scholarly journals Aperture Ratio Improvement by Optimizing the Voltage Slope and Reverse Pulse in the Driving Waveform for Electrowetting Displays

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 862 ◽  
Author(s):  
Zichuan Yi ◽  
Wenyong Feng ◽  
Li Wang ◽  
Liming Liu ◽  
Yue Lin ◽  
...  
Keyword(s):  
Inflection Point ◽  
Charge Trapping ◽  
Response Speed ◽  
Driving Voltage ◽  
Hysteresis Characteristic ◽  
Aperture Ratio ◽  
Dynamic Display ◽  
Capacitance Voltage ◽  
Reverse Pulse ◽  
Driving Waveform

Electrowetting display (EWD) performance is severely affected by ink distribution and charge trapping in pixel cells. Therefore, a multi structural driving waveform is proposed for improving the aperture ratio of EWDs. In this paper, the hysteresis characteristic (capacitance–voltage, C-V) curve of the EWD pixel is tested and analyzed for obtaining the driving voltage value at the inflection point of the driving waveform. In the composition of driving waveform, a voltage slope is designed for preventing ink dispersion and a reverse pulse is designed for releasing the trapped charge which is caused by hysteresis characteristic. Finally, the frequency and the duty cycle of the driving waveform are optimized for the max aperture ratio by a series of testing. The experimental results show that the proposed driving waveform can improve the ink dispersion behavior, and the aperture ratio of the EWD is about 8% higher than the conventional driving waveform. At the same time, the response speed of the driving waveform can satisfy the dynamic display in EWDs, which provides a new idea for the design of the EWD driving scheme.

scholarly journals A Combined Pulse Driving Waveform With Rising Gradient for Improving the Aperture Ratio of Electrowetting Displays

2021 ◽  
Vol 9 ◽  
Author(s):  
Lixia Tian ◽  
Pengfei Bai
Keyword(s):  
Charge Trapping ◽  
Fast Response ◽  
Driving Voltage ◽  
Film Rupture ◽  
Aperture Ratio ◽  
Full Color ◽  
Display Technology ◽  
Display Performance ◽  
The Stability ◽  
Driving Waveform

As a reflective display technology, electrowetting displays (EWDs) have the advantages of paper-like display, low power consumption, fast response, and full color, but the aperture ratio of EWDs is seriously affected by oil dispersion and charge trapping. In order to improve the aperture ratio and optimize the display performance of EWDs, a combined pulse driving waveform with rising gradient design was proposed. First, an initial driving voltage was established by the threshold voltage of oil film rupture (Vth). And then, a rising gradient was designed to prevent oil from dispersing. At last, the oil splitting and movement were controlled to achieve the target aperture combined with the pulse waveform. Experimental results showed that the oil dispersion of EWDs can be effectively improved by using the proposed driving waveform, the aperture ratio of EWDs was increased by 3.16%, and the stability was increased by 71.43%.

scholarly journals Driving Waveform Design of Electrowetting Displays Based on a Reset Signal for Suppressing Charge Trapping Effect

2021 ◽  
Vol 9 ◽  
Author(s):  
Taiyuan Zhang ◽  
Yong Deng
Keyword(s):  
Charge Trapping ◽  
Recovery Phase ◽  
Driving Voltage ◽  
Aperture Ratio ◽  
Trapping Effect ◽  
Display Performance ◽  
Reset Signal ◽  
A Charge ◽  
Driving Waveform ◽  
Driving Signal

Electrowetting display (EWD) device is a new type of reflective optoelectronic equipment with paper-like display performance. Due to the oil backflow phenomenon, it is difficult for pixels to be maintained a stable aperture ratio, so the grayscale of EWDs cannot be stabilized. To reduce the oil backflow in EWDs, a driving waveform composed of a driving signal and a periodic reset signal was proposed in this paper. A direct current (DC) signal was designed as the driving signal for driving pixels. The aperture ratio of pixels was determined by the amplitude of the DC signal. The periodic reset signal was divided into a charge release phase and a driving recovery phase. During the charge release phase, the driving voltage was abruptly dropped to 0 V for a period to release trapped charges. In the driving recovery phase, the driving voltage was rapidly increased from 0 V to a maximum value. To reach the same grayscale of EWDs, the driving waveform was returned to the driving signal at the end of the driving recovery phase. Experimental results showed that the aperture ratio of EWDs was unchanged when the driving waveform was applied. However, the aperture ratio of pixels was gradually decreased with the conventional driving waveform. It was indicated that the charge trapping effect and the oil backflow phenomenon can be effectively inhibited by the proposed driving waveform. Compared with the conventional driving waveform, the speed of oil backflow was reduced by 90.4%. The results demonstrated that the proposed driving waveform is beneficial for the achievement of stable grayscale in EWDs.

