JPH0371054A - Electrostatic sensor device - Google Patents

Abstract

PURPOSE:To prevent the Q of a resonator from decreasing even when the fine electrostatic capacity with a body to be detected which is low in impedance and Q by providing a C-L converting circuit between a detection part with fine electrostatic capacity and the resonator of a resonance circuit. CONSTITUTION:When a detector 3 detects variation in the fine electrostatic capacity with the body to be detected, the variation in this fine electrostatic capacity is converted into impedance by the C-L converting circuit 7. The conversion of the impedance is performed as the conversion of inductance, and the variation in the inductance is applied to the resonator 12 of the resonance circuit 2. Thus, the detected variation in the fine electrostatic capacity is converted by the circuit 7 into the variation in the inductance, so even when the body to be detected is low in impedance and Q, that does not operate as a factor which decreases the Q of the resonator 12 and a high-output detection signal corresponding to the variation in the electrostatic capacity is led out of the resonance circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] Raikori J relates to an electrostatic sensor device that detects minute changes in capacitance with an object to be detected.

(Prior art) An electrostatic sensor device that has been very commonly used changes the oscillation frequency by changing the external capacitance of the capacitance used in the tank circuit of the oscillation circuit. However, the sensitivity is low, and for this reason, in recent years, the more sensitive RCA method (a method for obtaining AM modulated waves by changing the capacitance of a resonant circuit with a resonant frequency that slightly deviates from the oscillation frequency of the oscillation circuit) As shown in Fig. 6, this RCA type electrostatic sensor device is designed to reduce the electrostatic charge between the oscillation circuit section 1, the resonant circuit 2, and the object to be detected. It consists of a detection section 3 that detects a capacitance change, a detection section 4, and an amplifier circuit 5.The oscillation circuit section 1 and the resonance circuit 2 each include a resonator, for example, a seventh
As shown in the figure, the resonant frequency fo of the resonant circuit 2 is set at a position slightly shifted from the fixed oscillation frequency fl of the oscillation circuit section l, and the minute capacitance changes detected by the detecting section 3. The resonant frequency is changed from fo to Δ in response to ΔC.
The change in capacitance ΔC is expressed as the output voltage Δ
The change in V is outputted from the resonant circuit 2, detected and amplified by the detection section 4 and the amplifier circuit 5, and extracted.

[Problems to be Solved by the Invention] The present inventors have focused on the fact that the detection sensitivity of minute capacitance can be increased by making the circuit around the resonator of the resonant circuit 2 a high impedance circuit. succeeded in developing a highly sensitive electrostatic sensor device.

However, even with this highly sensitive developed device, if the impedance or Q of the object to be detected is low, for example, when attempting to detect the human body or ionic components in water, detection may be difficult due to the low impedance of these objects. If the detection object detection electrode in section 3 and the resonator are directly coupled, the Q of the resonator of resonant circuit 2 will be significantly lowered, and this Q
In the RCA type electrostatic sensor device, in which the output voltage depends on the magnitude of the detection output, there is a problem in that the detecting ability decreases and becomes unusable due to this significant decrease in the detection output.

The present invention has been made to solve the above problems, and its purpose is to reduce the Q of the resonator of the resonant circuit even when detecting minute capacitance with a detected object having low impedance or Q.
It is an object of the present invention to provide a highly sensitive electrostatic sensor device that does not cause a decrease in performance.

[Means for Solving the Problems] In order to achieve the above object, the present invention is configured as follows. That is, the present invention includes an oscillation circuit section that outputs an oscillation frequency signal, a detection section that detects a change in capacitance with the object to be detected, and a resonant frequency that is determined by a minute change in capacitance detected by this detection section. In an electrostatic sensor device having a changing resonant circuit, a C-L is provided between the detecting section and the resonant circuit to convert a change in capacitance detected by the detecting section into a change in inductance and transmitting it to the resonant circuit. A characteristic feature of the present invention is that the oscillator of the oscillation circuit section and the resonator of the resonant circuit are both composed of ceramic resonators. Further, a stabilization control circuit for stabilizing the tuning point between the oscillation frequency of the oscillation circuit section and the resonance frequency of the resonant circuit is connected to the resonance circuit or the CL conversion circuit. This is a characteristic configuration of the present invention.

