JPH1047993A - Variable capacitance sensor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relieve the overall linearity deterioration of the characteristic curve of a variable capacitance sensor system by reducing the rate of change of the curve by impressing a feedback voltage upon a first capacitance serially through a variable capacitance diode. SOLUTION: Since the output voltage of a variable capacitance sensor system varies depending upon the capacitance ratio CB/CA between a pair of capacitances CA 16 and CB 17, it can be regarded that the capacitance CA of a transducer 16 excessively increases than a preferable value against the change of a pressure P or increases at a small rate of change when the capacitance CA is small or at a large rate of change when the capacitance is small against the capacitance increase when a charge-locked loop type CV converter which impresses a negative feedback voltage upon the CA by fixing the second capacitance CB as a reference capacitance and making the capacitance CA of the transducer 16 variable is used. Therefore, the rate of change of the capacitance can be increased when the capacitance is small or can be decreased when the capacitance is large by impressing a feedback voltage upon the first capacitance CA 16 serially through a variable capacitance diode DC 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable capacitance type sensor system which is used for a pressure sensor or the like and detects a change in electric capacitance of a variable capacitance capacitor which operates as a transducer.

[0002]

2. Description of the Related Art For example, when controlling a refrigeration system mounted on an automobile, a device such as a pressure sensor which detects the refrigerant pressure, converts the refrigerant pressure into an electric signal, and outputs the electric signal to a control system is effective. By the way, as such a pressure sensor, there is a pressure sensor used for a diaphragm made of a silicon semiconductor.However, such a pressure sensor is mounted under severe conditions such as a device mounted on an automobile, particularly under an environmental condition with severe fluctuations. Its use is problematic in terms of durability and reliability.

[0003] As a pressure sensor considered to be most suitable under such environmental conditions, there is a variable capacitance transducer. This variable capacitance transducer
When the distance between two electrode plates forming a capacitor changes due to a change in pressure applied to one of the electrodes, the amount of change is derived as a change in capacitance, and an electric signal is obtained by a capacitance-voltage converter. . In constructing such a variable capacitance transducer, a circular diaphragm made of a thin plate of a ceramic material whose pressure-receiving surface can be regarded as a completely elastic body that does not cause plastic deformation is used. A thin plate electrode which is flexible against the deflection of the diaphragm by means of vapor deposition is formed, and the periphery of the diaphragm is adhered to a base member having a counter electrode with a small gap through a spacer via a spacer. Have been.

The bending w of a model in which an evenly distributed load is applied to a diaphragm having a fixed radius and a radius a as shown in FIG. 13 is widely known as the following Timoshenko formula. w = Pa ⁴ (1−r ² / a ² ) / 64D Here, 0 <r <a, r is the distance from the center of the diaphragm to the deflection measurement point, D is a constant, and P is the pressing force. In such a pressure sensor using a diaphragm, the facing distance between the electrode on the diaphragm and the electrode on the base is expressed by a characteristic curve in the radial direction according to the dimensions of the effective diameter and the like and the characteristics of the material such as the elastic coefficient. And the change in the capacitance between the electrodes increases exponentially with the applied pressure.

[0005] Various conversion methods for converting capacitance to voltage have been proposed. However, as a method of obtaining stability with a simple configuration, a reference method prepared in advance for a capacitance Cx of a variable capacitance transducer is used. There is a method in which a reference capacitance Cr is provided, and a converted output is obtained in accordance with the ratio of the capacitances Cx and Cr.

An example of this method is disclosed in, for example,
As shown in Japanese Patent Application Laid-Open No. 8-200119, a charging circuit is configured by connecting a first capacitance and a second capacitance in series, and a voltage fluctuation of one reference capacitance is monitored, and the other capacitance is monitored. If the voltage of the reference capacitance fluctuates due to the fluctuation, a negative feedback of the charging voltage sufficient to compensate for this fluctuation is performed to maintain the balance, and the negative feedback voltage at which the equilibrium state is obtained is used as the output voltage. There is a so-called charge lock loop system.

