Electronic paper display system and driver

1 Introduction

Many people believe that with the popularity of computers, information can be stored in electronic media, thus reducing the amount of paper used. However, due to the convenience of paper carriers and the good quality of computer printing, many electronic information is still printed on paper for easy reading. The increase in paper use has caused waste, led to excessive felling of trees and environmental degradation.

If paper carriers can be replaced by electronic carriers, the environmental problems mentioned above can be solved. Although many conventional display solutions, such as LCD, OLED and plasma displays, can achieve some of the functions of paper, these technologies inevitably consume energy because various displays must be constantly updated to maintain the content of the image. These flat panel displays are also not as soft as paper, so they must be placed in a flat device. People have been looking for a new type of display technology that has the same characteristics as paper, that is, the image can be maintained without power consumption, and it can be rolled into surfaces of different curvatures for application in various devices of different appearance specifications. Thanks to the unremitting efforts of scientists, electronic paper technology based on electrophoretic display (EPD) technology came out in 1969.

The EPD panel itself cannot operate independently, and its image display requires a driver IC. As a pioneer and leading manufacturer in the display integrated circuit industry, Solomon Systech has developed an E-Paper display driver IC to turn this innovative concept into reality.

2 Electronic paper display mechanism

The electronic paper is made up of a large number of capsules. Each capsule contains a colored dielectric fluid and a large number of positively charged colored particles. The transparent ITO row electrode covers the upper surface of the electronic paper, while the column electrode is buried in the bottom layer. The column and row electrodes are respectively connected to the segmented and common drive modules of the electronic paper driver IC.

When the electronic paper driver IC provides a positive voltage waveform to the column electrodes, the positively charged particles are repelled by the applied positive electric field and move to the upper side of the capsule. The white particles are reflective and can reflect ambient light, allowing readers to see the electronic paper as white. If the electronic paper driver IC provides a negative voltage waveform to the column electrodes, the positively charged particles are attracted by the negative electric field and move to the bottom of the capsule. At this time, there will be no white particles on the upper surface of the electronic paper, and readers can see the colored dielectric liquid.

3 Advantages of electronic paper

With the same readability as paper, e-paper is a non-luminous display device. White particles and colored dielectric fluid reflect different colors of light from the ambient lighting, allowing the reader to see the image. Therefore, it is similar to paper in terms of readability, but has a wide viewing angle and extremely high image contrast. As long as the ambient light is sufficient, e-paper does not need to add front or back lighting to illuminate the image. E-paper has good display quality in both low light and strong light conditions.

(1) The structure of light and thin electronic paper is very simple, and it only includes a few layers of materials. Therefore, the thickness of a light and thin electronic paper is only 200 μm. These two points are very important factors affecting the application of electronic paper in portable devices.

(2) Bendable electronic paper is made of soft plastic that encapsulates tiny particles and fluids. Since there is no hard material, electronic paper is highly flexible and can be twisted or bent into different curved surfaces. Electronic paper can be attached to products of different shapes without being restricted to flat display panels. The final product will allow people to use their imagination more in terms of shape and style.

(3) Low power consumption After the image is updated by the driver of the electronic paper, the panel does not need any refresh to maintain the image display. Even if the power supply of the electronic paper display system is cut off, the particles in the fluid can maintain their original position for a long time until the electric field is applied again. This demonstrates the bistable nature of the electronic paper. In the absence of power, the image of the electronic paper can be maintained for several days. Therefore, the power consumption of the entire system is reduced, which can extend the battery life of portable devices, which is suitable for products such as e-books that do not require frequent updates. Photo 1 shows that the electronic paper can be flexibly bent.

(4) Simple manufacturing process The manufacturing process uses a continuous conveyor roller (roll-roll) method, which is similar to the printing of newspapers. The dielectric fluid and charged particles are injected into the capsule layer and then the top layer is sealed. The manufacturing process can be run at a high speed. In addition, large sheets of electronic paper can be made and then cut into the required size and shape at will to meet different applications. .

