Dual-frequency constant temperature crystal oscillator and manufacturing method thereof

Abstract

The application discloses a kind of dual-frequency constant temperature crystal oscillator and its manufacturing method, it is related to crystal oscillator technical field, it includes ceramic base and ceramic bottom plate, both are integrally formed using LTCC process;High-frequency quartz crystal and low-frequency quartz crystal are respectively placed in independent sealed cavity, and unified heating and precision temperature control are realized by high-thermal-conductivity diamond copper substrate, metallized heat-conducting hole and partition temperature sensing chip;Two-way signal is output through independent interconnection path, and crosstalk is lower than-50dBm.The application realizes dual-frequency high-stable low-noise output under similar volume, meets the demand of high-integration, high-reliability frequency source for flight control system.

Description

Technical Field

[0001] This invention relates to the field of crystal oscillator technology, and more specifically, to a dual-frequency isothermal crystal oscillator and its manufacturing method. Background Technology

[0002] A crystal oscillator is an electronic component that uses the piezoelectric effect of a quartz crystal to generate a constant, precise frequency signal. When a quartz crystal is subjected to an external electric field, it will produce mechanical vibrations. When an external force is applied to the crystal, causing mechanical deformation, an electric field is also induced inside the crystal. This unique bidirectional coupling effect gives the crystal oscillator highly stable frequency characteristics. Utilizing its stable frequency characteristics, the crystal oscillator, in conjunction with a phase-locked loop (PLL) circuit, can provide a stable clock signal for the system, and therefore has found wide application in the field of communications.

[0003] Based on differences in function and implementation technology, crystal oscillators can be classified into ordinary crystal oscillators, voltage-controlled crystal oscillators (VCOs), temperature-compensated crystal oscillators (TCCOs), and oven-controlled crystal oscillators (OCCs). Ordinary oscillators have a relatively simple structure and lack temperature control or compensation devices; their frequency characteristics primarily depend on the quartz crystal used. VCOs adjust the frequency by controlling the voltage, thereby achieving specific offsets or modulations. Their key feature is that the frequency can be flexibly adjusted according to changes in the external modulation voltage, supporting frequency fine-tuning or phase-locked loop synchronization. Temperature-compensated crystal oscillators are equipped with a temperature compensation system designed to reduce frequency fluctuations caused by temperature changes. Their key technology lies in using a thermistor compensation network to optimize the temperature characteristics of the quartz crystal, thus meeting a wide range of temperature requirements. Oven-controlled crystal oscillators, by strictly controlling the temperature of the quartz crystal, can significantly improve the frequency-temperature characteristics of the crystal oscillator, thereby ensuring stable frequency output. Due to this high stability, oven-controlled crystal oscillators are used in microwave components with high precision requirements, such as frequency sources and harmonic generators.

[0004] As the frequency source for microwave components, the cryogenic crystal oscillator (CSO) is easily affected by changes in external environmental conditions due to the inherent structure and working principle of the quartz crystal device. This leads to variations in the crystal oscillator's output frequency and deterioration of the output signal phase noise, ultimately affecting the normal operation of the microwave component. To improve the performance of CSOs, enabling them to have a wider operating temperature range, better acceleration sensitivity, lower power consumption, and smaller package size, scholars both domestically and internationally have conducted numerous experimental studies and achieved some preliminary research results. Li Peng et al. from Hebei Boway Integrated Circuits studied the impact of heating current on the frequency temperature stability of CSOs and proposed methods such as adding grounding leads and using the temperature change of the varactor tube to compensate for the bias voltage change to eliminate the influence of heating current. Wang Xu from Chengdu Tian'ao analyzed the impact of vibration on the phase noise of the crystal oscillator and designed a 100MHz vibration-resistant cryogenic crystal oscillator using a miniature vibration damper and a low-acceleration-sensitivity crystal resonator, optimizing the phase noise index of the CSO under vibration conditions. Larry et al. analyzed the impact of quartz crystal coating methods on the acceleration sensitivity of cryogenic crystal oscillators (CSOs), proposing to change the vibration mode of the crystal by coating electrodes on its surface, thereby reducing the acceleration sensitivity. Nikonov AG et al. from Morion Corporation in Russia optimized the cryogenic bath structure of a CSO using thermal simulation technology, successfully reducing the temperature gradient in the central temperature control region to less than 1°C. This CSO performed well under temperature shock, and its short-term stability and phase noise were also improved to some extent. However, the above studies all focused on improving the performance indicators of CSOs, without expanding or integrating their applicable frequencies.