According to this method, the output voltage is the ratio of the first capacitance CB to the second capacitance CA, CB /
Since the capacitance is obtained in accordance with CA, the capacitance changes in proportion to the variation of the measurement target. For example, in a variable capacitance transducer CB in which the area of the counter electrode is proportional, a constant capacitance CA is used as the reference capacitance. ,
In the case of the variable capacitance transducer CA in which the capacitance changes in a hyperbolic manner due to the change in the distance of the counter electrode, if a constant capacitance CB is combined as the reference capacitance, a so-called output which is faithful in a proportional relation to the fluctuation of the measurement object. A sensor having good linearity can be easily configured. However, in the above-described peripheral fixed diaphragm type pressure transducer, the change in capacity according to the change in pressure is not completely proportional to the pressure, nor does it change in a hyperbolic manner according to the pressure. Is not linear, and the output of the sensor tends to be excessive with respect to the pressure change.

In the above-described sensor, when the amount of deflection of the diaphragm is small, the curvature of the capacitance change curve with respect to the pressure change is small, so that the tolerance is within an allowable range, and this is regarded as a part of a straight line or a hyperbola. Can also be used. However, in order to obtain a so-called high-sensitivity transducer having a large amount of change in capacitance with a small amount of deflection using this configuration, a large-sized transducer having a large-area diaphragm is required. The use of such a diaphragm to form a sensor is not only difficult to manufacture, but also unsuitable for responding to the recent demand for miniaturization of the sensor, which is an important requirement from consumers.

In order to cope with this, various proposals have been made to reduce the influence of exponential function capacity change and to obtain an output as proportional as possible to the pressing force. For example, in the inverse proportional conversion, there is a method of dividing the center of the electrode of the transducer to obtain a correction capacitance and using it as a part of the reference capacitance. The disadvantages of this method are that the electrode pattern of the transducer is complicated and
Since the number of lead-out terminals increases, manufacturing becomes difficult, and eventually, there are problems such as a decrease in reliability and yield, an increase in price, and the like.

The change in capacitance CP with respect to the pressure P is shown in FIG.
As shown in FIG. 4, an exponentially increasing curve C is exhibited. When the pressure P is small, that is, when the deflection of the diaphragm is small, the ratio of the error to the ideal linear change A is small, but the ratio of the error sharply increases as the pressure P increases. Therefore, when a proportional capacity-voltage conversion unit (hereinafter, CV conversion unit) is used, the rate of increase in the conversion output tends to increase with an increase in pressure. In the case where an inverse proportional CV conversion means in which the output voltage B decreases to the right as shown in FIG. Although the output voltage B 'can be corrected to obtain an output similar to that of the proportional type, it is difficult to obtain a means having a characteristic corresponding to a change in the capacitance of the variable capacitor. , The error in the output voltage B 'cannot be eliminated.

As a method for improving the linearity of an output signal,
Conventionally, an approximation circuit is added to the output circuit of the operational amplifier,
In many cases, the output was within the specified range. However, according to the broken line approximation method, the inherent curvature of the curve itself is not improved, and it is not suitable for securing smooth continuity of output characteristics accompanied by a sudden change in curvature at the time of correcting a broken line.

[0012]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a CV converter that increases the rate of change of the feedback voltage when the capacity is small and decreases the rate when the capacity is large, thereby reducing the gradual change rate. It is an object of the present invention to provide a variable capacitance sensor system having a characteristic curve having improved linearity. Another object of the present invention is to provide a CV
An object of the present invention is to provide a variable-capacitance sensor system that improves linearity by suppressing and reducing the output voltage in accordance with the output voltage at the time of high voltage output in the output signal amplification after conversion.

[0013]

In order to achieve the above object, a variable capacitance type sensor system according to the present invention has a first capacitance and a second capacitance each having one end connected to the ground side of a power supply. A capacitance, a charging circuit for charging a first capacitance connected to the other ends of the first and second capacitances, a commutation circuit for commutating the charge of the first capacitance to a second capacitance, and a first and a second commutation circuit. A switching means for performing switching control so that a discharge circuit for discharging the charge of the second capacitance is formed sequentially and periodically; and a commutation circuit for the first and second capacitances formed by the switching means. A comparator for detecting a voltage occurring in both capacitances, a memory for taking in an output of the comparator in synchronization with a clock signal, and a memory for taking out an output of the memory. Is integrated to detect a voltage proportional to the first capacitance or a voltage inversely proportional to the capacitance of the second capacitance, and to provide the output voltage when the charging circuit of the first capacitance is formed by the switching means. And an output terminal for sending the output of the integrator as a detection output of the sensor. The charging circuit has a variable capacitance diode inserted between the output terminal of the integrator and the switching means. Are connected in series to a first capacitance via a switching means, and a shared voltage determined by a capacitance ratio between the intrinsic capacitance of the variable capacitance diode and the first capacitance is applied to the first capacitance.

