Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-10-08
2002-04-16
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S658000, C324S666000, C324S674000, C324S680000, C324S681000
Reexamination Certificate
active
06373264
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a detection apparatus and method for detecting an amount of a physical variable, and more particularly to a detection apparatus and method for detecting an amount of a physical variable to provide a signal corresponding to an amount which can be digitally processed.
BACKGROUND ART
As a prior art example of a detection circuit adapted to detect a change in a physical amount, it is described in Japanese Patent Public Disclosure (Laid-Open or Kokai) No. 63-108257 issued in 1988, for example.
FIG. 1
is a block diagram illustrating the prior art detection circuit described in the No. 63-108257. The detection circuit, which is intended to detect humidity as a physical amount, comprises an oscillation unit
51
having a humidity sensor
54
, a F-V converter
52
, and a logarithmic amplifier
53
. The humidity sensor
54
is designed to vary its resistance in accordance with variations in ambient humidity. Then, the resistance variation causes the oscillation unit
51
to change its oscillation frequency. An output signal of the oscillation unit
51
is next input to the F-V converter
52
, where the frequency of the signal is converted to a direct current voltage. The direct current voltage signal output from the F-V converter circuit
52
is next inputted to the logarithmic amplifier
53
, where the direct current voltage is logarithmically amplified. In this way, this detection circuit can reveal the ambient humidity on the bases of the output voltage value from the logarithmic amplifier
53
.
Another prior detection circuit is described in Japanese Patent Publication (Kokoku) No. 2-22338. This detection circuit also detects a change in humidity as is the case of the above-mentioned No. 63-108257. Although not shown here, the detection circuit comprises an integrator for detection including a humidity sensor as a capacitance which changes its value in response to humidity, and a reference integrator for comparison which does not change the time constant. In an operation of the detection circuit, the same pulse signal is input to both the integrators, and the difference between signals output from the respective integrators is delivered from a differential amplifier, and a maximum value of the difference is further output from a peak hold circuit as a direct current voltage signal. Thus, the detection circuit can provide the ambient humidity based on the output voltage of the peak hold circuit.
Another prior art example of a detection circuit is described in Japanese Patent Public Disclosure (Kokai) No. 63-27720.
FIG. 2
is a circuit diagram illustrating the detection circuit which is for weight detection described in No. 63-27720.
SUMMARY OF THE INVENTION
In recent years, integrated circuit technologies have advanced and digital signal processing requiring complicated product/sum operations can be readily performed by using a processor dedicated to signal processing or the like. Since such digital signal processing enables time division processing or the like using a software control, a large amount of complicated signals can be processed to precisely reveal a variety of information while avoiding a system from requiring a larger size and an increased cost.
Each of the detection circuits described in the above-mentioned Japanese Patent Public Disclosure Nos. 63-108257 and 2-22338, however, outputs, from its output terminal, an analog signal or voltage which has magnitude depending on the physical amount. It is therefore necessary to convert the output voltage into a digital signal by an additional A/D converter in order to digitally process it. For this reason, if the digital processing apparatus such as a microcomputer is introduced to process the output of the detection circuit, a more complicated configuration such as an A/D converter is required therebetween, thus causing a problem of an increased size and an increased cost of the entire system. Particularly, when parallel real time processing is required for a large number of signals output from such detection circuits, it is necessary to parallelly provide a number of A/D converters equal to the number of signals from the detection circuits, making the above problem more prominent.
On the other hand, as illustrated in
FIG. 2
, the detection circuit described in Japanese Patent Public Disclosure No. 63-27720 comprises an oscillation unit
42
including operational amplifiers
42
a,
42
b
and a sensor
41
which changes the capacitance in accordance with a weight applied thereto. An oscillation frequency of the oscillation unit
42
changes in response to a change in the capacitance of the sensor
41
. A variable resistor
43
is also provided in the oscillation unit
42
for adjusting a basis of the oscillation frequency.
An output signal of the oscillation circuit
42
is input to an amplifier
46
including a transistor
46
a.
The amplifier
46
amplifies the output signal of the oscillation unit
42
so as to have an enough amplitude that a counter
47
in a microcomputer
45
can count the number of waves of the oscillation signal. Thus, the counter
47
counts the number of the waves in the amplified signal during a predetermined time period, and outputs a count value to a processing unit
48
in the microcomputer
45
. A voltage setting circuit
44
in turn sets a predetermined direct current voltage. This direct current voltage is input to an A/D converter
49
in the microcomputer
45
where it is converted into a digital signal, and then output to the processing unit
48
. The processing unit
48
calculates the capacitance of the sensor
41
from the count value, using the digital value input from the A/D converter
49
as a conversion coefficient.
In the detection circuit shown in
FIG. 2
, the oscillation unit
42
converts a change in the capacitance of the sensor
41
into a change in frequency. Then, the counter
47
counts the number of the waves in the frequency signal from the oscillation unit
42
so that the capacitance change of the sensor
41
can be revealed as a digital signal.
However, in the detection circuit shown in
FIG. 2
, any parasitic capacitance is inevitably formed at an input terminal of the operational amplifier
42
a
or the like. Therefore, when a sensor
41
having an extremely small capacitance must be used, a change in the capacitance of the sensor
41
does not induce an apparent change in frequency of the output signal due to the influence of the parasitic capacitance. Particularly, in the approach which counts the number of waves in the signal output from the oscillation unit
42
in a predetermined period to reveal a change in the capacitance of the sensor
41
, only a change in frequency exceeding a certain level eventually represents a change in the number of the waves. Therefore, it causes a problem in that a change in the capacitance of the sensor
41
is difficult to be captured when a change in the oscillating frequency does not reach the level. It is contemplated to make the oscillating frequency of the oscillation unit
42
higher and use a very high speed counter
47
in order to solve such a problem as above. However, the solution would result in a more complicated circuit configuration and therefore a very expensive apparatus. Furthermore, the parasitic capacitance as mentioned becomes significantly larger when the operational amplifier
42
a
of the oscillation unit
42
and the sensor
41
are formed on separate chips. Consequently, such an increased parasitic capacitance would make it difficult to produce stable oscillation in the oscillation unit
42
.
Further, in the detection circuit shown in
FIG. 2
, a change in the counted number of the waves must be converted into a change in a capacitance through digital processing in the processing unit
48
. However, the oscillation frequency of the oscillation unit
42
as mentioned above hardly exhibits a simple proportional relationship with the capacitance value of the sensor
41
. In other words, complicated operations such as square and inversion operati
Harada Muneo
Hirota Yoshihiro
Matsumoto Toshiyuki
Miyano Takaya
Barnes & Thornburg
Deb Anjan
Sumitomo Metal Industries Ltd.
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