JPH082013B2 - Piezoelectric oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a piezoelectric oscillator, and particularly suppresses generation of microphonic noise, further suppresses generation of microphonic noise, and influence of EMI (electromagnetic interference). The present invention relates to a crystal oscillator that prevents

(Background of the Invention) Among piezoelectric oscillators that use piezoelectric oscillators such as quartz, lithium niobate, and PZT, a quartz oscillator that is particularly excellent in frequency stability is used to obtain the fundamental frequency of satellite communication equipment, for example. Many are used.

However, with the recent increase in data communication, it has become stricter to improve the quality of important signals such as reference frequency, and to prevent the occurrence of microphonic noise in piezoelectric oscillators and prevent the effects of EMI. It was strongly requested.

Microphonic noise of a piezoelectric oscillator is generated according to the following principle. For example, in the crystal unit shown in FIG. 5A, when an external mechanical shock or vibration is transmitted to the airtight container 51 of the crystal unit via the circuit board 58, the crystal vibrating piece 53 is placed inside the airtight container 51. Since it is cantilevered by the cage 54,
It vibrates mechanically.

Generally, inside the crystal unit, for example, as shown in the equivalent circuit of another crystal unit in FIG. 6C, stray capacitances C1 and C2 are provided between the electrode of the crystal vibrating piece 64 and the airtight container 63. There is a corresponding stray capacitance.

Therefore, in the airtight container 51 shown in FIG.
When mechanically vibrates, the stray capacitance changes in synchronism with this mechanical vibration, giving the same effect to the oscillation circuit as changing the load capacitance of the oscillation circuit connected to the crystal unit. As a result, the oscillation frequency is FM-modulated to generate noise, which deteriorates the quality of the output frequency. The name is given because the demodulated sound of this noise is observed just like the sound generated when a microphone is hit.

Generally, for example, in a crystal oscillator of a portable wireless communication device, in order to have a structure that does not easily mechanically vibrate against external mechanical shock or vibration, or to avoid collision or approach with other parts, for example, A method of soldering and fixing the crystal unit shown in FIG. 3B to the ground pattern 59 of the circuit board 58 with a fixture 57 is adopted.

Moreover, in order to reduce power consumption, it is necessary to select the load capacitance of the crystal oscillator of the oscillation circuit as small as possible. For example, in the crystal oscillation circuit of FIG. 7, the capacitor C4,
The load capacitance determined by the phase rotation of the oscillation circuit impedance configured by C5 and C6, the CMOS-IC 71, the resistors R1 and R2, and the crystal oscillator 74 may be selected to a value of a dozen or more PF.

At this time, for example, when the stray capacitance between the electrode of the crystal oscillator 74 of FIG. 7 and the airtight container changes due to external mechanical shock or vibration, when the load capacitance is small, the rate of change is relative. It is easy to generate microphonic noise, and the level of EMI incident from the outside is relatively higher than the oscillation level, so it is easily affected by EMI.

(Prior Art) Conventionally, in order to prevent the crystal unit from being affected by external mechanical vibration or impact, for example, as shown in the example of the crystal unit in FIG. It has been considered that the method of grounding and fixing the container 51 to the ground pattern 59 of the circuit board 58 via the fixture 57 is effective.

However, considering the internal structure of the crystal unit, fixing and grounding the airtight container 51 cannot always be an effective means for stabilizing the oscillation frequency.

That is, for example, a linear retainer made of an elastic material such as a piano wire, which is not shown, can flexibly support the crystal vibrating piece and has little influence on oscillation. This mechanical resonance point is low because it has a weak elastic cantilever support, and the vibration damping effect is inferior to the mechanical shock and vibration applied in the direction perpendicular to the principal surface of the quartz crystal vibrating piece. The crystal unit with a system was easy to generate microphonic noise.

Therefore, for example, as shown in the example of the crystal resonator of FIG. 5 (a), a plate-shaped cage 54 made of a thin elastic material is used, and the crystal resonator piece is sandwiched shallowly by the peripheral edge portion of the crystal resonator piece 53. By fixing with a small amount of adhesive, the mechanical resonance point of this holding system shifts to a high frequency range, the vibration damping effect against mechanical shock and vibration applied in the direction perpendicular to the main surface is enhanced, and the crystal vibrating piece 53 In this way, it is possible to obtain an oscillation with less generation of microphonic noise without suppressing the oscillation.

To prevent the crystal vibrating piece 53 from contacting the airtight container 51,
The insulator 52 may be inserted into the airtight container 51.

However, when the frequency of external mechanical shock or vibration coincides with the mechanical resonance point of the holding system of the quartz crystal vibrating piece 53, resonance vibration occurs. Furthermore, if many small components are already mounted on the circuit board on which this crystal unit is mounted with high density, the mechanical resonance frequency of the circuit board as a whole tends to increase. Easy to match with.

