AD8002

Data Sheet

Rev. E | Page 16 of 21

DRIVING ADCs

The AD8002 is well suited for driving high speed analog-to-

digital converters, such as the AD9058. The AD9058 is a dual,

8-bit, 50 MSPS ADC. In Figure 55, the AD8002 drives the

inputs of the AD9058, which are configured for 0 V to 2 V

ranges. Bipolar input signals are buffered, amplified (−2×), and

offset (by 1.0 V) into the proper input range of the ADC. Using

the internal 2 V reference of the AD9058 connected to both

ADCs (as shown in Figure 55) reduces the number of external

components required to create a complete data acquisition

system. The 20 Ω resistors in series with the ADC inputs help

the ADCs drive the 10 pF ADC input capacitance. The AD8002

adds only 100 mW to the power consumption, while not

limiting the performance of the circuit.

SINGLE-ENDED-TO-DIFFERENTIAL DRIVER USING

AN AD8002

The two halves of an AD8002 can be configured to create a

single-ended-to-differential high speed driver with a −3 dB

bandwidth in excess of 200 MHz, as shown in Figure 54.

Although the individual op amps are each current feedback op

amps, the overall architecture yields a circuit with attributes

normally associated with voltage feedback amplifiers, yet offers

the speed advantages inherent in current feedback amplifiers. In

addition, the gain of the circuit can be changed by varying a

single resistor, RF, which is often not possible in a dual op amp

differential driver.

50Ω

OUTPUT 1

50Ω

OUTPUT 2

RG

511Ω

RF 511Ω

CC = 0.5pF TO 1.5pF

1/2

AD8002

1/2

AD8002

OP AMP 1

OP AMP 2

VIN

RA

511Ω

RA

511Ω

511Ω

RB

511Ω

RB

Figure 54. Differential Line Driver

0.1µF

+VS

–VS

20Ω

50Ω

1kΩ

18

17

16

15

14

13

12

11

–VREF

10pF

CLOCK

5, 9, 22,

24, 37, 41

4,19, 21

25, 27, 42

0.1µF

38

8

–VREF

6

+VINT

2

3

+VREF

AIN

549Ω

274Ω

ANALOG

IN A

±0.5V

1.1kΩ

AD8597

43

+VREF

20kΩ

0.1µF

–2V

1.1kΩ

20kΩ

549Ω

ANALOG

IN B

±0.5V

274Ω

20Ω

0.1µF

40

COMP

1

AIN

ENCODE

ENCODE

10

36

ENCODE

74ACT04

0.1µF

+5V

28

29

30

31

32

33

34

35

RZ1

RZ2

D0 (LSB)

D7 (MSB)

D0 (LSB)

D7 (MSB)

7, 20,

26, 39

–5V

1N4001

AD9058

(J-LEAD)

RZ1, RZ2 = 2,000Ω SIP (8-PKG)

8

8

1/2

AD8002

1/2

AD8002

50Ω

50Ω

Figure 55. AD8002 Driving a Dual ADC