2 PSec/DIV

VSW

ICOM

2PSec/DIV

VSW

VCOM

LM6584

www.ti.com

SNOSA44C – MAY 2003 – REVISED MARCH 2013

Figure 31. VSW and VCOM Waveforms from VCOM

Figure 32. VSW and IOUT Waveforms from VCOM 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 33. 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 VCOM (high polarity gamma

levels). VGMA6 to VGMA10 set grayscale voltages negative with respect to VCOM (low polarity gamma levels).

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