TW2866C datasheet(13/143 Pages) RENESAS

13 / 143 page

TW2866C

FN8253 Rev. 0.00

Page 13 of 143

February 3, 2012

Automatic Gain Control and Clamping

All four analog channels have built-in clamping circuit that restores the signal DC level. The Y channel

restores the back porch of the digitized video to a level of 60. This operation is automatic through internal

feedback loop. The Automatic Gain Control (AGC) of the Y channel adjusts input gain so that the sync tip is

at a desired level. Programmable white peak protection logic is included to prevent saturation in the case

of abnormal signal proportion between sync and white peak level.

Sync Processing

The sync processor of TW2866 detects horizontal synchronization and vertical synchronization signals in

the composite video or in the Y signal of an S-video or component signal. The processor contains a digital

phase-locked-loop and decision logic to achieve reliable sync detection in stable signal as well as in

unstable signals such as those from VCR fast forward or backward.

The vertical sync separator detects the vertical synchronization pattern in the input video signals. In

addition, the actual sync determination is controlled by a detection window to provide more reliable

synchronization. An option is available to provide faster responses for certain applications. The field status

is determined at vertical synchronization time. The field logic can also be controlled to toggle automatically

while tracking the input.

Y/C Separation

The color-decoding block contains the luma/chroma separation for the composite video signal and multi-

standard color demodulation. For NTSC and PAL standard signals, the luma/chroma separation can be

done either by comb filter or notch/band-pass filter combination. For SECAM standard signals, adaptive

notch/band-pass filter is used. The default selection for NTSC/PAL is comb filter.

In the case of comb filter, the TW2866 separates luma (Y) and chroma (C) of a NTSC/PAL composite video

signal using a proprietary 4H adaptive comb filter. The filter uses a four-line buffer. Adaptive logic

combines the upper-comb and the lower-comb results based on the signal changes among the previous,

current and next lines. This technique leads to excellent Y/C separation with small cross luma and cross

color at both horizontal and vertical edges.

Due to the line buffer used in the comb filter, there is always two lines processing delay at the output

except for the component input mode which has only one line delay.

If notch/band-pass filter is selected, the characteristics of the filters are shown in the filter curve section.

TW2866C Datasheet(PDF) 13 Page - Renesas Technology Corp