U.S. patent application number 09/380315 was filed with the patent office on 2002-02-21 for magnetic sensor with a signal processing circuit having a constant current circuit.
Invention is credited to ISHIBASHI, KAZUTOSHI, SHIBASAKI, ICHIRO.
Application Number | 20020021126 09/380315 |
Document ID | / |
Family ID | 26386487 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020021126 |
Kind Code |
A1 |
ISHIBASHI, KAZUTOSHI ; et
al. |
February 21, 2002 |
MAGNETIC SENSOR WITH A SIGNAL PROCESSING CIRCUIT HAVING A CONSTANT
CURRENT CIRCUIT
Abstract
A magnetic sensor with a signal processing circuit includes a
magnetic sensor section 4 composed of a compound semiconductor thin
film or a magnetic thin film, and a signal processing circuit 5 for
amplifying a magnetic signal the magnetic sensor section detects as
an electrical output. The signal processing circuit 5 includes an
operational amplifier 51 and a constant current circuit 52 for
carrying out feedback. The constant current circuit 52 in the
signal processing circuit 5 includes a plurality of resistors with
two or more different temperature coefficients, and the current
output from the constant current circuit has a temperature
coefficient inversely proportional to the temperature coefficient
of the combined resistance of the plurality of the resistors.
Inventors: |
ISHIBASHI, KAZUTOSHI;
(SHIZUOKA, JP) ; SHIBASAKI, ICHIRO; (SHIZUOKA,
JP) |
Correspondence
Address: |
PENNIE & EDMONDS
1155 AVENUE OF THE AMERICAS
NEW YORK
NY
100362711
|
Family ID: |
26386487 |
Appl. No.: |
09/380315 |
Filed: |
August 27, 1999 |
PCT Filed: |
February 27, 1998 |
PCT NO: |
PCT/JP98/00841 |
Current U.S.
Class: |
324/251 |
Current CPC
Class: |
G01R 33/07 20130101;
G01D 3/036 20130101 |
Class at
Publication: |
324/251 |
International
Class: |
G01R 033/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 1997 |
JP |
046,376/1997 |
Jun 27, 1997 |
JP |
172,114/1997 |
Claims
What is claimed is:
1. A magnetic sensor with a signal processing circuit comprising: a
magnetic sensor section composed of one of a compound semiconductor
thin film and a magnetic thin film; and a signal processing circuit
for amplifying a magnetic signal said magnetic sensor section
detects as an electrical output, wherein said signal processing
circuit includes an operational amplifier and a constant current
circuit for carrying out feedback.
2. The magnetic sensor with a signal processing circuit as claimed
in claim 1, wherein said constant current circuit feeds a different
current value corresponding to an output of the operational
amplifier back to an non-inverting input terminal of the
operational amplifier.
3. The magnetic sensor with a signal processing circuit as claimed
in claim 2, wherein said constant current circuit includes a
plurality of resistors with at least two different temperature
coefficients, and the current said constant current circuit outputs
has a temperature coefficient which is inversely proportional to a
temperature coefficient of a combined resistance of the plurality
of the resistors.
4. The magnetic sensor with a signal processing circuit as claimed
in claim 3, wherein the combined resistance of the plurality of
resistors has a temperature coefficient that corrects a temperature
coefficient of an internal resistance of said magnetic sensor
section and a temperature coefficient of sensitivity of said
magnetic sensor section.
5. The magnetic sensor with a signal processing circuit as claimed
in claim 4, wherein the plurality of resistors have temperature
coefficients that correct not only the temperature coefficient of
the internal resistance of said magnetic sensor section and the
temperature coefficient of the sensitivity of said magnetic sensor
section, but also a temperature coefficient of an object to be
detected by said magnetic sensor section.
6. The magnetic sensor with a signal processing circuit as claimed
in any one of claims 1-5, wherein said signal processing circuit is
a monolithic IC.
7. The magnetic sensor with a signal processing circuit as claimed
in any one of claims 1-5, wherein said signal processing circuit is
formed on one of an insulated substrate and an insulating layer
formed on a semiconductor substrate.
8. The magnetic sensor with a signal processing circuit as claimed
in claim 6, wherein said signal processing circuit is formed on one
of an insulated substrate and an insulating layer formed on a
semiconductor substrate.
