Pixel driving circuit and electrowetting display

Abstract

The present invention provides a pixel driving circuit and an electrowetting display. The pixel driving circuit includes a timing control unit, a first switching unit, a second switching unit, and a power supply unit. The power supply unit supplies a constant driving voltage. One control period includes a first period and a second period. In the first period, the timing control unit controls the first switching unit to be on and the second switching unit to be off, so as to conduct the first electrode of the electrowetting pixel device to ground. In the second period, the timing control unit controls the first switching unit to be off and the second switching unit to be on, so as to conduct the second electrode of the electrowetting pixel device to ground.

Description

[Technical Field]

[0001] This invention claims priority from Chinese Application No. 202210309153.9, filed on March 28, 2022, the entire contents of which are incorporated herein by reference. The present invention relates to the field of display technology, in particular to pixel driving circuits and electrowetting displays. [Background technology]

[0002] Currently, the mainstream displays are mainly LCD (Liquid Crystal Display) displays and OLED (Organic Light-Emitting Diode) displays. However, LCD displays require a backlight module as a light source, while OLED displays use organic light-emitting materials that emit light themselves in an excited state, making the display effect susceptible to ambient light. In strong ambient light, both LCD and OLED displays need to increase the display brightness to improve the display effect.

[0003] Electrowetting displays, which use reflective light emission as their display principle, can ensure excellent visibility even in strong illumination environments. Electrowetting displays have advantages such as portability, thinness, lightness, flexibility, high contrast, low power consumption, and fast response, making them an important part of the display field. Research on electrowetting displays has made good progress in recent years, but current electrowetting displays still suffer from problems such as charge trapping and ink splitting. Summary of the Invention [Problem to be solved by the invention]

[0004] An embodiment of the present invention provides a pixel driving circuit and an electrowetting display that can solve the problems of charge trapping and ink splitting in the electrowetting display. [Means for solving the problem]

[0005] In a first aspect, an embodiment of the present invention provides a pixel driving circuit for use in an electrowetting display, comprising a timing control unit, a first switching unit, a second switching unit, and a power supply unit. The timing control unit is electrically connected to a control end of the first switching unit and a control end of the second switching unit, respectively. The first switching unit is connected in series between a first electrode of an electrowetting pixel device and ground. The second switching unit is connected in series between a second electrode of the electrowetting pixel device and ground. The power supply unit is electrically connected to the first electrode of the electrowetting pixel device and the second electrode of the electrowetting pixel device, respectively. The power supply unit supplies a constant driving voltage. The timing control unit periodically controls the first switching unit and the second switching unit. One control period includes a first period and a second period. During the first period, the timing control unit controls the first switching unit to be on and the second switching unit to be off, thereby conducting the first electrode of the electrowetting pixel device to ground. During the second period, the timing control unit controls the first switching unit to be turned off and the second switching unit to be turned on, thereby conducting the second electrode of the electrowetting pixel device to ground.

[0006] In a second aspect, embodiments of the present invention provide an electrowetting display, comprising a first substrate, a second substrate, a display panel and the pixel driving circuit of any of the first aspects. The display panel is disposed between the first substrate and the second substrate. The display panel comprises electrowetting pixel devices arranged in an array. The pixel driving circuit is electrically connected to the electrowetting pixel devices.

[0007] Compared with the prior art, the advantageous effects of the embodiments of the present invention are as follows: When the electrowetting pixel device is driven by the pixel driving circuit, the timing control unit periodically controls the first switching unit and the second switching unit to periodically turn on and off the first switching unit and the second switching unit. One control period includes a first period and a second period. During the first period, the timing control unit controls the first switching unit to be on and the second switching unit to be off, thereby connecting the first electrode of the electrowetting pixel device to ground and the second electrode of the electrowetting pixel device to the power supply unit, and operating the electrowetting pixel device with the driving voltage output from the power supply unit. During the second period, the timing control unit controls the first switching unit to be off and the second switching unit to be on, thereby connecting the first electrode of the electrowetting pixel device to the power supply unit and the second electrode of the electrowetting pixel device to ground, and operating the electrowetting pixel device with the driving voltage output from the power supply unit. In one control period, the voltage difference between the first electrode and the second electrode of the electrowetting pixel device is reversed, which can prevent the problems of charge trapping and ink splitting caused by charge accumulation at the first electrode and the second electrode of the electrowetting pixel device. [Brief explanation of the drawings]

