AT-cut temperature-compensated crystal oscillator with comb-shaped metal film

Abstract

A temperature-compensated crystal oscillator with a comb-shaped metal film includes a rectangular quartz wafer with rectangular upper and lower surfaces and two rectangular bosses on the upper surface. A central electrode is plated on the upper and lower surfaces of the quartz wafer, and an extension layer is provided at one corner of the central electrode. The two ends of the comb-shaped metal film are placed on the two rectangular bosses on the upper surface of the quartz wafer, and the comb-shaped metal film is separated from the central electrode. The comb-shaped metal film is composed of multiple metal strips arranged at equal intervals, symmetrically about the y-axis, with the lengths of the metal strips aligned with the x-axis of the rectangular quartz wafer and their midpoints on the z-axis. The thermal expansion coefficient of the metal strip material is greater than that of the quartz wafer. The comb-shaped metal film of the present invention does not increase the overall mass of the electrode region and does not increase the load effect in this region. Furthermore, the use of a comb-shaped structure can reduce the force applied by the compensation strips in the z-direction, thereby reducing the impact on the operating mode of the crystal oscillator or avoiding the occurrence of other parasitic modes.

Description

Technical Field

[0001] The present invention relates to a quartz crystal resonator, in particular to an AT-cut temperature-compensated crystal oscillator with a comb-shaped metal film. Technical Background

[0002] Quartz crystal resonators are core components of frequency reference sources in modern electronic communications and information systems. With the development of related technologies in fields such as aviation, aerospace, electronics, communications, and machinery, the requirements for the precision of quartz crystal resonators are becoming increasingly higher. Improving the frequency stability of quartz crystal resonators has become a major issue.

[0003] The temperature-frequency characteristics of a quartz crystal oscillator will cause its resonant frequency to change when the operating temperature changes. Its temperature-frequency characteristics are mainly related to the cut type of the quartz crystal. Common cut types include AT cut, BT cut, and SC cut. Among them, the relationship between the resonant frequency and temperature of the AT-cut quartz crystal oscillator is a cubic function. Therefore, it has a zero temperature coefficient point and the zero temperature coefficient point falls within the ambient temperature range. The excellent frequency-temperature characteristics make the AT cut one of the most widely used cut types.

[0004] While temperature-induced changes in the resonant frequency of a crystal oscillator are unavoidable, there are measures that can be taken to compensate for the resulting frequency deviation, thereby improving the frequency stability of the quartz crystal. Existing crystal oscillator temperature compensation technologies primarily fall into two categories: the first utilizes circuit processing based on the frequency-temperature characteristics of the quartz crystal oscillator. For example, analog, digital, or microcomputer-based processing generates a compensation voltage to compensate for frequency variations; the second utilizes a thermostat to maintain the operating temperature of the quartz crystal oscillator at a constant value. While this method, which utilizes an external control voltage, offers high precision and effective temperature compensation, it is complex and costly to manufacture. Furthermore, the volume of certain electronic components hinders the trend toward miniaturization of crystal oscillators and is insufficient to meet the demands of current technological advancements, particularly in mobile communications such as mobile phones. Furthermore, this temperature compensation technology is generally only applied to fundamental frequency quartz crystal oscillators, not overtone quartz oscillators. The reason for this is that fundamental frequency quartz crystal oscillators have good pullability, but poor stability and aging characteristics. Overtone quartz crystal oscillators have better stability and aging characteristics than fundamental frequency quartz crystal oscillators, but this temperature compensation technology has difficulty in pulling overtone quartz crystal oscillators over a wide frequency range, making it difficult to solve the temperature compensation technology problem of overtone quartz crystal oscillators. Using a constant temperature device such as a thermostat can keep the operating temperature of the quartz crystal oscillator constant, but this method is costly, bulky, and consumes a lot of power, and is generally only used in specific situations.

[0005] When a quartz crystal is subjected to stress, its resonant frequency will change. This characteristic is called the force-frequency characteristic of the quartz crystal. The following is the relationship between the frequency change of the quartz crystal and the stress change it is subjected to:

[0006] or

[0007] Where: L is the length of the quartz crystal; f0 is the resonant frequency of the quartz crystal; F is the force on the quartz crystal; K f is the force-frequency coefficient of the quartz crystal.

