AD847

REV. F

–10–

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.

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.

0.1

µF

0.1

µF

500

Ω

500

Ω

75

Ω

AD847

75

Ω

75

Ω

C

C

SEE TABLE I

V

IN

–V

S

IN

R

100

Ω

75

Ω

COAX

75

Ω

COAX

Figure 23. Video Line Driver

Table I. Video Line Driver Performance Chart

Over-

0 dB or

±500 mV Step

±15

20 pF

23 MHz

4%

0 dB or

±500 mV Step

±15

15 pF

21 MHz

0%

0 dB or

±500 mV Step

±15

0 pF

13 MHz

0%

0 dB or

±500 mV Step

±5

20 pF

18 MHz

2%

0 dB or

±500 mV Step

±5

15 pF

16 MHz

0%

0 dB or

±500 mV Step

±5

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.

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

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

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 R

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.

AD9048

50

Ω

1.5k

Ω

10k

Ω

2k

0.1

0.1

100

27

2N3906

AD741

5

0.1

µF

AD847

1.5k

Ω

V

EE

ANALOG

INPUT

(0V TO +2V)

TTL

CONVERT

SIGNAL

0.1

µF

0.1

µF

–5.2V +5.0V

CONVERT

D1

(MSB)

D8

(LSB)

–5.2V

43

Ω

1k

1k

AD589

Figure 25. Flash ADC Input Buffer