BenQ PB8220 - XGA DLP Projector, Service Manual

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A/D-decoder (AD9883) is used for decode VGA analog signal to digital signal (RGB 888) which
provide 24bit true color resolution. The input signal is analog RGB format and the YPbPr
component video input, which comes from the standard VGA D_SUB connector and Video RCA
jack, the analog signal input to ADC converter, which output RGB digital data stream to Image
Processor. The Image Processor also known as “Scaler”, which indicate its main function,
expand or downsize the digital picture from ADC to a fixed size digital image output.
As the diagram shown above, here is the function of every discrete block.
D_SUB input
Analog RGB data input; the standard maximum analog input resolution is SXGA. There also
some interface signals from the VGA cable, they are
GHS
– Providing the Horizontal Synchronization signal to Image Processor.
GVS
– Providing the Vertical Synchronization signal to Image Processor.
DDC interface
– Providing Digital Display Channel , which include VCC(Pin9) , SCL(Pin15) , SDA(Pin12) .
Analog Flat Panel Interface (ADC Converter), AD9883
The ADC converter digitizes the input analog RGB data signal from D_SUB and output the
digital data streams to Image Processor. The normal voltage level of analog RGB input signals is
about 0.7V, while the ADC digital signal output to Image Processor is LVTTL level, about 3.3V.
The ADC, AD9883 could supports up to pixel rate at about 140MHZ, which is about SXGA
75HZ analog input signal. It also includes an internal PLL clock generator which frequency is
according to GREF. The GREF is another version of GHS that comes from Image Processor.
There are some other interface signals related to AD9883.
SOGIN
– Sync On Green input from Image Processor, the signal enable the DX760 support the very special VGA
input signal.
GCOAST
– Input signal from Image Processor, the signal enable the DX760 support the Mac analog input format.
GREF
– Input signal from Image Processor, another version of GHS which providing the ADC to output the pixel
clock for Image Processor.
GCLK
– Output to Image Processor as Pixel Clock, providing the reference clock for Image Processor.
GRO, GGO, GBO, GRE, GGE, GBE –
Digital data stream to Image Processor which is Even/Odd mode if the
resolution of analog input is higher than SXGA 75HZ.
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