JPH0769371B2 - Variable output circuit of ceramic electrostatic sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a variable output circuit of a ceramic type electrostatic sensor that changes a sensor output by changing Q of a ceramic resonator as a tuning circuit.

[Conventional technology]

The electrostatic sensor device that has been generally used in the past changes the oscillation frequency by changing the capacitance used in the tank circuit of the oscillation circuit according to the change in the external capacitance. However, since the detection sensitivity is low, the capacitor capacitance of the tuning circuit having a resonance frequency slightly deviated from the oscillation frequency of the oscillation circuit as disclosed in, for example, Japanese Patent Application Laid-Open No. 58-85948 in recent years. The device of the method of changing AM to obtain an AM (Amplitude Modulation) modulated wave is being used.

As shown in FIG. 4, this type of electrostatic sensor device includes an oscillation circuit 1, a tuning circuit 2, a detection unit 3 for detecting a change in electrostatic capacitance between a detected object, a detection circuit 4, and an amplification circuit. And a circuit 5. The oscillation circuit 1 and the tuning circuit 2 each include an independent resonator. For example, as shown in FIG. 5, the resonance frequency of the operation reference point of the tuning circuit 2 with respect to the fixed oscillation frequency f ₁ of the oscillation circuit 1. With f ₀ set to a fixed position slightly deviated, the resonance frequency is deviated from f ₀ by Δf in response to the change ΔC of the small capacitance detected by the detection unit 3, and the fixed oscillation frequency f ₁ is obtained. The tuning point A is changed to A ′, the change ΔC in the capacitance is converted into a change in the output voltage ΔV to generate an AM modulated wave having the oscillation frequency signal of the oscillation circuit 1 as a carrier, and this is detected and amplified. To take out.

[Problems to be Solved by the Invention]

The present inventors have used a ceramic resonator for each resonator of the oscillation circuit 1 and the tuning circuit 2, and have an oscillation frequency signal of 0.5 GHz to 10 GHz.
By using a super high frequency signal of z, the size is small and 1 × 10
^-We have succeeded in developing an ultra-sensitive ceramic type electrostatic sensor capable of detecting a small electrostatic capacitance of about ^-5 PF.

Generally, when measuring a change in capacitance, there are cases in which it is necessary to detect under ultra-high sensitivity as described above, and cases in which detection sensitivity is lower than that does not cause any particular problems. . When a change in capacitance is detected by using a ceramic type electrostatic sensor with ultra-high sensitivity developed by the present inventors in a field that does not require measurement with ultra-high sensitivity, the sensitivity is too good and environmental changes and disturbances occur. In some cases, the tuning point may deviate from the setting area due to the influence of the above. On the other hand, if the sensitivity of the ceramic electrostatic sensor is lowered, there arises a problem that when it is desired to detect the change in the minute electrostatic capacitance at the ultra-high sensitivity, the change cannot be detected.

The present invention has been made to solve the above problems, and an object thereof is to variably adjust the Q of a ceramic type electrostatic sensor, thereby requiring ultrahigh sensitivity from the measurement field that does not require high sensitivity. It is an object of the present invention to provide a variable output circuit of a ceramic type electrostatic sensor capable of detecting a change in electrostatic capacitance under the sensitivity according to the purpose of use in the measurement field.

[Means for Solving the Problems]

The present invention is configured as follows to achieve the above object. That is, the variable output circuit of the ceramic type electrostatic sensor of the present invention includes an oscillator circuit which has a resonator therein and outputs an oscillation frequency signal of a fixed frequency, and an operation reference point of the resonance frequency with respect to the fixed oscillation frequency of the oscillation circuit. Is set at a fixed position deviated by a set amount, and the tuning point with the fixed oscillation frequency is changed by the deviation of the resonance frequency corresponding to the change of the detected external capacitance, and the amplitude modulation corresponding to the change of the tuning point. And a ceramic resonator as a tuning circuit that is independent of the resonator of the oscillation circuit that outputs a wave. The ceramic resonator as the tuning circuit has an electric resistance value changed by a control input. The resistance variable element for changing Q is connected in parallel.

[Action]

In the present invention, the resistance variable element is initially set to have the highest impedance, at which time the ceramic resonator has the highest Q.
Has become. When a control input is applied to the resistance variable element in this state, for example, as the control input increases, the impedance of the resistance variable element decreases, and with this,
Q dump of the ceramic resonator as a tuning circuit occurs,
The sensitivity is also low, and the output from the ceramic resonator is low.

