Datasheet

AD8250 Data Sheet
Rev. C | Page 20 of 24
APPLICATIONS
DIFFERENTIAL OUTPUT
In certain applications, it is necessary to create a differential
signal. High resolution ADCs often require a differential input.
In other cases, transmission over a long distance can require
differential signals for better immunity to interference.
Figure 57 shows how to configure the AD8250 to output a
differential signal. An op amp, the AD817, is used in an inverting
topology to create a differential voltage. V
REF
sets the 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.
When using this circuit to drive a differential ADC, V
REF
can be
set using a resistor divider from the ADC reference to make the
output ratiometric with the ADC.
SETTING GAINS WITH A MICROCONTROLLER
+15
V
MICRO-
CONTROLLER
–15V
A0
A1
WR
+IN
–
IN
10μF0.1µF
10μF0.1µF
REF
AD8250
06288-063
+
–
DGNDDGND
Figure 56. Programming Gain Using a Microcontroller
+12
V
–12V
A0
A1
WR
+IN
10μF
0.1μF
10μF
0.1μF
AD8250
REF
G = 1
0.1µF
4.99kΩ
4.99kΩ
AD817
0.1µF
+12V
–12V
V
REF
0V
V
OUT
A = V
IN
+ V
REF
2
2
V
OUT
B = –V
IN
+ V
REF
+2.5V
–2.5V
0V
+2.5V
–2.5V
0V
TIME
AMPLITUDE
0V
TIME
AMPLITUDE
+5
V
–5V
AMPLITUDE
10pF
+12V
–12V
V
IN
06288-064
+
–
+–
DGND
DGND
Figure 57. Differential Output with Level Shift