4 Electronic paper driver

Electronic paper requires high-performance driver ICs to exhibit impressive image quality and longer bi-stability so that the image is maintained even after the power is cut off. Basically the driver IC receives input signals from the microcontroller and then converts these signals into appropriate analog waveforms to drive the electronic paper.

4.1 Driver requirements for electronic paper

EPD-based electronic paper requires the driver to have some special and demanding functions to complete the driving function. In order to allow the charged color particles to migrate from one side to the other, a very high potential difference needs to be formed between the two electrodes embedded on both sides of the e-book tablet. The voltage value is about 40V (peak-to-peak), which is a very high value for battery-driven handheld device applications.

Figure 1 Driving waveform of electronic paper

4.2 Functional characteristics of electronic paper drivers

The e-paper driver IC provided by Solomon Technology has realized the application of e-paper technology in reality. This driver IC is a single-chip solution with 160 segment channels, a common channel and a background channel. It can receive display data from the microcontroller and convert the data into a driving waveform to realize e-paper image display. .

The input logic supply voltage is 2.5V to 5.5V, and the output drive voltage to the EPD is 15V to 40V. Considering that the output voltage is very high (especially for handheld devices), a DC-DC converter is integrated into the driver. Only a single logic voltage is needed to supply the driver, and the DC-DC converter can convert the very low logic voltage to a very high output voltage to drive the EPD panel. To further reduce the power consumption of the electronic paper display system, the driver also has a power saving mode. As long as the content of the EPD panel does not need to be updated, the microcontroller can command the driver to enter this mode, thereby minimizing the power consumption of the driver IC.

The EPD driver output waveform of the EPD driver IC is available in unipolar or bipolar form, and the waveform can be set by the user. Another functional feature of the driver is the SPI interface connected to the MCU, which allows the microcontroller to configure the characteristics and functions of the driver. The EPD driver IC has a bidirectional cascade interface to support larger EPD panels. Solomon Technology provides EPD driver ICs in both COF and COG packages.

4.3 System application diagram

Figure 2 Schematic diagram of electronic paper display system

In the picture, Positive Charged pigment particle——positively charged color particle. Top Transparent ITO Electrode——top transparent ITO electrode, User View as White in this area——the part seen by the user is white, User View as blue in this area——the part seen by the user is blue. Common line signal——common line signal, Segment Line Signal——segment line signal, Bottom Electrode——bottom electrode, Segment Output driver——segment output driver, COM Output driver——common output driver, Data Latch——data latch, Switch Register——switch register, Voltage converter——voltage converter, Electronics paper display driver controller IC——electronic paper display driver controller IC.

5 Applications of electronic paper

The characteristics of electronic paper are similar to those of traditional paper. It has good readability in both strong and weak light conditions, and is thin, light, and flexible. In addition, the displayed content can be updated at any time through the electronic paper driver IC. Electronic paper will be a substitute for paper in some fields. The following are the best examples of electronic paper applications.

5.1 Electronic Shelf Labels

In large department stores or supermarkets, multiple labels and signs showing product prices are placed on the shelves. Once the price information changes, it becomes a tedious task to replace the price labels one by one. If electronic paper is used to replace paper labels, the price information can be easily refreshed by connecting the electronic paper price tags together through a wireless network. The display on the electronic paper price tag does not need to be maintained by batteries, and the price information can be refreshed by relying on the energy of RF waves.

Photo electronic paper for shelf labels

5.2 Electronic clocks

Electronic paper technology can make watch design more vivid and imaginative. For example, watches using electronic paper can display time and images on the strap.

5.3 Smart Card Display

Today, many credit cards come with a smart card that stores information such as accumulated deposits and spending amounts, etc. Since e-paper has the advantage of lower power consumption and can be folded with the card, it is an excellent solution for displaying this type of information.

Photo: Paper meter and bendable module

6 Summary

Solomon Systech's e-paper driver controller ICs have made revolutionary technologies a reality, which have changed the display industry and are introducing new technology products into our daily lives. This also helps to achieve a paperless world and protect the environment of our planet.