[0008] In order to more clearly explain the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings necessary for explaining the embodiments. Of course, the drawings described below are only a part of the embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without any creative efforts. [Figure 1] 1 is a diagram showing the configuration of an electrowetting pixel device according to an embodiment of the present invention; [Figure 2] 4 is a timing chart showing driving of an electrowetting pixel device by a pixel driving circuit according to an embodiment of the present invention; [Figure 3] FIG. 2 illustrates the connections of an electrowetting pixel device according to an embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing the configuration of an electrowetting pixel device according to another embodiment of the present invention. [Figure 5] FIG. 10 is a diagram illustrating the connections of an electrowetting pixel device according to another embodiment of the present invention. [Figure 6] 1 is a diagram showing the configuration of an electrowetting display according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following description, for purposes of illustration and not limitation, specific details are provided, such as particular system structures and techniques, in order to thoroughly understand embodiments of the present invention. However, those skilled in the art will recognize that the present invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted, so that the present invention may be described without obscuring it with unnecessary detail.

[0010] It is to be understood that when used in the present description and claims, the term "comprising" indicates the presence of stated features, wholes, steps, operations, elements, and / or modules, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, modules, and / or groups thereof.

[0011] As used in the present specification and claims, the term "when" may be interpreted as "when," "once," "in response to determining," or "in response to detecting," depending on the context. Similarly, the phrases "when it is determined" or "when [a described condition or event] is detected" may be interpreted to mean "once it is determined" or "in response to determining" or "once [a described condition or event] is detected" or "in response to detecting [a described condition or event]," depending on the context.

[0012] Furthermore, in describing the present specification and claims, terms such as "first," "second," "third," etc. are intended solely for the purpose of differentiation and description, but shall not be understood as indicating or implying relative importance.

[0013] References in the present specification to "one embodiment" or "some embodiments" or the like mean that one or more embodiments of the present invention have the particular feature, structure, or characteristic described with reference to the embodiment. Thus, the phrases "in one embodiment," "in some embodiments," "in some other embodiments," "in some additional embodiments," and the like appearing in different parts of this specification do not necessarily mean to refer to the same embodiment, unless otherwise emphasized, but rather mean "one or more, but not all, embodiments." The terms "comprise," "include," "includes," "having," and variations thereof mean "including but not limited to," unless otherwise emphasized.

[0014] The operating principle of the electrowetting pixel device is as follows: Applying a DC driving voltage between the first and second electrodes of the electrowetting pixel device causes the ink in the electrowetting pixel device to contract and spread, thereby realizing the optical switching function. When no voltage is applied to the first and second electrodes of the electrowetting pixel device, the ink spreads evenly on the surface of the insulating medium, and the electrowetting pixel device is in a completely dark state, corresponding to the color of the ink, i.e., the electrowetting pixel device is in the "off" state. When a voltage is applied to the first and second electrodes of the electrowetting pixel device, the ink begins to contract, and due to the driving voltage and surface tension, the ink contracts toward one side like an oil droplet, causing the electrowetting pixel device to reflect the color of the substrate, i.e., the electrowetting pixel device is in the "on" state.

[0015] Currently, the driving method for controlling the degree of ink contraction in an electrowetting pixel device is mainly to adjust the magnitude of the DC voltage applied to the first and second electrodes, and the higher the voltage, the greater the degree of ink contraction and the higher the grayscale brightness of the electrowetting pixel device. However, if a DC voltage is applied to the first and second electrodes of the electrowetting pixel device for a long period of time, the electrowetting pixel device is prone to charge trapping and ink splitting, which can cause problems such as uneven grayscale voltage and slow or no ink recovery. First Example

[0016] Based on the above problems, an embodiment of the present invention provides a pixel driving circuit. As shown in Figure 1, the pixel driving circuit includes a timing control unit 100, a first switching unit 200, a second switching unit 300, and a power supply unit 400. The timing control unit 100 is electrically connected to the control end of the first switching unit 200 and the control end of the second switching unit 300, respectively. The first switching unit 200 is connected in series between a first electrode of an electrowetting pixel device 500 and ground. The second switching unit 300 is connected in series between a second electrode of the electrowetting pixel device 500 and ground. The power supply unit 400 is electrically connected to the first electrode of the electrowetting pixel device 500 and the second electrode of the electrowetting pixel device 500, respectively.

