U.S. patent application number 10/157123 was filed with the patent office on 2002-10-17 for temperature sensor.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Kishi, Masakazu.
Application Number | 20020150141 10/157123 |
Document ID | / |
Family ID | 14237531 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020150141 |
Kind Code |
A1 |
Kishi, Masakazu |
October 17, 2002 |
Temperature sensor
Abstract
In a temperature sensor, especially in a temperature sensor
using a resonator, based on a frequency of one oscillator circuit
(resonator), frequencies of the other one or more oscillator
circuits (resonators) are measured, and frequency-temperature
characteristics of a plurality of resonators are synthesized in
order to realize an accurate temperature sensor which does not
require an accurate frequency reference regardless of a temperature
change, and has a linear characteristic and a wide measurable
temperature range. Also, two oscillator circuits have two
resonators respectively with quadratic characteristics in which
quadratic coefficients are the same and linear characteristics are
different from each other, and a difference between oscillation
frequencies of both oscillator circuits is obtained.
Inventors: |
Kishi, Masakazu; (Kawasaki,
JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN & HATTORI, LLP
1725 K STREET, NW.
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
14237531 |
Appl. No.: |
10/157123 |
Filed: |
May 30, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10157123 |
May 30, 2002 |
|
|
|
PCT/JP99/06946 |
Dec 10, 1999 |
|
|
|
Current U.S.
Class: |
374/141 ;
374/163; 374/170; 374/E11.012 |
Current CPC
Class: |
G01K 11/265 20130101;
G01K 7/32 20130101 |
Class at
Publication: |
374/141 ;
374/170; 374/163 |
International
Class: |
G01K 001/14; G01K
013/00; G01K 007/00 |
Claims
What we claim is:
1. A temperature sensor comprising: two oscillator circuits using
resonators having different temperature characteristics of
resonance frequencies; and a detection circuit for relatively
obtaining, with a frequency of one oscillator circuit being made a
reference, a frequency of the other oscillator circuit, for
performing a predetermined calculation between both frequencies,
and for outputting a calculation result as a temperature
signal.
2. The temperature sensor as claimed in claim 1 wherein the
detection circuit is composed of a reference counter for counting a
predetermined time interval based on a frequency of one oscillator
circuit, a temperature counter for counting an output of the other
oscillator circuit during the predetermined time interval, and a
calculating circuit for calculating a difference between values of
the temperature counter and the reference counter.
3. The temperature sensor as claimed in claim 1 wherein the
detection circuit is composed of a reference counter for counting a
predetermined time interval based on a frequency of one oscillator
circuit, a temperature counter for counting an output of the other
oscillator circuit during the predetermined time interval, and a
calculating circuit for calculating a ratio between values of the
temperature counter and the reference counter.
4. The temperature sensor as claimed in claim 1, further comprising
one or more oscillator circuits using another resonator having a
different temperature characteristic of a resonance frequency, the
detection circuit obtaining, with a frequency of a first oscillator
circuit among the oscillator circuits being made a reference,
frequencies of the remaining two or more second oscillator
circuits, performing a predetermined calculation between all the
frequencies, and outputting a calculation result as a temperature
signal.
5. The temperature sensor as claimed in claim 4 wherein the
detection circuit includes a reference counter for counting a
predetermined time interval based on a frequency of the first
oscillator circuit, a total counter for totalizing outputs of the
remaining oscillator circuits either in an up direction or a down
direction during the predetermined time interval to be counted, and
a calculating circuit for calculating a difference between values
of the total counter and the reference counter.
6. The temperature sensor as claimed in claim 4 wherein the
detection circuit includes a reference counter for counting a
predetermined time interval based on a frequency of the first
oscillator circuit, a total counter for totalizing outputs of the
remaining oscillator circuits either in an up direction or a down
direction during the predetermined time interval to be counted, and
a calculating circuit for calculating a ratio between values of the
total counter and the reference counter.
7. A temperature sensor comprising: two oscillator circuits having
two resonators respectively with quadratic characteristics in which
quadratic coefficients are same and linear characteristics are
different from each other; and a detection circuit for detecting a
difference between a frequency of one oscillator circuit and a
frequency of the other oscillator circuit and for detecting a
temperature corresponding to the difference.
8. The temperature sensor as claimed in claim 1 wherein the
detection circuit multiplies or divides a frequency of at least one
oscillator circuit.
9. The temperature sensor as claimed in claim 1 wherein the
detection circuit further converts the temperature signal into a
predetermined temperature value.
10. The temperature sensor as claimed in claim 4 wherein the
resonator comprises an SAW resonator.
11. The temperature sensor as claimed in claim 10 wherein the SAW
resonator is formed on a same substrate.
12. The temperature sensor as claimed in claim 11 wherein a
propagation direction of one SAW resonator is angled with respect
to a propagation direction of the other resonator.
13. The temperature sensor as claimed in claim 10 wherein at least
one SAW resonator utilizes a Rayleigh wave, and at least another
SAW resonator utilizes an SH wave.
14. The temperature sensor as claimed in claim 10 wherein the
oscillator circuit has a separator for separating a Rayleigh wave
from an SH wave of one SAW resonator, a mixer for mixing the
separated Rayleigh wave and the SH wave, and two oscillation
portions for respectively oscillating with frequencies of the
Rayleigh wave and the SH wave.
15. A VCTCXO device using the temperature sensor as claimed in
claim 1.
16. The temperature sensor as claimed in claim 15 wherein an
oscillator of a VCO portion and a resonator of the temperature
sensor in the VCTCXO device are formed in one piece on a same
substrate.
17. The temperature sensor as claimed in claim 7 wherein the
detection circuit further converts a temperature signal into a
predetermined temperature value.
18. The temperature sensor as claimed in claim 7 wherein the
resonator comprises an SAW resonator.
19. The temperature sensor as claimed in claim 18 wherein the SAW
resonator is formed on a same substrate.
