JPH0454465A - Variable output circuit for ceramic type electrostatic sensor - Google Patents

Abstract

PURPOSE:To detect a minute electrostatic capacity under an adequate sensitivity by making the dump amount of Q of a ceramic resonator variable with a control input of variable impedance circuit. CONSTITUTION:When the change of minute electrostatic capacity is detected by a detection part 3 under the state that an oscillating frequency signal is being outputted from an oscillation circuit 1, the resonance frequency of ceramic resonator 12 is deviated, and an amplitude modulation wave, the carrier wave of which is the oscillating frequency signal of circuit 1, is produced and applied to a detection circuit 4. In the circuit 4, the AM wave is detected and outputted as a detection signal for electrostatic capacity change. When a DC input is applied from a control input terminal 11, at the detection of this minute electrostatic capacity, the value of voltage level outputted from the resonator 12 is changed in accordance with the amount of the input. Consequently, in the case the Q of resonator 12 is made large to detect the minute electrostatic capacity with ultrahigh sensitivity, the control input is made to zero, and when the detection is made with low detection sensitivity, the control input signal is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable output circuit for a ceramic electrostatic sensor that changes the sensor output by changing the Q of a ceramic resonator as a tuning circuit.

[Conventional technology]

The electrostatic sensor device that has been very commonly used changes the oscillation frequency by changing the capacitance used in the tank circuit of the oscillation circuit in response to changes in external capacitance. However, the detection sensitivity is low, so
In recent years, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-85948, A M (Amplitude Module
tion) A device that obtains a modulated wave has come into use.

As shown in FIG. 4, this type of electrostatic sensor device includes an oscillation circuit 1, a tuning circuit 2, a detection section 3 for detecting changes in capacitance with the detected object, a detection circuit 4, and an amplification circuit. It consists of a circuit 5. The oscillation circuit 1 and the tuning circuit 2 each include separate and independent resonators, and for example, as shown in FIG.

is set at a slightly shifted position, and the resonant frequency is shifted by Δf from fo in response to the minute capacitance change ΔC detected by the detection unit 3, and the capacitance change ΔC is set as the output voltage. This is converted into a change in Δ■ to create an AM modulated wave using the oscillation frequency signal of the oscillation circuit 1 as a carrier wave, which is detected and amplified and extracted.

[Problem to be solved by the invention]

The present inventors used ceramic resonators for each resonator of the oscillation circuit 1 and the tuning circuit 2, and set the oscillation frequency signal to 0.5 GHz.
~l0C) By using an ultra-high frequency signal of fz,
We have succeeded in developing a small, ultra-sensitive ceramic electrostatic sensor that can detect minute capacitances on the order of I Xl0-'PF.

Generally, when measuring changes in capacitance, there are cases where it is necessary to detect with ultra-high sensitivity as described above, and cases where detection sensitivity can be lowered without causing any particular problems. . When detecting changes in capacitance using the ultra-high-sensitivity ceramic capacitive sensor developed by the present inventors in fields that do not require ultra-high sensitivity measurements, the sensitivity is so high that environmental changes and disturbances can be detected. On the other hand, if the sensitivity of the ceramic electrostatic sensor is lowered, it may be difficult to detect minute changes in capacitance with ultra-high sensitivity. The problem arises that it cannot be done.

The present invention has been made to solve the above problems, and its purpose is to variably adjust the Q of a ceramic electrostatic sensor, thereby changing the field of measurement from a measurement field that does not require high sensitivity to a field that requires ultra-high sensitivity. An object of the present invention is to provide a variable output circuit for a ceramic electrostatic sensor that can detect changes in capacitance with sensitivity depending on the purpose of use in various measurement fields.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as follows. That is, the variable output circuit of the ceramic capacitive sensor of the present invention includes an oscillation circuit that includes a built-in resonator and outputs an oscillation frequency signal, and a tuning circuit that is tuned to the oscillation circuit in response to changes in external capacitance to be detected. and a ceramic resonator as a tuning circuit separate from the resonator of the oscillation circuit that outputs an amplitude modulated wave corresponding to a change in the tuning point, the ceramic resonator as the tuning circuit The structure is characterized in that a variable impedance circuit that changes impedance according to a control input is connected in parallel.