[0017] Specifically, when the electrowetting pixel device 500 is driven by the pixel driving circuit, the timing control unit 100 periodically controls the first switching unit 200 and the second switching unit 300 to periodically turn on and off the first switching unit 200 and the second switching unit 300. One control period includes a first period and a second period. During the first period, the timing control unit 100 controls the first switching unit 200 to turn on and the second switching unit 300 to turn off, thereby connecting the first electrode of the electrowetting pixel device 500 to ground and connecting the second electrode of the electrowetting pixel device 500 to the power supply unit 400, and operating the electrowetting pixel device 500 with the driving voltage output from the power supply unit 400. During the second period, the timing control unit 100 controls the first switching unit 200 to be off and the second switching unit 300 to be on, thereby electrically connecting the first electrode of the electrowetting pixel device 500 to the power supply unit 400 and electrically connecting the second electrode of the electrowetting pixel device 500 to ground, and operating the electrowetting pixel device 500 with the driving voltage output from the power supply unit 400. During one control period, the voltage difference between the first electrode and the second electrode of the electrowetting pixel device 500 is reversed, which can prevent problems such as charge trapping and ink splitting due to charge accumulation at the first electrode and the second electrode of the electrowetting pixel device 500.

[0018] In one embodiment of the present invention, one control period further includes a third period and a fourth period. During the third period, the timing control unit 100 controls the first switching unit 200 to turn on and the second switching unit 300 to turn on, thereby connecting both the first electrode and the second electrode of the electrowetting pixel device 500 to ground. In this case, the electrowetting pixel device 500 does not operate. During the fourth period, the timing control unit 100 controls the first switching unit 200 to turn off and the second switching unit 300 to turn off, thereby connecting both the first electrode and the second electrode of the electrowetting pixel device 500 to the power supply unit 400. In this case, the electrowetting pixel device 500 does not operate. The third period is between the first period and the second period, or the fourth period is between the first period and the second period.

[0019] Specifically, the electrowetting pixel device 500 is in an operating state during both the first and second periods, and the voltages of the first and second electrodes are reversed when transitioning from the first period to the second period. The electrowetting pixel device 500 is in an inactive state during the third and fourth periods, with the third period occurring between the first and second periods, or the fourth period occurring between the first and second periods. This allows the electrowetting pixel device 500 to transition from an operating state to an inactive state and then from an inactive state to an operating state, preventing the problem of charge trapping due to charge accumulation caused by applying a DC voltage to the first and second electrodes of the electrowetting pixel device 500 for a long period of time. The ink in the electrowetting pixel device 500 can transition from a contracted state to a diffusing state and then from the diffusing state to a contracted state, achieving rapid contraction and diffusion of the ink and preventing the occurrence of ink splitting.

[0020] 2, one driving period of the timing control unit 100 includes T1, T2, T3, and T4. The timing control unit 100 outputs a first pulse signal PWM1 to control the first switching unit 200 and outputs a second pulse signal PWM2 to control the second switching unit 300.

[0021] During the T1 period, the first pulse signal PWM1 is at a high level and the second pulse signal PWM2 is at a low level, the first switching unit 200 is turned on and the second switching unit 300 is turned off, the voltage of the first electrode of the electrowetting pixel device 500 is zero, the voltage of the second electrode of the electrowetting pixel device 500 is V, the voltage difference between the first electrode and the second electrode of the electrowetting pixel device 500 is -V, and the ink in the electrowetting pixel device 500 contracts.

[0022] During the T2 period, the first pulse signal PWM1 is at a high level, the second pulse signal PWM2 is at a high level, the first switching unit 200 is turned on, the second switching unit 300 is turned on, the voltage of the first electrode of the electrowetting pixel device 500 is zero, the voltage of the second electrode of the electrowetting pixel device 500 is zero, the voltage difference between the first electrode and the second electrode of the electrowetting pixel device 500 is zero, and the ink in the electrowetting pixel device 500 diffuses and returns to its initial state.

[0023] During the T3 period, the first pulse signal PWM1 is at a low level, the second pulse signal PWM2 is at a high level, the first switching unit 200 is turned off, the second switching unit 300 is turned on, the voltage of the first electrode of the electrowetting pixel device 500 is V, the voltage of the second electrode of the electrowetting pixel device 500 is zero, the voltage difference between the first electrode and the second electrode of the electrowetting pixel device 500 is V, and the ink in the electrowetting pixel device 500 contracts.

