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

Abstract

The present invention discloses a low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonators and a method for preparing the same. The duplexer prepared by the preparation method comprises a bandpass portion and a low-pass portion connected in series; one or more bulk acoustic wave resonators are provided in the bandpass portion; the bulk acoustic wave resonators are connected in series to the input end of the bandpass portion; the bulk acoustic wave resonators cascaded in the bandpass portion improve the isolation between the two working areas of the duplexer while retaining the large bandwidth of the low-temperature co-fired ceramic filter. The low-temperature co-fired ceramic duplexer is prepared by integrating all bulk acoustic wave resonators in the duplexer on a common substrate to obtain a first device module; integrating the components of the duplexer other than the bulk acoustic wave resonators into a common ceramic body using a low-temperature co-fired ceramic process to obtain a second device module; and cascading the bulk acoustic wave resonators in the first device module with the components 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 in particular 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 component for bidirectional signal transmission in wireless communications. It isolates transmit and receive signals through two sets of filters—a low-pass filter and a bandpass filter—at different frequencies. This allows transmission and reception to share a single antenna, preventing transmit power from interfering with the receiving circuit. Through precise filtering or timing control, duplexers address the coexistence challenges of transmit and receive signals, becoming a fundamental component for the efficient operation of modern wireless communication systems.

[0003] Because the low-temperature co-fired ceramic (LTCC) process can integrate components such as inductors and capacitors in a relatively small volume, allowing for flexible circuit design and significantly reducing the size of devices or modules, existing technologies typically use duplexers constructed from LTCC filters to achieve low costs. However, due to the low Q factor (quality factor) and low self-resonant frequency of LTCC filters, filters using the LTCC process struggle to achieve a significant roll-off. This low self-resonant frequency causes the filter to operate to the right of the self-resonant point when using larger capacitor and inductor values, resulting in poor high-frequency characteristics. Furthermore, the use of more components increases the overall size of the filter. Summary of the Invention

[0004] The object 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 method for preparing a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator. The prepared duplexer includes a bandpass portion and a low-pass portion connected in series; one or more bulk acoustic wave resonators are provided in the bandpass portion; the individual acoustic wave resonators are connected in series to the input end of the bandpass portion;

[0006] The low-temperature co-fired ceramic duplexer preparation method comprises the following steps: integrating all bulk acoustic wave resonators in the duplexer on a common substrate to obtain a first device module; integrating the devices in the duplexer except the bulk acoustic wave resonators into a common ceramic body through a low-temperature co-fired ceramic process to obtain a second device module; and cascading the bulk acoustic wave resonators in the first device module with the devices in the second device module to obtain a low-temperature co-fired ceramic duplexer.

[0007] Preferably, 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; 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.

[0008] Preferably, the devices in the second device module and the first device module are cascaded as follows: the first device module and the second device module are soldered on the same PCB substrate; and microstrip lines are used on the PCB substrate to connect the corresponding interfaces on the first device module and the second device module respectively.

[0009] Preferably, the devices in the second device module and the first device module are cascaded as follows: multiple pads are provided on an opposite surface of the second device module; during the integration of the second device module, two interfaces in the second device module connected to the bulk acoustic wave resonator are provided on two adjacent pads; the first device module is directly welded to the second device module through the pads to obtain a low-temperature co-fired ceramic duplexer.

[0010] In a second aspect, the present invention provides a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator, comprising a bandpass portion and a lowpass portion connected in series; the bandpass portion comprises a bandpass trunk, a first bandpass branch, and a plurality of second bandpass branches; the bandpass trunk comprises one or more bulk acoustic wave resonators and one or more LC resonators connected in series between an input end and an output end of the bandpass portion; the LC resonator comprises an inductive and a capacitive element connected in series;

[0011] The first bandpass branch is connected to the connection end of the last bulk acoustic wave resonator and the first LC resonator; the first bandpass branch includes one or more bulk acoustic wave resonators connected in series between the bandpass trunk and the ground line; 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 connected in series between the bandpass trunk and the ground line.

[0012] Preferably, 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 the low-pass input terminal and the low-pass output terminal; the low-pass branches are connected in series between the low-pass main circuit and the 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.

[0013] Preferably, part or all of the capacitive elements are bulk acoustic wave resonators.

[0014] Preferably, the film thicknesses of all BAW resonators in the low-pass part and the band-pass part are different.