[Effect]

In the present invention, the variable impedance circuit is initially set to the highest impedance, and the ceramic resonator has the highest Q at this time. If a control input is applied to the variable impedance circuit in this state, for example, as the control input becomes larger, the impedance of the variable impedance circuit becomes smaller, which causes a Q-dump of the ceramic resonator as a tuned circuit, and the sensitivity also decreases. The output from the ceramic resonator becomes smaller.

On the other hand, when the control input is made smaller, the impedance of the variable impedance circuit becomes larger, the Q dump amount of the ceramic resonator becomes smaller, the sensitivity decreases less, and the output of the ceramic resonator also decreases less. In this way, the Q-dump amount of the ceramic resonator changes depending on the magnitude of the control input applied to the variable impedance circuit, and the magnitude of the output signal of the ceramic resonator changes.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
The figure shows a first embodiment of the invention. The circuit of this embodiment consists of a ceramic type electrostatic sensor circuit 9 and a variable impedance circuit 13. consists of a ceramic resonator 12 as a separate and independent circular circuit, a detection unit 3 that detects a change in capacitance and applies it to the output terminal of the ceramic resonator 12, a coupling capacitor 6, and an inductance element 7. The high-impedance circuit 8 includes a detection circuit 4 including a diode 10, and an amplifier circuit 5 including an operational amplifier 21.

The variable impedance circuit 13 has the ceramic resonance δ
This variable impedance circuit 3 is connected in parallel with 12, and includes resistors 14 to 16, 19, a field effect transistor (FET) 17, and a capacitor 18. The FET 17 is made of a high frequency element, and its source is connected to the output terminal of the ceramic resonator 12. Further, the source of the FET 17 is connected to the FE via the resistor 14.
Connected to the drive power supply of T17. The drain of FET 17 is connected to ground through bias resistor 19. Further, the base of the FET is connected to the control input terminal 11 via a resistor 16 and grounded via a capacitor 18. A resistor 15 is provided between the source and base of the FET 17. This FET
17 operates as a class A amplifier.

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

When the detection unit 3 detects a minute change in capacitance while the oscillation circuit 1 is outputting an oscillation frequency signal of an extremely high frequency of, for example, IGHz, as shown in FIG. 5, the ceramic resonator 12 The resonant frequency of the oscillation circuit 1 shifts, and in response to the change in the tuning point, an amplitude modulated wave (AM
This AM modulated wave is applied to the detection circuit 4 via the high impedance circuit 8. The detection circuit 4 detects the AM modulated wave, converts it into a signal in a capacitance change detection band, and outputs this as a detection signal.

The detection signal is amplified by the amplifier circuit lIr5 and applied to a desired signal processing circuit.

When detecting this minute capacitance, when a DC control input is applied from the control input terminal 11, the magnitude of the voltage level output from the ceramic resonator 12 changes depending on the magnitude of the control input. That is, as the control input increases, the resistance between the source and drain of the FET 17 decreases, and as shown in FIG. 3, the Q of the ceramic resonator 2 is dumped (Q becomes smaller). This dump amount of Q increases as the control input increases. When Q is damped, the detection sensitivity also becomes low, and the output level of the ceramic resonator 12 also becomes smaller as the amount of Q damping increases.

On the other hand, if the magnitude of the control input signal is reduced, F
The resistance between the source and drain of the ET17 becomes thicker, and the amount of Q damping of the ceramic resonator 12 becomes smaller.As a result, the detection sensitivity decreases less and the output level from the ceramic resonator 12 also decreases less. In this way, by adjusting the magnitude of the control input signal, it becomes possible to variably adjust the output of the ceramic resonator 12.

Therefore, if you want to increase the Q of the ceramic resonance 512 and detect minute capacitance with ultra-high sensitivity, this can be achieved by setting the control input to O. When it is desired to detect a change in capacitance, this purpose can be achieved by applying a control input signal to the base side of FET 17. By variably adjusting the magnitude of the control input signal, the amount of Q dump changes, making it possible to arbitrarily variably adjust the level of the output signal of the ceramic resonator 12.