9. A magnetic sensor with a signal processing circuit comprising: a
magnetic sensor section composed of one of a compound semiconductor
thin film and a magnetic thin film; and a signal processing circuit
for amplifying a magnetic signal said magnetic sensor section
detects as an electrical output, wherein said signal processing
circuit includes a plurality of feedback resistors with at least
two different temperature coefficients, and the plurality of
resistors feed an output of an operational amplifier back to its
non-inverting input terminal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a magnetic sensor, and more
particularly to a magnetic sensor with a signal processing circuit,
which is usable as a sensor such as a proximity switch, current
sensor, or encoder.
BACKGROUND ART
[0002] As a magnetic sensor with a signal processing circuit, a
Hall IC is well known which employs a Hall element as its sensor.
As a typical conventional Hall IC, a silicon (Si) monolithic Hall
IC (referred to as "Si Hall IC" from now on) has a magnetic sensor
section in the form of a Hall element made of silicon (Si), and a
signal processing IC section for processing a signal detected by
the magnetic sensor section.
[0003] This type of the magnetic sensor has a low sensitivity to
magnetic field because the magnetic sensor section of the Si Hall
IC consists of the Hall element made of Si with a small electron
mobility, and hence to operate the Hall IC as a magnetic sensor,
large magnetic field must be applied to it. In other words, the
Hall IC has a problem of a low sensitivity to magnetic field.
[0004] In addition, it is known that Si generates some voltage when
mechanical stress is applied from outside.
[0005] Thus, the Si Hall IC has another problem of varying its
sensitivity to magnetic field because of the voltage generated in
the Hall element of the magnetic sensor section when external
stress is applied.
[0006] Such problems must be considered when fabricating highly
accurate, highly reliable proximity switches, current sensors or
encoders by using the Si Hall IC.
[0007] Therefore, a magnetic sensor with a signal processing
circuit is desired which can achieve accurate detection of a magnet
position or magnetic field strength with a high sensitivity
independent of external stress and with stable characteristics.
Such a magnetic sensor has not yet been realized because of great
difficulty.
[0008] On the other hand, various methods are studied to achieve
highly accurate detection of the magnet position or magnetic field
strength. For example, sensors, which use a Hall element as their
magnetic sensor and include a signal processing circuit composed of
discrete components such as an operational amplifier or resistors,
are applied to the proximity switches, current sensors or
encoders.
[0009] In these methods, however, users are required to have
special technical expertise to understand the characteristics of
the sensor, to implement optimum circuit design, and to acquire
discrete components and assemble them. In addition, it is
unavoidable that their cost and size increase because the sensors
are implemented by mounting on a circuit board the magnetic sensor
element and the signal processing circuit consisting of the
discrete components, and this presents a critical problem in the
field of sensors that requires low cost and small size.
[0010] For example, in a conventional technique as shown in FIG. 12
(Japanese Patent Application Laid-open No. 38920/1990), the signal
processing circuit comprises magnetoresistive elements 60 and 70
constituting a discrete magnetic sensor, resistors 6, 7 and 7' and
an operational amplifier 51, and its feedback resistance is
composed of the combined resistance of the resistors 6, 7 and 7'
with different temperature coefficients to form a feedback loop
from the output terminal of the operational amplifier 51 to its
inverting input terminal, thereby implementing magnetic
characteristics with a desired temperature characteristic. This
circuit configuration, however, has the foregoing problem of
increasing the cost and size. Besides, the circuit configuration
has another problem of decreased yield when obtaining an intended
output because of the variations in the output voltage due to the
variations in the midpoint potential of the magnetoresistive
elements 60 and 70. Furthermore, since the midpoint potential
usually drifts in accordance with temperature, the drift appears in
the output voltage of the circuit, and has an adverse effect on the
temperature characteristic of the output signal of the sensor. This
offers a problem of making it difficult to obtain the desired
temperature characteristic.
[0011] In addition, although the configuration of FIG. 12 can
freely use the discrete resistors 6, 7 and 7' with different
temperature coefficients to implement the magnetic characteristics
with the desired temperature characteristic, it discloses nothing
about the implementation of a circuit like the Si monolithic
IC.
[0012] Still another problem arises in that a common conventional
Si Hall IC as shown in FIG. 14, which includes a signal processing
circuit section 20a and a magnetic sensor section 30a that are
electrically isolated from a substrate 21a only through the PN
junction, for example, cannot perform stable operation in an
ambient temperature above 125.degree. C., and cannot operate at all
beyond 150.degree. C.
[0013] On the other hand, a technique is known which improves the
temperature characteristics by reflecting the temperature
dependence of the output resistance of a Hall element to a
threshold voltage by employing the output resistance of the Hall
element as the input resistance of a Schmidt trigger circuit.
