U.S. patent application number 09/879904 was filed with the patent office on 2001-11-15 for semiconductor device.
Invention is credited to Fiedler, Horst-Lothar, Nagano, Shuichi.
Application Number | 20010040241 09/879904 |
Document ID | / |
Family ID | 18449998 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040241 |
Kind Code |
A1 |
Nagano, Shuichi ; et
al. |
November 15, 2001 |
Semiconductor device
Abstract
A sensor 1 produces an output that changes linearly with
absolute temperature. In response to the output, a reference
voltage generator 13 produces reference voltages Vhigh and Vlow
that change linearly with absolute temperature. A Schmidt trigger
14 compares the output signal from a sensor signal amplifier 12
with the reference voltages for performing on-off output. A sensor
signal amplifier 12 with a temperature-independent amplification
factor amplifies the output signal from the sensor 1 while
performing offset compensation. A sensor signal processing circuit
2 is formed out of thin-film silicon disposed on an insulating
substrate. The output from the sensor 1 undergoes accurate
temperature compensation over a wide temperature range from a low
temperature to a high temperature, achieving a reliable operation
with accuracy at high temperature.
Inventors: |
Nagano, Shuichi;
(Numazu-shi, JP) ; Fiedler, Horst-Lothar;
(Duisburg, DE) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18449998 |
Appl. No.: |
09/879904 |
Filed: |
June 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09879904 |
Jun 14, 2001 |
|
|
|
PCT/JP99/06992 |
Dec 13, 2000 |
|
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Current U.S.
Class: |
257/159 ;
257/123; 257/157; 257/158; 257/160; 374/E7.027 |
Current CPC
Class: |
G01D 3/02 20130101; G01K
7/21 20130101; G01P 21/02 20130101 |
Class at
Publication: |
257/159 ;
257/123; 257/160; 257/157; 257/158 |
International
Class: |
H01L 029/74; H01L
031/111 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 1998 |
JP |
10-356631 |
Claims
1. A semiconductor device comprising: amplifying means for
receiving a sensor output signal from a sensor, amplifying the
sensor output signal at a required temperature-independent
amplification factor, and canceling an offset, reference signal
producing means for producing a reference signal varying at a
temperature coefficient equal to that of the sensor signal from
said sensor, comparing means which compares a magnitude of an
amplification output signal from said amplifying means with that of
the reference signal from said reference signal producing means and
outputs a required signal according to a comparison result, and
constant voltage generating means for generating
temperature-independent constant voltage to be supplied to said
sensor, characterized in that said amplifying means, said reference
signal producing means, said comparing means, and said constant
voltage generating means are formed using a semiconductor layer
provided on an insulating substrate.
2. The semiconductor device according to claim 1, characterized in
that said semiconductor layer is composed of a silicon thin
film.
3. The semiconductor device according to claim 2, characterized in
that said silicon thin film is 30 nm to 1000 nm in thickness.
4. The semiconductor device according to claim 1, 2, or 3,
characterized in that said reference signal producing means is
based on the previous measurement of a temperature coefficient of
the sensor output signal of said sensor and produces a reference
signal having an equal temperature coefficient.
5. The semiconductor device according to claim 4, characterized in
that said reference signal changes linearly with absolute
temperature.
6. The semiconductor device according to any one of claims 1 to 5,
characterized in that said amplifying means includes signal
amplifying means which is composed of a plurality of operational
amplifiers and amplifies said sensor output signal at a
temperature-independent amplification factor, and offset
compensating means for compensating for each offset of said
plurality of operational amplifiers every predetermined period.
7. The semiconductor device according to claim 6, characterized in
that said operational amplifier includes a differential amplifying
section for performing differential amplification on said sensor
output signal and an offset compensating section for canceling an
offset voltage of said differential amplifying section, and said
offset compensating section receives an offset compensating signal
according to an offset voltage of said differential amplifying
section every predetermined period and cancels the offset voltage
of said differential amplifying section in response to the offset
compensation signal.
8. The semiconductor device according to claim 7, characterized in
that said offset compensation section further includes a capacitor,
which holds a voltage for canceling an offset voltage of said
differential amplifying section, and said capacitor periodically
holds a voltage according to the offset voltage of said
differential amplifying section, and said offset compensating
section cancels the offset voltage of said differential amplifying
section according to the held voltage.
9. The semiconductor device according to any one of claims 1 to 8,
characterized in that said comparing means compares a magnitude of
an amplification output signal from said amplifying means with
those of two reference voltages, and the output is turned on/off
according to a comparison result.
10. The semiconductor device according to any one of claims 1 to 8,
characterized in that said comparing means computes a ratio of a
magnitude of reference voltage between that of the amplification
output signal from said amplifying means and outputs a digital
signal according to the ratio.
11. The semiconductor device according to any one of claims 1 to
10, characterized in that said reference signal producing means
includes at least a constant voltage source for generating
temperature-independent constant voltage and a constant current
source for generating constant current being directly proportional
to absolute temperature and inversely proportional to the
resistance of a reference resistor, and said reference signal
producing means produces two reference voltages changing linearly
with absolute temperature, according to the constant voltage
generated in said constant voltage source and the constant current
generated in said constant current source.
12. The semiconductor device according to any one of claims 1 to
10, characterized in that said reference signal producing means
includes a first constant current source for generating a constant
current being directly proportional to absolute temperature and
inversely proportional to the resistance of reference resistor, a
second constant current source which is connected in series to said
first constant current source and generates constant current by
applying temperature-independent constant voltage to
voltage/current converting resistor, a third constant current
source for generating constant current being fixed times larger
than a difference between a current of the second constant current
source and a current of said first constant current source, and an
upper limit reference voltage generating resistor and a lower limit
reference voltage generating resistor which are connected in series
to said third constant current source and are applied constant
current from said third constant current source, and one or both of
potentials generated in said upper limit reference voltage
generating resistor and said lower limit reference voltage
generating resistor are taken out as reference potentials.
13. The semiconductor device according to claim 12, characterized
in that said reference resistor, said voltage/current converting
resistor, said upper limit reference voltage generating resistor,
and said lower limit reference voltage generating resistor are
equal to one another in temperature coefficient.
14. A semiconductor device comprising a sensor which converts a
measured physical quantity to an electric signal and outputs the
signal, which has a peculiar temperature coefficient, amplifying
means which receives a sensor output signal of said sensor,
amplifies the sensor output signal at a required amplification
factor of temperature independence, and cancels an offset,
reference signal producing means for producing a reference signal
varying at a temperature coefficient equal to that of the sensor
output signal of said sensor, comparing means for comparing a
magnitude of the amplification output signal from said amplifying
means with a magnitude of the reference signal from said reference
signal producing means and for outputting a required signal
according to a comparison result, and constant voltage generating
means for generating temperature-independent constant voltage to be
supplied to said sensor, characterized in that said amplifying
means, said reference signal producing means, said comparing means,
and said constant voltage generating means are formed using a
semiconductor layer provided on an insulating substrate.
15. The semiconductor device according to claim 14, characterized
in that said semiconductor layer is a silicon thin film.
16. The semiconductor device according to claim 15, characterized
in that said silicon thin film is 30 nm to 1000 nm in
thickness.
17. The semiconductor device according to claim 14, 15, or 16,
characterized in that a sensor output signal has a peculiar
temperature coefficient in said sensor and the sensor output signal
is produced in a linear function of absolute temperature.
18. The semiconductor device according to any one of claims 14 to
17, characterized in that said sensor is a magnetic sensor.
19. The semiconductor device according to claim 18, characterized
in that said magnetic sensor is a Hall element.
20. The semiconductor device according to claim 19, characterized
in that said Hall element has a magnetic sensitive part made of
GaAs.
21. The semiconductor device according to any one of claims 14 to
20, characterized in that said reference signal producing means is
based on the previous measurement of a temperature coefficient of
the sensor output signal of said sensor and produces a reference
signal having an equal temperature coefficient.
22. The semiconductor device according to claim 21, characterized
in that said reference signal changes linearly with absolute
temperature.
23. The semiconductor device according to any one of claims 14 to
22, characterized in that said amplifying means includes signal
amplifying means which is composed of a plurality of operational
amplifiers and amplifies a sensor output signal at a
temperature-independent amplification factor, and offset
compensating means for compensating for each offset of said
plurality of operational amplifiers every predetermined period.
24. The semiconductor device according to claim 23, characterized
in that said operational amplifier includes a differential
amplifying section for performing differential amplification on
said sensor output signal and an offset compensating section for
canceling an offset voltage of said differential amplifying
section, and said offset compensating section receives an offset
compensating signal according to an offset voltage of said
differential amplifying section every predetermined period and
cancels the offset voltage of said differential amplifying section
in response to the offset compensation signal.
25. The semiconductor device according to claim 24, characterized
in that said offset compensation section further includes a
capacitor, which holds voltage for canceling an offset voltage of
said differential amplifying section, and said capacitor
periodically holds a voltage according to the offset voltage of
said differential amplifying section, and said offset compensating
section cancels the offset voltage of said differential amplifying
section according to the held voltage.
26. The semiconductor device according to any one of claims 14 to
25, characterized in that said comparing means compares a magnitude
of an amplification output signal from said amplifying means with
the magnitudes of two reference voltages, and the output is turned
on/off according to a comparison result.
27. The semiconductor device according to any one of claims 14 to
25, characterized in that said comparing means computes a ratio of
a magnitude of reference voltage between that of the amplification
output signal from said amplifying means and outputs a digital
signal according to the ratio.
28. The semiconductor device according to any one of claims 14 to
27, characterized in that said reference signal producing means
includes at least a constant voltage source for generating
temperature-independent constant voltage and a constant current
source for generating constant current being directly proportional
to absolute temperature and inversely proportional to the magnitude
of a reference resistor, and said reference signal producing means
produces two reference voltages changing linearly with absolute
temperature, according to the constant voltage generated in said
constant voltage source and the constant current generated in said
constant current source.
29. The semiconductor device according to any one of claims 14 to
27, characterized in that said reference signal producing means
includes a first constant current source for generating a constant
current being directly proportional to absolute temperature and
inversely proportional to a magnitude of reference resistor, a
second constant current source which is connected in series to said
first constant current source and generates constant current by
applying temperature-independent constant voltage to a
voltage/current converting resistor, a third constant current
source for generating constant current being fixed times larger
than a difference between a current of the second constant current
source and a current of said first constant current source, and an
upper limit reference voltage generating resistor and a lower limit
reference voltage generating resistor which are connected in series
to said third constant current source and are applied constant
current from said third constant current source, and one or both of
potentials generated in said upper limit reference voltage
generating resistor and said lower limit reference voltage
generating resistor are taken out as reference electric
potentials.
30. The semiconductor device according to claim 29, characterized
in that said reference resistor, said voltage/current converting
resistor, said upper limit reference voltage generating resistor,
and said lower limit reference voltage generating resistor are
equal to one another in temperature coefficient.
Description
TECHNICAL FIELD
[0001] The present invention relates to a semiconductor device and
particularly concerns an integrated circuit (hereinafter, referred
to as an IC) having a function of temperature compensation to be
used in combination with a variety of sensors, and a sensor IC
combining a sensor with the IC having the temperature compensation
function.
BACKGROUND ART
[0002] Conventionally, a sensor IC, which combines a sensor and an
IC for processing a signal, has been used in a variety of fields.
As a sensor IC with the function of turning on/off in response to
an output signal of a sensor, a sensor IC for detecting magnetic
fields has been particularly known. For example, a magnetic sensor
IC is used for detecting rotation of a cooling fan for a CPU of a
personal computer and so on.
[0003] Incidentally, in case of an IC which operates amplification
on an output signal (electric signal) from the sensor and turns
on/off the output at predetermined sensitivity, the output from the
sensor normally changes with temperature. Thus, a
temperature-compensating circuit is necessary for turning on/off
the output of the IC at predetermined sensitivity all the time
regardless of temperature. As temperature compensation, a
conventional method has been known which changes an amplification
degree of an output signal or voltage and current applied to the
sensor according to a temperature characteristic of the output
signal from the sensor.
