adv7189b Analog Devices, Inc., adv7189b Datasheet - Page 30

• Manufacturer Part Number: adv7189b
• Description: Multiformat Sdtv Video Decoder
• Manufacturer: Analog Devices, Inc.

ADV7189B
CSFM[2:0] C-Shaping Filter Mode, Address 0x17[7]
The C-shaping filter mode bits allow the user to select from a
range of low-pass filters, SH1 to SH5, and wideband mode for
the chrominance signal. The auto-selection options
automatically select from the filter options to give the specified
response. (See settings 000 and 001 in
Table 32. CSFM Function
CSFM[2:0]
000 (default)
001
010
011
100
101
110
111
F igure 16 shows the responses of SH1 (narrowest) to SH5
1 8 3 H
(widest) in addition to the wideband mode.
–10
–20
–30
–40
–50
–60
0
0
Figure 16. Chroma Shaping Filter Responses
1
Description
Autoselect 1.5 MHz bandwidth
Autoselect 2.17 MHz bandwidth
SH1
SH2
SH3
SH4
SH5
Wideband mode
COMBINED C ANTIALIAS, C SHAPING FILTER,
2
MINIMUM
VOLTAGE
FREQUENCY (MHz)
C RESAMPLER
3
MAXIMUM
VOLTAGE
4
T able 32).
1 8 2 H
CLAMP
LEVEL
5
6
Figure 17. Gain Control Overview
Rev. B | Page 30 of 104
ANALOG VOLTAGE
RANGE SUPPORTED BY ADC (1.6V RANGE FOR ADV7189B)
ADC
GAIN OPERATION
The gain control within the ADV7189B is done on a purely
digital basis. The input ADCs support a 12-bit range, mapped
into a 1.6 V analog voltage range. Gain correction takes place
after the digitization in the form of a digital multiplier.
Advantages of this architecture over the commonly used
programmable gain amplifier (PGA) before the ADCs include
the fact that the gain is now completely independent of supply,
temperature, and process variations.
As shown in
as long as it fits into the ADC window. The two components to
this are the amplitude of the input signal and the dc level it resides
on. The dc level is set by the clamping circuitry (see the
Operation section).
If the amplitude of the analog video signal is too high, clipping
can occur, resulting in visual artifacts. The analog input range
of the ADC, together with the clamp level, determines the
maximum supported amplitude of the video signal.
The minimum supported amplitude of the input video is
determined by the ADV7189B’s ability to retrieve horizontal
and vertical timing and to lock to the colorburst, if present.
There are separate gain control units for luma and chroma data.
Both can operate independently of each other. The chroma unit,
however, can also take its gain value from the luma path.
The possible AGC modes are summarized in
It is possible to freeze the automatic gain control loops. This
causes the loops to stop updating, and the AGC determined
gain at the time of the freeze to stay active until the loop is
either unfrozen or the gain mode of operation is changed.
The currently active gain from any of the modes can be read
back. Refer to the description of the dual-function manual gain
registers, LG[11:0] Luma Gain and CG[11:0] Chroma Gain, in
the
PROCESSOR
L uma Gain and the
1 8 7 H
DATA
(DPP)
PRE-
F igure 17, the ADV7189B can decode a video signal
1 8 4 H
SDP
(GAIN SELECTION ONLY)
C hroma Gain sections.
1 8 8 H
CONTROL
GAIN
T able 33.
1 8 6 H
C lamp
1 8 5 H