BUF12800 Datasheet, PDF (11/20 Pages) Burr-Brown (TI) – REFERENCE VOLTAGE GENERATOR for LCD GAMMA CORRECTION

BUF12800
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 12 shows a
block diagram using the BUF12800 for dynamic gamma
control.
The BUF12800 is ideally suited for rapidly changing the
gamma curves due to 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 Output Latch sections.
The double register input structure saves programming
time by allowing updated DAC values to be pre-stored into
the first register bank. Storage of this data can occur while
SBOS315 − DECEMBER 2004
a picture is still being displayed. Because the data is 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 12 registers simultaneously via
software.
Step 1: Check if LD pin is placed in HIGH state.
Step 2: Write DAC Registers 1−12 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.
Digital
Picture
Data
Histogram
Gamma
Adjustment
Algorithm
Black
White
Timing Controller/µController
SDA
BUF12800
Gamma References
SCL
A through L
Source Driver Source Driver
Figure 12. Dynamic Gamma Control
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