Datasheet

REV. D
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 Figure 10, the AD8002 is shown driv-
ing 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
0.1␮F
+V
S
–V
S
20⍀
50⍀
1k⍀
18
17
16
15
14
13
12
11
–V
REF A
10pF
CLOCK
5, 9, 22,
24, 37, 41
4,19, 21 25, 27, 42
0.1␮F
38
8
–V
REF B
6
+V
INT
2
3
+V
REF A
A
IN A
549⍀
274⍀
ANALOG
IN A
ⴞ0.5V
1.1k⍀
AD707
43
+V
REF B
20k⍀
0.1␮F
–2V
1.1k⍀
20k⍀
549⍀
ANALOG
IN B
ⴞ0.5V
274⍀
20⍀
0.1␮F
40
COMP
1
A
IN B
ENCODE A ENCODE B
10
36
ENCODE
74ACT04
0.1␮F
+5V
28
29
30
31
32
33
34
35
RZ1
RZ2
D
0A
(LSB)
D
7A
(MSB)
D
0B
(LSB)
D
7B
(MSB)
7, 20,
26, 39
–5V
1N4001
AD9058
(J-LEAD)
RZ1, RZ2 = 2,000⍀ SIP (8-PKG)
74ACT 273
74ACT 273
8
8
1/2
AD8002
1/2
AD8002
50⍀
50⍀
Figure 10. AD8002 Driving a Dual A-to-D Converter
the AD9058’s internal 2 V reference connected to both ADCs
as shown in Figure 10 reduces the number of external compo-
nents required to create a complete data acquisition system. The
20 Ω resistors in series with ADC inputs are used to help the
AD8002s drive the 10 pF ADC input capacitance. The AD8002
adds only 100 mW to the power consumption, while not limit-
ing the performance of the circuit.