Further, when the crystal unit is fixed to the circuit board, external mechanical shock and vibration are not attenuated but directly propagate to the crystal unit, and the crystal vibrating piece 53 is easily vibrated strongly.

Alternatively, due to a strong shock, the plate-shaped cage 54 could not absorb and relax the shock, and the crystal vibrating piece 53 could be easily broken.

In order to solve these problems, for example, in the crystal unit of FIG. 6 (a), an outer container 61 is provided in an airtight container 63, a cushioning material 62 is filled between the outer container 61, and an external lead wire 66 and a crystal. A buffer wire 65 is connected between the vibrator lead wires to provide a means for mechanically relaxing mechanical shock and vibration from the outside.

This technology is preferably used in crystal oscillators that use an outer container 61 as a thermostatic chamber, and the effect that the cushioning material 62 absorbs and attenuates high frequency components included in mechanical shock and vibration from the outside, and plate-shaped holding Due to the inconsistency of moving the mechanical resonance point of the device to the higher frequency range, it has the desired complementary effect.

Further, in FIG. 6 (c) which is an equivalent circuit of the crystal unit of FIG. 6 (a), the electric capacitance C3 generated between the outer container 61 and the airtight container 63 is connected in series with the stray capacitances C1 and C2. Therefore, it functions to electrically mitigate the change in the stray capacitance.

Due to these synergistic effects, generation of microphonic noise is effectively suppressed.

(Disadvantages of conventional technology) However, even with these technologies, a fundamental solution still cannot be achieved, and a solution that enables fundamental suppression of the generation of microphonic noise and prevention of the influence of EMI. Was strongly desired.

That is, when a plate-shaped cage is used, the mechanical resonance point of this holding system can be shifted to a high frequency range of a relatively low level, and the occurrence of microphonic noise can be reduced. Not resolved for vibrations with frequencies close to.

Further, this plate-shaped retainer gives strain to the crystal vibrating piece to change its frequency-temperature characteristic, suppresses oscillation, and easily raises the equivalent resistance value, thereby deteriorating the frequency / output characteristic of the crystal oscillator.

Further, the crystal resonator element was easily damaged by an impact because it was close to a rigid support.

In order to prevent the influence of EMI, it is necessary to use a paramagnetic material for the airtight container 51 in FIG. 5 (a) or the external device 61 in FIG. 6 (a). There was a difference between the material conditions required for stopping and the material conditions required for EMI prevention, and it was sometimes difficult to match them.

In addition to these problems, for example, the crystal resonator of FIG. 6 (a) tends to be large in shape, and is not suitable for the purpose of housing in a narrow space. Further, when the airtight container 63 vibrates in the cushioning material 62, the capacitance C3 changes, which may cause new microphonic noise.

Further, the absorption and attenuation of the vibration energy by the cushioning material 62 are closely related to the thickness thereof, and the size must be limited by downsizing the crystal oscillator, and the desired absorption and attenuation effect cannot be expected.

(Object of the Invention) A first object of the present invention is to provide a piezoelectric oscillator in which generation of microphonic noise is suppressed.

A second object of the present invention is to provide a piezoelectric oscillator that suppresses the occurrence of microphonic noise and prevents the influence of EMI.

(Means for Solving the Invention) According to the present invention, a piezoelectric vibrator, which is hermetically sealed in a piezoelectric vibrating piece held in an airtight container having a lead wire penetrating and electrically connected to the lead wire, is connected to an oscillation circuit. In the piezoelectric oscillator described above, the first solution is to provide at least a double electric multi-layer electrically insulated from each other in the airtight container of the piezoelectric vibrator and to generate an electric capacitance therebetween.

A second solution means of the present invention is that the electric multi-layer is an electrically insulated layer including at least one layer containing a paramagnetic material, and an electric capacity is generated therebetween.

(Operation of the invention) Letting C1 and C2 be the stray capacitances existing between the electrodes of the crystal resonator and the good electrical conductors installed in the airtight container, the crystal resonator is located almost at the center of the airtight container. , Even if it is assumed that C1 = C2 = C in the stationary state, generality is not lost,
There is no problem in actual application.

Therefore, the impedance of the crystal resonator element of the crystal unit
If the capacitance between Zx and the airtight container and a good electric conductor provided in the airtight container is C3, and the quartz crystal vibrating piece is mechanically vibrating, the stray capacitances C1 and C2 are respectively expressed as follows.

C1 = C (1 + a) C2 = C (1-a) where a represents the rate of change of the stray capacitance due to mechanical vibration.

