Precision amplifier for bridge circuits
EXAMPLE APPLICATION
AM457
Offset and span compensation for a Wheatstone bridge with discrete adjusting resistors.
AM457 is suitable for the amplification of all resistance bridge circuits (four-resistor bridges)
with low sensitivity.
To compensate for or calibrate the offset and span and to amplify the signal as necessary a network
was developed (see Figure 2) for a four-resistor resistance bridge circuit (such as a DMS sensing
element, for example) consisting of the resistance bridge, an AM457 IC, four resistors and a
maximum of six capacitors (see [1]). AM457's characteristics define the network and the IC
amplifies the bridge output signal to the required output values.
R
4
C
2
R
1
7
AM457
OUTOP
VCC 8
OP
1k
9k
V
CC
V
CC
=5V
C
5
C
4
3
IN+
IN-
INOP
C
6
R
3
2
6
AMP
Temp
Diagnostic
unit
DIAG 5
OUT
1
V
DIAG
C
1
V
OUT
4
GND
GND
Figure 2:
Schematic circuit diagram for resistance bridges with low sensitivity
The formulae used here to calibrate the offset and span of a bridge circuit are calculated using a
model which is based on the classic Wheatstone bridge circuit of four resistors.
On the basis of this model three simple equations were approximated for the setting of the resistors;
they are also suitable for calibration using a minimum of data pertinent to the sensing element and
without any need for further correction.
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
May 2005
7/10
Rev. 2.2
AME [ ANALOG MICROELECTRONICS ]
