AD720 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD720 Datasheet PDF : 8 Pages
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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 Ω 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 Ω 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
75Ω 75Ω
7 AGND
8 GRIN
75Ω 75Ω
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
75Ω 75Ω
11 STND
4FSC 20
DGND 19
AGND
VNEG
12 13 14 15 16 17 18
+5V FROM
ANALOG SUPPLY
0.1µF
75Ω
75Ω
75Ω
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
75Ω
75Ω
+5V FROM
ANALOG SUPPLY
75Ω
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
75Ω 75Ω
7 AGND
8 GRIN
75Ω 75Ω
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
75Ω 75Ω
11 STND
4FSC 20
DGND 19
AGND
VNEG
12 13 14 15 16 17 18
+5V FROM
ANALOG SUPPLY
0.1µF
75Ω
75Ω
75Ω
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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