On the other hand, when the control input is reduced, the impedance of the variable resistance element increases, the amount of Q dump of the ceramic resonator decreases, the sensitivity decreases less, and the output of the ceramic resonator decreases less. In this way, the Q dump amount of the ceramic resonator changes depending on the size of the control input applied to the variable resistance element, and the size of the output signal of the ceramic resonator also changes.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
The drawing shows a first exemplary embodiment of the invention. The circuit of this embodiment comprises a ceramic type electrostatic sensor circuit 9 and a variable impedance circuit 13. The ceramic type electrostatic sensor circuit 9 includes an oscillation circuit 1 including a ceramic resonator and a ceramic resonator of the oscillation circuit 1. Is a separate and independent tuning circuit for the ceramic resonator 12, and a detecting section 3 for detecting a change in electrostatic capacitance and applying this to the output terminal of the ceramic resonator 12.
A high impedance circuit 8 including a coupling capacitor 6 and an inductance element, a detection circuit 4 including a diode 10, and an amplifier circuit 5 including an operational amplifier 21.

The variable impedance circuit 13 includes the ceramic resonator 12
This variable impedance circuit 13 is connected in parallel with the resistors 14 to 16 and 19 and a field effect transistor (FET) 1 as a variable resistance element characteristic of this embodiment.
It consists of 7 and a capacitor 18. The FET 17 is composed of a high frequency element, the source of which is connected to the output terminal of the ceramic resonator 12 and the drain of which is connected to the ground via the bias resistor 19, so that the FET 17 is connected to the ceramic resonator 12
And are connected in parallel. The source of the FET 17 is connected to the drive power source of the FET 17 via the resistor 14. The base of the FET is connected to the control input terminal 11 through the resistor 16 and grounded through the capacitor 18. The resistor 15 is provided between the source and the base of the FET 17. The FET 17 operates as a class A amplifier.

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

As shown in FIG. 5, while the oscillation circuit 1 outputs a fixed ultrahigh frequency oscillation frequency signal of 1 GHz, for example,
The resonance frequency of the ceramic resonator 12 as a tuning circuit is at the operation reference point f ₀ at a fixed position that is slightly deviated from the fixed oscillation frequency f ₁ by a set amount, but the detection unit 3 changes the minute capacitance. When is detected, as shown in FIG. 5, the resonance frequency of the ceramic resonator 12 is deviated, and the fixed oscillation frequency f ₁
Amplitude modulation wave (AM (Amplitude Modu
(modulation wave) is generated, and this AM modulation 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 the detection band of capacitance change, and outputs this as a detection signal. The detection signal is amplified by the amplifier circuit 5 and added to a desired signal processing circuit.

When a DC control input is applied from the control input terminal 11 when detecting this minute capacitance, the magnitude of the voltage level output from the ceramic resonator 12 changes according to the magnitude of the control input. That is, as the control input increases, FE
The resistance between the source and drain of T17 decreases, and the Q of the ceramic resonator 12 dumps (Q
Is smaller). This Q dump amount increases as the control input increases. When Q dumps, the detection sensitivity also decreases, and the output level of the ceramic resonator 12 also decreases as the Q dump amount increases.

On the other hand, if the magnitude of the control input signal is reduced, FE
The resistance between the source and drain of T17 increases, and the dump amount of Q of the ceramic resonator 12 decreases. Then, the decrease in detection sensitivity will be small, and the ceramic resonator 12
The output level drop from is also small. in this way,
The output of the ceramic resonator 12 can be variably adjusted by adjusting the magnitude of the control input signal.

Therefore, when it is desired to increase the Q of the ceramic resonator 12 and detect the detection of the minute electrostatic capacitance with ultrahigh sensitivity, it is achieved by setting the control input to 0, and the detection sensitivity is lowered. When it is desired to detect a change in capacitance, the purpose can be achieved by applying a control input signal to the base side of the FET 17. By variably adjusting the magnitude of the control input signal, the dump amount of Q changes, and the level of the output signal of the ceramic resonator 12 can be variably adjusted. Of course FET1
Even if the Q value of the ceramic resonator 12 is changed by changing the resistance value of 7, the variable resistance value does not affect the capacitance of the ceramic resonator 12, so the resonance frequency of the ceramic resonator 12 relative to the fixed oscillation frequency f ₁ The operation reference point f ₀ does not deviate from the fixed position.