Specifically, in a circuit configuration as shown in FIG. 15, the
threshold voltage Vth of the Schmidt trigger circuit is expressed
as Vth=(Vdo-V1).multidot.Rho/RF, where V1 is the potential at the
inverting input terminal of the operational amplifier 51; RF is the
feedback resistance; Vdo is the output potential of the amplified
output signal 18 of the operational amplifier 51; and Rho is half
the output resistance of the Hall element 4 (Japanese Patent
Application Laid-open No. 226982/1986).
[0014] Here, the potential V1 causes a problem. Since the potential
V1, which is the output potential of the Hall element 4, is about
half the product of the input resistance Rhi of the Hall element 4
and the Hall element driving current Ic, the variations in Rhi
causes the variations in V1. This in turn causes the variations in
Vth, which makes it impossible to establish the threshold voltage
exactly at a value designed. This results in the Hall IC with
magnetic characteristics different from those designed, thereby
reducing the yield.
[0015] The potential at the output terminal of the Hall element 4,
which equals about half the input voltage to the Hall element, is
referred to as a midpoint potential of the Hall element. The value
has certain distribution due to the production variations of the
Hall elements, and the variations in the midpoint potential also
cause the variations in V1, resulting in the reduction in the
yield.
DISCLOSURE OF THE INVENTION
[0016] The inventors of the present invention intensively conducted
the research to implement practical magnetic sensors capable of
solving the foregoing problems of the magnetic sensor.
[0017] We aim to fabricate a highly sensitive, stable operation
magnetic sensor with a signal processing circuit by forming the
magnetic sensor with a structure of isolating the magnetic sensor
section from the signal processing circuit consisting of a Si
IC.
[0018] To implement a highly sensitive magnetic sensor with a
signal processing circuit with stable operation characteristics, we
study a magnetic sensor with a signal processing circuit that
combines the signal processing circuit with a highly sensitive
magnetic sensor composed of a compound semiconductor thin film or a
magnetic thin film, which has a higher sensitivity in the magnetic
field than the Si Hall element and can provide a stable magnetic
sensor output independently of the mechanical external stress.
[0019] As a result, the inventors of the present invention invented
a hybrid Hall IC which employed the compound semiconductor as the
sensor, and combined it with a Si monolithic IC to be packed in a
single package.
[0020] The present invention can implement a versatile,
inexpensive, small size, high performance magnetic sensor with a
signal processing circuit that does not require users to have any
technical expertise such as special circuit technique, thereby
making it possible to achieve detection of a magnet position or
magnetic field strength at high accuracy.
[0021] In contrast with this, the conventional techniques cannot
avoid the reduction in the yield of the Hall ICs because of the
variations involved in producing the Hall elements or ICs. In
addition, it cannot solve a problem of an increase in cost for
improving the accuracy of circuit components of the ICs.
[0022] Furthermore, there is another problem in that as the
temperature rises, the resistance increases of the compound
semiconductor thin film or magnetic thin film constituting the
magnetic sensor, and the output of the magnetic sensor reduces.
Therefore, the magnetic sensor, when combined with the signal
processing circuit without any change, has a problem of reducing
the output of the magnetic sensor with a signal processing circuit
as the temperature rises, that is, a problem of large dependence on
temperature. This causes a critical problem in implementing highly
accurate, practical detection because a magnet, a common object to
be detected by the magnetic sensor with a signal processing
circuit, has an inclination to reduce its magnetic flux density as
the temperature rises.
[0023] The inventors of the present invention conducted researches
to solve the problems.
[0024] The present invention is implemented to solve the problems,
that is, to provide a magnetic sensor with a signal processing
circuit without being affected from the magnetic sensor side. In
other words, an object of the present invention is to prevent the
reduction in the yield of the Hall IC due to the variations
involved in producing the Hall elements or the variations in ICs,
and to make it possible to reduce the number of components in the
IC circuit and the demand for the accuracy, thereby achieving the
improvement in the yield and reducing the cost.
[0025] Another object of the present invention is to implement a
high performance magnetic sensor with a signal processing circuit
having little dependence on temperature over a wide temperature
range by correcting the temperature coefficients of the resistors
and sensitivity of the magnetic sensor with a simple structure.
Still another object of the present invention is to implement a
high performance magnetic sensor with a signal processing circuit
that can reduce the dependence of the sensor output on the
temperature even if the magnetic field to be detected has large
dependence on temperature as in the case of detecting the magnetic
field of a permanent magnet.