[Function] In the present invention, when a change in minute capacitance with the object to be detected is detected by the detection unit, this change in minute capacitance is calculated as C-L.
Conversion to impedance is performed by a conversion circuit.

This impedance transformation is performed as an inductance transformation, and this inductance change is applied to the resonator of the resonant circuit.

In this way, in the present invention, the detected minute capacitance change is converted into an inductance change by the C-L impedance conversion circuit, so even if the impedance or Q of the object to be detected is low, this can be converted into a resonant circuit. This does not act as a factor that lowers the Q of the resonator, and a high-output detection signal corresponding to the change in capacitance is extracted from the resonant circuit.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained based on the drawings. FIG. 1 shows a circuit diagram of an embodiment of an electrostatic sensor device according to the present invention. The device of this embodiment includes an oscillation circuit section 1, a high impedance conversion circuit 6, a resonance circuit 2 consisting of a ceramic resonator 12, a CL conversion circuit 7, a detection section 4, an amplifier circuit 5, and a stable AF as a control circuit
It consists of a C circuit 8. If we consider 11g1 in detail in this FIG. The discussion is proceeding on the assumption that it is composed only of the ceramic resonator 12 excluding the L conversion circuit 7. Incidentally, the head of the circuit middle triangular symbol in FIG. 1 indicates the grounding point.

The oscillation circuit section 1 is a well-known circuit, and in this embodiment,
The resonator of this circuit uses an ultra-high frequency (IC) (in this example)
A ceramic resonator 10 is used which oscillates at a fixed and constant oscillation frequency in the range from z to 10 GHz. This oscillation circuit section 1 oscillates the high frequency oscillation signal,
This is connected to the resonant circuit 2 via the high impedance conversion circuit 6.
Add to. The ceramic resonator 12 of this resonant circuit 2 has a frequency characteristic as shown in FIG.
The oscillation frequency rl of is set at a slightly shifted position. Methods for setting the oscillation frequency rl include a so-called up-porch method in which the oscillation frequency is set at a frequency f2 on the right side of the resonant frequency fo of the ceramic resonator 12, and a resonant frequency f. There is a hack pouch method in which the frequency fo is set to the left side of I will explain.

The detection section 3 is connected to the ceramic resonator 12 via the C-L conversion circuit 7. A desired electrode such as a plate, a needle, an ion electrode, an insulated electrode, a heat cutoff electrode, etc., for detecting a change in capacitance with the object to be detected is connected to the detection section 3.

The CL conversion circuit 7 can be constructed of an impedance gyrator using elements such as a Hall element, a waveguide, or a non-reciprocal circuit, and an example of the circuit is shown in FIG. The circuit shown in Figure 2 is called a transistor gyrator, and consists of three 1-transistors 1/1,
15 and 16 and a resistor, its input side is connected to the ceramic resonator 12 side, and its output side is connected to the detection unit 3 side. This impedance gyrator performs impedance inversion,
This converts a change in capacitance seen from the output side into a change in inductance seen from the input side.

