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Tel: (602) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (602) 889-1510 鈥?Immediate Product Info: (800) 548-6132
precision resistor network. The self-contained INA105 makes
it ideal for many applications. One such application is
precision level shifting.
appearing on pin 3 of the OPA27. An
operational amplifier is used to drive the INA105鈥檚 鈥淩ef鈥?/div>
pin (pin 1) with a low impedance source to preserve true
differential operational of the INA105.
A basic understanding of the circuit operation can be gained
by considering the INA105 as a three input summing ampli-
fier. The voltage transfer function is then E
OUT
= E
2
鈥?E
1
+
V
REF
. As this relation shows, the output will respond to a
difference signal and algebraically add the voltage at the
鈥淩ef鈥?input. Therefore, V
REF
may take on any arbitrary value
that will not saturate the INA105 amplifier鈥檚 output. In the
case of the circuit in Figure 1, V
REF
= V
SHIFT
, yielding an
output of E
O
= E
2
鈥?E
1
+V
SHIFT
.
Precision fixed level shifting can be easily accomplished by
the use of a voltage reference source such as the REF102. A
REF102 used with an additional INA105 can be used to
provide an accurate, low drift, +5V reference to drive the
鈥淩ef鈥?pin of the differentially connected INA105 as shown
in Figure 2. If, for example, the input signal is a bipolar
鹵5V
signal, the output will be level shifted to a unipolar 0-10V
signal. The same reference circuit also has 鈥?V available
and may thus be used for the opposite conversion from
unipolar 0-10V to bipolar
鹵5V
signals. (Request PDS-1018
for INA105 and PDS-900 for REF102.)
E
1
2
5
E
1
2
5
鈥?/div>
6
6
E
2
3
E
O
+V
CC
2
2
E
2
3
E
O
+
2
3
OPA27
6 1
INA105
6 1
REF102
1k鈩?/div>
4
鈥?V
INA105
V
SHIFT
5
FIGURE 1. Level Shifting Circuit Using the INA105鈥檚 V
REF
Pin.
鈥?/div>
6
+
INA105
1
3
FIGURE 2. Precision Level Shift Circuit from a Fixed Volt-
age Reference.
漏
1994 Burr-Brown Corporation
AB-087
Printed in U.S.A. January, 1994
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