Doubly rotated qas-type resonators with reduced sensitivity to acceleration

Abstract

A quartz crystal resonator comprises an orthogonally mounted doubly rotated QAS-type resonating element having a pair of bridges positioned at a defined angle in relation to the resonating element's ZI or XI axes. The resonator has reduced sensitivity to mechanical acceleration.

Description

[0001] DOUBLY ROTATED QAS-TYPE RESONATORS WITH REDUCED SENSITIVITY TO ACCELERATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to frequency control products used in a variety of applications where accurate and stable frequency reference and / or timing signals are required. More specifically, the present invention relates to doubly rotated QAS-type resonators and crystal oscillator devices with reduced sensitivity to mechanical acceleration.

[0004] BACKGROUND OF THE INVENTION

[0005] High frequency stability electronic oscillators are often built with quartz crystal resonators. The latter comprise a piezo-electric resonating element mounted in, and encased in, a case ('package"), and means of connecting the resonator to an electronic circuit that functions to sustain stable vibrations in the resonator.

[0006] The quartz crystal resonating element is typically made from a quartz plate ("quartz wafer") that is produced by cutting up a piece of quartz material ("quartz bar") at certain angles relative to the material's crystallographic axes. Various properties of the resonating element are dependent on the cut angles applied during the manufacture of the quartz plate. While there is an infinite number of ways the quartz plate can be cut in relation to the crystallographic axes x, y, and z, certain cuts have been identified that result in particularly useful properties of the resonator. Fig. 1 shows the orientation of widely used singly rotated cuts and doubly rotated cuts. A singly rotated cut plate 1 is obtained when the quartz plate is made by applying a rotation around the x axis from the z axis (the e angle). Such a rotation defines new axes y1and z1for the singly rotated plate 1, whereas the plate's x1axis remains parallel to the crystallographic axis x. A doubly rotated cut plate 2 is obtained when the quartz plate is made by applying double rotation: by the cp angle relative to the x axis around the z axis, and by the e angle relative to the z axis around the x1axis, thus defining new x1, y1, and z1axes for the doubly rotated plate 2. An example of a singly rotated cut is the commonly used AT cut, obtained when the quartz plate is made by applying a rotation around the x axis of approximately 35° (the e angle) from the z axis. The AT cut exhibits properties that are useful for designing and manufacturing temperature compensated crystal oscillators. The stress compensated cut "SC cut" is an example of a doubly rotated cut, obtained when the quartz plate is made by applying double rotation: of approximately 22° (the cp angle) relative to the x axis around the z axis, thus defining a new x1axis for the SC cut plate, and approximately 34° (the e angle) relative to the z axis around the x1axis. The SC cut quartz crystal resonator is said to be compensated for mechanical stresses applied along its in-plane axes. The IT cut is another example of a doubly rotated cut (cp ~ 19°, e ~ 34°) that exhibits properties that are similar to those of the SC cut.

[0007] Individual quartz crystal resonating elements are manufactured by cutting ("dicing") up quartz plates into individual "crystal blanks"; the resonating elements can be made of various shapes, with round and rectangular ("strip") resonating elements being the commonly used ones.

[0008] A well-recognized problem associated with quartz crystal resonators and oscillator devices utilizing quartz crystal resonators is their sensitivity to mechanical acceleration. It manifests itself as a change in the resonant frequency of the resonator, or a change in the frequency of the output signal of the crystal oscillator, caused by externally applied mechanical acceleration. Sensitivity of doubly rotated quartz crystal resonators to mechanical acceleration is often problematic in oven-controlled crystal oscillators (OCXO) and temperature-compensated crystal oscillators (TCXO) used in applications where significant mechanical acceleration is present.

[0009] Several approaches to the problem of reducing sensitivity to acceleration in quartz crystal resonators and oscillators are known in prior art.

[0010] One of such approaches involves arranging at least partial mechanical isolation of the active vibration area of the quartz crystal resonating element from the externally applied mechanical stresses.

[0011] In particular, QAS-type (from French "Quartz Auto Suspendu") resonating elements have a stress isolating gap, or void, between the vibration area of the resonating element and the surrounding it holding area typically used for mounting the resonating element in its case ("package"), and one or more bridges used to mechanically secure the vibration area and to route the required electrical connections through the bridges. Patent application CA1225706A presents an example of such QAS-type resonator. Typically, as shown therein, the QAS-type resonating element is mounted in such a way that the flat surfaces of the resonating element are parallel to the surface of the base of the resonator's case (or "package") facing the resonating element.

