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 /270
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 75W 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.