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.

Figure 23. A Video Line Driver

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

Over-

shoot

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%

NOTE

*–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 AD827

output and the cable input, in order to damp any reflected

characteristic impedance. This will result in a flatter frequency

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

A HIGH SPEED 3 OP AMP INSTRUMENTATION

AMPLIFIER CIRCUIT

The instrumentation amplifier circuit shown in Figure 24 can

provide a range of gains. The chart of Table II details

performance.

–

+

+

–

+

–

1

3

2

2

3

6

7

6

5

AD847

AD827

AD827

0.1µF

1k

Ω

2k

Ω

2k

Ω

1k

Ω

2k

Ω

0.1µF

0.1µF

2k

Ω

2 – 8pF

0.1µF

R

G

4

7

2k

Ω

8

4

TRIM FOR BEST

SETTLING TIME

1/2

1/2

3pF

CIRCUIT GAIN =

+ 1

G

R

2000

TRIM FOR

OPTIMUM

BANDWIDTH

7 – 15 pF

NOTE: PINOUT SHOWN IS FOR MINIDIP PACKAGE

–V

IN

–V

S

V

OUT

Figure 24. A High Bandwidth Three Op Amp

Instrumentation Amplifier

Table II. Performance Specifications for the

Three Op Amp Instrumentation Amplifier

Small Signal

Bandwidth

Gain

@ 1 V p-p Output

1

Open

16.1 MHz

2

2 k

14.7 MHz

10

226

Ω

4.9 MHz

100

20

Ω

660 kHz

A TWO-CHIP VOLTAGE-CONTROLLED AMPLIFIER

(VCA) WITH EXPONENTIAL RESPONSE

Voltage-controlled amplifiers are often used as building blocks

in automatic gain control systems. Figure 25 shows a two-chip

VCA built using the AD827 and the AD539, a dual, current-

output multiplier. As configured, the circuit has its two

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

CONTROL

W1

Z1

CH1

OUT

BASE

COM

CH2

OUT

Z2

W2

HF COMP

CH 1

IN

CH2

IN

INPUT

COM

OUTPUT

COM

AD539

0.01µF

+

–

AD827

5

6

2

3

+

–

AD827

1/2

0.1µF

0.1µF

4.7

Ω

4.7

Ω

+5V

–5V

1/2

+5V

0.1µF

8

1

–5V

0.1µF

2pF

2pF

4

7

50

Ω

50

Ω

COAX LINE

OUTPUT

INPUT RANGE:

10MV TO 3V (55dB)

*PINOUT SHOWN IS FOR MINI-DIP PACKAGE

*

*

V

IN

–V

S

V

AT TERMINATION RESISTOR, R =

T

OUT

V

AT PIN & OF AD827 =

OUT

V

X

2

IN

V

V

X

2

IN

V

Figure 25. A Wide Range Voltage-Controlled

Amplifier Circuit