ADV7182 datasheet(33/96 Pages) AD

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Data Sheet

ADV7182

Rev. A | Page 33 of 96

CG[11:0], Chroma Gain, Address 0x2D[3:0],

Address 0x2E[7:0]; CMG[11:0], Chroma Manual Gain,

Address 0x2D[3:0], Address 0x2E[7:0]

Chroma gain[11:0] is a dual-function register. If written to, a

desired manual chroma gain can be programmed. This gain

becomes active if the CAGC[1:0] function is switched to manual

fixed gain. See Equation 2 for calculating a desired gain.

If read back, this register returns the current gain value. Depending

on the setting in the CAGC[1:0] bits, this is either:

•

The chroma manual gain value (CAGC[1:0] set to chroma

manual gain mode).

•

The chroma automatic gain value (CAGC[1:0] set to either

of the automatic modes).

Table 47. CG/CMG Function

CG[11:0]/CMG[11:0]

Read/Write

Description

CMG[11:0]

Write

Manual gain for chroma path

CG[11:0]

Read

Currently active gain

Chroma_Gain

tor

brationFac

ChromaCali

CMG

decimal

]

[

≅

(2)

where ChromaCalibrationFactor is a decimal value between 0

and 4095.

Calculation of Chroma Calibration Factor

Take the following steps to calculate the chroma calibration factor:

1. Apply a CVBS signal with the color bars/SMPTE bars test

pattern content directly to the measurement equipment.

2. Ensure correct termination of 75 Ω on the measurement

equipment. Measure chroma output levels.

3. Reconnect the source to the CVBS input of the ADV7182

system that has a back end gain of 1. Repeat the measurement

of chroma levels.

4. Turn off the chroma AGC and manually change the

chroma gain control register, CMG[11:0], until the chroma

level matches that measured directly from the source.

This value, in decimal, is the chroma calibration factor.

CKE, Color Kill Enable, Address 0x2B[6]

The color kill enable bit allows the optional color kill function

to be switched on or off.

For QAM-based video standards (PAL and NTSC), as well as

FM-based systems (SECAM), the threshold for the color kill

decision is selectable via the CKILLTHR[2:0] bits.

If color kill is enabled and the color carrier of the incoming

video signal is less than the threshold for 128 consecutive video

lines, color processing is switched off (black and white output).

To switch the color processing back on, another 128 consecutive

lines with a color burst greater than the threshold are required.

The color kill option works only for input signals with a modulated

chroma part. For component input (YPrPb), there is no color kill.

Set CKE to 0 to disable color kill.

Set CKE to 1 (default) to enable color kill.

CKILLTHR[2:0], Color Kill Threshold, Address 0x3D[6:4]

The CKILLTHR[2:0] bits allow the user to select a threshold for

the color kill function. The threshold applies only to QAM-based

(NTSC and PAL) or FM-modulated (SECAM) video standards.

To enable the color kill function, the CKE bit must be set. For the

000, 001, 010, and 011 settings, chroma demodulation inside

the ADV7182 may not work satisfactorily for poor input video

signals.

Table 48. CKILLTHR Function

Description

CKILLTHR[2:0]

NTSC, PAL

SECAM

000

Kill at <0.5%

No color kill

001

Kill at <1.5%

Kill at <5%

010 (default)

Kill at <2.5%

Kill at <7%

011

Kill at <4%

Kill at <8%

100

Kill at <8.5%

Kill at <9.5%

101

Kill at <16%

Kill at <15%

110

Kill at <32%

111

Reserved for Analog Devices internal use only;

do not select

ADV7182 Datasheet(PDF) 33 Page - Analog Devices

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