Low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonator and preparation method of low-temperature co-fired ceramic duplexer

Abstract

The invention discloses a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator and a preparation method of the low-temperature co-fired ceramic duplexer. The duplexer prepared by the preparation method comprises a band-pass part and a low-pass part which are sequentially connected in series, one or more bulk acoustic wave resonators are arranged in the band-pass part; the bulk acoustic wave resonator is connected in series with the input end of the band-pass part; the isolation degree between two working areas of the duplexer is improved on the basis of retaining the large bandwidth of the low-temperature co-fired ceramic filter through the bulk acoustic wave resonators cascaded at the band-pass part. According to the preparation of the low-temperature co-fired ceramic duplexer, all bulk acoustic wave resonators in the duplexer are integrated on the same substrate to obtain a first device module; integrating devices except the bulk acoustic wave resonator in the duplexer into the same ceramic body through a low-temperature co-fired ceramic process to obtain a second device module; and cascading the bulk acoustic wave resonator in the first device module and the devices in the second device module to obtain the low-temperature co-fired ceramic duplexer.

Description

Technical Field

[0001] The present invention belongs to the technical field of filter circuits, and particularly relates to a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] A duplexer is a core device for realizing two-way signal transmission in wireless communication. It isolates the transmitted and received signals through two sets of filters with different frequencies, namely a low-pass part and a band-pass part, enabling the transmitter and receiver to share a single antenna and avoiding interference of the transmitted power on the receiving circuit. The duplexer solves the problem of coexistence of transmitted and received signals through precise filtering or timing control and becomes a basic component for the efficient operation of modern wireless communication systems.

[0003] Since the low-temperature co-fired ceramic (LTCC) process can integrate components such as inductors and capacitors in a smaller volume, thus enabling flexible circuit design and greatly reducing the volume of devices or modules, the prior art usually uses a duplexer composed of LTCC filters to achieve low cost. However, due to the low Q value (quality factor) and low self-resonant frequency of LTCC filters, it is difficult for filters under the LTCC process to achieve a large roll-off. The low self-resonant frequency will cause the filter to work on the right side of the self-resonant point when using capacitors and inductors with larger device values, resulting in deteriorated high-frequency characteristics. Moreover, after using more devices, the overall size of the filter will also increase. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator and a preparation method thereof.

[0005] In a first aspect, the present invention provides a preparation method of a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator. The prepared duplexer includes a band-pass part and a low-pass part connected in series in sequence; one or more bulk acoustic wave resonators are provided in the band-pass part; and each bulk acoustic wave resonator is connected in series at the input end of the band-pass part. The preparation method of the low-temperature co-fired ceramic duplexer is as follows: Integrate all the bulk acoustic wave resonators in the duplexer on the same substrate to obtain a first device module; Integrate the devices in the duplexer except the bulk acoustic wave resonators into the same ceramic body through the low-temperature co-fired ceramic process to obtain a second device module; Cascade the bulk acoustic wave resonators in the first device module with the devices in the second device module to obtain the low-temperature co-fired ceramic duplexer.

[0006] Preferably, the devices in the first device module and the second device module are cascaded in the following manner: through holes are formed at all the interfaces on the second device module that need to be connected to the bulk acoustic wave resonators; a plurality of interfaces corresponding one by one to the through holes on the second device module are arranged on the first device module; the first device module is stacked on the second device module, and the through holes on the second device module are respectively aligned with the interfaces on the first device module; traces are used to pass through the through holes on the second device module to respectively connect the corresponding interfaces on the first device module and the second device module.

[0007] Preferably, the devices in the second device module and the first device module are cascaded in the following manner: the first device module and the second device module are soldered on the same PCB substrate; microstrip lines are used on the PCB substrate to respectively connect the corresponding interfaces on the first device module and the second device module.