[0015] Preferably, 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 a high frequency outside the desired suppression frequency band.

[0016] Preferably, the inductance of the inductor in the low-temperature co-fired ceramic duplexer is less than 6 nH; the capacitance of the capacitive element in the low-temperature co-fired ceramic duplexer is less than 4 pF.

[0017] The present invention has the following beneficial effects:

[0018] 1. The present invention reduces the left transition band of the bandpass portion to within 150 MHz by cascading BAW resonators in the bandpass portion while retaining the large bandwidth of the LTCC filter and utilizing the high roll-off characteristic of the BAW resonator, thereby improving the isolation between the two working areas of the duplexer.

[0019] 2. The present invention connects a bulk acoustic wave resonator in series on the low-pass branch of the low-pass part, thereby generating a transmission zero without affecting the transmission curve trend of the original filter, thereby improving the performance of the filter; at the same time, some capacitors with larger device values in the low-pass part of the traditional LTCC filter are replaced with bulk acoustic wave resonators, thereby reducing the overall size of the duplexer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the low-pass part of the duplexer in Example 1 of the present invention.

[0021] Figure 2 Schematic diagram of the LC low-pass filter in Comparative Example 1 of the present invention.

[0022] Figure 3 3 is a comparison diagram of S parameter simulations of Example 1 of the present invention and Comparative Example 1.

[0023] Figure 4 Schematic diagram of the bandpass portion of the duplexer in Example 2 of the present invention.

[0024] Figure 5 Schematic diagram of the bandpass portion of the LC duplexer in Comparative Example 2 of the present invention.

[0025] Figure 6 2 is a comparison diagram of S parameter simulations of Example 2 of the present invention and Comparative Example 2.

[0026] Figure 7 for Figure 6 A partial enlarged schematic diagram.

[0027] Figure 8 Schematic diagram of the overall topology of the duplexer in Example 3 of the present invention.

[0028] Figure 9 This is a simulation diagram of the overall S parameters of the duplexer in Example 3 of the present invention.

[0029] Figure 10 This is a simulation diagram of the S parameters of the low-pass part of the duplexer in Example 3 of the present invention.

[0030] Figure 11 This is a simulation diagram of the S parameters of the bandpass part of the duplexer in Example 3 of the present invention.

[0031] Figure 12 Schematic top view of the duplexer cascade method in Example 4 of the present invention.

[0032] Figure 13 Schematic side view of the duplexer cascade mode in embodiment 4 of the present invention.

[0033] Figure 14 Schematic top view of the duplexer cascade mode in embodiment 5 of the present invention.

[0034] Figure 15 Schematic side view of the duplexer cascade method in Example 6 of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] Example 1

[0037] like Figure 1 As shown, a low-pass filter constituting the low-pass portion of a low-temperature co-fired ceramic duplexer includes a low-pass main circuit and three low-pass branches; the low-pass main circuit includes an inductor L1, an inductor L2, and an inductor L3 connected in series between the filter input and output terminals; the three low-pass branches are respectively arranged at the connection terminal between the inductor L1 and the inductor L2, the connection terminal between the inductor L2 and the inductor L3, and the connection terminal between the inductor L3 and the output terminal; the low-pass branch arranged at the connection terminal between the inductor L1 and the inductor L2 includes a first bulk acoustic wave resonator 101 (BAW resonator) connected in series between the low-pass main circuit and a ground line; the low-pass branch arranged at the connection terminal between the inductor L2 and the inductor L3 includes a second bulk acoustic wave resonator 102 connected in series between the low-pass main circuit and the ground line; and the low-pass branch arranged at the connection terminal between the output terminal and the inductor L3 includes a third bulk acoustic wave resonator 103 connected in series between the low-pass main circuit and the ground line.

[0038] Comparative Example 1

[0039] like Figure 2As shown, an LC low-pass filter includes a series main circuit and three parallel branches. The series main circuit includes inductors L1, L2, and L3 connected in series between the filter input and output terminals. The three parallel branches are respectively provided at the connection between inductors L1 and L2, the connection between inductors L2 and L3, and the connection between inductor L3 and the output terminal. The three parallel branches have the same structure, each including a capacitor connected in series between the series main circuit and ground. This comparative example differs from Example 1 in that Comparative Example 1 uses capacitors as components of the parallel branches.