[0024] During the T4 period, the first pulse signal PWM1 is at a low level, the second pulse signal PWM2 is at a low level, the first switching unit 200 is turned off, the second switching unit 300 is turned off, the voltage of the first electrode of the electrowetting pixel device 500 is V, the voltage of the second electrode of the electrowetting pixel device 500 is V, the voltage difference between the first electrode and the second electrode of the electrowetting pixel device 500 is zero, and the ink in the electrowetting pixel device 500 diffuses and returns to its initial state.

[0025] The conventional electrowetting pixel device 500 adjusts the gray level brightness by changing the output voltage of the power supply 400. The pixel driving circuit of the present invention adjusts the gray level brightness of the electrowetting pixel device 500 by controlling the duty ratio of the first pulse signal PWM1 and the duty ratio of the second pulse signal PWM2, and only requires one constant DC driving voltage to be supplied by the power supply 400, which reduces the requirements for the power supply 400 and further reduces the design and production costs of the pixel driving circuit.

[0026] 3, the first switching unit 200 includes a first switch tube Q1. The control end of the first switch tube Q1 is electrically connected to the timing control unit 100. The first switch tube Q1 is connected in series between the first electrode of the electrowetting pixel device 500 and ground.

[0027] Specifically, the first control signal output from the timing control unit 100 controls the on / off of the first switch tube Q1. Illustratively, when the first control signal output from the timing control unit 100 is at a high level, the first switch tube Q1 is turned on, and the first electrode of the electrowetting pixel device 500 is connected to ground. In this case, the first electrode voltage of the electrowetting pixel device 500 is zero. When the first control signal output from the timing control unit 100 is at a low level, the first switch tube Q1 is turned off, and the first electrode of the electrowetting pixel device 500 is not connected to ground. In this case, the first electrode voltage of the electrowetting pixel device 500 is the driving voltage supplied from the power supply unit 400.

[0028] Illustratively, the first switch tube Q1 is an NMOS tube.

[0029] 3, the second switching unit 300 includes a second switch tube Q2. The control end of the second switch tube Q2 is electrically connected to the timing control unit 100. The second switch tube Q2 is connected in series between the second electrode of the electrowetting pixel device 500 and ground.

[0030] Specifically, the second control signal output from the timing control unit 100 controls the on / off of the second switch tube Q2. Illustratively, when the second control signal output from the timing control unit 100 is at a high level, the second switch tube Q2 is turned on, and the second electrode of the electrowetting pixel device 500 is connected to ground. In this case, the second electrode voltage of the electrowetting pixel device 500 is zero. When the second control signal output from the timing control unit 100 is at a low level, the second switch tube Q2 is turned off, and the second electrode of the electrowetting pixel device 500 is not connected to ground. In this case, the second electrode voltage of the electrowetting pixel device 500 is the driving voltage supplied from the power supply unit 400.

[0031] Illustratively, the second switch tube Q2 is an NMOS tube. Second Example

[0032] 4 is a diagram showing the configuration of an electrowetting pixel device 500 according to another embodiment of the present invention. Referring to FIG. 4, the pixel driving circuit further includes a first current limiting unit 600 and a second current limiting unit 700. The first current limiting unit 600 is connected in series between a first electrode of the electrowetting pixel device 500 and the power supply unit 400, and the second current limiting unit 700 is connected in series between a second electrode of the electrowetting pixel device 500 and the power supply unit 400.

[0033] Specifically, the driving voltage output from the power supply unit 400 is applied to a first electrode of the electrowetting pixel device 500 by the first current limiting unit 600, and is applied to a second electrode of the electrowetting pixel device 500 by the second current limiting unit 700. The first current limiting unit 600 and the second current limiting unit 700 have the function of limiting the current, and prevent damage to the electrowetting pixel device 500 due to an excessive current flowing through the electrowetting pixel device 500.

[0034] 5, the first current limiting unit 600 includes a first resistor R1. The first resistor R1 is connected in series between the first electrode of the electrowetting pixel device 500 and the power supply unit 400. The second current limiting unit 700 includes a second resistor R2. The second resistor R2 is connected in series between the second electrode of the electrowetting pixel device 500 and the power supply unit 400.