[0008] Preferably, the devices in the second device module and the first device module are cascaded in the following manner: a plurality of pads are provided on a relative surface of the second device module; during the process of integrating the second device module, two interfaces in the second device module that are connected to the bulk acoustic wave resonator are arranged on two adjacent pads; the first device module is directly soldered to the second device module through the pads to obtain a low-temperature co-fired ceramic duplexer.

[0009] In a second aspect, the present invention provides a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator, including a band-pass part and a low-pass part connected in series in sequence; the band-pass part includes a band-pass main path, a first band-pass branch, and a plurality of second band-pass branches; the band-pass main path includes one or more bulk acoustic wave resonators and one or more LC resonators connected in series between the input end and the output end of the band-pass part; the LC resonator includes an inductor and a capacitive element connected in series; The first band-pass branch is connected to the connection end between the last bulk acoustic wave resonator and the first LC resonator; the first band-pass branch includes one or a plurality of bulk acoustic wave resonators connected in series between the band-pass main path and the ground wire; the second band-pass branches are arranged in pairs at the connection ends of adjacent LC resonators; each second band-pass branch includes an LC resonator connected in series between the band-pass main path and the ground wire.

[0010] Preferably, the low-pass part includes a low-pass main path and one or more low-pass branches; the low-pass main path includes one or more inductors connected in series between the low-pass input end and the low-pass output end; the low-pass branches are connected in series between the low-pass main path and the ground wire; there is an inductor between adjacent low-pass branches; the low-pass branches include capacitive elements; all or part of the capacitive elements are bulk acoustic wave resonators.

[0011] Preferably, part or all of the capacitive elements are bulk acoustic wave resonators.

[0012] Preferably, the film thicknesses of all the bulk acoustic wave resonators in the low-pass part and the band-pass part are different.

[0013] Preferably, the film thickness of the bulk acoustic wave resonator and the circuit parameters of the LC resonator in the second band-pass branch are set according to the required suppression frequency band, so that the resonance peak generated by the bulk acoustic wave resonator moves to a high frequency outside the required suppression frequency band.

[0014] Preferably, the inductance value of the inductor in the low-temperature co-fired ceramic duplexer is less than 6 nH; the capacitance value of the capacitive element in the low-temperature co-fired ceramic duplexer is less than 4 pF.

[0015] The beneficial effects of the present invention are as follows: 1. By cascading bulk acoustic wave resonators in the band-pass part, on the basis of retaining the large bandwidth of the LTCC filter, the left transition band of the band-pass part is reduced to within 150 MHz by utilizing the high roll-off characteristic of the bulk acoustic wave resonator, thereby improving the isolation between the two working regions of the duplexer.

[0016] 2. A bulk acoustic wave resonator is connected in series on the low-pass branch of the low-pass part of the present invention to generate a transmission zero point without affecting the trend of the transmission curve of the original filter, thereby improving the performance of the filter; at the same time, some capacitors with relatively large device values in the low-pass part of the traditional LTCC filter are replaced with bulk acoustic wave resonators, reducing the overall size of the duplexer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the low-pass part of the duplexer in Embodiment 1 of the present invention.

[0018] Figure 2 It is a schematic diagram of the LC low-pass filter in Comparative Example 1 of the present invention.

[0019] Figure 3 It is a comparison diagram of S-parameter simulations between Embodiment 1 and Comparative Example 1 of the present invention.

[0020] Figure 4 It is a schematic diagram of the band-pass part of the duplexer in Embodiment 2 of the present invention.

[0021] Figure 5 It is a schematic diagram of the band-pass part of the LC duplexer in Comparative Example 2 of the present invention.

[0022] Figure 6 It is a comparison diagram of S-parameter simulations between Embodiment 2 and Comparative Example 2 of the present invention.

[0023] Figure 7 It is Figure 6 a partial enlarged schematic diagram.

[0024] Figure 8Schematic diagram of the overall topology of the duplexer in Embodiment 3 of the present invention.

[0025] Figure 9 S-parameter simulation diagram of the overall duplexer in Embodiment 3 of the present invention.

