LCD TVs look better

Response time compensation is a new display technology from National Semiconductor that has been developed to improve the picture quality of LCD TVs.

Response time compensation (RTC) is a new display technology from National Semiconductor that has been developed to improve the picture quality of LCD TVs.

Response time compensation technology compensates for the delayed response time between the electrical command and the optical response that occurs in LCDs. Using digital signal processing, RTC detects and accelerates grey-to-grey transitions in the panel.

The response time of a liquid crystal display is not constant across grey levels because of the complex interaction between the controlling electric field from the command voltage, the individual molecular orientations, the flow dynamics of the liquid crystal molecules sandwiched between two sheets of glass and the difference between the restoring and exciting forces operating on the molecules. The optical response can lag behind the electrical command to the pixel by several image frames, resulting in smearing and other distracting image artifacts.

In typical computer monitor applications, the image is largely stationary so the lag goes unnoticed. However, with fast motion video, like that in TV, DVD movies and video games, the resulting image on the LCD can be smeared, blurred, and have colour and contrast distortions as a result of the slow response.

National’s response time compensation prevents this performance degradation. The RTC timing controller intercepts the incoming video stream to the display panel, compares the grey-level command with the previous command to the same pixel, and inserts an appropriate, surrogate grey level. This new grey level is pre-determined to accelerate the grey-to-grey response time precisely to the commanded state just before the next command to the pixel arrives in the next frame.

Consequently, all the grey-to-grey transitions take place in a single image frame and the result is a moving image with detail that does not blur, smear or fade as it moves.

HannStar Display Corporation, a leading Taiwan-based manufacturer of LCD products, is already using National’s panel timing controller, which uses RTC, in its latest 23-inch LCD television panel.