20. The temperature sensor as claimed in claim 19 wherein a
propagation direction of one SAW resonator is angled with respect
to a propagation direction of the other resonator.
21. The temperature sensor as claimed in claim 18 wherein one SAW
resonator utilizes a Rayleigh wave, and the other SAW resonator
utilizes an SH wave.
22. The temperature sensor as claimed in claim 18 wherein the
oscillator circuit has a separator for separating a Rayleigh wave
from an SH wave of one SAW resonator, a mixer for mixing the
separated Rayleigh wave and the SH wave, and two oscillation
portions for respectively oscillating with frequencies of the
Rayleigh wave and the SH wave.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a temperature sensor, and
in particular to a temperature sensor using a resonator.
[0003] Various temperature sensors have been proposed depending on
the applications thereof and have been reduced to practice. For any
temperature sensor, a temperature reproducibility, a temperature
range, a temperature characteristic, and an accuracy required for
the applications are important.
[0004] 2. Description of the Related Art
[0005] FIG. 17 shows a frequency-temperature characteristic of a
Surface Acoustic Wave (hereinafter, abbreviated as SAW) resonator
receiving attention in various fields for its superior temperature
reproducibility. This characteristic is shown by a quadratic curve
in which a frequency "f" exhibits a maximum value (peak) at a
temperature T1.
[0006] FIG. 18 shows a prior art arrangement of a temperature
sensor using an SAW resonator. In this example, an oscillator
circuit 20 is arranged so as to connect an SAW resonator 21 as an
oscillator to an amplifier 22 and a temperature sensor 10 measuring
the oscillation frequency of the oscillator circuit 20 by a
reference frequency is composed.
[0007] A counter 31 counts an output of the oscillator circuit 20.
A reference frequency oscillator circuit 40 produces a latch signal
92 for latching, in a register 41, a value of the counter 31 at a
fixed time interval (e.g. 1 sec.) based on an internal reference
frequency, and a reset signal 91 provided to the counter 31 after
the latching.
[0008] A frequency/temperature converter 50 includes a table
storing a relationship between the frequency "f" and the
temperature "T" shown in FIG. 17 preliminarily obtained by
experiments or the like, and outputs, referring to this table, a
temperature signal 90 obtained by converting a frequency value from
the register 41 into a temperature value.
[0009] In such a temperature sensor 10, an accurate frequency
reference signal corresponding to a required temperature accuracy
becomes necessary, so that the circuit price is increased as the
accuracy increases.
[0010] As for a measurable temperature range at this time, it is
supposed that either a temperature range higher than a temperature
T1 or a temperature range lower than the temperature T1 is
preliminarily selected lest two temperatures correspond to the same
frequency. Also, since a gradient around the temperature T1 is
small, the temperature greatly changes even for a little frequency
change and the measurement accuracy declines. For this reason, it
is common to remove the range around the temperature T1 from
available ranges.
[0011] Namely, when the frequency-temperature characteristic is a
quadratic curve, a cubic curve, or more, there is a possibility
that two or more temperatures correspond to the same frequency.
Therefore, the measurable temperature range is disadvantageously
limited by the frequency-temperature characteristic of the SAW
resonator.
[0012] It is to be noted that the above-mentioned problems are
common to the temperature sensors using not only the SAW resonator
but also a general oscillator.
SUMMARY OF THE INVENTION
[0013] It is accordingly an object of the present invention to
provide a temperature sensor not requiring an accurate frequency
reference regardless of a temperature change.
[0014] It is another object to provide a temperature sensor with a
wide measurable temperature range.
[0015] It is a further object to provide an accurate temperature
sensor having a linear characteristic.
[0016] (1) In order to achieve the above-mentioned objects, a
temperature sensor according to the present invention comprises:
two oscillator circuits using resonators having different
temperature characteristics of resonance frequencies; and a
detection circuit for relatively obtaining, with a frequency of one
oscillator circuit being made a reference, a frequency of the other
oscillator circuit, for performing a predetermined calculation
between both frequencies, and for outputting a calculation result
as a temperature signal.
[0017] Namely, a temperature characteristic of a resonance
frequency of a resonator used for one oscillator circuit is
different from that of a resonator used for the other oscillator
circuit. With an output frequency, which may depend on a
temperature, of one oscillator circuit being made a reference, a
detection circuit relatively measures an output frequency, which
may also depend on a temperature, of the other oscillator
circuit.
[0018] Then, a predetermined calculation is performed to both
output frequencies, so that the result is outputted as a
temperature signal corresponding to an actual temperature. It is to
be noted that the relationship between the temperature signal and
the actual temperature can be easily obtained by a well-known
relationship.
[0019] Thus, even if the oscillation frequencies may depend on a
temperature, since one oscillation frequency is relatively measured
from the other oscillation frequency, it becomes possible to
realize a temperature sensor having a temperature characteristic
which can not be realized by a single resonator, without a
conventional absolute frequency reference with a high accuracy.
[0020] In other words, it becomes possible to realize a temperature
sensor which outputs a desired temperature signal by selecting the
frequency-temperature characteristics of two oscillator
circuits.
[0021] It is needless to say that a delay-type oscillator circuit
using a resonator may be included in the above-mentioned oscillator
circuit.
[0022] (2) Also, in the present invention according to the
above-mentioned present invention (1), the detection circuit may
comprise a reference counter for counting a predetermined time
interval based on a frequency of one oscillator circuit, a
temperature counter for counting an output of the other oscillator
circuit during the predetermined time interval, and a calculating
circuit for calculating a difference between values of the
temperature counter and the reference counter.
[0023] Namely, the reference counter counts the predetermined time
interval, which may depend on a temperature, by inputting an output
frequency signal of one oscillator circuit and by counting until a
predetermined counter value is reached.
[0024] The temperature counter can obtain a counter value
corresponding to the oscillation frequency by counting an output of
the other oscillator circuit at the predetermined time intervals.
