JPH0365682B2 - - Google Patents

Description

[Detailed description of the invention]

[Summary] A composite vertical vibrator made of two piezoelectric ceramics that utilizes the transverse effect is coupled with two bending vibration couplers, and the vibration vibration couplers are connected in opposite directions to each other with respect to the center of the piezoelectric ceramics. A residual polarization is formed, and a constant elastic metal plate having a length that is approximately 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 suppress unnecessary modes. [Industrial Application Field] The present invention is applicable to a digital transmission system.
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. [Prior Art] 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. [Problems to be solved by the invention] In low-speed digital transmission systems, for example, filters in the 200 to 320 KHz band are required, and LC filters are composed of capacitors and coils, so they need to be miniaturized. However, there are also limitations and the drawback is that the resonant frequency must be adjusted.
On the other hand, mechanical filters have the advantage that they can be miniaturized and do not require adjustment, but conventional mechanical filters (filters that do not require electrical matching circuits at the input and output ends and consist only of mechanical vibration systems) ) could not satisfy the characteristics required for timing extraction. In other words, timing extraction in the aforementioned frequency band requires (1) wideband characteristics (fractional bandwidth 1% or more), and (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-mentioned requirements. [Means for Solving the Problems] Referring to FIGS. 1 and 2, the mechanical filter for timing extraction of the present invention is a composite longitudinal vibration filter made of two piezoelectric ceramics 1 and 1' using transverse effect. The piezoelectric ceramics 1, 1' are connected by two bending vibration couplers 6, 7, and residual polarization is formed on both sides of the piezoelectric ceramics 1, 1' in opposite directions with respect to the central part of the piezoelectric ceramics 1, 1'. Constant elastic metal plates 2, 3, 2', and 3' having a width approximately the same as the width of the piezoelectric ceramic and a length 0.80 to 0.84 times the length of the piezoelectric ceramic are placed on both electrode surfaces of the electrode 1'. They are joined so that their longitudinal centers coincide. [Operation] The residual polarization of the piezoelectric ceramics is formed in opposite directions on both sides, and the second resonance mode is utilized. By selecting the length of the constant elastic metal plate as described above, unnecessary modes can be suppressed. [Examples] Examples 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, in which piezoelectric ceramics 1 and 1' are
It is made of PZT or the like, and both sides of the center are polarized in opposite directions. Arrows 4 and 5 indicate the polarization direction. Furthermore, constant elastic metal plates 2, 3,
2' and 3' are joined by solder or the like to form a composite longitudinal vibrator. Further, the two composite longitudinal vibrators are mechanically coupled by two bending vibration couplers 6 and 7. 8 is a constant elastic metal plate 2, 3,
This shows a support line that supports either one of 2' and 3' to the substrate or the like at a position that becomes a node of the second-order resonance mode. Also, the length of piezoelectric ceramics 1 and 1' is 2l ₁ +
2l ₂ , thickness 2t _p and width b, and constant elastic metal plates 2, 3, 2', 3' length 2 ₁ , thickness t _n , width piezoelectric ceramics 1, 1' Same as b, connector 6,
The spacing between the piezoelectric ceramics 1 and 1' connected at 7 is l _c , and in particular, compared to the length 2l ₁ + 2l ₂ of the piezoelectric ceramics 1 and 1', the length 2l ₁ is 0.80 to 0.84 times that length.
Constant elastic metal plates 2, 3, 2', and 3' are provided. 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. Figure 3 shows an equivalent circuit near the resonance point of a composite longitudinal resonator, with equivalent series inductance L, equivalent series capacitance C, equivalent resistance R, and equivalent parallel capacitance C ₀
The capacitance ratio γ of the vibrator is defined as γ=C ₀ /C. 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 is, the greater the excitation is, and conversely, the larger the capacitance ratio γ is, the more the response is suppressed. Figure 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 lengths of the constant elastic metal plate 2l ₁ and This shows the capacitance ratio γ of the composite longitudinal oscillator,
Each figure is normalized by the total length of the composite longitudinal vibrator 2l ₁ +2l ₂ and the capacitance ratio γ ₀ of the piezoelectric ceramic alone. Also, curve a is the second resonance mode, curve b
indicates the fourth-order resonance mode, and curve c indicates the sixth-order resonance 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 the capacitance ratio changes greatly in the fourth-order resonance mode and the sixth-order resonance mode. For example, as the length 2l ₁ of the constant elastic metal plate increases, the capacitance ratio of the fourth resonance mode increases, but the capacitance ratio of the sixth resonance mode decreases, and becomes l ₁ / (l ₁ + l ₂ )=
Both become the same around 0.82. Including this point,
By making the length of the constant elastic metal plates 2, 3, 2', 3' 0.80 to 0.84 times the length of the piezoelectric ceramics 1, 1', the capacitance ratio of the second resonance mode is The capacitance ratio of the 4th and 6th resonance modes is
Since it is nearly 100 times as large, the fourth-order resonance mode and the sixth-order resonance mode can be sufficiently suppressed within this range. or
In a range other than l ₁ / (l ₁ + l ₂ ) = 0.80 to 0.84, the fourth
Either the capacitance ratio of the next resonance mode or the capacitance ratio of the sixth resonance mode becomes small, and spurious suppression becomes insufficient. FIG. 5 is a plan view of another embodiment of the present invention,
An unpolarized part 9 with a length of 2l _e is formed in the center of the piezoelectric ceramic, and residual polarization of the piezoelectric ceramic is formed in opposite directions on both sides of the unpolarized part 9, and the length of the unpolarized part 9 is
2l _e is expressed as l _e / by the relationship between the length 2l ₁ of the constant elastic metal plates 2 and 3 and the length 2 (l ₁ + l ₂ ) of the piezoelectric ceramic 1.
(l ₁ +l ₂ )=0.13 to 0.15. FIG. 6 shows the calculation results of the capacitance ratio γ 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 ，
c, the vertical axis, and the horizontal axis are the same as in FIG.
As can be seen from the figure, when l _e /(l ₁ + l ₂ ) = 0.13, the capacitance ratio between the fourth-order resonance mode and the sixth-order resonance mode increases, and the dimensional ratio l ₁ /
The existence of (l ₁ + l ₂ ) can be seen. That is, l ₁ /(l ₁ +l ₂ )=
0.80 to 0.84, the capacitance ratio of the 4th resonance mode and the 6th resonance mode is the same as that of the 2nd resonance mode.
Since it reaches nearly 10,000 times, both the fourth-order resonance mode and the sixth-order resonance mode can be suppressed even more sufficiently. Figure 7 is a measurement curve diagram of the attenuation characteristics, and the first
The compound longitudinal vibrator of the embodiment shown in the figure has the dimensions shown in Table 1, and the dimensions of each part correspond to the symbols shown in FIGS. 1 and 2, and the unit is mm.

