REV. C

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 42. The accompanying graph

909

500

Figure 42. Driving Capacitive Loads

worth noting that the frequency response of the circuit when

driving large capacitive loads will be dominated by the passive

40

0

025

30

10

5

20

15

20

10

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

measure 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 Fig-

ure 44. Here the worst third order products are plotted vs. input

power. The third order intercept of the AD8002 is +33 dBm at

10 MHz.

–80

3

–7

–75

2

1

0

–4

–5

6

–2

–70

–65

–60

–55

–50

–45

–1

INPUT POWER – dBm

–6

–8

4

5

–3

G = +2

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 45, 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

750

75

CABLE

75

75

0.1 F

4.7 F

1/2

AD8002

0.1 F

4.7 F

75

CABLE

75

75

75

CABLE

75

75

75

CABLE

75

75

1/2

AD8002

750

750

75

CABLE

75

+

Figure 45. Video Line Driver