AD815 Просмотр технического описания (PDF) - Analog Devices

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AD815

High Output Current Differential Driver

Analog Devices 

AD815

~20pF

+15V

RF

499⍀

RI

499⍀

VCC

0.1␮F 10␮F

(OPTIONAL)

VIN

4

8

1/2

50⍀

AMP1 AD815 6

5

250

(50⍀)

(OPTIONAL)

RA

499⍀

RA

499⍀

RB

499⍀

RB

499⍀

100⍀

10

1/2

50⍀

AMP2 AD815 9

11

7 VCC

–15V

0.1␮F 10␮F

Figure 53. Single-Ended-to-Differential Driver

If a resistor (RF) 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 (RI) 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 ± RF/

RI. Or the single-ended-to-differential gain will be 2 × RF/RI.

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.

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°.

+15V

499⍀

0.1␮F

10␮F

12 ؋ 75⍀

499⍀

5

100⍀

4

8

6

VIDEO IN

75⍀

AD815

100⍀

11

10

9

7

12 ؋

VIDEO OUT

TO 75⍀

CABLES

499⍀

499⍀

0.1␮F

–15V

10␮F

Figure 54. AD815 Video Distribution Amp Driving

12 Video Cables

C1

B2

+15V

TP4 TP3

B1

B3

–15V

TP2 C2

R3

+15V

0.1␮F

J1

R1

C3

4

8 10␮F

R5

R19

1/2

AD815

6

R7

5

U1

R2

R6

R17

R4

1

2

J2

3

C13 R16

R15

TP1 C10

–15V

0.1␮F

C6

R8

1

2

J7

3

C9

R14

J3

R10

11

C11

7 10␮F

R13

R9

R21

R12

1/2

AD815

9

10

U1

R11

R18

J5

T1

2

4

1

7

5

R22

10

6

9 11 8

12

JP1

1

R20

2

J4

3

J6

Figure 55. AD815 Evaluation Board Schematic

–14–

REV. B

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