[0005] As advanced air combat platforms evolve towards higher stealth, higher maneuverability, and higher situational awareness, flight control systems have evolved from traditional single-function flight attitude control to highly integrated comprehensive management systems. These systems need to directly receive and process information from airborne radar, electro-optical distributed aperture systems, electronic warfare systems, and data links. After integrating engine thrust vectoring nozzle control with aerodynamic surface control, the engine control system sends commands and interconnects with the power, hydraulic, environmental control, and fuel management systems. This multi-mission integrated management requirement has driven the demand for integrating multiple high-precision crystal oscillators into flight control systems. However, existing flight control system control boards still use discrete crystal oscillators for assembly and integration, which cannot meet the miniaturization and integration requirements of flight control systems. Therefore, there is an urgent need to develop an integrated crystal oscillator that integrates multiple quartz crystals into a miniaturized package.

[0006] System-in-package (SiP) is a packaging technology that integrates multiple devices with different functions into a single package using high-density interconnection methods, forming a fully functional microsystem. Due to its advantages in miniaturization, lightweight design, and low power consumption, SiP has been widely used in the manufacture of microwave components. The 29th Research Institute of China Electronics Technology Group Corporation (CETC) designed a four-channel direct-modulation electro-optical conversion component based on optoelectronic hybrid packaging. This component integrates multiple functional chips, realizing the conversion of four channels of radio frequency signals into optical signals. The Xi'an Branch of the China Academy of Space Technology achieved a three-dimensional layout of microwave circuits based on silicon-aluminum materials. The developed amplification, frequency conversion, and filtering packaging module can achieve high-reliability packaging in the L to W bands, with internal module isolation exceeding 70dB. These application examples demonstrate the technical feasibility of using SiP to integrate quartz crystals with different resonant frequencies and achieve signal isolation. Summary of the Invention

[0007] The purpose of this invention is to provide a dual-frequency isothermal crystal oscillator and its manufacturing method, which mainly solves the problems of existing isothermal crystal oscillators in advanced air combat platform flight control systems, such as single function, low integration, large package size, and difficulty in meeting the requirements for synchronous output of multi-frequency reference signals.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A dual-frequency isothermal crystal oscillator includes a ceramic base plate, a ceramic substrate disposed on the ceramic base plate, a high-frequency generating circuit and a low-frequency generating circuit solidified on the upper surface of the ceramic substrate by printing and sintering, an isothermal structure disposed within the ceramic substrate to provide an isothermal environment for the high-frequency generating circuit and the low-frequency generating circuit, and a control unit disposed on the ceramic base plate for controlling the isothermal structure.

[0010] Furthermore, in this invention, the high-frequency generating circuit is composed of a high-frequency quartz crystal and its associated matching inductor, chip capacitor, and adjustment resistor; the low-frequency generating circuit is composed of a low-frequency quartz crystal and its associated matching inductor, chip capacitor, and adjustment resistor; the high-frequency quartz crystal is encapsulated in a high-frequency cavity formed by a high-frequency cavity frame and a high-frequency cavity cover plate enclosed by the upper surface of a ceramic substrate; the low-frequency quartz crystal is encapsulated in another low-frequency cavity formed by a low-frequency cavity frame and a low-frequency cavity cover plate enclosed by the upper surface of a ceramic substrate.

[0011] Furthermore, in this invention, the constant temperature structure includes an embedded recessed cavity inside the ceramic substrate, a diamond copper substrate embedded in the embedded recessed cavity, a heating chip mounted on the upper surface of the diamond copper substrate, a metallized heat-conducting hole penetrating the thickness direction of the ceramic substrate and corresponding to the bottom regions of the high-frequency quartz crystal and the low-frequency quartz crystal, and a metal connecting plate disposed on the upper surface of the ceramic substrate and connected to the upper end of the heat-conducting hole; wherein, the lower end of the metallized heat-conducting hole contacts the upper surface of the diamond copper substrate; the heating chip is connected to the heating connection circuit inside the ceramic substrate through a connecting gold strip.