[0004] For example, according to the invention disclosed in
Japanese Patent Laid-Open No. 57-197883, temperature compensation
is performed by applying to a sensor voltage increasing
monotonously with temperature and driving the sensor by the
voltage. However, some sensors require an extremely high voltage
for driving, thereby increasing power consumption or heat
generation. Consequently, the operation becomes unstable with
temperature.
[0005] Further, the invention disclosed in Japanese Patent
Publication No. 3-51118 has been known. The invention is provided
with a Hall element (sensor) for generating Hall voltage, a
reference voltage generating means for generating reference voltage
relative to current passing through the Hall element, a comparing
means for generating an output signal depending upon a relative
magnitude of the Hall voltage and the reference voltage, and so on.
Temperature compensation can be performed on a variety of sensors
having sensitivity as a function of applied current.
[0006] As described above, the invention described in Japanese
Patent Publication No. 3-51118 is applicable to a sensor where
sensitivity is a function of applied current. However, the
invention is not applicable to a sensor where sensitivity has no
correlation to applied current. Moreover, the
temperature-compensating circuit is not for general purpose use and
cannot be combined with other sensors, resulting in narrow
applicability.
[0007] Additionally, even in the case where a sensor is formed in
the same manner, the same current is not always applied at the same
sensitivity. Conversely, the same sensitivity is not always
obtained at the same current. Therefore, in case of a large
irregularity in characteristic of the sensor, monitoring current
may be an adverse effect.
[0008] Incidentally, in the temperature-compensating circuit formed
on widely used bulk silicon, leakage current rapidly increases on a
PN-junction at a high temperature of 125.degree. C. or above,
causing a problem in temperature compensation. Temperature
compensation is not possible particularly at a high temperature of
150.degree. C. or above.
[0009] Meanwhile, as a technique for a high-temperature IC, a
method has been known, which forms circuits on a semiconductor
layer on an insulating base such as an SOI (silicon on insulator)
substrate. It has been known that this method makes it possible to
reduce an area of a PN-junction, reduce leakage current in a high
temperature range, prevent a latch-up phenomenon, and permits an
operation at a higher temperature. Hence, if the
temperature-compensating circuit according to the conventional
method is formed on the semiconductor layer on the SOI substrate,
it is expected to somewhat improve the operation at a high
temperature.
[0010] However, in the case where the temperature-compensating
circuit of the conventional method is formed on the semiconductor
layer on the SOI substrate, it is difficult to achieve accurate
temperature compensation with reliability at a high temperature,
and durability is deteriorated at a high temperature due to heat
generated by power consumption.
[0011] In order to solve the above problem, it is necessary to
accurately amplify a fine signal from the sensor and to perform
accurate temperature compensation with a low driving voltage and
small power consumption at a high temperature. However, it is not
easy to realize a sensor IC meeting these conditions.
[0012] Hence, a sensor IC combining a sensor and an IC with
temperature compensation, that accurately operates in a stable
manner at a high temperature of 200.degree. C. or above, has not
been achieved yet. Also, the IC for temperature compensation for
the sensor IC has not been achieved. Such a sensor IC has been
demanded.
[0013] Further, as a detector for rotation of a gear wheel, a
silicon-monolithic sensor IC using a CMOS circuit has been known.
However, the highest temperature of the sensor IC is limited to
150.degree. C. in practical use. It has been desirable to set the
highest temperature at 200.degree. C. or above.
[0014] The present invention is therefore devised against the above
backdrop. The first object thereof is to provide a semiconductor
device as an IC with temperature compensation (hereinafter,
referred to as an IC for a sensor IC) that combination can be made
with various sensors and can perform accurate temperature
compensation on an output signal from the sensor with reliability
at a high temperature.
[0015] The second object of the present invention is to provide a
semiconductor device as a sensor IC (hereinafter, referred to as a
sensor IC) that can accurately operate with reliability in a stable
manner at a high temperature.
DISCLOSURE OF THE INVENTION
[0016] The present invention provides a semiconductor device (IC
for a sensor IC) including amplifying means for inputting a sensor
output signal from the sensor, amplifying the sensor output signal
at a required temperature-independent amplification factor, and
canceling an offset, reference signal producing means for producing
a reference signal varying at a temperature coefficient equal to
that of the sensor output signal from the sensor, comparing means
which compares the magnitude of an amplification output signal from
the amplifying means with that of the reference signal from the
reference signal producing means and outputs a required signal
according to a comparison result, and constant voltage generating
means for generating temperature-independent constant voltage to be
supplied to the sensor, characterized in that the amplifying means,
the reference signal producing means, the comparing means, and the
constant voltage generating means are formed using a semiconductor
layer provided on an insulating substrate.
[0017] Here, the above "equal temperature coefficient" includes not
only an equal temperature coefficient but also a substantially
equal temperature coefficient. A permissible error value depends
upon the accuracy of the semiconductor device (sensor IC).
[0018] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable, in which the
semiconductor layer is composed of a silicon thin film.
[0019] Further, as an embodiment of the IC for the sensor IC of the
present invention, an IC for a sensor IC is applicable, in which
the silicon thin film is 30 nm to 1000 nm in thickness.
[0020] As described above, according to the IC for the sensor IC,
the amplifying means receives a sensor output signal, amplifies the
sensor output signal at a required temperature-independent
amplification factor, and operates to cancel an offset, thereby
accurately amplifying the sensor output signal.
[0021] Furthermore, the reference signal producing means produces a
reference signal varying at a temperature coefficient equal to that
of the sensor output signal of the sensor. The signal is used as a
reference signal, that of which the comparing means makes
comparison with the magnitude of the amplification output signal of
the amplifying means and outputs a required signal. Even when the
output signal of the sensor is affected by temperature, the
influence can be cancelled.
[0022] Additionally, the amplifying means, the reference signal
producing means, the comparing means, and the constant voltage
generating means are formed using the semiconductor layer provided
on the insulating substrate, the semiconductor layer is preferably
composed of a silicon thin film, and leakage current is reduced in
a high temperature range and latch-up can be prevented.
[0023] For this reason, according to the IC for the sensor IC of
the present invention, when one of the sensors changes the outputs
at a temperature coefficient equal to that of the reference signal
produced by the reference signal producing means, combination can
be made with the sensor. In this case, accurate temperature
compensation is performed for the output of the sensor over a wide
temperature range from a low temperature to a high temperature
(e.g., from -40.degree. C. to 200.degree. C. or above), achieving
an accurate operation with reliability even at a high
temperature.
[0024] Furthermore, in case of forming the sensor IC combined with
the sensor, the IC for sensor IC of the present invention can be
realized only by changing the components of the reference signal
producing means according to a temperature characteristic of the
sensor. Thus, combination can be made with a variety of sensors,
achieving wide applicability.
[0025] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
reference signal producing means is based on the previous
measurement of a temperature coefficient of the sensor output
signal of the sensor and produces a reference signal having an
equal temperature coefficient.
[0026] According to the embodiment, the reference signal producing
means previously measures a temperature coefficient of the sensor
output signal of the sensor and produces a reference signal having
an equal temperature coefficient. The signal is used as a reference
signal, that of which the comparing means makes comparison with the
magnitude of the amplification output signal of the amplifying
means and outputs a required signal. Thus, in case of forming the
sensor IC with the combination of the sensor, accuracy of
comparison is improved.
[0027] Further, the sensor can be severely selected for each
characteristic upon manufacturing and assembling and the reference
signal producing means can produce a reference signal according to
the selected characteristic of the sensor. Thus, it is possible to
readily realize a sensor IC having a desired specification by
making combination with the sensor.
[0028] As an embodiment of the IC for the sensor IC of the present
invention, an IC for the sensor IC is applicable in which the
reference signal producing means has a temperature coefficient
equal to that of the sensor output signal of the sensor and
produces a reference signal changing linearly with absolute
temperature.
[0029] According to the embodiment, the reference signal producing
means has a temperature coefficient equal to that of the sensor
output signal of the sensor and produces a reference signal
changing linearly with absolute temperature. The signal is used as
a reference signal, that of which the comparing means makes
comparison with the magnitude of the amplification output signal of
the amplifying means and outputs a required signal.
[0030] Therefore, in the embodiment, when one of the sensors has
the output changing linearly with absolute temperature, a reference
signal provided by a linear function of absolute temperature is
produced according to the sensor, achieving the combination with
the sensor. In this case, accurate temperature compensation is
realized for the output of the sensor over a wide temperature range
from a low temperature to a high temperature, achieving an accurate
operation with reliability even at a high temperature. Moreover,
even in a wide temperature range whose output is not a linear
function but is approximate to a linear function, an accurate
operation is possible.
[0031] As an embodiment of the IC for the sensor IC of the present
invention, a sensor for a sensor IC is applicable in which the
amplifying means includes a signal amplifying means which is
composed of a plurality of operational amplifiers and amplifies the
sensor output signal at a temperature-independent amplification
factor and an offset compensating means for compensating for each
offset of the plurality of the operational amplifiers every
predetermined period.
[0032] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
operational amplifier includes a differential amplifying section
for performing differential amplification on the sensor output
signal and an offset compensating section for canceling an offset
voltage of the differential amplifying section, the offset
compensating section receives an offset compensating signal
according to an offset voltage of the differential amplifying
section every predetermined period and cancels the offset voltage
of the differential amplifying section in response to the offset
compensation signal.
[0033] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the offset
compensation section further includes a capacitor for holding
voltage to cancel the offset voltage of the differential amplifying
section, the capacitor periodically holds a voltage according to
the offset voltage of the differential amplifying section, and the
offset compensating section cancels the offset voltage of the
differential amplifying section according to the held voltage.
[0034] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
comparing means compares the magnitude of the amplification output
signal from the amplifying means with the magnitudes of two
reference voltages, and the output is turned on/off according to a
comparison result.
[0035] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
comparing means computes a ratio of a reference voltage and the
magnitude of the amplification output signal from the amplifying
means and outputs a digital signal according to the ratio.
[0036] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
reference signal producing means includes at least a constant
voltage source for generating temperature-independent constant
voltage and a constant current source for generating constant
current being directly proportional to absolute temperature and
inversely proportional to the resistance of a reference resistor,
and the reference signal producing means produces two reference
voltages changing linearly with absolute temperature, by utilizing
the constant voltage generated in the constant voltage source and
the constant current generated in the constant current source.
[0037] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
reference signal producing means is constituted by a first constant
current source for generating a constant current being directly
proportional to absolute temperature and inversely proportional to
the resistance of the reference resistor, a second constant current
source which is connected in series to the first constant current
source and applies temperature-independent constant voltage to a
voltage/current converting resistor to generate constant current, a
third constant current source for generating constant current being
fixed times larger than a difference between a current of the
second constant current source and a current of the first constant
current source, and an upper limit reference voltage generating
resistor and a lower limit reference voltage generating resistor
which are connected in series to the third constant current source
and are applied constant current from the third constant current
source, and one or both of potentials generated in the upper limit
reference voltage generating resistor and the lower limit reference
voltage generating resistor are taken out as reference
potentials.
[0038] As an embodiment of the IC for the sensor IC of the present
invention, an IC for a sensor IC is applicable in which the
reference resistor, the voltage/current converting resistor, the
upper limit reference voltage generating resistor, and the lower
limit reference voltage generating resistor are equal to one
another in temperature coefficient.
[0039] Meanwhile, the present invention provides a semiconductor
device (sensor IC) including a sensor for converting a measured
physical quantity to an electric signal and outputting the signal,
the outputted signal having a peculiar temperature coefficient, an
amplifying means which inputs a sensor output signal of the sensor,
amplifies the sensor output signal at a required amplification
factor of temperature independence, and cancels an offset, a
reference signal producing means for producing a reference signal
varying at a temperature coefficient equal to that of the sensor
output signal of the sensor, a comparing means for comparing the
magnitude of the amplification output signal from the amplifying
means with the magnitude of the reference signal from the reference
signal producing means and for outputting a required signal
according to a comparison result, and a constant voltage generating
means for generating temperature-independent constant voltage to be
supplied to the sensor, characterized in that the amplifying means,
the reference signal producing means, the comparing means, and the
constant voltage generating means are formed using a semiconductor
layer provided on an insulating substrate.
