JPH05126884A - Electrostatic sensor - Google Patents

Abstract

PURPOSE:To eliminate background noise due to a high-frequency current which is discharged from an oscillation circuit and vibration noise due to a vibration displacement of a shield wire of a power supply. CONSTITUTION:This electrostatic sensor is constituted of an oscillation circuit 1, a resonance circuit 2, a sensing electrode 3, a detection circuit 4, an amplification circuit 5, and a power-supply circuit 7. An ultra-high-frequency filter 8 is provided between a high-frequency circuit side which consists of the oscillation circuit 1, the resonance circuit 2, and a high-frequency part of a power supply and a low-frequency circuit side which includes the amplification circuit 5 and the low-frequency part of the power supply. thus enabling a high-frequency current which flows from the high-frequency circuit side to the low-frequency circuit side to be interrupted.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an ATM (Automated Telecommunications)
llerMachine), bill validator, ticket gate, paper industry,
The present invention relates to an electrostatic sensor device that detects the thickness and properties of an object to be detected in various fields such as pulp industry, plate making, woodworking, food industry, robots, information equipment, and the like.

[0002]

2. Description of the Related Art The applicant has previously proposed, for example, in Japanese Patent Application No. 1-126234, a highly sensitive electrostatic sensor device capable of detecting a change in a minute electrostatic capacitance.

As shown in FIG. 3, the proposed device has an oscillation circuit 1, a resonance circuit 2, a detection electrode 3 for detecting a change in electrostatic capacitance between an object to be detected, a detection circuit 4, and an amplification circuit 5. And have. The oscillation circuit 1 and the resonance circuit 2 each include a ceramic resonator as an independent dielectric resonator, and for example, as shown in FIG. 4, the oscillation circuit 1 resonates at a fixed oscillation frequency f _{1 in} the GHz band. Resonance frequency f of circuit 2
₀ is set at a position slightly deviated, and the resonance frequency is deviated from f ₀ by Δf in accordance with the change ΔC of the small electrostatic capacitance detected by the detection electrode 3, and the change ΔC of the electrostatic capacitance is changed. Converting to output voltage ΔV change (ΔV modulation signal using oscillation frequency signal as carrier wave), detecting this to make a voltage signal of several mmV in the low frequency band, and further amplifying and extracting it to the order of volts Is.

In this proposed device, the oscillation frequency of the oscillation circuit 1 oscillates at a high frequency of, for example, 1 to 3 GHz, and the sensitivity is very high. Therefore, for example, when a hand is brought close to the detection electrode 3, the detection electrode is detected. 3 affects the resonance frequency of the resonance circuit 2, or the length of the conductor lead between the detection electrode 3 and the ceramic resonator incorporated in the resonance circuit 2 is the wavelength of the oscillation frequency. Where n is λ / 4 (n is an integer of 1 or more), an unstable phenomenon occurs. In order to solve such a problem, the applicant repeatedly improved the proposed device, and arranged the detection electrode 3 on the same surface as the chassis at the ground potential or slightly retracted from the chassis, thereby causing the floating distribution capacitance, etc. Succeeded in eliminating the effect of
In addition, the destabilization phenomenon was successfully eliminated by making the conductor lead from the detection electrode 3 to the ceramic resonator of the resonance circuit 2 shorter than nλ / 4. As a result, it became possible to detect the change of the small electrostatic capacitance of 10 ^-4 PF stably.

[0005]

However, if the detection sensitivity is further increased to detect a change in the minute electrostatic capacitance of 10 ^-5 to 10 ^-8 PF, a characteristic problem when the circuit is driven in the GHz band is encountered. There has been a problem in that a stable phenomenon occurs, and even if the improved electrostatic sensor device is used, it is impossible to stably detect a change in the minute electrostatic capacitance. That is, in this type of electrostatic sensor device, it is inevitable that the high-frequency circuit portion and the low-frequency circuit portion are mixed, and if the oscillation circuit 1 oscillates at a high frequency in the GHz band,
When this oscillating frequency signal is radiated and a high-frequency current flows as noise in the surrounding circuit conductors, and this high-frequency current flows from the high-frequency circuit portion to the low-frequency circuit portion, the oscillation condition of the oscillation circuit 1 fluctuates, causing a small electrostatic capacitance. caused a problem that the resolution of detection is reduced, also, the capacitance around the sensing electrode and the circuit subjected to mechanical vibrations changes from around the noise due to the vibration is generated due to this, the 10 ^-5 This has led to the problem that it is no longer possible to stably detect changes in the small electrostatic capacitance of 10 ^-8 PF.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide noise (hereinafter referred to as background noise) due to high frequency radiation interference from an oscillation circuit and noise due to mechanical vibration (hereinafter referred to as noise). , Vibration noise) is significantly reduced, and an electrostatic sensor device that enables stable detection of a minute electrostatic capacitance with higher resolution is provided.

