AD8002
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
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.
ENCODE
10
ENCODE A
549
ANALOG
IN A
0.5V
274
8
38
–V
REF A
–V
REF B
A
IN A
36
ENCODE B
+V
S
50
74ACT04
1k
10pF
5, 9, 22,
24, 37, 41
0.1 F
RZ1
+5V
1.1k
–2V
50
1/2
AD8002
20
6
D
0A
(LSB)
18
17
15
14
13
12
11
RZ2
74ACT 273
74ACT 273
–5V
1N4001
16
2
AD707
0.1 F
20k
1.1k
549
ANALOG
IN B
0.5V
274
+V
INT
+V
REF A
+V
REF B
D
7A
(MSB)
8
20k
0.1 F
3
43
AD9058
(J-LEAD)
D
0B
(LSB)
28
29
30
31
32
33
34
8
50
1/2
AD8002
20
40
A
IN B
1
COMP
0.1 F
D
7B
(MSB)
–V
S
RZ1, RZ2 = 2,000
SIP (8-PKG)
4,19, 21
25, 27, 42
35
7, 20,
26, 39
0.1 F
CLOCK
Figure 46. AD8002 Driving a Dual A-to-D Converter
–12–
REV. C
AD [ ANALOG DEVICES ]
