AD8002ARM datasheet(11/20 Pages) AD

11 / 20 page

REV. D

AD8002

–11–

Driving Capacitive Loads

The AD8002 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

resistance as shown in Figure 6.

909

RSERIES

500

Figure 6. Driving Capacitive Loads

Figure 7 shows the optimum value for RSERIES versus 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

Figure 7. Recommended RSERIES vs. Capacitive Load

Communications

Distortion is a key specification in communications applications.

Intermodulation distortion (IMD) is a measure of the ability of

an amplifier to pass complex signals without the generation of

spurious harmonics. The third order products are usually the

most problematic since several of them fall near the fundamen-

tals and do not lend themselves to filtering. Theory predicts that

the third order harmonic distortion components increase in

power at three times the rate of the fundamental tones. The

specification of third order intercept as the virtual point where

fundamental and harmonic power are equal is one standard mea-

sure of distortion performance. Op amps used in closed-loop

applications do not always obey this simple theory. At a gain of

two, the AD8002 has performance summarized in Figure 8. Here

the worst third order products are plotted versus. input power.

The third order intercept of the AD8002 is 33 dBm at 10 MHz.

–80

–7

–75

–4

–56

–2

–70

–65

–60

–55

–50

–45

–1

INPUT POWER – dBm

–6

–84

–3

2F2 – F1

2F1 – F2

G = +2

F1 = 10MHz

F2 = 12MHz

Figure 8. Third Order IMD; F1 = 10 MHz, F2 = 12 MHz

Operation as a Video Line Driver

The AD8002 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 AD8002 also drives four back-terminated

loads (two each), as shown in Figure 9, with equally impressive

performance (0.01%, 0.07

°). Another important consideration

is isolation between loads in a multiple load application. The

AD8002 has more than 40 dB of isolation at 5 MHz when driv-

ing two 75

Ω back-terminated loads.

750

CABLE

VOUT #1

VOUT #2

+VS

–VS

VIN

0.1 F

4.7 F

1/2

AD8002

0.1 F

4.7 F

CABLE

VOUT #3

VOUT #4

CABLE

1/2

AD8002

750

CABLE

Figure 9. Video Line Driver

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