Precision amplifier for bridge circuits
AM457
EXAMPLE APPLICATION
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.
AM457
C2
R1
C4
R4
VCC
8
VCC=5V
VCC
7
3
OP
1k
9k
OUTOP
C5
C1
Diagnostic
unit
DIAG
OUT
5
1
IN+
VDIAG
VOUT
Temp
AMP
IN-
2
6
C6
INOP
GND
4
R3
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
May 2005
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone: +49 (0)6131/91 073 – 0
Fax: +49 (0)6131/91 073 – 30
Email: info@analogmicro.de
7/10
Rev. 2.2
AME [ ANALOG MICROELECTRONICS ]