In general, ceramic dielectrics have a high (large) Q, and high detection sensitivity can be expected by configuring the resonator of the resonant circuit with ceramic resonators 10°12. If it is directly connected to the circuit section 1, the impedance of the oscillation circuit section 1 is lower than the impedance at the operating point of the ceramic resonator 12, so the Q of the ceramic resonator 12 decreases and the impedance at the resonance point (tuning point) decreases. A problem arises in that the output voltage of the ceramic resonator 12 becomes low and the original performance (performance of high Q) of the ceramic resonator 12 cannot be fully exhibited. In order to solve this problem, in this embodiment, a high impedance conversion circuit 6 is interposed between the oscillation circuit section 1 and the resonance circuit 2. This high impedance conversion circuit 6 has a transistor 13
It is configured as a high impedance circuit by combining circuit elements such as resistors and capacitors, and transistor 1
3 is an emitter follower connection that adds high impedance to the ceramic resonator 12, and also connects the ceramic resonator I.
Q (Mutual interference between the oscillation circuit section 1 of the jl and the resonant circuit 2 on the ceramic resonator 12 side is blocked.

The detection section 4 is connected to the ceramic resonator 12 via a coupling capacitor 25, and the detection section 4 includes an inductance element 21, a diode 22, a capacitor 23,
The output signal from the ceramic resonator 12 is applied to the detection section 4 via a coupling capacitor 25. The diode 22, capacitor 23, and resistor 24 constitute a detection circuit, and in this embodiment, the bias point of the operating point of the diode 22 is set sufficiently deep on the negative side of the O voltage. The detection circuit performs envelope detection of the ultra-high frequency output signal (image signal) emitted from the ceramic resonator 12 and converts it into a signal in the signal band of the detected object.

In this way, the detection circuit detects the ultra-high frequency signal from the ceramic resonance 2i12, but at this time, the diode 22
Considering the characteristic impedance of this diode 2
The forward impedance of the diode 2 has a large influence on the ceramic resonator 12, and this diode 22 is directly connected to the resonator 1.
2, the problem arises that the Q of the resonator 12 is lowered. In order to prevent this inconvenience, the inductance element 21 is connected to the anode side of the diode 22. In other words, the capacitor 25 and the inductance element 21 function as a high impedance circuit.

The amplifier circuit 5 is configured using elements such as a transistor 27 and a resistor, and this amplifier circuit 5 amplifies the signal applied from the detection section 4 and supplies it to a signal processing circuit (not shown), while simultaneously supplying the signal to the AFC circuit 8. Add.

This AFC circuit 8 includes an operational amplifier 28 and a capacitor 2.
6.29.30, variable resistor 31, and resistor 32.3
5, variable capacitance diode 33, and coupling capacitor 34
The main circuit elements are: One side terminal of the operational amplifier 28 is connected to the output terminal of the amplifier circuit 5, and the + side terminal of the operational amplifier 28 is connected to the variable resistor 3.
1 sliding terminal. A capacitor 29 is connected between the first terminal of the operational amplifier 28 and the output terminal.
Further, one end side of a capacitor 30 is connected to the output end of the operational amplifier 28 via a resistor 32.
The other end is connected to ground. Furthermore, the output terminal of the operational amplifier 28 is connected to a resistor 32.35 and a coupling capacitor 3.
4 to the output end side of the ceramic resonator 12. The cathode side of the variable capacitance diode 33 is connected to the connecting portion between the coupling capacitor 34 and the resistor 35, and the anode side of the variable capacitance diode 33 is grounded.

This AFC circuit 8 amplifies the signal applied from the amplifier circuit 5 using the operational amplifier 28. When amplifying this signal, the output signal from the operational amplifier 28 becomes a low frequency almost DC signal due to the smoothing effect of the capacitors 29 and 30. Generally, a time constant is set corresponding to the operating speed of the object to be detected.

Furthermore, the output signal from the operational amplifier 28 is amplified to the required level by passing through two integrating circuits: a capacitor 30 and a resistor 32, and a capacitor 26 and a resistor 35. 3
3 is applied.

The variable capacitance diode 33 is used in a reverse bias state, and in this embodiment, when the lightning voltage of the lightning source is 12V, a reverse bias voltage of 6 or more is applied to the variable capacitance diode 33 to change the operating point of the diode 33. is set to a deep bias point on the negative side from 0 voltage.

