AD8251

Rev. 0 | 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 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.

–70

–80

–90

–100

–110

–120

–130

–140

–150

–160

–170

–180

05

FREQUENCY (kHz)

0

5

1015

202530354045

Figure 60. FFT of the AD825x DAQ Demo Board

Using the AD8251 1 kHz Signal

AD8251

2

+IN

–IN

A1

A0

VOUT

VREF

DGND

5

3

4

9

1

7

10

11

12

13

14

15

16

6

2

S1A EN

S2A

S3A

S4A

S1B

S2B

S3B

S4B

A0

A1

JMP

JMP

JMP

+12V –12V

+12V

–12V

JMP

JMP

+5V

+5V

DGND

806Ω

806Ω

806Ω

806Ω

806Ω

806Ω

806Ω

806Ω

0Ω

0Ω 49.9Ω

0Ω

–CH1

+CH1

+CH2

–CH2

+CH3

–CH3

+CH4

–CH4

1nF

2kΩ

2kΩ

0.1µF

GND

+12V

–12V

+

+

10µF

10µF

0.1µF

C3

0.1µF

C4

0.1µF

+5V

+5V

DGND

DGND

R8

2kΩ

+IN

AD7612

ADR435

ADG1209

DGND

ALTERA

EPF6010ATC144-3

8

0Ω

0Ω

1

10

6

WR

9

4

5

8

3

7

+

–

DGND

2kΩ

DGND

Figure 61. Schematic of ADG1209, AD8251, and AD7612 in the AD825x DAQ Demo Board