AN20

Application Note 20
Issue 1 April 1996
Magnetoresistive Sensors
Principles of Operation and Applications
Stefan Hübschmann
Matthias Schneider
This a pplication note provides an
overview of the Zetex range of
Magnetoresistive sensors.
The layout of a typical magnetoresistive
chip (parent device 174B) is shown in
Figure 1, and is for example the chip
used in the ZMY20 sensor. Thin film
stripes are a characteristic feature of a
magnetoresistive chip. These stripes are
made by photolithography and consist
of Permalloy (Ni81Fe19), a magnetic
material evaporated on an oxidised
silicon wafer. The electrical resistivity of
the stripes is changed by a magnetic
field Hy due to the magnetoresistive
effect. The field Hy causes a rotation of
Figure 1
Magnetoresistive Magnetic Field Sensor,
(Parent Device 174B).
the magnetisation in the stripe. This is
shown in Figure 2. The resistivity R of a
permalloy stripe depends on the angle
betwe en the directions of electric
current (I) and magnetisation (M):
R = Ro + ∆Ro cos2α
where ∆R0 describes the strength of the
magnetoresistive effect.
T h e m a x i m u m r e l a t iv e cha n g e o f
resistivity ∆R0/R is approximately 2 to 3%
for permalloy. The relationship between
an external field Hy and angle α is
Figure 2
The magnetoresistive effect depends on
the angle between the direction of electric
current (I) and magnetisation (M). A
rotation of the magnetisation in a
permalloy stripe takes place when a
magnetic field in the y-direction is applied.
Without an external field the
magnetisation is along the x-direction
due the shape of the stripe.
AN20 - 1
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
determined by the geometrical
di m e n s io ns of the s tri pe and the
magnetic anisotropy of permalloy. This
is taken into account by introducing a
f i e l d H0 t h a t r e p r e s e n t s t h e
demagnetising and anisotropic field.
One obtains
sin2 α =
Hy2
H02
sin2 α = 1
Figure 3
Covering the stripe with “Barber poles”
consisting of aluminium changes the
direction of the current. This does not
influence the direction of magnetisation.
for H < H0
for H > H0
The characteristic of a magnetoresistive
stripe as a field sensor is:
 Hy 2 
R = R0 + ∆R0 1− 2 
 H0 
for H < H0
A linear characteristic of the
magnetoresistive sensor is required to
measure a small magnetic field. The
linear behaviour of the magnetoresistive
sensor is achieved by using a “Barber
pole” geometry. The stripes in Figure 1
are covered with aluminium bars having
an inclination of 45° to the stripe axis.
Aluminum has a low resistivity
compared to permalloy. Therefore the
Barber poles cause a change of the
current direction. The angle between
current and magnetisation is shifted by
45° as shown in Figure 3. The
relationship between resistance and
magnetic field is now
 Hy 
R =Ro + ∆R0 ± ∆Ro  
2
 Ho 
H

√
1− 
H
y
0
The stripes of the magnetoresistive chip
are arranged as a meandering pattern.
They form a Wheatstone bridge which is
shown schematically in Figure 5. The
applied voltage is Vb. Each half bridge
consists of two resistors with different
“Barber pole” orientations. The voltage
between the resistors of a half bridge
changes upon application of a magnetic
field.
R
R0+∆R0
with Barber poles
without Barber poles
R0
2
-1
2
A linear characteristic of the sensor is
given around Hy2/H20 = 0. The sign in this
equation is determined by the
inclination of the “Barber poles” (±45°)
Figure 6
Safe operating area of ZMY20/ZMZ20.
Hxtot=Hx + Hd ; Tamb = 25°C
Hd = disturbing field.
to the stripe axis. The characteristic of a
sensor with and without Barber poles is
presented in Figure 4.
-0,5
0
0,5
1
Hy
H0
Figure 4
Characteristics of magnetoresistive
sensors. The Barber pole structure
enables a linear behaviour of the sensor
for a small magnetic field.
AN20 - 2
Figure 5
Wheatstone bridge of a magnetoresistive
sensor with “Barber pole” structure. The
bridge is balanced by laser trimming.
