Datasheet
AD8251
Rev. B | Page 22 of 24
DATA ACQUISITION
The AD8251 makes an excellent instrumentation amplifier
for use in data acquisition systems. Its wide bandwidth, low
distortion, low settling time, and low noise enable it to
condition signals in front of a variety of 16-bit ADCs.
Figure 63 shows a schematic of the AD825x data acquisition
demonstration board. The quick slew rate of the AD8251 allows
it to condition rapidly changing signals from the multiplexed
inputs. An FPGA controls the AD7612, AD8251, and ADG1209.
In addition, mechanical switches and jumpers allow users to pin
strap the gains when in transparent gain mode.
This system achieved −106 dB of THD at 1 kHz and a signal-to-
noise ratio of 91 dB during testing, as shown in Figure 62.
–
70
–80
–90
–100
–110
–120
–130
–140
–150
–160
–170
–180
05
06287-062
FREQUENCY (kHz)
AMPLITUDE (dB)
0
5 1015202530354045
Figure 62. FFT of the AD825x DAQ Demo Board
Using the AD8251 1 kHz Signal
AD8251
2
+IN
–IN
A1
A0
OUT
REF
–V
S
+V
S
DGND
5
3
4
9
1
7
10
11
12
13
14
15
16
6
2
S1A
EN
S2A
S3A
S4A
DA
DB
GND
S1B
S2B
S3B
S4B
A0
A1
V
SS
V
DD
JMP
JMP
JMP
+12V –12V
+12V
–12V
JMP
JMP
–V
S
+5V
+5V
DGND
806
806
806
806
806
806
806
806
0
0 49.9
0
–CH1
+CH1
+CH2
–CH2
+CH3
–CH3
+CH4
–CH4
1nF
2k
2k
0.1µF
GND
+12V
–12V
+
+
10µF 10µF
0.1µF
C
D
C
C
C
C
C3
0.1µF
C4
0.1µF
+5V
+5V
DGND
DGND
R8
2k
+IN
AD7612
ADR435
ADG1209
DGND
ALTERA
EPF6010ATC144-3
8
0
0
1
10
6
WR
9
4
5
8
3
7
+
–
DGND
2k
DGND
06287-067
Figure 63. Schematic of ADG1209, AD8251, and AD7612 in the AD825x DAQ Demo Board