[0012] Furthermore, in this invention, temperature sensing chips are respectively provided in the high-frequency cavity and the low-frequency cavity, and the temperature sensing chips are attached to the upper surface of the ceramic substrate and adjacent to the corresponding quartz crystal.

[0013] Furthermore, in this invention, the control unit includes a high-frequency connection port for outputting high-frequency quartz crystal signals, which is led out to the ceramic base plate through a high-frequency connection circuit inside the ceramic base and a high-frequency connection circuit inside the ceramic plate; a low-frequency connection port for outputting low-frequency quartz crystal signals, which is led out to the ceramic base plate through a low-frequency connection circuit inside the ceramic base and a low-frequency connection circuit inside the ceramic plate; a heating connection port for receiving output signals from a temperature sensing chip, which is led out to the ceramic base plate through a temperature control connection circuit inside the ceramic base and a temperature control connection circuit inside the ceramic plate.

[0014] Furthermore, in this invention, the high-frequency connection port, low-frequency connection port, heating connection port and temperature control connection port are all located on the side wall of the ceramic base plate, and each port adopts a side wall metallized hole structure.

[0015] This invention also provides a method for manufacturing a dual-frequency thermostatic crystal oscillator, which includes the following steps:

[0016] S1: Metallized holes are prepared on the sidewalls of LTCC green ceramic sheets using mechanical punching and extrusion filling processes to form high-frequency connection ports, low-frequency connection ports, heating connection ports and temperature control connection ports.

[0017] S2: Different melting point solders are used sequentially for multi-temperature zone assembly to complete the assembly of the ceramic base and the ceramic plate;

[0018] S3: Using a gold strip bonding device, one end of the gold strip is bonded to the electrode of the heating chip, and the other end is bonded to the pad of the heating connection circuit inside the ceramic substrate, so as to realize the electrical connection between the heating chip and the internal circuit.

[0019] S4: Manually spot solder the assembled ceramic base to the pads on the ceramic substrate using tin-silver-copper solder, and connect the external test circuit for frequency tuning;

[0020] S5: Laser sealing process is used to weld and seal the high-frequency cavity cover plate to the high-frequency cavity frame, and at the same time, the low-frequency cavity cover plate is welded and sealed to the low-frequency cavity frame to form two independent sealed cavities.

[0021] S6: Finally, apply tin-silver-copper solder to the welding area at the edge of the ceramic base plate, and weld and fix the ceramic tube shell through a constant temperature heating table to complete the fully sealed encapsulation.

[0022] Further, the specific steps of S1 are as follows: First, through holes are formed on the green ceramic sheet by mechanical punching. Then, metal paste is densely filled into the holes by extrusion filling to avoid metal loss at the edge of the holes due to the rebound of the steel mesh after printing filling. After filling, the green ceramic sheet is dried in an oven at 70°C for 1 hour and then left to stand for 24 hours to allow the metal paste to fully solidify. Then, multiple layers of green ceramic sheets are stacked and laminated to form a green ceramic block, and half-cut along the diameter direction of the metallized holes to remove excess metal paste from the holes. Finally, the green ceramic block is sintered in a nitrogen-hydrogen mixed atmosphere to form a ceramic base and a ceramic bottom plate, and the integrated manufacturing of internal heat conduction holes, multi-layer interconnection circuits, thick film adjustment resistors and side wall connection ports is completed simultaneously.

