ADV7120KN50 AD [Analog Devices], ADV7120KN50 Datasheet - Page 9

• Manufacturer Part Number: ADV7120KN50
• Description: CMOS 80 MHz, Triple 8-Bit Video DAC
• Manufacturer: AD [Analog Devices]

REV. B
The unused analog outputs should be terminated with the same
load as that for the used channel. In other words, if the red
channel is used and IOR is terminated with a doubly terminated
75
37.5
Figure 6. Input and Output Connections for Stand-Alone
Gray Scale or Composite Video
VIDEO
INPUT
load (37.5 ), IOB and IOG should be terminated with
resistors. (See Figure 6.)
R0
R7
G0
G7
B0
B7
ADV7120
DACs
IOR, IOG, IOB
TERMINATION)
(SOURCE
GND
Z
IOR
IOG
IOB
S
Z
2
= 75
2
3
37.5
37.5
Figure 7. AD848 As an Output Buffer
AD848
–V
+V
7
4
Z
S
S
1
DOUBLY
TERMINATED
75 LOAD
0.1 F
0.1 F
6
75
–9–
GAIN (G) = 1 +
Video Output Buffers
The ADV7120 is specified to drive transmission line loads,
which is what most monitors are rated as. The analog output
configurations to drive such loads are described in the Analog
Interface section and illustrated in Figure 5. However, in some
applications it may be required to drive long “transmission line”
cable lengths. Cable lengths greater than 10 meters can attenu-
ate and distort high frequency analog output pulses. The inclu-
sion of output buffers will compensate for some cable distortion.
Buffers with large full power bandwidths and gains between 2
and 4 will be required.
These buffers will also need to be able to supply sufficient cur-
rent over the complete output voltage swing. Analog Devices
produces a range of suitable op amps for such applications.
These include the AD84X series of monolithic op amps. In very
high frequency applications (80 MHz), the AD9617 is recom-
mended. More information on line driver buffering circuits is
given in the relevant op amp data sheets.
Use of buffer amplifiers also allows implementation of other
video standards besides RS-343A and RS-170. Altering the gain
components of the buffer circuit will result in any desired
video level.
Z
Z
Z
1
2
(CABLE)
O
= 75
Z
(MONITOR)
L
= 75
ADV7120