[0007]

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 dielectric resonator and outputs an oscillation frequency signal of high frequency, and that changes the resonance frequency in response to a change in capacitance detected by a detection unit that includes a dielectric resonator. A resonance circuit that modulates and outputs a signal corresponding to the change in the resonance frequency; an amplification circuit that amplifies and outputs the detection output after the modulation output signal is detected as a signal in a low frequency band; and a power supply circuit. In the electrostatic sensor device formed on the common circuit board, between the high frequency circuit side including the oscillation circuit, the resonance circuit, and the high frequency portion of the power supply, and the low frequency circuit side including the amplification circuit and the low frequency portion of the power supply. Is characterized in that a high-frequency separation circuit for interrupting the flow of high-frequency current from the high-frequency circuit side to the low-frequency circuit side is interposed.

[0008]

In the present invention having the above structure, a high frequency signal is radiated from the oscillator circuit and a high frequency current tends to flow from the high frequency circuit side to the low frequency circuit side. As a result of blocking the flow of the high frequency current to the circuit side, the interference between the low frequency circuit side and the high frequency circuit side is prevented, and the oscillation frequency signal of the oscillation circuit is kept stable.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration of one embodiment of the electrostatic sensor device according to the present invention, and FIG. 2 shows an equivalent circuit when driving the device of the same embodiment. The electrostatic sensor device according to the present embodiment includes a dielectric resonator (ceramic resonator) and outputs an oscillation frequency signal in the GHz band (1 to 3 GHz in this embodiment), similarly to the proposed device. A resonance circuit 2 having a ceramic resonator 6 as a dielectric resonator, a detection circuit 4, an amplification circuit 5, and a power supply circuit 7. As for the circuit operation, as in the case of the proposed device, when the small electrostatic capacitance of the detected object is detected by the detection electrode 3 of the detection unit, the resonance frequency of the resonance circuit 2 changes due to the change of the electrostatic capacitance. Then, a signal corresponding to the change in the resonance frequency is generated as an amplitude modulation signal by using the oscillation frequency signal as a carrier, and the amplitude modulation signal is envelope-detected by the detection circuit 4 into a low frequency band signal, and the detection output is low. The signal is amplified by the frequency amplifying circuit 5 and added to the desired signal processing circuit.

A feature of this embodiment is that the high frequency circuit side including the oscillation circuit 1, the resonance circuit 2 and the high frequency portion of the power source, and the low frequency circuit side including the amplifier circuit 5 and the low frequency portion of the power source are provided. That is, the super high frequency filter 8 serving as a high frequency separation circuit cuts off at high frequencies.

When the circuit of the electrostatic sensor device is driven, the oscillation circuit 1 radiates a high frequency oscillation signal in the GHz band.
In the equivalent circuit of FIG. 2, the oscillation circuit 1 acts as a noise source of background noise. A high-frequency signal radiated from a noise source causes a high-frequency current to flow everywhere, such as in the surrounding power supply line and ground line, and on the high-frequency circuit side, the stray capacitance CS ₁
.About.CS ₄ are generated, and components of the inductances Lm _{1 to} Lm ₄ appear on a thin portion such as a copper foil on the circuit board.

In this equivalent circuit, in order to reduce the background noise, the bypass capacitors Cb ₁ and Cb _{2 are used.}
Need to be provided. In this case, if the capacitance of Cb ₂ is made larger than the capacitance of Cb ₁ , a noise current (high frequency current) Ib ₂ flows on the Cb ₂ side and the bypass capacitor Cb
The potential between the _two becomes high, the noise potential of the electrostatic sensor device and the potential of the shield line 9 of the power supply unit become equal potential, a noise current flows on the shield line 9, and the background noise against noise is reduced, There is a problem that vibration noise is newly generated due to the shake of the shielded wire 9. In order to reduce both the vibration noise and the background noise, it is necessary to make the capacitance of the bypass capacitor Cb ₁ much larger than the capacitance of Cb ₂ . However, it is difficult to make a large-capacity high-frequency capacitor with the current technology, and in general, Cb ₂ which is a capacitor having a lower frequency than that of Cb ₁ which is a high-frequency capacitor.
If the capacity of a big capacity, the capacity of Cb ₁ Cb ₂
It is difficult to make it much larger than the capacity.