11 2 The position of the operating point of the variable capacitance diode 33 can be adjusted at the DC level by varying the resistance value of the variable resistor 31. In other words, AF
The central operating point of the C circuit can be variably set. The variable capacitance diode 33 changes its capacitance according to the voltage applied from the integrating circuit, transmits this capacitance change to the ceramic resonator 12 via the coupling capacitor 34, and changes the resonant frequency of the resonator 12. . That is, for some reason, the resonant frequency of the ceramic resonator 12 may change, for example.
If the output from the resonator 12 is shifted to the right side of "." set in the back porch method shown in FIG. 4, the output from the resonator 12 will decrease.
This causes the inconvenience of falling outside the set range. In such a case, by adding an AFC signal to the resonator 12, the oscillation frequency fl is automatically shifted to the right, and the output from the resonator 12 is changed. ~V, so as not to deviate from the setting range, and in this sense, this AFC circuit also functions as a type of AGC circuit.

The present invention is configured as described above, and its operation will be described below.

For example, as shown in FIG. 7, when the oscillation frequency 11 of the oscillation circuit section l is set to a value slightly different from the resonant frequency (tuning frequency) ro of the ceramic resonator 12, the detection section If there is no change in capacitance with the detected object detected by 3, the ceramic resonator 12
A constant voltage of vo is output from. On the other hand, if a person approaches the electrode section of the detection section or an uneven surface such as a VHD disk passes near the electrode of the detection section, the capacitance detected by the detection section changes by ΔC. , this change in ΔC is converted into a change in inductance by the CL conversion circuit 7 as follows.

As shown in FIG. 3, the C-L conversion circuit 7 is expressed as a black box using the Y parameter (Y matrix) when expressing the four-terminal circuit constant of the electric circuit as a lumped constant.
Let the conductance of the gyrator be G, the voltage at the input end (ceramic resonator 12 side) be Vl, the current be i, the pressure on the output side (detecting part 33 4 side) be v2, and the current be 2, then il, 2 is expressed by the following equation showing the entire gyrator.

When a capacitor is connected to the output side of this impedance gyrator, the input side acts as an inductance component, so the input side is expressed as an impedance change ΔZ divided by a change in capacitance ΔC on the output side.

ΔZ; =V+/i+ = j ωΔC/G”, where ω is the angular frequency and the minute change in capacitance Δ detected on the output side as described above.
C is converted into a minute change in impedance ΔZ by the −L conversion circuit 7, and this change in ΔZ is applied to the ceramic resonator 12. During this CL conversion, as can be seen from the equation of ΔZo, the detected The impedance of the body at rest does not directly affect the resonance of the resonant circuit.In response to this impedance change ΔZ, the resonant frequency of the ceramic resonator 12 changes, for example, from f to f in FIG.
Move to ol. At this time, since the oscillation frequency fl is kept at a constant value, the output pressure V taken out from the ceramic resonator 12. It is taken out as a voltage of v0 + Δ■, which is added by Δ■ to .

Generally, as shown in FIG. 5, a certain response f (G
), the output signal “(o
It is known that a signal of f (out) = f (G) f (x) can be obtained as f (out) = f (G) f (x), and if this is applied to this example, "(to)" a single frequency of ωL1 , that is,
If the oscillation frequency is fixed and f(G) is given as an image signal or a P8 signal corresponding to the movement of a person, then f(out)=jωL, ±P, and an amplitude-modulated output is extracted. In this embodiment, the oscillation frequency is set to a very high frequency, for example, IC! If ilz, then f(ou
t) becomes an ultra-high frequency signal having a width of +/-P8 with a width of 1F centered on IGHz, and this ultra-high frequency signal is applied to the detection circuit. The detection circuit performs envelope detection of this ultra-high frequency signal to detect the signal area of the detected object (3M in this example).
IIz signal). This band 5 G converted signal is amplified by an amplifier circuit 5, a part of the output signal is sent to a signal processing circuit (not shown), and another part of the signal is branched and supplied to an AFC circuit 8.

