Datasheet

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⍀
R
SERIES
R
L
500⍀
I
N
C
L
Figure 6. Driving Capacitive Loads
Figure 7 shows the optimum value for R
SERIES
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 R
SERIES
and C
L
.
40
0
0
25
30
10
5
20
15 2010
R
SERIES
– V
C
L
– pF
Figure 7. Recommended R
SERIES
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
3–7
–75
210–4–56–2
–70
–65
–60
–55
–50
–45
–1
THIRD ORDER IMD – dBc
INPUT POWER – dBm
–6–845–3
2F
2
– F
1
2F
1
– F
2
G = +2
F
1
= 10MHz
F
2
= 12MHz
Figure 8. Third Order IMD; F
1
= 10 MHz, F
2
= 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⍀
750⍀
75⍀
CABLE
75⍀
75⍀
V
OUT
#1
V
OUT
#2
+V
S
–V
S
V
IN
0.1␮F
4.7␮F
1/2
AD8002
0.1␮F
4.7␮F
75⍀
CABLE
75⍀
75⍀
75⍀
CABLE
75⍀
75⍀
V
OUT
#3
V
OUT
#4
75⍀
CABLE
75⍀
75⍀
1/2
AD8002
750⍀
750⍀
75⍀
CABLE
75⍀
+
Figure 9. Video Line Driver