AD811SQ/883B AD [Analog Devices], AD811SQ/883B Datasheet - Page 11

• Manufacturer Part Number: AD811SQ/883B
• Description: High Performance Video Op Amp
• Manufacturer: AD [Analog Devices]

REV. D
Operation as a Video Line Driver
The AD811 has been designed to offer outstanding perfor-
mance at closed-loop gains of one or greater, while driving
multiple reverse-terminated video loads. The lowest differential
gain and phase errors will be obtained when using 15 volt
power supplies. With 12 volt supplies, there will be an insig-
nificant increase in these errors and a slight improvement in
gain flatness. Due to power dissipation considerations, 12 volt
supplies are recommended for optimum video performance.
Excellent performance can be achieved at much lower supplies
as well.
The closed-loop gain vs. frequency at different supply voltages
is shown in Figure 36. Figure 37 is an oscilloscope photograph
of an AD811 line driver’s pulse response with 15 volt supplies.
The differential gain and phase error vs. supply are plotted in
Figures 38 and 39, respectively.
Another important consideration when driving multiple cables
is the high frequency isolation between the outputs of the
cables. Due to its low output impedance, the AD811 achieves
better than 40 dB of output to output isolation at 5 MHz driv-
ing back terminated 75
V
IN
Figure 35. A Video Line Driver Operating at a Gain of +2
Figure 36. Closed-Loop Gain vs. Frequency, Gain = +2
75
CABLE
12
–3
–6
649
9
6
3
0
75
1
G = +2
R
R
L
G
0.1 F
= 150
= R
FB
AD811
–V
+V
649
S
S
cables.
FREQUENCY – MHz
10
0.1 F
V
R
75
75
S
FB
=
= 562
75
75
V
R
5V
S
FB
=
CABLE
= 649
CABLE
15V
100
75
75
V
V
OUT
OUT
#1
#2
–11–
Figure 38. Differential Gain Error vs. Supply Voltage for
the Video Line Driver of Figure 35
Figure 39. Differential Phase Error vs. Supply Voltage for
the Video Line Driver of Figure 35
Figure 37. Small Signal Pulse Response, Gain = +2,
V
S
V
V
OUT
0.20
0.08
0.06
0.04
0.02
IN
= 15 V
0.18
0.16
0.14
0.12
0.10
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
100
90
10
0%
5
5
a
6
6
b
a
b.
a.
1V
1V
7
7
DRIVING A SINGLE, BACK TERMINATED,
75
DRIVING TWO PARALLEL,
BACK TERMINATED, COAX CABLES
SUPPLY VOLTAGE –
COAX CABLE
a.
b.
SUPPLY VOLTAGE –
8
8
DRIVING A SINGLE, BACK TERMINATED,
75
DRIVING TWO PARALLEL,
BACK TERMINATED, COAX CABLES
COAX CABLE
9
9
10
10
11
11
b
Volts
Volts
R
F
100 IRE
MODULATED
RAMP
C
F
= 649
= 3.58MHz
12
12
10ns
R
F
100 IRE
MODULATED
RAMP
C
F
13
13
= 649
= 3.58MHz
AD811
14
14
15
15