The resistance of one resistor increases,
whilst the other resistor has a lower
resistance due to the differing field
characteristic. Adding a second half
bridge with an opposite arrangement of
“Barber poles” provides a Wheatstone
bridge. The voltage difference V0 is the
output signal of the sensor. Each half
bridge is trimmed to Vb/2 w ith an
additional resistor in order to get an
output voltage close to zero when no
external field is applied. The trimming
structures of the resistors in Figure 1
mark off the meander stripes on the left
and right side of the chips.
Operating conditions and
parameters
The shape of the stripe and the
anisotropy of permalloy only define an
ax is along the x-direction for the
magnetisation without external field Hy.
This means that in this state the stripe
can have areas with a different direction
of magnetisation (magnetic domains)
and the sensor does not work in a stable
way. A safe operation of the sensor is
achieved by applying an auxiliary field
Hx. This field defines the direction of the
magnetisation. The range of Hy for safe
sensor operation is determined by the
strength of the auxiliary field. The safe
operating area (SOA) of the sensor is
demonstrated in Figure 6.
The field Hxtot = Hy + Hd determines the
allowed field values for Hy, where Hd is
an external disturbing field in the
x-direction.
There is no limitation for Hy in the case of
Hxtot ≥ 2.6 kA/m (ZMY20/ZMZ20). A small
permanent magnet is sufficient to create
the auxiliary field. The magnet can be
glued on the sensor package (ZMZ 20/30
or ZMY 20/30). Another option is the
ZMY20M which provides a very compact
sensor including an integrated magnet,
and is available in a surface mount
package.
AN20 - 3
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
determined by the geometrical
di m e n s io ns of the s tri pe and the
magnetic anisotropy of permalloy. This
is taken into account by introducing a
f i e l d H0 t h a t r e p r e s e n t s t h e
demagnetising and anisotropic field.
One obtains
sin2 α =
Hy2
H02
sin2 α = 1
Figure 3
Covering the stripe with “Barber poles”
consisting of aluminium changes the
direction of the current. This does not
influence the direction of magnetisation.
for H < H0
for H > H0
The characteristic of a magnetoresistive
stripe as a field sensor is:
 Hy 2 
R = R0 + ∆R0 1− 2 
 H0 
for H < H0
A linear characteristic of the
magnetoresistive sensor is required to
measure a small magnetic field. The
linear behaviour of the magnetoresistive
sensor is achieved by using a “Barber
pole” geometry. The stripes in Figure 1
are covered with aluminium bars having
an inclination of 45° to the stripe axis.
Aluminum has a low resistivity
compared to permalloy. Therefore the
Barber poles cause a change of the
current direction. The angle between
current and magnetisation is shifted by
45° as shown in Figure 3. The
relationship between resistance and
magnetic field is now
 Hy 
R =Ro + ∆R0 ± ∆Ro  
2
 Ho 
H

√
1− 
H
y
0
The stripes of the magnetoresistive chip
are arranged as a meandering pattern.
They form a Wheatstone bridge which is
shown schematically in Figure 5. The
applied voltage is Vb. Each half bridge
consists of two resistors with different
“Barber pole” orientations. The voltage
between the resistors of a half bridge
changes upon application of a magnetic
field.
R
R0+∆R0
with Barber poles
without Barber poles
R0
2
-1
2
A linear characteristic of the sensor is
given around Hy2/H20 = 0. The sign in this
equation is determined by the
inclination of the “Barber poles” (±45°)
Figure 6
Safe operating area of ZMY20/ZMZ20.
Hxtot=Hx + Hd ; Tamb = 25°C
Hd = disturbing field.
to the stripe axis. The characteristic of a
sensor with and without Barber poles is
presented in Figure 4.
-0,5
0
0,5
1
Hy
H0
Figure 4
Characteristics of magnetoresistive
sensors. The Barber pole structure
enables a linear behaviour of the sensor
for a small magnetic field.
AN20 - 2
Figure 5
Wheatstone bridge of a magnetoresistive
sensor with “Barber pole” structure. The
bridge is balanced by laser trimming.