[0040] As an embodiment of the sensor IC of the present invention,
an sensor IC is applicable in which the semiconductor layer is
composed of a silicon thin film.
[0041] Additionally, as an embodiment of the sensor IC of the
present invention, an sensor IC is applicable in which the silicon
thin film is 30 nm to 1000 nm in thickness.
[0042] As described above, according to the sensor IC of the
present invention, the amplifying means inputs a sensor output
signal of the sensor, amplifies the sensor output signal at a
required amplification factor of temperature independence, and
cancels an offset, thereby accurately amplifying the output signal
of the sensor.
[0043] Further, the reference signal producing means produces a
reference signal changing at a temperature coefficient equal to
that of the sensor output signal of the sensor. The signal is used
as a reference signal, that of which the comparing means makes
comparison with the magnitude of the amplification output signal of
the amplifying means and outputs a required signal. Hence, even
when the output signal of the sensor is changed due to the
influence of temperature, the influence can be cancelled.
[0044] Moreover, the amplifying means, the reference signal
producing means, the comparing means, and the constant voltage
producing means are formed by using a semiconductor layer provided
on an insulating substrate. The semiconductor layer is preferably
composed of a silicon thin film, and leakage current can be reduced
in a high temperature range and latch-up can be prevented.
[0045] For this reason, according to the sensor IC of the present
invention, over a wide temperature range from a low temperature to
a high temperature (e.g., from -40.degree. C. to 200.degree. C. or
above), temperature compensation can be performed accurately for
the output of the sensor, achieving an accurate operation with
reliability even at a high temperature.
[0046] As mentioned above, according to the sensor IC of the
present invention, the reference signal producing means produces a
reference signal changing at a temperature coefficient equal to
that of the sensor output signal of the sensor. The signal is used
as a reference signal, that of which the comparing means makes
comparison with the magnitude of the amplification output signal of
the amplifying means and outputs a required signal. Furthermore,
the amplifying means amplifies the sensor output signal from the
sensor at a required amplification factor of temperature
independence and cancels an offset. Hence, the sensor IC of the
present invention can perform accurate temperature compensation on
the output of the sensor over a wide temperature range from a low
temperature and a high temperature, thereby achieving an accurate
operation with reliability even at a high temperature.
[0047] As an embodiment of the sensor IC of the present invention,
an sensor IC is applicable in which a sensor output signal has a
peculiar temperature coefficient in the sensor and the sensor
output signal is produced in a linear function of absolute
temperature.
[0048] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the sensor is a magnetic
sensor.
[0049] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the magnetic sensor is a Hall
element.
[0050] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the Hall element has a magnetic
sensitive part made of GaAs.
[0051] The invention of the embodiment is completed by the inventor
et al. who considered a characteristic of GaAs having a resistance
increasing with temperature and earnestly studied the
characteristic for positive and effective use.
[0052] Therefore, in the present invention, GaAs is adopted for the
magnetic sensitive part of the Hall element. A resistance of GaAs
increases with temperature. Thus, it is possible to reduce current
of the magnetic sensitive part and to reduce source current with
temperature. Hence, the sensor IC decreases in power consumption at
a higher temperature and it is possible to suppress an increase in
temperature caused by consumption of current, thereby operating in
a stable manner even at a high temperature.
[0053] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the reference signal producing
means previously measures a temperature coefficient of the sensor
output signal of the sensor and produces a reference signal having
an equal temperature coefficient.
[0054] According to the embodiment, the reference signal producing
means previously measures a temperature coefficient of the sensor
output signal of the sensor and produces a reference signal having
an equal temperature coefficient. The signal is used as a
reference, that of which the comparing means makes comparison with
the magnitude of the amplification output signal of the amplifying
means and outputs a required signal. Consequently, accuracy of
comparison is improved.
[0055] Also, the sensor can be severely selected for each
characteristic in manufacturing and assembling and the reference
signal producing means can produce a reference signal according to
the selected characteristic of the sensor. Thus, it is possible to
readily realize a sensor IC having a desired specification by
making combination with the sensor.
[0056] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the reference signal producing
means produces a reference signal having a temperature coefficient
equal to that of the sensor output signal and changing linearly
with absolute temperature.
[0057] According to the embodiment, the reference signal producing
means produces a reference signal having a temperature coefficient
equal to that of the sensor output signal of the sensor and
changing linearly with absolute temperature. The signal is used as
a reference signal, that of which the comparing means makes
comparison with the magnitude of the amplification output signal of
the amplifying means and outputs a required signal. Thus, even when
the output signal of the sensor is changed due to the influence of
temperature, the influence can be cancelled.
[0058] For this reason, accurate temperature compensation is
possible for the output of the sensor over a wide temperature range
from a low temperature to a high temperature, achieving an accurate
operation with reliability even at a high temperature. Further,
even in a wide temperature range whose output is not a linear
function but is close to a linear function in some temperature
range, an accurate operation can be realized in that temperature
range.
[0059] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the amplifying means is composed
of a plurality of operational amplifiers and includes a signal
amplifying means for amplifying the sensor output signal at a
temperature-independent amplification factor and an offset
compensating means for compensating for each offset of the
plurality of the operational amplifiers every predetermined
period.
[0060] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the operational amplifier
includes a differential amplifying section for performing
differential amplification on the sensor output signal and an
offset compensating section for canceling an offset voltage of the
differential amplifying section, the offset compensating section
receives an offset compensating signal according to an offset
voltage of the differential amplifying section every predetermined
period, and the offset voltage of the differential amplifying
section is cancelled in response to the offset compensation
signal.
[0061] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the offset compensation section
further includes a capacitor for holding voltage for canceling the
offset voltage of the differential amplifying section, the
capacitor periodically holds a voltage according to the offset
voltage of the differential amplifying section, an the offset
compensating section cancels the offset voltage of the differential
amplifying section according to the held voltage.
[0062] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the comparing means compares the
magnitude of the amplification output signal from the amplifying
means with the magnitudes of two reference voltages, and the output
is turned on/off according to a comparison result.
[0063] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the comparing means computes a
ratio of a reference voltage and the magnitude of the amplification
output signal from the amplifying means and outputs a digital
signal according to the ratio.
[0064] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the reference signal producing
means includes at least a constant voltage source for generating
temperature-independent constant voltage and a constant current
source for generating constant current being directly proportional
to absolute temperature and inversely proportional to the
resistance of a reference resistor, and the reference signal
producing means produces two reference voltages changing linearly
with absolute temperature, by utilizing to the constant voltage
generated in the constant voltage source and the constant current
generated in the constant current source.
[0065] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the reference signal producing
means is constituted by a first constant current source for
generating a constant current being directly proportional to
absolute temperature and inversely proportional to the magnitude of
the reference resistor, a second constant current source being
connected in series to the first constant current source and
applying temperature-independent constant voltage to a
voltage/current converting resistor to generate constant current, a
third constant current source for generating constant current being
constant-times larger than a difference between a current of the
second constant current source and a current of the first constant
current source, and an upper limit reference voltage generating
resistor and a lower limit reference voltage generating resistor
being connected in series to the third constant current source and
being applied constant current from the third constant current
source, and one or both of potentials generated in the upper limit
reference voltage generating resistor and the lower limit reference
voltage generating resistor are taken out as reference
potentials.
[0066] As an embodiment of the sensor IC of the present invention,
a sensor IC is applicable in which the reference resistor, the
voltage/current converting resistor, the upper limit reference
voltage generating resistor, and the lower limit reference voltage
generating resistor are equal to one another in temperature
coefficient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] FIG. 1 is a block diagram showing the configuration of a
signal processing circuit together with a sensor. The signal
processing circuit is provided in a semiconductor device (IC for a
sensor IC) of the present invention;
[0068] FIG. 2 is a circuit diagram showing an example of the
configuration of a sensor signal amplifier;
[0069] FIG. 3 is a circuit diagram showing an example of the
configuration of an operational amplifier, which constitutes the
sensor signal amplifier of FIG. 2;
[0070] FIG. 4 is a circuit diagram showing an example of the
configuration of a reference voltage generator;
[0071] FIG. 5 is a diagram showing a temperature characteristic of
a Hall voltage when a bias voltage is 3 (V) and a magnetic flux
density is .+-.4 (mT) in a GaAs Hall element according to Example 1
of the present invention;
[0072] FIG. 6 is a diagram showing a temperature characteristic of
an operating input voltage of the signal processing circuit
according to Example 1 of the present invention;
[0073] FIG. 7 is a diagram showing a temperature characteristic of
an operating magnetic flux density of a Hall IC using the GaAs Hall
element according to Example 1 of the present invention;
[0074] FIG. 8 is a diagram showing a temperature characteristic of
source current when a source voltage is 5 (V) in the Hall IC using
the GaAs Hall element according to Example 1 of the present
invention;
[0075] FIG. 9 is a diagram showing the configuration of a rotation
sensor IC for high temperatures according to Example 2 of the
present invention;
[0076] FIG. 10 is a diagram showing an example of arranging members
in a package of the rotation sensor IC for high temperatures
according to Example 2 of the present invention;
[0077] FIG. 11 is a circuit diagram showing a reference voltage
generator in the rotation sensor IC for high temperatures according
to Example 2 of the present invention;
[0078] FIG. 12 is a diagram showing the configuration of a system
for detecting a gear wheel that uses the rotation sensor IC for
high temperatures according to Example 2 of the present
invention;
[0079] FIG. 13 is a diagram showing a change in temperature of
amplitude of output from the rotation sensor IC for high
temperatures according to Example 2 of the present invention;
[0080] FIG. 14 is a diagram showing the relationship of a
difference in magnetic flux density between an A block and a B
block and an amplification signal of output from a bridge circuit
in the rotation sensor IC for high temperature, according to
Example 2 of the present invention;
[0081] FIG. 15 is a diagram showing the configuration of a pressure
sensor IC for high temperatures according to Example 3 of the
present invention;
[0082] FIG. 16 is a sectional view showing the configuration of the
pressure sensor IC for high temperatures according to Example of
the present invention;
[0083] FIG. 17 is a circuit diagram showing a reference voltage
generator in the pressure sensor IC for high temperature according
to Example 3 of the present invention;
[0084] FIG. 18 is a diagram showing a temperature characteristic of
an output of the pressure sensor for high temperatures according to
Example 3 of the present invention; and
[0085] FIG. 19 is a diagram showing the relationship of a
temperature and an operating pressure of the pressure sensor IC for
high temperatures according to Example 3 of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0086] Referring to figures, the following will describe preferred
embodiments of the present invention. FIG. 1 is a block diagram
showing the configuration of a signal processing circuit disposed
in a sensor IC of a semiconductor device of the present invention
together with a sensor.
[0087] As shown in FIG. 1, the sensor IC is constituted by a sensor
1, which converts a physical quantity to an electric signal and
outputs the signal, and an integrated signal processing circuit 2,
which processes an output signal of the sensor 1. The following
will describe that the sensor 1 and the signal processing circuit 2
are combined in a hybrid manner. Here, the sensor IC may be
realized by a monolithic IC as well.
[0088] As shown in FIG. 1, the sensor 1 is provided with a ground
terminal 3, a bias terminal 4, and output terminals 5 and 6. Types
of the sensor 1 is not particularly limited and includes a magnetic
sensor, a pressure sensor, an optical sensor, a temperature sensor,
a humidity sensor, a position sensor, a speed sensor, an rpm
sensor, and so on. However, it is preferable to adopt a sensor
capable of indicating an output in an ideal manner or closely
analogous to a linear function of temperature when it is applied a
fixed voltage of temperature-independence. For example, a Hall
element (Hall sensor), which is one of magnetic sensors, is
applicable, and it is particularly preferable that a magnetic
sensitive part thereof is made of GaAs (gallium arsenide).
