a

FUNCTIONAL BLOCK DIAGRAM

SYNC

DECODER

BURST

C-SYNC

4FSC

ENCD

RED

GREEN

BLUE

QUADRATURE

DECODER

DELAYED C-SYNC

SC 90

°

SC 0

°

CLOCK

AT 8FSC

DC

RESTORE

AND C-SYNC

INSERTION

5MHz

2-POLE

LP POST-

FILTER

COMPOSITE OUTPUT*

–0.572V TO 2V NTSC

–0.6V TO 2V PAL

LUMINANCE OUTPUT*

–0.572V TO 1.43V NTSC

–0.6V TO 1.4V PAL

CHROMINANCE OUTPUT*

572mVp-p NTSC

600mVp-p PAL

NTSC/PAL

C-SYNC

DELAY

±180

°

(PAL ONLY)

RGB-TO-YUV

ENCODING

MATRIX

BURST

Y

U

V

SC 90

5MHz

4-POLE LP

PRE-FILTER

1.2MHz

4-POLE

LPF

1.2MHz

4-POLE

LPF

SAMPLED-

DATA

DELAY LINE

∑

3.6MHz (NTSC)

4.4MHz (PAL)

3-POLE LPF

∑

X2

X2

X2

POWER AND GROUNDS

+5V

AGND

DGND

LOGIC

ANALOG

ANALOG ONLY

ANALOG

LOGIC

+5V

–5V

*NOTE:

THE LUMINANCE, COMPOSITE, AND CHROMINANCE

OUTPUTS ARE AT TWICE NORMAL LEVELS FOR

DRIVING 75

Ω REVERSE-TERMINATED LINES.

ASNC

NTSC/PAL

BALANCED

MODULATORS

NTSC/PAL

X2

X2

X2

ROUT

1.5Vp-p

GOUT

1.5Vp-p

BOUT

1.5Vp-p

AD721

(ONLY)

NTSC/PAL

AD720/AD721

FEATURES

Composite Video Output

Chrominance and Luminance (S-Video) Outputs

No External Filters or Delay Lines Required

Drives 75

Ω Reverse-Terminated Loads

Compact 28-Pin PLCC

Logic Selectable NTSC or PAL Encoding Modes

Automatically Selects Proper Chrominance Filter

Cutoff Frequency for Encoding Standard

Logic Selectable Encode or Power-Down Mode (AD720

Only)

Logic Selectable Encode or Bypass Mode (AD721 Only)

Low Power: 200 mW typical

APPLICATIONS

RGB to NTSC or PAL Encoding

Drive RGB Signals into 75

Ω Load (AD721 Only)

PRODUCT DESCRIPTION

The AD720 and AD721 RGB to NTSC/PAL Encoders convert

red, green and blue color component signals into their corre-

sponding luminance (baseband amplitude) and chrominance

(subcarrier amplitude and phase) signals in accordance with

either NTSC or PAL standards. These two outputs are also

combined to provide a composite video output. All three out-

puts are available separately at voltages of twice the standard

signal levels as required for driving 75

Ω reverse terminated

cables. The AD721 also features a bypass mode, in which the

RGB inputs may bypass the encoder section of the IC via three

gain-of-two amplifiers suitable for driving 75

Ω reverse termi-

nated cables.

The AD720 and AD721 provide a complete, fully calibrated

function, requiring only termination resistors, bypass capacitors,

a clock input at four times the subcarrier frequency, and a com-

posite sync pulse. There are two control inputs: one input

selects the TV standard (NTSC/PAL) and the other (ENCD)

powers down most sections of the chip when the encoding func-

tion is not in use (AD720) or activates the triple bypass buffer to

drive the RGB signals when RGB encoding is not required

(AD721). All logical inputs are CMOS compatible. The chip

operates from

±5 V supplies.

(continued on page 5)

RGB to NTSC/PAL Encoders

One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.

Tel: 617/329-4700

Fax: 617/326-8703

REV. 0

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.