The resistance of one resistor increases,
whilst the other resistor has a lower
resistance due to the differing field
characteristic. Adding a second half
bridge with an opposite arrangement of
“Barber poles” provides a Wheatstone
bridge. The voltage difference V0 is the
output signal of the sensor. Each half
bridge is trimmed to Vb/2 w ith an
additional resistor in order to get an
output voltage close to zero when no
external field is applied. The trimming
structures of the resistors in Figure 1
mark off the meander stripes on the left
and right side of the chips.
Operating conditions and
parameters
The shape of the stripe and the
anisotropy of permalloy only define an
ax is along the x-direction for the
magnetisation without external field Hy.
This means that in this state the stripe
can have areas with a different direction
of magnetisation (magnetic domains)
and the sensor does not work in a stable
way. A safe operation of the sensor is
achieved by applying an auxiliary field
Hx. This field defines the direction of the
magnetisation. The range of Hy for safe
sensor operation is determined by the
strength of the auxiliary field. The safe
operating area (SOA) of the sensor is
demonstrated in Figure 6.
The field Hxtot = Hy + Hd determines the
allowed field values for Hy, where Hd is
an external disturbing field in the
x-direction.
There is no limitation for Hy in the case of
Hxtot ≥ 2.6 kA/m (ZMY20/ZMZ20). A small
permanent magnet is sufficient to create
the auxiliary field. The magnet can be
glued on the sensor package (ZMZ 20/30
or ZMY 20/30). Another option is the
ZMY20M which provides a very compact
sensor including an integrated magnet,
and is available in a surface mount
package.
AN20 - 3
Application Note 20
Issue 1 April 1996
The operating datasheet parameters of
the Wheatstone bridge are referred to an
input voltage Vb= 1V, due to the linear
relationship between input and output
voltage in this region.
The sensitivity S [mV/V/kA/m] of the
magnetoresistive sensor is defined as
the slope of the output voltage versus
external field for -1 kA/m ≤ Hy ≤1 kA/m.
This parameter depends on the
geometry of the permalloy meander and
t h e a u x i l i a r y f i e l d . T h e l a t te r i s
demonstrated in Figure 7 for Hx = 3 kA/m
a n d Hx = 6 k A / m . N o te t h e s m a l l
operating area in the case of Hy = 0 kA/m.
A high sensitivity of the sensor leads to
a small operating area for H y.
Further details and complete Magnetoresistive Product information is provided in
the Appropriate Technical Handbook: please see Technical Publication section.
Application Note 20
Issue 1 April 1996
The Wheatstone bridge is balanced
without the application of an external
field (Hy≤ 0.1 kA/m). In this case the
output voltage of the sensor is close to
zero at room temperature. The deviation
of the output voltage from zero is called
the offset voltage V0ff/Vb [mV/V]. The
offset is caused by small geometric
variations of the bridge which occur
during the photolithographic process.
The offset of the bridge is adjusted by
laser trimming. The voltage output of
each half bridge is Vb/2.
The bridge resistance Rbr [%/K] of the
ma gnetor esi sti v e s e n so r d e p e n d s
linearly on temperature. The
te m p e ra t ure coeff icient of bri dg e
resistance TCRbr [%/K] is positive. This
is typical for metals. The temperature
coefficient of sensitivity TCS [%/K] of the
sensor is negative for VB = const (TCSV),
because the strength of the
m a g n e t o r e s i s t i v e e f f e c t be c om e s
smaller with increasing temperature. In
the case of IB = const (TCSI), when the
sensor is powered by a constant current
supply, the temperature dependence of
the sensitivity is reduced due to the
linear relationship between input and
o u t p u t v o l t a ge . A hi g h e r br i d g e
resistance caused by a rise in
temperature leads to an increased
applied voltage, partly compensating
the change of sensitivity.
Figure 7
Sensor output characteristic of ZMY20/ZMZ20. The sensitivity of the sensor can be
controlled by applying an auxiliary field Hx. This auxiliary field is necessary for sensor
operation in a large field range. V0=f(Hy); HX-parameter;VB=const;Tamb=25°C.
