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2000 Sep 06 24
Philips Semiconductors
Magnetoresistive sensors for
magnetic field measurement
General
Flipping causes a change in the polarity of the sensor
output signal and this can be used to separate the offset
signal from the measured signal. Essentially, the unknown
field in the ‘normal’ positive direction (plus the offset) is
measured in one half of the cycle, while the unknown field
in the ‘inverted’ negative direction (plus the offset) is
measured in the second half. This results in two different
outputs symmetrically positioned around the offset value.
After high pass filtering and rectification a single,
continuous value free of offset is output, smoothed by low
pass filtering. See Figs 29 and 30.
Offset compensation using flipping requires additional
external circuitry to recover the measured signal.
Fig.28 Flipping coil.
MLC762
H
y
H
x
coil
V
O
current
pulses
sensor
Fig.29 Block diagram of flipping circuit.
handbook, full pagewidth
MBH617
L
F
I
F
FLIPPING
SOURCE
PRE-
AMPLIFIER
CLOCK
T
OFFSET
FILTER
V
out
PHASE
SENSITIVE
DEMODULATOR