JPH0334714A - Thickness-shear crystal resonator - Google Patents

Abstract

PURPOSE:To facilitate the oscillation of overtone by setting the length a, b of the crystal chip and the electrode in the X axis direction within a specific range so that crystal impedances R1, R3 by a fundamental wave and its overtone have a relation of R1>R3 thereby suppressing the fundamental wave. CONSTITUTION:The 3rd order overtone oscillation is caused by setting the length a, b of the crystal chip and the electrode in the X axis direction accord ing to the relation of R1/R3=51.85+18.64*LN{(b/a)*t} (where LN is natural logarithm and (t) is the thickness of the crystal chip) within a range of + or -10% so as to establish the relation of R1>R3 in the crystal impedances R1, R3 by a fundamental wave and its overtone. For example, the diameter (a) of the crystal chip 1 is selected to be 5.0mm to vary the diameter (b) of the exciting electrode 2. Then the diameter (b) of the exciting electrode 2 is selected to be 2.8mm or below, then the oscillation in the overtone is facilitated. Since the overtone wave is 1/1.5 of the fundamental wave or below with the CI value 20ohms or below with a diameter (b) of nearly 3mm or below especially, the practical overtone oscillation is attained.

Description

Detailed Description of the Invention (Industrial Field of Application) The field of the present invention is a thickness-shear crystal resonator. Concerning the axial dimension ratio.

(Background of the Invention) Thickness-shear crystal resonators have excellent frequency-temperature characteristics and are therefore frequently used as resonators in various electronic devices. In recent years, for example, overtone vibration is frequently used due to the increase in communication frequencies.

(Prior Art) Figure 4 and the following are diagrams of a crystal oscillator to explain a conventional example of this type. - Fish the z-axis plane from the y-axis to the 2nd axis 3
It consists of an AT-cut crystal piece l rotated 5915'. Note that the crystal axis newly generated after one rotation is defined as the y' z axis.

The crystal piece 1 has a rectangular shape, for example, and has excitation molds 412 facing each other on both principal surfaces to excite thickness shear vibration. The excitation electrode 2 is, for example, a crystal piece 1. Formed eccentrically from the center of gravity of
In addition, when the excitation electrode 2 is aligned with the center of gravity of the crystal blank l, for example, the center of each of the four pieces of the crystal blank is cut out. That is, in either case, a part of the outline of the crystal piece 1 is made close to the excitation current 412. In addition.

An extraction electrode 3 is extended from the excitation electrode 2 to a corner.

In such a device, the crystal impedance (hereinafter referred to as CI) value at overtone vibration is made smaller (for example, l/'2 or less) than the fundamental wave to facilitate overtone vibration.

(A long-awaited point of the prior art) However, in the L crystal resonator, when the excitation electrode 2 is formed eccentrically from the center of gravity of the crystal blank J, the asymmetry causes, for example, the secondary vibration of the inharmonic mode to be emphasized. Damages the vibration characteristics of the overtone. Particularly when used as filter element I, there was a problem of lowering the guaranteed attenuation.

Further, when the excitation pole 2 is located at the center of gravity of the crystal blank 1, there is a problem that the shape of the crystal blank 1 becomes complicated, which complicates its manufacture.

(5! Ming's L4 style) An object of the present invention is to provide a deep-cut crystal resonator that suppresses the fundamental wave to facilitate overtone vibration, and also has good vibration characteristics and productivity. 4゜(Solution Means) The present invention provides the crystal-1 beam dance R+-R,3 due to the fundamental wave and the overtone in the X-axis direction of the crystal piece and the electrode so that RI>RI. Length a.

b is expressed by the following formula (% formula %)) (ate, 1.N is the natural logarithm 11. is the thickness of the crystal piece):! The overtone vibration is determined by setting rs8 within the range of jO%.This 2- is a solution. From now on, (d') is a diagram of a crystal oscillator to explain an embodiment of the present invention. FIG. 5(h) is a sectional view, and the same parts 92 as in the conventional example diagram 11iI are given the same numbers, and the explanation 1iJ is omitted.

The crystal resonator is formed by making the AT-cut crystal piece 1 described above into a circular shape, for example, and making the centers of gravity substantially coincide with each other to form an excitation tf@2 that excites thickness shear vibration. However, crystal piece j
- and Kushinichi M 2. Let the diameters be a and b, and the thickness be t.3 Figure 2 shows the fundamental wave and overtone when the diameter of the excitation electrode 2 is changed with the III shuttle a of the crystal blank 1- being 5.0 mm. It is a figure showing CI value. However, the curve (a) in the figure is the fundamental wave, and ui (b) is the overtone. The thickness at par is approximately 0°11 mm, the fundamental wave is 15.15 MHz, and the overtone is 45-45 MHz.