[0026] In the first aspect of the present invention, there is
provided a magnetic sensor with a signal processing circuit
comprising:
[0027] a magnetic sensor section composed of one of a compound
semiconductor thin film and a magnetic thin film; and
[0028] a signal processing circuit for amplifying a magnetic signal
the magnetic sensor section detects as an electrical output,
[0029] wherein the signal processing circuit includes an
operational amplifier and a constant current circuit for carrying
out feedback.
[0030] Here, the constant current circuit may feed a different
current value corresponding to an output of the operational
amplifier back to an non-inverting input terminal of the
operational amplifier.
[0031] The constant current circuit may include a plurality of
resistors with at least two different temperature coefficients, and
the current the constant current circuit outputs may have a
temperature coefficient which is inversely proportional to a
temperature coefficient of a combined resistance of the plurality
of the resistors.
[0032] The combined resistance of the plurality of resistors may
have a temperature coefficient that corrects a temperature
coefficient of an internal resistance of the magnetic sensor
section and a temperature coefficient of sensitivity of the
magnetic sensor section.
[0033] The plurality of resistors may have temperature coefficients
that correct not only the temperature coefficient of the internal
resistance of the magnetic sensor section and the temperature
coefficient of the sensitivity of the magnetic sensor section, but
also a temperature coefficient of an object to be detected by the
magnetic sensor section.
[0034] The signal processing circuit may be a monolithic IC.
[0035] The signal processing circuit may be formed on one of an
insulated substrate and an insulating layer formed on a
semiconductor substrate.
[0036] In the second aspect of the present invention, there is
provided a magnetic sensor with a signal processing circuit
comprising:
[0037] a magnetic sensor section composed of one of a compound
semiconductor thin film and a magnetic thin film; and
[0038] a signal processing circuit for amplifying a magnetic signal
the magnetic sensor section detects as an electrical output,
[0039] wherein the signal processing circuit includes a plurality
of feedback resistors with at least two different temperature
coefficients, and the plurality of resistors feed an output of an
operational amplifier back to its non-inverting input terminal.
[0040] Here, the magnetic sensor with a signal processing circuit
in accordance with the present invention has the magnetic sensor
section consisting of a compound semiconductor thin film, which can
be any type of magnetic sensor that utilizes the Hall effect,
magnetoresistance effect, or magnetic thin film based
magnetoresistance effect. It is particularly preferable to utilize
Hall elements or magnetoresistive elements which are composed of
InAs (indium arsenic), GaAs (gallium arsenic), InGaAs (indium
gallium arsenic), InSb (indium antimony), InGaSb (indium gallium
antimony), etc., or magnetic thin film magnetoresistive elements
composed of NiFe (nickel iron), NiCo (nickel cobalt), etc., or the
magnetic sensors combining them.
[0041] Here, the compound semiconductor thin film refers to a thin
film formed on a substrate by a common process technique of the
semiconductor such as CVD (chemical vapor deposition), MBE
(molecular beam epitaxy), vacuum evaporation, or sputtering, or to
a thin film formed by shaving a semiconductor ingot, or to an
active layer formed on the surface of a semiconductor substrate by
ion implantation or diffusion.
[0042] The signal processing circuit of the magnetic sensor with a
signal processing circuit in accordance with the present invention
can be a common circuit produced with micro-structure. A circuit
integrated on a Si substrate is preferable regardless of whether
the circuit components have the MOS structure, bipolar structure,
or hybrid structure thereof. Furthermore, as long as having the
signal processing function, a circuit integrated on a GaAs
substrate is also preferable. Moreover, a micro-structure circuit
with a small size formed on a ceramic substrate is preferable, as
well.
[0043] The foregoing plurality of resistors can have temperature
coefficients that can correct not only the temperature coefficient
of the internal resistance of the magnetic sensor section and the
temperature coefficient of the sensitivity, but also the
temperature coefficient of the object to be detected by the
magnetic sensor section.
[0044] The signal processing circuit of the magnetic sensor of the
signal processing circuit can be a circuit fabricated in
micro-structure. For example, it can have such a structure that the
circuit is formed on an insulated substrate like a circuit formed
on a ceramic substrate. Alternatively, the signal processing
circuit can be a circuit integrated on an insulating layer or
high-resistance layer formed on a Si substrate. It can also be
structured integrally with the semiconductor or ferromagnetic
sensor formed on the surface of an IC.
