adv101 Analog Devices, Inc., adv101 Datasheet - Page 9

• Manufacturer Part Number: adv101
• Description: Cmos 80 Mhz, Triple 8-bit Video Dac
• Manufacturer: Analog Devices, Inc.

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 termi-
nated 75
with 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
resistors. (See Figure 6.)
R0
R7
G0
G7
B0
B7
ADV101
GND
TERMINATION)
IOG
IOR
IOB
IOR, IOG, IOB
DACs
(SOURCE
Z = 75
S
Z
2
37.5
37.5
Figure 7. AD848 As an Output Buffer
2
3
AD848
+
–
DOUBLY
TERMINATED
75 LOAD
V
7
4
V
S
S
Z
1
0.1 F
6
0.1 F
75
–9–
GAIN (G) = 1 +
Video Output Buffers
The ADV101 is specified to drive transmission line loads, which
is what most monitors are rated as. The analog output configu-
rations to drive such loads are described in the Analog Interface
section and illustrated in Figure 5. However, in some applica-
tions it may be required to drive long “transmission line” cable
lengths. Cable lengths greater than 10 meters can attenuate and
distort high frequency analog output pulses. The inclusion of
output buffers will compensate for some cable distortion. Buff-
ers with large full power bandwidths and gains between 2 and 4
will be required. These buffers will also need to be able to sup-
ply sufficient current 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 recommended. More information on line driver buff-
ering 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 = 75
(CABLE)
O
Z
Z
1
2
Z = 75
(MONITOR)
L
ADV101