[0040] The S parameter simulation comparison diagram of Example 1 and Comparative Example 1 is as follows: Figure 3 As shown, Figure 3 The horizontal axis is frequency, and the vertical axis is insertion loss. Curve 1 is the frequency response curve of the filter provided in Example 1; Curve 2 is the frequency response curve of the LC low-pass filter provided in Comparative Example 1. In Curve 1, the BAW resonator 101 self-resonates to generate a transmission zero 201 and a resonance peak on the right side of the transmission zero; the BAW resonator 102 self-resonates to generate a transmission zero 202 to suppress the resonance peak generated by the BAW resonator 101; because the BAW resonator 102 generates a resonance peak on the right side of the transmission zero 202, the BAW resonator 103 self-resonates to generate a transmission zero 203 to suppress the resonance peak generated by the BAW resonator 102. After connecting the three BAW resonators in parallel, the resonance peak is moved to a high frequency outside the desired suppression band, and the out-of-band suppression meets the requirements within the required frequency range. Curve 1 maintains good consistency with Curve 2 within the passband, and there is a large out-of-band suppression only at the position where the BAW resonator generates a zero. The out-of-band suppression curve is slightly higher than Curve 2 due to the BAW resonant peak, but the overall trend is consistent. Simultaneously, replacing certain capacitive components with BAW resonators can introduce transmission zeros with higher suppression. Furthermore, because BAW resonators 101, 102, and 103 have extremely high quality factors, this replacement provides a larger roll-off for the filter.

[0041] By using BAW resonators in parallel branches, the size of the LTCC low-pass filter is significantly reduced, resulting in a circuit structure consisting of only three series inductors. This simplifies the original low-pass circuit without compromising its original functionality. Because BAW resonators inherently exhibit electrostatic capacitance, after certain parameters are set to equalize their electrostatic capacitance with that of the replaced capacitors, the BAW resonator can now assume the role of a capacitor in the LC filter. By replacing all three capacitors with BAW resonators, the original functionality of the low-pass filter remains unchanged. Due to the characteristics of the low-temperature co-fired ceramic process, capacitor components occupy a significant amount of space in the design. Therefore, certain capacitor components are replaced with BAW resonators to reduce the size of the low-temperature co-fired ceramic component.

[0042] Example 2

[0043] like Figure 4 As shown, a bandpass filter constituting the bandpass portion of a low-temperature co-fired ceramic duplexer includes a bandpass main circuit, a first bandpass branch, and four second bandpass branches. The bandpass main circuit includes a bulk acoustic wave resonator 104, a bulk acoustic wave resonator 105, and three LC resonators connected in series between the input and output terminals; each of the three LC resonators includes an inductor and a capacitor connected in series. The first bandpass branch, disposed at the connection between the bulk acoustic wave resonator and the LC resonator, includes a bulk acoustic wave resonator 106 and a bulk acoustic wave resonator 107 connected in series between the bandpass main circuit and ground. The four second bandpass branches are disposed, in pairs, at the connection between adjacent LC resonators, and each includes a capacitor and an inductor connected in series between the bandpass main circuit and ground.

[0044] Based on the principle of impedance, the present invention increases the suppression and steepness of the filter by using BAW resonators of different film thicknesses in the bandpass main circuit and the bandpass branch circuit. Since replacing the capacitor in the bandpass branch with a BAW resonator will produce a peak, it is suitable for the right band. Example 2 improves the performance of the left band. If the same operation as Example 1 is performed, a peak and a dip will be produced in the passband. Therefore, it is necessary to connect two BAW resonators in series on the main circuit to act as a high-impedance circuit breaker. Because the high impedance characteristics of the BAW resonator are utilized, the resonant peak generated by the low impedance will appear to the left of the transmission zero point without affecting the passband. Subsequently, the BAW resonator in the first bandpass branch is used to exert a suppressive effect without affecting the passband. At the same time, by adjusting the values of the inductance and capacitance in the second bandpass branch, the out-of-band transmission zero point of the bandpass filter can be changed (increasing the capacitance and inductance will shift the transmission zero point to the left). By adjusting the transmission zero point, the resonant peak is moved to a high frequency outside the desired suppression band to obtain an S-parameter curve that meets the index requirements.

[0045] In some embodiments, the capacitors in the bandpass trunk are replaced with bulk acoustic wave resonators.

