AD815
REV. B
–14–
6
4
5
8
10
7
–15V
R
A
499
V
9
11
0.1
m
F
10
m
F
0.1
m
F
10
m
F
AMP1
AMP2
V
IN
+15V
V
CC
R
F
499
V
~
20pF
R
B
499
V
R
A
499
V
R
B
499
V
V
CC
250
(50
V
)
(OPTIONAL)
R
I
499
V
50
V
50
V
(OPTIONAL)
100
V
1/2
AD815
1/2
AD815
Figure 53. Single-Ended-to-Differential Driver
If a resistor (R
F
) is connected from the output of Amp 2 to the
+ input of Amp 1, negative feedback is provided which closes
the loop. An input resistor (R
I
) will make the circuit look like a
conventional inverting op amp configuration with differential
outputs. The inverting input to this dual output op amp becomes
Pin 4, the positive input of Amp 1.
The gain of this circuit from input to either output will be
±
R
F
/
R
I
. Or the single-ended-to-differential gain will be 2
×
R
F
/R
I.
The differential outputs can be applied to the primary of a
transformer. If each output can swing
±
10 V, the effective swing
on the transformer primary is 40 V p-p. The optional capacitor
can be added to prevent any dc current in the transformer due
to dc offsets at the output of the AD815.
Figure 55. AD815 Evaluation Board Schematic
Figure 54. AD815 Video Distribution Amp Driving
12 Video Cables
Twelve Channel Video Distribution Amplifier
The high current of the AD815 enables it to drive up to twelve
standard 75
reverse terminated video loads. Figure 54 is a
schematic of such an application.
The input video signal is terminated in 75
and applied to the
noninverting inputs of both amplifiers of the AD815. Each
amplifier is configured for a gain of two to compensate for the
divide-by-two feature of each cable termination. Six separate
75
resistors for each amplifier output are used for the cable
back termination. In this manner, all cables are relatively
independent of each other and small disturbances on any cable
will not have an effect on the other cables.
When driving six video cables in this fashion, the load seen by
each amplifier output is resistive and is equal to 150
/6 or
25
. The differential gain is 0.05% and the differential phase
is 0.45
°
.
+15V
4
5
1/2
AD815
C2
0.1
m
F
C3
10
m
F
6
TP2
+15V
R10
R21
R18
R12
R9
J3
J6
R13
C10
0.1
m
F
C11
10
m
F
9
TP1
–15V
U1
R11
C13
R16
R15
U1
R6
R17
TP4 TP3
+15V
–15V
B2
B1
B3
C9
JP1
R20
J4
1
2
3
T1
J5
C1
R3
R7
R2
R4
J1
R5
R19
R1
R14
R8
2
1
10
9
R22
4
7
5
6
11
12
8
8
1
2
3
J2
J7
1
2
3
C6
11
10
7
1/2
AD815
6
8
7
–15V
9
11
0.1
m
F
10
m
F
10
5
4
100
V
100
V
75
V
VIDEO IN
499
V
0.1
m
F
10
m
F
499
V
499
V
499
V
12
3
75
V
12
3
VIDEO OUT
TO 75
CABLES
AD815