[0045] The insulated substrate, insulating layer, or
high-resistance layer refers to a substrate or a layer with a
resistivity of equal to or more than 10 raised to the fifth to
seventh power .OMEGA..multidot.cm excluding the PN junction
insulation structure, such as a substrate or layer made of ceramic,
silicon oxide or alumina.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a circuit diagram showing a first embodiment in
accordance with the present invention;
[0047] FIG. 2 is a circuit diagram showing a sixth embodiment in
accordance with the present invention;
[0048] FIG. 3 is a circuit diagram showing a second embodiment in
accordance with the present invention;
[0049] FIG. 4 is a circuit diagram showing a variation of a third
embodiment in accordance with the present invention;
[0050] FIG. 5 is a circuit diagram showing a variation of a fourth
embodiment in accordance with the present invention;
[0051] FIG. 6 is a circuit diagram showing a fifth embodiment in
accordance with the present invention;
[0052] FIG. 7 is a graph showing the results of comparing the
dependence of operating magnetic flux density on temperature when
carrying out the digital signal processing using the circuit in
accordance with the present invention and a circuit for
comparison;
[0053] FIG. 8 is a characteristic diagram illustrating
relationships between the output voltage after digital conversion
and applied magnetic flux density;
[0054] FIG. 9 is a graph showing the results of comparing the
dependence of the operating magnetic flux density on temperature
when carrying out the digital signal processing using the circuit
in accordance with the present invention and a circuit for
comparison;
[0055] FIG. 10 is a characteristic diagram illustrating the
dependence of the operating magnetic flux density on temperature
when comparing that of the signal processing circuit in accordance
with the present invention formed on a ceramic substrate with that
of a common Si integrated circuit;
[0056] FIG. 11A is a cross-sectional view showing a substrate
structure including the signal processing section of FIGS. 1-5;
[0057] FIG. 11B is a cross-sectional view showing another substrate
structure;
[0058] FIG. 12 is a diagram showing a conventional signal
processing circuit for comparison;
[0059] FIG. 13 is a diagram showing another conventional signal
processing circuit for comparison;
[0060] FIG. 14 is a cross-sectional view showing a substrate
structure of the signal processing section of a conventional
circuit;
[0061] FIG. 15 is a diagram showing a still another conventional
signal processing circuit for comparison,
[0062] FIG. 16 is a diagram showing a detail of an amplifier in the
signal processing circuit in accordance with the present
invention;
[0063] FIG. 17 is a diagram showing the details of the circuit
diagram of FIG. 16; and
[0064] FIG. 18 is a diagram showing another detail of the amplifier
in the signal processing circuit in accordance with the present
invention;
BEST MODE FOR CARRYING OUT THE INVENTION
[0065] The embodiments in accordance with the present invention
will now be described with reference to the accompanying
drawings.
[0066] Embodiment 1
[0067] In the embodiment as shown in FIG. 1, a voltage source 1
drives a signal processing circuit 5, and a Hall element 4 through
a constant current source 50. The two output terminals of the Hall
element 4 are connected to the inverting input terminal and
non-inverting input terminal of an operational amplifier in the
signal processing circuit 5. Besides, a constant current i.sub.f
fed from a constant current circuit 52 in the signal processing
circuit 5 is fed back to the non-inverting input terminal of the
operational amplifier. With such an arrangement, the present
embodiment forms a Schmidt trigger circuit, that is, a digital
processing circuit.
[0068] In the embodiment of FIG. 1, since the feedback consists of
the constant current i.sub.f fed from the constant current source
rather than the resistance RF, the threshold voltage Vth of the
digital processing circuit is expressed as Vth=Rho.times.i.sub.f,
where Rho is about half the Hall element output resistance.
Accordingly, threshold voltage Vth is free from the effect of the
potential V1 at the inverting input. terminal of the operational
amplifier. This means that the threshold voltage Vth is unaffected
by the variations in the input resistance of the Hall element 4 or
the variations in the midpoint potential, thereby implementing the
designed magnetic characteristics and improving the yield
markedly.
[0069] The detailed structure of the signal processing circuit as
shown in FIGS. 1-5 will now be described by way of example of the
structures as shown in FIGS. 16 and 18.