The calculating circuit obtains a difference between the
predetermined counter value and the counter value of the
temperature counter to be outputted as a temperature signal
corresponding to the temperature.
[0025] It is to be noted that in order to obtain an actual
temperature from this temperature signal, a relationship has only
to be used between the temperature signal and the temperature
preliminarily obtained based on e.g. the frequency-temperature
characteristics in two oscillator circuits, and a calculating
equation of a calculating circuit=difference.
[0026] Thus, by obtaining the difference between the counter values
of both counters, it becomes unnecessary to use the absolute
oscillator circuit with a high accuracy that is stable for the
temperature and it becomes possible to realize a temperature sensor
outputting a desired temperature signal.
[0027] (3) Also, in the present invention according to the
above-mentioned present invention (1), the detection circuit may
comprise a reference counter for counting a predetermined time
interval based on a frequency of one oscillator circuit, a
temperature counter for counting an output of the other oscillator
circuit during the predetermined time interval, and a calculating
circuit for calculating a ratio between values of the temperature
counter and the reference counter.
[0028] Namely, the operations of the reference counter and the
temperature counter are the same as those in the above-mentioned
present invention (2). The calculating circuit, different from the
present invention (2), obtains a ratio between the counter values
of the temperature counter and the reference counter to be
outputted as a value corresponding to the temperature.
[0029] Thus, by obtaining the ratio between the counter values of
both counters, it becomes unnecessary to use the absolute
oscillator circuit with a high accuracy, and it becomes possible to
realize a temperature sensor having a desired relationship between
a temperature signal and a temperature.
[0030] (4) Also, in the above-mentioned present invention (1), the
temperature sensor according to the present invention may further
comprise one or more oscillator circuits using another resonator
having a different temperature characteristic of a resonance
frequency, and the detection circuit may obtain, with a frequency
of a first oscillator circuit among the oscillator circuits being
made a reference, frequencies of the remaining two or more second
oscillator circuits, perform a predetermined calculation between
all the frequencies, and output a calculation result as a
temperature signal.
[0031] Namely, by using the resonators, three or more oscillator
circuits are composed. The temperature characteristics of the
resonance frequencies of the resonators used for the oscillator
circuits are different from each other. The detection circuit
relatively measures, with an output frequency of one oscillator
circuit among them being made a reference, the respective
frequencies of the remaining two or more oscillator circuits.
[0032] Based on all of the frequencies obtained, a predetermined
calculation is performed, so that the calculation result is
outputted as a temperature signal. From this temperature signal, an
actual temperature is recognized.
[0033] Thus, it becomes possible to realize a temperature sensor
having the frequency-temperature characteristic in which the
frequency-temperature characteristics of three or more resonators
are synthesized, so that the frequency-temperature characteristic
synthesized by e.g. two resonators can be corrected to a further
preferable characteristic.
[0034] (5) Also, in the present invention according to the
above-mentioned present invention (4), the detection circuit may
include a reference counter for counting a predetermined time
interval based on a frequency of the first oscillator circuit, a
total counter for totalizing outputs of the remaining oscillator
circuits either in an up direction or a down direction during the
predetermined time interval to be counted, and a calculating
circuit for calculating a difference between values of the total
counter and the reference counter.
[0035] Namely, the reference counter counts the output of the first
oscillator circuit, and makes the time until the counter becomes a
predetermined counter value the predetermined time interval. The
total counter inputs the frequency output signal of the other
oscillator circuits at the predetermined time interval, and counts
the signal in an up direction or a down direction, so that the
result is outputted as a total counter value.
[0036] The calculating circuit outputs the difference between the
counter values of the total counter and the reference counter as a
temperature signal.
[0037] Thus, a temperature is measured by a single desired
frequency-temperature characteristic obtained from the
frequency-temperature characteristics of three or more oscillator
circuits. It becomes possible to correct the frequency-temperature
characteristic close to a straight line obtained by calculating the
frequency-temperature characteristics of e.g. two oscillator
circuits to the frequency-temperature characteristic of a complete
straight line by further adding the temperature characteristics of
the remaining oscillator circuits to the calculation.
[0038] (6) Also, in the present invention according to the
above-mentioned present invention (4), the detection circuit may
include a reference counter for counting a predetermined time
interval based on a frequency of the first oscillator circuit, a
total counter for totalizing outputs of the remaining oscillator
circuits either in an up direction or a down direction during the
predetermined time interval to be counted, and a calculating
circuit for calculating a ratio between values of the total counter
and the reference counter.
[0039] Namely, the operations of the reference counter and the
total counter are the same as those in the present invention (5).
However, the calculating circuit calculates not the difference
between both counter values but the ratio between both counter
values, and outputs the calculation result as a temperature signal
corresponding to a temperature.
[0040] Thus, by obtaining the ratio, it becomes possible to obtain
a temperature signal corresponding to a temperature based on the
frequency-temperature characteristic obtained from the
frequency-temperature characteristics of three or more oscillator
circuits.
[0041] (7) Also, a temperature sensor according to the present
invention comprises: two oscillator circuits having two resonators
respectively with quadratic characteristics in which quadratic
coefficients are same and linear characteristics are different from
each other; and a detection circuit for detecting a difference
between a frequency of one oscillator circuit and a frequency of
the other oscillator circuit and for detecting a temperature
corresponding to the difference.
[0042] FIG. 1 shows characteristic curves of two resonators whose
frequency-temperature characteristics are different from each
other. These characteristic curves are expressed in the form of
equations:
f1=a1(T-T1).sup.2+c1, f2=a2(T-T2).sup.2+c2,
[0043] where a quadratic coefficient is supposed to be a1=a2. The
detection circuit inputs frequency output signals of the f1 and f2
respectively from the oscillator circuits to detect the difference.