[0089] Many sensors monotonously increase and decrease outputs
within a range of an operating temperature and indicate a
temperature change as a linear function of temperature in an
approximate or ideal manner. Especially by selecting a range of an
operating temperature, outputs of many sensors can be approximate
to a linear function of temperature, so that many sensors can be
used as the sensor 1.
[0090] Here, the output of the sensor 1 changes linearly with
absolute temperature. This change includes constant output making
no changes as well as output increasing or decreasing linearly with
absolute temperature.
[0091] Referring to FIG. 1, the following will discuss the
configuration of the signal processing circuit 2.
[0092] As shown in FIG. 1, the signal processing circuit 2 is
provided with at least a protective circuit 7, a band gap reference
voltage generator 8, an internal voltage generator 9, a sensor bias
voltage generator 10 constituting a constant-voltage generating
means for the sensor 1, a clock generator 11, a sensor signal
amplifier 12 constituting an amplifier, a reference voltage
generator 13 constituting a reference signal generator, a Schmidt
trigger 14 constituting a comparing means 14, and an NMOSFET
15.
[0093] Regarding the protective circuit 7, power source connects a
power source connecting terminal 16 and a ground terminal 17. This
connection applies source voltage across the terminals. In the case
where power source is connected inversely when the above connection
is made, protection against backward voltage is provided on the
band gap reference voltage generator 8, the internal voltage
generator 9, and the sensor bias voltage generator 10 that are
connected on the output side.
[0094] The band gap reference voltage generator 8 generates
reference voltage supplied to the internal voltage generator 9, the
sensor bias voltage generator 10, and the reference voltage
generator 13, and also generates constant current supplied to the
reference voltage generator 13.
[0095] The internal voltage generator 9 generates voltage Vdd for
driving each section of the signal processing circuit 2, and the
generated voltage Vdd (not shown) is supplied to the sensor signal
amplifier 12, the reference voltage generator 13, and so on.
[0096] The sensor bias voltage generator 10 generates constant
voltage of temperature-independence, that is supplied to the sensor
1, as bias voltage. The generated bias voltage Vbias is applied
between the ground terminal 3 and the bias terminal 4 of the sensor
1, so that the sensor 1 is operated.
[0097] The clock generator 11 generates a clock for opening and
closing switches SW1-1 to SW1-2, switches SW2-1 to SW2-3, and
switches SW3-1 to SW3-3, that are disposed as illustrated in FIG.
2, to cancel offset of operational amplifiers OP1 to OP3
constituting the sensor signal amplifier 12.
[0098] The sensor signal amplifier 12 has the functions of
inputting output signals from the sensor 1 to two input terminals
via sensor input terminals 19 and 20, performing amplification with
amplification factor (gain) of temperature-independence, and
canceling offset. Also, output Voutp of the sensor signal amplifier
12 is supplied to the Schmidt trigger 14, and output Voutn thereof
is supplied to the input terminal of an operational amplifier OP5
of the reference voltage generator 13.
[0099] The reference voltage generator 13 generates two different
upper limit reference voltage Vhigh and lower limit reference
voltage Vlow that are used when the Schmidt trigger 14 compares the
output voltages of the censor signal amplifier 12, and the upper
limit reference voltage Vhigh and the lower limit reference voltage
Vlow are each supplied to the Schmidt trigger 14. Further, the
reference voltage generator 13 generates two reference voltages
Vhigh and Vlow whose output changes with a temperature coefficient
equal to that of the output of the sensor 1 and whose magnitude
changes linearly with absolute temperature. The meaning of a
temperature coefficient will be discussed later.
[0100] Here, the reference voltages change linearly with absolute
temperature. This includes remaining constant making no change as
well as increasing or decreasing linearly with absolute
temperature.
[0101] The NMOSFET 15 is connected to the output of the Schmidt
trigger 14, and the drain of the NMOSFET 15 is connected to an
output terminal 21. Moreover, the Schmidt trigger 14 compares
output voltage of the sensor signal amplifier 12 with the upper
limit reference voltage Vhigh and the lower limit reference voltage
Vlow from the reference voltage generator 13. In the case where the
output voltage is higher than the upper limit reference voltage
Vhigh, output Vout is set at "L" level, and in the case where the
output voltage is lower than the lower limit reference voltage
Vlow, the output Vout is set at "H" level. Additionally, since the
Schmidt trigger 14 acts as a comparator having hysteresis, a dead
band appears between the upper limit reference voltage Vhigh and
the lower limit reference voltage Vlow and the output Vout is not
inverted.
[0102] The signal processing circuit 2 configured as above is
formed in an IC (integrated circuit). The following will discuss
the formation thereof.
[0103] The process of integrating the signal processing circuit 2
includes a C-MOS process and a bipolar process and is not
particularly limited. Further, as for a semiconductor substrate
constituting the IC, a semiconductor layer on an insulating base,
i.e., a semiconductor layer provided on an insulating substrate is
used. In this case, leakage current is small at a high temperature,
latch-up is not likely to occur, accuracy can be improved on an
element such as a capacitor, and a circuit function for reducing
offset voltage of the sensor signal amplifier 12 can be obtained
even in a high temperature range like at room temperature.
[0104] Particularly, an SOI (Silicon On Insulator) substrate is a
proven material, and it is more preferable to form a circuit on the
SOI substrate (silicon thin film formed on an insulating
substrate). As for the insulating base (insulating substrate) used
in the SOI structure, sapphire, .gamma.-Al.sub.2O.sub.3, fluoride,
silicon oxide are available. Other materials are applicable as long
as the same insulation is presented.
[0105] Furthermore, a manufacturing method thereof is not
particularly limited. For example, in the case where the insulating
base is made of silicon oxide, any one of a SIMOX (separation by
ion implanted oxide) substrate, a bonded SOI substrate, and a solid
epitaxial growth SOI substrate is applicable.
[0106] Here, it is preferable to set a thickness of the silicon
thin film (silicon layer) at 30 nm to 1000 nm. The silicon thin
film is a semiconductor layer provided on the insulating substrate
with the signal processing circuit 2 formed thereon. When the
thickness is smaller than 30 nm, a problem occurs in the operation
of the device due to the influence of a defect around an interface
between the silicon layer and the insulating layer. Meanwhile, when
the thickness is larger than 1000 nm, an area of a PN-junction
increases, leakage current reaches the same level as a bulk silicon
substrate. Thus, it is difficult to operate the device at a high
temperature of 150.degree. C. or above. Therefore, it is more
preferable to set a thickness of the silicon thin film at 50 nm to
200 nm. In the example of the present invention (described later),
a silicon thin film with a thickness of 120 nm is used.
[0107] Referring to FIG. 2, the following will discuss the detail
of the configuration of the sensor signal amplifier 12.
[0108] As shown in FIG. 2, the sensor signal amplifier 12 is
constituted by operational amplifiers OP1 to OP3. The operational
amplifiers OP1 to OP3 are each provided with a non-inverting input
terminal 25 and an inverting input terminal 26 for offset
compensation in addition to a non-inverting input terminal 23 and
an inverting input terminal 24 for amplifying a sensor signal.
[0109] The sensor signal amplifier 12 is provided with two input
terminals 19 and 20 for inputting an output signal from the sensor
1. An input terminal 19 is connected to the non-inverting input
terminal 23 of the operational amplifier OP1 via the switch SW2-2
and is directly connected to the non-inverting input terminal 23 of
the operational amplifier OP2. Also, the other input terminal 20 is
connected to the non-inverting input terminal 23 of the operational
amplifier OP1 via the switch SW3-1 and is directly connected to the
non-inverting input terminal 23 of the operational amplifier
OP3.
[0110] The switch SW1-1 connects the non-inverting input terminal
23 and the inverting input terminal 24 of the operational amplifier
OP1. Further, the inverting input terminal 24 of the operational
amplifier OP1 is connected to the inverting input terminal 24 of
the operational amplifier OP2 via the switch SW2-1 and is connected
to the inverting input terminal 24 of the operational amplifier OP3
via the switch SW3-2. The switch SW1-2 connects the output terminal
and the inverting input terminal 26 of the operational amplifier
OP1, and the inverting input terminal 26 is grounded via a
capacitor C1.
[0111] The output terminal of the operational amplifier OP1 is
connected to the non-inverting input terminal 25 of the operational
amplifier OP2 via the switch SW2-3, and the non-inverting input
terminal 25 is grounded via a capacitor C2. Moreover, the output
terminal of the operational amplifier OP1 is connected to the
non-inverting input terminal 25 of the operational amplifier OP3
via the switch SW3-3, and the non-inverting input terminal 25 is
grounded via a capacitor C3.
[0112] A resistor R1 connects the inverting input terminal 24 and
the output terminal of the operational amplifier OP2. The output of
the operational amplifier OP2 is taken out from an output terminal
27. Further, a resistor R2 connects the inverting input terminal 24
of the operational amplifier OP2 and the inverting input terminal
24 of the operational amplifier OP3. Additionally, the output of
the operational amplifier OP3 is fed back to the inverting input
terminal 24, and the output is taken out from an output terminal
28. Furthermore, reference potential Vo is equally applied to the
non-inverting input terminal 25 of the operational amplifier OP1,
and the inverting input terminal 26 of the operational amplifiers
OP2 and OP3.
[0113] Moreover, the above switches SW1-1 and SW1-2, switches SW2-1
to SW2-3, and switches SW3-1 to SW3-3 carry out an open/close
operation at predetermined period based on a clock from the clock
generator 11, which is illustrated in FIG. 1.
[0114] The operational amplifiers OP1 to OP3 of the sensor signal
amplifier 12 configured as above each have a configuration
illustrated in FIG. 3. The configuration of the operational
amplifier will be described.
[0115] As shown in FIG. 3, the operational amplifier is constituted
by an offset compensating section 31, an amplifying section 32, and
a secondary amplifying section 33.
[0116] As shown in FIG. 3, the offset compensating section 31 is
composed of PMOSFET (hereinafter, referred to as a PMOS transistor)
Q1 and Q6 constituting a current mirror circuit, PMOS transistors
Q2 and Q5 constituting a current mirror circuit, a resistor R0 for
offset compensation that connects the drains of the PMOS
transistors Q5 and Q6, NMOSFET (hereinafter, referred to as NMOS
transistors) Q3 & Q4 that input an offset compensating signal
and control source-drain current of the MOS transistors Q1, Q2, Q5,
and Q6, and a current source Ia.
[0117] To be specific, the source of the PMOS transistor Q1 is
connected to a positive-side source line 34, the gate and the drain
thereof are connected to each other, and the common connecting part
is connected to the drain of the NMOS transistor Q3 and the gate of
the PMOS transistor Q6. Further, the source of the PMOS transistor
Q2 is connected to the positive-side source line 34, the gate and
the drain thereof are connected to each other, and the common
connecting part is connected to the drain of the NMOS transistor Q4
and the gate of the PMOS transistor Q5.
[0118] The sources of the PMOS transistors Q5 and Q6 are connected
to the positive-side source line 34, and the resistor R0 for
temperature compensation connects the drains thereof. The gate of
the NMOS transistor Q3 is connected to the input terminal 26, and
the gate of the NMOS transistor Q4 is connected to the input
terminal 25. Moreover, the sources of the NMOS transistors Q3 and
Q4 are connected to each other, and the common connecting part is
connected to a negative-side source line 35 via a constant current
source Ia.
[0119] As shown in FIG. 3, the amplifying section 32 is composed of
PMOS transistors Q7 and Q8 for inputting a signal and NMOS
transistors Q9 and Q10 constituting a current mirror circuit.
[0120] To be specific, the drain of the PMOS transistor Q5 is
connected to the source of the PMOS transistor Q7. The gate of the
PMOS transistor Q7 is connected to the input terminal 24, and the
drain thereof is connected to the drain of the NMOS transistor Q9.
Additionally, the gate and the drain of the NMOS transistor Q9 are
connected to each other, and the source thereof is connected to the
negative-side source line 35.
