A cholesteric liquid crystal display device and its driving method

Abstract

This invention discloses a cholesteric liquid crystal display device and its driving method, belonging to the field of display technology. The device includes a display panel, a driving chip, a common voltage generation module, and a voltage superposition module integrated on a TFT substrate. The voltage superposition module includes a series capacitor network and a control switch unit. During driving, the control switch unit is first turned on, and the driving chip provides a first voltage to the pixel electrode; then, the control switch unit is turned off to isolate the pixel electrode, and the AC common voltage is changed to a second voltage of opposite polarity; the bootstrap effect of the series capacitor network is used to raise the pixel electrode potential to generate an additional voltage. The first voltage, the second voltage, and the additional voltage are superimposed at both ends of the cholesteric liquid crystal layer to form a high-voltage driving signal, driving the liquid crystal layer to switch between planar and vertical states. This application significantly reduces system cost and design threshold, while improving integration and reliability.

Description

Technical Field

[0001] This invention relates to the field of display technology, and in particular to a cholesteric liquid crystal display device and its driving method. Background Technology

[0002] Cholesteric liquid crystal (CLC) is a chiral liquid crystal material with a periodic helical structure. Its unique property lies in its ability to exhibit bistable or multistable states; that is, after the removal of an applied electric field, the liquid crystal molecules can stabilize in two or more different alignment states without continuously consuming electrical energy to maintain the image. This characteristic makes CLC highly promising for the fabrication of low-power, passively reflective "electronic paper" display devices, making it ideal for applications requiring long-term static display, such as e-book readers, electronic shelf labels, and IoT status indicators.

[0003] Common stable states of cholesteric liquid crystals include:

[0004] Planar State (P-state): The helical axis of the liquid crystal molecules is perpendicular to the substrate surface. In this state, cholesteric liquid crystals selectively reflect incident light of a specific wavelength (the wavelength of which is determined by the pitch), thus exhibiting a specific color or black-and-white display effect. This is its main operating state as a reflective display.

[0005] Homeotropic State (H state): Under a sufficiently strong applied electric field, the long axis of the liquid crystal molecules tends to align parallel to the direction of the electric field, that is, perpendicular to the substrate surface, and the helical structure is unraveled. At this time, the cholesteric liquid crystal layer exhibits a transparent state.

[0006] To achieve display, cholesteric liquid crystal needs to be reversibly switched between the P-state (reflective state, displaying content) and the H-state (transparent state, corresponding to displaying the background or erasing state). However, switching from the P-state to the H-state requires applying a high voltage, typically tens of volts (e.g., 40V to 60V, depending on parameters such as the cell thickness of the liquid crystal material), which is much higher than the voltage required to drive ordinary nematic liquid crystals.

[0007] Currently, the mainstream solution for driving such display panels is to directly use dedicated driver integrated circuits (driver ICs) capable of outputting corresponding high voltages. However, this solution has significant limitations: high cost – driver chips with high-voltage output capabilities are far more expensive than general-purpose low-voltage driver chips (such as those used in mobile phones and tablets, which output voltages below 15V) due to their specialized manufacturing processes and relatively small market size. Limited selection – the limited selection of suppliers and models of high-voltage driver chips increases supply chain risks and flexibility constraints in display module design. System complexity – in some cases, even with high-voltage driver chips, the output voltage may still be at a critical state, leading to insufficient liquid crystal state switching, decreased contrast, or slower response speed, affecting display quality.

[0008] To overcome the problems caused by high-voltage driver ICs, some attempts have been made in existing technologies, such as using external discrete charge pumps or boost converter circuits to boost the output voltage of low-voltage driver ICs. However, these solutions typically have the following drawbacks: They are complex and space-consuming; the additional boost circuit requires the introduction of discrete components such as inductors, capacitors, and diodes, increasing the area and layout complexity of the printed circuit board (PCB), which contradicts the trend towards thinner and lighter display devices. Efficiency and noise issues arise; the boost conversion process introduces energy loss, reducing system efficiency, and may also generate electromagnetic interference (EMI), affecting the purity of the display signal and leading to unstable display quality. Timing control matching is difficult; perfect synchronization between the external boost circuit and the precise timing of the display driver is difficult to achieve, potentially causing voltage waveform distortion and affecting the driving effect of the liquid crystal. Summary of the Invention

[0009] To address the technical problems existing in the background art, the present invention proposes a cholesteric liquid crystal display device and its driving method.