[0070] In FIG. 16, reference numeral 5 designates the signal
processing circuit comprising the operational amplifier 51, the
constant current circuit 52 and a buffer circuit 53. The inverting
input terminal and non-inverting input terminal of the operational
amplifier 51 are connected to the two output terminals of the Hall
element 4 so that the output resistance of the Hall element 4
serves as the input resistance of the operational amplifier 51. In
response to the output of the operational amplifier 51, the
constant current circuit 52 can output one of the two constant
current values i1 and i2 (i1>i2), and feeds the output current
back to the non-inverting input terminal of the operational
amplifier 51. More specifically, the constant current circuit 52
outputs i1 when the output of the operational amplifier 51 is
"High", and i2 when the output of the operational amplifier 51 is
"Low" to achieve the positive feedback so that the operational
amplifier 51 and the constant current circuit 52 function as a
Schmidt trigger circuit. The buffer circuit 53 extracts the output
of the operational amplifier 51 without disturbing the operation of
the Schmidt trigger circuit composed of the operational amplifier
51 and constant current circuit 52. FIG. 18 shows another example
of the signal processing circuit 5 composed of the operational
amplifier 51, constant current circuit 52 and buffer circuit 53
connected in cascade, whose operation is the same as that of FIG.
16.
[0071] Embodiment 2
[0072] FIGS. 3-5 show different configurations of the embodiments
in accordance with the present invention.
[0073] FIG. 3 shows a circuit configuration in which the Hall
element 4 is sandwiched between a pair of driving resistors 2 and 3
at its top and bottom, which are used in place of the Hall element
driving constant current source 50 as shown in FIG. 1. It is not
necessary to match the resistance values of the resistors 2 and 3
because they are free from the effect of V1. This can obviate the
relative accuracy of the resistors, thereby offering an advantage
of being able to prevent the reduction in the yield when forming
the magnetic sensor in a monolithic IC.
[0074] Embodiments 3 and 4
[0075] FIG. 4 shows a circuit configuration in which the driving
resistor 2 is connected to only the plus side of the input of the
Hall element 4; and FIG. 5 shows a circuit configuration in which
the driving resistor 3 is connected to only the minus side of the
input of the Hall element 4. The configurations as shown in FIGS.
3-5 can each achieve similar effect to that of the configuration as
shown in FIG. 1.
[0076] Embodiment 5
[0077] FIG. 6 shows a fifth example in accordance with the present
invention. It is an example of the signal processing circuit for
implementing a high performance magnetic sensor with a signal
processing circuit that can stabilize the output by reducing the
temperature dependence of the output signal to approximately zero
in a wide temperature range. The present invention makes it
possible to obtain the sensor output independent of the temperature
even when detecting the magnetic field with considerable
temperature dependence like the magnetic field of a permanent
magnet.
[0078] In the present embodiment, resistors 6 and 7 are connected
in series across the output signal after the amplification by the
operational amplifier 51 and the non-inverting input terminal, as a
digital signal processing feedback resistance. This forms a Schmidt
trigger circuit (which may be simply called "digital processing
circuit" from now on) with a threshold voltage proportional to the
feedback quantity. Thus, the operational amplifier 51 has a maximum
output voltage when the voltage at the non-inverting input terminal
is higher than the voltage at the inverting input terminal, and a
minimum output voltage in the opposite case, thereby operating as a
comparator. FIG. 8 is a diagram illustrating the relationships
between the output voltage (Vdo) after the digital conversion and
the magnetic flux density applied to the Hall element. The magnetic
flux density at which the output voltage varies from high to low is
referred to as operating magnetic flux density (Bop), whereas the
magnetic flux density at which the output voltage changes from low
to high is called return magnetic flux density (Brp).
[0079] As shown in FIG. 6, the voltage source 1 drives the
operational amplifier 51 and the InAs Hall element 4 through the
driving resistors 2 and 3. The InAs Hall element constitutes a
magnetic sensor section 30. The output resistance of the InAs Hall
element 4 serves as the input resistance of the operational
amplifier 51 so as to form a Schmidt trigger circuit with a pair of
feedback resistors 6 and 7 (Rf1 and Rf2) with different temperature
coefficients, which are fed back to the non-inverting input
terminal of the operational amplifier 51. With such an arrangement,
the threshold voltage is expressed as
Vth=(Vdo-V1).multidot.Rho/(Rf1+Rf2). The signal processing circuit
section 20 is composed of the driving resistors 2 and 3,
operational amplifier 51 and resistors 6 and 7. When the effect of
V1 is negligible, setting the resistance values of Rf1 and Rf2 at
appropriate values can adjust the temperature coefficient of Vth.
This makes it possible to correct the temperature coefficients of
both the internal resistance and sensitivity of the InAs Hall
element 4, thereby enabling the Bop and Brp to have any desired
temperature coefficients. The resistors 6 and 7 can also be
connected in parallel.
[0080] In this way, the sensor output without the temperature
dependence with respect to the magnetic field can be obtained.