[0121] Also, the drain of the PMOS transistor Q6 is connected to
the source of the PMOS transistor Q8. Further, the gate of the PMOS
transistor Q8 is connected to the input terminal 23, and the drain
thereof is connected to the drain of the NMOS transistor Q10 and
the input of the secondary amplifying section 33. Furthermore, the
gate of the NMOS transistor Q10 is connected to the gate of the
NMOS transistor 9, and the source thereof is connected to the
negative-side source line 35.
[0122] Referring to FIGS. 2 and 3, the following will describe the
operation of the sensor signal amplifier 12 configured as
above.
[0123] First, the compensating operation (canceling operation) will
be discussed regarding each offset in the operational amplifiers
OP1 to OP3.
[0124] While clock .O slashed.1 from the clock generator 11, which
is shown in FIG. 1, is turned on, only the switches SW1-1 and SW1-2
shown in FIG. 2 are closed simultaneously, the non-inverting input
terminal 23 and the inverting input terminal 24 of the operational
amplifier OP1 are connected to each other, and the input terminals
are short-circuited. For this reason, offset voltage outputted from
the operational amplifier OP1 is held in the capacitor C1, and the
held voltage is supplied to the inverting input terminal 26 of the
offset compensating section 31, which is shown in FIG. 3.
[0125] Incidentally, in the amplifying section 32 of FIG. 3, input
voltage to be amplified is applied from the gate of a differential
pair of the PMOS transistors Q7 and Q8. A threshold voltage for
operating the PMOS transistors Q7 and Q8 is varied due to mismatch
of the PMOS transistors Q7 and Q8, causing input offset
voltage.
[0126] Here, currents I.sub.1, I.sub.2, I.sub.5, I.sub.6, I.sub.7,
I.sub.8, I.sub.9, and I.sub.10 each flow between the drain and
source of the MOS transistors Q1, Q2, Q5, Q6, Q7, Q8, Q9, and Q10,
inputs voltages U.sub.n1 and U.sub.p1 are applied between the
negative-side source line 35 and the gates of the MOS transistors
Q3 and Q4, input voltages U.sub.p2 and U.sub.n2 are applied between
the negative source line 35 and the gates of the MOS transistors Q7
and Q8, and current I.sub.out flows from the drain of the MOS
transistor Q8 to the secondary amplifying section 33. In this case,
the MOS transistors Q1 and Q6 and the MOS transistors Q2 and Q5
respectively form current mirror circuits. Hence, according to the
relationship of the current mirrors, the following equations (1)
and (2) are held.
I.sub.5=h.times.I.sub.2 (1)
I.sub.6=h.times.I.sub.1 (2)
[0127] Here, h is a constant and both are equal in mirror
ratio.
[0128] Additionally, the current Ia flowing through the constant
current source Ia is a constant current. Thus, the following
equation (3) is held.
Ia=I.sub.1+I.sub.2 (3)
[0129] Furthermore, the MOS transistor Q9 and Q10 form the current
mirror circuit. Thus, the following equation (4) is held.
I.sub.9=I.sub.10 (4)
[0130] Here, an offset voltage, which is obtained when the inputs
of the MOS transistors Q7 and Q8 are set at 0, is held in the
capacitor C1 as described above, and the held voltage is applied to
the gate of the MOS transistor Q4 of the offset compensating
section 31.
[0131] Therefore, a ratio of currents flowing through the MOS
transistors Q3 and Q4 of the offset compensating section 31, that
is, a ratio of the current I.sub.1 and current I.sub.2 changes, and
the currents I.sub.5 and I.sub.6 change accordingly.
[0132] Here, assuming that the transistors Q3 and Q4 have a
transconductance of g1, the following equation (5) is held.
I.sub.2-I.sub.1=g1.times.(U.sub.p1-U.sub.n1) (5)
[0133] Further, since the current I.sub.out and the current I.sub.8
have the relationship of I.sub.out<<I.sub.8, the following
equation (6) is held.
I.sub.9=I.sub.10=I.sub.7.apprxeq.I.sub.8 (6)
[0134] At this moment, the following equation (7) is held regarding
the current I.sub.R flowing through the resistor R0.
I.sub.R=I.sub.5-I.sub.7=I.sub.8-I.sub.6 (7)
[0135] Also, the following equation (8) is held according to the
equations (6) and (7).
I.sub.R=(I.sub.5-I.sub.6)/2 (8)
[0136] Further, the following equation (9) is held according to the
equations (1), (2), and (5).
I.sub.R=h.times.(I.sub.2-I.sub.1)/2=g1.times.h.times.(U.sub.p1-U.sub.n1)/2
(9)
[0137] Moreover, when the transistors Q7 and Q8 have a
transconductance of g and g/{1+(g.times.R0/2)} is defined as g2,
the output V.sub.out is expressed by the following equation (10)
with k serving as a constant.
V.sub.out=k.times.I.sub.out=k.times.(I.sub.8-I.sub.7)=k.times.g2.times.(U.-
sub.p2-U.sub.n2-I.sub.R.times.R0)=k.times.g2.times.{U.sub.p2-U.sub.n2-R0.t-
imes.g1.times.h.times.(U.sub.p1-U.sub.n1)/2} (10)
[0138] According to the equation (10), an offset voltage, which is
caused by the mismatch of the transistors Q7 and Q8, is expressed
by a difference between a voltage U.sub.p2 and a voltage U.sub.n2.
Thus, the inputs of the transistors Q3 and Q4, i.e., a voltage
(U.sub.p1-U.sub.n1) is inputted as a suitable value so as to cancel
the offset voltage.
[0139] Next, while a clock .O slashed.2 from the clock generator 11
is turned on, only the switches SW3-1 to SW3-3 are closed
simultaneously. Thus, an offset voltage which is concerned with the
operational amplifier OP3 is outputted from the operational
amplifier OP1 and is held in the capacitor C3, and the held voltage
is supplied to the non-inverting input terminal 25 of the offset
compensating section 31, which is illustrated in FIG. 3. As a
result, the offset voltage of the operational amplifier OP3 is
cancelled according to the foregoing principle.
[0140] Subsequently, while a clock .O slashed.3 from the clock
generator 11 is turned on, only the switches SW2-1 to SW2-3 are
closed simultaneously. Hence, an offset voltage which is concerned
with to the operational amplifier OP2 is outputted from the
operational amplifier OP1 and is held in the capacitor C2, and the
held voltage is supplied to the non-inverting input terminal 25 of
the offset compensating section 31, which is illustrated in FIG. 3.
As a result, the offset voltage of the operational amplifier OP2 is
cancelled according to the foregoing principle.
[0141] Meanwhile, while performing the offset compensating
operations of the operational amplifiers OP1 to OP3, a sensor
signal voltage Vhall, which is applied to the sensor signal input
terminals 19 and 20 from the sensor 1, is amplified by the
operational amplifiers OP1 and OP2. The amplified voltage is
outputted from the output terminals 27 and 28.
[0142] Further, in the case where the foregoing operation can
completely cancel the offset voltages of the operational amplifiers
OP1 to OP3, assuming that a sensor signal voltage is Vhall applied
to the sensor signal input terminals 19 and 20 from the sensor 1,
an output voltage Vout outputted to the output terminals 27 and 28
of the sensor signal amplifier 12 is expressed by the following
equation (11)
V.sub.out={(R1/R2)+1}.multidot.Vhall (11)
[0143] Here, R1 represents a resistance of a resistor connecting
between the inverting input terminal 24 and the output terminal of
the operational amplifier OP2, a resistor R2 represents a
resistance of a resistor connecting between the inverting input
terminal 24 of the operational amplifier OP2 and the inverting
input terminal 24 of the operational amplifier OP3 (see FIG.
2).
[0144] According to the equation (11), the sensor signal amplifier
circuit 12 can amplify a sensor signal with a necessary
amplification degree, which is temperature-independent, if the
resistances of R1 and R2 are equal in temperature coefficient.
[0145] Referring to FIG. 4, the following will discuss the detail
of the configuration of the reference voltage generator 13, which
is illustrated in FIG. 1.
[0146] As shown in FIG. 4, the reference voltage generator 13 is
provided with a current mirror circuit 41, which is composed of
PMOS transistors Q11 and Q12 and functions as a constant current
source, a constant current circuit 42, which supplies a constant
current by applying a temperature-independent voltage Vbg to a
voltage-current converting resistor R3, a current mirror circuit
43, which is composed of PMOS transistors Q14, Q15, and Q16 and
functions as a constant current source, a reference voltage
generator 44, which is composed of an upper limit reference voltage
generating resistor Rhigh, a lower reference voltage generating
resistor Rlow, and so on, and a current mirror circuit 45, which is
composed of NMOS transistors Q17 and Q18. An upper limit reference
voltage Vhigh and a lower limit reference voltage Vlow are
outputted from output terminals 46 and 47 and are supplied to the
Schmidt trigger 14 illustrated in FIG. 1.
[0147] As shown in FIG. 4, the current mirror circuit 41 is
composed of the PMOS transistors Q11 and Q12, the gates thereof
connect to each other, and the common connecting part connects to
the drain of the PMOS transistor Q11. Further, the sources of the
PMOS transistors Q11 and Q12 are connected to a positive-side
source line 51. Additionally, the drain of the PMOS transistor Q12
connects to the drain of the NMOS transistor Q13.
[0148] A current Iptat generated in the band gap reference voltage
generator 8 is supplied to the PMOS transistor Q11 of the current
mirror circuit 41 configured as above, and the current Iptat flows
through the MOS transistor Q12 as a constant current. The current
Iptat is directly proportional to absolute temperature T and
inversely proportional to a resistor R4 (not shown) disposed in the
band gap reference circuit 8. Assuming that K is a constant, the
Iptat is represented by the following equation.
Iptat=K.multidot.(T/R4) (12)
[0149] As shown in FIG. 4, the constant current circuit 42 is
constituted of the NMOS transistor Q13, the voltage-current
converting resistor R3, and the operational amplifier OP4. Namely,
the drain of the NMOS transistor Q13 connects to the drain of the
MOS transistor Q12, the source thereof connects to the terminal of
the voltage-current converting resistor R3, and the other terminal
connects to the negative-side source line 52. Moreover, the
regarding operational amplifier OP4, the temperature-independent
constant voltage Vbg is applied to the non-inverting input terminal
from the band gap reference circuit 8 via the input terminal 48,
the output terminal of the operational amplifier OP4 connects to
the gate of the NMOS transistor Q13, and the inverting input
terminal thereof connects to the common connecting part between the
source of the NMOS transistor Q13 and the voltage-current
converting resistor R3.
[0150] As shown in FIG. 4, the current mirror circuit 43 is
constituted of the MOS transistors Q14, Q15, and Q16. Namely, the
gates of the MOS transistors Q14, Q15, and Q16 connect to one
another, and the common connecting part connects to the drain of
the MOS transistor Q14 and the common connecting part between the
drains of the MOS transistors Q12 and the MOS transistor Q13.
Further, the sources of the MOS transistors Q14, Q15, and Q16
connect to the positive-side source line 51. Moreover, the drain of
the MOS transistor Q15 connects to the terminal of the upper limit
reference voltage generating resistor Rhigh, and the drain of the
MOS transistor Q16 connects to the drain of the MOS transistor
Q18.
[0151] As shown in FIG. 4, the reference voltage generator 44 is
constituted of the operational amplifier OP5, the upper reference
voltage generating resistor Rhigh, and the lower reference voltage
generating resistor Rlow. Namely, regarding the operational
amplifier OP5, an output Voutn from the sensor signal amplifier 12
is supplied to the non-inverting input terminal, and the output
terminal directly connects to the inverting input terminal.
Further, the upper reference voltage generating resistor Rhigh and
the lower reference generating resistor Rlow connect to each other
in series, and the output terminal of the operational amplifier OP5
connects to the common connecting part. Additionally, the terminal
of the upper limit reference voltage generating resistor Rhigh
connects to the drain of the MOS transistor Q15 and the output
terminal 46, and the terminal of the lower limit reference voltage
generating resistor Rlow connects to the drain of the MOS
transistor Q17 and the output terminal 47.
