JPH03172012A - At-cut thickness-shear crystal oscillator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Part of the Invention! H) The present invention relates to an AT-cut thick edge crystal resonator that can easily perform overtone oscillation.

(Technical background of the invention and its problems) In general, there are various vibration modes of a crystal resonator, such as bending vibration, flexural vibration, and thickness vibration. The thickness-shear vibration mode is used for this.The resonance frequency of a crystal resonator excited in this thickness-shear vibration mode is inversely proportional to the thickness of the crystal piece.For example, the thickness of a crystal unit with a resonance frequency of 10 MHz is approximately 0.167 mm. Resonant frequency is 30 MHz
The thickness is approximately 0.056 mm. Therefore, as the resonant frequency increases, the thickness becomes significantly thinner and the strength of the crystal piece decreases.
Manufacturing is extremely difficult due to processing problems.

For this reason, when a crystal resonator with a high resonance frequency is required, an overtone mode is used. In the overtone mode, resonance occurs at a frequency that is an odd multiple of the resonant frequency of the fundamental wave, and generally the 3rd, 5th, and 7th
Modes such as the following are used, the order being determined by the constants of the oscillator circuit, for example of the tuning circuit on the output side.

In recent years, in order to downsize oscillation circuits and eliminate the need for adjustment, micro-sized oscillators, in which a crystal resonator and an integrated circuit are integrated to form a non-adjustment oscillation circuit, have been manufactured and used in large quantities. However, since an oscillation circuit with such a configuration does not have a tuning circuit, it is not possible to use the overtone mode, so the maximum frequency of the oscillation output is limited to, for example, 30 MHz due to the processing limitations of the crystal piece.
It will be limited to a certain extent.

(Object of the Invention) The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an AT-cut thickness-slip crystal resonator that can oscillate at an overtone frequency using an unadjusted oscillation circuit. This is the purpose.

(Summary of the Invention) The present invention provides a round plate-shaped AT-cut thickness-shear crystal resonator in which the resonant frequency is f (Mhz) and the diameter of the crystal piece is a.
, where φ is the diameter of the excitation electrode, 12.52≦r − a /φ≦85.17, and the main surface is not chamfered.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to a perspective view of a crystal piece shown in FIG.

In the figure, 1l is an AT-cut thick sliding crystal piece made by cutting a quartz crystal at a predetermined angle with respect to its crystal axis and forming it into a round plate shape. A circular excitation electrode l2 is formed at the center of the front and back surfaces of this crystal piece lI, respectively.

Note that extraction electrodes (not shown) are led out from the excitation electrode l2 in opposite directions to the peripheral edge of the crystal piece 11, and these lead-out ends are held by a holding member (not shown), and the excitation electrode and external circuit are connected via this holding member. I am trying to make an electrical connection with.

Here, the resonant frequency of the crystal piece l1 is f (Mtlz
), the diameter is a, and the diameter of the excitation electrode l2 is φ, so that the following formula holds true.
Determine the size of 2.

12.52≦fa/φ≦85. 17 --■ And in order to inhibit the fundamental wave vibration and thereby facilitate the relative ζ over 1 · -n vibration, the main surface of the crystal blank 1l is not chamfered. Furthermore, crystal piece 1
The reason why the size of the excitation electrode l2 with respect to the size of l is determined as shown in the formula (2) is as follows.

In other words, in an AT-cut thickness-shear crystal resonator, the resonant frequency is determined by the thickness of the crystal piece, and the relationship is as follows.
It is given by the following formula.

h=1.67・N/f...■ Here, h is the thickness of the crystal piece (mm), N is the order of the overtone, f is the frequency (MHz), and the resonance frequency f, the diameter of the crystal piece a (at- a5 no 5
A large number of crystal resonator samples with different diameters φ of excitation electrodes were manufactured for different types (types), and for these samples, the ratio of the thickness h to the diameter a of the crystal blank, that is, the side ratio a/
The ratio a/h/φ of the electrode diameter φ with respect to h, and the ratio Rl/R of the equivalent resistance at the fundamental frequency and the third overtone
3 was investigated, and the results shown in the graph of FIG. 2 were obtained.

That is, in order to suppress resonance at the fundamental frequency and cause resonance at the overtone, the equivalent resistance Rl at the fundamental frequency should be larger than the equivalent resistance R3 at the tertiary overtone frequency, that is, R1/R3>1. For this purpose, the value of side ratio/electrode diameter should be 17 or less.

Also, if the value of the side ratio/electrode diameter is too small, the relative condition of equivalent resistance can be maintained, but the absolute value of the equivalent resistance becomes too large, so the value of side ratio/electrode diameter is set to 2.
Must be 5 or more.

In addition, in order to more reliably maintain the above-mentioned relative equivalent resistance condition and obtain good resonance at the overtone frequency, it is sufficient to set Rl/R3>3, and for this purpose, the side ratio/
The value of the diameter of the electrode may be 13 or less and 2.5 or more.

Therefore, by setting the diameter φ of the excitation electrode to a dimension that satisfies the following formula (2), regardless of the resonance frequency f and the diameter a of the crystal piece, it is possible to The equivalent resistance R3 can be made small and a practical equivalent resistance value can be obtained, thereby suppressing the resonance of the fundamental wave and making it resonate at the frequency of the third overtone.

2.5≦side ratio/diameter of excitation electrode φ≦17...■and■
By substituting the third-order overtone equation (2) into the equation, the above-mentioned equation (2) can be obtained.

2.5≦f-a/1.67・3/φ≦17, that is, 1
2.52≦fa/φ≦85.17 A crystal resonator manufactured satisfying these conditions has an equivalent resistance R of the fundamental wave.
Since the equivalent resistance R3 of the third-order overtone can be made smaller than l, it can be used, for example, in a Kolbitz-type unadjusted oscillation circuit as shown in FIG. 3, and can be stably oscillated at the frequency of the third-order overtone.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to perform overtone oscillation using an unadjusted oscillation circuit, and it is possible to obtain a high frequency oscillation output with a small size and no adjustment. It is possible to provide an AT-cut thickness-slip crystal resonator.

[Brief explanation of the drawing]

Fig. 1 is a perspective view illustrating a crystal resonator according to an embodiment of the present invention, and Fig. 2 shows the difference between the fundamental wave and the third overtone, with the side ratio/electrode diameter value of the sample crystal resonator plotted on the horizontal axis. FIG. 3 is a graph showing the ratio of equivalent resistances on the vertical axis. FIG. 3 is a circuit diagram showing an example of an unadjusted Corvitz circuit that oscillates with a third-order overtone using the crystal resonator of the present invention. It・・・Crystal piece 12・・・Excitation electrode Tsuta 1 diagram Tsuta 3 diagram 12 11 v52 diagram

Claims (1)

[Claims] If the resonance frequency is f (MHz), the diameter of the crystal piece is a, and the diameter of the excitation electrode formed at the center of the crystal piece is φ, then 12.52≦f・a/φ≦85.17 A round plate-shaped AT-cut thickness-slide crystal resonator characterized in that the main surface is not chamfered.