[0010] The present invention proposes a cholesteric liquid crystal display device, comprising a display panel, a driving chip, a common voltage generation module, and a voltage superposition module; the display panel includes a TFT substrate and a CF substrate, with a cholesteric liquid crystal layer disposed between the TFT substrate and the CF substrate; pixel electrodes and a series capacitor network are disposed on the TFT substrate; an AC common electrode is disposed on the CF substrate; the voltage superposition module is integrated on the TFT substrate and includes a series capacitor network and a control switch unit, the control switch unit being connected between the pixel electrodes and the driving chip;

[0011] The control switch unit responds to the switch control signal to turn on or off the electrical connection between the pixel electrode and the driver chip; the common voltage generation module responds to the timing control signal to change the voltage polarity of the AC common stage; wherein, the switch control signal and the timing control signal cooperate to execute the following steps in sequence:

[0012] When the control switch unit is turned on, the driver chip provides a first voltage to the pixel electrode;

[0013] The control switch unit is turned off by the switch control signal, thus isolating the pixel electrode from the driver chip;

[0014] The polarity of the AC common voltage is changed by a timing control signal, switching it to a second voltage with the opposite polarity to the first voltage.

[0015] During the AC common voltage polarity change, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode that is already in isolation to generate an additional voltage.

[0016] The first voltage, the second voltage, and the additional voltage are superimposed at both ends of the cholesteric liquid crystal layer to generate a superimposed voltage, thereby driving the cholesteric liquid crystal layer to switch between planar and vertical alignment states.

[0017] Preferably, a first electrode layer and a second electrode layer are sequentially formed on the TFT substrate. The first electrode layer includes a plurality of pixel electrodes, and the second electrode layer includes a series capacitor network.

[0018] Preferably, after the control switch unit is turned off, the pixel electrode is isolated from the driver chip and is in a high-resistance state; the bootstrap effect of the series capacitor network acts on the pixel electrode in the high-resistance state through capacitive coupling, causing its potential to rise.

[0019] Preferably, the driving chip provides a first voltage to the control switch unit with an absolute value equal to a preset voltage value V; the common voltage generation module provides a second voltage to the AC common stage with an absolute value equal to the preset voltage value V.

[0020] Preferably, when the voltage polarity of the AC common stage changes, the polarity of the second voltage is opposite to that of the first voltage.

[0021] Preferably, the control switch unit includes multiple thin-film transistors, the gates of each thin-film transistor are connected to a switch control signal, the sources are connected to the corresponding pixel electrodes, and the drains are connected to the output terminals of each channel of the driver chip.

[0022] Preferably, one end of the series capacitor network is connected to a fixed potential terminal, and the other end is a floating terminal; the fixed potential terminal is a ground terminal or a DC bias voltage terminal.

[0023] The present invention proposes a driving method for a cholesteric liquid crystal display device, comprising the following steps:

[0024] Generate mutually coordinating switching control signals and timing control signals;

[0025] Under the control of the switch control signal, the control switch unit is turned on, and the driver chip provides a first voltage to the pixel electrode;

[0026] The control switch unit is cut off by the switch control signal, thus isolating the pixel electrode from the driver chip;

[0027] The polarity of the AC common voltage is changed by a timing control signal, switching to a second voltage with the opposite polarity to the first voltage.

[0028] In the process of changing the polarity of the AC common voltage, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode that is already in the isolated state to generate an additional voltage.

[0029] This results in the superposition of a first voltage, a second voltage, and an additional voltage at both ends of the cholesteric liquid crystal layer, generating a superimposed voltage.

[0030] The cholesteric liquid crystal layer is switched from a planar state to a vertically aligned state by superimposing a voltage.

