Datasheet
AD8014
–9–
DRIVING CAPACITIVE LOADS
The AD8014 was designed primarily to drive nonreactive loads.
If driving loads with a capacitive component is desired, best
settling response is obtained by the addition of a small series
resistance as shown in Figure 26. The accompanying graph
shows the optimum value for R
SERIES
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 R
SERIES
and C
L
.
40
30
20
010152025
C
L
– pF
10
R
SERIES
– V
5
Figure 26. Driving Capacitive Load
Choosing Feedback Resistors
Changing the feedback resistor can change the performance of
the AD8014 like any current feedback op amp. The table below
illustrates common values of the feedback resistor and the per-
formance which results.
Table II.
–3 dB BW –3 dB BW
V
O
= ⴞ0.2 V V
O
= ⴞ0.2 V
Gain R
F
R
G
R
L
= 1 k⍀ R
L
= 150 ⍀
+1 1 kΩ Open 480 430
+2 1 kΩ 1 kΩ 280 260
+10 1 kΩ 111 Ω 50 45
–1 1 kΩ 1 kΩ 160 150
–2 1 kΩ 499 Ω 140 130
–10 1 kΩ 100 Ω 45 40
+2 2 kΩ 2 kΩ 200* 180*
+2 750 Ω 750 Ω 260* 210*
+2 499 Ω 499 Ω 280* 230*
*V
O
= ± 1 V.
Video Drivers
The AD8014 easily drives series terminated cables with video
signals. Because the AD8014 has such good output drive you
can parallel two or three cables driven from the same AD8014.
Figure 23 shows the differential gain and phase driving one
video cable. Figure 24 shows the differential gain and phase
driving two video cables. Figure 25 shows the differential gain
and phase driving three video cables.
0.10
0.05
0.00
–0.05
–0.10
0.60
0.40
0.20
–0.20
–0.40
0.00
–0.60
0.00 0.02 0.04 0.05 0.05 0.05 0.04 0.04 0.04 0.04 0.03
0.00 0.01 0.10 0.21 0.26 0.28 0.29 0.30 0.30 0.30 0.30
1ST 2ND 3RD 4TH 5TH 6TH 7TH 8TH 9TH 10TH 11TH
DIFFERENTIAL
PHASE – Degrees
DIFFERENTIAL GAIN – %
Figure 23. Differential Gain and Phase R
F
= 500,
±
5 V, R
L
=
150
Ω
, Driving One Cable, G = +2
0.30
0.20
0.10
–0.10
–0.20
0.60
0.40
0.20
–0.20
–0.40
0.00
–0.60
0.00 –0.02 0.03 0.05 0.06 0.06 0.05 0.05 0.07 0.10 0.14
0.00 0.07 0.24 0.40 0.43 0.44 0.43 0.40 0.35 0.26 0.16
1ST 2ND 3RD 4TH 5TH 6TH 7TH 8TH 9TH 10TH 11TH
0.00
–0.30
DIFFERENTIAL
PHASE – Degrees
DIFFERENTIAL GAIN – %
Figure 24. Differential Gain and Phase R
F
= 500,
±
5 V, R
L
=
75
Ω
, Driving Two Cables, G = +2
0.60
0.40
0.20
–0.40
–0.60
0.00
–0.80
0.00 0.44 0.52 0.54 0.52 0.52 0.50 0.48 0.47 0.44 0.45
0.00 0.10 0.32 0.53 0.57 0.59 0.58 0.56 0.54 0.51 0.48
1ST 2ND 3RD 4TH 5TH 6TH 7TH 8TH 9TH 10TH 11TH
–0.20
0.80
0.60
0.40
0.20
–0.40
–0.60
0.00
–0.80
–0.20
0.80
DIFFERENTIAL
PHASE – Degrees
DIFFERENTIAL GAIN – %
Figure 25. Differential Gain and Phase R
F
= 500,
±
5 V, R
L
=
50
Ω
, Driving Three Cables, G = +2
Rev. C