scholarly journals Driving Waveform Design of Electrowetting Displays Based on an Exponential Function for a Stable Grayscale and a Short Driving Time

Micromachines ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 313 ◽  
Author(s):  
Zichuan Yi ◽  
Zhenyu Huang ◽  
Shufa Lai ◽  
Wenyao He ◽  
Li Wang ◽  
...  
Keyword(s):  
Time Constant ◽  
Exponential Function ◽  
Waveform Design ◽  
Hysteresis Curve ◽  
Optimal Time ◽  
Driving Voltage ◽  
Aperture Ratio ◽  
Driving Time ◽  
Long Time ◽  
Driving Waveform

The traditional driving waveform of the electrowetting display (EWD) has many disadvantages, such as the large oscillation of the target grayscale aperture ratio and a long time for achieving grayscale. Therefore, a driving waveform based on the exponential function was proposed in this study. First, the maximum driving voltage value of 30 V was obtained by testing the hysteresis curve of the EWD pixel unit. Secondly, the influence of the time constant on the driving waveform was analyzed, and the optimal time constant of the exponential function was designed by testing the performance of the aperture ratio. Lastly, an EWD panel was used to test the driving effect of the exponential-function-driving waveform. The experimental results showed that a stable grayscale and a short driving time could be realized when the appropriate time constant value was designed for driving EWDs. The aperture ratio oscillation range of the gray scale could be reduced within 0.95%, and the driving time of a stable grayscale was reduced by 30% compared with the traditional driving waveform.

scholarly journals Design of an AC Driving Waveform Based on Characteristics of Electrowetting Stability for Electrowetting Displays

2020 ◽  
Vol 8 ◽  
Author(s):  
Linwei Liu ◽  
Zhuoyu Wu ◽  
Li Wang ◽  
Taiyuan Zhang ◽  
Wei Li ◽  
...  
Keyword(s):  
Response Time ◽  
Indium Tin Oxide ◽  
Pulse Width Modulation ◽  
Charge Trapping ◽  
Driving Voltage ◽  
Reverse Voltage ◽  
Dc Voltage ◽  
Voltage Curve ◽  
Voltage Frequency ◽  
Driving Waveform

In traditional electrowetting display (EWD) drivers, direct current (DC) voltage and pulse width modulation are often used, which easily caused an electrowetting charge trapping phenomenon in a hydrophobic insulating layer. Therefore, the driving voltage must be increased for driving EWDs, and oil backflow cannot be solved. Aqueous solutions are often used as polar liquids for EWDs, and the reverse voltage of alternating current (AC) driving can cause chemical reactions between water and indium tin oxide (ITO). So, a driving waveform was proposed, which included a DC waveform and an AC waveform, to separately drive EWDs for oil rupture and open state. Firstly, a DC waveform was used when the oil was broken, and the response time was reduced by designing the DC voltage and duration. Secondly, an AC waveform was used when the oil required to be stable. Oil backflow could be suppressed by the AC waveform. The main parameters of AC waveform include reverse voltage, frequency and duty cycle. The reverse voltage of EWDs could be obtained by voltammetry. The frequency could be obtained by analyzing the rising and falling edges of the capacitance voltage curve. The experimental results showed that the proposed waveform can effectively suppress oil backflow and shorten the response time. The response time was about 86% lower than the conventional driving waveforms, and oil backflow was about 72% slower than the DC driving waveform.

scholarly journals Design of Driving Waveform Based on Overdriving Voltage for Shortening Response Time in Electrowetting Displays

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenjun Zeng ◽  
Zichuan Yi ◽  
Yiming Zhao ◽  
Weibo Zeng ◽  
Simin Ma ◽  
...  
Keyword(s):  
Response Time ◽  
Physical Model ◽  
Performance Testing ◽  
Charge Trapping ◽  
Response Speed ◽  
Fast Response ◽  
Optimal Performance ◽  
Experimental Results ◽  
Target Luminance ◽  
Driving Waveform