[0031] Preferably, the step of utilizing the bootstrap effect of a series capacitor network to raise the potential of the pixel electrode, which is already in an isolated state, to generate an additional voltage specifically includes:

[0032] After the pixel electrode is in a high-resistivity state isolated from the driver chip, the series capacitor network raises the potential of the pixel electrode through capacitive coupling, and the additional voltage is equal to the absolute value of the voltage change of the storage capacitor electrode.

[0033] This invention presents a cholesteric liquid crystal display device and its driving method. Through a unique voltage superposition module design, the boost circuit is seamlessly integrated into the display panel, fundamentally eliminating reliance on external high-voltage chips or complex boost circuits, significantly reducing system material costs and design barriers. This architecture utilizes the inherent structure of the panel to achieve voltage multiplication, avoiding space occupation and signal interference issues caused by external components, and improving system integration and reliability. Precise timing control ensures the matching of the voltage superposition process with the liquid crystal driving requirements, effectively optimizing key performance indicators such as contrast and response speed. It fully leverages the bistable characteristics of cholesteric liquid crystals, achieving excellent display effects while maintaining low power consumption, providing a more competitive technical solution for applications such as electronic paper. Attached Figure Description

[0034] Figure 1 This is a schematic diagram showing the distribution of an embodiment of a cholesteric liquid crystal display device proposed in this invention;

[0035] Figure 2 This is a circuit connection diagram of an embodiment of a cholesteric liquid crystal display device proposed in this invention;

[0036] Figure 3 This is a schematic diagram showing the distribution of the storage capacitor in a cholesteric liquid crystal display device according to the present invention.

[0037] Figure 4 This is a schematic diagram of the display panel architecture of a cholesteric liquid crystal display device proposed in this invention;

[0038] Figure 5 This is a schematic diagram of the display panel voltage boost in one embodiment of a cholesteric liquid crystal display device proposed in this invention;

[0039] Figure 6 This is a timing diagram for the existing technology.

[0040] Figure 7 This is a driving timing diagram of one embodiment of a cholesteric liquid crystal display device proposed in this invention;

[0041] Figure 8 This is a schematic diagram illustrating the workflow of a driving method for a cholesteric liquid crystal display device proposed in this invention. Detailed Implementation

[0042] Reference Figures 1-7 The present invention proposes a cholesteric liquid crystal display device, comprising a display panel, a driving chip, a common voltage generation module, and a voltage superposition module; the display panel comprises a TFT substrate and a CF substrate, wherein a cholesteric liquid crystal layer is disposed between the TFT substrate and the CF substrate; a pixel electrode and a series capacitor network are disposed on the TFT substrate; an AC common electrode is disposed on the CF substrate; the voltage superposition module is integrated on the TFT substrate and includes a series capacitor network and a control switch unit, wherein the control switch unit is connected between the pixel electrode and the driving chip;

[0043] The control switch unit responds to the switch control signal to turn on or off the electrical connection between the pixel electrode and the driver chip; the common voltage generation module responds to the timing control signal to change the voltage polarity of the AC common stage; wherein, the switch control signal and the timing control signal cooperate to execute the following steps in sequence:

[0044] When the control switch unit is turned on, the driver chip provides a first voltage to the pixel electrode;

[0045] The control switch unit is turned off by the switch control signal, thus isolating the pixel electrode from the driver chip;

[0046] The polarity of the AC common voltage is changed by a timing control signal, switching it to a second voltage with the opposite polarity to the first voltage.

[0047] During the AC common voltage polarity change, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode that is already in isolation to generate an additional voltage.

[0048] The first voltage, the second voltage, and the additional voltage are superimposed at both ends of the cholesteric liquid crystal layer to generate a superimposed voltage, thereby driving the cholesteric liquid crystal layer to switch between planar and vertical alignment states.

[0049] In this embodiment, a first electrode layer and a second electrode layer are sequentially formed on the TFT substrate. The first electrode layer includes a plurality of pixel electrodes, and the second electrode layer includes a series capacitor network.