AN20 - 4
The Wheatstone bridge cannot fully
compensate
the
temperature
de pe nd en c e of the r es i stor s. The
t e m p e r a t u r e c oe ff i c i e n t o f o f f s e t
voltage TCVoff [µV/V/K] is due to local
changes of resistivity in the permalloy
thin film and photolithographic
variations. This characteristic of the
magnetoresistive sensor limits the
measurement of small magnetic fields in
a wide temperature range, especially in
the case of static fields. Two sensors can
b e s e l e c t ed h a v in g a c omp ar a b l e
temperature coefficient. The offset drift
i s p a r t l y e l i m in a t e d b y u si n g t h e
difference of the output voltages of both
sensors. Another elegant way to avoid
offset drift is to invert the direction of the
auxiliary field and thus inverting the
output voltage of the sensor. This can be
d o n e b y s m al l c oil s p r ov idi ng an
auxiliary field that can change its
direction.
The hysteresis of output voltage V0ffH/Vb
[µV/V] describes the accuracy of the
magnetoresistive
sensor.
The
magnetisation of the permalloy stripe is
not completely homogenous. There are
small areas of the meander, especially at
the corners of the stripes, where the
magnetisation is pinned and does not
correctly follow the external field. The
hysteresis is measured in a magnetic
field loop, where H y goes from -3 kA/m
to 3 kA/m and back to 0 kA/m (Hx = 3
kA/m). V0ffH/Vb denotes the shift of the
offset voltage caused by this loop.
The maximum range of output voltage
∆V0/Vb [ m V / V ] i s d e f i n e d a s th e
difference of output voltage for α = 0°
and α = 90°, where α denotes the angle
between current and magnetisation of
the magnetoresistive stripe. This means
that ∆V0/Vb represents the strength of the
magnetoresistive effect. This parameter
decreases with temperature and
determines the sensitivity of the sensor.
(An
example
of
a
typical
Magnetoresistive sensor datasheet, is
partially reproduced in Appendix B.)
AN20 - 5
Application Note 20
Issue 1 April 1996
The operating datasheet parameters of
the Wheatstone bridge are referred to an
input voltage Vb= 1V, due to the linear
relationship between input and output
voltage in this region.
The sensitivity S [mV/V/kA/m] of the
magnetoresistive sensor is defined as
the slope of the output voltage versus
external field for -1 kA/m ≤ Hy ≤1 kA/m.
This parameter depends on the
geometry of the permalloy meander and
t h e a u x i l i a r y f i e l d . T h e l a t te r i s
demonstrated in Figure 7 for Hx = 3 kA/m
a n d Hx = 6 k A / m . N o te t h e s m a l l
operating area in the case of Hy = 0 kA/m.
A high sensitivity of the sensor leads to
a small operating area for H y.
Further details and complete Magnetoresistive Product information is provided in
the Appropriate Technical Handbook: please see Technical Publication section.
Application Note 20
Issue 1 April 1996
The Wheatstone bridge is balanced
without the application of an external
field (Hy≤ 0.1 kA/m). In this case the
output voltage of the sensor is close to
zero at room temperature. The deviation
of the output voltage from zero is called
the offset voltage V0ff/Vb [mV/V]. The
offset is caused by small geometric
variations of the bridge which occur
during the photolithographic process.
The offset of the bridge is adjusted by
laser trimming. The voltage output of
each half bridge is Vb/2.
The bridge resistance Rbr [%/K] of the
ma gnetor esi sti v e s e n so r d e p e n d s
linearly on temperature. The
te m p e ra t ure coeff icient of bri dg e
resistance TCRbr [%/K] is positive. This
is typical for metals. The temperature
coefficient of sensitivity TCS [%/K] of the
sensor is negative for VB = const (TCSV),
because the strength of the
m a g n e t o r e s i s t i v e e f f e c t be c om e s
smaller with increasing temperature. In
the case of IB = const (TCSI), when the
sensor is powered by a constant current
supply, the temperature dependence of
the sensitivity is reduced due to the
linear relationship between input and
o u t p u t v o l t a ge . A hi g h e r br i d g e
resistance caused by a rise in
temperature leads to an increased
applied voltage, partly compensating
the change of sensitivity.