[0008] At present, there are also some methods that use the force-frequency characteristics of quartz crystals to compensate for the temperature-frequency characteristics based on the fact that the thermal expansion and contraction of the metal when the working temperature of the metal film changes will exert a stress on the crystal oscillator. According to the force-frequency characteristics of the crystal, when pressure is applied to the x-axis direction of the quartz crystal oscillator, the frequency of the crystal will be raised and deviate upward from the resonant frequency; when tension is applied to the x-axis direction of the center electrode, the frequency of the crystal will be lowered and the resonant frequency will be shifted downward; and the greater the force, the greater the frequency offset, and the magnitude of the force is proportional to the frequency offset; therefore, when the temperature rises, since the thermal expansion coefficient of the metal film is greater than that of the quartz material, the expansion amplitude of the metal film is greater than that of the quartz crystal oscillator. Similarly, when the temperature drops, the contraction amplitude of the compensation film is greater than that of the quartz crystal oscillator. This can offset part of the change in the resonant frequency of the quartz crystal oscillator caused by the change in working temperature.

[0009] A crystal resonator using a strip compensation film for stress compensation (application number: 202010238766.9) uses the above method to perform temperature compensation based on the force-frequency characteristics of the quartz crystal oscillator based on the metal film. It has the advantages of relatively simple structure, small size, low power consumption and low cost. However, since its compensation strip is placed on the electrode and in contact with the electrode, it will not only cause the metal film to generate stress in the x-direction when the operating temperature changes, but also generate a relatively large stress in the z-direction, thereby leading to the emergence of some parasitic modes; it will also increase the overall mass of the electrode area, resulting in a more serious load effect, which will affect the performance of the crystal oscillator. Summary of the Invention

[0010] The present invention aims to overcome the above-mentioned shortcomings of the prior art and provides an AT-cut temperature-compensated crystal oscillator with a comb-shaped metal film.

[0011] The purpose of the present invention is to innovate the temperature compensation method of quartz crystal oscillators, and to use the force-frequency characteristics of quartz crystal oscillators through comb-shaped metal films to compensate for the frequency difference caused by temperature changes, which is conducive to the development of quartz crystal oscillators towards miniaturization.

[0012] This invention innovates the temperature compensation method for quartz crystal oscillators and proposes an AT-cut temperature-compensated crystal oscillator with a comb-shaped metal film. This method uses the stress generated by the metal film when the temperature changes to adjust the frequency deviation of the crystal oscillator. The characteristic that the operating frequency of the crystal oscillator varies with the magnitude and direction of the applied stress is utilized to compensate for the temperature effect on the operating frequency of the crystal oscillator. The use of multiple rectangular metal strips allows the generated thermal stress to be applied in the X-direction, effectively reducing the change in resonant frequency caused by operating temperature changes, thereby improving the frequency stability of the crystal oscillator.

[0013] The temperature-compensated crystal oscillator of the comb-shaped metal film includes a quartz wafer 1, characterized in that: the quartz wafer 1 is a rectangular parallelepiped, the upper and lower surfaces of the quartz wafer 1 are rectangular, and there are two rectangular bosses on the upper surface; a central electrode 2 is plated on the upper and lower surfaces of the quartz wafer 1, and an extension layer 3 is provided at one corner of the central electrode 2, and the end of the extension layer 3 is connected to a glue point 5, which is the lead-out end of the central electrode 2; the longitudinal axis direction of the upper surface of the quartz wafer 1 is set as the X axis, the horizontal axis direction is set as the Z axis, and the direction perpendicular to the upper surface of the quartz wafer 1 and passing through the intersection of the X axis and the Z axis is set as the Y axis; the upper and lower surfaces The projections of the central electrode 2 in the Y-axis direction coincide with each other, and the extension layers 3 of the central electrode 2 on the upper and lower surfaces are respectively biased to the two sides of the X-axis; the comb-shaped metal film 4 is arranged along the X-axis, and the two ends of the comb-shaped metal film 4 are respectively placed on two rectangular bosses on the upper surface of the quartz wafer 1, and the comb-shaped metal film 4 is separated from the central electrode 2; the comb-shaped metal film 4 is composed of a plurality of metal strips arranged at equal intervals, and the plurality of metal strips are arranged symmetrically about the y-axis, and the length direction of the metal strips is consistent with the x-axis direction of the rectangular quartz wafer and the midpoint should be on the z-axis; the thermal expansion coefficient of the material of the metal strips is greater than the thermal expansion coefficient of the quartz wafer 1.

[0014] Preferably, the cross section of the metal strip is rectangular.

[0015] Furthermore, the rectangular cross section of the metal strip has a side length in the Z-axis direction that is smaller than a side length in the X-axis direction.