Further, in this embodiment, since the FET 17 is used as the variable resistance element, this FET 17 is used as the ceramic resonator 12
It is possible to dispose the ceramic type electrostatic sensor circuit 9 in the vicinity of the above, and it is possible to maintain excellent super high frequency characteristics of the ceramic electrostatic sensor circuit 9.

FIG. 2 shows a second embodiment of the present invention. This second embodiment differs from the first embodiment in that the FET1
The source of No. 7 and the output terminal of the ceramic resonator 12 are connected via the coupling capacitor 20, and the other structure is almost the same as that of the first embodiment.

The present invention is not limited to the above embodiments,
Various embodiments may be adopted. For example, in each of the above embodiments, the resistance variable element is configured by using the FET 17, but this resistance variable element is a circuit element other than the FET 17 as long as it is a high impedance element whose electric resistance value changes according to the size of the control input. Can be configured using.

The output signal of the ceramic electrostatic sensor circuit 9 may be fed back to the control input terminal 11 or a control signal may be added from another external circuit. In this way, the ceramic electrostatic sensor circuit 9
If a feedback loop is formed by the variable impedance circuit 13 and the variable impedance circuit 13, for example, when the tuning point of the ceramic resonator 12 is largely deviated due to environmental change or disturbance, the signal fluctuation due to the environmental change is used as the control input signal by the FET 17
Will be added to. Therefore, the Q of the ceramic resonator 12 can be dumped when the environment changes to reduce the sensitivity, and the influence of these environmental changes can be mitigated, which stabilizes the detection operation in the ceramic electrostatic sensor circuit 9. Can be realized.

It is also possible to provide a sensor separately from the ceramic electrostatic sensor circuit 9 and use the signal from this sensor as a control input signal. By doing so, a composite signal processing circuit is configured, and various highly functional circuit development becomes possible. For example, if a sensor for measuring ambient noise is provided 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 excludes ambient noise and selectively takes in sound pressure in the distance.

〔The invention's effect〕

According to the present invention, the Q dump amount of the ceramic resonator as a tuning circuit is varied by the control input of the variable resistance element, and the output magnitude of the ceramic resonator is variably adjusted. Capacitance detection ranging from ultra-sensitive detection to less sensitive detection,
It is possible to detect a minute electrostatic capacitance with a desired and appropriate sensitivity. Moreover, since the amount of dump of Q of the ceramic resonator as the tuning circuit is varied by varying the electric resistance value of the variable resistance element, the variable resistance does not affect the capacitance of the ceramic resonator, and therefore the variation with respect to the fixed oscillation frequency is The operating reference point of the resonance frequency of the ceramic resonator does not deviate from the fixed position due to the variable adjustment of Q,
As a result, the circuit operation for detecting the small electrostatic capacitance can always be stably performed regardless of the change in the Q dump amount.

Also, the control input signal of the variable resistance element can be used by feeding back the output signal of the ceramic electrostatic sensor, or by using separate and independent sensor signals. Stabilization of circuit operation in the electrostatic sensor can be achieved.

Further, since the control input applied to the variable resistance element is generally a DC or low-frequency signal, no special consideration is required in circuit design and wiring, and handling is very easy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a variable output circuit of a ceramic type electrostatic sensor according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. FIG. 4 is an explanatory view of a Q dump of a 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 minute diagram of the electrostatic sensor of FIG. It is explanatory drawing which shows the detection operation of electrostatic capacitance. 1 ... Oscillation circuit, 2 ... Tuning circuit, 3 ... Detector, 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 to 16 ......
Resistor, 17 …… Field effect transistor (FET), 18 ……
Capacitor, 20 ... Coupling capacitor, 21 ... Operational amplifier.

Claims (1)

[Claims] 1. An oscillation circuit which has a built-in resonator and outputs an oscillation frequency signal of a fixed frequency, and an operation reference point of the resonance frequency with respect to the fixed oscillation frequency of the oscillation circuit is set at a fixed position deviated by a set amount. A resonator of the oscillation circuit, which changes a tuning point with the fixed oscillation frequency by biasing the resonance frequency corresponding to a change in the detected external capacitance, and outputs an amplitude modulation wave corresponding to the change of the tuning point; Has a ceramic resonator as a tuning circuit which is independent of each other, and a resistance variable element that changes an electric resistance value by a control input to change the Q of the ceramic resonator is connected in parallel to the ceramic resonator as the tuning circuit. Variable output circuit of connected ceramic type electrostatic sensor.