THS7313 datasheet(25/48 Pages) TI

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OUTPUT MODES OF OPERATION – AC COUPLED

GND

CH.2 IN B

CH.3 IN B

I 2C-A0

SDA

VS+ 11

SCL

CH.3 SAG

I 2C-A1

CH.1 IN B

CH.2 IN A

CH.3 IN A

CH.1 IN A

CH.3 OUT

CH.2 SAG

CH.2 OUT

CH.1 SAG

CH.1 OUT

CVBS

Out 1

C’

Out 1

C’

Out 2

Y’

Out 1

Y’

Out 2

CVBS

Out 2

CBVS

Y’

C’

3.3 V

75 W

0.1 F

0.01 F

470 F

(See Note A)

470 F

(See Note A)

470 F

(Note A)

470 F

(Note A)

100 F

0.1 F

3.3 V

I C

Controller

External

Input

CVBS

S-Video C’

S-Video Y’

S-Video 1

S-Video 2

DAC /

Encoder

(THS8200)

SDTV

CVBS

S-Video Y’

S-Video C’

480i

576i

G’B’R’

THS7313

SLOS483 – NOVEMBER 2005

APPLICATION INFORMATION (continued)

The most common method of coupling the video signal to the line is by using a large capacitor. This capacitor is

typically between 220

µF and 1000 µF, although 470 µF is most common. This value of this capacitor must be

this large to minimize the line tilt (droop) and/or field tilt associated with ac coupling as described previously in

this document. Just like the dc output configuration, connection of the output pin of each channel directly to the

SAG output pin of the corresponding channel should be as close as possible to the output pins of the THS7313.

The most common reason ac coupling is to ensure full interoperability with the receiving video system. This

eliminates possible ground loops. It also ensures that regardless of the reference dc voltage used on the transmit

side, the receive side re-establishes the dc reference voltage to its own requirements.

As with the dc output mode of operation, each line should have a 75-

Ω source termination resistor in series with

the ac-coupling capacitor. If 2 lines are to be driven, it is best to have each line use its own capacitor and resistor

rather than sharing these components as shown in Figure 53.This helps ensure line-to-line dc isolation and

potential problems. Using a single 1000-

µF capacitor for 2-lines can be done, but there is a chance for ground

loops and interference creation between the two receivers.

Due to the high frequency content of the video signal, it is recommended, but not required, to add a 0.01-

µF capacitor

in parallel with these large capacitors.

Figure 53. Typical SDTV CVBS/Y'/C' System Driving 2 AC-Coupled Video Lines

Due to the edge rates and frequencies of operation, it is recommended – but not required – to place a 0.1-

µF to

0.01-

µF capacitor in parallel with the large 220-µF to 1000-µF capacitors. These large value capacitors are most

commonly aluminum electrolytic. It is known that these capacitors have significantly large equivalent series

resistance (ESR), and their impedance at high frequencies is large due to the associated inductances involved

with their construction. The small 0.1-

µF to 0.01-µF capacitors help pass these high frequency (>1 MHz) signals

with lower impedance than the large capacitors.

THS7313 Datasheet(PDF) 25 Page - Texas Instruments

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