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Resolution timing controller TCON

In Electronic Infomation Category: R | on April 19,2011

This paper describes the principles of TFT-LCD display, the system structure and LF8505 datasheet and the timing controller TCON design.

1 TFT-LCD Display principle and LF8505 price and system structure

TCON timing signal is based on the TFT-LCD panel (Panel) the need to generate, and LF8505 suppliers and understand the principles of TCON, we must first understand the principles of LCD panel display. The typical internal structure of TFT-LCD panel shown in Figure 1. LCD with light controllable to change the voltage applied to the liquid crystal, liquid crystal light transmission rate will change.

A liquid crystal cell to achieve a sampling point of the show, so if binary images based on the data structure of the liquid crystal cell arranged as a matrix liquid crystal array (Crystal Array), an image display can be realized. Typically, the liquid crystal array, the arrangement of the Strip and the Delta in two ways. Determine the different arrangement of the order of the different RGB sample, while a pixel unit by the three liquid crystal composition (RGB). Therefore, the liquid crystal cell in the array determines the number of display resolution. TFT-LCD is a super twisted nematic STN, based on the TFT transistor will be displayed through the pixels and scan electrodes separated form, which is characterized overcome the cross-effects of STN-LCD.

TFT-LCD system consists of two parts: LCD control module and the LCD panel TCON module, shown in Figure 2. LCD display used by rows, columns, active matrix driving method, the line cord is connected to the pixel control gate NMOS (gate), the column line is connected to the NMOS control of the source (Source). In the LCD module, the line line and column line is driven separately, drive line drive line of the circuit Mengen (Gate Driver); driven out of the circuit is called the source line drive (Source Driver).

Source driver and gate driver jointly controlled liquid crystal cell charge and discharge process. When the scanning signal is valid, the line open while all the TFT module, RGB to the storage capacitor voltage charge through the TFT. Therefore, the voltage difference between RGB and Vcom to determine the voltage of liquid crystal column. When the scanning signal is invalid, this unit off the line on the TFT, the charge storage capacitor at a time can be essentially unchanged, in order to achieve near 100% duty cycle of the static display.

TCONs primary function is to TFT-LCD panel source driver and gate drivers provide the necessary timing control signals. According to panel (Panel) requirements, TCON output signal is the most basic: STV, OEV, CPV, STH, CPH, OEH, PLC, etc.; In addition, in order to achieve different display modes, as well as L / R, U / D, MOD, Q2H and other control signals.

2 timing controller TCON module design

Timing controller TCON module include: phase-locked loop PLL, I2C interface, the divider DIV, line synchronization module HSB, VSB field sync module and the control signal output module CSB. The basic structure of TCON shown in Figure 3. Among them, the VSB field sync generation module gate driver control signals required: HSB production line synchronization module needs the source drive control signal; control signal output module produces the scanning direction control signal CSB. The system design was introduced in I2C interface, control signals available through internal registers to control the software can be realized by changing the display mode change, thus greatly reducing the number of external hardware pins. PLL 1 920,1 440,1 200,1 provides resolution of a corresponding system clock 152, and 960,480,400,320 resolution of the corresponding clock frequency obtained by the DIV module.

Due to different resolution LCD, the different modes of output control signals needed to be different, so TCON work, the first judge to select the correct mode, so that a corresponding appropriate control signals. These options include LCD resolution selection, external / phase-locked loop circuit PLL clock mode selection, separation / composite mode selection, NTSC / PAL standard options.

LCD resolution options: in the actual display system, TFT-LCD have different sizes and resolutions, most middle and small sized TFT-LCDs resolution is 480x234 (2.5 ", 3.5"), 960x234 (3.6 ", 5 ",*"), 1 200x234 (6.5"), 1400x234 (6.2 ", 7"), 1 920x234 (9 ") and so on. for different resolution LCD, the Some control signals need to be different.

External / PLL clock mode selection: the clock source to provide work in two ways, phase-locked loop circuit PLL mode and external clock mode. Work in PLL mode, VCO circuit to oscillate, after phase modulation through the PLL circuit to provide a stable work TCON clock; in the external mode, the work provided by external clock.

Separate / composite mode selection: the input sync signal can be divided into separate composite sync signal and synchronous signal, the two sync signals are not the same sync pulse flag.

NTSC / PAL format choice: NTSC and PAL formats, and the number of lines per frame sync pulse flag is completely different, so in dealing with the input signal and generate control signals should be made before the judge selection. High resolution display mode options: high-resolution under FULL, Center, Wide, Zoom1, Zoom2, Left, Right, Zoom3 8 different display mode, different display mode, the display area, performance and output control pulse width will be different.

