adv7188 Analog Devices, Inc., adv7188 Datasheet - Page 17

• Manufacturer Part Number: adv7188
• Description: Multiformat Sdtv Video Decoder With Fast Switch Overlay Support
• Manufacturer: Analog Devices, Inc.

•
•
System Diagram
A block diagram of the ADV7188 fast blanking configuration is
shown in Figure 9.
The CVBS signal is processed by the ADV7188 and converted
to YPrPb. The RGB signals are processed by a color space
converter (CSC), and samples are converted to YPrPb. Both sets
of YPrPb signals are input to the subpixel blender, which can be
configured to operate in any of the four modes previously
outlined in this section.
The fast blank position resolver determines the time position of the
FB pin accurately (<1 ns). This position information is then used
by the subpixel blender in dynamic switching modes, enabling
the ADV7188 to implement high performance multiplexing
between the CVBS and RGB sources even when the RGB data
source is completely asynchronous to the sampling crystal reference.
An antialiasing filter is required on all four data channels (R, G,
B, and CVBS). The order of this filter is reduced because all signals
are sampled at 54 MHz.
MAN_ALPHA_VAL [6:0]. Overlay is not possible in fixed
alpha blending mode.
Dynamic Switching (Fast Mux). The FB pin can be used to
select the source. This enables dynamic multiplexing between
the CVBS and RGB sources. With default settings, when
Logic 1 is applied to the FB pin, the RGB source is selected;
when Logic 0 is applied to the FB pin, the CVBS source is
selected. This mode is suitable for the overlay of subtitles,
teletext, or other material. Typically, the CVBS source
carries the main picture, and the RGB source has the
overlay data.
Dynamic Switching with Edge Enhancement. This provides
the same functionality as the dynamic switching mode,
but with the benefit of Analog Devices’ proprietary edge-
enhancement algorithms, which improve the visual appearance
of transitions for signals from a wide variety of sources.
Rev. A | Page 17 of 112
The switched or blended data is output from the ADV7188 in
the standard output formats (see Table 102).
FAST BLANK CONTROL
FB_MODE [1:0], Address 0xED [1:0]
FB_MODE controls which fast blank mode is selected.
Table 12. FB_MODE [1:0] Function
FB_MODE [1:0]
00 (default)
01
10
11
Static Mux Selection Control
CVBS_RGB_SEL, Address 0xED [2]
CVBS_RGB_SEL controls whether the video from the CVBS or
RGB source is selected for output from the ADV7188.
0 (default)—Data from the CVBS source is selected for output.
1—Data from the RGB source is selected for output.
Alpha Blend Coefficient
MAN_ALPHA_VAL [6:0], Address 0xEE [6:0]
When fixed alpha blending is selected (FB_MODE [1:0] = 01),
MAN_ALPHA_VAL [6:0] determines the proportion in which
the video from the CVBS and RGB sources are blended. Equation
1 shows how these bits affect the video output.
The maximum valid value for MAN_ALPHA_VAL [6:0] is
1000000, such that the alpha blender coefficients remain
between 0 and 1. The default value for MAN_ALPHA_VAL [6:0]
is 0000000.
Video
+
Video
out
RGB
=
Video
×
MAN
CVBS
Description
Static switch mode
Fixed alpha blending
Dynamic switching (fast mux)
Dynamic switching with edge enhancement
_
×
ALPHA
⎛
⎜ ⎜
⎝
1
−
64
MAN
_
VAL
_
ALPHA
6 [
:
] 0
64
_
VAL
6 [
ADV7188
:
] 0
⎞
⎟ ⎟
⎠
(1)