[0152] As shown in FIG. 4, the current mirror circuit 45 is
composed of the NMOS transistors Q17 and Q18, the gates of the MOS
transistors Q17 and Q18 connect to each other, and the common
connecting part connects to the drain of the MOS transistor Q18 and
the drain of the MOS transistor Q16. Moreover, the drain of the MOS
transistor Q17 connects to the terminal of the lower reference
voltage generating resistor Rlow. Additionally, the sources of the
MOS transistors Q17 and Q18 connect to the negative-side source
line 52.
[0153] Referring to FIG. 4, the following will discuss the
operation of the reference voltage generator 13 configured as
above.
[0154] The MOS transistors Q11 and Q12 constitute the current
mirror circuit, so that current mirror is performed on the current
Iptat flowing the MOS transistor Q11 and an equal current flows
between the source and drain of the MOS transistor Q12.
[0155] Meanwhile, the voltage Vbg is a constant voltage with
temperature-independence. The voltage Vbg is supplied from the band
gap reference voltage generator 8 to the operational amplifier OP4.
Since the voltage Vbg is supplied to the MOS transistor Q13 via the
operational amplifier OP4, a current of (Vbg/R3) flows between the
source and drain of the MOS transistor Q13. Here, R3 denotes a
resistance of the resistor R3.
[0156] Therefore, a current I.sub.14 flowing between the source and
drain of the MOS transistor Q14 is a difference between a current
flowing through the MOS transistor Q13 and a current flowing
through the MOS transistor Q12. The current I.sub.14 is represented
by the following equation (13) according to the equation (12).
I.sub.14=(Vbg/R3)-K.multidot.(T/R4) (13)
[0157] Also, the PMOS transistors Q14, Q15, and Q16 have a current
mirror relationship. Thus, when the mirror ratio is m, a current m
times larger than the above current I.sub.14 flows to the MOS
transistors Q15, Q16, and Q18. Since the transistor Q17 has a
mirror relationship with the transistor Q18, an equal current
I.sub.14.times.m flows to the transistor Q17, and the current
I.sub.14.times.m flows through the upper limit reference voltage
generating resistor Rhigh and the lower limit reference voltage
generating resistor Rlow. Consequently, an upper reference
potential Vhigh and a lower reference potential Vlow, which are
generated in the upper reference voltage generating resistor Rhigh
and the lower reference voltage generating resistor Rlow, are
represented by the following equations (14) and (15).
Vhigh=m.multidot.{(Vbg/R3)-K.multidot.(T/R4)}.multidot.Rhigh+Voutn=-m.mult-
idot.K.multidot.T.multidot.(Rhigh/R4)+m.multidot.Vbg.multidot.(Rhigh/R3)+V-
outn (14)
Vlow=-m.multidot.{(Vbg/R3)-K.multidot.(T/R4)}Rlow+Voutn=m.multidot.K.multi-
dot.T.multidot.(Rlow/R4)-m.multidot.Vbg.multidot.(Rlow/R3)+Voutn
(15)
[0158] Here, in the equations (14) and (15), Voutn represents a
potential when a signal value amplified in the sensor signal
amplifier 12 is 0. Further, the resistors R3, R4, Rhigh, and Rlow
are equal in temperature coefficient. Thus, regarding the upper
limit reference potential Vhigh and the lower limit reference
potential Vlow, resistor is not affected by temperature change, so
that the potentials are always set at a linear function of absolute
temperature T. Moreover, the upper limit reference potential Vhigh
and the lower limit reference potential Vlow can be generated as
linear functions of arbitrary absolute temperatures only by
changing the resistances of the resistors R3, R4, Rhigh, and Rlow,
and a mirror ratio m.
[0159] Namely, of variety of sensors, regarding sensors being able
to express an output with a linear function of absolute temperature
in an ideal or approximate manner in case of driving with a
constant voltage, only the values of the resistors R3, R4, Rhigh,
and Rlow in the signal processing circuit 2 and a mirror ratio m
are changed so as to form a sensor IC turning on/off at a fixed
sensitivity all the time.
[0160] Also, particularly in the case where the resistors Rhigh and
Rlow are equal in resistance and characteristic, the upper limit
reference potential Vhigh and the lower reference potential Vlow
can be set at perfectly symmetric values with respect to a 0 level
(Voutn) of a signal amplified in the sensor signal amplifier 12.
Here, as a reference signal, the temperature coefficients of the
upper limit reference potential Vhigh and the lower limit reference
potential Vlow will be discussed. Firstly, a temperature
coefficient of a reference signal V is defined in the following
manner. Namely, a reference signal is represented by V(T) at
absolute temperature T(K). Assuming that a reference room
temperature is T=300K, a temperature coefficient .alpha. of the
reference signal V(T) at temperature T(K) is definded by the
following equation (16).
.alpha.=(1/V(300)).multidot..DELTA.V/.DELTA.T (16)
[0161] Here, in the equation (16), .DELTA.V represents an amount of
change in reference signal and .DELTA.T represents an amount of
change in absolute temperature T.
[0162] According to the equation (16), if temperature coefficients
of the upper limit reference potential Vhigh and the lower limit
reference potential Vlow are found based on the equations (14) and
(15), the temperature coefficients are constant regardless of
temperature, as shown in the following equation (17).
Temperature coefficients of Vhigh=temperature coefficients of
Vlow=K/(300.multidot.K-Vbg.multidot.R4/R3) (17)
[0163] Therefore, when an output signal from the sensor 1 is a
linear function of absolute temperature, appropriate resistances
can be set for the resistors R3 and R4, so that the temperature
coefficients can be equal to that of the equation (17). Conversely,
in the case of equal temperature coefficients, if an amplification
factor of an output signal from the sensor 1, a mirror ratio m, and
the resistors Rhigh and Rlow are provided appropriately, at a
predetermined sensitivity, a temperature characteristic of an
amplified signal of the signal from the sensor can be made equal to
those of the equations (14) and (15). Namely, it is possible to
form a sensor IC turning on/off at a fixed sensitivity all the
time.
[0164] As described above, the sensor IC of the present embodiment
is constituted of the sensor land the signal processing circuit 2,
which is formed on the semiconductor layer provided on the
insulating substrate. Further, the sensor 1 changes the output
linearly with absolute temperature. In response, the reference
voltage generator 13 on the side of the sensor signal processing
circuit 2 produces the reference voltages Vhigh and Vlow that
changes the output at a temperature coefficient equal to that of
the output of the sensor 1 and changes the output linearly with
absolute temperature. The voltages are used as reference voltages
used for making a comparison with an output voltage of the sensor
signal amplifier 12 and for producing an on-off output.
Furthermore, the sensor signal amplifier 12 has functions of
amplifying the output signal from the sensor 1 with a
temperature-independent amplification factor and canceling an
offset voltage.
[0165] Therefore, according to the sensor IC of the present
embodiment, it is possible to realize accurate temperature
compensation over a wide temperature range from a low temperature
to a high temperature, thereby achieving an accurate operation with
reliability at a high temperature of 200.degree. C. or above that
has not been possible in the conventional art.
[0166] Further, according to the sensor IC of the present
embodiment, in the case where the sensor 1 is a Hall element and
the magnetic sensitive part is made of GaAs, since the resistor of
the GaAs increases with temperature, current flowing to the
magnetic sensitive part decreases and source current also
decreases. Hence, the sensor IC decreases in power consumption with
temperature and holds down the heat liberation, resulting in a
stable operation at a high temperature.
[0167] Furthermore, in the signal processing circuit 2, which is an
embodiment of an IC for the sensor of the present invention, the
reference voltage generator 13 produces the reference voltages
Vhigh and Vlow that changes in magnitude at a temperature
coefficient equal to that of the output signal provided between the
input terminals 19 and 20 from the sensor 1 and linearly with
absolute temperature. The Schmidt trigger 14 uses the voltage as a
reference voltage for comparing the output voltage of the sensor
signal amplifier 12 to produce an on-off output. Moreover, the
signal processing circuit 2 is formed on the semiconductor layer
provided on the insulating substrate.
[0168] Therefore, according to the signal processing circuit 2 of
the present embodiment, when one of the sensors changes the output
linearly with absolute temperature, a reference signal is produced
by a temperature linear function for the sensor, so that the signal
processing circuit 2 can be combined with the sensor. In this case,
according to the IC for the sensor IC of the present embodiment,
accurate temperature compensation is possible on the output of the
sensor over a wide temperature range from a low temperature and a
high temperature, thereby achieving an accurate operation with
reliability at a high temperature of 200.degree. C. or above, which
has not been possible in the conventional art.
[0169] Additionally, with the signal processing circuit of the
present embodiment, it is possible to provide a magnetic sensor IC
combined with a magnetic sensor used on a part having a high
temperature and a large difference in temperature in an automobile
and the like. And it is also possible to realize a variety of
sensor IC that can be used at a high temperature by making
combination with sensors such as a pressure sensor and a
temperature sensor.
[0170] Moreover, in the sensor IC of the present embodiment, the
sensor 1 is driven with a constant voltage generated by the sensor
bias voltage generator 10, and the reference voltage generator 13
performs temperature compensation of the sensor 1. Thus, it is
possible to reduce power consumption of the sensor 1 at a high
temperature, thereby suppressing heat liberation at a high
temperature. Consequently, a stable operation is possible even at a
high temperature of 200.degree. C. or above.
[0171] Here, although the above embodiment uses the Schmidt trigger
14 having hysteresis as a comparing means, a comparator having no
hysteresis is also applicable instead.
[0172] Also, the Schmidt trigger 14 can be replaced with an A/D
converter (analog/digital converter). In this case, an
amplification signal of the sensor 1 is used as an analog input
signal of the A/D converter. Further, the reference voltage
generator 13 generates reference voltages that change the outputs
at a temperature coefficient equal to that of the output from the
sensor 1 and that change in magnitude linearly with absolute
temperature. And then, the reference voltages are supplied to the
A/D converter as reference voltages. The A/D converter uses the
reference voltages to convert an input voltage to a digital
signal.
[0173] Furthermore, in the above embodiment, the sensor changes the
output linearly with absolute temperature and accordingly, the
generated voltage of the reference voltage generator 13 changes
linearly with absolute temperature. However, in the present
invention, it is not always necessary to set a fixed temperature
coefficient for the output of the sensor. In this case, the
reference voltage generator 13 is configured to produce reference
voltages changing at a temperature coefficient equal to that of the
output from the sensor. For example, in the case where the
temperature coefficient is not constant and the output of the
sensor is produced curvilinearly with absolute temperature, the
curving part can be divided into a plurality of sections so that
the sections are made to approximate as a straight line. And, to be
specific, for each of the sections approximating as a straight
line, a plurality of circuits corresponding to the reference
voltage generator 13 according to the section are provided. Analog
switches are provided between the reference voltages Vhigh and Vlow
and the Schmidt trigger 14 and the analog switches are switched in
accordance with temperature to select the reference voltage. With
this arrangement, it is always possible to produce a reference
voltage in response to the output of the sensor and to respond to a
sensor having an arbitrary temperature coefficient.
[0174] Here, according to the above embodiment, it is preferable
that the sensor is a Hall element and the magnetic sensitive part
of the Hall element is made of GaAs. However, in case of using a
material like GaAs, whose resistance increases with temperature, as
a component of the sensing section of the sensor, it is possible to
achieve the same effect as GaAs.
[0175] Moreover, in the case of the above embodiment, it is
preferable that an error of a temperature coefficient is 30% or
less based on a permissible range of irregular densities of
operating magnetic fluxes when the output of the sensor has a
temperature coefficient of about 0.20%/.degree. C. In the case of a
larger temperature coefficient, the permissible range of an error
is narrowed, and in the case of a smaller temperature coefficient,
a permissible range of a temperature coefficient is greatly
widened.
EXAMPLE 1
[0176] Next, a Hall IC manufactured as below will be discussed as
Example 1 of the sensor IC of the present invention.
[0177] The Hall IC according to Example 1 is formed as follows: an
IC including signal processing circuits shown in FIGS. 1 to 4 is
formed on a SIMOX substrate including silicon oxide as an
insulating base, by using CMOS process. Further, a crystalline
silicon layer on the insulating base is 120 nm in thickness.
