Datasheet

V
IN
(0toV )
OFFSET
V
REF
R
OS
2kW
R
SET
2kW
XTR300
OPA
I
Feedback
a)NoninvertingInput
b)NoninvertingInput
V
IN
(V )
MIDSCALE
V
MIDSCALE
R
SET
1kW
XTR300
OPA
I
Feedback
c)InvertingInput(V =V )
REF OFFSET
V
IN
( V )±
OFFSET
V
OFFSET
R
SET
1kW
XTR300
OPA
I
Feedback
XTR300
www.ti.com SBOS336C –JUNE 2005– REVISED JUNE 2011
INPUT SIGNAL CONNECTION
It is possible to drive the XTR300 with a unidirectional input signal and still get a bidirectional output by adding an
additional resistor, R
OS
, and an offset voltage signal, V
REF
. It can be a mid-point voltage or a signal to shift the
output voltage to a desired value.
This design is illustrated in Figure 42a, Figure 42b, and Figure 42c. As with a normal operational amplifier, there
are several options for offset-shift circuits. The input can be connected for inverting or noninverting gain. Unlike
many op amp input circuits, however, this configuration uses current feedback, which removes the voltage
relationship between the noninverting input and output potential because there is no feedback resistor.
Figure 42. Circuit Options for Op Amp Output Level-Shifting
The input bias current effect on the offset voltage can be reduced by connecting a resistor in series with the
positive input that matches the approximate resistance at the negative input. This resistor placed close to the
input pin acts as a damping element and makes the design less sensitive to RF noise. See R
3
in Figure 39.
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