AD815

REV. B

–14–

6

4

5

8

10

7

–15V

499

9

11

0.1 F

10 F

0.1 F

10 F

AMP1

AMP2

+15V

499

499

499

499

250

(50 )

(OPTIONAL)

499

50

50

(OPTIONAL)

100

1/2

AD815

1/2

AD815

Figure 53. Single-Ended-to-Differential Driver

+ input of Amp 1, negative feedback is provided which closes

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

× R

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

Ω reverse terminated video loads. Figure 54 is a

schematic of such an application.

The input video signal is terminated in 75

Ω 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

Ω 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

Ω/6 or

25

Ω. The differential gain is 0.05% and the differential phase

is 0.45

°.

4

5

1/2

AD815

C2

0.1 F

C3

10 F

TP2

+15V

R10

R21

R18

R12

R9

J3

J6

R13

C10

0.1 F

C11

10 F

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

6

1

2

3

J2

J7

1

2

3

C6

11

10

7

9

1/2

AD815

6

+15V

8

7

–15V

9

11

0.1 F10 F

10

5

4

100

100

75

VIDEO IN

499

0.1 F

10 F

499

499

499

12

75

12

VIDEO OUT

TO 75

CABLES

AD815