Datasheet

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SBOS146A − OCTOBER 1986 − REVISED AUGUST 2004
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10
SIGNAL SUPPRESSION AND ELEVATION
In some applications, it is desired to have suppressed zero
range (input signal elevation) or elevated zero range (input
signal suppression). This is easily accomplished with the
XTR101 by using the current sources to create the
suppression/elevation voltage. The basic concept is
shown in Figure 7 and Figure 8(a). In this example, the
sensor voltage is derived from R
T
(a thermistor, RTD, or
other variable resistance element) and excited by one of
the 1mA current sources. The other current source is used
to create the elevated zero range voltage. Figure 8(b), (c),
and (d) show some of the possible circuit variations. These
circuits have the desirable feature of noninteractive span
and suppression/elevation adjustments.
Note: It is not recommended to use the optional offset
voltage null (pins 1, 2, and 14) for elevation/suppression.
This trim capability is used only to null the amplifier’s input
offset voltage. In many applications the already low offset
voltage (typically 20µV) will not need to be nulled at all.
Adjusting the offset voltage to non-zero values will disturb
the voltage drift by ±0.3µV/°C per 100µV or induced offset.
−
0+
I
O
(mA)
20
15
10
5
0
Elevated
Zero
Range
Suppressed
Zero
Range
Span Adjust
e
IN
(V)
Figure 7. Elevation and Suppression Graph
−
e
IN
e’
2
+
1mA
1mA
−
+
R
4
V
4
2mA
−
+
−
+
−
+
−
+
−
+
−
+
2mA
−
+
−
+
−
+
− +
R
T
e’
2
R
T
e
IN
1mA1mA
R
4
V
4
2mA
e’
2
R
4
V
4
e
IN
2mA
e
IN
2mA
2mA
e’
2
R
4
V
4
e
IN
=(e’
2
−
V
4
)
V
4
=1mA
×
R
4
e’
2
=1mA
×
R
T
(a) Elevated Zero Range
e
IN
=(e’
2
+V
4
)
V
4
=1mA
×
R
4
e’
2
=1mA
×
R
T
(b) Suppressed Zero Range
e
IN
=(e’
2
−
V
4
)
V
4
=2mA
×
R
4
(c) Elevated Zero Range
e
IN
=(e’
2
+V
4
)
V
4
=2mA
×
R
4
(d) Suppressed Zero Range
Figure 8. Elevation and Suppression Circuits
APPLICATION INFORMATION
The small size, low offset voltage and drift, excellent
linearity, and internal precision current sources make the
XTR101 ideal for a variety of two-wire transmitter
applications. It can be used by OEMs producing different
types of transducer transmitter modules and by data
acquisition systems manufacturers who gather transducer
data. Current-mode transmission greatly reduces noise
interference. The two-wire nature of the device allows
economical signal conditioning at the transducer. Thus the
XTR101 is, in general, very suitable for individualized and
special-purpose applications.