Moreover, a switching period of offset compensation is set at 1/500
(second) regarding the sensor signal amplifier 12 shown in FIGS. 2
and 3.
[0178] Next, as the sensor 1, the IC including the sensor signal
amplifier 12 is combined with a Hall element whose magnetic
sensitive part is made of GaAs (hereinafter, referred to as a GaAs
Hall element), in a hybrid manner. Thus, the Hall IC is formed.
[0179] And then, a temperature-independent constant voltage 3 (V)
is applied to the GaAs Hall element, an output characteristic is
measured in a magnetic field of .+-.4 (mT), and measurement results
of FIG. 5 are obtained.
[0180] As shown in FIG. 5, in the case of .+-.4 (mT), a temperature
coefficient of the output is a negative temperature coefficient of
about -0.18 to -0.20%/.degree. C. in a temperature range of
-40.degree. C. to 200.degree. C., and the output can be expressed
as a linear function of absolute temperature. Further, the output
at -4 (mT) is substantially symmetric with respect to a temperature
axis, as compared with an output at +4 (mT).
[0181] Next, a bias voltage from the sensor bias voltage generator
10 of FIG. 1 is set at 3 (V), the voltage is applied to the GaAs
Hall element, an amplification factor computed by the equation (8)
of the sensor signal amplifier 12 is set at 50 times, and
resistances of the resistors R3, Rhigh, and Rlow of the reference
voltage generator 13 are respectively set at 23.81 (k.OMEGA.),
5.009 (k.OMEGA.), and 5.009 (k.OMEGA.) so as to meet a temperature
characteristic of the output of the GaAs Hall element. Moreover,
the constant voltage Vbg is set at 1.15 (V), and the constant K of
the equation (12) is set at 2.69.times.10.sup.-4
(A.multidot..OMEGA./K), and the resistance of the resistor R4 is
set at 4.492 (k.OMEGA.). Also, the equations (14) and (15) express
a mirror ratio m=1. Consequently, the equations (14) and (15) are
expressed by the following equations (18) and (19).
Vhigh(mV)=241.9-0.30.multidot.T (18)
Vlow(mV)=-241.9+0.30.multidot.T (19)
[0182] The results are substantially equal to 3V applied as a bias
voltage shown in FIG. 5 and an output voltage of GaAs that is
multiplied by 50 times in a magnetic field of 4 (mT). Additionally,
at this moment, the temperature coefficients of the reference
voltages Vhigh and Vlow are about -0.20%/.degree. C., which is
equal to that of GaAs.
[0183] FIG. 6 shows a temperature characteristic of an operating
input voltage of the signal processing circuit 2 in the case of the
operation under the above conditions. As shown in FIG. 6, the
resistor Rhigh and the resistor Rlow are equal in resistance. Thus,
it is possible to obtain an operating characteristic which is
completely symmetric with respect to a temperature axis. In
addition, it is found that the temperature characteristic is the
same as that of the GaAs Hall element shown in FIG. 5. Further, in
a temperature range of -40.degree. C. to 200.degree. C. or more,
the offset voltage is small and a required characteristic symmetry
to the temperature axis is realized.
[0184] Consequently, as shown in FIG. 7, it is understood that the
Hall IC of Example 1 is always turned on/off with magnitude of a
constant magnetic field of .+-.4 (mT) in a temperature range of
-40.degree. C. to 200.degree. C. and the Hall IC is superior in
symmetry of operating points.
[0185] FIG. 8 shows a temperature characteristic of a source
current when a source voltage of the Hall IC of the present
embodiment 1 is 5 (V). As shown in FIG. 8, an excellent
characteristic can be realized such that the source current and the
power consumption decrease with temperature. The source current
decreases in this way for the following reason: the GaAs Hall
element has the magnetic sensitive part made of GaAs and the
resistance of the GaAs increases with temperature, thereby reducing
current flowing to the magnetic sensitive part, and consequently,
the source current decreases.
EXAMPLE 2
[0186] Referring to FIGS. 9 to 14, the following will discuss a
rotation sensor IC for high temperatures that is used at a high
temperature, as Example 2 of the sensor IC according to the present
invention.
[0187] As shown in FIG. 9, the rotation sensor IC for high
temperatures are constituted of a magnetic sensor 71 and a signal
processing circuit 72 for processing an output signal of the
magnetic sensor 71. The magnetic sensor 71 corresponds to the
sensor 1 of FIG. 1, and the signal processing circuit 72 is
identical to the signal processing circuit 2 of FIG. 1 in basic
configuration. They are different from each other in the following
points.
[0188] As shown in FIG. 9, the magnetic sensor 71 forms a bridge
circuit using four magnetic resistor elements MR1 to MR4, and the
four magnetic resistor elements MR1 to MR4 are disposed to act as
detection sensors for rotation of a gear wheel as will be described
later. In the bridge circuit, for example, a bias voltage of 1 (V)
is supplied between bias voltage supplying terminals thereof from
the signal processing circuit 72, and an output signal outputted
from the output terminal of the circuit is inputted to the signal
input terminal of the signal processing circuit 72.
[0189] The magnetic sensor 71 and the signal processing circuit 72
formed as an integrated circuit are disposed (included) in a
package 75, for example, as shown in FIG. 10. Regarding the
magnetic resistor elements MR1 to MR4 constituting the magnetic
sensor 71, as shown in FIG. 10, the magnetic resistor elements MR1
and MR4 are vertically disposed to form an A block 73, and the
magnetic resistor elements MR2 and MR3 are vertically disposed to
form a B block 74. A spacing between the A block 73 and the B block
74 corresponds to a spacing between a convex part and a concave
part of a gear wheel 82, that will be discussed later. Furthermore,
the magnetic sensor 71 and the signal processing circuit 72 are
electrically connected to each other via wires 76, and the signal
processing circuit 72 connects to pins 77, which connect to the
outside, via wires 78.
[0190] Although the signal processing circuit 72 is substantially
identical to the signal processing circuit 2 of FIG. 1 in basic
configuration, the signal processing circuit 72 is different in the
following point. As compared with the sensor IC using the foregoing
GaAs Hall element, an amplification factor of the sensor signal
amplifier 12 is changed as will be discussed later, and the
reference voltage generator 13 is replaced with a reference voltage
generator 79 shown in FIG. 11.
[0191] The signal processing circuit 72 is configured as above to
handle a temperature coefficient as 0 regarding an output signal
from the bridge circuit. Here, to adjust the temperature
coefficient, the reference voltage generator 13 is replaced with
the reference voltage generator 79. Thus, generated reference
voltage has a temperature coefficient of 0.
[0192] Therefore, the reference voltage generator 79 is identical
to the reference voltage generator 13 of FIG. 4 in basic
configuration. However, the PMOS transistors Q11 and Q12 are
omitted from the reference voltage generator 13 of FIG. 4.
Additionally, other configurations of the reference voltage
generator 79 are equal to those of the reference voltage generator
13 shown in FIG. 4. Hence, the same members are indicated by the
same reference numerals and the description thereof is omitted.
[0193] Next, the following will discuss a rotation sensor 81 for
high temperatures that is configured as above and is used for,
e.g., detecting the rotation of a gear wheel and for a rotation
detecting system, as shown in FIG. 12.
[0194] As shown in FIG. 12, in the rotation detecting system, the
rotation sensor IC 81 for high temperatures is disposed at the
outer edge of the gear wheel 82 such that blocks 73 and 74 of the
sensor 71 are opposed to the outer surface. The gear wheel 82 is
made of a ferromagnet and is disposed rotatively. On the back of
the rotation sensor IC 81 for high temperatures, a samarium-cobalt
magnet 83 is disposed for intensifying the magnetic property of the
gear wheel 82 to readily detect a magnetic field. Also, to drive
the bridge circuit of the sensor 71, a constant voltage of 1 (V) is
supplied from the signal processing circuit 72. Moreover, a
magnetic flux density detected in the A block 73 of the sensor 71
and a magnetic flux density detected in the B block 74 of the
sensor 71 are taken out as voltage signals, and the voltage signals
are inputted to the signal processing circuit 72.
[0195] Referring to FIG. 12, the following will discuss the
principle of detecting rotation of the rotation detecting system
having the above configuration.
[0196] Regarding the magnetic sensitive parts (magnetic resistor
elements MR1 and MR4) of the A block 73 and the magnetic sensitive
parts (magnetic resistor elements MR2 and MR3) of the B block 74,
the magnetic flux densities vary in accordance with the rotation of
the gear wheel 82 because the gear wheel 82 has convex and concave
parts thereon. A difference between the densities of magnetic
fluxes also varies in synchronization with the rotation. When a
difference between the magnetic flux densities is larger than a
fixed reference voltage value, an output signal of the signal
processing circuit 2 is turned on, and when the difference is
smaller than the reference value, the output signal is turned
off.
[0197] Here, as for the signal processing circuit 72, the entire
system including the gear wheel 82, the samarium-cobalt magnet 83,
and the sensor 71 is a target of temperature compensation.
[0198] FIG. 13 shows an output amplitude from the bridge circuit.
The output amplitude is obtained when a constant voltage of 1 (V)
is applied from the signal processing circuit 72 to the bridge
circuit of the sensor 71 and the gear wheel 82 is rotated. In the
sensor system, due to a change in temperature of the gear wheel 82,
the magnet 83, or the bridge circuit, regarding the amplitude of
the output signal, that is obtained when the gear wheel 82 is
rotated, from the bridge circuit of the sensor 71, the magnitude of
the amplitude and temperature coefficient is about -0.01%/.degree.
C. Therefore, considering a temperature range of -40.degree. C. to
200.degree. C., any problems do not occur in practical use even
when the temperature coefficient is approximated to 0 within the
temperature range. The reference voltage generator for temperature
compensation can be configured as shown in FIG. 11, and a
temperature coefficient of the generated comparative reference
voltage can be set at 0.
[0199] Further, the magnetic flux densities acting upon the
magnetic sensitive parts of the A block 73 and the B block 74 of
the sensor 71 determine the parameter of the signal processing
circuit 72 such that the output of the signal processing circuit 72
is turned on at +1.5 (mT) and is turned off at -1.5 (mT). The
values of a resistor R3, an upper limit reference voltage
generating resistor Rhigh, and a lower limit reference voltage
generating resistor Rlow of the reference voltage generator 79 are
set as follows: R3.apprxeq.20 K.OMEGA., Rhigh=780 .OMEGA., and
Rlow=780 .OMEGA..
[0200] Further, other parameters of the equations (14) and (15) are
the same as those of the GaAs Hall IC.
[0201] At this moment, according to the equations (14) and (15),
the reference voltages Vhigh and Vlow of the reference voltage
generator 79 are computed as follows: Vhigh=+45 mV and Vlow=-45 mV.
The reference voltages are compared with an amplified signal, which
is produced by amplifying an output signal from the bridge circuit
of FIG. 14 by 150 times in the sensor signal amplifier. The output
of the signal processing circuit 72 is turned on/off according to
the result. Thus, the output is switched at a magnetic flux density
of 1.5 (mT) or more.
[0202] The rotation sensor IC for high temperatures configured as
above in Example 2 can detect the rotation of the gear wheel
without any problems at a high temperature of 200.degree. C.
[0203] Additionally, like Example 2, a conventional sensor IC has
been known, which uses a CMOS circuit in a silicon monolithic
manner to detect the rotation of a gear wheel. The upper limit
temperature is 150.degree. C. in practical use. However, in Example
2, the practical upper limit temperature is 200.degree. C. or above
as mentioned above.
EXAMPLE 3
[0204] Referring to FIGS. 15 to 19, the following will discuss a
pressure sensor IC for high temperatures that can be used at a high
temperature, as Example 3 of the sensor IC of the present
invention.
[0205] Conventionally, it has been known that the pressure sensor
for high temperatures using a SOI (Silicon on Insulator) structure
is applicable at a high temperature of 200.degree. C. or above.