Supposing that a1=a2=a, the difference assumes a linear equation as
follows:
Difference=f2-f1=2a(T1-T2)T+a(T2.sup.2-T1.sup.2)+c2-c1 Eq.(1)
[0044] Thus, the temperature sensor outputs the value having a
relationship of a linear function with a temperature. This output
value can be easily converted into a temperature only from e.g. a
linear coefficient of the linear function and a constant.
[0045] It is to be noted that a case of c1=c2 is shown in FIG.
1.
[0046] Accordingly, the difference (f2-f1) is expressed by the
following equation:
Difference=f2-f1=2a(T1-T2) (T-(T1+T2)/2) Eq.(2)
[0047] Namely, the difference (=f2-f1) assumes a linear line
passing through a midpoint between T1 and T2 on a temperature (T)
axis.
[0048] While an absolute reference frequency with a high accuracy
is required in this invention, both sides of the characteristic
curves f1 and f2 can be used for the temperature measurable range,
which leads to a wider temperature measurable range in comparison
with the case shown in FIG. 17.
[0049] (8) Also, in the present invention according to the
above-mentioned present invention (1), the detection circuit may
multiply or divide a frequency of at least one oscillator
circuit.
[0050] Namely, the detection circuit can change the frequency of
the oscillator circuit to a frequency multiplied or divided. Thus,
it becomes possible to change the frequency observed from the side
of the detection circuit, i.e. to convert the frequency-temperature
characteristic of the resonator, and the calculation of the
temperature signal having a predetermined temperature
characteristic becomes easy, thereby enabling the arrangement of
the detection circuit to be simplified.
[0051] Also, it is possible to bring the frequencies of two
oscillator circuits close until a beat arises.
[0052] (9) Also, in the present invention according to the
above-mentioned present inventions (1) and (7), the detection
circuit may convert the temperature signal into a predetermined
temperature value.
[0053] Thus, it becomes possible to correct the temperature signal
into the actual temperature value.
[0054] (10) Also, in the present invention according to the
above-mentioned present inventions (4) and (7), an SAW resonator
may be used as the resonator.
[0055] Namely, an SAW resonator superior in the temperature
reproduction characteristic can be used as a resonator.
[0056] (11) Also, in the present invention according to the
above-mentioned present invention (10), the SAW resonator may be
formed on a same substrate.
[0057] Thus, in comparison with the case where the SAW resonators
are discrete, variations of the temperature characteristics and
variations of the detected temperatures due to a difference of
detected positions can be avoided. Also, it becomes possible to
make a temperature detection accurate, and to downsize a body of a
resonator.
[0058] (12) Also, in the present invention according to the
above-mentioned present invention (11), a propagation direction of
one SAW resonator may be angled with respect to a propagation
direction of the other resonator.
[0059] Thus, it becomes possible to make a coating thickness of
electrodes same, and to make a production process simple.
[0060] (13) Also, in the present invention according to the
above-mentioned present invention (10), at least one SAW resonator
may utilize a Rayleigh wave, and at least another SAW resonator may
utilize an SH wave.
[0061] (14) Also, in the present invention according to the
above-mentioned present invention (10), the oscillator circuit may
have a separator for separating a Rayleigh wave from an SH wave of
one SAW resonator, a mixer for mixing the separated Rayleigh wave
and the SH wave, and two oscillation portions for respectively
oscillating with frequencies of the Rayleigh wave and the SH
wave.
[0062] Namely, a separator separates a Rayleigh wave from an SH
wave included in a single SAW resonator to be respectively provided
to oscillation portions. The oscillation portions respectively
oscillate with frequencies of the Rayleigh wave and the SH wave, so
that the output is provided to a mixer. The mixer mixes both waves
to be provided to the SAW resonator.
[0063] Thus, it becomes possible to use two frequencies in a single
SAW resonator, and to make the SAW resonator downsized and highly
accurate.
[0064] (15) Also, in the present invention, a VCTCXO device may be
realized by using a temperature sensor according to the
above-mentioned present invention (1).
[0065] Namely, it is possible to control a VCO portion of a VCTCXO
device with the output of the temperature sensor being made
temperature information.
[0066] (16) Also, in the present invention according to the
above-mentioned present invention (15), an oscillator of a VCO
portion and a resonator of the temperature sensor in the VCTCXO
device may be formed in one piece on a same substrate.
[0067] Thus, it becomes possible to make the VCTCXO device
downsized and highly accurate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0068] The above and other objects and advantages of the invention
will be apparent upon consideration of the following detailed
description, taken in conjunction with the accompanying drawings,
in which the reference numbers refer to like parts throughout and
in which:
[0069] FIG. 1 is a graph showing frequency-temperature
characteristics of two SAW resonators used in a temperature sensor
according to the present invention, and a frequency-temperature
characteristic example of a linear function obtained by
synthesizing the frequency-temperature characteristics;
[0070] FIG. 2 is a block diagram showing an embodiment (1) of a
temperature sensor according to the present invention;
[0071] FIG. 3 is a block diagram showing an embodiment (1) of a
detection circuit in a temperature sensor according to the present
invention;
[0072] FIG. 4 is a graph showing frequency-temperature
characteristics of two SAW resonators used in a temperature sensor
according to the present invention, and a frequency-temperature
signal characteristic example obtained by synthesizing the
frequency-temperature characteristics;
[0073] FIG. 5 is a block diagram showing an embodiment (2) of a
detection circuit in a temperature sensor according to the present
invention;
[0074] FIG. 6 is a block diagram showing an embodiment (2) of a
temperature sensor according to the present invention;
[0075] FIG. 7 is a block diagram showing an embodiment (3) of a
temperature sensor according to the present invention;
[0076] FIG. 8 is a block diagram showing an embodiment (4) of a
temperature sensor according to the present invention;
[0077] FIG. 9 is a block diagram showing an embodiment (5) of a
temperature sensor according to the present invention;
[0078] FIG. 10 is a graph showing frequency-temperature
characteristics of two SAW resonators used in a temperature sensor
according to the present invention and a characteristic example (1)
of a difference therebetween;
[0079] FIG. 11 is a graph showing frequency-temperature
characteristics of two SAW resonators used in a temperature sensor
according to the present invention and a characteristic example (2)
of a difference therebetween;
[0080] FIG. 12 is a block diagram showing an embodiment (6) of a
temperature sensor according to the present invention;
[0081] FIG. 13 is a block diagram showing an embodiment (7) of a
temperature sensor according to the present invention;
[0082] FIG. 14 is a block diagram showing an embodiment (8) of a
temperature sensor according to the present invention;
[0083] FIG. 15 is a block diagram showing an embodiment (9) of a
temperature sensor according to the present invention;
[0084] FIG. 16 is a block diagram showing an embodiment of a VCTCXO
device using a temperature sensor according to the present
invention;
[0085] FIG. 17 is a graph showing a frequency-temperature
characteristic example of a general SAW resonator used in a
temperature sensor; and
[0086] FIG. 18 is a block diagram showing an arrangement of a prior
art temperature sensor.