[0016] According to the crystal's force-frequency characteristics, when the comb-shaped metal film applies pressure in the x-axis direction, the crystal's resonant frequency rises, exceeding the pre-designed resonant frequency. When the metal strip applies tension in the x-axis direction, the crystal's resonant frequency drops, falling below the pre-designed resonant frequency. Furthermore, the magnitude of the offset from the pre-designed resonant frequency is related to the applied force: greater tension (pressure) results in a greater offset, and the offset is a linear function of the applied force. Therefore, when the crystal's operating temperature rises, the comb-shaped metal film expands more than the rectangular quartz wafer, exerting a tensile force on it, thereby offsetting some of the drop in crystal frequency caused by the temperature increase. Similarly, when the operating temperature drops, the comb-shaped metal film contracts more than the rectangular quartz wafer, exerting a compressive force on it, thereby offsetting some of the increase in crystal frequency caused by the temperature drop. This allows the comb-shaped metal film to deform accordingly with temperature changes, compensating for the crystal's own frequency deviation caused by temperature fluctuations.

[0017] The metal strips used in the present invention have very small dimensions in the z direction, so that the stress generated can be concentrated in the x direction. However, the stress generated by a single metal wire in the x direction is not sufficient to achieve the best temperature compensation effect. Therefore, a comb-shaped metal wire structure composed of multiple metal wires is used to achieve the best effect.

[0018] A boss is provided on the upper surface of the quartz wafer for connecting the comb-shaped metal wire with the quartz wafer, thereby avoiding contact between the central electrode and the comb-shaped metal wire and not increasing the negative mass of the central electrode area.

[0019] The advantages of the present invention are as follows: A comb-shaped metal film is added to the upper surface of a conventional quartz crystal resonator. When the temperature changes, the comb-shaped metal film and the quartz crystal have different thermal expansion coefficients, so they expand and contract to different degrees. This creates a compressive force where the two contact each other, and the greater the operating temperature change, the greater the thermal stress generated. This allows the force-frequency characteristics of the rectangular quartz crystal to be used to compensate for the frequency change caused by temperature. The comb-shaped metal film material has a greater thermal expansion coefficient than the rectangular quartz crystal, and the comb-shaped metal film 4 does not contact the center electrode 2. Because the thickness shear vibration of the crystal oscillator is primarily concentrated in the electrode region, this region also determines the magnitude of the resonant frequency. Avoiding contact with the electrode region does not increase the overall mass of the electrode region, nor does it increase the load effect in this region. Furthermore, the use of a comb-shaped structure can reduce the force applied by the compensation strip in the z-direction, thereby reducing the impact on the operating mode of the crystal oscillator or preventing the occurrence of other parasitic modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1It is a structural diagram of a comb-shaped metal film temperature-compensated crystal oscillator;

[0021] Figure 2 This is the frequency variation curve of AT-cut crystal oscillator with temperature;

[0022] Figure 3 is the stress-frequency characteristic curve of the quartz crystal;

[0023] Figure 4 This is the temperature-frequency characteristic curve after compensation. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below with reference to the accompanying drawings.

[0025] like Figure 1 As shown, an AT temperature-compensated crystal oscillator with a comb-shaped metal film mainly includes 1-a quartz wafer, which is a rectangular parallelepiped with rectangular upper and lower surfaces. The upper surface (where the comb-shaped metal film is placed) has two rectangular bosses; a central electrode 2 is plated on the upper and lower surfaces of the rectangular quartz wafer, respectively, and an extension layer 3 is provided at one corner of the central electrode 2. The end of the extension layer 3 is connected to a glue point 5, which is the lead-out end of the central electrode 2; the longitudinal axis direction of the upper surface of the quartz wafer 1 is set as the X-axis, the transverse axis direction is set as the Z-axis, and the direction perpendicular to the upper surface of the quartz wafer 1 and passing through the intersection of the X-axis and the Z-axis is set as the Y-axis; the projections of the central electrodes 2 on the upper and lower surfaces in the Y-axis direction coincide, and the extension layers 3 of the central electrodes 2 on the upper and lower surfaces are respectively biased to the two sides of the X-axis; a comb-shaped metal film 4 is arranged along the X-axis, and the two ends of the comb-shaped metal film 4 are placed on the two bosses on the upper surface of the quartz wafer 1, and the comb-shaped metal film 4 is separated from the central electrode 2. The comb-shaped metal film 4 is composed of multiple metal strips with rectangular cross sections arranged at equal intervals, and the multiple metal strips are arranged symmetrically about the y-axis. The length direction of the metal strip is consistent with the x-axis direction of the rectangular quartz wafer and the midpoint should be on the z-axis.

[0026] The reverse side of the quartz wafer is also plated with electrodes. The electrodes on the front and reverse sides extend in different directions, and each extends to the dispensing position of the respective electrodes.

[0027] For the sake of convenience in the following examples, we assume that the material of the comb-shaped metal film is silver. The length a, thickness b, and width c of the quartz crystal; the width d and thickness e of the rectangular metal strip; and the material properties of the quartz and silver materials are described as follows:

[0028] a=2mm; b=0.1mm; c=0.1mm; d=0.02mm; e=0.0002mm

[0029] Silver Material:

[0030] Elastic modulus: E = 7.32 × 10 10 N / m;

[0031] Thermal expansion coefficient: α = 7.32 × 10 -5 / ℃

[0032] Quartz crystal material:

[0033] Elastic coefficient matrix:

[0034]

[0035] Thermal expansion coefficient: 1.371×10 -5 / ℃

[0036] Force-frequency coefficient K f :20×10 -8

[0037] When the operating temperature of the comb-shaped metal film temperature-compensated crystal oscillator changes, the thermal stress generated is

[0038]

[0039] Where: α1 is the thermal expansion coefficient of the quartz crystal; α2 is the thermal expansion coefficient of the rectangular metal strip; A1 is the cross-sectional area of the quartz wafer; A2 is the cross-sectional area of the rectangular metal strip; E1 is the elastic modulus of the quartz crystal; E2 is the elastic modulus of the rectangular metal strip; T is the actual temperature; T0 is the initial temperature.

[0040] It can also be seen from the above formula that the magnitude of the thermal stress generated will increase as the temperature change increases.

[0041] Therefore, the force applied to the rectangular quartz crystal plate in the X-axis direction should be:

[0042] F=nσA2=-1.84×10 -6 n(T-T0)

[0043] Where n is the number of rectangular metal strips.

[0044] The operating frequency of the crystal oscillator is calculated as follows:

[0045]

[0046] The frequency of the AT-cut crystal oscillator changes with force as follows:

[0047]

[0048] where K f is the force-frequency coefficient, f is the operating frequency of the crystal oscillator, and a is the length of the rectangular quartz crystal.

[0049] When the slope of the force-frequency characteristic line is -0.3, the temperature compensation effect is the best, so:

[0050]

[0051] Therefore, ten rectangular metal strips are used.

[0052]

[0053] That is, the resonant frequency of the crystal oscillator will decrease (increase) by 0.3ppm for every 1°C rise (fall) in the temperature of the ten stressed metal strips. Figure 3 shown.

[0054] The frequency variation curve after stress compensation is completed is as follows Figure 4 As shown, the frequency difference is within 8ppm.

[0055] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the inventive concept. The scope of protection of the present invention should not be regarded as limited to the specific forms described in the embodiments. The scope of protection of the present invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A comb-shaped metal film temperature-compensated crystal oscillator, comprising a quartz crystal (1), characterized in that: The quartz wafer (1) is a rectangular parallelepiped, and the upper and lower surfaces of the quartz wafer (1) are rectangular, and there are two rectangular bosses on the upper surface; a central electrode (2) is plated on the upper and lower surfaces of the quartz wafer (1), and an extension layer (3) is provided at one corner of the central electrode (2); the end of the extension layer (3) is connected to a glue point (5), and the glue point (5) is the lead-out end of the central electrode (2); the longitudinal axis direction of the upper surface of the quartz wafer (1) is set as the X axis, the transverse axis direction is set as the Z axis, and the direction perpendicular to the upper surface of the quartz wafer (1) and passing through the intersection of the X axis and the Z axis is set as the Y axis; the central electrodes (2) on the upper and lower surfaces are arranged at the Y axis. The projections in the axial direction coincide with each other, and the extension layers (3) of the central electrodes (2) on the upper and lower surfaces are respectively biased toward the two sides of the X-axis; the comb-shaped metal film (4) is arranged along the X-axis, and the two ends of the comb-shaped metal film (4) are respectively placed on two rectangular bosses on the upper surface of the quartz wafer (1), and the comb-shaped metal film (4) is separated from the central electrode (2); the comb-shaped metal film (4) is composed of a plurality of metal strips arranged at equal intervals, and the plurality of metal strips are arranged symmetrically about the y-axis, and the length direction of the metal strips is consistent with the x-axis direction of the rectangular quartz wafer, and the midpoint should be on the z-axis; the thermal expansion coefficient of the material of the metal strips is greater than the thermal expansion coefficient of the quartz wafer (1).

2. The comb-shaped metal film temperature-compensated crystal oscillator according to claim 1, wherein: The cross section of the metal strip is rectangular.

3. The comb-shaped metal film temperature-compensated crystal oscillator according to claim 1, wherein: The rectangular cross section of the metal strip has a side length in the Z-axis direction that is smaller than the side length in the X-axis direction.

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