[0026] Figure 10 S-parameter simulation diagram of the low-pass part of the duplexer in Embodiment 3 of the present invention.

[0027] Figure 11 S-parameter simulation diagram of the band-pass part of the duplexer in Embodiment 3 of the present invention.

[0028] Figure 12 Top view schematic diagram of the cascading mode of the duplexer in Embodiment 4 of the present invention.

[0029] Figure 13 Side view schematic diagram of the cascading mode of the duplexer in Embodiment 4 of the present invention.

[0030] Figure 14 Top view schematic diagram of the cascading mode of the duplexer in Embodiment 5 of the present invention.

[0031] Figure 15 Side view schematic diagram of the cascading mode of the duplexer in Embodiment 6 of the present invention. Detailed implementation manners

[0032] The present invention will be further described below with reference to the accompanying drawings.

[0033] Embodiment 1

[0034] As Figure 1 shown, a low-pass filter constituting the low-pass part of a low-temperature co-fired ceramic duplexer includes a low-pass main path and three low-pass branches; the low-pass main path includes inductors L1, L2, and L3 connected in series between the input end and the output end of the filter; the three low-pass branches are respectively arranged at the connection end of inductor L1 and inductor L2, the connection end of inductor L2 and inductor L3, and the connection end of inductor L3 and the output end; the low-pass branch arranged at the connection end of inductor L1 and inductor L2 includes a first bulk acoustic wave resonator 101 (BAW resonator) connected in series between the low-pass main path and the ground wire; the low-pass branch arranged at the connection end of inductor L2 and inductor L3 includes a second bulk acoustic wave resonator 102 connected in series between the low-pass main path and the ground wire; the low-pass branch arranged at the connection end of the output end and inductor L3 includes a third bulk acoustic wave resonator 103 connected in series between the low-pass main path and the ground wire.

[0035] Comparative Example 1 As Figure 2As shown in the figure, an LC low-pass filter includes a series main path and three parallel branches. The series main path includes inductors L1, L2, and L3 connected in series between the input end and the output end of the filter; the three parallel branches are respectively arranged at the connection end of inductor L1 and inductor L2, the connection end of inductor L2 and inductor L3, and the connection end of inductor L3 and the output end; the structures of the three parallel branches are the same, and each includes a capacitor connected in series between the series main path and the ground wire. The difference between this comparative example and Embodiment 1 is that Comparative Example 1 uses a capacitor as a component of the parallel branch.

[0036] The S-parameter simulation comparison diagram between Embodiment 1 and Comparative Example 1 is as Figure 3 shown Figure 3 In the figure, the abscissa is the frequency and the ordinate is the insertion loss. Curve 1 is the frequency response curve of the filter provided by Embodiment 1; Curve 2 is the frequency response curve of the LC low-pass filter provided by Comparative Example 1. In Curve 1, the bulk acoustic wave resonator 101 self-resonates to generate a transmission zero point 201 and a resonance peak on the right side of the transmission zero point; the resonance peak generated by the bulk acoustic wave resonator 101 is suppressed by the self-resonance of the bulk acoustic wave resonator 102 to generate a transmission zero point 202; since the bulk acoustic wave resonator 102 generates a resonance peak on the right side of the transmission zero point 202, the resonance peak generated by the bulk acoustic wave resonator 102 is suppressed by the self-resonance of the bulk acoustic wave resonator 103 to generate a transmission zero point 203. After three bulk acoustic wave resonators are connected in parallel, the resonance peak is shifted to a higher frequency outside the required suppression frequency band, and the out-of-band suppression within the required frequency range meets the requirements. Curve 1 shows good consistency with Curve 2 in the passband, and there is only significant out-of-band suppression at the positions where the bulk acoustic wave resonators generate zero points. At the out-of-band suppression, the resonance peak curve of the bulk acoustic wave resonator is slightly higher than Curve 2, but the overall trend is the same. At the same time, replacing certain capacitor components with bulk acoustic wave resonators can introduce transmission zero points with higher suppression; and because the bulk acoustic wave resonators 101, 102, and 103 have extremely high quality factors, a larger roll-off can be provided for the filter after replacement.

