Philips Magnetoresistive Sensor - Manual (Page 14)

2000 Sep 06 14
Philips Semiconductors
Magnetoresistive sensors for
magnetic field measurement
General
Fig.16 KMZ10B application circuit with instrumentation amplifier.
handbook, full pagewidth
MLC145
KMZ10B
offset
R2
VO
VS
R1
R3
OP2
R7
R4
R6
R
KTY82-110
R5
R9
R10
R12
R11
R13
R14
OP1
OP3
T
RA
R B
The amplification of the input stage (‘OP1’ and ‘OP2’) is
given by:
(9)
where R
T
is the temperature dependent resistance of the
KTY82 sensor and R
B
is the bridge resistance of the
magnetoresistive sensor.
The amplification of the complete amplifier can be
calculated by:
(10)
The positive temperature coefficient (TC) of the
amplification is:
(11)
For the given negative ‘TC’ of the magnetoresistive sensor
and the required amplification of the input stage ‘A1’, the
resistance ‘R
A
’ and ‘R
B
’ can be calculated by:
(12)
(13)
where TC
KTY
is the temperature coefficient of the KTY
sensor and TC
A
is the temperature coefficient of the
amplifier. This circuit also provides for adjustment of gain
and offset voltage of the magnetic-field sensor.
A1 1
R
T
R
B
+
R
A
--------------------- + =
A A1
R
14
R
10
---------
×
=
TC
A
R
T
TC
KTY
×
R
A
R
B
R
T
+ +
----------------------------------- =
R
B
R
T
TC
KTY
TC
A
------------------ 1
1
A1
------- –  
 
1 –
Ч
 
 
Ч
=
R
A
R
T
R
B
+
A1 1 –
--------------------- =