DESCRIPTION OF THE EMBODIMENTS
[0087] FIG. 2 shows an embodiment (1) of a temperature sensor 10
according to the present invention. In this embodiment, oscillator
circuits 20_1 and 20_2 respectively provide output frequency
signals f1 and f2 to a detection circuit 30. Either the signal f1
or f2 (the signal f1 in this example) is made a reference
frequency. The detection circuit 30 detects the frequency of the
frequency signal f2 based on the reference frequency signal f1 to
output a temperature signal 90.
[0088] The oscillator circuits 20_1 and 20_2, where SAW resonators
21_1 and 21_2 (occasionally represented by a reference numeral 21)
are simply connected to amplifiers 22_1 and 22_2 like a loop
respectively, are loop oscillator circuits.
[0089] As is well-known, any oscillator circuit among various prior
art oscillator circuits may be used for the circuits 20.
[0090] FIG. 3 shows an embodiment (1) of the detection circuit 30,
which is composed of a counter (temperature counter) 31 for
inputting the frequency f2 from the oscillator circuit 20_2, a
centesimal counter (reference counter) 32 for inputting the
reference frequency signal f1 from the oscillator circuit 20_1 and
for outputting a counter value and a reset signal 91, a determiner
33 for inputting the counter value and for outputting a latch
signal 92 when the counter value assumes "99", a register 41 for
temporarily storing the value of the counter 31, and a subtractor
34 for outputting the temperature signal 90 obtained by subtracting
"100" from the value of the register 41.
[0091] In operation, the centesimal counter 32 repeats the
operation of counting the signal f1 between 0-99 in order to count
a predetermined time interval to output its carry signal as the
reset signal 91. The determiner 33 determines that the value of the
counter 32 is "99", and then outputs the latch signal 92.
[0092] It is to be noted that since the frequency of the signal f1
depends on a temperature, the predetermined time interval is not
always the same time interval.
[0093] The counter 31 counts the signal f2 after the counter is
reset to "0" with the reset signal 91 until the following reset
signal 91 is inputted. The register 41 stores the counter value of
the counter 31 with the latch signal 92. The subtractor 34
subtracts "100" from this counter value to be outputted as the
temperature signal 90.
[0094] It is to be noted that the frequency signals f1 and f2 are
assumed to be a pulse signal. However, even if the outputs of the
oscillator circuits 20_1 and 20_2 are signals of another form, they
can be inputted to the above-mentioned detection circuit 30
unchanged or by shaping them into pulse signals.
[0095] FIG. 4 shows a relationship between the above-mentioned
frequency signals f1 and f2 and the output temperature signal 90.
Data values in FIG. 4 are calculated values shown for reference in
order to simplify understanding the operation.
[0096] Also, the frequency-temperature characteristics of two
resonators are shown to exhibit characteristics of the same
quadratic coefficient and their peak temperatures respectively
assume temperatures T1 and T2 different from each other at the
frequency="100".
[0097] In FIG. 3, the time interval when the centesimal counter 32
counts "0"-"99" is 100/f1. During this time interval, the value
counted by the counter 31, that is the counter value stored in the
register 41 is f2 (100/f1). The value of the temperature signal 90
which is the output of the subtractor 34 where 100 (=the value
corresponding to the centesimal of the centesimal counter 32) is
subtracted from the counter value f2 (100/f1) assumes
f2(100/f1)-100=100(f2-f1)/f1.
[0098] A curve A of FIG. 4 shows a relationship between the
above-mentioned calculated value and the temperature signal 90
(=100(f2-f1)/f1: indicated by calibrations M1 of ordinate on the
right of FIG. 4). This curve A is almost a straight line. It is to
be noted that a curve B will be described later.
[0099] In this example, a calculation corresponding to a
calculating circuit which calculates the difference between the
both counters 31 and 32 described in the present invention (2) in
Summary of the Invention is realized by the centesimal counter 32
and the subtractor 34. Namely, the centesimal counter 32 is made a
reference counter and a subtraction value of the subtractor 34 is
made "100", thereby subtracting the signal f1 from the signal
f2.
[0100] Thus, without using an accurate frequency reference such as
a reference frequency oscillator circuit 40 shown in FIG. 18, the
temperature signal 90 having another temperature characteristic can
be obtained from resonators having different frequency-temperature
characteristics. It is to be noted that in order to accurately make
the temperature signal 90 coincide with a desired temperature
characteristic further for correcting the temperature
characteristic of a VCTCXO device described later for example, the
correction has only to be performed by using a method described
later.
[0101] Also, it is needless to say that if a resonator having
another frequency-temperature characteristic is used, a temperature
sensor 10 having a temperature characteristic different from that
of the curve A can be arranged.
[0102] FIG. 5 shows an embodiment (2) of the detection circuit 30.