Therefore, in order to solve such a difficulty, the present inventor installs an inductance L having a large load resistance in the high frequency between the low frequency circuit side and the high frequency circuit side, and the bypass capacitors Cb ₁ and Cb. _The ultra high frequency filter 8 is formed by ₂ and. By thus providing the inductance L, the high frequency current flowing to the high frequency circuit side is blocked at the inductance L having a large load resistance, and the high frequency current is surely blocked from flowing from the high frequency circuit side to the low frequency circuit side. By cutting off the high-frequency current, the high-frequency current does not flow through the shielded wire 9, so that vibrational noise is not generated even when the shielded wire 9 is displaced by vibration, and the oscillation operation of the oscillation circuit 1 is stably performed. Is possible.

In this embodiment, as shown in FIG. 1, an ultra high frequency filter 8 as a high frequency separation circuit is composed of an inductance L, an electrolytic capacitor 11 and a capacitor 12, and a power supply and an ultra high frequency filter 8 are a three-terminal regulator.
Connect using 10 and ground line GN on the high frequency circuit side
₁ and a ground line GN ₂ on the low frequency circuit side are provided with an inductance L having a large load resistance in terms of high frequency, and further, a power source line Vcc ₁ on the high frequency circuit side and a power source line Vcc ₂ on the low frequency circuit side. Similarly, an inductance L having a large load resistance at high frequency is interposed between the two. Note that FIG.
In the circuit diagram, the ground line GN is connected to either the ground line GN ₁ on the high frequency circuit side or the ground line GN ₂ on the low frequency circuit side, depending on the circuit specifications.

According to this embodiment, even if a high frequency signal radiated from the oscillation circuit 1 causes a high frequency current to flow to the high frequency circuit side as background noise, the high frequency current is blocked by the inductance L having a large load resistance. Since it does not flow to the low frequency circuit side and flows along the loop on the high frequency circuit side, interference does not occur between the high frequency circuit side and the low frequency circuit side, and thus,
The oscillation frequency can be stabilized, and vibration noise caused by the vibration of the shielded wire 9 does not occur and 10 ^-5 to 10 ^-8
It has become possible to stably detect an extremely small change in capacitance called PF under high resolution.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted.

[0017]

According to the present invention, a high-frequency separation circuit is provided between the high-frequency circuit side and the low-frequency circuit side of the electrostatic sensor device to block a high-frequency current from flowing from the high-frequency circuit side to the low-frequency circuit side. Therefore, the high-frequency current does not flow from the high-frequency circuit side to the low-frequency circuit side to cause interference between the high-frequency circuit side and the low-frequency circuit side. It is possible to provide an electrostatic sensor device having almost no vibration noise due to vibration of the shielded wire. This way, it is possible to remove noise, resolution is also remarkably improved, the proposed device enables 10 times more stabilized compared to, detectability With this also dramatically improved, 10 ^- It is possible to stably detect a change in minute electrostatic capacitance of ⁵ to 10 ^-8 .

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an electrostatic sensor device according to the present invention.

FIG. 2 is an equivalent circuit diagram of a circuit operation of the device of the embodiment.

FIG. 3 is a block diagram of an electrostatic sensor device previously proposed by the applicant.

FIG. 4 is an explanatory diagram of a detection operation of a small capacitance of the proposed apparatus and the apparatus of this embodiment.

[Explanation of symbols]

 1 Oscillation Circuit 2 Resonance Circuit 3 Detection Electrode 4 Detection Circuit 5 Amplification Circuit 8 Ultra High Frequency Filter 10 3 Terminal Regulator L Inductance

Claims (1)

[Claims] 1. An oscillation circuit that includes a dielectric resonator and outputs an oscillation frequency signal of high frequency; and a resonance frequency that changes the capacitance in response to a change in capacitance detected by a detection unit that includes the dielectric resonator, The resonance circuit that modulates and outputs a signal corresponding to the change in the resonance frequency, the amplification circuit that amplifies the detection output after the modulation output signal is detected as a low frequency band signal, and the power supply circuit are common. In the electrostatic sensor device formed on the circuit board of, between the high frequency circuit side including the oscillation circuit, the resonance circuit, and the high frequency portion of the power supply, and the low frequency circuit side including the amplification circuit and the low frequency portion of the power supply. Is an electrostatic sensor device in which a high-frequency separation circuit that blocks a high-frequency current from flowing from the high-frequency circuit side to the low-frequency circuit side is provided.