[0037] By using bulk acoustic wave resonators in the parallel branches, the volume of the LTCC low-pass filter is greatly reduced, forming a circuit structure with only three inductors connected in series, which simplifies the original low-pass part of the circuit without affecting its original function. Since the bulk acoustic wave resonator itself has the characteristic of static capacitance, after certain parameter settings make the static capacitance value of the bulk acoustic wave resonator equal to the capacitance value of the replaced capacitor, the bulk acoustic wave resonator can then undertake the role of the capacitor in the LC filter at this time. By replacing all three capacitors with bulk acoustic wave resonators, the original function of this part of the low-pass filter is not affected. Due to the characteristics of the low-temperature co-fired ceramic process, capacitor components will occupy a relatively large space in the design. Therefore, certain capacitor components are replaced with bulk acoustic wave resonators to reduce the size of the low-temperature co-fired ceramic part.

[0038] Embodiment 2

[0039] As Figure 4 shown, a band-pass filter constituting the band-pass part of a low-temperature co-fired ceramic duplexer includes a band-pass main path, a first band-pass branch, and four second band-pass branches. The band-pass main path includes a bulk acoustic wave resonator 104, a bulk acoustic wave resonator 105, and three LC resonators connected in series between an input end and an output end; the three LC resonators each include an inductor and a capacitor connected in series. The first band-pass branch is disposed at the connection end of the bulk acoustic wave resonator and the LC resonator, and includes a bulk acoustic wave resonator 106 and a bulk acoustic wave resonator 107 connected in series between the band-pass main path and a ground wire; the four second band-pass branches are disposed in pairs at the connection ends of adjacent LC resonators, and each includes a capacitor and an inductor connected in series between the band-pass main path and a ground wire.

[0040] Based on the impedance principle, the present invention increases the suppression and steepness of the filter by using bulk acoustic wave resonators with different film thicknesses on the band-pass main path and the band-pass branches respectively. Since replacing the capacitor in the band-pass branch with a bulk acoustic wave resonator will generate a spike, it is applicable to the right sideband. In Embodiment 2, to improve the performance of the left sideband, if the same operation as in Embodiment 1 is performed, spikes and dips will be generated in the passband. Therefore, two bulk acoustic wave resonators need to be connected in series on the main path to play the role of high-impedance open circuit. Since the high-impedance characteristic of the bulk acoustic wave resonator is utilized, the resonance peak generated by the low impedance will appear on the left side of the transmission zero point and will not affect the passband. Then, using the bulk acoustic wave resonator of the first band-pass branch to exert the suppression effect will not affect the passband. At the same time, by adjusting the values of the inductor and capacitor in the second band-pass branch, the out-of-band transmission zero point of the band-pass filter can be changed (increasing the capacitor and inductor shifts the transmission zero point to the left). By adjusting the transmission zero point, the resonance peak is moved to a high frequency outside the required suppression frequency band to obtain an S-parameter curve meeting the index requirements.

[0041] In some embodiments, the capacitor in the band-pass main path is replaced with a bulk acoustic wave resonator.

[0042] Comparative Example 2 As Figure 5 shown, a filter constituting the band-pass part of a duplexer includes a series main path and four parallel branches. The series main path includes three LC resonators connected in series between an input end and an output end; the three LC resonators each include an inductor and a capacitor connected in series. The four parallel branches are disposed in pairs at the connection ends of adjacent LC resonators; the parallel branches disposed at the connection ends of adjacent LC resonators each include a capacitor and an inductor connected in series between the band-pass main path and a ground wire. The difference between this comparative example and Embodiment 2 is that: in Embodiment 2, two bulk acoustic wave resonators are connected in series between the input end and the LC resonator, and two bulk acoustic wave resonators connected in series between the band-pass main path and a ground wire are provided at the connection end of the bulk acoustic wave resonator and the LC resonator.