[0023] Furthermore, the specific steps of S2 are as follows: First, use Au 80 Sn 20 In a vacuum eutectic soldering machine, the high-frequency cavity frame and the low-frequency cavity frame are soldered to designated positions on the upper surface of the ceramic substrate, and the heating chip is soldered to the upper surface of the diamond copper substrate. Then, using Sn-10Sb solder, the temperature sensing chip, matching inductor, and chip capacitor are mounted to the corresponding pads on the upper surface of the ceramic substrate on a constant temperature heating stage. Next, high-temperature resistant conductive silver paste is applied to the mounting positions of the high-frequency and low-frequency quartz crystals. After placing the quartz crystals, they are cured in an oven at 110°C for 2 hours to complete the crystal mounting. At the same time, the diamond copper substrate with the heating chip is mounted into the embedded recessed cavity inside the ceramic substrate using conductive silver paste and cured at 110°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) This invention integrates high-frequency quartz crystal and low-frequency quartz crystal into the same ceramic package through system-in-package (SiP) technology, replacing multiple crystal oscillators assembled separately in the traditional flight control system. It can output high-stability dual-frequency signals simultaneously in a compact volume of 20mm×20mm×8mm, effectively solving the problems of low integration and large space occupation of existing discrete crystal oscillators, and adapting to the development trend of miniaturization and high integration of advanced flight control systems.

[0026] (2) The present invention adopts a constant temperature structure of high thermal conductivity diamond copper substrate, metallized thermal holes combined with partitioned temperature sensing chip to achieve unified heating and independent precise temperature control of high frequency and low frequency crystals, and stabilizes the crystal working temperature at 75℃±0.5℃; at the same time, through independent sealed cavity and electromagnetic shielding design, the crosstalk of the two output signals is lower than -50dBm, which significantly improves the frequency stability and signal purity of the crystal oscillator and meets the stringent requirements of flight control system for high precision frequency source.

[0027] (3) The ceramic base and ceramic base plate of the present invention are integrally formed by LTCC process, and the internal heat conduction holes, multi-layer interconnect circuits and thick film resistors are manufactured simultaneously. Combined with multi-temperature zone orderly assembly and laser sealing and fully sealed packaging process, the number of soldering points of discrete components is greatly reduced, and the vibration resistance and long-term working reliability of crystal oscillator are improved. The standardized manufacturing process is also more conducive to mass production, reducing the integration cost and maintenance difficulty of flight control system. Attached Figure Description

[0028] Figure 1 This is a three-dimensional schematic diagram of the dual-frequency isothermal crystal oscillator of the present invention;

[0029] Figure 2 This is a three-dimensional schematic diagram of the dual-frequency isothermal crystal oscillator of the present invention without the ceramic tube shell;

[0030] Figure 3 This is a top-view three-dimensional schematic diagram of the dual-frequency isothermal crystal oscillator of the present invention without the ceramic tube shell;

[0031] Figure 4 This is a perspective view of the ceramic base of the present invention;

[0032] Figure 5 This is a perspective view of the ceramic base plate of the present invention;

[0033] Figure 6 This is a bottom view of the present invention after the ceramic tube shell and ceramic base plate have been removed;

[0034] Figure 7 This is a schematic diagram illustrating the manufacturing process of the ceramic base plate temperature control connection port of the present invention;

[0035] Figure 8 This is a schematic diagram of the assembly and fabrication process of the dual-frequency isothermal crystal oscillator of the present invention;

[0036] Figure 9 This is a spectrum test result diagram of the low-frequency output interface (10MHz) of the present invention;

[0037] Figure 10 This is a spectrum test result diagram of the high-frequency output interface (50MHz) of the present invention.

[0038] The names corresponding to the reference numerals in the attached figures are as follows:

[0039] 1. High-frequency quartz crystal; 2. Low-frequency quartz crystal; 3. Ceramic base; 31. High-frequency connection circuit inside the ceramic base; 32. Low-frequency connection circuit inside the ceramic base; 36. Heating connection circuit inside the ceramic base; 39. Temperature control connection circuit inside the ceramic base; 4. Ceramic base plate; 41. High-frequency connection circuit inside the ceramic base plate; 42. Low-frequency connection circuit inside the ceramic base plate; 43. Solder pad; 46. Heating connection circuit inside the ceramic base plate; 48. Soldering block; 49. Inside the ceramic base plate Temperature control connection circuit; 401, high-frequency connection port; 402, low-frequency connection port; 406, heating connection port; 409, temperature control connection port; 5, diamond copper substrate; 6, heating chip; 7, connecting gold strip; 8, ceramic tube shell; 9, temperature sensing chip; 10, matching inductor; 11, chip capacitor; 12, adjusting resistor; 13, high-frequency cavity cover plate; 14, high-frequency cavity frame; 15, low-frequency cavity cover plate; 16, low-frequency cavity frame; 17, heat conduction hole; 18, metal connecting plate. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0041] This invention discloses a dual-frequency isothermal crystal oscillator and its fabrication method, using the output of a 10MHz low-frequency signal and a 50MHz high-frequency signal as an example for detailed explanation. The crystal oscillator adopts a system-in-package (SiP) structure, with a ceramic substrate 3, a ceramic base plate 4, and a ceramic housing 8 forming the main hermetically sealed package structure. Internally, it integrates key components such as a high-frequency quartz crystal 1, a low-frequency quartz crystal 2, a heating chip 6, a temperature sensing chip 9, a matching inductor 10, a chip capacitor 11, and an adjustment resistor 12. Electrical connection and thermal management functions are achieved through multi-level interconnection circuits. Figures 1-3 As shown, the entire crystal oscillator has a cubic configuration with typical dimensions of 20mm×20mm×8mm. Its top is provided with a high-frequency cavity cover plate 13 and a low-frequency cavity cover plate 15, which respectively cover the high-frequency cavity frame 14 and the low-frequency cavity frame 16, forming two mutually isolated sealed cavities. The ceramic tube shell 8 surrounds the entire structure and is sealed to the ceramic base plate 4 through the welding block 48 to ensure the long-term airtightness of the internal environment.

[0042] like Figure 4As shown, the ceramic base 3 is manufactured using a low-temperature co-fired ceramic (LTCC) process. It contains densely arranged metallized heat-conducting holes 17 embedded within it. These holes 17 are located directly below the mounting areas of the high-frequency quartz crystal 1 and the low-frequency quartz crystal 2, extending through the thickness of the ceramic base 3. The hole walls are filled with silver or copper paste and sintered to form a continuous heat-conducting path. The upper ends of the heat-conducting holes 17 are connected to a metal connecting pad 18 on the upper surface of the ceramic base 3, and the lower ends are in contact with a diamond copper substrate 5 embedded in a recessed cavity. An adjustment resistor 12 and connecting lines (not shown) are also printed and sintered on the upper surface of the ceramic base 3 to form two independent frequency generating circuits. The high-frequency quartz crystal 1, the low-frequency quartz crystal 2, the matching inductor 10, and the chip capacitor 11 are all mounted on designated pad positions on the upper surface of the ceramic base 3. The high-frequency quartz crystal 1 is located within the area enclosed by the high-frequency cavity frame 14, and the low-frequency quartz crystal 2 is located within the area enclosed by the low-frequency cavity frame 16. The ceramic base 3 is also equipped with a high-frequency connection circuit 31, a low-frequency connection circuit 32, a heating connection circuit 36, and a temperature control connection circuit 39, which are used to lead out the signals of each functional module to the side wall.

[0043] For example Figure 5 As shown, the ceramic base plate 4 is also manufactured using the LTCC process. Internally, it houses a high-frequency connection circuit 41, a low-frequency connection circuit 42, a heating connection circuit 46, and a temperature control connection circuit 49. These circuits are vertically interconnected with their corresponding circuits in the ceramic base 3 during the stacking process. The ceramic base plate 4 has four connection ports on its sidewall: a high-frequency connection port 401, a low-frequency connection port 402, a heating connection port 406, and a temperature control connection port 409. These ports are formed by metallized holes in the sidewall, filled with metal paste, which, after sintering, forms a continuous conductive path for soldering interconnection with the microwave component motherboard. Furthermore, the upper surface of the ceramic base plate 4 has solder pads 43 for fixing the ceramic base 3, and the edge has solder blocks 48 for sealing the ceramic tube shell 8.

[0044] like Figure 6 As shown, after removing the ceramic tube shell 8 and the ceramic base plate 4, the layout of the various connection circuit outlets and pads at the bottom of the ceramic base 3 can be clearly seen. The high-frequency connection circuit 31 and the low-frequency connection circuit 32 inside the ceramic base are led out from both sides, while the heating connection circuit 36 ​​and the temperature control connection circuit 39 inside the ceramic base are distributed on the other two sides to avoid signal crosstalk. Simultaneously, the diamond copper substrate 5 is embedded in the recessed cavity below the center of the ceramic base 3. Its upper surface supports the heating chip 6, and its lower surface is tightly fitted to the inner wall of the ceramic base 3 to maximize heat conduction efficiency.