According to the first aspect of the present invention, if the output of the comparator is Vc, the reference voltage of the comparator is Vr, and the specific capacitance of the variable capacitance diode is CD, Vc = (CA + CB) (1 / CA + 1 / CD) Vr. As compared with the conventional operation in which Vc increases when CA is small, the shared voltage of Vc with respect to Vc decreases, resulting in Cd
Increases and Vc tends to decrease. Also, in contrast to the conventional operation in which Vc decreases when CA is large, CD with respect to Vc
As a result, CD decreases and Vc tends to increase. As a result, the output curve is corrected so as to approach a straight line as shown in FIG.

In the variable capacitance type sensor system according to the second aspect of the present invention, the first capacitance and the second capacitance each having one end connected to the ground side of the power supply, and the first capacitance and the second capacitance. A charging circuit that charges a first capacitance connected to the other end of the capacitance, a commutation circuit that diverts the charge of the first capacitance to a second capacitance, and first and second
Switching means for performing switching control so as to sequentially form a discharging circuit for discharging the charge of the capacitance, and a commutation circuit for the first and second capacitances formed by the switching means. A comparator for detecting a voltage generated in the capacitance; a memory for capturing an output of the comparator in synchronization with a clock signal; and an output of the memory integrated and proportional to the first capacitance or a second capacitance of the second capacitance. An integrator that detects the voltage as being inversely proportional to the capacitance and provides the output voltage when the first capacitance charging circuit is formed by the switching means;
An amplifier for amplifying the output of the integrator, and an output terminal for sending the output of the amplifier as a detection output of a sensor, and a transistor for controlling a feedback amount according to the output voltage of the amplifier is provided at an input terminal of the amplifier. They are connected in parallel, and the output voltage of the amplifier is applied to the control terminal of the transistor.

According to the second aspect of the present invention, the transistor controls the output voltage of the amplifier by increasing or decreasing the current flowing to the input terminal according to the output voltage of the amplifier. That is, since the current controlled by the transistor is a function of the output voltage, the current flowing from the output terminal to the input terminal is gradually reduced with respect to the increase in the output voltage, and the increase in the output voltage is suppressed.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a variable capacitance type sensor according to an embodiment of the present invention. (First Embodiment) FIG. 1 shows a circuit configuration of a variable capacitance sensor according to a first embodiment of the present invention. The variable-capacitance sensor according to the present embodiment includes a clock pulse oscillator 11
A comparator 12, a digital memory 13 composed of a flip-flop circuit, an integrating circuit 14, and a voltage dividing means 15.
, A variable capacitance capacitance CA16, a reference capacitance CB17, a variable capacitance diode CD18 whose capacitance changes according to an applied voltage, and a first switch S1 and a second switch S2.

This variable capacitance diode DC18 is basically a diode consisting of a PN junction.
When shown as an equivalent circuit, the equivalent capacitance CD is connected in parallel with the diode DC as shown in FIG. 2A, but as shown in FIG. It has the characteristic that the CD changes greatly.
In such a circuit, the clock oscillation output signal Sc output from the clock pulse oscillator 11 is supplied to a pulse distributor (not shown), and the pulse signal distributed by the pulse distributor is supplied to the comparator 12 and the flip-flop circuit 13.
Is supplied to the driving means of the first switch S1 and the second switch S2.

The clock pulse Sc is supplied to the comparator 12 and the first
The switch S1, the second switch S2, and the flip-flop circuit 13 are operated in the following manner. A charging circuit for charging the first capacitance CA16 with the output voltage Vf of the voltage dividing means 15;
A mode in which a discharge circuit for discharging the charge of the second capacitance CB17 is formed. A mode in which the first capacitance CA16 is separated from the output Vf of the voltage dividing means 15 and a commutation circuit for moving the charge of the first capacitance CA16 to the second capacitance CB17 is formed. The terminal voltage Vb of the second capacitance CB17 (= V
A mode in which i) is compared with a reference voltage Vr. The output state of the comparator 12 is determined by the flip-flop circuit 13
The form to take in.