When the connection terminal impedance Zo of the oscillator is connected between one terminal of the crystal unit and the ground, the input end impedance Zi viewed from the other terminal side of the crystal unit is approximately represented by the following equation.

Zi = (1-a) Zx / A + (sC3 + A) * {(1 + a) Zx + AZo} / A {(1 + a) sC3Zx + AsC3Zx + sC3 + A} where A = 2 + sCZx, a << 1, s = jω (angular frequency), where , To examine the effects of C3, consider a special case of C3.

(B) Case of C3 = 0 This corresponds to the case where the airtight container is not grounded, or the case where the electric capacity of the electric double layer is sufficiently small and can be ignored. At this time, Zi = 2Zx / (2 + sCZx) + Zo, that is, since Zi does not include the change rate a of the stray capacitances C1 and C2, no microphonic noise is generated.

(B) Case of C3 = ∽ This corresponds to the case where an airtight container made of only a metal airtight container is directly grounded, or the good electric conductor provided in the airtight container is directly grounded. At this time, Zi = (Zo + 2Zx + 2Zx) / A-2aZx / A (1 + 2Zx) That is, microphonic noise is remarkably generated including the change rate a of the stray capacitances C1 and C2.

The present invention was made by paying attention to the principle of (a), and an electric double layer composed of a good electric conductor and an electric insulator is formed in an airtight container, and an electric capacity is generated between them. In this case, in order to reduce the generated electric capacity as much as possible, for example, by forming an electric multi-layer having a configuration in which a large number of the electric double layers are laminated, and the electric capacities of the respective laminated layers are connected in series, The electric capacity can be reduced to almost one-third of the number of multilayers of the electric capacity generated in the single electric double layer.

By combining a paramagnetic material and a good electric conductor in the electric multi-layer, it is possible to use, for example, an electromagnetic shielding effect and prevent the influence of EMI incident from the outside.

(Embodiment) FIG. 1 (a) is a diagram of a crystal resonator in which an electric double layer is provided in a metal airtight container for explaining an embodiment of the present invention, and FIG. 1 (a) is a perspective view thereof. FIG. 1B is a sectional view thereof, and FIG. 1C is a perspective view of the inner layer of the electric double layer. The electric double layer is composed of a good electric conductor 13 which is in close contact with the inner wall of the airtight container 11 and is covered with an electric insulator 12 shown in FIG. The electric capacitance value of the electric double layer can be set small by changing the dielectric constant and the thickness of the electric insulator 12 and the effective area of the electric conductor 13. The good electric conductor 13 is arranged at a position substantially facing the electrode 15 of the crystal piece 14. Further, the crystal vibrating piece 14 is supported by a retainer 16 made of an elastic wire, and the configuration of the conventional retaining system is used as it is.

FIG. 2A is a diagram of a surface-mounting crystal oscillator showing another embodiment, FIG. 2A is a perspective view thereof, and FIG. 2B is a sectional view thereof. In this embodiment, the electric double layer is provided on the inner and outer wall surfaces of the airtight container 21 made of an electric insulator. This electric double layer is formed by bringing the film surfaces or plate surfaces 22 and 27 made of a good electrical conductor or paramagnetic material into close contact with the airtight container 21 by vapor deposition or adhesion, and generally the EMI of the airtight container 21 made of an electrical insulator. The problem that is easily affected by is solved at the same time as suppressing the generation of microphonic noise.

FIG. 3 is a diagram of a crystal resonator showing still another embodiment,
1 is a simplified version of the electric double layer of the embodiment of FIG. That is, the electrical insulator 32 and the good electrical conductor 33 are adhered on the inner wall surface of the airtight container 31 so as to face the electrodes of the crystal vibrating piece 34 to form an electrical double layer. The electric double layer may be formed by mechanically adhering to the wall surface of the tubular portion of the airtight container 31, for example, a tubular electrical insulator inscribed in the airtight container 31.
By bending and crimping the plate-shaped good electrical conductor 33 made of an elastic material, the 32 can be easily formed without using adhesion.

Further, a partially electrically good conductive film 33 is formed on one surface of the single plate-shaped electric insulator 32 by using a method such as painting or vapor deposition, and this is pressure-bonded or adhered in the airtight container 31 to form an electric double layer. You can also

FIG. 4 is a view of a button-type crystal unit which is a further embodiment of the present invention. An electric insulator 42 and a good electric conductor 43 are laminated and adhered on the inner wall surface of a cover 44 which is an airtight container to form a crystal. An electric double layer is formed so as to face the electrode 45 of the vibrating piece substantially. The electric double layer on the inner surface of the base 47, which is an airtight container, is also formed in the same manner. Here, similarly to the embodiment of FIG. 3, it is also possible to form an electric double layer by forming a good electric conductor film 43 or 49 on the electric insulator 42 or 48 and adhering it to the inner surface of the airtight container. it can.

