JPS61172425A - Mechanical filter for extracting timing - Google Patents

Abstract

PURPOSE:To suppress the spurious mode by forming a residual polarization to both sides of the center of a piezoelectric ceramics oppositely and bonding a constant elasticity metallic plate having nearly same width as that of the piezoelectric ceramics and shorter than the length of the ceramics to the electrode face. CONSTITUTION:Composite longitudinal vibrators comprising two lateral effect piezoelectric ceramics 1, 1' are connected by two bending vibration couplers 6, 7 so as to form the residual polarization where both sides are made in opposite direction to the center of the piezoelectric ceramics 1, 1'. Then the constant elasticity metallic plates 2, 3, 2', 3' having nearly the same width as that of the piezoelectric ceramics and the length of 0.80-0.84 time of that of the piezoelectric ceramics are bonded to both the electrode faces of the ceramics 1, 1' so that the lengthwise centers are made coincident. Thus, the spurious characteristic is improved, the operation is made stable and the space is decreased.

Description

[Detailed Description of the Invention] [Summary] A composite vertical vibrator made of two piezoelectric ceramics that utilizes a transverse effect is coupled by two bending vibration couplers. The residual polarization is formed in opposite directions, and a constant elastic metal plate with a length that is almost the same as the width of the piezoelectric ceramic and shorter than the length of the piezoelectric ceramic is bonded to the electrode surface of the piezoelectric ceramic to eliminate unnecessary modes. It is something that has been suppressed.

[Industrial application field]

The present invention relates to a mechanical filter for timing extraction, which operates stably and is miniaturized, for extracting a timing signal from a received digital signal in a digital transmission system.

[Conventional technology]

In a digital transmission system, in order to identify and reproduce a received digital signal, it is necessary to reproduce a timing signal synchronized with the digital signal. For this purpose, a filter whose center frequency is the timing signal frequency is used, and conventionally, an LC filter consisting of a capacitor C and an inductance L is often used. Recently, mechanical filters that can be made smaller have also been proposed.

[Problem that the invention seeks to solve]

In low-speed digital transmission systems, for example, 20
Filters in the 0-320KHz band are required, and LC
Since the filter is composed of a capacitor or a coil, there is a limit to its miniaturization, and it also has the disadvantage of requiring adjustment of the resonant frequency. On the other hand, mechanical filters have the advantage that they can be miniaturized and do not require adjustment. ) could not satisfy the characteristics required for timing extraction. In other words, timing extraction in the aforementioned frequency band requires (11 wideband characteristics (fractional bandwidth 1% or more), (2) good spurious characteristics (effective attenuation of 30 dB or more up to 1.5 MHz), There were strict requirements such as the ability to obtain a large amount of raw materials, and it was difficult to satisfy these requirements.

An object of the present invention is to provide a mechanical filter that can meet the above requirements.

[Means for solving problems]

The mechanical filter for timing extraction of the present invention has a first
Referring to the figure and FIG.
, 1", so that residual polarization is formed on both sides of the piezoelectric ceramic in opposite directions to the center of the piezoelectric ceramic. 0.80 to 0.84 times the length (7
) lengths of constant elastic metal plates 2.3, 2°, and 3° are joined so that their longitudinal centers coincide.

[Effect]

This method utilizes the second resonance mode by forming the residual polarization of piezoelectric ceramics in opposite directions on both sides.
By selecting the length of the piezoelectric ceramic 1.1° and the length of the constant elastic metal plate bonded to the picture electrode surface as described above, the i-mode can be suppressed.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view of an embodiment of the present invention, and FIG. 2 is a side view. The piezoelectric ceramic 1.1° is made of PZT or the like, and both sides are polarized in opposite directions with respect to the center. ing. Arrow 4.5 indicates the polarization direction. Further, constant elastic metal plates 2.3.2' and 3' are bonded to the 1.1° piezoelectric ceramic picture electrode surface by soldering or the like, thereby constructing a composite longitudinal vibrator. Furthermore, the two composite longitudinal vibrators are mechanically coupled by two flexural vibration couplers 6.7. Further, reference numeral 8 indicates a support line that supports one side of the constant elastic metal plate 2, 3.2', or 3° to the substrate or the like at a position that becomes a node of the second resonance mode.

Also, the length of piezoelectric ceramics 1,1@ is 2i1+2z2
, the thickness is 2t2, the width is b, and the constant elastic metal plate is 2.3
．． 2', 3'' length is 2E8, thickness is t, width is piezoelectric ceramic l, b same as 11, piezoelectric ceramic 1.1° interval connected by connector 6.7 is Jc, In particular, piezoelectric ceramics 1.1" length 2g, +212 are provided with constant elastic metal plates 2.3.2', 3' having a length 2N, 0.80 to 0.84 times that length. It is.