[0043] S-parameter simulation comparison between Example 2 and Comparative Example 2 is as follows Figure 6 shown Figure 6 In the figure, the abscissa is frequency and the ordinate is insertion loss. Curve 3 is the frequency response curve of the band-pass filter provided by Example 2; Curve 4 is the frequency response curve of the LC band-pass filter provided by Comparative Example 2. The passband is set within 5.15 GHz to 5.85 GHz, and out-of-band rejection is required to reach -25 dB at 5 GHz. By connecting the fourth bulk acoustic wave resonator 104 in series at the input end of the band-pass filter, and using the maximum impedance value at its self-resonance, it acts as an open circuit to the main path, thereby introducing an out-of-band transmission zero 401; after introducing the transmission zero, a resonance peak will be generated again. Therefore, another bulk acoustic wave resonator 105 needs to be connected in series to generate the transmission zero 402; The sixth bulk acoustic wave resonator 106 is connected in parallel at the input end of the band-pass filter, and using the minimum impedance value at its self-resonance, it acts as a short circuit to the main path, thereby introducing an out-of-band transmission zero 403. After introducing the transmission zero, a resonance peak will be generated again. Therefore, another bulk acoustic wave resonator 107 needs to be connected in series to generate the transmission zero 404. At this time, the frequency band to be suppressed already meets the requirements. The transmission zero 404 coincides with the transmission zero 403 because it provides high suppression at 5 GHz to increase the suppression effect provided by the bulk acoustic wave resonator. Therefore, its existence cannot be observed in Curve 3. When modifying the film thickness of the seventh bulk acoustic wave resonator 107, by reducing its film thickness, the transmission zero 404 can be shifted towards higher frequencies, so that the existence of the transmission zero 404 can be observed within the passband.

[0044] As can be seen from Curve 4, it is difficult to meet the requirement of -25 dB out-of-band rejection at 5 GHz. This is because the quality factor of the LC device is relatively low. Therefore, it is difficult to achieve a steep roll-off. While from Curve 3, it can be seen that through the introduction of 4 zeros, the insertion loss at 5 GHz can be suppressed below -25 dB, and at the same time, it can play a certain inhibitory role to some extent on the left side of 5 GHz. At the same time, outside the effective part of the bulk acoustic wave resonator, Curve 3 and Curve 4 have good consistency, and the waveform hardly changes. In Figure 7Among them, the two zeros on the left side of the transmission zero point 401 are the transmission zeros of the band-pass filter itself. The transmission zeros generated by the series resonator and the transmission zeros generated by the bulk acoustic wave resonator are matched and adjusted to obtain the S-parameter curve that meets the index requirements. From the comparison between Curve 3 and Curve 4, it can be seen that the transmission zeros of the band-pass filter itself are at the same frequency. The bulk acoustic wave resonators 104, 105, 106, and 107 only play the role of short-circuiting at low impedance, so as to keep the filter maintaining the original working curve. At high frequencies, due to the introduction of the bulk acoustic wave resonator, the high-frequency impedance is inconsistent with the original, so the insertion loss increases, but the overall waveform remains the same. It can be seen from this that the filter provided in Embodiment 2 has the characteristics of excellent roll-off and no change in the original frequency response curve, and can improve the performance of the filter without changing the original waveform.

[0045] Embodiment 3

[0046] As Figure 8 shown, a low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonators includes a series-connected low-pass part and a band-pass part; the low-pass part uses the low-pass filter in Embodiment 1; the band-pass part uses the band-pass filter in Embodiment 2. The output end of the band-pass part is connected to the input end of the low-pass filter. If the output end of the band-pass part is connected to the output end of the low-pass filter, the bulk acoustic wave resonator 103 in the low-pass filter will generate a low impedance at the resonance point, resulting in a depression of the duplexer at the passband due to the short-circuit caused by the low impedance.