Figure 7
Sensor output characteristic of ZMY20/ZMZ20. The sensitivity of the sensor can be
controlled by applying an auxiliary field Hx. This auxiliary field is necessary for sensor
operation in a large field range. V0=f(Hy); HX-parameter;VB=const;Tamb=25°C.
AN20 - 4
The Wheatstone bridge cannot fully
compensate
the
temperature
de pe nd en c e of the r es i stor s. The
t e m p e r a t u r e c oe ff i c i e n t o f o f f s e t
voltage TCVoff [µV/V/K] is due to local
changes of resistivity in the permalloy
thin film and photolithographic
variations. This characteristic of the
magnetoresistive sensor limits the
measurement of small magnetic fields in
a wide temperature range, especially in
the case of static fields. Two sensors can
b e s e l e c t ed h a v in g a c omp ar a b l e
temperature coefficient. The offset drift
i s p a r t l y e l i m in a t e d b y u si n g t h e
difference of the output voltages of both
sensors. Another elegant way to avoid
offset drift is to invert the direction of the
auxiliary field and thus inverting the
output voltage of the sensor. This can be
d o n e b y s m al l c oil s p r ov idi ng an
auxiliary field that can change its
direction.
The hysteresis of output voltage V0ffH/Vb
[µV/V] describes the accuracy of the
magnetoresistive
sensor.
The
magnetisation of the permalloy stripe is
not completely homogenous. There are
small areas of the meander, especially at
the corners of the stripes, where the
magnetisation is pinned and does not
correctly follow the external field. The
hysteresis is measured in a magnetic
field loop, where H y goes from -3 kA/m
to 3 kA/m and back to 0 kA/m (Hx = 3
kA/m). V0ffH/Vb denotes the shift of the
offset voltage caused by this loop.
The maximum range of output voltage
∆V0/Vb [ m V / V ] i s d e f i n e d a s th e
difference of output voltage for α = 0°
and α = 90°, where α denotes the angle
between current and magnetisation of
the magnetoresistive stripe. This means
that ∆V0/Vb represents the strength of the
magnetoresistive effect. This parameter
decreases with temperature and
determines the sensitivity of the sensor.
(An
example
of
a
typical
Magnetoresistive sensor datasheet, is
partially reproduced in Appendix B.)
AN20 - 5
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
6
+5V
R1
10k
R3
10k
P1 10k
4
*
U1D
13
14
R3
R17
R19
10k
200k
1M
ZMZ20
6
R4 24k
B1
ZMC20
*
R14
100k
VDD
U1B
7
4
*
3
U2D
13
14
R4
R18
R20
10k
200k
1M
1k
*
R7
R2
10k
1
R21
1M
4
TL064
U3B
3
VSS
R12
1
2
10k
Output
Figure 9
Sensor for Revolution Measurement.
from disturbing fields (generated by
supp ly lines, c ar alt ernato rs e tc.)
Supporting software for these systems
is available on request.
Adjust
Offset
4
Ground
Figure 8
Overcurrent Switch using the ZMC20, for Protection of Power IGBTs.
AN20 - 7
330R
TL064
11
R22
T1
R8
20k
AN20 - 6
*
11
*
R11
10k
1
T1
BC369
680k
10k
U3A
MC33172
3
VSS
C2 470n
TL064
MC33172
4
R8
*
U2C
10
VDD
R15
100k
TL064
TL064
8
+5V
R16
100k
6
10k
9
2
7
2
TL064
4
5
R6
12
3
U2B
5
U2A
1
R9
6
2
R10
10k
*
R2
10k
TL064
5
5
U1A
3
1
R5 24k
VSS
C1 470n
8
10
*
8
1
*
*
R7
U1C
9
10k
TL064
11
*
B1
R6
680k
8
6
10k
TL064
TL064
Output
I mess
+
8,9,10
R5
1
7
2
12
Adjust Offset
11,12,13
-
R9
10k
U1B
5
U1A
3
*
Figure 10 shows an application circuit for
t h r e e - d i m e ns i on a l m a g ne ti c fi e l d
observation. When the unit is enabled, it
calibrates itself to the existing magnetic
field of the earth, and then generates a
warning signal if it is moved. The system
employs three ZMY20 sensors (one for
each dimension) and a CMOS EPROM
microcontroller with an A/D converter.