The AFC circuit 8 converts this input signal into a 400 m
[Z], further amplify the signal to the required level using an integrating circuit, and add this to the variable capacitance diode 33. The variable capacitance diode 33 changes its capacitance according to this applied signal, and the resonant frequency 1° of the ceramic resonator 12 is optimally adjusted based on this change in customer volume.

According to this embodiment, since both the resonator of the oscillation circuit section l and the resonator of the resonant circuit 2 are constituted by the ceramic resonator 1012, it is possible to make Q a large value. Moreover, since the circuits around the ceramic resonator 12, that is, the impedance conversion circuit 6, the resonant circuit of the inductance element 21 and the capacitor 25, and the AFC circuit 8 are configured with high impedance circuits, the ceramic resonator Q does not decrease during operation, making it possible to detect minute changes in capacitance with high sensitivity.

Furthermore, in this embodiment, the minute change in capacitance detected by the detection unit 3 is converted into a minute change in inductance by the -L conversion circuit 7 and applied to the ceramic resonator 12. Even when detecting changes in capacitance of an object to be detected with low impedance, the impedance and Q of the ceramic resonator 12 are not reduced, and high sensitivity is achieved regardless of the Q and impedance of the object to be detected. It becomes possible to detect minute changes in capacitance.

Furthermore, since the resonator is constructed from a ceramic resonator 1.0.12 without using a strip line, it is possible to make the device extremely compact. In other words, if the resonator is constructed with a stripline, the length of the stripline must be at least % of the oscillation frequency wavelength, which increases the length of the stripline and makes it difficult to miniaturize the device. The problem is that it becomes difficult. If the resonator is configured using the electrical conductor 7 8 , the length of the resonator can be reduced to ε-172 compared to that using a strip line.

If this dielectric is made of ceramic as in this example, the dielectric constant ε of ceramic is 40 to 90, so
This means that the color scheme can be significantly reduced in size.

In this example, 20 vertical ribs x 20 horizontal ribs [IIIQ x 2 on height]
We were able to create an extremely small device of +m.

According to the apparatus of this embodiment, I Xl0-3 to lXl0-'
It is now possible to detect the minute capacitance of the PF with high sensitivity. Therefore, the device of this embodiment can be used to detect changes in capacitance between a video disk and a stylus, which are conventional general applications. Not only can it be used as a detection device, but it can also be used for applications that are only possible with highly sensitive detection of minute capacitance, such as human body capacitance sensors (human intrusion sensors), minute position detection sensors, and high temperature position sensors (e.g. in 800"C atmosphere). extreme position detection sensor), high-resolution rotary encoder, minute component detection element (e.g. detection element such as a chip capacitor on a carrier tape), gas sensor (gas identification using the difference in capacitance that occurs depending on the type of gas) sensor), pulse sensor (pulse detection sensor that uses changes in the amount of iron in the blood passing through), liquid phase and solid phase phase transition point detection sensor (liquid phase and solid phase transition point sensor in the solid, liquid, and gas phase diagram) We have developed a highly sensitive and reliable ultra-compact electrostatic sensor device with completely new functions such as a sensor for detecting changes in dielectric constant at the transition point with the solid phase), an ion detection sensor, and a humidity detection sensor. It becomes possible to provide the product at low cost.

Further, in this embodiment, since the operating point of the diode 22 is set at a position optically separated from 0 voltage to the negative side, it is possible that the amplitude component of the signal of the diode 22 enters the positive side region and becomes conductive. Therefore, the impedance of the variable capacitance diode 33 can be maintained at a high value at all times, and Q-dump of the ceramic resonator 12 can be prevented.

Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented in various ways.

For example, in the above embodiment, both the resonator of the oscillation circuit section 1 and the resonator of the resonant circuit 2 are composed of ceramic resonators 190 to 12, but one or both of these resonators may be formed by a strip line. may be configured. However, in this case, the device will be large.