[0081] In addition, since the temperature coefficient of a
permanent magnet can be measured in advance, even if the magnetic
field to be detected has the temperature dependence like the
magnetic field of the permanent magnet, adjusting the ratio of the
resistance values of Rf1 and Rf2 enables the temperature
coefficient of the permanent magnet to be corrected, thereby making
it possible to eliminate the temperature dependence of the sensor
output.
[0082] Although the InAs Hall element is used as the magnetic
sensor in the fifth embodiment, a magnetic thin film
magnetoresistive element (NiFe) is usable in place of it.
[0083] Embodiment 6
[0084] FIG. 2 shows a sixth example in accordance with the present
invention, and FIG. 17 shows a detailed structure of its signal
processing circuit. As part of a structural component for
determining the two constant current values i1 and i2 are applied a
plurality of resistors (two resistors R1 and R2 in this case) with
different temperature coefficients in the signal processing circuit
51, particularly in the constant current circuit 52, so that the
two or more constant current values i1 and i2 are inversely
proportional to the temperature coefficient of the combined
resistance of the resistors R1 and R2 with the different
temperature coefficients, which are connected in series or in
parallel or in a combination thereof, that is, i1.varies.1/(R1+R2)
and i2.varies.1/(R1+R2), thereby making it possible to provide any
desired temperature coefficient such as Vth1=Rho.times.i1 and
Vth2=Rho.times.i2. In addition to the effect of FIG. 6, this can
eliminate the influence of V1, and hence can ensure that the output
signal of the signal processing circuit 5 has any desired
temperature coefficient such as the temperature coefficient for
correcting the temperature coefficients of both the internal
resistance and sensitivity of the magnetic sensor section 4, or the
temperature coefficient for correcting the temperature coefficient
of the object to be detected by the magnetic sensor section.
[0085] Although the circuit configurations of the foregoing
embodiments can each realize their signal processing circuit
section using a Si monolithic IC, resistance implemented by a
common Si monolithic IC can include both a low sheet resistance
with a rather low temperature coefficient, and a high sheet
resistance with a rather high temperature coefficient. In the Si
monolithic IC, the difference in the temperature coefficients has
long been considered as a negative factor or an unacceptable
characteristic in the circuit technique. The present invention,
however, positively utilizes the difference to create the desired
temperature coefficient in the form of the combined resistance
composed of a series or parallel connection, or the combination of
the series and parallel connections. This makes it possible to
generate the constant current to be fed back, which is inversely
proportional to the temperature coefficient, thereby implementing
in the Si monolithic IC the magnetic sensor with a signal
processing circuit having a temperature coefficient of any desired
magnetic characteristics, which has been conventionally considered
as impossible.
[0086] Embodiment 7
[0087] The operation of the circuit elements in the signal
processing circuit section formed in a common Si IC have been
considered to be unstable at high temperatures beyond 125.degree.
C. because they are formed in the surface of the Si substrate with
a structure which electrically isolates them from the substrate by
the PN junction, and the current leakage of the PN junction for the
isolation increases at high temperatures. In view of this, we form
the circuit elements on the surface of an insulated substrate, as a
circuit configuration with a small leakage current to the
substrate. As a result, we found that the leakage current to the
substrate has large effect on the stable operation at the high
temperatures.
[0088] The present embodiment employs a signal processing circuit
with the structure that can reduce the leakage current to the
substrate, and arranges the magnetic sensor by combining the signal
processing circuit with a compound semiconductor magnetic sensor or
with a magnetic thin film magnetoresistive element.
[0089] FIG. 11A shows a structure of a substrate including the
signal processing circuit section 20 as shown in each of FIGS. 1-6.
The integrated circuit of the signal processing circuit section 20
has a structure formed on an insulated ceramic substrate. In other
words, the semiconductor circuit elements as the signal processing
circuit section 20 are formed on an insulated substrate 21. Such a
structure enables a stable operation in the high ambient
temperature.
[0090] Furthermore in FIG. 1A, a magnetic sensor section 30 is
formed on the insulated substrate 21 on which the signal processing
circuit section 20 is formed. The magnetic sensor 30 can also be
formed on the signal processing circuit section 20 via an
insulating layer, or formed on a substrate other than the insulated
substrate 21.
[0091] Embodiment 8
[0092] FIG. 11B shows another example of the substrate structure
including the signal processing circuit section 20. An insulating
layer 22 such as SiO.sub.2 is formed on a Si substrate 23, and the
semiconductor circuit elements are formed on the insulating layer
22 as the signal processing circuit section 20. The structure also
offers an advantage of being able to achieve stable operation at
high temperatures.