This embodiment is different from the embodiment (1) of FIG. 3 in
the following points: The centesimal counter 32 is substituted for
a millesimal counter (reference counter) 32, no subtractor 34 is
provided, and the output of the register 41 storing the counter
value of the counter (temperature counter) 31 is made a temperature
signal 90.
[0103] In operation, the millesimal counter 32 inputs the signal f1
and repeats the count between "0"-"999" in order to set a
predetermined time interval. When the counter value changes from
"999" to "0", the reset signal 91 is outputted to reset the counter
31 to "0". Namely, the reset signal 91 is outputted at time
intervals of 1000/f1 to repeat the reset of the counter 31.
[0104] The counter 31 counts the pulse number of the signal f2
between the reset signal 91 and the following reset signal 91. The
determiner 33 determines that the counter value of the millesimal
counter 32 assumes "999" to provide the latch signal 92 to the
register 41.
[0105] Accordingly, the timing of outputting the latch signal 92 is
when the counter value of the counter 31 assumes a maximum before
the reset signal 91. The counter value at this time is
(1000/f1)f2=1000f2/f1. The value in which the decimal point of the
temperature signal 90 outputted from the register 41 is moved by
three digits toward the upper digit assumes f2/f1. Thus, by the
calculating circuit composing the detection circuit 30, the ratio
between the temperature counter 31 and the reference counter 33 is
calculated.
[0106] The above-mentioned curve B in FIG. 4 shows a relationship
between the temperature T (abscissa) and the temperature signal 90
(=f2/f1: calibrations M2 of ordinate within parentheses on the
right of FIG. 4). In this example, the curve B is also nearly a
straight line, but is different from the curve A.
[0107] It is to be noted that in FIG. 4 the curves A and B appear
to be almost the same curves. This is because both curves are
plotted by calibrations different from each other, so that the
values of the temperature signal 90 on both curves are different
for the same temperature T. For example, at the same temperature
T2, the temperature signal 90 synthesized with the difference=4.2,
and the temperature signal 90 synthesized with the ratio=1.04.
[0108] Thus, in the same way as the embodiment (1), an accurate
absolute reference frequency is not required. Also when resonators
having the same frequency-temperature characteristics as the
embodiment (1) are used, a temperature sensor of a different
temperature characteristic can be arranged since the calculation is
different in terms of difference and ratio of the counter
values.
[0109] FIG. 6 shows an embodiment (2) of the temperature sensor 10
according to the present invention. This example is different from
the embodiment (1) of FIG. 2 in that the SAW resonators 21_1 and
21_2 are provided on the same substrate 80.
[0110] Thus, the SAW resonators 21_1 and 21_2 in their entirety can
be downsized. Also, in comparison with the case where the
resonators are discrete, the temperature sensing positions are
close and the temperature characteristics are the same, so that the
accuracy is improved.
[0111] FIG. 7 shows an embodiment (3) of the temperature sensor 10
according to the prevent invention. This example is different from
the embodiment (2) of FIG. 6 in that the directions of the two SAW
resonators 21_1 and 21_2 provided on the same substrate 80 are
respectively angled by 0 on the surface of the substrate 80.
[0112] In the embodiment (2), because of the same substrate 80,
that is, the same cut angle, the number of design parameters for
making only peak temperatures different is decreased by one in
comparison with the case where the SAW resonators 21 are
discrete.
[0113] Therefore, in order to make only the peak temperatures
different, an electrode pitch and a coating thickness have to be
made different. As a result, a frequency adjustment of the SAW
resonators 21_1 and 21_2 has to be independently performed.
[0114] Therefore, according to the embodiment (3), it becomes
possible to equate an electrode coating thickness by using a
parameter of a rotation on the surface of the substrate, and to
simplify a manufacturing process.
[0115] FIG. 8 shows an embodiment (4) of a temperature sensor
according to the present invention. This embodiment is different
from the embodiment (2) of FIG. 6 in that frequency dividers 60_1
and 60_2 (occasionally represented by a reference numeral 60) are
respectively inserted between the oscillator circuits 20_1, 20_2
and the detection circuit 30.
[0116] Namely, it becomes possible to change the
frequency-temperature characteristic of the oscillator circuit as
observed from the side of the detection circuit. Thus, by
introducing a parameter which makes frequencies of the two SAW
resonators different, it becomes possible to increase a flexibility
of a design.
[0117] For example, the frequency dividers 60_1 and 60_2 can
respectively divide the frequency signals f1 and f2 into
frequencies which are almost the same as the frequency f0 but are
different from each other. Thus, it is possible to generate beats
at two frequencies.
[0118] It is to be noted that either one or both of the frequency
dividers 60_1 and 60_2 may be a frequency multiplier. Also, one of
the frequency dividers 60 or the frequency multipliers may be
omitted.
[0119] Also, the SAW resonators may be arranged by discrete
resonators.
[0120] FIG. 9 shows an embodiment (5) of the temperature sensor 10
according to the present invention. This example is different from
the embodiment (2) shown in FIG. 6 in that one of the SAW
resonators 21 uses a Rayleigh wave, and the other SAW resonator 21
uses an SH wave.
[0121] In this embodiment, since an available mode is different, it
is difficult to obtain temperature characteristics in which only
the peak temperatures of the SAW resonators 21_1 and 21_2 are
different from each other. Conversely, it becomes possible to
obtain various temperature characteristics, and to use the
temperature characteristics for a temperature correction of a
device which is not linear.
[0122] FIGS.10 and 11 show characteristics of the Rayleigh wave
signal f1 and the SH wave signal f2.
[0123] Depending on a selection of a cut angle of a substrate, i.e.
which mode should be the object, e.g. the temperature
characteristic of the difference (f2-f1) differs greatly.
[0124] FIG. 10 shows a case where a cut angle (around ST38.degree.)
for the Rayleigh wave is selected, and a linear characteristic
remarkably appears in the SH wave signal f2.