[0046] Comparative Example 2

[0047] like Figure 5As shown, a filter constituting the bandpass portion of a duplexer includes a series trunk and four parallel branches. The series trunk includes three LC resonators connected in series between the input and output ends; each of the three LC resonators includes an inductor and a capacitor connected in series. The four parallel branches are arranged in pairs at the connection ends of adjacent LC resonators; each of the parallel branches arranged at the connection ends of adjacent LC resonators includes a capacitor and an inductor connected in series between the bandpass trunk and the ground line. The difference between this comparative example and Example 2 is that in Example 2, two bulk acoustic wave resonators are connected in series between the input end and the LC resonator, and two bulk acoustic wave resonators are provided in series between the bandpass trunk and the ground line at the connection end between the bulk acoustic wave resonator and the LC resonator.

[0048] The S parameter simulation comparison between Example 2 and Comparative Example 2 is as follows: Figure 6 As shown, Figure 6 The horizontal axis is frequency, and the vertical axis is insertion loss. Curve 3 is the frequency response curve of the bandpass filter provided in Example 2; Curve 4 is the frequency response curve of the LC bandpass filter provided in Comparative Example 2. The passband is set to be within 5.15GHz~5.85GHz, and the out-of-band suppression is required to reach -25dB at 5GHz. The fourth bulk acoustic wave resonator 104 is connected in series to the input end of the bandpass filter, and the impedance maximum at its self-resonance is used to cut off the main circuit, thereby introducing an out-of-band transmission zero point 401; after the transmission zero point is introduced, another resonance peak will be generated, so it is necessary to connect a bulk acoustic wave resonator 105 in series to generate a transmission zero point 402; the sixth bulk acoustic wave resonator 106 is connected in parallel to the input end of the bandpass filter, and the impedance minimum at its self-resonance is used to short-circuit the main circuit, thereby introducing an out-of-band transmission zero point 403. After introducing the transmission zero, a new resonance peak is generated, necessitating the addition of a BAW resonator 107 in series to generate transmission zero 404. At this point, the required suppression frequency band already meets the required frequency band. Because transmission zero 404 provides high suppression at 5 GHz, it overlaps with transmission zero 403, thereby increasing the suppression effect provided by the BAW resonator. Therefore, its presence is not observable in Curve 3. By modifying the film thickness of the seventh BAW resonator 107, its thickness can be reduced, shifting transmission zero 404 toward higher frequencies, thereby making it observable within the passband.

[0049] As can be seen from curve 4, it is difficult to achieve the requirement of -25dB out-of-band suppression at 5GHz. This is because the quality factor of the LC device is low, so it is difficult to achieve a steep roll-off. On curve 3, it can be seen that by introducing four zero points, the insertion loss at 5GHz can be suppressed to below -25dB, and at the same time, it can play a certain role in suppressing the left side of 5GHz. At the same time, outside the active part of the bulk acoustic wave resonator, curves 3 and 4 have good consistency, and the waveforms hardly change. Figure 7 In the figure, the two zero points on the left side of the transmission zero point 401 are the transmission zero points of the bandpass filter itself. The transmission zero point generated by the series resonator and the transmission zero point generated by the bulk acoustic wave resonator are matched and adjusted to obtain an S-parameter curve that meets the index requirements. In the comparison of curve 3 and curve 4, it can be seen that the transmission zero point of the bandpass filter itself is at the same frequency. The bulk acoustic wave resonator 104, bulk acoustic wave resonator 105, bulk acoustic wave resonator 106, and bulk acoustic wave resonator 107 only play the role of short circuit at low impedance, thereby keeping the filter maintaining its original working curve. At high frequencies, the high-frequency impedance is inconsistent with the original due to the introduction of the bulk acoustic wave resonator, so the insertion loss increases, but the overall waveform remains consistent. It can be seen that the filter provided in Example 2 has the characteristics of excellent roll-off and does not change the original frequency response curve, and can improve the performance of the filter without changing the original waveform.

[0050] Example 3

[0051] like Figure 8 As shown, a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator (BAW) comprises a low-pass section and a band-pass section connected in series. The low-pass section employs the low-pass filter described in Example 1, while the band-pass section employs the band-pass filter described in Example 2. The output of the band-pass section is connected to the input of the low-pass filter. If the output of the band-pass section is connected to the output of the low-pass filter, the BAW resonator 103 in the low-pass filter will generate a low impedance at the resonance point, causing the duplexer to be depressed in the passband due to the short circuit created by the low impedance.