[0012] The object of the present invention is to provide new ways of reducing sensitivity to mechanical acceleration in QAS-type resonators.

[0013] SUMMARY OF THE INVENTION

[0014] In one aspect, the invention may be said to comprise a quartz crystal resonator comprising a doubly rotated resonating element having two substantially flat surfaces, a vibration area, and a void mechanically isolating, or at least partially isolating, the vibration area from a holding area, and one or more bridges connecting the vibration area and the holding area, a base having a surface facing the resonating element, and wherein the resonating element is mounted orthogonally in relation to the base (i.e., the resonating element is positioned so that the substantially flat surfaces of the resonating element are substantially perpendicular to the base surface facing the resonating element).

[0015] In another aspect, the invention may be said to comprise a quartz crystal resonator as described above, wherein at least one of the one or more bridges is positioned at an angle of 20° to 45° in relation to any one of the resonating element's axes X1and Z1.

[0016] In yet another aspect, the invention may be said to comprise a quartz crystal resonator as described above, wherein any one of the resonating element's axes X1and Z1is substantially parallel to the base surface facing the resonating element.

[0017] In another aspect, the invention may be said to comprise a quartz crystal resonator as described above, wherein holding arms extending substantially in parallel to the substantially flat surfaces of the resonating element are holding the resonating element in an orthogonal position (i.e., in a position such that the substantially flat surfaces of the resonating element are substantially perpendicular to the base surface facing the resonating element).

[0018] In yet another aspect, the invention may be said to comprise a quartz crystal resonator as described above, wherein a line connecting holding points of the two holding arms is substantially parallel to the base surface facing the resonating element. In another aspect, the invention may be said to comprise an electronic apparatus or device comprising a quartz crystal resonator as per the statements above.

[0019] In this patent specification, the term "substantially flat" as related to the two opposing surfaces of a resonating element, means that the said surfaces are, to a large extent, flat or close to being flat: in practical embodiments, either one of the two substantially flat surfaces, or both of them, may either be manufactured to be predominantly flat (within manufacturing tolerances) or incorporate a slight curvature to optimize vibration mode control or / and to contain vibrations in the active vibration zone of the resonating element.

[0020] In this patent specification, the term "substantially parallel" means that the described objects, elements, or structures are close to being parallel but might not be perfectly parallel. The term "substantially in parallel to" is to be interpreted in the same manner. Similarly, the term "substantially perpendicular" means that that the described objects, elements, or structures are close to being perpendicular but might not be perfectly perpendicular.

[0021] The term "comprising" as used in this specification means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention is further described with reference to the accompanying figures in which, -

[0024] Fig. 1 (prior art) shows the orientation of singly rotated and doubly rotated cuts.

[0025] Fig. 2 and Fig. 2a show an example of a QAS-type resonator according to the present invention.

[0026] Fig. 3 shows how sensitivity to acceleration of a QAS-type SC cut resonator of the present invention depends on the value of angle A that determines the position of connecting bridges.

[0027] Fig. 3a shows plots of optimal ranges of angle A versus the value of rotation angle cp, for doubly rotated QAS resonators of the present invention.

[0028] Fig. 4 to Fig. 7 show examples of possible holding arm configurations. DETAILED DESCRIPTION OF THE INVENTION

[0029] Without limiting the scope of the present invention, the invention is illustrated herein by the following specific embodiment of a doubly rotated QAS-type resonator with reduced sensitivity to acceleration.

[0030] Shown in Fig. 2 (front view) and Fig. 2a (right-side view), the resonator implemented according to the present invention comprises a QAS-type SC cut resonating element 1 of a substantially round shape having two substantially flat surfaces 12 and 13, a void 2 that mechanically isolates, or at least partially isolates, the vibration area 3 of the resonating element 1 from the holding area 4 that surrounds the vibration area 3, and two bridges 5 and 6 that connect the vibration area 3 and the holding area 4. The resonator comprises a base 7 that has a surface 8 facing the resonating element 1, and the QAS resonating element 1 is positioned so that its substantially flat surfaces are positioned substantially perpendicular to the base surface 8 (i.e., the resonating element is orthogonally mounted).

[0031] The resonating element 1 can be installed so that either one of its axes X1and Z1is substantially parallel to the base surface 8. Two holding arms 9 and 10 extending substantially in parallel to the substantially flat surfaces of the resonating element 1 are holding the resonating element 1 in a position such that the substantially flat surfaces of the resonating element 1 are substantially perpendicular to the base surface 8 (i.e., the resonating element is mounted orthogonally in relation to the base).