[0050] Specifically, the series capacitor network consists of multiple sets of pixel electrodes inherent in the display panel and storage capacitor electrodes below them. The pixel electrodes are connected to the source of their corresponding TFTs. The multiple sets of pixel electrodes are independent of each other, while the storage capacitor electrode sets are connected in series with each other. This network is specifically used to apply bootstrap signals to the first electrode layer through capacitive coupling.

[0051] In this embodiment, after the control switch unit is turned off, the pixel electrode is isolated from the driver chip and is in a high-resistance state; the bootstrap effect of the series capacitor network acts on the pixel electrode in the high-resistance state through capacitive coupling, causing its potential to rise.

[0052] In this embodiment, the driver chip provides a first voltage to the control switch unit with an absolute value equal to a preset voltage value V; the common voltage generation module provides a second voltage to the AC common stage with an absolute value equal to the preset voltage value V.

[0053] Specifically, when the voltage polarity of the AC common stage changes, the polarity of the second voltage is opposite to that of the first voltage.

[0054] In this embodiment, the control switch unit includes multiple thin-film transistors. The gates of each thin-film transistor are connected to the switch control signal, the sources are connected to the corresponding pixel electrodes, and the drains are connected to the output terminals of each channel of the driver chip.

[0055] Specifically, one end of the series capacitor network is connected to a fixed potential terminal, and the other end is a floating terminal; the fixed potential terminal is either a ground terminal or a DC bias voltage terminal.

[0056] like Figure 1 As shown, the voltage superposition module is integrated on the TFT substrate and includes a series capacitor network and a control switching unit. This module is preferably located in a non-display area of ​​the display panel, such as above or around the bonding area, and receives drive signals via traces on a flexible printed circuit board (FPC). The control switching unit connects the pixel electrode and the driving chip, and is preferably implemented using multiple thin-film transistors (TFTs). Figure 2As shown, the gates of each TFT are connected to a common switch control signal, the sources are connected to the corresponding pixel electrodes, and the drains are connected to the output of the driver chip, thereby achieving synchronous control of all pixel electrodes.

[0057] like Figure 3 and Figure 4 As shown, the storage capacitors corresponding to each pixel unit are connected end to end to form a complete capacitor series branch. The common electrode is on the CF substrate side, the pixel electrode and the storage electrode are on the TFT substrate side, and the storage capacitor electrode is directly below the pixel electrode and separated from the pixel electrode by an insulating layer.

[0058] like Figure 4 As shown, the bootstrap process of the bootstrap effect in a series capacitor network includes:

[0059] Step 1: The pixel TFT gate is turned on, and a positive charge voltage +A is charged to the pixel electrode through the source (at this time, the common electrode is charged with a negative charge -A while the storage electrode is 0). After the charge is completed, the gate is turned off and the source is also turned off. At this time, the charge on the pixel electrode remains unchanged. The common electrode is provided with active input by the printed circuit board, and the charge remains unchanged (forming a capacitor saturation with the pixel electrode).

[0060] Step 2: The storage electrode is instantly charged with +A charge from 0V. At this time, the pixel electrode is in a floating state. According to the capacitive bootstrap effect (or capacitive coupling effect), the charge on it will double, and the voltage will become +2A. The voltage across the common electrode is 3A, which increases the voltage across the upper and lower sides of the liquid crystal.

[0061] Specifically, such as Figure 5 and Figure 7 As shown, the workflow of the driving method is as follows:

[0062] Charging Phase: The common voltage generation module starts operating according to the timing control signal, switching the AC common voltage from the initial potential (0V) to a second voltage (e.g., -17.5V), the polarity of which is opposite to the first voltage. The timing controller generates coordinated switching control signals and timing control signals. First, the switching control signal (e.g., high level) controls the control switch unit to turn on. At this time, the driver chip provides a first voltage (e.g., +15V) to the pixel electrode of the first electrode layer, charging the pixel electrode and the series capacitor network of the second electrode layer. During this phase, the AC common voltage is maintained at an initial potential, such as the reference ground potential (-17.5V).