A fast response speed of a pixel is important for electrowetting displays (EWDs). However, traditional driving waveforms of EWDs have the disadvantage of long response time. So, a driving waveform, which based on overdriving voltages and charge trapping theory, was proposed in this paper to shorten the response time of EWDs. The driving waveform was composed of an overdriving stage and a driving stage. Firstly, a simplified physical model was introduced to analyze the influence of driving voltages on the response time. Then, an overdriving voltage was applied in the overdriving stage to increase the respond speed of oil, and a target voltage was applied in the driving stage to obtain a target luminance. In addition, the effect of different overdriving voltages and overdriving time values on the response time was analyzed by charge trapping theory to achieve an optimal performance. Finally, the driving waveform was imported into an EWD for performance testing. Experimental results showed that the response time of the EWD can be shortened by 29.27% compared with a PWM driving waveform.

scholarly journals Design Method of Equivalent Driving Waveform Based on Electrowetting Response Characteristics

2021 ◽  
Vol 9 ◽  
Author(s):  
Lixia Tian ◽  
Hao Li
Keyword(s):  
Contact Angle ◽  
Design Method ◽  
Contact Angle Hysteresis ◽  
Response Speed ◽  
Hysteresis Effect ◽  
Hysteresis Phenomenon ◽  
Driving Voltage ◽  
Interface Tension ◽  
Response Characteristics ◽  
Driving Waveform

As a new reflective display technology, electrowetting displays (EWDs) have many important characteristics, such as high reflectivity, low power consumption, and paper-like display. However, the contact angle hysteresis, which is the inconsistency between the advancing contact angle and the receding contact angle of oil droplet movement, seriously affects the response speed of EWDs in the driving process. According to the hysteresis phenomenon of contact angle in an oil switch motion with the action of interface tension, the brightness curve of EWDs in the process of pixel switching by different driving voltages was tested in this paper, and driving voltage was changed from 30 to 100 V at the same time. Then, in order to reduce the influence of the hysteresis effect, an equivalent driving waveform design method with overdriving voltage was proposed, and the overvoltage was set to 100 V according to the hysteresis effect and driving characteristic of EWDs. Experimental results showed that the response rising time of EWDs was reduced to 21 ms by using the proposed driving waveform, and the response performance of EWDs can be effectively improved.

scholarly journals Driving Waveform Optimization by Simulation and Numerical Analysis for Suppressing Oil-Splitting in Electrowetting Displays

2021 ◽  
Vol 9 ◽  
Author(s):  
Shufa Lai ◽  
Qinghua Zhong ◽  
Hailing Sun
Keyword(s):  
Low Voltage ◽  
Response Speed ◽  
Fast Response ◽  
Display Device ◽  
Waveform Optimization ◽  
Aperture Ratio ◽  
Maintenance Stage ◽  
Driving Waveform ◽  
The Relationship ◽  
Reflective Display

Electrowetting display (EWD) is a new reflective display device with low power consumption and fast response speed. However, the maximum aperture ratio of EWDs is confined by oil-splitting. In order to suppress oil-splitting, a two-dimensional EWD model with a switch-on and a switch-off process was established in this paper. The process of oil-splitting was obtained by applying different voltage values in this model. Then, the relationship between the oil-splitting process and the waveforms with different slopes was analyzed. Based on this relationship, a driving waveform with a narrow falling ramp, low-voltage maintenance, and a rising ramp was proposed on the basis of square waveform. The proposed narrow falling ramp drove the oil to rupture on one side. The low-voltage maintenance stage drove the oil to shrink with a whole block. The proposed rising ramp was pushed the oil into a corner quickly. The experimental results showed that the oil splitting can be suppressed effectively by applying the proposed driving waveform. The aperture ratio of the proposed driving waveform was 2.9% higher than that of the square waveform with the same voltage.

scholarly journals Driving Waveform Design with Rising Gradient and Sawtooth Wave of Electrowetting Displays for Ultra-Low Power Consumption

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 145 ◽  
Author(s):  
Wei Li ◽  
Li Wang ◽  
Taiyuan Zhang ◽  
Shufa Lai ◽  
Linwei Liu ◽  
...  
Keyword(s):  
Power Consumption ◽  
Low Power ◽  
Driving Voltage ◽  
Ultra Low Power ◽  
Sawtooth Wave ◽  
Aperture Ratio ◽  
Initial Stage ◽  
Display Technology ◽  
Three Stages ◽  
Driving Waveform