[0045] like Figure 7As shown, the manufacturing process of the temperature control connection port 409 includes the following steps: First, through holes are formed on the green ceramic sheet using mechanical punching to avoid the ablation of the hole walls caused by laser drilling, which would affect the metal adhesion; then, a high-conductivity metal paste is densely filled into the holes using an extrusion filling process to prevent metal loss at the hole edges due to the rebound of the steel mesh during printing filling; after filling, the green ceramic sheet is dried in a 70°C oven for 1 hour to allow the paste to surface dry, and then left to stand for 24 hours to fully cure; then, multiple layers of green ceramic sheets are stacked and laminated into a green ceramic block, and half of the hole is cut off along the diameter direction of the metallized hole using a hot cutting machine, and excess paste in the hole is manually scraped off; finally, high-temperature sintering is carried out in a nitrogen-hydrogen mixed atmosphere to firmly adhere the metal to the hole wall, forming a side-wall metallized connection port. This process simultaneously completes the integrated manufacturing of the heat-conducting hole 17, the internal interconnection circuit, and the adjusting resistor 12.

[0046] like Figure 8 As shown, the assembly and fabrication process of the dual-frequency isothermal crystal oscillator is carried out sequentially according to the multi-temperature zone sequence: First, using vacuum eutectic welding equipment, Au80Sn20 eutectic solder (melting point 280℃) is used to precisely weld the high-frequency cavity frame 14 and the low-frequency cavity frame 16 to the designated positions on the upper surface of the ceramic substrate 3, and the heating chip 6 is welded to the center of the diamond copper substrate 5; then, on the isothermal heating stage, Sn-10Sb solder (melting point 245℃) is used to mount the temperature sensing chip 9, matching inductor 10, and chip capacitor 11 to the corresponding pads on the upper surface of the ceramic substrate 3; next, high-temperature resistant conductive silver paste is applied to the mounting positions of the high-frequency quartz crystal 1 and the low-frequency quartz crystal 2, and after placing the crystals, they are cured in a 110℃ oven for 2 hours to complete the crystal mounting; at the same time, the diamond copper substrate 5 with the heating chip 6 is mounted in the embedded recessed cavity inside the ceramic substrate 3 using conductive silver paste and cured under the same conditions; then, gold strip bonding is used to... One end of the gold strip 7 is bonded to the electrode of the heating chip 6, and the other end is bonded to the pad of the heating connection circuit 36 ​​inside the ceramic substrate to achieve electrical connection. Then, the assembled ceramic substrate 3 is manually spot-welded to the pad 43 on the ceramic base plate 4 using Sn-3.0Ag-0.5Cu solder (melting point 217℃), and connected to an external test circuit for frequency debugging. If the output frequency deviates from the design value, the adjusting resistor 12 is adjusted using a laser trimming device, or the matching inductor 10 and chip capacitor 11 are replaced to meet the accuracy requirements. After debugging, the high-frequency cavity cover plate 13 and the high-frequency cavity frame 14, and the low-frequency cavity cover plate 15 and the low-frequency cavity frame 16 are welded and sealed using a laser sealing process to form two independent sealed cavities. Finally, Sn-3.0Ag-0.5Cu solder is applied to the welding block 48 on the edge of the ceramic base plate 4, and the ceramic tube shell 8 is welded and fixed using a constant temperature heating table to complete the fully sealed encapsulation.

