ADV7180WBSTZ datasheet(35/120 Pages) AD

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Data Sheet

ADV7180

Rev. G | Page 35 of 120

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 Setting 000

and Setting 001 in Table 37).

Table 37. CSFM Function

CSFM[2:0]

Description

000 (default)

Autoselection 1.5 MHz bandwidth

001

Autoselection 2.17 MHz bandwidth

010

SH1

011

SH2

100

SH3

101

SH4

110

SH5

111

Wideband mode

Figure 26 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 28, the ADV7180 can decode a video signal

as long as it fits into the ADC window. The components for 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 27 shows a typical voltage divider network that is required

to keep the input video signal within the allowed range of the ADC,

0 V to 1 V. This circuit should be placed before all analog inputs

to the ADV7180.

100nF

ANALOG VIDEO

INPUT

AIN_OF_ADV7180

Figure 27. Input Voltage Divider Network

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 38.

Table 38. AGC Modes

Input

Video Type

Luma Gain

Chroma Gain

Any

Manual gain luma

Manual gain chroma

CVBS

Dependent on

horizontal sync depth

Dependent on color-burst

amplitude taken from

luma path

Peak white

Dependent on color-burst

amplitude taken from

luma path

Y/C

Dependent on

horizontal sync depth

Dependent on color-burst

amplitude taken from

luma path

Peak white

Dependent on color-burst

amplitude

YPrPb

Dependent on

horizontal sync depth

Taken from luma path

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.

ANALOG VOLTAGE

RANGE SUPPORTED BY ADC (1V RANGE FOR ADV7180)

DATA PRE-

PROCESSOR

(DPP)

ADC

VIDEO PROCESSOR

(GAIN SELECTION ONLY)

MAXIMUM

VOLTAGE

MINIMUM

VOLTAGE

CLAMP

LEVEL

GAIN

CONTROL

Figure 28. Gain Control Overview

ADV7180WBSTZ Datasheet(PDF) 35 Page - Analog Devices

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