Datasheet

VGMA1
VGMA3
VGMA5
VGMA2 VGMA4
CMOS
TRANSMISSION
GATES
RESISTIVE
DAC
HIGH POLARITY GAMMA
LEVEL INPUTS
COLUMN DRIVER
BUFFERS
VGMA6
VGMA8
VGMA10
VGMA7
VGMA9
CMOS TRANSMISSION
GATES
RESISTIVE
DAC
LOW POLARITY GAMMA LEVEL
INPUTS
COLUMN DRIVER
BUFFERS
2 PSec/DIV
(5 V/DIV)
(200 mA/DIV)
V
SW
I
COM
LM6588
SNOSA77D –MAY 2003–REVISED MARCH 2013 www.ti.com
Figure 31. V
SW
and I
OUT
Waveforms from V
COM
Test Circuit
GAMMA BUFFER
Illumination in a TFT display, also referred to as grayscale, is set by a series of discrete voltage levels that are
applied to each LCD pixel. These voltage levels are generated by resistive DAC networks that reside inside each
of the column driver ICs. For example, a column driver with 64 Grayscale levels has a two 6 bit resistive DACs.
Typically, the two DACs will have their 64 resistors grouped into four segments, as shown in Figure 32. Each of
these segments is connected to external voltage lines, VGMA1 to VGMA10, which are the Gamma Levels.
VGMA1 to VGMA5 set grayscale voltage levels that are positive with respect to V
COM
(high polarity gamma
levels). VGMA6 to VGMA10 set grayscale voltages negative with respect to V
COM
(low polarity gamma levels).
Figure 32. Simplified Schematic of Column Driver IC
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