ISL51002 datasheet(24/32 Pages) INTERSIL

24 / 32 page

December 22, 2006

SOG

For component YPbPr signals, the sync signal is embedded

on the Y channel’s video, which is connected to the green

input, hence the name SOG (Sync on Green). The horizontal

sync information is encoded onto the video input by adding

the sync tip during the blanking interval. The sync tip level is

typically 0.3V below the video black level.

To minimize the loading on the green channel, the SOG input

for each of the green channels should be AC-coupled to the

ISL51002 through a series combination of a 10nF capacitor

and a 500

Ω resistor.

SOG Slicer (Figure 2)

The SOG input has programmable threshold, 40mV of

hysteresis, and an optional low pass filter than can be used

to remove high frequency video spikes (generated by

overzealous video peaking in a DVD player, for example)

that can cause false SOG triggers. The SOG threshold sets

the comparator threshold relative to the sync tip (the bottom

of the SOG pulse).

Inside the ISL51002, a 1µA pulldown ensures that each sync

tip triggersthe clamp circuit causing the tip to be clamped to a

600mV level. A comparator compares the SOG signal with an

internal 4-bit programmable threshold level reference ranging

from 0mV to 300mV above the sync clamp level. The SOG

threshold level, hysteresis, and low-pass filter is programmed

via registers 0x30and 0x31. If the Sync-On-Green function is

not needed, the SOGIN pin(s) may be left unconnected.

SYNC Processing

The ISL51002 can process sync signals from 3 different

sources: discrete HSYNC and VSYNC, composite sync on

the HSYNC input, or composite sync from a Sync-On-Green

(SOG) signal embedded on the Green video input. The

ISL51002 has SYNC activity detect functions to help the

firmware determine which sync source is available.

Macrovision

The ISL51002 automatically detects the presense of

Macrovision-encoded video. When Macrovision is detected,

it generates a mask signal that is ANDed with the incoming

SOG CSYNC signal to remove the Macrovision before the

HSYNC goes to the PLL. No additional programming is

required to support Macrovision.

The mask signal is also applied to the HSYNCOUT signal.

When Sync Mask Disable = 0, any Macrovision present on

the incoming sync will not be visible on HSYNCOUT. If the

application requires the Macrovision pulses to be visible on

HSYNCOUT, set the HSYNCOUT Mask Disable bit (register

0x7A bit 4).

Headswitching from Analog Videotape Signals

Occasionally this AFE may be used to digitize signals

coming from analog videotape sources. The most common

example of this is a Digital VCR (which for best signal quality

would be connected to this AFE with a component YPbPr

connection). If the digital VCR is playing an older analog

VHS tape, the sync signals from the VCR may contain the

worst of the traditional analog tape artifacts: headswitching.

Headswitching is traditionally the enemy of PLLs with large

capture ranges, because a headswitch can cause the

HSYNC period to change by as much as ±90%. To the PLL,

this can look like a frequency change of -50% to +900%,

causing errors in the output frequency (and obviously the

phase) to change. Subsequent HSYNCs have the correct,

original period, but most analog PLLs will take dozens of

lines to settle back to the correct frequency and phase after

a headswitch disturbance. This causes the top of the image

to “tear” during normal playback. In “trick modes” (fast

forward and rewind), the HSYNC signal has multiple

headswitch-like discontinuities, and many PLLs never settle

to the correct value before the next headswitch, rendering

the image completely unintelligible.

R(GB)IN0

CLAMP

GENERATION

R(GB)GND0

R(GB)IN1

R(GB)GND1

VGA0

VGA1

VGA2

VGA3

VIN+

VIN-

DC RESTORE

CLAMP DAC

VCLAMP

10-BIT ADC

OFFSET

DAC

FIXED

OFFSET

ABLC™

OFFSET

CONTROL

REGISTERS

ABLC™

FIXED

OFFSET

0X000

ABLC

BLOCK

TO OUTPUT

FORMATTER

AUTOMATIC BLACK LEVEL

COMPENSATION (ABLC™) LOOP

DC RESTORATION

INPUT

BANDWIDTH

PGA

BANDWIDTH

CONTROL

R(GB)IN2

R(GB)GND2

R(GB)IN3

R(GB)GND3

FIGURE 1. VIDEO FLOW (INCLUDING ABLC™)

ISL51002

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