[0047] In actual operation, the microwave component motherboard provides bias voltage to the high-frequency quartz crystal 1 and receives a 50MHz output signal through the high-frequency connection port 401, and provides bias voltage to the low-frequency quartz crystal 2 and receives a 10MHz output signal through the low-frequency connection port 402. Simultaneously, the motherboard supplies power to the heating chip 6 through the heating connection port 406. The heat generated by the heating chip 6 is laterally diffused through the diamond copper substrate 5 and then rapidly conducted to the bottom surfaces of the high-frequency quartz crystal 1 and the low-frequency quartz crystal 2 through the heat-conducting holes 17 and the metal connecting plate 18, maintaining them at a set constant temperature (typically 75℃±0.5℃). The temperature sensing chips 9 in the two cavities monitor the temperature of their respective crystals in real time and feed the temperature signal back to the motherboard through the ceramic base plate temperature control connection port 409. The motherboard adjusts the heating power accordingly to achieve zoned closed-loop temperature control. Because the high-frequency and low-frequency cavities are physically isolated and the frame and cover have electromagnetic shielding functions, crosstalk between the two signals is effectively suppressed. Figure 9 and Figure 10 As shown, the spurious signal measured at the 10MHz output terminal at 50MHz is below -50dBm, and the spurious signal measured at the 50MHz output terminal at 10MHz is also below -50dBm, verifying the effectiveness of the signal isolation. Experiments show that this crystal oscillator exhibits better stability at 10MHz output frequency than [previous standard] within an operating temperature range of -55℃ to +85℃. The 50MHz output has a phase noise better than -150dBc / Hz at a 1kHz offset, which fully meets the application requirements of advanced air combat platform flight control systems for a high-stability, low-phase-noise, and highly integrated dual-frequency reference source.

[0048] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A dual-frequency isothermal crystal oscillator, characterized in that, The ceramic base plate (4), the ceramic base (3) set on the ceramic base plate (4), the high frequency generation circuit and the low frequency generation circuit solidified on the upper surface of the ceramic base (3) by printing and sintering, the constant temperature structure set in the ceramic base (3) to provide a constant temperature environment for the high frequency generation circuit and the low frequency generation circuit, and the control unit set on the ceramic base plate (4) for controlling the constant temperature structure; The high-frequency generating circuit consists of a high-frequency quartz crystal (1) and its associated matching inductor (10), chip capacitor (11), and adjustment resistor (12); the low-frequency generating circuit consists of a low-frequency quartz crystal (2) and its associated matching inductor (10), chip capacitor (11), and adjustment resistor (12); the high-frequency quartz crystal (1) is encapsulated in a high-frequency cavity formed by a high-frequency cavity frame (14) and a high-frequency cavity cover plate (13) encapsulated in the upper surface of a ceramic base (3); the low-frequency quartz crystal (2) is encapsulated in another low-frequency cavity formed by a low-frequency cavity frame (16) and a low-frequency cavity cover plate (15) encapsulated in the upper surface of a ceramic base (3); The constant temperature structure includes an embedded recessed cavity inside the ceramic base (3), a diamond copper substrate (5) embedded in the embedded recessed cavity, a heating chip (6) attached to the upper surface of the diamond copper substrate (5), a metallized heat-conducting hole (17) penetrating the thickness direction of the ceramic base (3) and corresponding to the bottom regions of the high-frequency quartz crystal (1) and the low-frequency quartz crystal (2), and a metal connecting plate (18) disposed on the upper surface of the ceramic base (3) and connected to the upper end of the heat-conducting hole (17); wherein, the lower end of the metallized heat-conducting hole (17) contacts the upper surface of the diamond copper substrate (5); the heating chip (6) is connected to the heating connection circuit (36) inside the ceramic base through a connecting gold strip (7).

2. The dual-frequency isothermal crystal oscillator according to claim 1, characterized in that, Temperature sensing chips (9) are respectively provided in the high-frequency cavity and the low-frequency cavity. The temperature sensing chips (9) are attached to the upper surface of the ceramic base (3) and adjacent to the corresponding quartz crystal.

3. A dual-frequency isothermal crystal oscillator according to claim 2, characterized in that, The control unit includes a high-frequency connection port (401) for output signals from a high-frequency quartz crystal (1) that is led out from the ceramic base through a high-frequency connection circuit (31) inside the ceramic base and a high-frequency connection circuit (41) inside the ceramic base; a low-frequency connection port (402) for output signals from a low-frequency quartz crystal (2) that is led out from the ceramic base through a low-frequency connection circuit (32) inside the ceramic base and a low-frequency connection circuit (42) inside the ceramic base; a heating connection port (406) for output signals from a ceramic base through a heating connection circuit (46) inside the ceramic base and a heating connection circuit (36) inside the ceramic base; and a temperature control connection port (409) for receiving output signals from a temperature sensing chip (9) that is led out from the ceramic base through a temperature control connection circuit (39) inside the ceramic base and a temperature control connection circuit (49) inside the ceramic base.