[0063] Isolation and Bootstrap Phase: Subsequently, the control switch unit is turned off via a switch control signal (such as a low level). This operation completely isolates the pixel electrode from the output of the driver chip, entering a high-impedance (floating) state. After confirming that the control switch unit is completely turned off, the electrode voltage of the storage capacitor switches from the initial 0V potential to a first voltage of +17.5V.

[0064] During the voltage transition of the storage capacitor electrode, the second electrode layer acts on the first electrode layer, which is in a high-resistivity state, utilizing the bootstrap effect (i.e., capacitive coupling) of the series capacitor network. This forces the pixel electrode potential to rise synchronously, thus generating an additional voltage. According to the law of conservation of charge (Q=C×U), the magnitude of the pixel electrode potential rise is equal to the absolute value of the AC common-stage voltage change. For example, if the pixel electrode potential is raised from +15V to +32.5V, the additional voltage rise is 17.5V.

[0065] High-voltage driving stage: At this time, the effective voltage applied across the cholesteric liquid crystal layer is the potential difference between the boosted pixel electrode voltage (+32.5V) and the AC common voltage (-17.5V), i.e., 50V. This superimposed voltage is formed by the first voltage provided by the driving chip, the second voltage provided by the common voltage generation module, and the additional voltage generated by bootstrapping, which is sufficient to drive the cholesteric liquid crystal to reliably switch from the planar state (P state) to the vertical alignment state (H state).

[0066] Reset Phase: The high-voltage drive pulse continues for a period of time to ensure that the liquid crystal completes the state switching. Then, the switch control signal controls the control switch unit to turn on again. Subsequently, the driver chip and the common voltage generation module reset their output to ground potential. The charge accumulated on the pixel electrodes is released to the output of the driver chip through the control switch unit, and the charge accumulated on the AC common electrode is released to the reference ground through the common voltage generation module. The potential of each node quickly returns to its initial state. After the potential difference between the two electrodes disappears, the cholesteric liquid crystal layer remains in the vertical alignment state due to its bistable characteristics, or relaxes back to the planar state after the electric field is removed, thus completing the stable storage of the display state.

[0067] Specifically, with the above architecture and timing, only ordinary driver chips with low output voltage (such as ±15V) are needed to generate a high voltage (such as 50V) sufficient to drive cholesteric liquid crystals inside the panel, which significantly reduces the requirements for driver chip process and the cost of the overall system.

[0068] In summary, this embodiment, through the above architecture and precise timing, only requires a common driver chip with a lower output voltage (e.g., +15V) to generate a high voltage (e.g., 50V) sufficient to drive cholesteric liquid crystals within the panel through a "two-layer electrode" structure and bootstrap effect. This significantly reduces the special requirements for the driver chip process and the overall system material cost.

[0069] Reference Figures 1-8 The present invention proposes a driving method for a cholesteric liquid crystal display device, comprising the following steps:

[0070] Generate mutually coordinating switching control signals and timing control signals;

[0071] Under the control of the switch control signal, the control switch unit is turned on, and the driver chip provides a first voltage to the pixel electrode;

[0072] The control switch unit is cut off by the switch control signal, thus isolating the pixel electrode from the driver chip;

[0073] The polarity of the AC common voltage is changed by a timing control signal, switching to a second voltage with the opposite polarity to the first voltage. During the process of changing the polarity of the AC common voltage, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode that is already in the isolated state to generate an additional voltage. Thus, the first voltage, the second voltage and the additional voltage are superimposed at both ends of the cholesteric liquid crystal layer to generate a superimposed voltage.

[0074] The cholesteric liquid crystal layer is switched from a planar state to a vertically aligned state by superimposing a voltage.

[0075] In this embodiment, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode, which is already in an isolated state, to generate an additional voltage. Specifically, this includes:

[0076] After the pixel electrode is in a high-resistivity state isolated from the driver chip, the series capacitor network raises the potential of the pixel electrode through capacitive coupling, and the additional voltage is equal to the absolute value of the voltage change of the storage capacitor electrode.