As a kind of paper-like display technology, power consumption is a very important index for electrowetting displays (EWDs). In this paper, the influence of driving waveforms on power consumption of the EWDs is analyzed, and a driving waveform with rising gradient and sawtooth wave is designed to reduce the power consumption. There are three stages in the proposed driving waveform. In the initial stage, the driving voltage is raised linearly from the threshold to the maximum value to reduce the invalid power consumption. At the same time, the oil breakup can be prohibited. And then, a section of sawtooth wave is added for suppressing oil backflow. Finally, there is a section of resetting wave to eliminate the influence of charge leakage. Experimental results show that the power consumption of the ultra-low power driving waveform is 1.85 mW, which is about 38.13% lower than that of the conventional used square wave (2.99 mW), when the aperture ratio is 65%.

scholarly journals Driving Waveform Design of Electrophoretic Display Based on Optimized Particle Activation for a Rapid Response Speed

Micromachines ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 498
Author(s):  
Wenyao He ◽  
Zichuan Yi ◽  
Shitao Shen ◽  
Zhenyu Huang ◽  
Linwei Liu ◽  
...  
Keyword(s):  
Inflection Point ◽  
Response Speed ◽  
Waveform Design ◽  
Testing Device ◽  
Activity Phase ◽  
Particle Activation ◽  
Two Phases ◽  
Motion Characteristics ◽  
Driving Waveform ◽  
Brightness Curve

Electrophoretic displays (EPDs) have excellent paper-like display features, but their response speed is as long as hundreds of milliseconds. This is particularly important when optimizing the driving waveform for improving the response speed. Hence, a driving waveform design based on the optimization of particle activation was proposed by analyzing the electrophoresis performance of particles in EPD pixels. The particle activation in the driving waveform was divided into two phases: the improving particle activity phase and the uniform reference grayscale phase. First, according to the motion characteristics of particles in improving the particle activity phase, the real-time EPD brightness value can be obtained by an optical testing device. Secondly, the derivative of the EPD brightness curve was used to obtain the inflection point, and the inflection point was used as the duration of improving particle activity phase. Thirdly, the brightness curve of the uniform reference grayscale phase was studied to set the driving duration for obtaining a white reference grayscale. Finally, a set of four-level grayscale driving waveform was designed and validated in a commercial E-ink EPD. The experimental results showed that the proposed driving waveform can cause a reduction by 180 ms in improving particle activity phase and 120 ms in uniform reference grayscale phase effectively, and a unified reference grayscale can be achieved in uniform reference grayscale phase at the same time.

scholarly journals Line of Sight Correction of High-Speed Liquid Crystal Using Overdriving Technology

Electronics ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 1477
Author(s):  
Hongyang Guo ◽  
Qing Li ◽  
Yangjie Xu ◽  
Yongmei Huang ◽  
Shengping Du
Keyword(s):  
Liquid Crystal ◽  
Response Time ◽  
High Speed ◽  
Pulse Width Modulation ◽  
Response Speed ◽  
Line Of Sight ◽  
Processing Unit ◽  
Driving Voltage ◽  
Light Modulator ◽  
Central Processing

In the line of sight correction system, the response time of the liquid crystal spatial light modulator under the normal driving voltage is too long to affect system performance. On the issues, an overdriving method based on a Field-Programmable Gate Array (FPGA) is established. The principle of the overdrive is to use a higher voltage difference to achieve a faster response speed of liquid crystal. In this scheme, the overdriving look-up table is used to seek the response time of the quantized phase, and the liquid crystal electrode is driven by Pulse–Width Modulation (PWM). All the processes are performed in FPGA, which releases the central processing unit (CPU) memory and responds faster. Adequate simulations and experiments are introduced to demonstrate the proposed method. The overdriving experiment shows that the rising response time is reduced from 530 ms to 34 ms, and the falling time is from 360 ms to 38 ms under the overdriving voltage. Typical light tracks are imitated to evaluate the performance of the line of sight correction platform. Results show that using the overdrive the −3 dB rejection frequency was increased from 1.1 Hz to 2.6 Hz. The suppression ability of the overdrive is about −20 dB at 0.1 Hz, however the normal-driving suppression ability is only about −13 dB.

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