JPH03131747A - Electrostatic sensor device - Google Patents

Abstract

PURPOSE:To reduce the size and improve the sensitivity by varying and adjusting the operating voltage of a varactor diode and adjusting an oscillation frequency. CONSTITUTION:When the slide terminal of a variable resistor 12 is slid, the operating voltage applied to the varactor diode 10 varies to vary the electrostatic capacity correspondingly. The diode 10 functions as one element of an oscillation circuit 1, whose oscillation frequency varies with the electrostatic capacity. Therefore, the operating voltage to the diode 10 is only adjusted through the resistor 12 to adjust the tuning point of a tuning circuit strictly. Further, since no large-sized, expensive trimmer capacitor is used, the size is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrostatic sensor device that detects a minute change in capacitance of an object to be detected using a high-frequency oscillation frequency signal.

[Conventional technology]

The electrostatic sensor device that has been very commonly used changes the oscillation frequency by changing the capacitance used in the dunk circuit of the oscillation circuit in response to changes in external capacitance. However, the detection sensitivity is low, so
In recent years, more sensitive RCA-type devices (a method of obtaining AM modulated waves by changing the capacitance of a tuned circuit with a resonant frequency that is slightly different from the oscillation frequency of the oscillation circuit) have come into use. It's coming.

As shown in FIG. 3, this RCA type electrostatic sensor device includes an oscillation circuit 1, a tuning circuit 2, a detection section 3 that detects a change in capacitance with the detected object, and a detection circuit 4. It consists of an amplifier circuit 5. The oscillation circuit l and the tuning circuit 2 each include separate and independent resonators. For example, as shown in FIG.
The resonance frequency f0 of is set at a slightly shifted position, and the minute capacitance change ΔC detected by the detection unit 3
The resonant frequency is shifted from f by Δf in response to
The change in capacitance ΔC is converted into a change in output voltage ΔV, which is detected and amplified and extracted.

Generally, in this type of conventional RCA type electrostatic sensor device, each resonator of the oscillation circuit 1 and the tuning circuit 2 is formed using a strip line.

[Problem to be solved by the invention]

As is well known, a stripline requires a length of at least X of the oscillation frequency wavelength, which inconveniences the equipment to be large.Also, equipment using this stripline has a low Q, so it is difficult to use in microstatics. The drawback is that changes in capacitance cannot be detected with ultra-high sensitivity.

The inventors of the present invention have succeeded in solving the above-mentioned conventional drawbacks by using dielectric resonators for each of the resonators of the oscillation circuit 1 and the tuning circuit 2. In other words, by using a dielectric resonator as a resonator, the inventor has determined that the length of the resonator is (ε1/εt)l/2 (ε,
is the dielectric constant of the substrate on which the stripline is constructed, ε
2 is the dielectric constant of the dielectric resonator), and this dielectric was made of ceramic. Since the dielectric constant ε of ceramic is 40 to 90, it is possible to significantly downsize the device, and the Q of ceramic is 2.
Since the value is as high as 00 to 300, it is possible to achieve ultra-high sensitivity of the device, and it is possible to detect minute capacitances on the order of I Xl0-'PF.

The prototype device of the present inventor includes an oscillation circuit, a tuning circuit 2, a detection section 3, a detection circuit 4, and an amplifier circuit 5, as in the conventional example, and FIG. Oscillation circuit l
is extracted and shown. In this prototype device, a trimmer capacitor 8 for finely adjusting the oscillation frequency is connected to the ceramic resonator υ constituting the oscillation circuit 1 via a coupling capacitor 7.

In such an ultra-sensitive electrostatic sensor device, the oscillation circuit l
It is necessary to set the tuning points of the tuning circuit 2 i-finely. As is well known, the capacitance of the trimmer capacitor 8 has a fixed capacitance component C0 and a variable capacitance component ΔC,
The size of this fixed capacitance component C0 is quite large, and furthermore, the variation in fixed capacitance component C0 for each product is also quite large.

As the fixed capacitance component C0 has an element as an oscillator as shown by the broken line in FIG.
When using an ultra-high frequency wave with an oscillation frequency called LOGI, the oscillation frequency of the oscillation circuit 1 fluctuates greatly due to this 00 variation, and even if the variation in the resonant frequency of the ceramic resonator 6 is suppressed to below the standard value, the purpose cannot be met. This has the disadvantage that a predetermined oscillation frequency cannot be obtained, and even if an attempt is made to adjust the capacitance with the variable capacitance component ΔC, it is impossible to adjust the capacitance to a specified tuning point.

Furthermore, even if the tuning point can be precisely aligned, if stray distributed capacitance occurs between the electrostatic sensor device and the surrounding components when it is attached to the device under test, this will cause the problem of deviating the oscillation frequency. arise.

