Decimation Filters - Analog Devices Advantiv ADV7604 Hardware Manual

• This mode is also available for external clock and clamp mode (refer to Section 10.16) when
the user needs to reduce delay with no decimation, downsampling, or color space conversion
in the DPP block.
• The DPP is never bypassed in decimated modes 2x1, 4x2, and 4x1.
• The
CP_CSC_EN
nondecimated mode with
Function
DPP_BYPASS_EN
0
1
8.3

Decimation Filters

In the ADV7604, the DPP contains two sets of decimation filters. The first set of three decimation
filters are positioned before the DPP CSC. They lie on channels A, B, and C respectively. (Refer to
Figure 51.) There are three fixed filter responses available for these filters. The user can use the filter
response selected by default or manually enable one of the three filter responses available.
The second set of three decimation filters is positioned after the DPP CSC. The first filter is
positioned on the channel A output of the DPP CSC, the second and third filters are positioned on
channels B and C. The user can use the default filter response or enable manually one of the seven
available filter responses.
The decimation filters are designed as linear phase FIR filters with a low pass response. They
should be enabled to reduce the bandwidth of the video stream prior to decimation. This can be
necessary under the following conditions:
•
The input is 2x oversampled at the ADCs and data must be decimated, for example, PR-
2X1 mode of operation:
If the intended output interface is 4:4:4, all three data streams must be decimated by 2.
If the user wants a 4:2:2 output interface, channel A must be decimated by 2, channels B
and C must be decimated by 4.
•
In case the mode of operation is not oversampled (for example, 1x1) or the output is not to
be decimated (for example, 2X2):
For a 4:4:4 output interface, no decimation is to be performed.
To achieve a 4:2:2 output data stream, channel A is not decimated, channels B and C
must be decimated by 2.
•
The input is 4x oversampled at the ADCs and data must be decimated, for example, SD-
4X1 mode of operation:
If the intended output interface is 4:4:4, all three data streams must be decimated by 4.
If the user wants a 4:2:2 output interface, channel A must be decimated by 4, channels B
and C must be decimated by 8.
Important: The decimation filters are automatically bypassed for HDMI 4:2:2 inputs. It is possible
to enable decimation filters for HDMI 4:2:2 inputs by setting
Rev. F August 2010
block is automatically enabled when the DPP is bypassed (i.e . in
DPP_BYPASS_EN
Description
DPP block enabled
DPP block bypassed
190
is set to 1b1).
DS_WITHOUT_FILTER
ADV7604
to 1.