a
Low Cost RGB to NTSC/PAL Encoder
with Luma Trap Port
AD725
FEATURES
Composite Video Output: Both NTSC and PAL
Chrominance and Luminance (S-Video) Outputs
Luma Trap Port to Eliminate Cross Color Artifacts
TTL Logic Levels
Integrated Delay Line and Auto-Tuned Filters
Drives 75 ⍀ Reverse-Terminated Loads
Low Power +5 V Operation
Power-Down to <1 A
Very Low Cost
PRODUCT DESCRIPTION
APPLICATIONS
RGB/VGA to NTSC/PAL Encoding
Personal Computers/Network Computers
Video Games
Video Conference Cameras
Digital Still Cameras
The AD725 features a luminance trap (YTRAP) pin that provides a means of reducing cross color generated by subcarrier
frequency components found in the luminance signal. For portable or other power-sensitive applications, the device can be
powered down to less than 1 µA of current consumption. All
logic levels are TTL compatible thus supporting the logic requirements of 3 V CMOS systems.
The AD725 is a very low cost general purpose RGB to NTSC/
PAL encoder that converts red, green and blue color component signals into their corresponding luminance (baseband
amplitude) and chrominance (subcarrier amplitude and phase)
signals in accordance with either NTSC or PAL standards.
These two outputs are also combined on-chip to provide a
composite video output. All three outputs are available separately at voltages of twice the standard signal levels as required for driving 75 Ω, reverse-terminated cables.
The AD725 is packaged in a low cost 16-lead SOIC and operates from a +5 V supply.
FUNCTIONAL BLOCK DIAGRAM
NTSC/PAL
HSYNC
VSYNC
4FSC CLOCK
XNOR
CSYNC
CSYNC
SYNC
SEPARATOR
BURST
4FSC
4FSC
QUADRATURE
+4
DECODER
FSC 90؇C
FSC 0؇C
NTSC/PAL
FSC 90؇C/270؇C
؎180؇C
(PAL ONLY)
CSYNC
RED
Y
DC
CLAMP
CLOCK
AT 8FSC
3-POLE
LP PREFILTER
SAMPLEDDATA
DELAY LINE
2-POLE
LP POSTFILTER
X2
LUMINANCE
OUTPUT
LUMINANCE
TRAP
GREEN
BLUE
DC
CLAMP
DC
CLAMP
RGB-TO-YUV
ENCODING
MATRIX
U
4-POLE
LPF
NTSC/PAL
U
CLAMP
BALANCED
MODULATORS
V
4-POLE
LPF
4-POLE
LPF
⌺
X2
COMPOSITE
OUTPUT
X2
CHROMINANCE
OUTPUT
V
CLAMP
BURST
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1997
