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AD725 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD725
Beschreibung Low Cost RGB to NTSC/PAL Encoder with Luma Trap Port
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 20 Seiten
AD725 Datasheet, Funktion
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
APPLICATIONS
RGB/VGA to NTSC/PAL Encoding
Personal Computers/Network Computers
Video Games
Video Conference Cameras
Digital Still Cameras
PRODUCT DESCRIPTION
The AD725 is a very low cost general purpose RGB to NTSC/
PAL encoder that converts red, green and blue color compo-
nent 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 sepa-
rately at voltages of twice the standard signal levels as re-
quired for driving 75 , reverse-terminated cables.
The AD725 features a luminance trap (YTRAP) pin that pro-
vides a means of reducing cross color generated by subcarrier
frequency components found in the luminance signal. For por-
table 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 re-
quirements of 3 V CMOS systems.
The AD725 is packaged in a low cost 16-lead SOIC and oper-
ates from a +5 V supply.
FUNCTIONAL BLOCK DIAGRAM
NTSC/PAL
HSYNC
VSYNC
4FSC CLOCK
RED
XNOR
CSYNC
4FSC
SYNC
SEPARATOR
CSYNC
BURST
4FSC
QUADRATURE
+4
DECODER
FSC 90؇C
FSC 0؇C
CSYNC
DC
CLAMP
Y 3-POLE
LP PRE-
FILTER
NTSC/PAL
؎180؇C FSC 90؇C/270؇C
(PAL ONLY)
CLOCK
AT 8FSC
SAMPLED-
DATA
DELAY LINE
2-POLE
LP POST-
FILTER
X2
GREEN
BLUE
DC
CLAMP
DC
CLAMP
RGB-TO-YUV
ENCODING
MATRIX
U
4-POLE
LPF
V 4-POLE
LPF
BURST
U
CLAMP
V
CLAMP
BALANCED
MODULATORS
NTSC/PAL
4-POLE
LPF
X2
X2
LUMINANCE
OUTPUT
LUMINANCE
TRAP
COMPOSITE
OUTPUT
CHROMINANCE
OUTPUT
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






AD725 Datasheet, Funktion
AD725–Typical Characteristics
1.0
APL = 46.6%
525 LINE NTSC NO FILTERING
SLOW CLAMP TO 0.00V
@ 6.63s
0.5
100
50
0.0 0
–0.5
0
–50
10 20 30 40 50 60
s
Figure 7. Modulated Pulse and Bar, NTSC
1.0
APL = 33.5%
625 LINE PAL NO FILTERING
SLOW CLAMP TO 0.00V
@ 6.72 s
0.5
0.0
–0.5
0
10 20 30 40 50 60
s
Figure 9. Modulated Pulse and Bar, PAL
200mV
1s
Figure 8. Zoom on Modulated Pulse, NTSC
200mV
1s
Figure 10. Zoom on Modulated Pulse, PAL
–6– REV. 0

6 Page









AD725 pdf, datenblatt
AD725
Displaying VGA Output on a TV
The AD725 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 AD725 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).
Figure 19 shows a circuit for connection to the VGA port of a
PC. The RGB outputs are ac coupled to the respective inputs of
the AD725. These signals should each be terminated to ground
with 75 .
The standard 15-pin VGA connector has HSYNC on Pin 13
and VSYNC on Pin 14. These signals also connect directly to
the same name signals on the AD725. For a synchronous NTSC
system, the internal 4FSC (14.318 180 MHz) clock that drives
the VGA controller can be used for 4FSC on the AD725. This
signal is not directly accessible from outside the computer, but it
does appear on the VGA card. (A 1FSC-input encoder, the
AD724, is also available.)
If a separate RGB monitor is also to be used, it is not possible to
simply connect it to the R, G and B signals. The monitor pro-
vides a termination that would double terminate these signals.
The R, G, and B signals should be buffered by three amplifiers
with high input impedances. These should be configured for a
gain of two, which is normalized by the divide by two termina-
tion scheme used for the RGB monitor.
The AD8073 is a low cost triple video amplifier that can pro-
vide the buffering required in this application. However, since
the R, G and B signals go all the way to ground during horizon-
tal sync, the AD8073 will require a –5 V supply to handle these
signals. To be able to buffer the R, G and B signals using a
single supply, a rail-to-rail amplifier is required. In this applica-
tion, the AD8051 (single) and AD8052 (dual) can be used to
provide the three required channels. These can be operated on a
single supply of 3 V to 5 V.
VGA OUTPUT
CONNECTOR
+5V +5V
POWER DOWN
10F
0.1F
0.1F
0.1F
0.1F
7575
75
+5V
4FSC CLOCK
14.318180MHz (NTSC)
OR
0.1F
17.734475MHz (PAL)
OSC
NTSC/PAL
+5V (VAA)
0.1F
47k
1N4148
9pF 68H
18pF
4
APOS
5 CE
14
DPOS
0.1F
6 RIN
7 GIN
8 BIN
CMPS 10
AD725
75
220F
16 HSYNC
15 VSYNC
4FSC
STND
LUMA 11
CRMA 9
75
220F
75
220F
YTRAP
AGND DGND
2 13
10F
COMPOSITE
VIDEO
Y
C
S-VIDEO
(Y/C VIDEO)
1/3
AD8073
75
1k1k
1/3
AD8073
75
1k1k
1/3
AD8073
75
1k
–5V
1k
0.1F
B
75
G
75
R
75
VSYNC
FROM VGA PORT
HSYNC
RGB MONITOR
Figure 19. Interfacing the AD725 to the (Interlaced) VGA Port of a PC
–12–
REV. 0

12 Page





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