5962-8964701PA データシートの表示（PDF） - Analog Devices

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5962-8964701PA

High Speed, Low Power Monolithic Op Amp

Analog Devices 

AD847

VIDEO LINE DRIVER

The AD847 functions very well as a low cost, high speed line

driver for either terminated or unterminated cables. Figure 23

shows the AD847 driving a doubly terminated cable in a fol-

lower configuration.

The termination resistor, RT, (when equal to the cable’s charac-

teristic impedance) minimizes reflections from the far end of the

cable. While operating from ± 5 V supplies, the AD847 main-

tains a typical slew rate of 200 V/µs, which means it can drive a

± 1 V, 30 MHz signal into a terminated cable.

+VS

75Ω

COAX

VIN

R IN

100Ω

75Ω

AD847

–VS

0.1 µF

75Ω

COAX

R BT

75Ω

0.1 µF

500Ω

VOUT

RT

75Ω

CC

SEE TABLE I

500Ω

Figure 23. Video Line Driver

Table I. Video Line Driver Performance Chart

VIN*

0 dB or ± 500 mV Step

0 dB or ± 500 mV Step

0 dB or ± 500 mV Step

0 dB or ± 500 mV Step

0 dB or ± 500 mV Step

0 dB or ± 500 mV Step

VSUPPLY

± 15

± 15

± 15

±5

±5

±5

Over-

CC –3 dB BW shoot

20 pF 23 MHz 4%

15 pF 21 MHz 0%

0 pF 13 MHz 0%

20 pF 18 MHz 2%

15 pF 16 MHz 0%

0 pF 11 MHz 0%

*–3 dB bandwidth numbers are for the 0 dBm signal input. Overshoot numbers

are the percent overshoot of the 1 volt step input.

A back-termination resistor (RBT, also equal to the characteristic

impedance of the cable) may be placed between the AD847 out-

put and the cable input, in order to damp any reflected signals

caused by a mismatch between RT and the cable’s characteristic

impedance. This will result in a flatter frequency response, al-

though this requires that the op amp supply ± 2 V to the output

in order to achieve a ± 1 V swing at resistor RT.

Figure 24 shows the AD847 driving 100 pF and 1000 pF loads.

Figure 24. AD847 Driving Capacitive Loads

FLASH ADC INPUT BUFFER

The 35 MHz unity gain bandwidth of the AD847 makes it an

excellent choice for buffering the input of high speed flash A/D

converters, such as the AD9048.

Figure 25 shows the AD847 as a unity inverter for the input to

the AD9048.

ANALOG

INPUT

(0V TO +2V)

TTL

CONVERT

SIGNAL

0.1

AD589

10kΩ

–5.2V

2k

0.1

1k

1.5kΩ

1.5kΩ

50Ω

AD847

100

AD741

1k

27

2N3906

5

0.1µF

43Ω

RB

VIN

RT

D1

(MSB)

0.1µF

AD9048

CONVERT

D8

(LSB)

VEE VCC

0.1µF

–5.2V +5.0V

Figure 25. Flash ADC Input Buffer

–10–

REV. F

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