ad8251nbsp Analog Devices, Inc., ad8251nbsp Datasheet - Page 22

• Manufacturer Part Number: ad8251nbsp
• Description: 10 Mhz, 20 V/?s, G = 1, 2, 4, 8 I Cmos Programmable Gain Instrumentation Amplifier
• Manufacturer: Analog Devices, Inc.

AD8251
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 61 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 60.
+CH1
+CH2
+CH3
+CH4
–CH4
–CH3
–CH2
–CH1
806Ω
806Ω
806Ω
806Ω
806Ω
806Ω
806Ω
806Ω
0.1µF
0.1µF
10
11
12
4
5
6
7
S1A EN
S2A
S3A
S4A
S4B
S3B
S2B
S1B
+12V
ADG1209
–12V
V
V
14
DD
SS
3
Figure 61. Schematic of ADG1209, AD8251, and AD7612 in the AD825x DAQ Demo Board
A1
16
2
JMP
A0
1
JMP
15
8
9
+12V
+5V
0Ω
0Ω
+5V
R8
2kΩ
DGND
10µF
+
DGND
DGND
2kΩ
0Ω
0Ω
GND
C
D
10µF
+
–12V
C
C
+IN
–IN
0.1µF
DGND
10
1
C3
Rev. 0 | Page 22 of 24
DGND
+
–
2
AD8251
+12V –12V
+V
8
WR
S
6
–V
3
A1
S
5
VREF
A0
4
C4
0.1µF
JMP
9
JMP
+5V
7
–100
–110
–120
–130
–140
–150
–160
–170
–180
DGND
2kΩ
VOUT
–70
–80
–90
+5V
0
0Ω 49.9Ω
DGND
2kΩ
Figure 60. FFT of the AD825x DAQ Demo Board
5
10
Using the AD8251 1 kHz Signal
JMP
–V
+IN
1nF
S
15
FREQUENCY (kHz)
AD7612
ADR435
20
25
EPF6010ATC144-3
30
ALTERA
35
40
45
5
0