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AD724 Datasheet(PDF) 10 Page - Analog Devices

Part No. AD724
Description  RGB to NTSC/PAL Encoder
Download  15 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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REV. B
–10–
AD724
220 F
75
75
75
–5V
FIN
OSC
0.1 F
+5V
**
CRYSTAL
0.1 F
+5V (VAA)
*
AGND
DGND
AD724
ENCD
RIN
GIN
BIN
HSYNC
VSYNC
SELECT
STND
CRMA
LUMA
CMPS
APOS
DPOS
10–30pF
0.1 F
10 F
0.1 F
10 F
75
75
JMP
* PARALLEL–RESONANT
CRYSTAL; 3.579545MHz (NTSC)
OR 4.433620MHz (PAL)
CAPACITOR VALUE DEPENDS ON
CRYSTAL CHOSEN
75
COMPOSITE
VIDEO
75
220 F
75
220 F
Y
C
S-VIDEO
(Y/C VIDEO)
75
75
75
B
G
R
RGB MONITOR
VSYNC
HSYNC
FROM VGA PORT
+5V
+5V
10k
+5V
10k
SELECT
75
JMP
+5V
VGA OUTPUT
CONNECTOR
***
*** 0.1 F CAPACITORS RECOMMENDED
649
649
649
649
649
649
**FSC OR 4FSC CLOCK; 3.579545MHz,
14.31818MHz (NTSC) OR 4.433620MHz,
17.734480MHz(PAL)
1/3
AD8013
1/3
AD8013
1/3
AD8013
0.1 F
0.1 F
0.1 F
Figure 15. Interfacing the AD724 to the (Interlaced) VGA Port of a PC
transmitted. Each output requires a 220
µF series capacitor to
work with the 75
Ω resistance to pass these low frequencies. The
CRMA signal has information mostly up at the chroma fre-
quency and can use a smaller capacitor if desired, but 220
µF
can be used to minimize the number of different components
used in the design.
Displaying VGA Output on a TV
The AD724 can be used to convert the analog RGB output from a
personal computer’s VGA card to the NTSC or PAL television
standards. To accomplish this it is important to understand that
the AD724 requires interlaced RGB video and clock rates that
are consistent with those required by the television standards. In
most computers the default output is a noninterlaced RGB
signal at a frame rate higher than used by either NTSC or PAL.
Most VGA controllers support a wide variety of output modes
that are controlled by altering the contents of internal registers.
It is best to consult with the VGA controller manufacturer to
determine the exact configuration required to provide an inter-
laced output at 60 Hz (50 Hz for PAL).
Both the analog and digital ground pins should be tied to the
ground plane by a short, low inductance path. Each power
supply pin should be bypassed to ground by a low inductance
0.1
µF capacitor and a larger tantalum capacitor of about 10 µF.
The three analog inputs (RIN, GIN, BIN) should be terminated
with 75
Ω to ground close to the respective pins. However, as
these are high impedance inputs, they can be in a loop-through
configuration. This technique is used to drive two or more
devices with high frequency signals that are separated by some
distance. A connection is made to the AD724 with no local
termination, and the signals are run to another distant device
where the termination for these signals is provided.
The output amplitudes of the AD724 are double that required
by the devices that it drives. This compensates for the halving of
the signal levels by the required terminations. A 75
Ω series
resistor is required close to each AD724 output, while 75
Ω to
ground should terminate the far end of each line.
The outputs have a dc bias and must be ac coupled for proper
operation. The COMP and LUMA outputs have information
down to 30 Hz for NTSC (25 MHz for PAL) that must be




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