JP3231055B2 - SC-cut crystal unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SC-cut quartz resonator, and more particularly to the prevention of jumps in frequency.

[0002]

2. Description of the Related Art In general, a piezoelectric crystal can excite piezoelectric vibration only at a specific cutting angle with respect to a crystal axis. For example, even in the case of a crystal resonator utilizing the piezoelectric characteristics of quartz, piezoelectric vibration can be excited only at a specific cutting angle with respect to the crystal axis. It exhibits unique vibration characteristics at the cutting angle. For example, an AT-cut quartz resonator most commonly used at a frequency of several MHz to several tens of MHz has a cubic curve-like temperature characteristic having an inflection point near 25 ° C. By the way, when the frequency stability is strictly required in a reference oscillator used for a measuring device, a wireless device, or the like, for example, a thermostatic oven is used. In this thermostatic oven, the crystal oscillator is housed in a thermostat heated to a constant temperature of about 80 ° C., thereby removing a change in frequency due to the temperature characteristics of the crystal oscillator and stabilizing the crystal oscillator. An SC-cut crystal resonator is known as a crystal resonator suitable for such an oscillator. This SC
The cut quartz crystal resonator 1 rotates, for example, a plane orthogonal to the Y axis of the quartz crystal about 33 ° about the X axis, and from this rotated position about 22 ° about the ZZ ′ axis. , For example, cut into strips. Thus, the SC-cut quartz resonator has better thermal shock characteristics than the AT-cut quartz resonator, exhibits a zero temperature coefficient at a relatively high temperature of about 80 ° C., and can obtain a high Q value. Such characteristics are extremely desirable characteristics for a highly stable crystal oscillator which is used by being housed in a thermostat heated to a constant temperature of about 80 ° C., for example. Therefore, for example, the 34th FCS held in May 1980
(FREQ.CONTROL SYMPOSIUM) Proceedings, pages 187 to 193, describe the fundamental mode SC-cut resonator (FUNDAMEN).
Various reports have been made as disclosed as TAL MODE SC-CUT RESONATORS).

[0003] By the way, such an SC-cut quartz-crystal vibrator is, for example, as shown in FIG. A sub-vibration occurs in the illustrated B) and the A mode (the illustrated A). Here, since the value of the crystal impedance (hereinafter abbreviated as CI) of the A mode vibration is larger than that of the C mode, it does not pose a particular problem. In contrast, the CI of the B mode is equal to or smaller than that of the C mode. For this reason, when an oscillator is actually manufactured, there is a problem that the oscillator often oscillates in a sub-mode B mode. Therefore, when an SC-cut crystal resonator is used, it is necessary to suppress the B-mode vibration and make its CI larger than that of the C-mode in order to surely excite the C-mode main vibration. For this purpose, the external shape of the crystal blank,
By making various improvements to the holding position, etc., B
The mode's sub-vibration is suppressed. However, even in this case, there is a problem that a so-called jump phenomenon occurs in which, for example, main vibration and sub-vibration are coupled due to a temperature change, and the frequency suddenly fluctuates greatly.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is an SC-cut crystal resonator that can reliably excite the C-mode main vibration and does not cause a frequency jump. The purpose is to provide.

[0005]

According to the present invention, a plane orthogonal to the Y axis of a crystal of quartz is rotated about 33 ° about the X axis,
In addition, in the SC-cut double-rotation crystal oscillator cut out from a plane rotated about 22 ° about the Z-axis from the rotated position, the thickness of the crystal blank is t, and only one of the front and back plate surfaces is subjected to convex processing. When the radius of curvature of the convex processing is R, 90.9 <R / t <727.3.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to a side view in which the thickness of a crystal blank shown in FIG. 1 is exaggerated. In the figure, reference numeral 11 denotes an SC-cut crystal blank. The crystal blank 11 has a plane orthogonal to the Y axis of the crystal of the crystal, about 3
It is a SC-cut crystal piece that is cut twice from a plane that is turned 3 °, for example, 33 ° 30 ′ to the left, and further rotated about 22 °, for example, 22 ° 30 ′ to the left about the ZZ ′ axis. Then, the resonance frequency f (K
Hz) is determined by the following equation, where t (mm) is the thickness of the crystal blank and n is the order of the overtone. f = 1797 · n / f According to this equation, for example, the thickness of the SC-cut crystal resonator having the resonance frequency of the third overtone and 5 MHz is about 1.1 mm. And the crystal piece 11 of this crystal oscillator
One of the front and back plate surfaces is flat, and the other plate surface is formed into a convex lens-like curved surface by convex processing to suppress sub-vibration.

