AD720_15 Datasheet, PDF (1/8 Pages) Analog Devices – RGB to NTSC/PAL Encoders

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RGB to NTSC/PAL Encoders
AD720/AD721
FEATURES
(subcarrier amplitude and phase) signals in accordance with
Composite Video Output
either NTSC or PAL standards. These two outputs are also
Chrominance and Luminance (S-Video) Outputs
combined to provide a composite video output. All three out-
No External Filters or Delay Lines Required
puts are available separately at voltages of twice the standard
Drives 75 Ω Reverse-Terminated Loads
signal levels as required for driving 75 Ω reverse terminated
Compact 28-Pin PLCC
cables. The AD721 also features a bypass mode, in which the
Logic Selectable NTSC or PAL Encoding Modes
RGB inputs may bypass the encoder section of the IC via three
Automatically Selects Proper Chrominance Filter
gain-of-two amplifiers suitable for driving 75 Ω reverse termi-
Cutoff Frequency for Encoding Standard
nated cables.
Logic Selectable Encode or Power-Down Mode (AD720
The AD720 and AD721 provide a complete, fully calibrated
OBSOLETE 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
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)
FUNCTIONAL BLOCK DIAGRAM
NTSC/PAL
ASNC
C-SYNC
SYNC
DECODER
C-SYNC
DELAY _NTSC/PAL
DELAYED C-SYNC
POWER AND GROUNDS
+5V
LOGIC
BURST
+5V
ANALOG
4FSC
ENCD
QUADRATURE
DECODER
BURST
SC 90°
SC 0°
±180°
(PAL ONLY)
SC 90°/270°
NTSC/PAL
CLOCK
AT 8FSC
–5V
AGND
DGND
ANALOG ONLY
ANALOG
LOGIC
RED
GREEN
BLUE
Y
5MHz
4-POLE LP
PRE-FILTER
RGB-TO-YUV _U
ENCODING
MATRIX
1.2MHz
4-POLE
LPF
V
1.2MHz
4-POLE
LPF
SAMPLED-
DATA
DELAY LINE
DC
5MHz
RESTORE
AND C-SYNC
2-POLE
LP POST-
X2
INSERTION
FILTER
NTSC/PAL
∑ X2
3.6MHz (NTSC)
∑ ^BALANCED
MODULATORS
4.4MHz (PAL)
3-POLE LPF
X2
LUMINANCE OUTPUT*
–0.572V TO 1.43V NTSC
–0.6V TO 1.4V PAL
COMPOSITE OUTPUT*
–0.572V TO 2V NTSC
–0.6V TO 2V PAL
CHROMINANCE OUTPUT*
572mVp-p NTSC
600mVp-p PAL
X2
ROUT
1.5Vp-p ^AD721
(ONLY)
X2
GOUT
1.5Vp-p
X2
BOUT
1.5Vp-p
*NOTE:
THE LUMINANCE, COMPOSITE, AND CHROMINANCE
OUTPUTS ARE AT TWICE NORMAL LEVELS FOR
DRIVING 75Ω REVERSE-TERMINATED LINES.
REV. 0
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