ad8251nbsp Analog Devices, Inc., ad8251nbsp Datasheet - Page 21

• 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.

APPLICATIONS
DIFFERENTIAL OUTPUT
In certain applications, it is necessary to create a differential
signal. High resolution analog-to-digital converters often
require a differential input. In other cases, transmission over
a long distance can require differential signals for better
immunity to interference.
Figure 59 shows how to configure the AD8251 to output a
differential signal. An op amp, the AD817, is used in an
inverting topology to create a differential voltage. V
output midpoint according to the equation shown in the figure.
Errors from the op amp are common to both outputs and are
thus common mode. Likewise, errors from using mismatched
resistors cause a common-mode dc offset error. Such errors are
rejected in differential signal processing by differential input
ADCs or instrumentation amplifiers.
+5V
–5V
AMPLITUDE
V
IN
+12V
+IN
10μF
–12V
0.1μF
0.1μF
10μF
+
–
AD8251
DGND
+12V
–12V
Figure 59. Differential Output with Level Shift
G = 1
DGND
REF
WR
sets the
A1
A0
REF
4.99kΩ
4.99kΩ
Rev. 0 | Page 21 of 24
10pF
0.1µF
–12V
When using this circuit to drive a differential ADC, V
set using a resistor divider from the ADC reference to make the
output ratiometric with the ADC.
SETTING GAINS WITH A MICROCONTROLLER
–
V
V
OUT
AD817
OUT
B = –V
A = V
0.1µF
+
2
2
IN
IN
+12V
Figure 58. Programming Gain Using a Microcontroller
–IN
+IN
10μF
10μF
+ V
+ V
REF
REF
V
0V
AMPLITUDE
AMPLITUDE
REF
0.1µF
0.1µF
+2.5V
–2.5V
+2.5V
–2.5V
0V
0V
0V
+15V
–15V
+
–
AD8251
DGND
WR
A1
A0
REF
CONTROLLER
DGND
TIME
TIME
MICRO-
AD8251
REF
can be