REV. C

AD8002

–12–

Driving A-to-D Converters

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 the circuit below the AD8002 is shown

driving 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

0.1 F

20

50

1k

18

17

16

15

14

13

12

11

10pF

CLOCK

5, 9, 22,

24, 37, 41

4,19, 21

25, 27, 42

0.1 F

38

8

6

2

3

549

274

ANALOG

IN A

0.5V

1.1k

AD707

43

20k

0.1 F

–2V

1.1k

20k

549

ANALOG

IN B

0.5V

274

20

0.1 F

40

COMP

1

ENCODE A

ENCODE B

10

36

ENCODE

74ACT04

0.1 F

+5V

28

29

30

31

32

33

34

35

RZ1

RZ2

7, 20,

26, 39

–5V

1N4001

AD9058

(J-LEAD)

RZ1, RZ2 = 2,000

SIP (8-PKG)

8

8

1/2

AD8002

1/2

AD8002

50

50

Figure 46. AD8002 Driving a Dual A-to-D Converter

ADC. Using the AD9058’s internal +2 V reference connected

to both ADCs as shown in Figure 46 reduces the number of

external components required to create a complete data

acquisition system. The 20

Ω resistors in series with ADC in-

puts are used to help the AD8002s drive the 10 pF ADC input

capacitance. The AD8002 only adds 100 mW to the power

consumption while not limiting the performance of the circuit.