The Research And Design On The Peripheral Driving Circuit Of Color AM-LCD

1. Significance of studyLCD becomes one of the most promising displays for its superior performance in the aspects of thin and light-weight, active emitting, wide visual angle, easily colored, no electromagnetic radiation and long life . LTPS (Low Temperature Ploy Silicon) is applied TFT-LCD technology derived from the new generation of products with the advantages of low power consumption, high resolution and small size thin-film circuit. The target of this paper is using EDA tools to realize the driving system for the240×3×320 resolution AM-LCD. The system can offer the AM-LCD the right data and control signals. That is to say, to design a driving system which can be used to test and drive the LCD, and to design an programmable application specific driving IC for the AM-LCD which has our own IP(Intellectual Property).2. Universal Project of the driving systemActive matrix Liquid Crystal Display (AM-LCD) adopts a circuit structure based on matrix addressing, and its driving circuit includes pixel driving circuit and peripheral driving circuit. The pixel circuit can make LCD emit light. continuously, while the peripheral driving circuit is designed to provide correct input signals for AM-LCD, for instance, provide the line-by-line scanning signals for row electrode of LCD matrix and the data signals with grey scale information for the pixel selected, therefore it is very important to LCD display technology that the pixel circuit and the peripheral driving circuit must supplement each other and drive LCD display panel together. Every AM-LCD pixel is integrated with a batch of Thin Film Transistors (TFT) and one store capacitance which constitutes the pixel circuit, and the pixel matrix controlled by TFT driving circuit can receive the data signal incessantly at one frame scanning interval. Though its technics is more complex and its cost is higher, AM-LCD has a low power dissipation and can be fit for the display equipment with high resolution and a good deal of display information, such as computer display,TV screen,PDA which have a high displayrequirements. Some peripheral driving circuits of AMOLED can be partially integrated on the substrate of panel after using poly-silicon thin film transistor (TFT), so p-Si TFT technology is also attracting much attention now.To achieve the required functions, the external drive circuit system is designed as shown in figure 1.The row driving signals are driven by the LCD Driver IC HX8312, and scanning signals are produced by the CPLD.CPLD used as the main system controller under the control of the situation produces scanning signals and HX8312 initialization signal .The paper's stress is the design of the outer driving system, which includes the digital circuit portion and the analog circuit portion. Command/dataThe row scanning DC-DCsignalsLCD display panelThe row driverHX8312 Driver ICIC controller Display cainrdc upitesripheral The row scanning moduleThe initialization module Figure 1 LCD Driving System Project DesignThe CPLD controller, which is droved by a global clock, will generate the initialization and line driving signals. The line driving signals must be transformed by DC-DC chip and analog switch chip, so their wave shape and meet the use of AM-LCD.The analog portion includes the voltage converter module. And by the effort of DC-DC converter and analog switch, the required control signals which have theright shape and voltage are generated.Take care of that: every function subdivision of the CPLD controller is mutually associated, and the design is an organic whole, design must be considered completely. The relationship between digital portion and analog portion should also be noticed.3. Realization of each function molds of systemThe design of the core devices is to use programmable logic device, and it makes the whole system not only toward small size, high level of integration, high reliability, high-speed development, but also greatly increases the flexibility of circuit design, debugs and modifies the circuit easily. CPLD controller seen from Figure 1 is divided into three modules. LCD driver module data will be combined in one data module and the initialization module. Figure 2 below shows LCD driver module initialization, and figure 3 shows the block scanning control module.The internal logic is considerably intricate. The paper mostly adopts a sort of modularized design. It is that each function of the controller is designed according to the modular mode. In this design the chip of Altera Corporation's Cyclone family is used EPM7256AETC144 and the hardware description language is adopted to design the controllers.4. Main content of the design1. We studied the AMOLED display with QVGA (240×3×320) resolution, and present the method for the data lines divided into some blocks based on the performance of hardware circuits. We ascertained the sequence relations and the swing of the clock and pulse which are needed by the driving circuit integrated on the substrate, and also figure out their actual periods.2. We found the module and flow for these clock pulses centering on the CPLD controller, and introduce all these module how to operate cooperatively; We make use of the hardware description language Verilog to program for these modules, such as control clock generator,data transfer circuit and video control circuit. Our design results were verified by simulation and synthesis, and we got the correct wave of the control clock. So the design has met the needs of the 240×3×320 resolution AM-LCD.3. The system is easy to use. It only requires an 18V power. When powered, theCPLD will be initialized automatically. So the driving system can get rid of PC entirely. So it's easy to test the AM-LCD.The specialties and virtues of LCD can be shown only through combining with a nicer driving technology, integrate circuits and high resolution, so the peripheral driving system and driver chip plays an important role in confirming the LCD's quality and performance. The purpose of this paper is designing a driving system for LCD display, which can provide a test and peripheral drive sustain for LCD displays.