Hence, as shown in FIG. 15, a pressure sensor 87 with the SOI
structure and a signal processing circuit 88 are combined with each
other, are included in the same package, and are used at a high
temperature of 200.degree. C. or above.
[0206] Although the signal processing circuit 88 is substantially
identical to the signal processing circuit 2 of FIG. 1 in basic
configuration, the signal processing circuit 88 is different in the
following points. An amplification factor of the sensor signal
amplifier 12 is changed as will discussed later, and the reference
voltage generator 13 is replaced with a reference voltage generator
101 shown in FIG. 17. These points will be described later on.
[0207] Therefore, the reference voltage generator 101 is basically
identical to the reference voltage generator 13 in configuration.
However, the reference voltage generator 101 is different in the
following points. The PMOS transistors Q11 and Q12 are omitted from
the reference voltage generator 13 of FIG. 4, and the connection of
the output terminal of the operational amplifier OP5 is changed
from the common connecting point of the upper reference voltage
generating resistor Rhigh and the lower reference voltage
generating resistor Rlow to the drain of the MOS transistor Q17.
Furthermore, the lower reference potential Vlow is taken out from
the common connecting point. Additionally, other configurations of
the reference voltage generator 101 is the same as those of the
reference voltage generator 13 shown in FIG. 4, so that the same
members are indicated by the same reference numerals and the
description thereof is omitted.
[0208] Incidentally, it is difficult to use a piezoresistor
pressure sensor using silicon diffused resistor at a high
temperature due to leakage current caused by PN-junction. Hence,
Example 3 adopts the pressure sensor 87 with the SOI structure
shown in FIG. 16, achieving an operation at a high temperature of
200.degree. C. or above.
[0209] As shown in FIG. 16, in the pressure sensor 87, an aluminum
oxide (Al.sub.2O.sub.3) film 92, a silicon film 93, and an aluminum
oxide (Al.sub.2O.sub.3) film 94 are stacked in this order on a
substrate 91, a piezoresistor element 95 is formed at the center of
the aluminum oxide film 94, the surfaces of the aluminum oxide film
94 and the piezoresistor element 95 are covered with an oxide film
(SiO.sub.2) 96, and the piezoresistor element 95 and four terminals
97 are connected to each other via a metal 98 (see FIG. 15).
Further, the four terminals 97 electrically connect to the signal
processing circuit 88.
[0210] FIG. 18 shows an output voltage relative to a temperature
that is obtained when driving the pressure sensor 87 with a
constant voltage of 3 V and applying the load of 0.05 Mpa
(mega-pascal). According to FIG. 18, a practical temperature
coefficient of the output voltage is about -0.01%/.degree. C. Even
when the temperature coefficient is approximately set at 0, any
problems do not occur in practical use. Thus, it is possible to
configure the reference voltage generator for temperature
compensation as shown in FIG. 17 and to set at 0 the temperature
coefficient of the produced comparative reference voltage.
[0211] Also, in Example 3, parameters of the signal processing
circuit 88 are set such that the output of the signal processing
circuit 88 is turned on at an operating pressure of 0.05 Mpa, and
the output is turned off at the pressure of 0.04 Mpa. An
amplification factor of the sensor signal circuit is set at 5
times, and the values of the resistor R3, the upper limit reference
voltage generating resistor Rhigh, and the lower limit reference
voltage generating resistor Rlow of the reference voltage generator
101 are set as follows: R3=20 K.OMEGA., Rhigh=310 .OMEGA., and
Rlow=1250 .OMEGA. (other parameters are the same as those of the
above GaAs Hall IC).
[0212] As shown in FIG. 19, in the pressure sensor IC for high
temperature having such a configuration, the output is turned on at
an operating pressure of 0.05 Mpa and the output is turned off at
an operating pressure of 0.04 Mpa in the temperature range from a
room temperature to 200.degree. C. In FIG. 19, Pon represents an
operating pressure for turning on the output and Poff represent an
operating pressure for turning off the output.
[0213] The pressure sensor IC for high temperatures with such a
configuration of Example 3 makes it possible to detect a pressure
without any problems even at a high temperature of 200.degree.
C.
EXAMPLE 4
[0214] The examples of the present invention described the
above-mentioned magnetic sensor IC and pressure sensor IC. However,
as Example 4, it is expected to realize a temperature switch for
switching in a temperature range of 100.degree. C. to 200.degree.
C. with the combination of (1) an oxygen sensor switch for high
temperatures using an electrochemical pump-type oxygen sensor
having a porous layer and (2) a PTC thermistor made of a material
such as a BaTiO.sub.3 material.
[0215] As earlier mentioned, the IC for the sensor IC of the
present invention can be combined with a variety of sensor
elements. Such combination makes it possible to realize kinds of
sensor ICs.
[0216] Generally, although it is necessary to design and
manufacture the sensor IC according to the sensor, three parameters
to be adjusted are an amplification factor, a temperature
coefficient, and a bias voltage regarding the sensor IC of the
present invention. Thus, the design is modified easily.
Additionally, if a plurality of ICs are previously designed and
manufactured with capability of temperature compensation at
different amplification factors and temperature coefficients, in
some combinations, typical sensor elements are more likely to form
a sensor IC having preferable temperature compensation in a wide
temperature range or in a part of a temperature range. In other
words, the IC for the sensor IC of the present invention is
applicable as a sensor IC for high temperatures for general purpose
use.
[0217] Further, since the sensor and the signal processing circuit
are mounted in the same package, it is possible to realize an IC
sensor operating accurately with a smaller size.
INDUSTRIAL APPLICABILITY
[0218] As described above, according to an IC for a sensor IC of
the present invention, an amplifying means inputs a sensor output
signal of the sensor, amplifies the sensor output signal with a
required amplification factor of temperature independence, and
cancels an offset, thereby accurately amplifying the output signal
of the sensor.
[0219] Moreover, a reference signal producing means produces a
reference signal which varies at a temperature coefficient equal to
that of the sensor output signal of the sensor. The signal is used
as a reference, that of which a comparing means makes comparison
with the magnitude of an amplification output signal of the
amplifying means and outputs a required signal. Hence, even when an
output signal of the sensor is changed due to the influence of
temperature, it is possible to cancel the influence.
[0220] Further, the following configuration is made: the amplifying
means, the reference signal producing means, the comparing means,
and a constant voltage generating means are formed using a
semiconductor layer provided on an insulating substrate, the
semiconductor layer is preferably composed of a silicon thin film,
and leakage current can be reduced in a high temperature range and
latch-up can be prevented.
[0221] For this reason, in the IC for the sensor IC of the present
invention, when one of sensors has an output changing at a
temperature coefficient equal to that of the reference signal
produced by the reference signal producing means, combination can
be made with the sensor. In this case, over a wide temperature
range from a low temperature to a high temperature (e.g., from
-40.degree. C. to 200.degree. C. or above), temperature
compensation can be performed accurately for the output of the
sensor, achieving an accurate operation with reliability even at a
high temperature.
[0222] Furthermore, in case of forming the sensor IC combined with
the sensor, the IC for sensor IC of the present invention can be
realized only by changing the components of the reference signal
producing means according to a temperature characteristic of the
sensor. Thus, combination is made with a variety of sensors,
achieving wide applicability.
[0223] Also, according to the IC for the sensor IC of the present
invention, the reference signal producing means is based on the
previous measurement of a temperature coefficient of a sensor
output signal of the sensor and produces a reference signal having
the same temperature coefficient. The signal is used as a reference
, that of which the comparing means makes comparison with the
magnitude of an amplification output signal of the amplifying means
and outputs a required signal. Hence, in the case where the sensor
IC is configured with the combination of a sensor, accuracy of
comparison can be improved.
[0224] Additionally, in the manufacturing and assembling, irregular
characteristics of the sensor can be severely selected, and the
reference signal producing means can produce a reference signal
according to a characteristic peculiar to the manufactured sensor,
thereby readily achieving a sensor IC with a desired specification
by making combination with the sensor.
[0225] Moreover, according to the IC for sensor IC of the present
invention, the reference signal producing means produces a
reference signal having a temperature coefficient equal to that of
the sensor output signal of the sensor and changing linearly with
absolute temperature. The signal is used as a reference, that of
which the comparing means makes comparison with the magnitude of
the amplification output signal of the amplifying means and outputs
a required signal.
[0226] For this reason, according to the IC for the sensor IC of
the present invention, when one of the sensors has output changing
linearly with absolute temperature, a reference signal provided by
a linear function of absolute temperature is produced according to
the sensor. Thus, combination can be made with the sensor. In this
case, accurate temperature compensation can be realized for the
output of the sensor over a wide temperature range from a low
temperature to a high temperature, achieving accurate temperature
compensation with reliability even at a high temperature. Moreover,
even in a wide temperature range whose output is not a linear
function but is approximate to a linear function, an accurate
operation can be performed in the temperature range.
[0227] On the other hand, according to the sensor IC of the present
invention, the amplifying means receives the sensor output signal
of the sensor, amplifies the received signal at a required
temperature-independent amplification factor and operates to cancel
an offset, thereby accurately amplifying the sensor output
signal.
[0228] Additionally, the reference signal producing means produces
a reference signal varying at a temperature coefficient equal to
that of the output signal of the sensor. The signal is used as a
reference, that of which the comparing means makes comparison with
the magnitude of the amplification output signal of the amplifying
means and outputs a required signal. Thus, even when the output
signal of the sensor is varied due to the influence of temperature,
the influence can be cancelled.
[0229] Further, the following configuration is made: the amplifying
means, the reference signal producing means, the comparing means,
and a constant voltage generating means are formed using a
semiconductor layer provided on an insulating substrate, the
semiconductor layer is preferably composed of a silicon thin film,
and leakage current can be reduced and latch-up can be prevented in
a high-temperature range.
[0230] Hence, according to the sensor IC of the present invention,
over a wide temperature range from a low temperature to a high
temperature (e.g., from -40.degree. C. to 200.degree. C. or above),
temperature compensation can be performed accurately for the output
of the sensor, causing an accurate operation with reliability even
at a high temperature.
[0231] Further, the sensor IC of the present invention is completed
by the inventor et al. who considered a characteristic of GaAs
having a resistance increasing with temperature and earnestly
studied the characteristic for positive and effective use.
[0232] Therefore, according to the present invention, GaAs whose
resistance increases with temperature is adopted as a magnetic
sensitive part of a Hall element. Thus, it is possible to reduce
current of the magnetic sensitive part and to reduce source current
with temperature. Hence, the sensor IC decreases in power
consumption with temperature, suppresses an increase in temperature
that is caused by consumption of current, and operates in a stable
manner even at a high temperature.
[0233] Furthermore, according to the sensor IC of the present
invention, the reference signal producing means is based on the
previous measurement of a temperature coefficient of the sensor
output signal of the sensor and produces a reference signal having
the same temperature coefficient. The signal is used as a reference
, that of which the comparing means makes comparison with the
magnitude of the amplification output signal of the amplifying
means and outputs a required signal, thereby improving accuracy of
temperature compensation.
[0234] Also, the sensor can be severely selected for each
characteristic upon manufacturing and assembling and the reference
signal producing means can produce a reference signal according to
the selected characteristic of the sensor. Thus, it is possible to
readily realize a sensor IC having a desired specification by
making combination with the sensor.
[0235] Moreover, according to the sensor IC of the present
invention, the reference signal producing means is equal to the
sensor output signal in temperature coefficient and produces a
reference signal changing linearly with absolute temperature. The
signal is used as a reference, that of which the comparing means
makes comparison with the magnitude of the amplification output
signal of the amplifying means and outputs a required signal. Even
when the output signal of the sensor is changed due to the
influence of the temperature, the influence can be cancelled.
[0236] For this reason, it is possible to realize accurate
temperature compensation for the output of the sensor over a wide
temperature range from a low temperature to a high temperature,
achieving an accurate operation with reliability even at a high
temperature. Additionally, even in a wide temperature range whose
output is not a linear function but is approximate to a linear
function, an accurate operation can be achieved in the temperature
range.
* * * * *