As is clear from this figure, the diameter of the excitation electrode 2 is 6.
．． ．． When the diameter is 8 mm, the CI value of the over-batone is 20.
As Ω, it is equivalent to the fundamental wave, and when it is less than that, it becomes smaller than the fundamental wave. Therefore, in this example, the diameter of the excitation electrode 2 is set to 2. If it is set below 8mmJj%, it will be easier to vibrate with overtones.In particular, if it is about 3mm or less, it will be less than 20Ω and less than 1/1.5 of the fundamental wave, so it will be possible to vibrate with overtones that match reality. 'ru.

Fig. 3 rIIl line (d)' is the crystal piece (taking into account the thickness) (
and the excitation fundamental wave J) t i'jl, the ratio b /' the fundamental wave and the overtone 4,'n 1' m
H・-"Rz is not shown, T is present.

In addition, the horizontal axis indicates -.
The vertical axis is (, ``old/k'' - CF, the 0 hit in C'r4 is actually 14.

This is the power of turning. , (
, ': I ratio ti/ua is thickness t (:, ta dimension 1<
to r I:3.・'a constant relation number 2 6.
, Part 2, we obtained the following formula, which was investigated by the present inventor.
However, LN is a natural Z4 number.

RI/R3=51.83', 18. ．． 64 palm f,
N((b/a)寥t) ・= (1) I, ga-)z
), 2. Based on the formula (L), the fundamental wave can be suppressed by changing b/a to i'A so that Ri/R: + is greater than l - 1 - /f, t, 7: Vibration at overtone Make it easier. Then, considering the specific value of R3, R
If I/R3 is set to 1.5 or more, it is possible to reproduce the vibrations of the overtones in accordance with reality. Since the symmetry is maintained by approximately matching the center of gravity of 7, for example, inharmonium; hetsukugi +-f, etc., are prevented from being stressed, and their construction is facilitated.

(Other matters) In the above example, the dimension ratio b/a is (,1)
Although it is assumed to be set by the formula, in practice it is set with an error of about 10% taken into account so that it falls within the curves (d) and (e) in FIG.

Further, the dimension ratio b/a has been explained as the diameter ratio of the crystal piece 1 and the electrode 2. However, since the main displacement direction of thickness shear vibration is the X-axis direction, basically the dimension ratio in the X-axis direction can be used.However, in this case, the electrode dimension in the 2' direction with respect to the crystal piece should be determined according to its CI value. be considered.

(Effects of the Invention) The present invention provides the crystal impedances R1 and R3 due to the fundamental wave and overtone so that Rl<R:i, the lengths a and b of the crystal piece and the electrode in the X-axis direction are as follows. (Formula %Formula %)) (However, L and N are natural logarithms, and t is the thickness of the crystal piece.) Since it is set within the range of ±10%, the fundamental wave is suppressed to facilitate vibration due to overtone, and A thickness-shear crystal resonator with good vibration characteristics and productivity can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram of crystal vibration: P (crystal piece) for explaining one embodiment of the present invention. FIG. 2 is a CI characteristic diagram for fundamental wave and overtone electrode dimensions of the same embodiment. FIG. 3 is a diagram showing the CI ratio of the fundamental wave and the old wave with respect to the size ratio of the crystal piece and the electrode in the same embodiment. Figure 4 shows the cutting direction of the crystal resonator, Figure 5 (,)
(b) It is a top view of a crystal resonator (crystal piece) explaining a conventional example. ′! J! J11!1 Figure 2 Figure 4 Figure 5

Claims (2)

[Claims] (1) In a thickness-shear crystal resonator consisting of a crystal piece with electrodes formed on both principal surfaces, the ratio R of the crystal impedances R_1 and R_3 due to the fundamental wave and the tertiary overtone
In order to make _1/R_3 greater than or equal to 1, the lengths a and b of the crystal piece and the electrode in the x-axis direction are determined by the following formula R_1/R_3=51.
83+18.64*LN{(b/a)*t} (However, L
A thickness-shear crystal oscillator characterized in that N is a natural logarithm and t is a thickness of a crystal piece within a range of ±10% to produce third-order overtone vibration. (2) Ratio R_1/R_3 of crystal impedances R_1 and R_3 due to the fundamental wave and the third-order overtone
1. A thickness-shear crystal resonator according to claim 1, wherein: 1.5 or more.