2.1 module gate driver control signal

Gate driver through the OG (TFT_LCD strobe) signal to strobe TFT, to control the storage capacitor charge and discharge. The basic gate driver input signal CPV (gate drive conversion clock), STV (gate driver start pulse) and OEV (gate driver output enable.) In addition, if the gate driver supports up to down and down to up scanning mode, also need to scan direction control signal U / D. The timing gate driver shown in Figure 4.

By changing the CPV, STV and OEV timing can be realized on the TFT switch control to control the image appears. Zoom1, Zoom2 and Zoom3 display mode is by changing the gate driver input signal timing to achieve.

2.2 source drive module control signal

Through the TFT switch gate driver to decide whether to charge the storage capacitor, and the source drive is to control how the storage capacitor to charge and discharge. The basic source driver control signals include: CPH (conversion clock source driver), STH (source driver start pulse) and OEH (Source driver output enable) and so on. If the source drive supports Left / Right scan control and Simultaneously / Sequential sampling mode, it has about scanning control signal (L / R) and the sampling mode control signal (MOD). Valid source drive begins in STHL scanning, when STHR valid end, the control signal timing shown in Figure 5.

Source drive time in a row to complete the sampling and display of two actions, shown in Figure 6. When the first line of the TFT k strobe OG (K) is valid, SWa1 and SWb2 closure: At this point, the first k lines of the video signal CH1 charge, all the pixels on this line of video information to be stored in the CH1; Also, because SWb2 also closed, CH2 on the adoption of Qk-1 to the first k-1 line to charge the storage capacitor Cd in order to achieve the first k-1 line of the image appears.

The sample according to the source drive display principle we know that change CPH, OEH and STH timing can be achieved on the image display control. Center, Wide, Left and Right such as the display mode is controlled by changing the source drive signal timing to achieve.

2.3 Vcom polarity control module and the display mode LCD column light

Detroit and voltage (V), independent of the direction, only with its size. However, if a long time to put the same liquid crystal column will make it to the voltage of electrolysis, which lost its transmission characteristics, so easy to damage caused by the LCD. Therefore, in order to extend the life of the LCD, the LCD requires changing the voltage applied to the V direction. The LCD screen is, Vcoms conversion There are 3: Flip the frame, the line flip, flip out. Low frequency frame flip mode (50 Hz), low power consumption, image quality generally: the lower the frequency of the line flip mode (15 kHz), low power, image quality is better: the column flip mode high frequency power consumption of large, image quality is best for large-size screen. Supports multiple display modes for the small size of simulation TFTLCD panel, the general form of the line flip, by changing the voltage polarity of Vcom public to achieve the purpose of flipping. TCON will output a line reversal signal POL, the signal generated by Vcom, by adjusting the Vcom of the DC side, change the color LCD, adjust AC side, you can change the LCD contrast.

ITU-601 standard video signals are two kinds of standard: PAL and NTSC; TCON output signal determined based on display mode and format. The design support FULI, Center, Wide, Zoom1, Zoom2, Left, Right, Zoom3 8 display modes. The PAL system signal as an example, PAL color signal system data structure is 312.5 lines per field, effectively accounting for 288 line image. 8 The following is the specific design of display modes.

FULL: full screen horizontally, no zoom, TCPH = 3TOSC, vertical sampling lines 288, 234 lines

Center: the horizontal direction is reduced to 3 / 4 centered, TCPH = 4TOSC, vertical sampling lines 288, 234 lines

Wide: full screen horizontally, zoom all, TCPH = 2TOSC, 3TOSC, 4TOSC, vertical sampling lines 288, 234 lines

ZOOM1: full screen horizontally, no zoom, TCPH = 3TOSC, vertical line interpolation 220, 234 lines

ZOOM2: full screen horizontally, no zoom, TCPH = 3TOSC, no vertical scale, 234-line display

Left: horizontal direction is reduced to 3 / 4 left home screen display, TCPH = 4TOSC, vertical sampling lines 288, 234 lines

Right: the horizontal direction is reduced to 3 / 4 of the Home screen display the right, TCPH = 4TOSC, vertical sampling lines 288, 234 lines

ZOOM3: full screen horizontally, no zoom, TCPH = 3TOSC, no vertical scale, 234-line display

3 Summary

TCON output signal generated mainly by the counter control, and its timing depends on two factors: the image signal data structure and display mode. LCD panels for different

, TCON timing is different, but the show basically the same. Therefore, TCON output signal is able to support different sub-LCD panel depends on the PLL frequency system clock is given to meet the requirements. The general design is strong, compared to only 2 ~ 3 kinds of resolution of driving panel TCON, supports 16:9 and 4:3 TFT-LCD panel, and also supports different display modes, and supports a large current market some manufacturers of LCD panels, such as: AU, PVI, Samsung, LG, Sharp, Panasonic, Toshiba, Foxconn. Timing controller design process has been SMIC018 separate silicon success, and with VideoProcessor integration, has been used in portable DVD, car TV and other fields. This also confirmed the feasibility of this plan.

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