Although the above embodiments have been described, in each case, since the electric multi-layer is provided in the airtight container, the microphonic noise is suppressed. Then, by making one layer of the electric double layer a paramagnetic material, the influence of EMI is prevented.

In these examples, a known structure, for example, a retainer structure using a piano wire or the like may be applied and an electric double layer may be added to the airtight container, so that it is not necessary to change the existing manufacturing process and conditions. . Therefore, it can be realized without increasing the manufacturing cost.

Furthermore, this crystal unit can be miniaturized without the need to fix it to the oscillator circuit board or to fill the outer container with a cushioning material, and does not require special consideration for grounding, etc. It is easy to handle and is advantageous for assembling and manufacturing a crystal oscillator.

That is, since this electric multi-layer is provided in close contact with the airtight container, its electric capacity can be stabilized without vibrating and changing due to mechanical shock or vibration. For example, as shown in FIG. There is no generation of new microphonic noise due to the change in the electric capacitance C3 due to the vibration of the airtight container 63, which was present in the conventional crystal oscillator.

(Other Matters) The present invention should not be limited to being applied to only a crystal oscillator. For example, in a piezoelectric vibrator made of a piezoelectric material such as lithium tantalate, lithium niobate, and ceramic piezoelectric material, the piezoelectric vibrator is held in an airtight container. The present invention can be widely applied to a piezoelectric oscillator using a piezoelectric vibrator having a structure in which it is hollowly supported by a container.

Also, in a small crystal oscillator etc. in which a crystal vibrating piece is mounted on an oscillator circuit board made of HIC (hybrid integrated circuit) etc. and it is hermetically sealed in an airtight container, this crystal vibrating piece is made hollow by a holder. For those that have a supporting structure,
The present invention can be applied to the airtight container.

Further, the electric multi-layer shown in the embodiments of the present invention is not limited to a double layer, but may be laminated in multiple layers.

In any of the examples, a good electrical conductor, for example,
It is possible to use a metal plate or the like in which a paramagnetic material is coated or vapor-deposited with an electrically conductive film.

(Effect of the Invention) As described in detail above, according to the present invention, since the electric multi-layer is provided in the airtight container for enclosing the piezoelectric vibrating piece and the electric capacitance is generated therebetween, the generation of the microphonic noise can be suppressed. . Then, by forming the electric multi-layer as a laminate of a good electric conductor and a paramagnetic material, the influence of EMI can be prevented.

[Brief description of drawings]

FIG. 1 is an embodiment of a crystal unit having a metal airtight container according to the present invention. FIG. 1A is a perspective view of the crystal unit, FIG. 1B is a side sectional view, and FIG. FIG. 6C is a structural perspective view of a portion constituting the electric double layer. FIG. 2 is a diagram showing another embodiment of the surface-mounting crystal unit according to the present invention. FIG. 2A is a perspective view of the crystal unit.
FIG. 2B is a side sectional view thereof. FIG. 3 is a side sectional view of another embodiment of the crystal unit having the metal airtight container according to the present invention. FIG. 4 is a side sectional view of another embodiment of the button type crystal unit according to the present invention. FIG. 5 is a view showing a conventional example of a crystal unit, FIG. 5 (a) is a side sectional view thereof, and FIG. 5 (b) is a side view of its mounting example. FIG. 6 is another conventional example of a crystal unit, which is shown in FIG.
Is a side sectional view of the crystal unit, FIG. 2B is an electrical schematic view thereof, and FIG. 1C is an equivalent circuit diagram thereof. FIG. 7 shows a circuit diagram of a crystal oscillator using a CMOS-IC. 11,21,31,41,47 …… Airtight container, 12,32,42 …… Electrical insulator, 13,22,27,43 …… Electrical conductor, 14,23,34 …… Crystal vibrating piece, 15, 24,45 …… Electrodes, 16,26,35,46 …… Cages, 71 …… CMOS-IC.

Claims (1)

[Claims] 1. A piezoelectric device in which a piezoelectric vibrator, which is held in an airtight container made of a metal having a lead wire penetrating therethrough and electrically connected to the lead wire, is hermetically sealed, is connected to an oscillation circuit. In the oscillator, the piezoelectric vibrator includes at least one layer which electrically insulates the airtight container and an electric conductor provided inside or on the surface of an electric insulator adhered to the inner surface thereof from each other and at least contains a paramagnetic substance. A piezoelectric oscillator, wherein the piezoelectric oscillator is formed by forming at least a double electric multi-layer and generating an electric capacitance therebetween.