Win2008

a

RGB to NTSC/PAL Encoder
AD724
operates from a single +5 V supply. No external delay lines or
filters are required. The AD724 may be powered down when
not in use.

FEATURES
Low Cost, Integrated Solution
+5 V Operation
Accepts FSC Clock or Crystal, or 4FSC Clock
Composite Video and Separate Y/C (S-Video) Outputs
Luma and Chroma Outputs Are Time Aligned
Minimal External Components:No External Filters or Delay Lines Required
Onboard DC Clamp
Accepts Either HSYNC and VSYNC or CSYNC
Phase Lock to External Subcarrier
Drives 75 Reverse-Terminated Loads
Logic Selectable NTSC or PAL Encoding Modes
Compact 16-Lead SOIC

The AD724 accepts either FSC or 4FSC clock. When a clock is
not available, a low cost parallel-resonant crystal (3.58 MHz
(NTSC) or 4.43 MHz (PAL)) andthe AD724’s on-chip oscillator generate the necessary subcarrier clock. The AD724 also
accepts the subcarrier clock from an external video source.
The interface to graphics controllers is simple: an on-chip logic
“XNOR” accepts the available vertical (VSYNC) and horizontal sync (HSYNC) signals and creates the composite sync
(CSYNC) signal on-chip. If available, the AD724 will also
accept astandard CSYNC signal by connecting VSYNC to
Logic HI and applying CSYNC to the HSYNC pin. The
AD724 contains decoding logic to identify valid horizontal sync
pulses for correct burst insertion.

APPLICATIONS
RGB to NTSC or PAL Encoding

Delays in the U and V chroma filters are matched by an on-chip
sampled-data delay line in the Y signal path. To prevent aliasing, a prefilter at 5 MHz isincluded ahead of the delay line and
a post-filter at 5 MHz is added after the delay line to suppress
harmonics in the output. These low-pass filters are optimized
for minimum pulse overshoot. The overall luma delay, relative
to chroma, has been designed to be time aligned for direct input to
a television’s baseband. The AD724 comes in a space-saving
SOIC and is specified for the 0°C to +70°Ccommercial temperature range.

PRODUCT DESCRIPTION

The AD724 is a low cost 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 to provide composite video output.All three outputs can
simultaneously drive 75 Ω, reverse-terminated cables. All logical inputs are TTL, 3 V and 5 V CMOS compatible. The chip

FUNCTIONAL BLOCK DIAGRAM

SUBCARRIER

4FSC
NTSC/PAL
HSYNC
VSYNC

PHASE
DETECTOR

FSC

CHARGE
PUMP

XOSC
4FSC

FSC

LOOP
FILTER

4FSC
VCO

CSYNC

SYNC
SEPARATOR

BURST

XNOR

NTSC/PAL

CSYNC
4FSC

FSC 90°QUADRATURE
+4
DECODER

± 180°
(PAL ONLY)

SC 90°/270°

FSC 0°
CSYNC

RED

GREEN

DC
CLAMP

Y

DC
CLAMP

RGB-TO-YUV
ENCODING
MATRIX

CLOCK
AT 8FSC

3-POLE
LP PREFILTER

SAMPLEDDATA
DELAY LINE

U

4-POLE
LPF

BALANCED
MODULATORS
BLUE

DC
CLAMP

V

4-POLE
LPF

X2

LUMINANCE
OUTPUT

NTSC/PAL

U
CLAMP

2-POLE
LP POSTFILTER

X2

COMPOSITEOUTPUT

4-POLE
LPF

X2

CHROMINANCE
OUTPUT

V
CLAMP

BURST

REV. B
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 anypatent 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., 1999

(Unless otherwise noted, VS = +5, TA = +25 C, using FSC synchronous clock. All loads are
5% at the IC pins. Outputs are measured at the 75 reverse terminated load.)...