[Table] In Figure 7, the horizontal axis shows the frequency and the vertical axis shows the magnitude of the response (attenuation amount).
11 and 12 indicate the responses of the second, fourth, and sixth resonance modes, respectively;
It can be seen that the second-order resonance mode and the sixth-order resonance mode are sufficiently suppressed. Table 2 shows equivalent constants in the second resonance mode for two experimentally manufactured mechanical filters A and B.

〔Effect of the invention〕

As explained above, the present invention connects two composite longitudinal oscillators with two bending vibration couplers 6, 7 to form a composite longitudinal oscillator using transverse effect piezoelectric ceramics 1, 1' remanent polarization is formed in opposite directions on both sides of the central part, or an unpolarized part 9 is formed in the central part, and remanent polarization is formed in opposite directions on both sides of the unpolarized part 9. Constant elastic metal plates 2, 3, 2', 3' with a length 0.80 to 0.84 times the length of the piezoelectric ceramics are joined by soldering or the like so as to align with the centers of the piezoelectric ceramics 1, 1'. and, as in the previous example, 320K
A Hz band mechanical filter can be realized with a total length of about 14 mm, and spurious characteristics can be improved. Therefore,
It can be applied to timing extraction in PCM transmission systems, 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 2nd, 4th, and 6th order resonances. 5 is a plan view of another embodiment of the present invention, and FIG. 6 is a diagram showing the relationship between modes, dimensions, and capacitance ratios. FIG. A curve diagram showing the relationship between modes, dimensions, and capacitance ratios. Figure 7 is a frequency characteristic curve diagram of the mechanical filter according to the embodiment of the present invention. Figure 8 is a frequency characteristic curve diagram of the mechanical filter according to the embodiment of the present invention up to around 1.5 MHz. Curve diagram, No. 9
10 is a frequency characteristic curve diagram near the passband of a mechanical filter according to an embodiment of the present invention, and FIG. 10 is a phase characteristic curve diagram of the mechanical filter according to an embodiment of the present invention. 1, 1' are piezoelectric ceramics, 2, 3, 2',
3' is a constant elastic metal plate, 4 and 5 are arrows indicating the direction of residual polarization, 6 and 7 are bending vibration couplers, 8 is a support wire, and 9 is an unpolarized portion.

Claims (1)

[Claims] 1. In a mechanical filter in which two composite longitudinal oscillators are coupled by two flexural vibration couplers, residual polarization of piezoelectric ceramics utilizing transverse effect constituting the composite longitudinal oscillators are formed on both sides of the piezoelectric ceramic in opposite directions relative to the center of the piezoelectric ceramic, and on both electrode surfaces 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 of the length of the piezoelectric ceramic. A mechanical filter for timing extraction, characterized in that constant elastic metal plates having twice the length are joined so that their longitudinal centers coincide with each other. 2. In a mechanical filter in which two composite longitudinal oscillators are coupled by two bending vibration couplers, an unpolarized portion is provided in the center of the piezoelectric ceramic utilizing transverse effect that constitutes the composite longitudinal oscillator. , forming remanent polarizations on both sides of the unpolarized portion in opposite directions to each other, and forming a polarization layer on both electrode surfaces of the piezoelectric ceramic with a width that is approximately the same as the width of the piezoelectric ceramic and a length of 0.80 to 0.80 the length of the piezoelectric ceramic. A mechanical filter for timing extraction, characterized in that constant elastic metal plates having 0.84 times the length are joined so that their centers in the length direction coincide with each other. 3. The two flexural vibration couplers that couple the two composite longitudinal oscillators are the fourth flexural vibration couplers of the composite longitudinal oscillators.
The mechanical filter for timing extraction according to claim 1 or 2, characterized in that the mechanical filter is joined approximately midway between the node of the next resonance mode and the node of the sixth resonance mode.