[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A cholesteric liquid crystal display device, characterized in that, It includes a display panel, a driver chip, a common voltage generation module, and a voltage superposition module; the display panel includes a TFT substrate and a CF substrate, with a cholesteric liquid crystal layer disposed between the TFT substrate and the CF substrate; pixel electrodes and a series capacitor network are disposed on the TFT substrate; an AC common electrode is disposed on the CF substrate; the voltage superposition module is integrated on the TFT substrate and includes a series capacitor network and a control switch unit, which is connected between the pixel electrodes and the driver chip. The control switch unit responds to the switch control signal to turn on or off the electrical connection between the pixel electrode and the driver chip; the common voltage generation module responds to the timing control signal to change the voltage polarity of the AC common stage; wherein, the switch control signal and the timing control signal cooperate to execute the following steps in sequence: When the control switch unit is turned on, the driver chip provides a first voltage to the pixel electrode; The control switch unit is turned off by the switch control signal, thus isolating the pixel electrode from the driver chip; The polarity of the AC common voltage is changed by a timing control signal, switching it to a second voltage with the opposite polarity to the first voltage. During the AC common voltage polarity change, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode that is already in isolation to generate an additional voltage. The first voltage, the second voltage, and the additional voltage are superimposed at both ends of the cholesteric liquid crystal layer to generate a superimposed voltage, thereby driving the cholesteric liquid crystal layer to switch between planar and vertical alignment states.

2. The cholesteric liquid crystal display device according to claim 1, characterized in that, A first electrode layer and a second electrode layer are sequentially formed on the TFT substrate. The first electrode layer includes a plurality of pixel electrodes, and the second electrode layer includes a series capacitor network.

3. The cholesteric liquid crystal display device according to claim 1, characterized in that, After the control switch unit is turned off, the pixel electrode is isolated from the driver chip and is in a high-resistance state; the bootstrap effect of the series capacitor network acts on the pixel electrode in the high-resistance state through capacitive coupling, causing its potential to rise.

4. The cholesteric liquid crystal display device according to claim 1, characterized in that, The driving chip provides a first voltage to the control switch unit, the absolute value of which is equal to the preset voltage value V; the common voltage generation module provides a second voltage to the AC common stage, the absolute value of which is equal to the preset voltage value V.

5. The cholesteric liquid crystal display device according to claim 1, characterized in that, The control switch unit includes multiple thin-film transistors. The gates of each thin-film transistor are connected to the switch control signal, the sources are connected to the corresponding pixel electrodes, and the drains are connected to the output terminals of each channel of the driver chip.

6. The cholesteric liquid crystal display device according to claim 1, characterized in that, One end of the series capacitor network is connected to a fixed potential terminal, and the other end is a floating terminal; the fixed potential terminal is either a ground terminal or a DC bias voltage terminal.

7. A driving method for a cholesteric liquid crystal display device, characterized in that, Includes the following steps: Generate mutually coordinating switching control signals and timing control signals; Under the control of the switch control signal, the control switch unit is turned on, and the driver chip provides a first voltage to the pixel electrode; The control switch unit is cut off by the switch control signal, thus isolating the pixel electrode from the driver chip; The polarity of the AC common voltage is changed by a timing control signal, switching to a second voltage with the opposite polarity to the first voltage. In the process of changing the polarity of the AC common voltage, the bootstrap effect of the series capacitor network is used to raise the potential of the pixel electrode that is already in the isolated state to generate an additional voltage. This results in the superposition of a first voltage, a second voltage, and an additional voltage at both ends of the cholesteric liquid crystal layer, generating a superimposed voltage. The cholesteric liquid crystal layer is switched from a planar state to a vertically aligned state by superimposing a voltage.

8. The driving method for the cholesteric liquid crystal display device according to claim 7, characterized in that, The method of utilizing the bootstrap effect of a series capacitor network to raise the potential of the pixel electrode, which is already in an isolated state, to generate an additional voltage specifically includes: After the pixel electrode is in a high-resistivity state isolated from the driver chip, the series capacitor network raises the potential of the pixel electrode through capacitive coupling, and the additional voltage is equal to the absolute value of the voltage change of the storage capacitor electrode.

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