The output Vf of the voltage dividing means 15 and the first switch S
1, a variable capacitance diode DC18 is inserted between the first capacitance CA16 and the voltage Va obtained by dividing the output voltage Vc of the voltage dividing means 15 by the equivalent capacitance CD of the variable capacitance diode DC18 and the capacitance CA16 when the first capacitance CA16 is charged.
Is applied to the capacitance CA16.

The CV conversion operation of the system according to the present invention will be described below with reference to FIG. FIG. 3 is a timing chart showing the operation of the switches S1 and S2 and the voltage at each point in the circuit shown in FIG. As shown in FIG. 3A, the first switch S1 and the second switch S2
It is periodically switched to a contact or b contact.

When the switch is on the a contact side, the first capacitance C
A13 is a voltage divider 1 via a variable capacitance diode DC18.
The terminal voltage Va is charged by the output voltage Vf of 5 and the charge is accumulated, and the terminal voltage Va becomes Vf · CD (1 / CA + CD) (FIG. 3).
(B)). At this time, the terminals of the second capacitance CB17 are short-circuited by the second switch S2, and the charge charged by the first capacitance CA16 is discharged (FIG. 3C). That is, the above is executed.
At this time, the output voltage Vc of the comparator 12 is at the low potential “L” (FIG. 3D), and the memory 13 including the flip-flop circuit maintains the previous state (FIG. 3).
(E)). That is, the arrow in FIG.
The theoretical timing for loading the contents of the memory 13 into the memory 13 is shown. The output voltage Vo of the integrating circuit 14 increases with a predetermined time constant when the output Vm of the memory 13 is at the high potential “H”, and decreases with a predetermined time constant when the output of the memory 13 is at the low potential “L”. (FIG. 3F).

When the switch is switched to the contact b side, the first capacitance CA13 is disconnected from the output voltage Vf of the voltage divider 15 and the second capacitance C13 in which the short circuit between the terminals is released.
B17, and the charge is transferred to the second capacitance CB1
7, the voltage Va between the terminals of the first capacitance CA13 and the voltage Vb between the terminals of the second capacitance CB17.
Are equal (FIGS. 3B and 3C).

The comparator 12 operates after the voltage Va between the terminals of the first capacitance CA13 is balanced with the voltage Vb between the terminals of the second capacitance CB17, and the comparator 12 operates with the reference voltage Vr and the input voltage Vi.
(= Vb = Va). The input voltage Vi is the reference voltage Vr
(Vr ≧ Vi), the output voltage Vc becomes “H”, and when the input voltage Vi exceeds the reference voltage Vr (Vr <V
i) The output voltage Vc becomes "L" (FIG. 3D).

The output Vm of the comparator 12 is input to the memory 13. The memory 13 is in a state corresponding to the current state of the input voltage Vc (FIG. 3E). The output voltage Vo of the integrating circuit 14 is
It changes according to the output Vm of the memory 13 (FIG. 3F).

The operation of the variable capacitance diode DC18 will be described with reference to FIG. Variable capacitance diode DC18
Is a first capacitance C constituting a variable capacitance element.
A16 connected in series with the first capacitance CA
16 only needs to be slightly corrected in accordance with Vf (= VO: output voltage of the operational amplifier 13).
As shown in (b), it is practical to use a capacitor having a small capacity change in parallel with the fixed capacity CE. Since the basic equation of the charge locked loop is represented by Va · CA = (CA + CB) Vr, Va = [1+ (CB / CA)] Vr (1) Here, the output Vd = Va. Output voltage V of comparator 12
O is the variable capacitance diode DC18 and the first capacitance C
When the voltage is equal to the voltage Vf applied to A16, Va = [CD / (CA + CD)] Vf (2) Since (1) = (2), Vf = [(CA + CD) / CD] Va = [1+ (CA / CD)] [1+ (CB / CA)] Vr = (CA + CB) [(1 / CA) + (1 / CD)] Vr Therefore, when the capacitance of the first capacitance CA becomes small,
In contrast to the conventional operation in which the feedback voltage Vf is large, the feedback voltage Vf
As a result, the equivalent capacitance CD of the variable capacitance diode DC increases and the feedback voltage Vf tends to decrease. In addition, when the capacitance of the first capacitance CA is large, the shared voltage of the variable capacitance diode DC with respect to the feedback voltage Vf is increased as compared with the conventional operation in which the feedback voltage Vf is small. CD decreases and the feedback voltage Vf tends to increase. As a result, the output curve is corrected so as to approach a straight line as shown in FIG.

