Active Matrix Liquid Crystal Displays
A definitive guide to the theory and applications of AMLCDs, this book contains numerous design and applications examples to help illustrate key points and make them relevant to real-world engineering tasks.
TABLE OF CONTENTS Active Matrix Liquid Crystal Displays
Chapter 4: AMLCD Electronics
The design of the display glass assembly plays an important role in the image quality of an AMLCD. Equally important are the display electronics, which must supply accurate data signals to each pixel. The incoming video signals are either computer-generated or processed from an image acquisition by, for example, a digital camera, television camera, or camcorder. The task of the display electronics is to obtain optimum image quality based on the incoming video signal information.
4.1 Drive Methods
As mentioned earlier, each pixel in the AMLCD is driven with a square wave AC voltage. Ideally, the residual DC component on the pixel voltage is negligible. In practical displays it is unfortunately almost impossible to eliminate the DC component entirely for all gray levels and across the entire display area. The result is that the transmittance of the pixel varies slightly between odd and even frames, as shown in Fig. 4.1.
Figure 4.1: Effect of DC voltage component dV of LC voltage on luminance variation.
When the refresh rate is 60 Hz, the frequency of this luminance variation will be 30 Hz since the complete cycle of positive and negative charging of the pixel occurs at 30 Hz. The human eye perceives luminance variations of a few percent at less than 40 50 Hz as flicker. The luminance variations can be smoothed out by using an LC fluid and cell structure with a slow response time, so that the luminance amplitude variations in Fig. 4.1 are below the flicker limit. However, this...
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