Further, in the above embodiment, the AFC signal of the AFC circuit 8 is applied to the ceramic resonator 12 via the coupling capacitor 34, but unlike this, the AFC signal is applied to the ceramic resonator 12 as shown by the chain line in FIG. In addition to the -L conversion circuit 7, the tuning point between the resonance frequency of the resonance circuit 2 and the oscillation frequency of the oscillation circuit section 1 may be similarly stabilized.

Further, in the above embodiment, the CL conversion circuit is formed using a transistor gyrator, but it may be formed using other passive non-reciprocal elements.

Furthermore, the oscillation frequency is not limited to the range of 1 to 10 GHz. MHz4W or GHz depending on usage
The optimal frequency is selected from within the band.

〔Effect of the invention〕

In the present invention, a C-L conversion circuit is interposed between the microcapacitance detection section and the resonator of the resonant circuit, so even when the Q or impedance of the detected object is low, this low The influence of impedance does not affect the resonator of the resonant circuit. Therefore, capacitance can always be detected with the resonator's Q and impedance being high, and this makes it possible to detect minute changes in capacitance with high sensitivity.

Further, by configuring both the resonator of the oscillation circuit section and the resonator of the resonant circuit with ceramic resonators, it is possible to significantly reduce the weight and size of the device.

Furthermore, by connecting a stabilization control circuit to the CL conversion circuit to stabilize the tuning point between the oscillation frequency of the oscillation circuit section and the resonance frequency of the resonant circuit, the tuning point is always operated at the optimal setting position. This makes it possible to significantly improve the reliability of capacitance detection.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the electrostatic sensor device according to the present invention, Fig. 2 is a circuit diagram of a C-L conversion circuit in the same embodiment, and Fig. 3 is a circuit diagram of the C-L conversion circuit in the same embodiment. 2. Figure 4 is an explanatory diagram showing the method of setting the tuning point between the oscillation frequency and the resonance frequency. Figure 5 is an explanatory diagram showing an example of signal response conversion. Figure 6 is a general diagram of the RCA method. FIG. 7 is a diagram of the electrostatic sensor manufacturing process, and is an explanatory diagram of the operation of detecting minute capacitance of the RCA type electrostatic sensor device. DESCRIPTION OF SYMBOLS 1... Oscillation circuit section, 2... No (oscillation circuit, 3... Detection section, 4... Detection section, 5... Amplification circuit, 6... High impedance conversion circuit, 7...・C-1-conversion circuit,
8... AFC circuit, 10... Ceramic resonator, I
2... Ceramic resonator, 13.14.15.16.
...Transistor, 21...Inductance element, 2
2...Diode, 23...Capacitor, 24...
・Resistor, 25... Coupling capacitor, 2G... Capacitor, 27... Transistor, 28... Operational amplifier, 29.30... Capacitor, 31... Variable resistor, 32... Resistor 33... Variable capacitance diode, 34... Coupling capacitor, 35... Resistor.

Claims (2)

[Claims] (1) An oscillation circuit section that outputs an oscillation frequency signal, a detection section that detects changes in capacitance with the detected object, and resonance in which the resonance frequency changes due to minute changes in capacitance detected by this detection section. In the electrostatic sensor device having a circuit, a C-L conversion circuit is provided between the detection section and the resonant circuit to convert a change in capacitance detected by the detection section into a change in inductance and transmit it to the resonant circuit. An electrostatic sensor device characterized in that an electrostatic sensor device is provided. (2) The electrostatic sensor device according to claim 1, wherein the oscillator of the oscillation circuit section and the resonator of the resonance circuit are both constituted by ceramic resonators. (3) Resonant circuit or C-
The electrostatic sensor device according to claim 1 or 2, wherein the L conversion circuit is connected to a stabilization control circuit that stabilizes the tuning point between the oscillation frequency of the oscillation circuit section and the resonance frequency of the resonance circuit. .