THS7374 Datasheet, PDF(18/37 Page) Texas Instruments – 4-Channel SDTV Video Amplifier with 6th-Order Filters and 6-dB Gain

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THS7374

SLOS590 â JULY 2008....................................................................................................................................................................................................... www.ti.com

TYPICAL CONFIGURATION AND VIDEO

TERMINOLOGY

A typical application circuit that uses the THS7374 as

a video buffer is shown in Figure 36. It shows a DAC

or encoder driving the input channels of the

THS7374. One channel is a composite video (CVBS)

channel of a standard definition (SD) video system.

The other channels are the component video Y'P'BP'R

(sometimes labeled Y'U'V' or incorrectly labeled

Y'C'BC'R) signals of a 480i or 576i system. These

channels could easily be the s-video Y'/C' channels

or the R'G'B' channels of a SCART system.

Note that the Y' term is used for the luma channels

throughout this document rather than the more

common luminance (Y) term. The reason for this

usage is to account for the definition of luminance as

stipulated by the CIE (International Commission on

Illumination). Video departs from true luminance

because a nonlinear term, gamma, is added to the

true RGB signals to form R'G'B' signals. These R'G'B'

signals are then used to mathematically create luma

(Y'). Thus, luminance (Y) is not maintained, providing

a difference in terminology.

This rationale is also used for the chroma (C') term.

Chroma is derived from the non-linear R'G'B' terms

and thus it is nonlinear. Chominance (C) is derived

from linear RGB, giving the difference between

chroma (C') and chrominance (C). The color

difference signals (P'B/P'R/U'/V') are also referenced

in this way to denote the nonlinear (gamma

corrected) signals.

R'G'B' (commonly mislabeled RGB) is also called

G'B'R' (again commonly mislabeled as GBR) in

professional video systems. The SMPTE component

standard stipulates that the luma information is

placed on the first channel, the blue color difference

is placed on the second channel, and the red color

difference signal is placed on the third channel. This

configuration is consistent with the Y'P'BP'R

nomenclature. Because the luma channel (Y') carries

the sync information and the green channel (G') also

carries the sync information, it makes logical sense

that G' be placed first in the system. Furthermore,

because the blue color difference channel (P'B) is

next and the red color difference channel (P'R) is last,

then it also makes logical sense to place the B' signal

on the second channel and the R' signal on the third

channel respectfully. Thus, hardware compatibility is

better achieved when using G'B'R' rather than R'G'B'.

Note that for many G'B'R' systems, sync is embedded

on all three channels, but this may not always be the

case in all systems.

+3.3 V

CVBS

DAC/Encoder

Y'/G'

SDTV

CVBS

S-Video

Y'P'BP'R

R'G'B'

PâB/B'

PâR/R'

THS7374

1 CH1 IN CH1 OUT 14

2 CH2 IN CH2 OUT 13

3 CH3 IN CH3 OUT 12

4 CH4 IN CH4 OUT 11

5 GND

VS+ 10

6 DISABLE BYPASS 9

7 NC

NC 8

CVBS/Sync

75 W

Y'/G' Out

75 W

P'B/B' Out

75 W

To GPIO Controller

or GND

+3 V to +5 V

P'R/R' Out

75 W

Figure 36. Typical SDTV CVBS/Y'P'BP'R Inputs from DC-Coupled Encoder/DAC

with DC-Coupled Line Driving

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