AD830
Loop Thr ough or Line Br idging Am plifier (Figur e 37)
T he AD830 is ideally suited for use as a video line bridging am-
plifier. T he video signal is tapped from the conductor of the
cable relative to its shield. T he high input impedance of the
AD830 provides negligible loading on the cable. More signifi-
cantly, the benign loading is maintained while the AD830 is
powered-down. Coupled with its good video load driving per-
formance, the AD830 is well suited to video cable monitoring
applications.
inputs VX1 and VY1 together and applying the input, VIN, to this
wired connection. T he output is exactly twice the applied volt-
age, VIN; VOUT = 2 ϫ VIN. Figure 39 below shows the connec-
tions for this highly useful application. T he most notable
characteristic of this alternative gain of two is that there is no
loss of bandwidth as in a voltage feedback op amp based gain of
+2 where the bandwidth is halved, therefore, the gain band-
width is doubled. Also, this circuit is accurate without the need
for any precise valued resistors, as in the op amp equivalents,
and it possess excellent differential gain and phase performance
as shown in Figures 40 and 41.
V
P
V
P
0.1µF
AD830
1
8
7
6
5
0.1µF
AD830
G
G
M
1
8
7
6
5
G
G
V
M
75Ω
OUT
V
R
2
3
4
IN
G
V
75Ω
OUT
A=1
2
3
4
A=1
249Ω
75Ω
M
75Ω
C
0.1µF
M
C
0.1µF
499Ω
499Ω
V
N
V
N
OPTIONAL C
C
Figure 39. Full Bandwidth Line Driver (G = +2)
.10
.20
Figure 37. Cable Tap Am plifier
Resistor less Sum m ing
GAIN = +2
= 150Ω
.09
.08
.07
.06
.05
.04
.03
.02
.01
.18
.16
.14
.12
.10
.08
.06
.04
.02
R
L
FREQ = 3.58MHz
0 TO 0.7V
Direct, two input, resistorless summing is easily realized from
the general unity gain mode. By grounding VX2 and applying the
two inputs to VX1 and VY1, the output is the exact sum of the
applied voltages V1 and V3, relative to common; VOUT = V1 +
V3. A diagram of this simple, but potent application is shown
below in Figure 38. T he AD830 summing circuit possesses sev-
eral virtues not present in the classic op amp based summing
circuits. It has high impedance inputs, no resistors, very precise
summing, high reverse isolation and noninverting gain. Achiev-
ing this function and performance with op amps requires signifi-
cantly more components.
PHASE
GAIN
5
6
7
8
9
10
11
12
13
14
15
SUPPLY VOLTAGE – ±Volts
V
P
AD830
Figure 40. Differential Gain and Phase for the Circuit of
Figure 39
1
8
G
G
M
V
1
OUT
0.2
0.1
2
3
4
7
6
5
A=1
V
= ±15V
S
0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
–0.7
–0.8
M
C
V
3
R
= 150Ω
L
GAIN = +2
V
N
V
= V + V
1 3
OUT
V
= ±10V
S
Figure 38. Resistorless Sum m ing Am plifier
2؋
Gain Bandwidth Line D r iver
A gain of two, without the use of resistors, is possible with the
AD830. T his is accomplished by grounding VX2, tying the two
V
= ±5V
S
10k
100k
1M
10M
100M
FREQUENCY – Hz
Figure 41. 0.1 dB Gain Flatness for the Circuit of Figure 39
–14–
REV. A
ADI [ ADI ]
