LCD Display Tragedy (Part 4) - Signal

In the previous article, we have made a relatively detailed introduction to various interfaces. This time we will further analyze the transmitted signal processing.

Scaler module function details

We will use the following block diagram to explain the signal flow. Through various interfaces, such as VGA, HDMI, and color difference component interfaces, we get input image signals in various formats, but the resolution of the LCD screen is fixed, so it needs to pass through the Scaler module first. As the name suggests, Scaler is scaling. By scaling, the horizontal and vertical resolutions of the image are changed so that the video content is suitable for the resolution of the display screen and can be displayed normally. At present, scaling is basically an intra-frame algorithm, and horizontal and vertical scaling are processed independently. Through FIR filtering or nonlinear filtering, a suitable display effect is achieved. Generally, the higher the order and phase of the filter, the better the processing effect will be, and of course the cost will be higher.

By the way, EDID (Extended Display Identification Data) is a VESA standard data format that contains parameters about the monitor and its performance, including vendor information, maximum image size, color settings, factory presets, frequency range limitations, and strings for the monitor name and serial number.
 

       TV mainboard functional block diagram

MEMC module function details

Through the scaler, we get the LVDS signal, which is a low-voltage differential signal. In the past, there was no MEMC unit. LVDS was directly provided to T/con, and T/con directly drove TFT LCD. MEMC means motion estimation and motion compensation in Chinese, which is a kind of frame insertion compensation technology for LCD TV. LCD display has been criticized for the presence of ghosting when displaying dynamic images. MEMC technology was developed to improve this problem. The principle is to use a dynamic imaging system to insert a motion compensation frame between two traditional frames of images, so as to achieve the effect of clearing the residual image of the previous frame and improving dynamic clarity. From the perspective of liquid crystal characteristics, the ghosting phenomenon cannot be completely eliminated, but as the dynamic response time of liquid crystal becomes shorter and shorter, compensation technologies such as MEMC become more and more advanced, and the dynamic ghosting phenomenon has basically been reduced to a level that is difficult for the human eye to perceive.

In addition, since a motion compensation frame is inserted between the original two frames, the original 50/60Hz refresh rate is increased to 100/120Hz. Of course, since the interpolation technology is implemented through a specific algorithm, it will also bring some defects, such as unclear edges of moving images, and failure to compensate for images in various scenes.

T/con module function brief description

T/con should be a module that everyone is familiar with. It is the abbreviation of Timing Controller. The function of the timing controller is to convert the image signal to be displayed into the column drive control signal and row drive control signal of the TFT-LCD display. The input of T/con can be TTL signal or LVDS signal, and the output can also be TTL signal, but in order to reduce EMI, mini-LVDS proposed by TI or RSDS proposed by NS are now more commonly used.

             T/con control diagram

The above is the general direction of the LCD display signal flow. Of course, due to different solutions from different manufacturers, the implementation methods may be slightly different, so I will not repeat them here.

This is the end of the LCD series of articles. I hope that people in the industry can provide more valuable suggestions, and I also hope that friends who are interested in the LCD industry can find this helpful.