In addition, in this embodiment, the variable impedance circuit is
17, this FET 17 can be placed around the ceramic resonator 120, making it possible to maintain good ultra-high frequency characteristics of the ceramic electrostatic sensor circuit 9.

A second embodiment of the invention is shown in FIG. The difference between this second embodiment and the first embodiment is that the FE
The source of T17 and the output terminal of the ceramic resonator 12 are connected via a coupling capacitor 20, but the other configuration is almost the same as that of the first embodiment.

Note that the present invention is not limited to the above embodiments,
Various implementation modes are possible. For example, in each of the above embodiments, the variable impedance circuit 13 is configured using the FET 17, but if the variable impedance circuit is a high impedance circuit whose impedance changes depending on the magnitude of the control input, circuit elements other than the FET 17 may be used. It can be configured using

Further, the output signal of the ceramic electrostatic sensor circuit 9 may be fed back and applied to the control input terminal 11, or a control signal may be applied from another external circuit. By configuring a feedback loop with the electrostatic sensor circuit 9 and the variable impedance circuit 13, for example, if the tuning point of the ceramic resonator 12 shifts significantly due to environmental changes or disturbances, signal fluctuations due to the environmental changes, etc. will be applied to FET 17 as a control input signal. Therefore, it is possible to damp the Q of the ceramic resonator 12 when the environment changes, lowering the sensitivity, and mitigating the effects of these environmental changes, etc., thereby stabilizing the detection operation in the ceramic electrostatic sensor circuit 9. This makes it possible to achieve

It is also possible to provide a sensor separately from the ceramic electrostatic sensor circuit 9 and use a signal from this sensor as a control input signal. In this way, a composite signal processing circuit will be constructed, and it will be possible to develop various circuits with rich functionality.For example, if a sensor is installed to measure ambient noise and the detection signal of this sensor is used as a control input signal, When the ceramic electrostatic sensor circuit 9 is configured as an electrostatic microphone device, it can be developed as a zoom microphone that selectively takes in distant sound pressure while excluding surrounding noise.

〔Effect of the invention〕

The present invention is configured to vary the amount of Q damping of a ceramic resonator as a tuning circuit by the control input of the variable impedance circuit, and to variably adjust the magnitude of the output of the ceramic resonator. Capacitance detection ranges from detection at ultra-high sensitivity to detection at lower sensitivity, and minute capacitance can be detected with the desired sensitivity.

In addition, various circuit developments are possible, such as using the control input signal of the variable impedance circuit by feeding back the output signal of the ceramic electrostatic sensor, or using separate sensor signals. Stabilization of circuit operation in an electrostatic sensor can be achieved.

Furthermore, since the control input applied to the variable impedance circuit is generally a direct current or low frequency signal, no special consideration is required in circuit design or wiring, making handling extremely easy.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of a variable output circuit for a ceramic electrostatic sensor according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. An explanatory diagram of the Q-dump of the ceramic resonator as a tuning circuit in each embodiment of the invention, FIG. 4 is a block diagram of a conventional general electrostatic sensor circuit, and FIG. 5 is a microscopic diagram of the electrostatic sensor of FIG. FIG. 3 is an explanatory diagram showing a capacitance detection operation. DESCRIPTION OF SYMBOLS 1... Oscillation circuit, 2... Tuning circuit, 3... Detection part, 4... Detection circuit, 5... Amplification circuit, 6... Coupling capacitor, 7... Inductance element, 8
... High impedance circuit, 9... Ceramic electrostatic sensor circuit, 10... Diode, 11... Control input terminal, 12... Ceramic resonator, 13...
Variable impedance circuit, 14-16...Resistor, 1
7...-field effect transistor CFET), 18...
・Capacitor, 20... Campling capacitor, 2
1...Operation amplifier. Figure 1

Claims (1)

[Claims] An oscillation circuit that has a built-in resonator and outputs an oscillation frequency signal,
A tuning point separate and independent from the resonator of the oscillation circuit that changes a tuning point with the oscillation circuit in response to a change in detected external capacitance and outputs an amplitude modulated wave corresponding to the change in the tuning point. A variable output circuit for a ceramic electrostatic sensor, which has a ceramic resonator as a circuit, and a variable impedance circuit that changes impedance according to a control input is connected in parallel to the ceramic resonator as a tuning circuit.