When an electric signal of a predetermined frequency is applied between the constant elastic metal plates 2 and 3, the piezoelectric ceramic vibrates in the second resonance mode because the polarization directions on both sides of the center part of the piezoelectric ceramic are opposite, as described above. FIG. 3 shows an equivalent circuit in the vicinity of the resonance point of a composite longitudinal resonator, in which there are two equivalent series inductances, two equivalent series capacitances, C1, equivalent resistance R, and equivalent parallel capacitance C.

The capacitance ratio γ of the vibrator is γ=G o / C
Defined by The magnitude of this capacitance ratio γ is a measure of the magnitude (bandwidth) of the excited response. That is, the smaller the capacitance ratio γ, the greater the excitation, and conversely, the larger the capacitance ratio T, the more the response is suppressed.

FIG. 4 shows the calculation results of the capacitance ratio γ and the second, fourth, and sixth resonance modes, where the horizontal and vertical axes are the length of the constant elastic metal plate, 21. and the capacitance ratio γ of the composite longitudinal oscillator, and the total length of the composite longitudinal oscillator is 211. +212 and the capacitance ratio TO of the piezoelectric ceramic alone. Also, curve a is the second resonance mode, curve A is the fourth resonance mode, and curve C is the sixth resonance mode.
This shows the next resonant mode.

As can be seen from the figure, in the second resonance mode, even if the relationship between the length of the constant-elastic metal plate and the piezoelectric ceramic is changed, the capacitance ratio does not change much, but in the fourth resonance mode and the sixth resonance mode, the capacitance ratio does not change much. mode, the capacitance ratio will change significantly. For example, the length of a constant elastic metal plate is 21. The capacitance ratio of the fourth resonance mode increases as the length of
The capacitance ratio of the next resonant mode decreases, J+/<It++j!
z) Both become the same near -0,82. Including this point, the length of the constant elastic metal plate 2, 3.2", 3' is 0.80 to 0.84 with respect to the length of the piezoelectric ceramic of 1.1°.
By doubling this, the capacitance ratio of the fourth and sixth resonance modes becomes nearly 100 times the capacitance ratio of the second resonance mode, so within this range, the fourth resonance mode The resonance mode and the sixth resonance mode can be sufficiently suppressed. Also 11/ (J 1 + j 2)
In a range other than -0.80 to 0.84, either the fourth-order resonance mode capacitance ratio or the sixth-order resonance mode capacitance ratio becomes small, resulting in insufficient spurious suppression.

FIG. 5 is a plan view of another embodiment of the present invention, in which the central portion of the piezoelectric ceramic has a length of 2I1. An unpolarized portion 9 is formed, and remanent polarizations of piezoelectric ceramics are formed on both sides of the unpolarized portion 9 in opposite directions, and the length of the unpolarized portion 9 is 21. , the length of the constant elastic metal plates 2 and 3 is 2It, and the length of the piezoelectric ceramic 1 is 2(
J++j! z), 1m/(Il+ +1
z) = 0.13 to 0.15.

FIG. 6 shows the calculation results of the capacitance ratio T and the second, fourth, and sixth resonance modes of the composite longitudinal vibrator of the example shown in FIG. 5, and curves a and b .

The C1 vertical axis and horizontal axis are the same as in FIG. 4.

As can be seen from the figure, Je / (J r +Il
2) When set to =0.13, the capacitance ratio between the fourth-order resonance mode and the sixth-order resonance mode increases, and it can be seen that there is a size ratio 1 + / (J + "12) that almost matches. That is, ,j
! 17 (r 1 + Jlz) = 0.80 to 0.84, the capacitance ratio of the 4th resonance mode and the 6th resonance mode is 2nd
Since it reaches nearly 10,000 times the capacitance ratio of the next-order resonance mode, both the fourth-order resonance mode and the sixth-order resonance mode can be further sufficiently suppressed.

FIG. 7 is a measurement curve diagram of the attenuation characteristics, and is for the composite longitudinal vibrator of the example shown in FIG. 1 with the dimensions shown in Table 1, and the dimensions of each part are shown in FIG. It corresponds to the code shown in 2, and the unit is mm.

In Table 1, Figure 7, the horizontal axis shows the frequency and the vertical axis shows the response magnitude (attenuation amount), and 1O111, 12 in the curve is
This shows the responses of the second, fourth, and sixth resonance modes, respectively, and it can be seen that the fourth resonance mode and the sixth resonance mode are sufficiently suppressed.

Further, Table 2 shows equivalent constants in the second resonance mode for two experimentally manufactured mechanical filters A and B.

At the resonant frequency of 320KHz in Table 2, the capacitance ratio T is 48
~50, making it possible to realize a vibrator with a low capacitance ratio.