[0035] Specifically, the designer sets the resistance value of the first resistor R1 and the resistance value of the second resistor R2 as needed to achieve a proper current limiting effect and protect the electrowetting pixel device 500 from being damaged. Third Example

[0036] FIG. 6 is a diagram illustrating the configuration of an electrowetting display according to one embodiment of the present invention. As shown in FIG. 6, the electrowetting display includes a first substrate 601, a second substrate 602, a display panel 603, and the above-described pixel driving circuit. The display panel 603 is located between the first substrate 601 and the second substrate 602 and includes electrowetting pixel devices arranged in an array. The pixel driving circuit electrically connects the electrowetting pixel devices. This electrowetting display can solve the problems of charge trapping and ink splitting that occur in conventional electrowetting displays. For details on the operating principle, please refer to the above description of the pixel driving circuit, and a detailed description will be omitted here.

[0037] The above embodiments are merely intended to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will understand that the technical solutions described in the above embodiments may be modified or some of the technical features may be replaced with equivalents. Furthermore, such modifications and replacements fall within the scope of protection of the present invention, provided that the essence of the corresponding technical solutions does not deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A pixel driving circuit applied to an electrowetting display, comprising: a timing control unit, a first switching unit, a second switching unit, and a power supply unit; the timing control unit is electrically connected to a control end of the first switching unit and a control end of the second switching unit, the first switching unit is connected in series between a first electrode of the electrowetting pixel device and ground; the second switching unit is connected in series between a second electrode of the electrowetting pixel device and ground; the power supply is electrically connected to a first electrode of the electrowetting pixel device and a second electrode of the electrowetting pixel device, respectively; The power supply unit supplies a constant driving voltage; the timing control unit periodically controls the first switching unit and the second switching unit; one control period includes a first period and a second period; During the first period, the timing control unit turns on the first switching unit and turns off the second switching unit, thereby conducting the first electrode of the electrowetting pixel device to ground; During the second period, the timing control unit controls the first switching unit to be turned off and the second switching unit to be turned on, thereby conducting the second electrode of the electrowetting pixel device to ground; the one control period further includes a third period and a fourth period; During the third period, the timing control unit turns on the first switching unit and turns on the second switching unit, thereby conducting both the first electrode and the second electrode of the electrowetting pixel device to ground; During the fourth period, the timing control unit turns off the first switching unit and turns off the second switching unit, thereby conducting both the first electrode and the second electrode of the electrowetting pixel device to the power supply unit; one of the third period and the fourth period is located between the first period and the second period of a current control period, and the other of the third period and the fourth period is located between the second period of the current control period and the first period of a next control period.

2. further including a first current limiting unit and a second current limiting unit; the first current limiter is connected in series between the first electrode of the electrowetting pixel device and the power supply; The pixel driving circuit according to claim 1 , wherein the second current limiting unit is connected in series between the second electrode of the electrowetting pixel device and the power supply unit.

3. the first current limiting unit includes a first resistor, 3. The pixel driving circuit of claim 2, wherein the first resistor is connected in series between the first electrode of the electrowetting pixel device and the power supply.

4. the second current limiting unit includes a second resistor, 3. The pixel driving circuit of claim 2, wherein the second resistor is connected in series between the second electrode of the electrowetting pixel device and the power supply.

5. the first switching unit includes a first switch tube; The control end of the first switch tube is electrically connected to the timing control unit; 2. The pixel driving circuit of claim 1, wherein the first switch tube is connected in series between the first electrode of the electrowetting pixel device and ground.

6. 6. The pixel driving circuit of claim 5, wherein the first switch tube is an NMOS tube.

7. the second switching unit includes a second switch tube; The control end of the second switch tube is electrically connected to the timing control unit; 2. The pixel driving circuit of claim 1, wherein the second switch tube is connected in series between the second electrode of the electrowetting pixel device and ground.

8. 8. The pixel driving circuit of claim 7, wherein the second switch tube is an NMOS tube.

9. 1. An electrowetting display, comprising: a first substrate, a second substrate, a display panel, and the pixel drive circuit according to any one of claims 1 to 8; the display panel is disposed between the first substrate and the second substrate; the display panel includes electrowetting pixel devices arranged in an array; Electrowetting display, characterized in that the pixel driving circuit is electrically connected to the electrowetting pixel device.

Images