adv7180 Analog Devices, Inc., adv7180 Datasheet - Page 32

• Manufacturer Part Number: adv7180
• Description: 10-bit, 4 X Oversampling Sdtv Video Decoder
• Manufacturer: Analog Devices, Inc.

ADV7180
CSFM[2:0], C Shaping Filter Mode, Address 0x17 [7:5]
The C shaping filter mode bits allow the user to select from a
range of low-pass filters for the chrominance signal. When
switched in automatic mode, the widest filter is selected based
on the video standard/format and user choice (see Settings 000
and 001 in Table 33).
Table 33. CSFM Function
CSFM[2:0]
000 (default)
001
010
011
100
101
110
111
Figure 23 shows the responses of SH1 (narrowest) to SH5
(widest) in addition to the wideband mode (shown in red).
GAIN OPERATION
The gain control within the ADV7180 is done on a purely
digital basis. The input ADC supports a 10-bit range mapped
into a 1.0 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 ADC include
the fact that the gain is now completely independent of supply,
temperature, and process variations.
As shown in Figure 25, the ADV7180 can decode a video signal
as long as it fits into the ADC window. The 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 Clamp
Operation section).
If the amplitude of the analog video signal is too high, clipping
may 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.
Figure 24 shows a typical voltage divider network that is
required to keep the input video signal within the allowed range
Description
Autoselect 1.5 MHz bandwidth
Autoselect 2.17 MHz bandwidth
SH1
SH2
SH3
SH4
SH5
Wideband mode
MINIMUM
VOLTAGE
MAXIMUM
VOLTAGE
CLAMP
LEVEL
Figure 25. Gain Control Overview
Rev. B | Page 32 of 112
ANALOG VOLTAGE
RANGE SUPPORTED BY ADC (1V RANGE FOR ADV7180)
ADC
of the ADC, 0 V to 1 V. This circuit should be placed before all
analog inputs to the ADV7180.
The minimum supported amplitude of the input video is
determined by the ability of the ADV7180 to retrieve horizontal
and vertical timing and to lock to the color burst, 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 shown in Table 34.
Table 34. AGC Modes
Input
Video Type
Any
CVBS
Y/C
YPrPb
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
Luma Gain and Chroma Gain sections.
PROCESSOR
DATA PRE-
ANALOG VIDEO
(DPP)
INPUT
Luma Gain
Manual gain luma
Dependent on
horizontal sync depth
Peak white
Dependent on
horizontal sync depth
Peak white
Dependent on
horizontal sync depth
Figure 24. Input Voltage Divider Network
(GAIN SELECTION ONLY)
36Ω
VIDEO PROCESSOR
CONTROL
GAIN
39Ω
100nF
Chroma Gain
Manual gain chroma
Dependent on color-
burst amplitude
taken from luma path
Dependent on color-
burst amplitude
taken from luma path
Dependent on color-
burst amplitude
taken from luma path
Dependent on color-
burst amplitude
Taken from luma path
AIN_OF_ADV7180