The first capacitance CA16 and the second capacitance CB17 can both have one end connected directly to one end of the power supply, so that one end of the transducer is at the same potential as one end of the power supply, which means that the On the other hand, this is equivalent to configuring a shield against an external electric field of the internal circuit, and accurate and highly reliable measurement can be performed without being affected by external noise. Also, since CB / CA is a factor for determining the sensitivity, the first capacitance CA
If the sixteenth or second capacitance CB can be easily adjusted from the outside, the sensitivity can be changed as appropriate. Further, an output that is proportional or inversely proportional to a change in capacitance can be arbitrarily selected as needed with exactly the same stability compensated by the same circuit configuration.

In the above, the comparator 12 supplies the reference voltage Vr
Is supplied from a DC power supply, but a logic IC having a substantially constant threshold level is connected to a comparator 12.
May be used.

According to the first embodiment, since the output voltage is determined by the capacitance ratio CB / CA of the pair of capacitances CA16 and CB17, the second capacitance CB is used as a fixed reference capacitance, and the capacitance of the transducer 16 is changed. When using a charge-locked loop type CV converter in which CA is variable and a negative feedback voltage is applied to CA,
When the pressure P changes, the capacity CA of the transducer 16 increases.
Can be considered as a result of an excessive increase with respect to a preferable capacity increase, and a result of a small increase in capacity with respect to an increase in capacity and a sharp increase in change rate with a large capacity. Therefore, by applying the feedback voltage to the first capacitance CA via the variable capacitance diode DC in series, the rate of change is substantially increased when the capacitance is small,
When the capacity is large, the function of reducing the change rate can be obtained. When the characteristic curve has a gradual change rate when the capacity is large, the overall decrease in linearity can be mitigated.

(Second Embodiment) Next, the first capacitor CA charged by the charging circuit is set as a fixed-capacitance capacitance 27 serving as a reference capacitance, and the second capacitance C charged by the first capacitance is used.
An example in which B is the capacitance 26 of the variable capacitance sensor will be described with reference to FIG. In this case, the variable capacitance diode DC18
Are connected in parallel to the first capacitance CA27.
Other configurations are not different from the example shown in FIG. For example, when the variable capacitance sensor 26 is a pressure sensor, the capacitance of the variable capacitance capacitance CB is small, and when the output voltage Vf of the voltage dividing circuit 15 is low, the combined capacitance of the fixed capacitance CA and the variable capacitance diode CD is large. , The output voltage Vf of the voltage dividing circuit 15 becomes a low voltage.
When the capacitance of the variable capacitance capacitance CB is large and the output voltage Vf of the voltage dividing circuit 15 is high, the combined capacitance of the fixed capacitance capacitance CA and the variable capacitance diode CD is small, and the output voltage Vf becomes higher. The general characteristic of the variable capacitance diode DC is that the reduction rate is small (or a small characteristic is selected) when a high voltage is applied. This is advantageous because it can achieve both an increase in amplitude and an improvement in linearity. According to this embodiment, the output voltage Vf and the Vf-CB characteristics of the variable capacitance CB shown in FIG. 7 can be obtained.

(Third Embodiment) Next, after CV conversion,
An amplifier that takes the output as an input and performs the conventional measures to settle the desired output voltage area is provided, and a function to suppress and reduce its own output voltage according to the output voltage at the time of high voltage output is added to the amplifier. This example will be described with reference to FIGS. That is, it has been conventionally performed to add a broken line approximation circuit to the output circuit of the comparator so that the output falls within a certain range. However, according to such a broken line approximation method, the curvature itself inherent in the curve is reduced. Since it cannot be improved and the curvature changes stepwise at the time of correcting the broken line, it is difficult to obtain output characteristics having smooth continuity.

