AD8079 datasheet(8/12 Pages) AD

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AD8079

REV. A

–8–

VOUT #1

Ω

CABLE

Ω

VOUT #2

Ω

CABLE

Ω

CABLE

VIN

+VS

–VS

VOUT #3

Ω

CABLE

Ω

VOUT #4

Ω

CABLE

Ω

1/2

AD8079

1/2

AD8079

4.7µF

0.1µF

Figure 26. Video Line Driver

Single-Ended to Differential Driver Using an AD8079

The two halves of an AD8079 can be configured to create a

single-ended to differential high speed driver with a –3 dB band-

width in excess of 110 MHz as shown in Figure 27. Although

the individual op amps are each current feedback with internal

feedback resistors, the overall architecture yields a circuit with

attributes normally associated with voltage feedback amplifiers,

while offering the speed advantages inherent in current feedback

amplifiers. In addition, the gain of the circuit can be changed by

varying a single resistor, RF, which is often not possible in a dual

op amp differential driver.

Ω

OUTPUT #1

Ω

OUTPUT #2

750

Ω

RF 750Ω

1/2

AD8079

1/2

AD8079

OP AMP #1

OP AMP #2

VIN

CC = 1.5pF

Figure 27. Differential Line Driver

VOUT

( INTERNAL)

I BI

I BN

( INTERNAL)

RSERIES

Figure 24. Output Offset Voltage

Driving Capacitive Loads

The AD8079 was designed primarily to drive nonreactive loads.

If driving loads with a capacitive component is desired, best

frequency response is obtained by the addition of a small series

output resistance (RSERIES). The graph in Figure 25 shows the

optimum value for RSERIES vs. capacitive load. It is worth noting

that the frequency response of the circuit when driving large

capacitive loads will be dominated by the passive roll-off of

RSERIES and CL.

CL – pF

025

Figure 25. Recommended RSERIES vs. Capacitive Load

Operation as a Video Line Driver

The AD8079 has been designed to offer outstanding perfor-

mance as a video line driver. The important specifications of

differential gain (0.01%) and differential phase (0.02

°) meet the

most exacting HDTV demands for driving one video load with

each amplifier. The AD8079 also drives four back terminated

loads (two each), as shown in Figure 26, with equally impressive

performance (0.01%, 0.07

°). Another important consideration is

isolation between loads in a multiple load application. The

AD8079 has more than 40 dB of isolation at 5 MHz when driv-

ing two 75

Ω back terminated loads.

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