[0047] By replacing the capacitors in the low-pass part with bulk acoustic wave resonators, the volume occupation of the original devices in the low-pass part is saved, and sufficient suppression is provided for the low-pass filter in the frequency band of the band-pass filter. Through the bulk acoustic wave resonators 104, 105, 106, and 107, sufficient out-of-band suppression and roll-off are provided for the band-pass filter at 5 GHz. By suppressing the resonance peaks between the bulk acoustic wave resonators 104, 105, 106, and 107, the band-pass filter reaches -25 dB from 3.3 GHz to 5 GHz. By adjusting the values of the inductance and capacitance in the 4 series resonators, the out-of-band transmission zeros of the band-pass filter can be adjusted (increasing the capacitance and inductance shifts the transmission zeros to the left). The transmission zeros generated by the series resonator and the transmission zeros generated by the bulk acoustic wave resonator are matched and adjusted to obtain the S-parameter curve that meets the index requirements.

[0048] In this embodiment, the device values of the low-temperature co-fired ceramic duplexer are less than 6 nH or 4 pF, avoiding the low self-resonance point caused by too large device values, as well as the increase in the number of turns of the inductor and the increase in the plate area of the capacitor.

[0049] The S-parameter simulation waveforms of Embodiment 3 are as Figure 9 , Figure 10 , Figure 11 shown. Figure 9 In it, the abscissa is the frequency and the ordinate is the insertion loss. Among them, Curve 5 is the insertion loss frequency response curve of the low-pass filter, Curve 6 is the return loss frequency response curve of the low-pass filter, Curve 7 is the insertion loss frequency response curve of the band-pass filter, and Curve 8 is the return loss frequency response curve of the band-pass filter. It can be seen from Figure 9 that the insertion loss of Curve 5 on the passband of 2.4 GHz to 2.5 GHz is only -0.35 dB, while the isolation degree for the frequency band of 5.15 GHz to 5.85 GHz reaches -40 dB. The return loss of Curve 6 on the passband of 2.4 GHz to 2.5 GHz reaches -20 dB, ensuring the low insertion loss of Curve 5. The insertion loss of Curve 7 on the passband of 5.15 GHz to 5.85 GHz is only -2.5 dB, while the isolation degree for the frequency band of 3.3 GHz to 5 GHz reaches -25 dB and the isolation degree for 2.4 GHz to 2.5 GHz reaches -40 dB. The return loss of Curve 8 on the passband of 5.15 GHz to 5.85 GHz reaches -17 dB, ensuring the low insertion loss of Curve 7. Curve 5 proves that by using the cascading method of this bulk acoustic wave resonator and LTCC filter, an out-of-band rejection of -25 dB can be achieved on a transition band of only 150 MHz, providing a relatively high roll-off for the overall filter.

[0050] Embodiment 4

[0051] As Figure 12 and Figure 13 shown, a preparation method of a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator is used to prepare the low-temperature co-fired ceramic duplexer in the above Embodiment 3; the preparation method of the low-temperature co-fired ceramic duplexer includes the following steps: Integrate all the bulk acoustic wave resonators in the duplexer on the same substrate to obtain a first device module; integrate the devices in the duplexer except the bulk acoustic wave resonators into the same ceramic body through the low-temperature co-fired ceramic process to obtain a second device module; open through holes at all the interfaces on the second device module that need to connect the bulk acoustic wave resonators; set a plurality of interfaces on the first device module that correspond one-to-one to the through holes on the second device module; stack the first device module on the second device module, and align each through hole on the second device module with each interface on the first device module respectively. Connect the corresponding interfaces on the first device module and the second device module through traces to obtain the low-temperature co-fired ceramic duplexer.

