BUF20800-Q1 Datasheet, PDF (20/32 Pages) Texas Instruments – 18-CHANNEL GAMMA VOLTAGE GENERATOR WITH TWO PROGRAMMABLE VCOM CHANNELS

BUF20800-Q1
SBOS571 – AUGUST 2011
www.ti.com
DYNAMIC GAMMA CONTROL
Dynamic gamma control is a technique used to improve the picture quality in LCD TV applications. The
brightness in each picture frame is analyzed and the gamma curves are adjusted on a frame-by-frame basis. The
gamma curves are typically updated during the short vertical blanking period in the video signal. Figure 16 shows
a block diagram using the BUF20800-Q1 for dynamic gamma control and V_COM output.
The BUF20800-Q1 is ideally suited for rapidly changing the gamma curves because of its unique topology:
• double register input structure to the DAC;
• fast serial interface;
• simultaneous updating of all DACs by software. See the Read/Write Operations to write to all registers and
the Output Latch sections.
The double register input structure saves programming time by allowing updated DAC values to be pre-loaded
into the first register bank. Storage of this data can occur while a picture is still being displayed. Because the
data are only stored into the first register bank, the DAC output values remain unchanged—the display is
unaffected. During the vertical sync period, the DAC outputs (and therefore, the gamma voltages) can be quickly
updated either by using an additional control line connected to the LD pin, or through software—writing a ‘1’ in bit
15 of any DAC register. For the details on the operation of the double register input structure, see the Output
Latch section.
Example: Update all 18 gamma registers simultaneously via software.
Step 1: Check if LD pin is placed in HIGH state.
Step 2: Write DAC Registers 1−18 with bit 15 always ‘0’.
Step 3: Write any DAC register a second time with identical data. Make sure that bit 15 is ‘1’. All DAC
channels will be updated simultaneously after receiving the last bit of data. (Note: this step may be
eliminated by setting bit 15 of DAC 18 to ‘1’ in the previous step.)
Digital
Picture
Data
Histogram
Gamma
Adjustment
Algorithm
Black
White
Timing Controller/mController
SDA
BUF20800-Q1
Gamma References
SCL
1 through 18
Source Driver Source Driver
Figure 16. Dynamic Gamma Control
V_COM
TOTAL TI PANEL SOLUTION
In addition to the BUF20800-Q1 programmable voltage reference, TI offers a complete set of ICs for the LCD
panel market, including gamma correction buffers, various power-supply solutions, and audio power solutions.
See Figure 17 for the total IC solution from TI.
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