Similar circuits have been designed for
automotive immobiliser/alarm systems
that monitor the position of the vehicle
by sensing the magnetic field of a
movab le permanent magnet. This
magnet is necessary to shield the sensor
VDD
4
Figure 8 shows a ZMC20 current sensor
being used as a basis for an overcurrent
trip switch used to protect power IGBTs
within a motor driver system. The circuit
reacts within 3µs to prevent latch-up
related failure under transient/pulse
conditions, and was built within a
module measuring 35 x 20 x 25mm. An
external 10kΩ preset is required for
offset adjustment. Supply voltage is +5V
± 10% at 10mA; output is via an open
collector transistor rated ar 1A, 20V;
operating temperature range is 0 to
80°C.
R13
100k
11
[Please refer to appendix A which
summarises some graphic examples of
applic ations for m a gnetore s is tiv e
sensors].
R1
10k
*
Figure 9 provides a method for
revolution measurement by reacting to
a modulated magnetic field due to a
rotating cog. The circuit gives a signal
whose frequency is proportional to the
rotational velocity of the cog, and a high
level output for no rotation.
Applications
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
6
+5V
R1
10k
R3
10k
P1 10k
4
*
U1D
13
14
R3
R17
R19
10k
200k
1M
ZMZ20
6
R4 24k
B1
ZMC20
*
R14
100k
VDD
U1B
7
4
*
3
U2D
13
14
R4
R18
R20
10k
200k
1M
1k
*
R7
R2
10k
1
R21
1M
4
TL064
U3B
3
VSS
R12
1
2
10k
Output
Figure 9
Sensor for Revolution Measurement.
from disturbing fields (generated by
supp ly lines, c ar alt ernato rs e tc.)
Supporting software for these systems
is available on request.
Adjust
Offset
4
Ground
Figure 8
Overcurrent Switch using the ZMC20, for Protection of Power IGBTs.
AN20 - 7
330R
TL064
11
R22
T1
R8
20k
AN20 - 6
*
11
*
R11
10k
1
T1
BC369
680k
10k
U3A
MC33172
3
VSS
C2 470n
TL064
MC33172
4
R8
*
U2C
10
VDD
R15
100k
TL064
TL064
8
+5V
R16
100k
6
10k
9
2
7
2
TL064
4
5
R6
12
3
U2B
5
U2A
1
R9
6
2
R10
10k
*
R2
10k
TL064
5
5
U1A
3
1
R5 24k
VSS
C1 470n
8
10
*
8
1
*
*
R7
U1C
9
10k
TL064
11
*
B1
R6
680k
8
6
10k
TL064
TL064
Output
I mess
+
8,9,10
R5
1
7
2
12
Adjust Offset
11,12,13
-
R9
10k
U1B
5
U1A
3
*
Figure 10 shows an application circuit for
t h r e e - d i m e ns i on a l m a g ne ti c fi e l d
observation. When the unit is enabled, it
calibrates itself to the existing magnetic
field of the earth, and then generates a
warning signal if it is moved. The system
employs three ZMY20 sensors (one for
each dimension) and a CMOS EPROM
microcontroller with an A/D converter.
Similar circuits have been designed for
automotive immobiliser/alarm systems
that monitor the position of the vehicle
by sensing the magnetic field of a
movab le permanent magnet. This
magnet is necessary to shield the sensor
VDD
4
Figure 8 shows a ZMC20 current sensor
being used as a basis for an overcurrent
trip switch used to protect power IGBTs
within a motor driver system. The circuit
reacts within 3µs to prevent latch-up
related failure under transient/pulse
conditions, and was built within a
module measuring 35 x 20 x 25mm. An
external 10kΩ preset is required for
offset adjustment. Supply voltage is +5V
± 10% at 10mA; output is via an open
collector transistor rated ar 1A, 20V;
operating temperature range is 0 to
80°C.
R13
100k
11
[Please refer to appendix A which
summarises some graphic examples of
applic ations for m a gnetore s is tiv e
sensors].