[0052] The cascading of the first device module and the second device module is completed through shorter vias, reducing the parasitic effect of the traces during cascading. At the same time, the vertical cascading method also saves the overall planar area of the low-temperature co-fired ceramic duplexer. The overall area of the low-temperature co-fired ceramic duplexer is determined by the second device module with a larger volume. Correspondingly, since the first device module is cascaded above the LTCC filter, it will occupy space in the vertical direction. Therefore, when designing the LTCC filter, a thinner layer thickness is used to save vertical space.

[0053] In addition, since the area of the first device module is usually limited to the size of 1109 (i.e., 1.1 mm * 0.9 mm), if each capacitor in each low-temperature co-fired ceramic duplexer is replaced with a bulk acoustic wave resonator, there will be a problem of being difficult to fit into the package. And when replacing, a bonding point with a large area is required at the cascading position, while replacing the capacitors in the band-pass part will generate multiple connection points, thus generating multiple bonding positions. That is, replacing the capacitors in the series main path of the band-pass part with bulk acoustic wave resonators will generate 3 bonding points, resulting in exceeding the package limit. And since the band-pass part has introduced transmission zeros through the bulk acoustic wave resonators in the band-pass series main path and the first parallel branch, the effect achieved after replacing the capacitors in the band-pass part is relatively small.

[0054] Embodiment 5

[0055] As Figure 14 shown, a method for manufacturing a low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonators is used to manufacture the low-temperature co-fired ceramic duplexer in the above Embodiment 3. This method for manufacturing the low-temperature co-fired ceramic duplexer includes the following steps: Integrate all the bulk acoustic wave resonators in the duplexer on the same substrate to obtain the first device module; integrate the devices in the duplexer except the bulk acoustic wave resonators into the same ceramic body through the low-temperature co-fired ceramic process to obtain the second device module; weld the second device module and the first device module composed of the bulk acoustic wave resonators on the same PCB substrate (printed circuit board) respectively; use microstrip lines on the PCB substrate to connect the corresponding interfaces in the first device module and the second device module respectively to obtain the low-temperature co-fired ceramic duplexer.

[0056] Although connecting the second device module and the first device module through microstrip lines will occupy a relatively large area, its advantage is that it is convenient for design, and the setting position of the connection ports is relatively free, without the need to specifically make the cascaded ports vertically aligned when designing the filter, avoiding various limitations in the filter design.

[0057] Embodiment 6

[0058] As Figure 15As shown in the figure, a method for fabricating a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator is used to fabricate the low-temperature co-fired ceramic duplexer in the above-mentioned Embodiment 3; the method for fabricating the low-temperature co-fired ceramic duplexer includes the following steps: Integrate all the bulk acoustic wave resonators in the low-pass part and the high-pass part on different substrates respectively to obtain a first device module; integrate the devices in the duplexer except the bulk acoustic wave resonators into the same ceramic body through the low-temperature co-fired ceramic process to obtain a second device module; there are multiple pads on a relative surface of the second device module; set the two interfaces connected to the bulk acoustic wave resonator in the second device module on two adjacent pads; directly weld the first device module to the second device module through the pads to obtain the low-temperature co-fired ceramic duplexer.

[0059] Since the second device module made by the low-temperature co-fired ceramic process has a relatively large thickness, and when integrating devices using low-temperature co-fired ceramics, setting the connection part with the bulk acoustic wave resonator on the side of the second device module can allow the bulk acoustic wave resonator device to be welded on the pads on the side, so as to achieve direct connection with the port to reduce the loss of the trace and avoid using bonding points.

[0060] Combined with the above embodiments, it can be seen that when designing a filter, cascading a bulk acoustic wave resonator with an LTCC filter can effectively reduce the volume of the filter and greatly improve the performance of the filter, making up for the defects of the LTCC filter with the advantages of the bulk acoustic wave resonator, and improving the roll-off, out-of-band rejection and insertion loss of the filter. And it is not limited to the situations described in the embodiments. The cascading of the two topological structures in Embodiment 1 and Embodiment 2 can also be applied in other circuits: replacing the original capacitor with the static capacitance of the bulk acoustic wave resonator to utilize the high Q value of the bulk acoustic wave resonator; introducing the bulk acoustic wave resonator to construct transmission zeros to meet the requirements of out-of-band rejection and roll-off. Only need to set appropriate parameters of the bulk acoustic wave resonator (film thickness and static capacitance) to match it with the original filter.

