BUF16820 Datasheet, PDF (19/30 Pages) Burr-Brown (TI) – 14-Channel GAMMA VOLTAGE GENERATOR with Programmable VCOM Outputs and OTP Memory

BUF16820
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 18 shows a
block diagram using the BUF16820 for dynamic gamma
control and V_COM output.
The BUF16820 is ideally suited for rapidly changing the
gamma curves because of its unique topology:
D Double register input structure to the DAC.
D Fast serial interface.
D Simultaneous updating of all DACs by software.
See the Read/Write Operations and the Output
Latch sections.
SBOS356A − FEBRUARY 2006 − REVISED OCTOBER 2006
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. Since 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 14 gamma registers simultaneously
via software.
Step 1: Check if LD pin is placed in HIGH state.
Step 2: Write DAC Registers 1−14 with bit 15 always ‘0’.
Step 3: Write any DAC register a second time with identi-
cal 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 14 to ‘1’ in the previous step.)
Digital
Picture
Data
Histogram
Gamma
Adjustment
Algorithm
Black
White
Timing Controller/µController
SDA
BUF16820
Gamma References
SCL
1 through 14
Source Driver
Source Driver
V_COM
Figure 18. Dynamic Gamma Control
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