[0125] Reversely, FIG. 11 shows a case where a cut angle (around
ST36.degree.) for the SH wave is selected. Both of the Rayleigh
wave signals f1 and the SH wave signal f2 are almost a quadratic
characteristic, but their coefficients are generally different from
each other (it is possible to make the coefficients the same).
[0126] It is to be noted that the SAW resonators can be arranged in
discrete form.
[0127] FIG. 12 shows an embodiment (6) of the temperature sensor
according to the present invention. This embodiment is different
from the embodiment (5) in that frequency multipliers 61_1 and 61_2
(occasionally represented by a reference numeral 61) are
respectively connected in series between the oscillator circuit
20_1 and the detection circuit 30, and the oscillator circuit 20_2
and the detection circuit 30.
[0128] Thus, in the same way as the embodiment (4), it becomes
possible to increase a flexibility of a design.
[0129] It is to be noted that either one or both of the frequency
multipliers 61 may be a frequency divider. Also, one of the
frequency divider 60 or the frequency multiplier 61 may be
omitted.
[0130] FIG. 13 shows an embodiment (7) of the temperature sensor 10
according to the present invention. This example is different from
the embodiment (4) shown in FIG. 8 in that a single SAW resonator
21 is provided, and the amplifiers 22_1 and 22_2 are connected to
the SAW resonator 21 through a frequency distributor 23 and a
frequency mixer 24.
[0131] In operation, the frequency distributor 23 distributes the
Rayleigh wave of the SAW resonator 21 to the amplifier 22_1, and
distributes the SH wave to the amplifier 22_2. The frequency mixer
24 mixes the Rayleigh wave from the amplifier 22_1 and the SH wave
from the amplifier 22_2 to be provided to the SAW resonator 21.
[0132] The oscillator circuits 20_1 and 20_2 respectively oscillate
at the frequencies of the Rayleigh wave and the SH wave. Thus, it
becomes possible to provide only a single SAW resonator 21, thereby
enabling the downsizing and high accuracy to be expected.
[0133] FIG. 14 shows an embodiment (8) of the temperature sensor
according to the present invention. This embodiment is different
from the embodiment (1) of FIG. 2 in that the oscillator circuits
20_1-20_n, respectively oscillating at the resonators 22_1-22_n
(not shown; "n" is a natural number equal to or more than three)
having the frequency-temperature characteristics different from
each other, provide the frequency signals f1-fn to the detection
circuit 30.
[0134] Also, the detection circuit 30 is different from that of
FIG. 3 in that the counter 31 is substituted for a total counter
31, and the frequency signals f2-fn are inputted to the counter
31.
[0135] The operations of the centesimal counter 32, the determiner
33, the register 41, and the subtractor 34 are the same as those in
FIG. 3. The total counter 31 counts the inputted frequency signals
f2-fn in an up direction or a down direction to output the
totalized counter value. It is to be noted that positive and
negative signs in the total counter 31 are shown as an example.
[0136] As a result, the counter value provided from the total
counter 31 to the register 41 at the timing of the latch signal 92
assumes e.g. 100(f2-f3+ . . . +fn)/f1.
[0137] Accordingly, the temperature signal 90=(100(f2-f3+ . . .
+fn)/f1)-100=100(f2-f1-f3+ . . . +fn)/f1 is outputted from the
subtractor 34.
[0138] The value of the temperature signal 90 is different from
that of FIG. 3 in that (-f3+ . . . +fn) term is added in the
parentheses of the numerator. The value of this term can be changed
together with the frequency-temperature characteristics of the
resonators 22_3-22_n or a count direction.
[0139] Thus, it is possible to correct the curve A shown in FIG. 4
to a complete straight line by further adding one or more
oscillator circuits 20 to provide three or more oscillator
circuits.
[0140] It is to be noted that the following circuit arrangement can
be considered for another method of measuring remaining frequencies
with a single frequency being made a reference frequency.
[0141] Namely, counters C1-Cn (not shown) for respectively counting
the frequency signals f1-fn and a counter C0 (not shown) for
counting the frequency signal f0 are provided. It is supposed that
the counter C1 corresponds to the above-mentioned reference
counter. Also, the counter C0 is newly provided, and the accuracy
of the temperature characteristic of the frequency signal f0 is not
cared.
[0142] The counter C0 counts a fixed time interval, so that the
counters C1-Cn respectively count the frequency signals f1-fn at
the fixed time intervals and obtain the maximum counter value of
the counters C1-Cn. The respective ratios between the counter C1
and the remaining counters C2-Cn are obtained. Namely, the other
frequency signals f2-fn are supposed to be obtained with the
frequency signal f1 being made a reference frequency. By
synthesizing the ratios, a predetermined temperature characteristic
can be obtained.
[0143] Also, for another method of measuring the remaining
frequencies with a single frequency being made a reference
frequency, it is possible to measure a time for a single wavelength
of the frequencies f1-fn respectively with the high frequency f0
(accuracy of the frequency f0 to the temperature is not cared), and
to obtain the frequencies f1-fn with e.g. a time for a single
wavelength of the frequency f1 being made a reference. Thus, a
temperature sensor having a fast response speed can be
arranged.
[0144] FIG. 15 shows an embodiment (9) of the temperature sensor 10
according to the present invention. The arrangement of this
embodiment is the same as that of the embodiment (1) shown in FIG.
2, so that the frequency signals f1 and f2 of the oscillator
circuits 20_1 and 20_2 are provided to the detection circuit
30.
[0145] However, the arrangement of the detection circuit 30 is
basically different from that of the detection circuit 30 shown in
FIG. 3. For example, the detection circuit 30 is not arranged such
that the other frequency signal f2 is measured with one frequency
signal f1 being made a reference.
