ADV101

–9–

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

Ω load (37.5 Ω), IOB and IOG should be terminated

with 37.5

Ω resistors. (See Figure 6.)

GND

ADV101

R0

R7

G0

G7

B0

B7

VIDEO

INPUT

DOUBLY

TERMINATED

75

Ω LOAD

IOR

IOG

IOB

37.5

Ω

37.5

Ω

Figure 6. Input and Output Connections for Stand-Alone

Gray Scale or Composite Video

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.

DACs

Z = 75

Ω

O

(CABLE)

Z = 75

Ω

S

(SOURCE

TERMINATION)

AD848

V

S

–

V

S

+

0.1

µF

0.1

µF

IOR, IOG, IOB

75

Ω

2

7

6

4

3

Z

2

Z = 75

Ω

(MONITOR)

L

GAIN (G) = 1 +

Figure 7. AD848 As an Output Buffer