DS90UB926Q Datasheet, PDF (47/57 Pages) Texas Instruments – 5 - 85 MHz 24-bit Color FPD-Link III Deserializer with Bidirectional Control Channel

DS90UB926Q
Image Enhancement Features
Several image enhancement features are provided. White balance LUTs allow the user to define and target the color temperature
of the display. Adaptive Hi-FRC dithering enables the presentation of “true-color” images on an 18–bit color display.
WHITE BALANCE
The White Balance feature enables similar display appearance when using LCD’s from different vendors. It compensates for native
color temperature of the display, and adjusts relative intensities of R, G, B to maintain specified color temperature. Programmable
control registers are used to define the contents of three LUTs (8-bit color value for Red, Green and Blue) for the White Balance
Feature. The LUTs map input RGB values to new output RGB values. There are three LUTs, one LUT for each color. Each LUT
contains 256 entries, 8-bits per entry with a total size of 6144 bits (3 x 256 x 8). All entries are readable and writable. Calibrated
values are loaded into registers through the I2C interface (deserializer is a slave device). This feature may also be applied to lower
color depth applications such as 18–bit (666) and 16–bit (565). White balance is enabled and configured via serial control bus
register.
LUT contents
The user must define and load the contents of the LUT for each color (R,G,B). Regardless of the color depth being driven (888,
666, 656), the user must always provide contents for 3 complete LUTs - 256 colors x 8 bits x 3 tables. Unused bits - LSBs -shall
be set to “0” by the user.
When 24-bit (888) input data is being driven to a 24-bit display, each LUT (R, G and B) must contain 256 unique 8-bit entries. The
8-bit white balanced data is then available at the output of the DS90UB926Q deserailizer, and driven to the display.
When 18-bit (666) input data is being driven to an 18-bit display, the white balance feature may be used in one of two ways. First,
simply load each LUT with 256, 8-bit entries. Each 8-bit entry is a 6-bit value (6 MSBs) with the 2 LSBs set to “00”. Thus as total
of 64 unique 6-bit white balance output values are available for each color (R, G and B). The 6-bit white balanced data is available
at the output of the DS90UB926Q deserializer, and driven directly to the display.
Alternatively, with 6-bit input data the user may choose to load complete 8-bit values into each LUT. This mode of operation provides
the user with finer resolution at the LUT output to more closely achieve the desired white point of the calibrated display. Although
8-bit data is loaded, only 64 unique 8-bit white balance output values are available for each color (R, G and B). The result is 8-bit
white balanced data. Before driving to the output of the deserializer, the 8-bit data must be reduced to 6-bit with an FRC dithering
function. To operate in this mode, the user must configure the DS90UB926Q to enable the FRC2 function.
Examples of the three types of LUT configurations described are shown in Figure 20
Enabling white balance
The user must load all 3 LUTs prior to enabling the white balance feature. The following sequence must be followed by the user.
To initialize white balance after power-on (Table 10):
1) Load contents of all 3 LUTs . This requires a sequential loading of LUTs - first RED, second GREEN, third BLUE. 256, 8-bit
entries must be loaded to each LUT. Page registers must be set to select each LUT.
2) Enable white balance
By default, the LUT data may not be reloaded after initialization at power-on.
An option does exist to allow LUT reloading after power-on and initial LUT loading (as described above). This option may only be
used after enabling the white balance reload feature via the associated serial control bus register. In this mode the LUTs may be
reloaded by the master controller via I2C. This provides the user with the flexibility to refresh LUTs periodically , or upon system
requirements to change to a new set of LUT values. The host controller loads the updated LUT values via the serial bus interface.
There is no need to disable the white balance feature while reloading the LUT data. Refreshing the white balance to the new set
of LUT data will be seamless - no interruption of displayed data.
It is important to note that initial loading of LUT values requires that all 3 LUTs be loaded sequentially. When reloading, partial LUT
updates may be made.
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