[0146] Namely, the detection circuit 30 is composed of the counter
31 for inputting the signal f1, the counter 35 for inputting the
signal f2, the reference frequency oscillator circuit 40 for
providing the reset signal 91 to the counters 31 and 35 and for
outputting the latch signal 92, the subtractor 34 for inputting the
counter values of the counters 31 and 35 and for outputting the
difference between the counter values, and the register 41 for
inputting the calculation result of the subtractor 34 and the latch
signal 92 and for outputting the temperature signal 90.
[0147] Also, the frequency-temperature characteristics of the
respective SAW resonators 21_1 and 21_2 (not shown) in the
oscillator circuits 20_1 and 20_2 are supposed to have a quadratic
characteristic as shown in FIG. 1 where quadratic coefficients are
the same, linear coefficients are different, and the peak
frequencies are equal.
[0148] It is to be noted that the peak frequencies are not
necessarily equal. In this embodiment, for a contrast with the
frequency-temperature characteristic of FIG. 4, the peak
frequencies are supposed to be equal.
[0149] In operation, the oscillator circuit 40 outputs the latch
signal 92, so that the register 41 stores the subtraction result of
the subtractor 34 with the latch signal 92. The oscillator circuit
40 outputs the reset signal 91 at the timing of completing the
storing operation. Namely, the oscillator circuit 40 repeatedly
outputs the latch signal 92 and the reset signal 91 at the fixed
intervals.
[0150] As a result, the value obtained by subtracting the maximum
counter value of the counter 31 from the maximum counter value of
the counter 35 at the subtractor 34 is stored in the register 41,
so that the value is outputted as the temperature signal 90.
[0151] Thus, as shown in the present invention (7) in Summary of
the Invention, the relationship between the temperature signal 90
and the actual temperature corresponding thereto becomes linear.
Since this embodiment uses the reference frequency oscillator
circuit 40, there is a possibility that the relationship of the
linear line changes with the temperature characteristic of the
circuit 40. However, it is possible to make a correction by the
circuit arrangement where the above-mentioned embodiments (1)-(8)
are combined.
[0152] Also, it becomes possible to compose the temperature sensor
10, having a linear characteristic not requiring a correction of
the temperature by an ROM or the like, with a wide measurable
temperature range and high accuracy.
[0153] It is to be noted that as a method of detecting the
difference between the frequency of one oscillator circuit and that
of the other oscillator circuit, and obtaining the difference, a
method of taking out a beat signal by using a frequency converter
which mixes and detects two oscillation frequencies is also
possible.
[0154] Thus, if the resonators used for the oscillator circuits
have the above-mentioned characteristic, the characteristic of the
linear line can be obtained. However, in this case, a symmetrical
line characteristic with respect to a measured value "0" is
obtained, so that whether the temperature signal is on the positive
side or the negative side can not be determined as it is.
[0155] Therefore, the circuit is prepared for simply obtaining the
relationship as to which one of e.g. two frequency signals f1 and
f2 is larger, and whether the signal is either on the
positive/negative side has only to be determined based on the above
relationship.
[0156] It is to be noted that while the temperature signal 90 from
the above-mentioned detection circuit is outputted as a digital
signal, it can be outputted as an analog signal.
[0157] FIG. 16 shows an embodiment of a VCTCXO device 70 to which
the temperature sensor 10 according to the present invention is
applied.
[0158] This device is composed of a voltage control oscillator
(VCO) 73, a temperature sensor 10 for detecting the temperature of
the VCO 73, an A/D converter 74 for AID converting the temperature
signal 90 (analog signal) of the temperature sensor 10, an ROM 71
for outputting the digital signal converted by the A/D converter 74
based on conversion data, and a D/A converter 72 for converting the
digital signal from the ROM 71 into an analog control signal 93 and
for providing the signal 93 to a control input terminal of the VCO
73.
[0159] Also, the conversion data for matching temperature
correction information of the VCO 73 with the output characteristic
of the temperature sensor 10 and for improving the temperature
characteristic of the VCTCXO device 70 in its entirety are written
in the ROM 71.
[0160] In operation, the temperature sensor 10 detects the
temperature of the VCO 73 as the temperature signal 90. The A/D
converter 74, the ROM 71, and the D/A converter 72 convert the
temperature signal 90 into the control signal 93 to control the
oscillation frequency of the VCO 73.
[0161] Thus, the frequency-temperature characteristic of the VCTCXO
device 70 in its entirety is improved, so that the VCTCXO device 70
stable for the temperature is arranged.
[0162] Also, according to the temperature sensor 10 of the present
invention, it is possible to design the temperature sensor 10
having a temperature characteristic of compensating the temperature
characteristic of the VCO 73. If such a temperature sensor 10 is
used, the A/D converter 74, the ROM71, and the D/A converter 72
become unnecessary, so that it becomes possible to directly input
the temperature signal 90 as the control signal 93 to the VCO 73
and to arrange the simple VCTCXO device 70.
[0163] As described above, a temperature sensor according to the
present invention is arranged such that based on a frequency of one
oscillator circuit (resonator), frequencies of the other one or
more oscillator circuits (resonators) are measured, and
frequency-temperature characteristics of a plurality of resonators
are synthesized. Therefore, it becomes possible to obtain a
predetermined temperature characteristic (relationship between an
actual temperature and an output temperature signal of a
temperature sensor) having a wide measurable range, without using
an accurate reference frequency which does not depend on a
temperature.
[0164] Also, two oscillator circuits have two resonators
respectively with quadratic characteristics in which quadratic
coefficients are the same and linear characteristics are different
from each other, and a difference between oscillation frequencies
of both oscillator circuits is obtained, thereby enabling an
accurate temperature sensor to be arranged which has a linear
characteristic and a wide oscillation measurable range, and which
requires a frequency reference with a favorable temperature
characteristic.
[0165] Furthermore, if the temperature sensor according to the
present invention is adopted for a temperature sensor portion of a
VCTCXO device, it becomes possible to easily compensate the
temperature characteristic of the VCO included in the VCTCXO
device.
* * * * *