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AD827SCHIPS

High Speed, Low Power Dual Op Amp

Analog Devices 

AD827

VIDEO LINE DRIVER

The AD827 functions very well as a low cost, high speed line

driver for either terminated or unterminated cables. Figure 23

shows the AD827 driving a doubly terminated cable in a

follower configuration.

+VS

0.1 µF

VIN

1/2

50Ω

AD827

RBT

50Ω

RT

50Ω

VOUT

0.1 µF

500Ω

–VS

CC

500Ω

Figure 23. A Video Line Driver

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

characteristic impedance) minimizes reflections from the far end

of the cable. While operating from ± 5 V supplies, the AD827

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

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

Table I. Video Line Driver Performance Summary

VIN*

VSUPPLY

0 dB or ± 500 mV Step ± 15

0 dB or ± 500 mV Step ± 15

0 dB or ± 500 mV Step ± 15

0 dB or ± 500 mV Step ± 5

0 dB or ± 500 mV Step ± 5

0 dB or ± 500 mV Step ± 5

CC

20 pF

15 pF

0 pF

20 pF

15 pF

0 pF

–3 dB BW

23 MHz

21 MHz

13 MHz

18 MHz

16 MHz

11 MHz

Over-

shoot

4%

0%

0%

2%

0%

0%

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

are the percent overshoot of the 1 V step input.

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

impedance of the cable) may be placed between the AD827

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

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

A HIGH SPEED THREE OP AMP INSTRUMENTATION

AMPLIFIER CIRCUIT

The instrumentation amplifier circuit shown in Figure 24 can

provide a range of gains. Table II details performance.

+VS

0.1µF

–VIN

3 + 1/2 8 1

2 AD827

–

1kΩ

TRIM FOR

RG

OPTIMUM

BANDWIDTH

7 – 15 pF

6 – 1kΩ

1/2

7

+VIN

5

AD827

+

4 0.1µF

TRIM FOR BEST

SETTLING TIME

2 – 8pF

2kΩ

2kΩ

3pF

2kΩ

+VS

0.1µF

27

–

6

AD847

3+

4 0.1µF

2kΩ

VOUT

2kΩ

RL

–VS

CIRCUIT GAIN = 2000 + 1

RG

–VS

NOTE: PINOUT SHOWN IS FOR MINIDIP PACKAGE

Figure 24. A High Bandwidth Three Op Amp

Instrumentation Amplifier

Table II. Performance Specifications for the

Three Op Amp Instrumentation Amplifier

Gain

1

2

10

100

RG

Open

2k

226 Ω

20 Ω

Small Signal

Bandwidth

@ 1 V p-p Output

16.1 MHz

14.7 MHz

4.9 MHz

660 kHz

REV. C

–7–

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