Philips Magnetoresistive Sensor - Manual (Page 29)

2000 Sep 06 29
Philips Semiconductors
Magnetoresistive sensors for
magnetic field measurement
General
The influence of other disturbing fields can also be
eliminated provided they are well known, by adding a
second current source to the compensating coil. Such
fields might be those arising from the set-up housing,
ferromagnetic components placed close to the sensor or
magnetic fields from electrical motors. The brief summary in Table 3 compares the types of
compensation and their effects, so they can be assessed
for their suitability in a given application. Because these
options encompass a range of costs, the individual
requirements of an application should be carefully
analysed in terms of the performance gains versus relative
costs.
Table 4 Summery of compensation techniques
TECHNIQUE EFFECT
Setting avoids reduction in sensitivity due to constant stabilization field
Flipping avoids reduction in sensitivity due to constant stabilization field, as well as
compensating for sensor offset and offset drift due to temperature
Current supply reduction of sensitivity drift with temperature by a factor of two
Electro-magnetic feedback accurate compensation of sensitivity drift with temperature
Fig.34 Block diagram of compensation circuit.
handbook, full pagewidth
MBH619
LF
LC
CURRENT
REGULATOR
FLIPPING
SOURCE
CLOCK
VOLTAGE & CURRENT
OUTPUT
PRE-AMPLIFIER
WITH
SUPRESSION
OF OFFSET
PHASE-
SENSITIVE
DEMODULATOR