[0032] In the embodiment shown in Fig. 2 and Fig. 2a, a line 11 connecting the holding points of the two holding arms 9 and 10 is substantially parallel to the base surface 8 facing the resonating element 1.

[0033] In this embodiment, the bridges 5 and 6 are positioned at an angle A=30° in relation to the either one of the resonating element's axes X1and Z1.

[0034] Fig. 3 shows how sensitivity to acceleration, commonly measured as fractional frequency deviation per unit of acceleration (dF / F / g), of an SC cut resonator according to the present invention depends on the value of angle A (measured in angular degrees (°)). Fig. 3 shows plots for sensitivity to acceleration in each of three mutually perpendicular directions Sx, SY, and Sz, as well as a plot for the magnitude of the total acceleration sensitivity SGQ. It follows from Fig. 3 that in order to reduce the total sensitivity to acceleration of an SC cut resonator of the present invention to a value not exceeding 1E- 09 (i.e., Ippb / g, or one part per billion per one unit of acceleration), the bridges would have to be positioned so that the value of angle A is within the range of 20° to 38°.

[0035] For cuts other than the SC cut, the optimal range of angle A values required to achieve total sensitivity to acceleration not exceeding Ippb / g depends on the value of the rotation angle cp. Fig. 3a serves to illustrates the point. Fig. 3a shows how the range of angle A values that allows to achieve acceleration sensitivity below Ippb / g depends on the value of rotation angle cp (phi). For each value of angle cp (phi), the optimal range of angle A values is represented in Fig. 3a by three values: minimum value of the range (min A, lower plot line), mean value of the range (mean A, middle line), and maximum value of the range (max A, upper line). It follows from Fig. 3a that for doubly rotated resonating elements manufactured with rotation angle cp values from 0° to 30°, the optimal range of angle A values required to achieve acceleration sensitivity below Ippb / g spans from 20° to 45°.

[0036] Without deviating from the concept of the present invention, a person skilled in the art will be able to come up with a number of different configurations of the holding arms to maintain the orthogonal position of the QAS resonating element in resonators of the present invention. Examples of some of the possible holding arm configurations are shown in Fig. 4 to Fig. 7. In these figures, reference numerals identifying the main features and elements are consistent with reference numerals used in Fig. 2 and Fig. 2a.

[0037] Doubly rotated QAS-type resonators of the present invention can be used in a variety of frequency control devices, including, but not limited to, crystal oscillators (XO), temperature-compensated crystal oscillators (TCXO), and oven-controlled crystal oscillators (OCXO). These devices, in turn, will benefit the performance of various electronic apparatuses and systems, including, but not limited to, radio communication apparatuses and systems where reduced sensitivity of the reference frequency to mechanical acceleration is important.

Claims

CLAIMS:

1. A quartz crystal resonator comprising a doubly rotated resonating element having two substantially flat surfaces, a vibration area, and a void at least partially mechanically isolating the vibration area from a holding area, and one or more bridges connecting the vibration area and the holding area, a base having a surface facing the resonating element, and wherein the resonating element is positioned so that the substantially flat surfaces of the resonating element are substantially perpendicular to the base surface facing the resonating element.

2. A quartz crystal resonator according to claim 1, wherein at least one of the one or more bridges is positioned at an angle of 20° to 45° in relation to any one of the resonating element's axes X1and Z1.

3. A quartz crystal resonator according to any one of claims 1 and 2, wherein any one of the resonating element's axes X1and Z1is substantially parallel to the base surface facing the resonating element.

4. A quartz crystal resonator according to any one of claims 1 to 3, comprising two holding arms extending substantially in parallel to the substantially flat surfaces of the resonating element and holding the resonating element in a position such that the substantially flat surfaces of the resonating element are substantially perpendicular to the base surface facing the resonating element.

5. A quartz crystal resonator according to claim 4, wherein a line connecting holding points of the two holding arms is substantially parallel to the base surface facing the resonating element.

6. A quartz crystal resonator according to any one of claims 1 to 5, wherein the doubly rotated resonating element is made with rotation angle cp within the range from 0° to 30°.

7. A quartz crystal resonator according to claim 6, wherein the doubly rotated resonating element is an SC cut resonating element.

8. An electronic device or apparatus comprising a quartz crystal resonator according to any one of claims 1 to 7.

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