With the advancement of technology, video playback applications have been widely used in commercial electronic products (such as mobile phones and MP3 players). Mobile phones and MP3 players are currently the two hottest and fastest growing commercial electronic products. The mobile phone market is expected to continue to grow in the next few years.
In these portable devices, high-quality displays are very important for watching videos. Organic light-emitting diode (OLED) display technology contains many different advantages (such as ultra-fast response time) and is considered a timely display solution. In order to fully utilize the benefits of OLED itself in video playback, a highly competitive smart driver chip is needed.
The popularity of color screen mobile phones has inspired a large number of new features that have not appeared on mobile phones before, such as recording and replaying video and video, taking and displaying photos, playing games, browsing the web, checking e-mails, and reading e-books. It is estimated that by 2009, the shipment of camera phones will reach 900 million. And with the upgrade of mobile phones from 2G to 2.75G and 3G, applications such as video conferencing, multimedia, video on demand, and DVB-H (digital video broadcasting for digital mobile TV applications) are gradually coming out. Therefore, the demand for mobile video applications is growing rapidly.
On the other hand, compression encoding of audio data into MP3 format has changed the way people listen to music. Since the first MP3 player came out in 1998, people can listen to music in MP3 format anytime, anywhere. Shipments of MP3 players are expected to increase from 27 million units in 2004 to more than 75 million units in 2009. In addition to decoding, each MP3 player also requires a display panel as an interface to communicate with the user. With the development of display technology, the display panels of MP3 players currently have multiple types such as monochrome, multicolor, grayscale and full color, and the resolutions are different. In addition to displaying the song number and song name, the previous OLED driver chip has been able to use the commercial OLED technology in the MP3 player to display still pictures. Now, users can even watch music videos while listening to MP3 players / PMP players.
Development trend of video display
From song titles to lyrics, caller number and caller photos, still photos to real-time video, people now hope that MP3 players and mobile phones can display more and more content. Common video data formats on PMP (such as MPEG-4 and H.263) require high frame rates (more than 25 frames per second) to ensure smooth video playback. In addition, the use of display panels with high resolution and true color and visible in the sun is also critical for video applications in mobile devices. The timely emergence of OLEDs as MP3 and PMP and mobile phone display solutions has overcome these challenges in display technology. Because it has indisputable advantages: response time less than 1 millisecond, self-illumination, high brightness, viewing angle of almost 180 degrees, good contrast, high visual clarity and low power consumption, it is very suitable for portable electronic devices.
Video display driver chip
The further development of chip technology enables high data transmission rate and true color. Video OLED displays for PMP have been put on the market, and video OLED displays for mobile phones will also be available. In order to make better use of the many inherent advantages of OLED displays in PMP and mobile video applications, a high-performance smart driver chip is necessary. Whether playing or shooting video, you need to make a smooth transition between each frame of image. OLED is known for its high-speed response time; however, in order to continuously provide data to the OLED screen, there must be a sufficiently high data transfer rate between the microprocessor (MCU) and OLED driver chip (see Figure 2). First, the driver chip must have a high-speed response MCU interface. Secondly, in order to display real video or images, the ability to handle complex color depths is also indispensable.
Figure 1: End products using OLED chips
Solomon Systech's SSD1339 chip upgrades mobile display terminal applications from static image display to dynamic video display. SSD1339 is a single-chip driver IC that controls the OLED screen. It supports a panel resolution of up to 132 × 132 and provides 262K true color to display realistic images. In order to achieve such high color and resolution, the MCU's data transmission bandwidth is increased to 18 bits, ensuring high-speed and smooth video display.
High-speed MCU interface
SSD1339 can support up to 9 different MCU bus interfaces, can provide up to 18-bit data bandwidth, data transfer rate and frame refresh rate of more than 180 frames per second. This special design meets those applications that require high-speed response, such as displaying video smoothly on PMP and mobile phones with higher performance, while maintaining the same cost. The response time of OLED display can reach even less than 1 millisecond, while that of TFT LCD is about 10 milliseconds, and the video display quality of OLED is much higher than that of TFT LCD. In addition to the ultra-high-speed MCU interface, the special design of the OLED driver of SSD1339 also keeps its power consumption low.
In addition, SSD1339 directly reads data from its built-in 132 × 132 × 18-bit SRAM display buffer; each pixel occupies 18-bit data; each sub-pixel corresponding to red, green, and blue occupies 6-bit data; the maximum color depth is 262K, and there are 256 levels of contrast control. This advanced color management enables true color video display.
In 262K color mode, you can use 16-bit and 18-bit MCU interface communication mode to access the data in the graphics memory in the OLED driver chip. However, 18-bit mode is twice as fast as 16-bit mode for the following reasons:
For the 18-bit interface mode, the communication includes only one 18-bit data transmission, and the MCU writes all the data bits to a corresponding 18-bit pixel in the OLED driver chip at once. Figure 3 shows the order of writing 18-bit color data. A, B, and C in the figure represent the three colors of red, green, and blue (the order is not counted).
Figure 3: 262K color data writing sequence in 18-bit MCU interface mode
For the 16-bit interface mode, the data communication must include two 16-bit transmissions, and the MCU transmits the 16-bit words twice to write an 18-bit pixel data to the OLED driver chip.
As shown in Figure 4, for each pixel, the 18-bit mode requires only one data transfer, while the 16-bit mode requires twice. This means that the time required to transfer each pixel data in the 18-bit mode is half that of the 16-bit mode. The 132x132 resolution display has about 17,000 pixels. Due to the 18-bit data width, a faster bit rate can be obtained. When using the 18-bit mode, the pixel data transfer time is only half, which makes a clear difference from the 16-bit mode.
Figure 4: 262K color data writing order in 16-bit MCU interface mode (X = any)
Summary of this article
For the built-in video display function of PMP and mobile phones, in order to achieve smooth video playback and bright colors, fast response time is very important. For this application, OLED display technology is a good solution, so it is very important to design a compact driver chip. Solomon Systech's SSD1339 can be packaged not only on glass (COG), but also on film (COF), which increases the flexibility of mobile application design.
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