Philips Magnetoresistive Sensor

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

signalfrom the measured signal. Essentially, the unknown

field in the ‘normal’ positive direction (plus the offset) is

measuredin 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,

continuousvalue 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

coil

current

pulses

sensor

Fig.29 Block diagram of flipping circuit.

handbook, full pagewidth

MBH617

FLIPPING

SOURCE PRE-

AMPLIFIER

CLOCK

OFFSET

FILTER Vout

PHASE

SENSITIVE

DEMODULATOR