R1
10k
*
Figure 9 provides a method for
revolution measurement by reacting to
a modulated magnetic field due to a
rotating cog. The circuit gives a signal
whose frequency is proportional to the
rotational velocity of the cog, and a high
level output for no rotation.
Applications
R10
100k
R9
100k
3
3
B1
ZMY20
1
2
ZMY20
B2
1
2
3
B3
ZMY20
X
X
X
X
2
3
X U1B
4066
VDD
11
4
11
1
4
4
11
4
Y
U1C Y
4066
U2A Y
4066
U2B Y
4066
2
3
MC33174
1
10
10
2
10
U3A
U2B Y
4066
12
1
2
C
13
C
12
C
5
C
13
C
C
12
4
11
8
4
X U2D
4066
9
3
T1 ZVP2106
Y
X U2C Y
4066
C
5
C
6
3
VCC
VO
33k
33k
R14
R13
33k
R12
VI
U5 ZSR600
12
13
R11
33k
9
10
1
8
14
D1 DIODE
MC33174
U3D
100k
R8
100k
R7
MC33174
U3C
S1
D3
ZRA500
R1
10k
R3 10k
R2 10k
7
Ground
22p
C2
QUARTZ
Q1
22p
C3
MC33174
U3B
100k
R5
+12V
R6
100k
5
6
*
*
*
*
*
*
R4
14
15
16
4
3
2
OSC2/CLK
OSC1
MCLR/VPP
RA4/RTCC
RA3/AIN3
RA2/AIN2
RA1/AIN1
11
12
13
RB6
RB7
10
9
8
RB5
RB4
RB3
RB2
RB1
7
1
6
RA0/AIN0 RB0/INT
1u5
C1
18
VCC
17
U4
PIC16C71
100k
VDD
VSS
X U1A Y
4066
GND
2
AN20 - 8
5
1
LS1
D2
LED
R15
430R
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
Figure 10
Sensor System used to Monitor Movement in the Earth’s Magnetic Field.
AN20 - 9
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
Appendix A
Magnetoresistive sensor Basic Function/Application Examples.
Measurement of Current (AC or DC)
Detection of Ferromagnetic Objects
Measurement of Angular Position
Measurement of Rotation Speed
Position Sensor
AN20 - 16
Measurement of the Earth’s Magnetic
Field
AN20 - 9
Application Note 20
Issue 1 April 1996
Application Note 20
Issue 1 April 1996
Appendix B
Partial Characterisation for ZMY20/30, ZMZ20/30 Magnetoresistive
Sensors.
ELECTRICAL CHARACTERISTICS (at Tamb = 25 °C and Hx = 3 kA/m unless otherwise stated)
AN20 - 12
Parameter
Symbol
Min.
Typ.
Max.
Unit
Bridge resistance
ZMY20/ZMZ20
ZMY30/ZMZ30
R br
Output voltage range
ZMY20/ZMZ20
ZMY30/ZMZ30
VO/VB
Open circuit sensitivity
ZMY20/ZMZ20
ZMY30/ZMZ30
1.2
2.0
1.7
3.0
2.2
4.0
kΩ
16
12
18
16
22
20
mV/V
S
3.2
2.0
4.0
3.0
4.8
4.0
(mV/V)/
(kA/m)
no disturbing
field Hd allowed
Hysteresis of output
voltage
VOH /VB
-
-
50
µV/V
Hy ≤ 2 kA/m
Offset voltage
Voff /VB
-1.0
-
+1.0
mV/V
Operating frequency
fmax
0
-
1
MHz
Temperature coefficient
of offset voltage
TCVoff
-3
-
+3
(µV/V)/K
Tamb =
-25...+125°C
Temperature coefficient
of bridge resistance
TCRbr
-
0.3
-
%/K
Tamb =
-25...+125°C
Temperature coefficient
of open circuit sensitivity
VB = 5 V
TCS V
-
-0.4
-
%/K
Tamb =
-25...+125°C
Temperature coefficient
of open circuit sensitivity
I B = 3 mA
TCS I
-
-0.1
-
%/K
Tamb =
-25...+125°C
AN20 -10
Test conditions
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