[0052] By replacing the capacitors in the low-pass section with bulk acoustic wave resonators (BAW resonators), the original low-pass device footprint is reduced and sufficient suppression is provided for the low-pass filter within the bandpass filter's frequency band. BAW resonators 104, 105, 106, and 107 provide sufficient out-of-band suppression and roll-off at 5 GHz for the bandpass filter. By suppressing the resonance peaks among BAW resonators 104, 105, 106, and 107, the bandpass filter achieves a -25 dB gain from 3.3 GHz to 5 GHz. By adjusting the values of the inductors and capacitors in the four series resonators, the out-of-band transmission zero of the bandpass filter can be adjusted (increasing the capacitance and inductance shifts the transmission zero to the left). The transmission zeros generated by the series resonators are matched and adjusted with those generated by the BAW resonators to obtain an S-parameter curve that meets the required specifications.

[0053] In this embodiment, the component value of the low-temperature co-fired ceramic duplexer is less than 6nH or 4pF, so as to avoid a low self-resonance point, increased inductor windings, and increased capacitor plate area caused by excessively large component values.

[0054] The S parameter simulation waveform of Example 3 is as follows: Figure 9 、 Figure 10 、 Figure 11 shown. Figure 9 The horizontal axis is frequency, and the vertical axis is insertion loss. 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. Figure 9 As can be seen from the figure, Curve 5 exhibits a low insertion loss of only -0.35 dB in the 2.4 GHz to 2.5 GHz passband, while achieving -40 dB isolation in the 5.15 GHz to 5.85 GHz band. Curve 6 exhibits a return loss of -20 dB in the 2.4 GHz to 2.5 GHz passband, ensuring the low insertion loss of Curve 5. Curve 7 exhibits a low insertion loss of only -2.5 dB in the 5.15 GHz to 5.85 GHz passband, while achieving -25 dB isolation in the 3.3 GHz to 5 GHz band and -40 dB isolation in the 2.4 GHz to 2.5 GHz band. Curve 8 exhibits a return loss of -17 dB in the 5.15 GHz to 5.85 GHz passband, ensuring the low insertion loss of Curve 7. Curve 5 demonstrates that this BAW resonator and LTCC filter cascade approach can achieve -25 dB out-of-band rejection in a transition band of only 150 MHz, providing a high roll-off for the overall filter.

[0055] Example 4

[0056] like Figure 12 and Figure 13 As shown, a method for preparing 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 method for preparing the low-temperature co-fired ceramic duplexer comprises the following steps:

[0057] All BAW resonators in a duplexer are integrated onto a common substrate to form a first device module. All components in the duplexer, excluding the BAW resonators, are integrated into a common ceramic body using a low-temperature co-fired ceramic process to form a second device module. Through-holes are provided at all interfaces on the second device module that require connection to the BAW resonators. Multiple interfaces are provided on the first device module that correspond to the through-holes on the second device module. The first device module is stacked on the second device module, with the through-holes on the second device module aligned with the interfaces on the first device module. Wiring is then used to connect the corresponding interfaces on the first and second device modules, resulting in a low-temperature co-fired ceramic duplexer.

[0058] The cascade connection between the first and second device modules is achieved through shorter vias, reducing parasitic effects of the cascaded traces. Furthermore, this vertical cascade approach conserves the overall planar area of the LTCC duplexer. The overall area of the LTCC duplexer is determined by the larger second device module. Consequently, since the first device module is cascaded above the LTCC filter, it occupies vertical space. Therefore, thinner layers are used in the LTCC filter design to conserve vertical space.

[0059] In addition, since the area of the first device module is usually limited to a size of 1109 (i.e., 1.1mm*0.9mm), if each capacitor in each low-temperature co-fired ceramic duplexer is replaced with a bulk acoustic wave resonator, it will be difficult to put it into the package. During the replacement, the cascade position will require a bonding point with a large area, and replacing the capacitor in the bandpass part will generate multiple connection points, thereby generating multiple bonding positions. That is, replacing all the capacitors on the series main path of the bandpass part with bulk acoustic wave resonators will generate 3 bonding points, which will exceed the packaging limit. Moreover, since the bandpass part has introduced a transmission zero point through the bandpass series main path and the bulk acoustic wave resonator in the first parallel branch, the effect achieved after replacing the capacitor in the bandpass part is relatively small.