4. A dual-frequency isothermal crystal oscillator according to claim 3, characterized in that, The high-frequency connection port (401), low-frequency connection port (402), heating connection port (406) and temperature control connection port (409) are all located on the side wall of the ceramic base plate (4), and each port adopts a side wall metallized hole structure.

5. A method for fabricating a dual-frequency isothermal crystal oscillator, characterized in that, To manufacture a dual-frequency isothermal crystal oscillator as described in claim 4, the following steps are included: S1: Metallized holes on the sidewalls are prepared in LTCC green ceramic sheets by mechanical punching and extrusion filling process to form high frequency connection port (401), low frequency connection port (402), heating connection port (406) and temperature control connection port (409). S2: Use solders with different melting points to assemble in multiple temperature zones in sequence to complete the assembly of the ceramic base (3) and the ceramic base plate (4); S3: By using a gold strip bonding device, one end of the gold strip (7) is bonded to the electrode of the heating chip (6), and the other end is bonded to the pad of the heating connection circuit (36) inside the ceramic substrate, so as to realize the electrical connection between the heating chip (6) and the internal circuit. S4: The assembled ceramic base (3) is manually spot-welded to the pads (43) on the ceramic base plate (4) using tin-silver-copper solder, and then connected to an external test circuit for frequency tuning; S5: The high-frequency cavity cover plate (13) and the high-frequency cavity frame (14) are welded and sealed using laser sealing process, and the low-frequency cavity cover plate (15) and the low-frequency cavity frame (16) are welded and sealed to form two independent sealed cavities. S6: Finally, apply tin-silver-copper solder to the welding block (48) at the edge of the ceramic base plate (4), and weld and fix the ceramic tube shell (8) through the constant temperature heating table to complete the full sealing encapsulation.

6. The method for manufacturing a dual-frequency isothermal crystal oscillator according to claim 5, characterized in that, The specific steps of S1 are as follows: First, through holes are formed on the green ceramic sheet by mechanical punching. Then, the metal paste is densely filled into the holes by extrusion filling method to avoid the metal loss at the edge of the hole due to the rebound of the steel mesh after printing filling. After filling, the green ceramic sheet is dried in an oven at 70°C for 1 hour and then left to stand for 24 hours to allow the metal paste to completely solidify. Then, multiple layers of green ceramic sheets are stacked and laminated to form a green ceramic block, and half-cut along the diameter direction of the metallized hole to remove excess metal paste in the hole. Finally, the green ceramic block is sintered in a nitrogen-hydrogen mixed atmosphere to form a ceramic base (3) and a ceramic base plate (4), and the integrated manufacturing of the internal heat conduction hole (17), multi-layer interconnection circuit, thick film adjustment resistor (12) and side wall connection port is completed simultaneously.

7. The method for manufacturing a dual-frequency isothermal crystal oscillator according to claim 6, characterized in that, The specific steps of S2 are as follows: First use Au 80 Sn 20 In a vacuum eutectic welding equipment, the high-frequency cavity frame (14) and the low-frequency cavity frame (16) are welded to the designated positions on the upper surface of the ceramic substrate (3) with eutectic solder, and the heating chip (6) is welded to the upper surface of the diamond copper substrate (5). Then, the temperature sensing chip (9), the matching inductor (10) and the chip capacitor (11) are mounted on the corresponding pads on the upper surface of the ceramic substrate (3) using Sn-10Sb solder on a constant temperature heating stage. Next, high-temperature resistant conductive silver paste is applied to the mounting positions of the high-frequency quartz crystal (1) and the low-frequency quartz crystal (2), and after the quartz crystal is placed, it is cured in an oven at 110°C for 2 hours to complete the crystal mounting. At the same time, the diamond copper substrate (5) with the heating chip (6) is mounted in the embedded recessed cavity inside the ceramic substrate (3) with conductive silver paste and cured at 110°C.

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