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AD721 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD721
Beschreibung RGB to NTSC/PAL Encoders
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
AD721 Datasheet, Funktion
a
RGB to NTSC/PAL Encoders
AD720/AD721
FEATURES
Composite Video Output
Chrominance and Luminance (S-Video) Outputs
No External Filters or Delay Lines Required
Drives 75 Reverse-Terminated Loads
Compact 28-Pin PLCC
Logic Selectable NTSC or PAL Encoding Modes
Automatically Selects Proper Chrominance Filter
Cutoff Frequency for Encoding Standard
Logic Selectable Encode or Power-Down Mode (AD720
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 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
(subcarrier amplitude and phase) signals in accordance with
either NTSC or PAL standards. These two outputs are also
combined to provide a composite video output. All three out-
puts are available separately at voltages of twice the standard
signal levels as required for driving 75 reverse terminated
cables. The AD721 also features a bypass mode, in which the
RGB inputs may bypass the encoder section of the IC via three
gain-of-two amplifiers suitable for driving 75 reverse termi-
nated cables.
The AD720 and AD721 provide a complete, fully calibrated
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
4FSC
ENCD
RED
GREEN
BLUE
SYNC
DECODER
C-SYNC
DELAY NTSC/PAL
BURST
DELAYED C-SYNC
POWER AND GROUNDS
+5V LOGIC
+5V ANALOG
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
Y 5MHz
4-POLE LP
PRE-FILTER
RGB-TO-YUV
ENCODING
MATRIX
U
V
1.2MHz
4-POLE
LPF
1.2MHz
4-POLE
LPF
SAMPLED-
DATA
DELAY LINE
DC
RESTORE
AND C-SYNC
INSERTION
5MHz
2-POLE
LP POST-
FILTER
X2
NTSC/PAL
X2
BALANCED
MODULATORS
3.6MHz (NTSC)
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 75REVERSE-TERMINATED LINES.
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: 617/329-4700
Fax: 617/326-8703






AD721 Datasheet, Funktion
AD720/AD721
The filtered output is summed with the luminance signal to cre-
ate a composite video signal. The separate luminance, chromi-
nance, and composite video signals are amplified by gain-of-two
amplifiers for driving 75 reverse-terminated lines. The sepa-
rate luminance and chrominance outputs together are known as
“S-Video.”
The digital section of the AD720/AD721 is clocked by the
4FSC input. It measures the width of pulses in the composite
sync input to separate vertical, horizontal, and serration pulses
and to insert the subcarrier burst only after a valid horizontal
sync pulse.
+5V FROM
ANALOG SUPPLY 0.1µF
Asserting the ENCD pin to a logical low routes the AD721’s
RGB inputs through three gain-of-two bypass buffers for driving
75 reverse-terminated lines, bypassing the encoder section of
the AD721. The triple bypass amplifier is utilized to overcome
the loading effects of a “TV-out” connection on the RGB moni-
tor output. When a video encoder is connected to outputs of a
current-out video RAMDAC or VGA controller, the R, G, and
B signals to the monitor are loaded-down. This requires the use
of a gain block to properly drive the monitor.
–5V FROM
0.1µF ANALOG SUPPLY
ENCODE INPUT
ENCODE = CMOS HIGH
POWER DOWN = CMOS LOW
4 3 2 1 28 27 26
AGND
VNEG
5 ENCD
DGND 25
IOR
VIDEO
RAM-DAC
ADV47X IOG
ADV71XX
6 RDIN
7575
7 AGND
8 GRIN
7575
9 AGND
SYNC 24
AD720
RGB TO NTSC/PAL
ENCODER
DPOS 23
ASNC 22
DPOS 21
0.1µF
0.1µF
COMPOSITE SYNC INPUT
CMOS LOGIC LEVEL
NEGATIVE SYNC TIPS
+5V FROM
DIGITAL SUPPLY
+5V FROM
DIGITAL SUPPLY
IOB
VIDEO STANDARD
SELECTION INPUT
NTSC = CMOS HIGH
PAL = CMOS LOW
10 BLIN
7575
11 STND
4FSC 20
DGND 19
AGND
VNEG
12 13 14 15 16 17 18
+5V FROM
ANALOG SUPPLY
0.1µF
75
75
75
0.1µF
4 X SUBCARRIER INPUT
CMOS LOGIC LEVELS
NTCS = 14.318 180MHz
PAL = 17.734 480MHz
–5V FROM ANALOG SUPPLY
LUMINANCE OUTPUT
COMPOSITE OUTPUT
CHROMINANCE OUTPUT
Figure 9. AD720 Application
0.1µF
75
75
+5V FROM
ANALOG SUPPLY
75
0.1µF
RED OUTPUT
GREEN OUTPUT
BLUE OUTPUT
–5V FROM
ANALOG SUPPLY
4 3 2 1 28 27 26
ENCODE INPUT
ENCODE = CMOS HIGH
BYPASS = CMOS LOW
AGND
5 ENCD
VNEG
DGND 25
IOR
VIDEO
RAM-DAC
ADV47X IOG
ADV71XX
6 RDIN
7575
7 AGND
8 GRIN
7575
9 AGND
SYNC 24
AD721
RGB TO NTSC/PAL
ENCODER
DPOS 23
ASNC 22
DPOS 21
0.1µF
0.1µF
COMPOSITE SYNC INPUT
CMOS LOGIC LEVEL
NEGATIVE SYNC TIPS
+5V FROM
DIGITAL SUPPLY
+5V FROM
DIGITAL SUPPLY
IOB
VIDEO STANDARD
SELECTION INPUT
NTSC = CMOS HIGH
PAL = CMOS LOW
10 BLIN
7575
11 STND
4FSC 20
DGND 19
AGND
VNEG
12 13 14 15 16 17 18
+5V FROM
ANALOG SUPPLY
0.1µF
75
75
75
0.1µF
4 X SUBCARRIER INPUT
CMOS LOGIC LEVELS
NTCS = 14.318 180MHz
PAL = 17.734 480MHz
–5V FROM ANALOG SUPPLY
LUMINANCE OUTPUT
COMPOSITE OUTPUT
CHROMINANCE OUTPUT
Figure 10. AD721 Application
–6– REV. 0

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