Claims

1. A method for preparing a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator, wherein the prepared duplexer comprises a bandpass part and a lowpass part connected in series in sequence; characterized in that: One or more BAW resonators are arranged in the bandpass part; the BAW resonators are connected in series to the input end of the bandpass part; The method for preparing the low temperature co-fired ceramic duplexer comprises: integrating all bulk acoustic wave resonators in the duplexer on the same substrate to obtain a first device module; Integrating the devices except the BAW resonator in the duplexer into the same ceramic body through a low temperature co-fired ceramic process to obtain a second device module; The bulk acoustic wave resonator in the first device module is cascaded with the device in the second device module to obtain a low temperature co-fired ceramic duplexer.

2. The method for preparing a low temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator according to claim 1, characterized in that: The devices in the first device module and the second device module are cascaded as follows: through holes are opened at all interfaces on the second device module that need to be connected to the bulk acoustic wave resonator; multiple interfaces corresponding to the through holes on the second device module are set on the first device module; the first device module is stacked on the second device module, and the through holes on the second device module are aligned with the interfaces on the first device module respectively; and wiring is used to pass through the through holes on the second device module to connect the corresponding interfaces on the first device module and the second device module respectively.

3. The method for preparing a low temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator according to claim 1, characterized in that: The second device module and the devices in the first device module are cascaded in the following manner: the first device module and the second device module are soldered on the same circuit board; and corresponding interfaces on the first device module and the second device module are respectively connected using microstrip lines on the circuit board.

4. The method for preparing a low temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator according to claim 1, characterized in that: The devices in the second device module and the first device module are cascaded in the following manner: a plurality of solder pads are provided on an opposite surface of the second device module; in the process of integrating the second device module, two interfaces in the second device module connected to the bulk acoustic wave resonator are provided on two adjacent solder pads; the first device module is directly soldered to the second device module through the solder pads to obtain a low-temperature co-fired ceramic duplexer.

5. A low temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator, comprising a bandpass part and a lowpass part connected in series in sequence; characterized in that: The bandpass section includes a bandpass trunk, a first bandpass branch, and a plurality of second bandpass branches; the bandpass trunk includes one or more bulk acoustic wave resonators and one or more LC resonators connected in series between the input end and the output end of the bandpass section; the LC resonator includes an inductor and a capacitive element connected in series; The first bandpass branch is connected to the connection end of the BAW resonator and the LC resonator; The first bandpass branch includes one or more bulk acoustic wave resonators connected in series; the second bandpass branches are arranged in pairs at the connection ends of adjacent LC resonators; The second bandpass branches each include an LC resonator.

6. The low temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 5, characterized in that: The low-pass part includes a low-pass main circuit and one or more low-pass branches; the low-pass main circuit includes one or more inductors connected in series between a low-pass input terminal and a low-pass output terminal; the low-pass branches are connected in series between the low-pass main circuit and a ground line; there is an inductor between adjacent low-pass branches; the low-pass branches include capacitive elements; all or part of the capacitive elements use bulk acoustic wave resonators.

7. The low temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 6, characterized in that: Some or all of the capacitive elements use bulk acoustic wave resonators.

8. The low temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 7, characterized in that: The film thicknesses of all BAW resonators in the low-pass section and the band-pass section are different.

9. The low temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 5, characterized in that: The film thickness of the BAW resonator and the circuit parameters of the LC resonator in the second bandpass branch are set according to the desired suppression frequency band, so that the resonance peak generated by the BAW resonator moves to the high frequency outside the desired suppression frequency band.

Images