[0060] Example 5

[0061] like Figure 14 As shown, a method for preparing 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 method for preparing the low-temperature co-fired ceramic duplexer comprises the following steps:

[0062] All BAW resonators in a duplexer are integrated on a common substrate to obtain a first device module; devices other than the BAW resonators in the duplexer are integrated into a common ceramic body through a low-temperature co-fired ceramic process to obtain a second device module; the second device module and the first device module consisting of the BAW resonator are respectively soldered on a common PCB substrate (circuit board); and microstrip lines are used on the PCB substrate to connect corresponding interfaces in the first device module and the second device module to obtain a low-temperature co-fired ceramic duplexer.

[0063] Although connecting the second device module and the first device module through a microstrip line will occupy a large area, its advantage is that it is convenient for design and the setting position of the connection port is relatively free. There is no need to specifically keep the cascaded ports vertical when designing the filter, avoiding various restrictions when designing the filter.

[0064] Example 6

[0065] like Figure 15As shown, a method for preparing 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 method for preparing the low-temperature co-fired ceramic duplexer comprises the following steps:

[0066] All BAW resonators in a low-pass part and a high-pass part are respectively integrated on different substrates to obtain a first device module; the devices in the duplexer except the BAW resonators are integrated into the same ceramic body through a low-temperature co-fired ceramic process to obtain a second device module; a plurality of solder pads are provided on one opposite surface of the second device module; two interfaces connected to the BAW resonators in the second device module are arranged 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.

[0067] Since the second device module manufactured by the low-temperature co-fired ceramic process has a large thickness, and when the low-temperature co-fired ceramic is used for device integration, the connection with the bulk acoustic wave resonator is set on the side of the second device module, it is possible to solder the bulk acoustic wave resonator device on the side pad, thereby achieving direct connection with the port to reduce routing loss and avoid the use of bonding points.

[0068] In conjunction with the above embodiments, it can be seen that when designing a filter, cascading a BAW resonator and an LTCC filter can effectively reduce the filter's size and significantly improve its performance. The advantages of the BAW resonator complement the shortcomings of the LTCC filter, improving the filter's roll-off, out-of-band rejection, and insertion loss. Furthermore, the two cascaded topologies of Examples 1 and 2 are not limited to the embodiments described. They can also be applied to other circuits: replacing the original capacitor with the BAW resonator's static capacitance to exploit the BAW resonator's high Q; and introducing the BAW resonator to create a transmission zero to meet out-of-band rejection and roll-off requirements. Simply setting the appropriate BAW resonator parameters (film thickness and static capacitance) to match the original filter requires.

Claims

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

2. The low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 1, 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 the low-pass input end and the low-pass output end; the low-pass branches are connected in series between the low-pass main circuit and the 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.

3. The low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 2, characterized in that: Some or all of the capacitive elements use bulk acoustic wave resonators.

4. The low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 2, characterized in that: The film thicknesses of all BAW resonators in the low-pass section and the band-pass section are different.

5. The low-temperature co-fired ceramic duplexer based on bulk acoustic wave resonator according to claim 1, 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 required suppression frequency band, so that the resonance peak generated by the BAW resonator moves to the high frequency outside the required suppression frequency band.

6. A method for preparing a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator, characterized by: Used to prepare the low-temperature co-fired ceramic duplexer according to claim 1; the preparation method of the low-temperature co-fired ceramic duplexer is: integrating all bulk acoustic wave resonators in the duplexer on the same substrate to obtain a first device module; Integrating the components of the duplexer except the bulk acoustic wave resonator 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 and the device in the second device module are cascaded to obtain a low-temperature co-fired ceramic duplexer.

7. The method for preparing a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator according to claim 6, 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 are set on the first device module that correspond one-to-one to the through holes on the second 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; 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.

8. The method for preparing a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator according to claim 6, 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 connected respectively using microstrip lines on the circuit board.

9. The method for preparing a low-temperature co-fired ceramic duplexer based on a bulk acoustic wave resonator according to claim 6, 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 one opposite surface of the second device module; during the integration of 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; and the first device module is directly soldered to the second device module via the solder pads to obtain a low-temperature co-fired ceramic duplexer.

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