POLARIZER

BOTTOM ITO

PLATE

TOP ITO

PLATE

POLARIZER

TRANSMITTED LIGHT

LIGHT SOURCE

GLASS

SUBSTRATE

LIQUID CRYSTAL

MATERIAL

GLASS

SUBSTRATE

± POLARITY

LM8207

SNOSAL5A – SEPTEMBER 2005 – REVISED MARCH 2013

www.ti.com

APPLICATION SECTION

INTRODUCTION

The performance capabilities of TFT-LCD’s increase rapidly, with constant improvements such as larger sizes,

higher resolution, and greater brightness. Today’s LCD’s have screen resolutions of over 1 Mega pixel and

higher. The LM8207 can be used to improve the performance of an LCD. It is designed for buffering 18 gamma

Reference, which is included in the LM8207. The LM8207 meets the design requirements that combine technical

improvement with the demand for cost effective solutions.

The following sections discuss the principle operation of a TFT-LCD and the principle operation of the LM8207

Buffer. After this, the next sections present a typical LM8207 configuration and consider the maximum power

dissipation. The end of this application section introduces the evaluation board and presents layout

recommendations.

PRINCIPLE OPERATION OF A TFT-LCD

This section offers a brief overview of the principle operating of TFT-LCD’s. There is a detailed description of

how information is presented on the display. An explanation of how data is written to the screen pixels and how

the pixels are selected is also included.

Figure 30. Individual LCD Pixel

Figure 30 shows a simplified illustration of an individual LCD pixel. The top and bottom plates of a pixel consist of

Indium-Tin Oxide (ITO), which is a transparent, electrically conductive material. ITO lies on the inner surfaces of

two glass substrates that are the front and back glass panels of a TFT display. Sandwiched between two ITO

plates is an insulating material (liquid crystal). This alters the polarization of light, depending on how much

substrates. In combination with the liquid crystal, the polarizer’s create a variable light filter that modulates light

transmitted from the back to the front of a display. A pixel’s bottom plate lies on the backside of a display where

a light source is applied, and the top plate lies on the front, facing the viewer. For most TFT displays, a pixel

increases with either a positive or negative polarity.

For color displays, each pixel is built with three individual sub pixels. Each sub pixel represents a primary color.

These colors are Red, Green and Blue (RGB). Combining these three primary colors every user-defined color

can be created.

Figure 31 shows a simplified diagram of a TFT display, showing how individual pixels are connected to the row,

plate. Pixels in a TFT panel are arranged in rows and columns. Row lines are connected to the NMOS gates,

and column lines to the NMOS sources. The back plate of every pixel is connected to a common voltage called

12

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