DISPLAY

COLUMN DRIVER

ROW

DRIVER

MULTI

SOURCE

DC/DC

CONVERTER

& LDO

TIMING

CONTROL

REFERENCE

GAMMA CORRECTION CURVE

LM8207

18 GAMMA BUFFER

BUFFER

LM8342

COLUMN DRIVERS

PIXEL

TFT-LCD PANEL

PIXEL

PIXEL

APPROX

LM8207

www.ti.com

SNOSAL5A – SEPTEMBER 2005 – REVISED MARCH 2013

column drivers supply this gamma voltage via the column lines, and ‘write’ this voltage to the pixels one row at a

time. This is accomplished by having the row drivers selecting an individual row of pixels when the column driver

writes the gamma voltage levels. The row drivers sequentially apply a large positive pulse (typically 25V to 35V)

to each row line. This turns on the NMOS transistors connected to an individual row, allowing voltage from the

column lines to be written to the pixels.

Figure 31. TFT Display

DC voltage that is in the middle of the gamma voltage range. As a result, when a column driver writes to a row of

reversed each time a row is selected, preventing a pattern from being ‘burned’ into the LCD.

Figure 32. Block Diagram of a Typical TFT-LCD

Figure 32 shows how the display information is refreshed. Using the row and column drivers, one pixel is

addressed at the display. The column driver receives the digital color data from the timing controller. The

corresponding gamma voltage will be determined, using the gamma correction curve. In fact, the gamma

correction curve is just a voltage reference with 18 output tabs, which presets the color intensity settings. This

gamma voltage is written to the pixel. The column driver selects one column at the time; the changing in the load

may affect the ‘tabs’ of the gamma correction curve. This problem can be solved using ‘gamma buffers’ to isolate

the gamma correction curve from the column driver.

Copyright © 2005–2013, Texas Instruments Incorporated

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