Furthermore, although it is ideal to install the trimmer capacitor 8 in close proximity to the ceramic resonator 6, due to the user's requests and restrictions on the location where the electrostatic sensor device is installed on the device under test, etc. In many cases, the trimmer capacitor 8 must be installed at a remote location, and in such cases, the length of the lead wire of the trimmer capacitor 8 becomes longer.
11. of this lead wire. There is a problem in that the Lx portion becomes a capacitance component or an inductive component, causing variations in the oscillation frequency and parasitic vibration, making the oscillation frequency unstable.

The present invention has been made to solve the above problems, and its purpose is to easily adjust the oscillation frequency, and to provide stable oscillation without causing fluctuations or variations in the oscillation frequency due to external factors. An object of the present invention is to provide a small and highly sensitive electrostatic sensor device that can generate a frequency.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention includes an oscillation circuit that includes a resonator and outputs an oscillation frequency signal, a detection section that detects a change in capacitance with an object to be detected, and a small change in capacitance detected by this detection section. In an electrostatic sensor device having a tuning circuit whose tuning point with an oscillation frequency signal changes, a variable capacitance diode that variably adjusts the oscillation frequency of the oscillation circuit;
A variable potential converter that variably adjusts the operating voltage applied to the variable capacitance diode, and a high frequency separation circuit interposed between the variable capacitance diode and the variable potential converter,
The resonator of the oscillation circuit is characterized in that it is constituted by a dielectric resonator.

[Effect]

In the present invention, when the operating voltage applied to the variable capacitance diode is adjusted to variable jJ4 by the variable potential converter, the capacitance of the variable capacitance diode changes in response to the change in the operating voltage. As a result of this variable capacitance diode functioning as an element of a resonator, the oscillation frequency changes in response to a change in the capacitance of the variable capacitance diode. That is, by variably adjusting the variable potential converter, the oscillation frequency can be matched to a desired predetermined set frequency. When making this variable adjustment of the frequency, the high-frequency separation circuit blocks the capacitance and inductive components generated in the lead wire section leading to the variable potential converter from reaching the resonator side, and stabilizes the oscillation frequency. .

[Example] Hereinafter, an example of the present invention will be described based on the drawings. In the description of this embodiment, the same reference numerals are given to circuit parts that are the same as those of the conventional example, and redundant explanation thereof will be omitted.The electrostatic sensor device of this embodiment is similar to the conventional example and the prototype device. , an oscillation circuit 1, a tuning circuit 2, a detection section 3, a detection circuit 4, and an amplifier circuit 5,
FIG. 1 shows details of an oscillation circuit l, which is characteristic of these circuits.

The device of this embodiment, like the prototype device, has an oscillation circuit l.
A ceramic resonator 6 is used as the resonator of the
The cathode side of a variable capacitance diode 10 is connected to the ceramic resonator 6 via a coupling capacitor 7. The anode side of the variable capacitance diode IO is grounded. This variable capacitance diode 10 is placed close to the ceramic resonator 6, and a resistor 11 as a high frequency isolation circuit is connected to the connection between the variable capacitance diode IO and the coupling capacitor 7. The other end of the device 11 is a variable resistor 1 as a variable potential converter.
It is connected to the sliding terminal of No. 2 via a lead wire 13.

This variable resistor 12 plays the role of adjusting the operating voltage applied to the variable capacitance diode 10.

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

When the sliding terminal of the variable resistor 12 is slid, the operating voltage applied to the variable capacitance diode 10 changes. The variable capacitance diode 10 changes its capacitance in response to changes in operating voltage. This variable capacitance diode 10 functions as one element of the oscillation circuit l, and therefore, as the capacitance of this variable capacitance diode 10 changes, the oscillation frequency changes. Therefore, in this embodiment, the oscillation frequency can be adjusted to a desired predetermined frequency by simply adjusting the operating voltage applied to the variable capacitance diode IO using the variable resistor 12, and the tuning circuit 2 It becomes possible to closely match the tuning point fg&.

Furthermore, as mentioned above, since the oscillation frequency can be adjusted by changing the voltage applied to the variable capacitance diode 10, the resistance value of the resistor 11 can be increased, and in this way, the resistance value can be increased. Then, this resistor 11
Almost no direct current flows through the oscillator 6, and the effect of this direct current component has almost no effect on the oscillator 6 side.Also, the presence of this resistor 11 reduces static on the lead wire 13 side even for high frequency components. Capacitance components and inductive components are dropped to the ground side and do not affect the resonator side. Therefore, even if the length of the lead wire 13 is increased, it has almost no effect on the ceramic resonator 6 side. It becomes possible to arrange the variable resistor 12 at any position according to the user's request, and it becomes possible to increase the degree of freedom in circuit design.

