ADV7180WBSTZ datasheet(38/120 Pages) AD

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ADV7180

Data Sheet

Rev. G | Page 38 of 120

CAGT[1:0], Chroma Automatic Gain Timing,

Address 0x2D[7:6]

The chroma automatic gain timing register allows the user to

influence the tracking speed of the chroma automatic gain

control. This register has an effect only if the CAGC[1:0]

Table 45. CAGT Function

CAGT[1:0]

Description

Slow (TC = 2 sec)

Medium (TC = 1 sec)

Reserved

11 (default)

Adaptive

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 any of

the automatic modes).

Table 46. 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 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 ADV7180

system that has a backend 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.

Setting CKE to 0 disables color kill.

Setting CKE to 1 (default) enables 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

Setting 000, Setting 001, Setting 010, and Setting 011, chroma

demodulation inside the ADV7180 may not work satisfactorily

for poor input video signals.

Table 47. CKILLTHR Function

Description

CKILLTHR[2:0]

SECAM

NTSC, PAL

000

No color kill

Kill at <0.5%

001

Kill at <5%

Kill at <1.5%

010

Kill at <7%

Kill at <2.5%

011 (default)

Kill at <8%

Kill at <4%

100

Kill at <9.5%

Kill at <8.5%

101

Kill at <15%

Kill at <16%

110

Kill at <32%

111

Reserved for Analog Devices internal use only;

do not select

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