Hall device biasing circuit and magnetism detection circuit...

Details Hall device biasing circuit and magnetism detection circuit... Hall device biasing circuit and magnetism detection circuit...

2000-10-26

2004-04-13

Le, N. (Department: 2858)

Electricity: measuring and testing

Magnetic

Displacement

C327S511000, C324S251000, C324S252000

Reexamination Certificate

active

06720761

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Hall device biasing circuit for applying a bias voltage to each of at least two Hall devices, and a magnetism detection circuit including the same.
2. Description of the Related Art
A Hall device is used for magnetism detection in a wide range of fields including motor driving circuits, pickup control of optical disks and the like, focusing control of cameras, and TPS mounted on automobiles and the like.
FIG. 6
shows an operating principle of a Hall device. When a magnetic field having magnetic flux density B is applied to a Hall device
41
, the Hall device
41
outputs a voltage V
H
in proportion to the applied magnetic flux density B.
Systems for driving a plurality of Hall devices are classified into a constant current driving system for supplying a constant current to drive the Hall devices (in which the Hall devices are connected in series) and a constant voltage driving system for applying a constant voltage to drive the Hall devices (in which the Hall devices are connected in parallel).
FIG. 7
shows a practical example of a constant voltage driving system for driving a plurality of Hall devices
41
a
through
41
c
connected in parallel.
FIG. 8
shows a practical example of a constant current driving system for driving a plurality of Hall devices
41
a
through
41
c
connected in series.
The constant voltage driving system shown in
FIG. 7
operates in the following manner. A constant voltage is applied to each of the Hall devices
41
a
,
41
b
, and
41
c
connected in parallel from a constant voltage source
42
. Then, signal output terminals H
1
+
and H
1
−
of the Hall device
41
a
, signal output terminals H
2
+
and H
2
−
the Hall device
41
b
, and signal output terminals H
3
+
and H
3
−
of the Hall device
41
c
each output a voltage in proportion to a magnetic flux density applied to each of the Hall devices
41
a
,
41
b
and
41
c.
According to this system, the Hall devices
41
a
,
41
b
and
41
c
are each driven at a constant voltage.
The constant current driving system shown in
FIG. 8
for driving the Hall devices
41
a
,
41
b
, and
41
c
connected in series is disclosed in, for example, Japanese Laid-Open Publication No. 9-65682. A voltage from a motor driving circuit
43
is applied to the Hall devices
41
a
,
41
b
, and
41
c
, and the Hall devices
41
a
through
41
c
are each driven by a constant current. Accordingly, even when the number of Hall devices is increased or decreased, the driving current of the entire driving circuit does not change much.
An output voltage V
H
of the Hall device driven by the constant current driving system is represented by expression (1), and an output voltage V
H
of the Hall device driven by the constant voltage driving system is represented by expression (
2
).
V
H
=(
RH/d
)·
Ic·B
  (1)
V
H
=&mgr;H·
(
W/L
)
·Vin·B
  (2)
In the expressions (1) and (2), B represents the magnetic flux density applied to the Hall device, d represents the thickness of a magnetic field sensing portion in the Hall device (thickness of the Hall device), and W and L respectively represent the width and length of the magnetic field sensing portion in the Hall device with respect to the driving voltage. Ic represents a driving current in the constant current driving system, and Vin is a driving voltage in the constant voltage driving system. In expression (1), RH represents a Hall coefficient of the Hall device and is represented by RH=1/(e·n), where e is a charge amount of electrons, and n is a carrier concentration of the Hall device. In expression (2), &mgr;H is an electron mobility of a semiconductor in the Hall device.
It is now assumed that the magnetic flux density B is constant and the size of the magnetic field sensing portion of the Hall device is constant. By the constant current driving system, since the driving current Ic is constant, the output voltage V
H
of the Hall device is in proportion to the Hall coefficient RH based on expression (1). By the constant voltage driving system, since the driving voltage Vin is constant, the output voltage V
H
of the Hall device is in proportion to the electron mobility &mgr;H based on expression (2). Generally, it is known that the Hall coefficient RH is high in temperature dependency and that the electron mobility &mgr;H is low in temperature dependency.
The constant voltage driving system shown in
FIG. 7
provides better temperature characteristics than the constant current driving system, and thus the Hall devices
41
a
through
41
c
in
FIG. 7
each output a voltage which is stable against a change in the ambient temperature. However, the constant voltage driving system requires a driving current in proportion to the number of Hall devices used, and thus has a disadvantage in that when a great number of Hall devices are used, the current consumption cannot be suppressed. This can be a very serious problem in a circuit having an especially large number of Hall devices due to the significant increase in the current consumption.
By the constant current driving system shown in
FIG. 8
, a driving current provided by the motor driving circuit
43
as a power source is used sequentially for the Hall devices
41
a
through
41
c
which are connected in series. Accordingly, even when the number of Hall devices is increased, the amount of the driving current passing through the Hall devices is not increased. However, in such a case, the problem that the temperature dependency is raised as described above.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a Hall device biasing circuit includes a plurality of terminals for applying a bias voltage to a plurality of Hall devices connected in series, respectively.
In one embodiment of the invention, the Hall device biasing circuit further includes a constant voltage supply section for supplying a constant bias voltage to each of the plurality of terminals.
In one embodiment of the invention, the constant voltage supply section includes a constant voltage supply circuit in correspondence to the plurality of Hall devices.
In one embodiment of the invention, the constant voltage supply section includes: a constant voltage supply circuit, at least one current path through which a bias correction current flows from one of the plurality of terminals to another of the plurality of terminals, and a correction current supply section for selecting one of the at least one current path based on a current amount therein and adjusting the current amount in the selected current path to supply the bias correction current.
In one embodiment of the invention, the correction current supply section includes: a constant voltage generation circuit, and a comparison section connected to the at least one current path for selecting one of the at least one current path based on a current amount therein and adjusting the current amount in the selected current path based on a current amount flowing through the at least one current path and a current amount generated in the constant voltage generation circuit.
In one embodiment of the invention, the constant voltage supply section uses a supply voltage outside the Hall device biasing circuit.
In one embodiment of the invention, the constant voltage supply section includes: at least one current path through which a bias correction current flows from one of the plurality of terminals to another of the plurality of terminals, and a correction current supply section for selecting one of the at least one current path based on a current amount therein and adjusting the current amount in the selected current path to supply the bias correction current.
In one embodiment of the invention, the correction current supply section includes: a reference voltage source, and a comparison section connected to the at least one current path for selecting one of the at least one current path based on a current amount therein and adjusting the current

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