor used here are symmetrical, the source and drain are interchangeable, and the source is preferably connected to the power supply. The middle terminal of the transistor is the gate, the signal input terminal is the source, and the signal output terminal is the drain. Switching transistors include P-type switching transistors and N-type switching transistors. In the embodiment of the present invention, all the thin film transistors described in the GOA unit are metal oxide semiconductor thin film transistors, polycrystalline silicon thin film transistors, or amorphous silicon thin film transistors, and are all N-type thin film transistors.

(36) Another embodiment of the present invention further provides a TFT substrate, including the GOA circuit described in the above embodiment.

(37) Another embodiment of the present invention further provides a display device, including the TFT substrate described in the above embodiment.

(38) Another embodiment of the present invention also provides an electronic device, including the display device described in the above embodiment. For example, the electronic device may be a product with a display function such as an LCD TV, a mobile phone, a digital camera, a tablet computer, a computer, an electronic paper, and a navigator.

(39) In summary, the GOA circuit structure of the present invention solves the problem that the GOA circuit buffer TFT in the prior art is subjected to the stress of the CK signal Vds, and the Vth of the TFT is prone to positive deviation, resulting in serious distortion of the output signal. To a large extent, the stability of the gate drive circuit is improved, which is beneficial to the improvement of the display effect of the liquid crystal display panel.

(40) Although the present disclosure has been shown and described with respect to one or more implementations, those skilled in the art will think of equivalent variations and modifications based on reading and understanding of this specification and the drawings. This disclosure includes all such modifications and variations, and is limited only by the scope of the appended claims. In particular with regard to the various functions performed by the above-mentioned components, the terminology used to describe such components is intended to correspond to any component (unless otherwise indicated) that performs the specified function of the component (eg it is functionally equivalent), even if it is structurally different from the disclosed structure that performs the functions in the exemplary implementation of the present specification shown herein.

(41) Furthermore, although specific features of this specification have been disclosed with respect to only one of several implementations, such features can be combined with one or more other features of other implementations as may be desired and advantageous for a given or specific application. Moreover, to the extent that the terms “including”, “having”, “containing” or variations thereof are used in specific embodiments or claims, such terms are intended to be included in a manner similar to the term “comprising”.

(42) The above are only the preferred embodiments of the present disclosure. It should be pointed out that those of ordinary skill in the art can make several improvements and retouching without departing from the principles of the present disclosure. protected range.

INDUSTRIAL APPLICABILITY

(43) The voltage of the GOA circuit VGL+Vth in the embodiment of the present invention is always stored at the Q point, the GOA circuit structure of the present invention solves the problem that the GOA circuit buffer TFT in the prior art is subjected to the stress of the CK signal Vds, and the Vth of the TFT is prone to positive deviation, resulting in serious distortion of the output signal. To a large extent, the stability of the gate drive circuit is improved, which is beneficial to the improvement of the display effect of the liquid crystal display panel.