FIG. 8 shows a circuit configuration of a third embodiment of the present invention. This example is an example in which the operational amplifier circuit 19 shown in FIG. 9 is added to the output Vo of the variable capacitance type sensor shown in FIG. The output terminal of the integrating circuit 14 is connected to the inverting terminal of the inverting amplifier A via the input resistor Rs. The output terminal of the inverting amplifier A is connected to the inverting terminal via a feedback resistor Rf and to the control terminal b of the transistor Q.
Furthermore, in order to obtain a smooth change in the current it, it is practical to use a self-bias type having an emitter resistance (source resistance) Ra.

FIG. 9 shows a circuit configuration of the operational amplifier 19.
In the circuit shown in FIG. 9A, generally, the gain G of the inverting amplifier A is represented by G =-(Rf / Rs). In the inverting amplifier A in which the input terminal current can be ignored, the current if flowing through the feedback resistor Rf is equal to the current is flowing through the input resistor Rs, and is represented by is = (Vs−Vin) / Rs, so that Vout = Rf · if + Vs. Become.

When a current it is introduced from the power supply Vcc shown in FIG. 9B to the inverting terminal of the inverting amplifier A through the transistor Q in the circuit of the operational amplifier, is = it + ift, and it becomes a function of Vout. Can be gradually reduced with the increase of. That is, Vout =
Rf.if + Vs, and the output Vout is suppressed from increasing.
In particular, a bipolar transistor can be used as the transistor Q. However, by using FETs having various control characteristics, those can be selected and used according to the situation.

For example, in an FET having both the depletion and enhancement characteristics shown in FIG. 10A, a wide output voltage Vou as shown in FIG.
A correction effect can be exhibited over the range of t.

FIG. 11 shows a modified example of the amplifier in the case where the output signal amplifier corresponds to the output signal amplifier after the CV conversion. The CV conversion is the same as the circuit configuration shown in FIGS. In this example, like a thermistor linearizer, a curve portion of the output characteristic is converted into an output having good linearity by a multi-stage broken line approximation method. In parallel with the feedback resistor Rf inserted between the output terminal of the operational amplifier A and the inverting terminal, a series connection of the resistor Rfn and the analog switch An (Rf1 + A1, Rf2 + A
2, Rf3 + A3, Rf4 + A4). At the output terminal of the operational amplifier A, comparators for generating operation signals of the respective switches A1, A2, A3, A4 of the analog switch A are provided with analog switches A1, A2, A3, A4.
Is provided in correspondence with. Different voltages obtained by appropriately dividing the output voltage Vout to operate the analog switches A1, A2, A3, A4 are applied to the terminals (+) of the respective comparators. A reference voltage is applied to the inverting terminal (-) of the comparator. With this configuration, output signals A1, A2, A3, A4 for sequentially operating the analog switches A1, A2, A3, A4 are generated at the output terminals of the comparators. In addition,
The resistance to adjust the feedback amount is not limited to four,
It can be composed of n pieces. n resistors (Rf1 to Rf
The adjustment of the feedback amount configured in n) can be automatically performed sequentially by adopting a laser trimming system that can be adjusted to a designated output while monitoring the output.

With such a configuration, the output voltage characteristic shown in FIG. 12 is obtained by multi-stage broken line approximation. The feature of the multi-step folding line approximation is that the folding lines have continuity, and the adjustment of the feedback amount of each folding line is independent of each other, so that the adjustment error can be reduced.

[0038]

As described above, according to the first aspect of the present invention, by applying the feedback voltage to the first capacitance CA via the variable capacitance diode DC in series, the capacitance of the first capacitance is substantially increased. Is small, the rate of change is increased, and when the capacity is large, the rate of change is reduced to obtain a gradual change rate characteristic curve, whereby the overall decrease in linearity can be mitigated. Further, according to the invention of claim 2, by applying the output voltage of the output signal amplifier after the CV conversion to the control terminal of the transistor and controlling the current flowing to the input terminal side of the amplifier, the output voltage at the time of high voltage output is controlled. The output voltage of the amplifier can be suppressed, and the decrease in linearity can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a variable capacitance sensor system according to the present invention.