Further, assuming that the thickness of the crystal blank 11 is t, the curvature radius R of the curved surface at the time of performing the convex working is set so as to satisfy the following equation. 90.9 <R / t <727.3 ... The reason why the ratio of the curvature radius R of the convex processing to the thickness t of the crystal blank 11 is set as in the equation is as follows. That is, the radii of curvature are 50, 75, 100, and 20 for the SC oscillator of 5 MHz and SC cut at the third overtone.
Convex processing of 0, 280, 400, 700, and 900 (mm) was performed, and the frequency at which spurious appeared was examined to prepare a spurious chart shown in FIG. In FIG. 2, the horizontal axis represents the radius of curvature (mm) of the convex processing, the vertical axis represents the normalized frequency normalized by the frequency of the main vibration, and the black dots represent the occurrence of spurious. As a result, the curvature radius of the convex working in which the main vibration is not coupled with the sub vibration is 100
８００800 (mm) (the area indicated by D in FIG. 2),
The ratio R between the radius of curvature R and the thickness t of the quartz piece that satisfies this condition.
/ T is given by the above equation. In addition, since the similar principle is generally established in such a crystal resonator, the resonance frequency is 8.129 MHz in the SC cut and the third overtone is 8.129 MHz.
A 10-MHz crystal oscillator was also manufactured, and only one of the plate surfaces was subjected to convex processing with various curvatures, and the frequency at which spurious appeared was examined. As a result, in the SC-cut crystal resonator processed so that the ratio R / t of the radius of curvature R of the convex processing to the thickness t of the crystal piece satisfies the above expression, the resonance frequency is 8.128 MHz and 10 MHz. No coupling between the main vibration and the sub-vibration occurred, and a spurious-free resonance was obtained without causing a frequency jump due to a temperature change. FIG. 3 is a graph showing a change in frequency deviation (illustrated curve F) and a change in CI (illustrated curve P) with respect to a temperature change of the resonator having the resonance frequency of 8.192 MHz. As is clear from this graph, according to the SC-cut crystal resonator of the above embodiment, the resonance frequency changes continuously and monotonously with a change in temperature, no jump or the like occurs, and the CI is almost constant. Value can be maintained, and good resonance characteristics can be obtained. In this way, by adjusting the radius of curvature of the convex processing in accordance with the thickness of the crystal piece, it is possible to obtain an SC-cut crystal resonator having good resonance characteristics without causing a frequency jump or spurious.

[0008]

As described above in detail, according to the present invention, it is possible to provide an SC-cut quartz resonator having good vibration characteristics with no spurious and no frequency jump due to a change in temperature.

[0009]

[Brief description of the drawings]

FIG. 1 is a side view illustrating the structure of a crystal resonator according to the present invention.

FIG. 2 is a graph showing the relationship between the diameter of the convex processing and the normalized frequency of the present invention.

FIG. 3 is a graph showing a change in frequency and CI with respect to a temperature change of an SC-cut quartz resonator according to the present invention.

FIG. 4 is a diagram showing resonance characteristics of an SC-cut quartz resonator.

[Explanation of symbols]

 11 Crystal pieces

Claims (1)

(57) [Claims] 1. A plane orthogonal to the Y-axis of a crystal of quartz is rotated by about 33 ° about the X-axis, and Z is rotated from this rotated position.
SC cut out from a plane rotated about 22 ° about the axis
In the cut quartz resonator, when the thickness of the crystal piece is t, and only one of the front and back plate surfaces is subjected to convex processing, and the radius of curvature of the convex processing is R, 90.9 <R / t <727. 3. An SC-cut crystal unit, characterized in that: