Integrated crystal resonator for constant temperature crystal oscillator

Abstract

The invention discloses an integrated crystal resonator for an oven controlled crystal oscillator, and relates to the technical field of crystal resonators. The device comprises a ceramic base, a cover plate, a vacuum sealing cavity formed by an inner cavity of the ceramic base and the cover plate, a wafer, a temperature measuring element and a heating element, the lower surface of the temperature measuring element is fixed at the bottom of the inner cavity, and an upper surface electrode is communicated with a bonding disc in the ceramic base in a bonding manner; the lower surface of the heating element is electrically connected with a bonding pad at the bottom of the inner cavity and led out to the leading-out end of the ceramic base, and an electrode on the upper surface is communicated with a bonding disc in the ceramic base in a bonding mode. Compared with a traditional crystal resonator with a single function, a temperature measuring element and a heating element are integrated in the resonator; as the heating element is arranged inside the crystal resonator instead of being arranged on an external PCB according to a traditional scheme, heat loss can be remarkably reduced, heating power is reduced, and therefore the overall power consumption of the OCXO is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal resonators, and more specifically, it is an integrated crystal resonator for an oven-controlled crystal oscillator. Background Art

[0002] A crystal resonator is an electronic component that uses the inverse piezoelectric effect of a piezoelectric crystal to generate resonance. The main crystal used is quartz. The crystal resonator needs to cooperate with an external circuit or IC to form a crystal oscillator, which can output a specific frequency signal when powered on. Since the frequency of the crystal resonator generally changes with temperature, to make the crystal oscillator output a stable frequency, the crystal resonator can be heated above room temperature and its temperature can be controlled to be constant. Such a crystal oscillator is an oven-controlled crystal oscillator (OCXO). The oven-controlled crystal oscillator can also be further enhanced with functions such as voltage control and temperature compensation to achieve higher frequency accuracy.

[0003] The crystal resonators used in traditional oven-controlled crystal oscillators generally adopt quartz wafers with special cuts (such as SC and IT cuts) and coated with electrodes, which are fixed to a bracket or a pad through conductive adhesive, and then encapsulated in a metal or ceramic crystal box through processes such as resistance welding, cold pressure welding or parallel sealing welding. When such a crystal resonator is used in an OCXO, independent heating and temperature measuring elements are also required inside the OCXO to control its temperature to achieve a stable temperature effect. Because these elements are at a certain distance from the crystal resonator, the heating efficiency is low and the power consumption of the OCXO will be relatively large. At the same time, because there are temperature differences and thermal resistances between these elements and the crystal resonator, it will affect the temperature control accuracy and sensitivity of the OCXO, reducing important indicators such as its frequency accuracy, frequency temperature stability, and phase noise.

[0004] To improve the temperature control accuracy, reduce the power consumption and volume, crystal resonators with heating and temperature measuring functions can be developed. Existing patents such as US8567041B1 describe a crystal resonator that includes a heater and a thermistor. However, this patent is fabricated using semiconductor technology such as photolithography, etching, and deposition processes. After etching a specific shape on the quartz wafer, electrodes, heaters, thermistors, etc. are deposited, and semiconductor materials such as silicon are used for encapsulation. This solution is completely different from traditional crystal resonators, and the design, process, equipment, materials, etc. are not compatible. Existing crystal resonator production lines cannot manufacture it, and it also requires the design of a dedicated oven-controlled crystal oscillator to be used.

[0005] Therefore, it is necessary to develop an integrated crystal resonator for an oven-controlled crystal oscillator that is compatible with existing crystal resonator production lines and OCXO products, can reduce the power consumption and volume of the oven-controlled crystal oscillator, and improve the temperature control accuracy. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the above-mentioned background art, and to provide an integrated crystal resonator for a temperature-controlled crystal oscillator.

[0007] To achieve the above object, the technical solution of the present invention is: an integrated crystal resonator for a temperature-controlled crystal oscillator, characterized in that it includes a ceramic base, a cover plate, a vacuum-sealed cavity formed by the inner cavity of the ceramic base and the cover plate, a wafer, a temperature-measuring element and a heating element located in the vacuum-sealed cavity;

[0008] The wafer is fixed on the pads of the ceramic base, so that the electrodes on both sides of the wafer are electrically connected to the lead-out ends of the ceramic base;

[0009] The lower surface of the temperature-measuring element is fixed to the bottom of the inner cavity, and the upper surface electrode is connected to the bonding pad in the ceramic base by bonding;

[0010] The lower surface of the heating element is electrically connected to the pad at the bottom of the inner cavity and led out to the lead-out end of the ceramic base, and the upper surface electrode is connected to the bonding pad in the ceramic base by bonding.

[0011] In the above technical solution, the lead-out ends of the ceramic base at least include the first lead-out end and the second lead-out end of the wafer electrode, power supply, ground, the signal output end of the temperature-measuring element, and the control signal input end of the heating element.

[0012] In the above technical solution, the temperature-measuring element is a thermistor, a metal thin-film resistor or a digital temperature sensor;

[0013] The heating element is a power triode or a field effect transistor.

[0014] In the above technical solution, when the temperature-measuring element is a thermistor and the heating element is a power triode, one electrode of the temperature-measuring element is grounded and one electrode is connected to the signal output end of the temperature-measuring element;

[0015] The c electrode of the heating element is grounded, the e electrode is connected to the power supply, and the b electrode is connected to the control signal input end of the heating element;

[0016] In the above technical solution, when the temperature-measuring element is a digital temperature sensor and the heating element is a field effect transistor, the power supply electrode of the temperature-measuring element is connected to the power supply and the ground electrode is connected to the ground;

[0017] The G electrode of the heating element is connected to the control signal input end of the heating element, the S electrode is connected to the power supply, and the D electrode is connected to the external load.

[0018] In the above technical solution, a groove is provided at the bottom of the inner cavity, the temperature-measuring element and the heating element are located in the groove, and the wafer is located above the temperature-measuring element and the heating element.

[0019] In the above technical solution, the upper surface electrode of the temperature measuring element is connected to the first bonding pad in the ceramic base through the first gold wire;

[0020] The upper surface electrode of the heating element is connected to the second bonding pad in the ceramic base through the second gold wire and is connected to the third bonding pad in the ceramic base through the third gold wire.

[0021] In the above technical solution, when heating the wafer to the operating temperature of 85 °C, the required heating power is 0.099 W.

[0022] In the above technical solution, the volume of the crystal resonator is 5 mm × 3.2 mm × 1.1 mm.

[0023] In the above technical solution, the cover plate is welded to the sealing ring of the ceramic base by parallel seam welding;

[0024] The wafer is fixed on the bonding pad of the ceramic base through conductive adhesive;

[0025] When electrical connection is required on the lower surface of the temperature measuring element, the temperature measuring element is fixed on the bonding pad at the bottom of the inner cavity through conductive adhesive; when electrical connection is not required on the lower surface of the temperature measuring element, the temperature measuring element is fixed at the bottom of the inner cavity through insulating adhesive;

[0026] The lower surface of the heating element is electrically connected to the bonding pad at the bottom of the inner cavity by means of conductive adhesive bonding or welding.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1) Compared with the traditional crystal resonator with a single function, the present invention integrates a temperature measuring element and a heating element inside the resonator; since the heating element is inside the crystal resonator instead of being placed on the external PCB board according to the traditional solution, the heat loss can be significantly reduced, the heating power can be decreased, thereby reducing the overall power consumption of the OCXO; for example, when heating an OCXO with a traditional crystal resonator from room temperature to 85 °C, the heating power consumption generally needs to be more than 0.3 W. The crystal resonator of the present invention only needs less than 0.1 W according to the simulation analysis result of the heating power consumption (see Figure 2 ).

[0029] 2) The wafer, the temperature measuring element, and the heating element of the present invention are located in the same package, with a short distance, a small temperature difference, and a fast response to temperature changes between the elements. Compared with the external temperature measuring and heating methods, it can improve the temperature control accuracy and sensitivity, reduce the temperature fluctuation of the wafer, and reduce the influence of temperature changes on the frequency, and finally improve the frequency temperature stability, phase noise and other indicators of the OCXO.

[0030] 3) The volume of the present invention can be as small as 5mm×3.2mm×1.1mm, and the temperature measurement and heating elements are integrated therein, which can reduce the complexity of the peripheral circuit and the number of components, and reduce the volume and weight of the OCXO.

[0031] 4) The present invention is compatible with the existing crystal resonator production line and OCXO products. By adopting bare chip type packaging components and micro-assembly process, the temperature measurement and heating elements are integrated in the crystal resonator, and the external circuit design can be further simplified. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of the present invention.

[0033] Figure 2 It is an internal top view structural diagram of the present invention.

[0034] Figure 3 It is a graph of the simulation analysis result of the heating power consumption of Embodiment 1 of the present invention.

[0035] Figure 4 It is the electrical schematic diagram of Embodiment 1 of the present invention

[0036] Figure 5 It is the electrical schematic diagram of Embodiment 2 of the present invention

[0037] Among them, 1 - ceramic base, 11 - inner cavity, 111 - groove, 12 - bonding pad, 121 - first bonding pad, 122 - second bonding pad, 123 - third bonding pad, 2 - cover plate, 3 - vacuum sealed cavity, 4 - wafer, 5 - temperature measurement element, 6 - heating element, 71 - first gold wire, 72 - second gold wire, 73 - third gold wire, Xtal1 - first lead-out terminal, Xtal2 - second lead-out terminal, VDD - power supply, GND - ground, Sout - signal output terminal of the temperature measurement element, Sin - control signal input terminal of the heating element. Detailed Description of the Invention

[0038] The implementation of the present invention will be described in detail below with reference to the drawings, but they do not constitute a limitation to the present invention, and are only for illustration. At the same time, the advantages of the present invention will become clearer and easier to understand through the description.

[0039] Referring to the drawings, it can be seen that an integrated crystal resonator for a constant temperature crystal oscillator, characterized in that it includes a ceramic base 1, a cover plate 2, a vacuum sealed cavity 3 formed by the inner cavity 11 of the ceramic base 1 and the cover plate 2, a wafer 4, a temperature measurement element 5 and a heating element 6 located in the vacuum sealed cavity 3;

[0040] The wafer 4 is fixed on the bonding pad of the ceramic base 1, so that the electrodes on both sides of the wafer 4 are electrically connected to the lead-out terminals of the ceramic base 1;

[0041] The lower surface of the temperature measuring element 5 is fixed to the bottom of the inner cavity 11, and the upper surface electrode is connected to the bonding pad 12 in the ceramic base 1 by bonding;

[0042] The lower surface of the heating element 6 is electrically connected to the pad at the bottom of the inner cavity 11 and led out to the lead-out end of the ceramic base 1, and the upper surface electrode is connected to the bonding pad 12 in the ceramic base 1 by bonding.

[0043] According to the different temperature measuring elements 5 and heating elements 6 used, the number of lead-out ends, internal bonding pads and pads required for the ceramic base 1 will also be different; ready-made ceramic bases can be used, or new bases can be redesigned, but the lead-out ends of the ceramic base 1 at least include the first lead-out end Xtal1 and the second lead-out end Xtal2 of the wafer 4 electrode, power supply VDD, ground GND, signal output end Sout of the temperature measuring element, and control signal input end Sin of the heating element.

[0044] The temperature measuring element 5 is a thermistor, a metal thin film resistor or a digital temperature sensor;

[0045] The heating element 6 is a power triode or a field effect transistor; when the user designs a temperature-controlled crystal oscillator, according to the characteristics of the integrated components, the corresponding external circuit can be designed to achieve the function.

[0046] When the temperature measuring element 5 is a thermistor and the heating element 6 is a power triode, one electrode of the temperature measuring element 5 is grounded to GND, and one electrode is connected to the signal output end Sout of the temperature measuring element;

[0047] The c electrode of the heating element 6 is grounded to GND, the e electrode is connected to the power supply VDD, and the b electrode is connected to the control signal input end Sin of the heating element;

[0048] When the temperature measuring element 5 is a digital temperature sensor and the heating element 6 is a field effect transistor, the power supply electrode of the temperature measuring element 5 is connected to the power supply VDD, and the ground electrode is connected to the ground GND;

[0049] The G electrode of the heating element 6 is connected to the control signal input end Sin of the heating element, the S electrode is connected to the power supply VDD, and the D electrode is connected to the external load Load.

[0050] A groove 111 is provided at the bottom of the inner cavity 11, the temperature measuring element 5 and the heating element 6 are located in the groove 111, and the wafer 4 is located above the temperature measuring element 5 and the heating element 6.

[0051] The upper surface electrode of the temperature measuring element 5 is connected to the first bonding pad 121 in the ceramic base 1 through the first gold wire 71;

[0052] The upper surface electrode of the heating element 6 is connected to the second bonding pad 122 in the ceramic base 1 through the second gold wire 72 and to the third bonding pad 123 in the ceramic base 1 through the third gold wire 73.

[0053] The wafer 4 is heated to the operating temperature of 85 °C, and the required heating power is 0.099 W.

[0054] The crystal resonator has a volume of 5 mm × 3.2 mm × 1.1 mm.

[0055] The cover plate 2 is welded to the sealing ring of the ceramic base 1 by parallel seam welding;

[0056] The wafer 4 is fixed on the bonding pad of the ceramic base 1 through conductive adhesive;

[0057] When electrical connection is required on the lower surface of the temperature measuring element 5, the temperature measuring element 5 is fixed on the bonding pad at the bottom of the inner cavity 11 through conductive adhesive; when electrical connection is not required on the lower surface of the temperature measuring element 5, the temperature measuring element 5 is fixed at the bottom of the inner cavity 11 through insulating adhesive; according to the fixing method of the temperature measuring element 5 and whether there is a bonding pad at the bottom of the inner cavity 11 of the ceramic base 1, electrical connection or insulation connection can be achieved on the lower surface of the temperature measuring element 5;

[0058] The lower surface of the heating element 6 is electrically connected to the bonding pad at the bottom of the inner cavity 11 by bonding or welding through conductive adhesive.

[0059] The bonding pads are conductively connected to the bottom bonding pads one by one through the wiring in the ceramic base 1.

[0060] The cover plate 2 is welded to the sealing ring of the ceramic base 1 by parallel seam welding to form a vacuum sealed cavity 3.

[0061] The temperature measuring element 5 is of bare chip type without outer package; the heating element 6 is of bare chip type without outer package.

[0062] The temperature measuring element 5 outputs the actually measured temperature signal to the peripheral circuit; according to the type of the temperature measuring element 5, the peripheral circuit can be an analog circuit or a digital circuit; the peripheral circuit converts the temperature difference between the actual temperature and the set temperature into a control signal to control the power of the heating element 6 to achieve the function of stable temperature control; at the same time, the peripheral circuit has a corresponding oscillation circuit connected to the first lead-out terminal Xtal1 and the second lead-out terminal Xtal2 to generate an oscillation output signal; therefore, the present invention can realize the function of a constant temperature crystal oscillator in cooperation with the peripheral circuit.

[0063] As Figure 1As shown, the ceramic base 1, cover plate 2, and wafer 4 of the present invention are basically the same as those of a traditional surface mount device (SMD) crystal resonator; after the ceramic base 1 and the cover plate 2 are hermetically sealed, a vacuum-sealed cavity 3 is formed, the wafer 4 is inside the vacuum-sealed cavity 3, and the electrodes on the wafer 4 are connected to the lead-out ends of the ceramic base 1 through conductive adhesive; the external shape structure of the present invention is basically the same as that of a traditional SMD crystal resonator, which can maintain the convenience in use; for the ceramic base 1 used in the present invention, according to different internal components, the settings of its internal bonding pads, solder pads, and external lead-out ends will be different, and the height may also be slightly higher than that of the traditional crystal resonator base by 0.1 mm - 0.5 mm.

[0064] The difference between the present invention and the traditional SMD crystal resonator is that the present invention integrally incorporates a temperature measuring element 5 and a heating element 6 inside; the temperature measuring element 5 and the heating element 6 are located below the wafer 4 and are fixed to the bottom of the inner cavity 11 of the ceramic base 1. The lower surface electrodes of the temperature measuring element 5 and the heating element 6 can be connected to the solder pads through bonding or soldering, and the upper surface electrodes are connected to the bonding pads of the ceramic base 1 through bonding.

[0065] Embodiment 1

[0066] As Figure 2 shown, the lower surface electrodes of the temperature measuring element 5 and the heating element 6 are bonded to the solder pads at the bottom of the inner cavity 11 of the ceramic base 1 through conductive adhesive; the upper surface electrodes of the temperature measuring element 5 and the heating element 6 are connected to the bonding pads inside the ceramic base 1 through gold wire bonding technology.

[0067] The results obtained from the simulation analysis of the structure of this embodiment are as Figure 3 shown. The results show that when heating the wafer 4 to the operating temperature of 85 °C, the required heating power is approximately 0.099 W; where the abscissa is the heating power of the heating element 5 and the ordinate is the average temperature of the wafer 4.

[0068] Figure 4 This is the electrical schematic diagram of this embodiment. Crystal represents the crystal resonator composed of the wafer 4 and the electrodes. Xtal1 and Xtal2 are the two lead-out ends of its circuit. The two lead-out ends are connected to the oscillation circuit of an external oscillator to form a basic oscillation output.

[0069] R is the temperature measuring element 5, which is a thermistor. One of its electrodes is connected to GND, and the other electrode is connected to the signal output terminal Sout of the temperature measuring element; the oscillator temperature control circuit can obtain the actual temperature by measuring the resistance value (voltage division) of R and output the corresponding control signal input terminal Sin (voltage) to control the heating power; BJT is the heating element 6, which is a power triode for heating. The corresponding electrodes are respectively connected to the power supply VDD and GND. Its base (b pole) is connected to Sin, and the magnitude of the current is controlled according to the signal fed back by the temperature control circuit to control the heating power.

[0070] Example 2

[0071] The difference between this embodiment and Embodiment 1 lies in that: the heating element 5 is a P-channel field effect transistor, the temperature measuring element 6 is a digital temperature sensor, and the electrical schematic diagram is different.

[0072] Figure 5 The electrical schematic diagram of this embodiment is shown. Crystal represents the resonator formed by the wafer 4 and the electrodes, and Xtal1 and Xtal2 are its circuit leads; MOSFET is the heating element 5, which is a P-channel field effect transistor. Its G pole is connected to Sin, its S pole is connected to VDD, and its D pole is connected to the external load Load; Temp sensor is the temperature measuring element 6, which is a digital temperature sensor. Its power supply and ground electrodes are respectively connected to VDD and GND, and its signal output terminal is connected to Sout.

[0073] The temperature measuring element 6 converts the measured temperature into a digital signal and outputs it through Sout. The logic processing unit in the oscillator temperature control circuit, such as MCU or FPGA, converts the received temperature value into an output value through the built-in temperature control function, and converts it into a voltage control signal Sin through DAC, and outputs it to the heating element 5 to adjust the output power.

[0074] Other parts not described belong to the prior art.

Claims

1. An integrated crystal resonator for a constant temperature crystal oscillator, characterized in that: It includes a ceramic base (1), a cover plate (2), a vacuum-sealed cavity (3) formed by the inner cavity (11) of the ceramic base (1) and the cover plate (2), a wafer (4), a temperature measuring element (5) and a heating element (6) located in the vacuum-sealed cavity (3); The wafer (4) is fixed on the pads of the ceramic base (1) to electrically connect the electrodes on both sides of the wafer (4) with the lead-out ends of the ceramic base (1); The lower surface of the temperature measuring element (5) is fixed to the bottom of the inner cavity (11), and the upper surface electrode is connected to the bonding pad (12) in the ceramic base (1) by bonding; The lower surface of the heating element (6) is electrically connected to the pad at the bottom of the inner cavity (11) and led out to the lead-out end of the ceramic base (1), and the upper surface electrode is connected to the bonding pad (12) in the ceramic base (1) by bonding.

2. The integrated crystal resonator for a constant temperature crystal oscillator according to claim 1, characterized in that: The lead-out ends of the ceramic base (1) at least include the first lead-out end (Xtal1) and the second lead-out end (Xtal2) of the wafer (4) electrode, a power supply (VDD), a ground (GND), a signal output end (Sout) of the temperature measuring element, and a control signal input end (Sin) of the heating element.

3. The integrated crystal resonator for a constant temperature crystal oscillator according to claim 2, characterized in that: The temperature measuring element (5) is a thermistor, a metal thin film resistor or a digital temperature sensor; The heating element (6) is a power triode or a field effect transistor.

4. An integrated crystal resonator for a constant temperature crystal oscillator according to claim 3, characterized in that: When the temperature measuring element (5) is a thermistor and the heating element (6) is a power triode, one electrode of the temperature measuring element (5) is grounded (GND), and one electrode is connected to the signal output end (Sout) of the temperature measuring element; The c electrode of the heating element (6) is grounded (GND), the e electrode is connected to the power supply (VDD), and the b electrode is connected to the control signal input end (Sin) of the heating element.

5. The integrated crystal resonator for a constant temperature crystal oscillator according to claim 3, characterized in that: When the temperature measuring element (5) is a digital temperature sensor and the heating element (6) is a field effect transistor, the power supply electrode of the temperature measuring element (5) is connected to the power supply (VDD), and the ground electrode is connected to the ground (GND); The G electrode of the heating element (6) is connected to the control signal input end (Sin) of the heating element, the S electrode is connected to the power supply (VDD), and the D electrode is connected to an external load (Load).

6. An integrated crystal resonator for a constant temperature crystal oscillator according to claim 1, characterized in that: A groove (111) is provided at the bottom of the inner cavity (11), the temperature measuring element (5) and the heating element (6) are located in the groove (111), and the wafer (4) is located above the temperature measuring element (5) and the heating element (6).

7. An integrated crystal resonator for a constant temperature crystal oscillator according to claim 6, characterized in that: The upper surface electrode of the temperature measuring element (5) is connected to the first bonding pad (121) in the ceramic base (1) through a first gold wire (71); The upper surface electrode of the heating element (6) is connected to the second bonding pad (122) in the ceramic base (1) through a second gold wire (72) and connected to the third bonding pad (123) in the ceramic base (1) through a third gold wire (73).

8. An integrated crystal resonator for a constant temperature crystal oscillator according to claim 4, characterized in that: To heat the wafer (4) to the working temperature of 85 °C, the required heating power is 0.099 W.

9. An integrated crystal resonator for a constant temperature crystal oscillator according to claim 1, characterized in that: The volume of the crystal resonator is 5 mm × 3.2 mm × 1.1 mm.

10. An integrated crystal resonator for a constant temperature crystal oscillator according to claim 1, characterized in that: The cover plate (2) is welded to the sealing ring of the ceramic base (1) by parallel seam welding; The wafer (4) is fixed on the pads of the ceramic base (1) through conductive adhesive; When electrical connection is required for the lower surface of the temperature measuring element (5), the temperature measuring element (5) is fixed on the pad at the bottom of the inner cavity (11) by conductive adhesive; when electrical connection is not required for the lower surface of the temperature measuring element (5), the temperature measuring element (5) is fixed at the bottom of the inner cavity (11) by insulating adhesive. The lower surface of the heating element (6) is electrically connected to the pad at the bottom of the inner cavity (11) by bonding or welding with conductive adhesive.

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