[0093] In FIG. 11B, the magnetic sensor section 30 is formed on the
insulating layer 22 of the Si substrate 23, on which the signal
processing circuit section 20 is formed. The magnetic sensor 30 can
also be formed on the signal processing circuit section 20 via an
insulating layer, or formed on a substrate other than the Si
substrate 23.
[0094] The circuit configuration as shown in FIG. 11A or 11B
enables the stable signal processing operation up to the
temperature 175.degree. C., which has been impossible previously.
This makes it possible to implement a highly accurate, highly
reliable magnetic sensor with an amplifier.
[0095] Next, some experimental results will be shown which
comparatively studied the foregoing embodiments in accordance with
the present invention with the conventional one.
EXPERIMENTAL EXAMPLES
Experimental Example 1
[0096] FIG. 7 comparatively shows the temperature dependence of the
operating magnetic flux density (Bop) obtained by using the InAs
Hall element 4 as the sensor in the circuit as shown in FIG. 2,
which was implemented in the form of the Si monolithic IC.
[0097] FIG. 7 shows the results of experiments in which the
temperature coefficient of the resistor R1 was set at 2000
ppm/.degree. C., that of the other resistor R2 was set at 7000
ppm/.degree. C., and the ratio of R1 and R2 was set at 2:8 or
7:3.
[0098] For comparison, the temperature dependence of the operating
magnetic flux density (Bop) is also illustrated which was obtained
by using the InAs Hall element 4 as a sensor in the circuit as
shown in FIG. 13.
[0099] Using the digital output circuit in accordance with the
present invention can establish the temperature coefficient of the
operating magnetic flux density at approximately zero in a wide
temperature range when the ratio of R1 and R2 is 7:3. Furthermore,
in the case where the ratio of R1 and R2 is 2:8, the temperature
coefficient can be set at -0.18%/.degree. C., which is the same as
the temperature coefficient of a common ferrite magnet. Thus, when
detecting the magnetic field formed by the ferrite magnet, the
temperature dependence of the sensor output can be reduced to
approximately zero by designing the ratio of R1 and R2 at 2:8.
[0100] Moreover, since the resistor R1 was formed using a common
resistance whose sheet resistance is rather small in the Si
integrated circuit, and the resistor R2 was formed using a
resistance whose sheet resistance is comparatively large to create
the high resistance, the circuit configuration in accordance with
the present invention can obviate the necessity for preparing the
resistors with special temperature coefficients that match the
temperature coefficients of the sensitivity and resistance of the
InAs Hall element because the resistors can be implemented by
combining the values of the two types of the resistors formed
through the common process. This offers an advantage of being able
to implement the IC circuit at low cost without adding any special
process to the IC fabrication.
Experimental Example 2
[0101] FIG. 9 also comparatively illustrates the temperature
dependence of the operating magnetic field strength (Hop) obtained
by using the magnetic thin film magnetoresistive element (NiFe) as
the sensor in the circuit as shown in FIG. 2 implemented in the
form of the Si monolithic IC, and in the circuit of FIG. 13 used as
a reference.
[0102] It is seen from the graph that the temperature coefficient
of the operating magnetic field strength can be set approximately
zero in a wide temperature range.
Experimental Example 3
[0103] FIG. 10 illustrates the temperature dependence of the
operating magnetic flux density in the case of FIGS. 11A and 11B,
in which the signal processing circuit as shown in FIG. 2 was
formed on the ceramic substrate in comparison with the temperature
coefficient of a corresponding integrated circuit formed on a
common conventional Si substrate. As seen from FIG. 10, the
operating magnetic flux density of the circuit in accordance with
the present invention was stable in the ambient temperature above
150.degree. C.
[0104] As described above, the magnetic sensor section, which is
composed of the compound semiconductor thin film, combined with the
constant current circuit for feeding back the current can prevent
the reduction in the yield due to the variations in the midpoint
potential of the Hall element, or to the variations in the
resistors of the circuit.
[0105] In addition, the temperature dependence of the operating
magnetic flux density can be reduced to approximately zero by
setting the temperature coefficient of the feedback current by the
constant current circuit at a value inversely proportional to the
temperature coefficient of the combined resistance of the plurality
of resistors with two or more different temperature coefficients in
the signal processing circuit. This also makes it possible to
obtain the sensor output that is independent of the temperature in
a wide temperature range, even if the magnetic field to be detected
has the temperature dependence as in the detection of the magnetic
field of a permanent magnet.
[0106] Moreover, the integrated circuit of the signal processing
circuit section which is formed on the insulated ceramic substrate
ensures the stable operation in high ambient temperatures.
* * * * *