FIG. 2 is a diagram illustrating the operation of a variable capacitance diode.

FIG. 3 is a time chart illustrating the operation and timing of the variable capacity system.

FIG. 4 is a conceptual diagram showing a configuration of a variable capacitance sensor system according to the present invention.

FIG. 5 is a Vf-CA characteristic diagram of the first embodiment.

FIG. 6 is a circuit configuration diagram showing a second embodiment of the variable capacitance sensor system according to the present invention.

FIG. 7 is a Vf-CB characteristic diagram of the second embodiment.

FIG. 8 is a circuit configuration diagram showing a third embodiment of the variable capacitance sensor system according to the present invention.

FIG. 9 is an explanatory diagram of an operational amplifier circuit.

FIG. 10 is a Vout-P characteristic diagram of the third embodiment.

FIG. 11 is a circuit diagram illustrating a circuit configuration of an output signal amplifier based on a multi-stage broken line approximation method.

FIG. 12 is a Vout-P characteristic diagram based on a multi-stage broken line approximation method.

FIG. 13 is a diagram showing a model of an evenly distributed load of the pressure receiving diaphragm.

FIG. 14 is a diagram showing a relationship between a capacitance change CP and a pressure P.

FIG. 15 is a diagram showing a relationship between an output voltage Vo and a pressure P.

[Explanation of symbols]

 Reference Signs List 11 clock signal generator 12 comparator 13 memory (flip-flop) 14 integrator 15 voltage divider 16 first capacitance 17 second capacitance 18 variable capacitance diode 19 operational amplifier circuit

Claims (2)

[Claims] 1. A first capacitance and a second capacitance each having one end connected to a ground side of a power supply and one of which is variable, and the first capacitance connected to the other end of the first capacitance. A charge circuit for charging the first capacitance, a commutation circuit for commutating the charge of the first capacitance to the second capacitance, and a discharge circuit for discharging the charge of the second capacitance are sequentially and periodically formed. Means for controlling the switching so as to perform switching control, a comparator for comparing a voltage occurring in both capacitances when the commutation circuit is formed with the reference voltage with a reference voltage, and synchronizing an output of the comparator with a clock signal. And a memory which is integrated with the output of the memory and which is integrated with the output of the memory to be proportional to the first capacitance or to the capacity of the second capacitance. An integrator for detecting the output voltage as an example and providing the output voltage to the charging circuit when the charging circuit of the first capacitance is formed by the switching means; and sending out the output of the integrator as a detection output of the sensor. An output terminal, wherein the charging circuit has a variable capacitance diode inserted between an output terminal of the integrator and the switching means, and connects the variable capacitance diode to a first capacitance via the switching means. A variable-capacitance sensor system, which is connected in series and configured to apply a shared voltage of a specific capacitance of the variable-capacitance diode and a capacitance of a first capacitance to the first capacitance. 2. A first capacitance and a second capacitance each having one end connected to a ground side of a power supply and one of which is variable, and the other end of the first capacitance and the second capacitance being connected to the other end of the first capacitance and the second capacitance. A charging circuit for charging the connected first capacitance, and charging the first capacitance to the second capacitance;
Switching means for performing switching control such that a commutation circuit for commutating to the first capacitance and a discharging circuit for discharging the charge of the first and second capacitances are sequentially and periodically formed; and Capacitance and the second
When a commutation circuit of capacitance is formed, a comparator that compares a voltage occurring in both capacitances with a reference voltage at that time, a memory that takes in an output of the comparator in synchronization with a clock signal, and an output of the memory Integrate and detect as a voltage proportional to the first capacitance or inversely proportional to the capacitance of the second capacitance, and charge the output voltage when the switching circuit forms the charging circuit of the first capacitance. An integrator to be provided to the circuit; an amplifier for amplifying the output of the integrator; and an output terminal for transmitting the output of the amplifier as a detection output of a sensor. The input terminal of the amplifier corresponds to the output voltage of the amplifier. A transistor for controlling the amount of feedback is connected in parallel, and the output voltage of the amplifier is applied to the control terminal of the transistor. Variable capacitive sensor system according to claim.