Furthermore, as mentioned above, the oscillation frequency is set to an ultra-high frequency,
When ultra-high sensitivity is used, when an electrostatic sensor device is attached to a device under test, the oscillation frequency changes due to the influence of stray distributed capacitance between the device and the device under test. Even if such floating distributed capacitance occurs, by changing the operating voltage applied to the variable capacitance diode 10, it becomes possible to easily adjust the deviation in the oscillation frequency, and it becomes possible to constantly adjust the tuning point with Mra.

Furthermore, since the device of this embodiment does not use any trimmer capacitor, which tends to be large and expensive, it is possible to further reduce the size and cost of the device.

It should be noted that the present invention is not limited to the above-mentioned embodiment, and various implementations of P4 may be adopted.

For example, in the above embodiment, the high frequency isolation circuit is connected to the resistor 11.
However, this can also be constructed using a high impedance coil.

Further, according to the above embodiment, as described above, the lead wire I3
Even if the length of lead wire m13 is increased, it is possible to perform oscillation operation without being affected by the capacitance component or inductive component generated in this lead wire 13, but the length of lead wire m13 becomes significantly longer. In this case, capacitors 14 and 15 are installed at both ends of the lead wire 13, as shown by the broken lines in FIG. The oscillation operation may be further stabilized by completely blocking harmful elements such as capacitance components.

Furthermore, in this example, the resonator of the oscillation circuit 1 and the resonator of the tuned circuit 2 are both made of ceramic resonators, as in the prototype device, but the resonator of the tuned circuit 2 is made of a strip line. It is also possible to do so. just,
If the resonators of both circuits 1 and 2 are constructed of dielectric resonators as in this embodiment, it is possible to further reduce the size of the device and increase the degree of excitation.

〔Effect of the invention〕

Since the present invention is configured to adjust the oscillation frequency by variably adjusting the operating voltage of the variable capacitance diode, there may be slight variations in the shape of the dielectric resonator of the oscillation circuit, and electrostatic Even if the oscillation frequency changes due to the occurrence of stray distributed capacitance when the sensor device is incorporated into the device under test, the oscillation frequency can be adjusted to the desired oscillation frequency by adjusting the operating voltage applied to the variable capacitance diode. can be easily adjusted.

In addition, since a high frequency isolation circuit is provided between the variable potential converter and the variable capacitance diode, the length of the lead wire from the high frequency isolation circuit to the variable potential converter can be increased (even if the lead wire is The oscillation frequency can be stabilized without the effects of capacitance and inductive components affecting the resonator side of the oscillation circuit.In addition, in this way, the oscillation frequency varies depending on the length of the lead wire. Therefore, there are no restrictions on the mounting position of the variable potential converter, and the degree of freedom in circuit design can be greatly increased.

Furthermore, since a large and expensive trimmer capacitor is not required as a component of the oscillation circuit, the oscillation circuit can be made sufficiently small and
Moreover, it can be made inexpensive, and accordingly, the electrostatic sensor device can also be made smaller and cheaper.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an oscillation circuit portion constituting an embodiment of an electrostatic sensor device according to the present invention, Fig. 2 is a circuit diagram of an oscillation circuit portion of an electrostatic sensor device prototyped by the inventor, and Fig. 3 is R.C.
Block diagram of the most suitable electrostatic sensor device of type A, 1st 4
The figure is an explanatory diagram showing the operation of detecting minute capacitance in an RCA type electrostatic sensor device. I... Oscillation circuit, 2... Tuning circuit, 3... Detection section, 4... Detection circuit, 5... Amplification circuit, 6... Ceramic resonator, 7... Coupling capacitor, 8... Trimmer capacitor, lO... Variable capacitance diode, 11.
...Resistor, 12...Variable resistor, 13...Lead wire, 14.15...Capacitor.

Claims (1)

[Claims] an oscillation circuit that includes a resonator and outputs an oscillation frequency signal;
In an electrostatic sensor device that includes a detection unit that detects a change in capacitance with a detected object, and a tuning circuit that changes a tuning point with an oscillation frequency signal due to a minute change in capacitance detected by the detection unit. , a variable capacitance diode that variably adjusts the oscillation frequency of the oscillation circuit, a variable potential converter that variably adjusts the operating voltage applied to the variable capacitance diode, and a variable potential converter that is interposed between the variable capacitance diode and the variable potential converter. and a high frequency separation circuit, wherein the resonator of the oscillation circuit is constituted by a dielectric resonator.