In addition, as shown in Fig. 2, the coupler 6.7 that connects the two composite longitudinal oscillators connects the node of the 4th resonance mode and the node of the 6th resonance mode of the composite longitudinal oscillator. It is located approximately in the middle of the The coupler 6.7 can suppress a desired resonance mode by coupling it to the node of the desired resonance mode, but it can suppress both the 4th and 6th resonance modes. In order to suppress this, as mentioned above, it is coupled to a position approximately in the middle of the nodes of those resonance modes. Also, the distance 2Xc between the connectors 6.7 is approximately 3.4 in the embodiment with the dimensions described above.
mm (Xc / C1+ +12) =0.2433
becomes.

FIG. 8 is a frequency characteristic curve diagram of the mechanical filter having the dimensions shown in Table 1, and is for the case where Xc=1.7 mm and the resonant frequency fo=322.1 KHz. Further, 4th and 6th indicate the responses of the fourth-order resonance mode and the sixth-order resonance mode. As can be seen from FIG. 8, the fourth and sixth resonance modes are sufficiently suppressed, and an attenuation of 30 dB or more can be obtained up to around 1.5 MHz.

FIG. 9 is a frequency characteristic curve diagram in the vicinity of the passband of the mechanical filter of the above-mentioned embodiment, and a broadband characteristic with a fractional bandwidth of 1% or more is obtained.

Further, FIG. 10 is a phase characteristic curve diagram near the passband of the mechanical filter of the above-mentioned embodiment, and the center frequency fo
It can be seen that the phase linearity in .

〔Effect of the invention〕

As explained above, the present invention connects two composite expansion/contraction oscillators with two flexural vibration couplers 6.7 to form a composite longitudinal oscillator using piezoelectric ceramics 1. 1"
forming remanent polarizations in opposite directions on both sides of the central part, or forming an unpolarized part 9 in the central part and forming remanent polarizations in opposite directions on both sides thereof,
Constant elastic metal plates 2.3.2" and 3", each having a length 0.80 to 0.84 times the length of this piezoelectric ceramic, were aligned with the center of 1.1 g of piezoelectric ceramic and joined by soldering, etc. As in the above embodiment, a 320 KHz mechanical filter can be realized with a total length of about 14 mm, and the spurious characteristics can be improved. Therefore, the present invention can be applied to timing extraction in a PCM transmission system, etc. to stabilize operation and reduce space.

[Brief explanation of drawings]

Figures 1 and 2 are a plan view and a side view of an embodiment of the present invention, Figure 3 is an equivalent circuit near the resonance point, and Figure 4 is the second, fourth, and sixth order resonances. FIG. 5 is a plan view of another embodiment of the present invention; FIG.
The figure is a curve diagram of the relationship between the second, fourth, and sixth resonance modes, dimensions, and capacitance ratio for the embodiment shown in Figure 5, and Figure 7 is a frequency characteristic curve diagram of the mechanical filter according to the embodiment of the present invention. , FIG. 8 shows one of the mechanical filters according to the embodiment of the present invention.
．． FIG. 9 is a frequency characteristic curve diagram near the passband of the mechanical filter according to the embodiment of the present invention; FIG. 10 is a phase characteristic curve diagram of the mechanical filter according to the embodiment of the present invention. . 1.1' is piezoelectric ceramics, 2.3.2'. 3° is a constant elastic metal plate, 4.5 is an arrow indicating the direction of residual polarization, 6.7 is a bending vibration coupler, 8 is a support line, and 9 is an unpolarized portion.

Claims (3)

[Claims] (1) In a mechanical filter in which two composite longitudinal oscillators are coupled by two flexural vibration couplers, the residual polarization of the transverse effect piezoelectric ceramic constituting the composite longitudinal oscillator is transferred to the piezoelectric ceramic. are formed in opposite directions with respect to the center of the piezoelectric ceramic, and on the picture electrode surface of the piezoelectric ceramic, the width is approximately the same as the width of the piezoelectric ceramic, and the length is 0.80 to 0.84. A mechanical filter for timing extraction, characterized in that constant elastic metal plates having twice the length are joined so that their centers in the length direction coincide with each other. (2) In a mechanical filter in which two composite longitudinal oscillators are coupled by two flexural vibration couplers, an unpolarized portion is located in the center of the piezoelectric ceramic using transverse effect that constitutes the composite longitudinal oscillator. to form residual polarization on both sides of the unpolarized portion in opposite directions to each other, and to form a remanent polarization on both sides of the unpolarized portion in opposite directions. A mechanical filter for timing extraction, characterized in that constant elastic metal plates each having a length of 0.80 to 0.84 times are joined so that their longitudinal centers coincide with each other. (3) The two flexural vibration couplers that couple the two composite longitudinal oscillators are arranged at a point approximately equal to the node of the fourth resonance mode and the node of the sixth resonance mode of the composite longitudinal oscillator. The mechanical filter for timing extraction according to claim 1 or 2, characterized in that the filter is joined in the middle.