a
RGB to NTSC/PAL Encoders
AD720/AD721
FEATURES
Com posite Video Output
(subcarrier amplitude and phase) signals in accordance with
either NT SC or PAL standards. T hese 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. T he 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.
Chrom inance and Lum inance (S-Video) Outputs
No External Filters or Delay Lines Required
Drives 75 Ω Reverse-Term inated Loads
Com pact 28-Pin PLCC
Logic Selectable NTSC or PAL Encoding Modes
Autom atically Selects Proper Chrom inance Filter
Cutoff Frequency for Encoding Standard
Logic Selectable Encode or Pow er-Dow n Mode (AD720
Only)
T he 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. T here are two control inputs: one input
selects the T V standard (NT SC/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. T he chip
operates from ±5 V supplies.
Logic Selectable Encode or Bypass Mode (AD721 Only)
Low Pow er: 200 m W typical
APPLICATIONS
RGB to NTSC or PAL Encoding
Drive RGB Signals into 75 Ω Load (AD721 Only)
P RO D UCT D ESCRIP TIO N
T he AD720 and AD721 RGB to NT SC/PAL Encoders convert
red, green and blue color component signals into their corre-
sponding luminance (baseband amplitude) and chrominance
(continued on page 5)
FUNCTIO NAL BLO CK D IAGRAM
NTSC/PAL
ASNC
DELAYED C-SYNC
C-SYNC
DELAY
POWER AND GROUNDS
SYNC
DECODER
NTSC/PAL
LOGIC
+5V
+5V
C-SYNC
BURST
ANALOG
ANALOG ONLY
ANALOG
LOGIC
–5V
AGND
DGND
±180
°
SC 90
°
/270
NTSC/PAL
CLOCK
AT 8FSC
°
(PAL ONLY)
SC 90
°
4FSC
ENCD
QUADRATURE
DECODER
SC 0
Y
°
BURST
5MHz
DC
LUMINANCE OUTPUT*
–0.572V TO 1.43V NTSC
–0.6V TO 1.4V PAL
5MHz
4-POLE LP
SAMPLED-
DATA
DELAY LINE
2-POLE
LP POST-
FILTER
RESTORE
AND C-SYNC
INSERTION
X2
RED
PRE-FILTER
COMPOSITE OUTPUT*
–0.572V TO 2V NTSC
–0.6V TO 2V PAL
RGB-TO-YUV
ENCODING
MATRIX
1.2MHz
4-POLE
LPF
NTSC/PAL
∑
X2
X2
U
V
GREEN
BLUE
3.6MHz (NTSC)
4.4MHz (PAL)
3-POLE LPF
BALANCED
MODULATORS
CHROMINANCE OUTPUT*
572mVp-p NTSC
600mVp-p PAL
∑
1.2MHz
4-POLE
LPF
*NOTE:
ROUT
1.5Vp-p
X2
X2
X2
THE LUMINANCE, COMPOSITE, AND CHROMINANCE
OUTPUTS ARE AT TWICE NORMAL LEVELS FOR
DRIVING 75Ω REVERSE-TERMINATED LINES.
AD721
(ONLY)
GOUT
1.5Vp-p
BOUT
1.5Vp-p
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood. MA 02062-9106, U.S.A.
Tel: 617/ 329-4700 Fax: 617/ 326-8703