Balanced circuit of FBAR filter and radio frequency filter

Abstract

The invention discloses an FBAR filter balanced circuit and a radio frequency filter, and belongs to the technical field of filters. The balanced circuit comprises a filtering module, a bandwidth expansion module and a stop-band optimization module, the filtering module comprises two resonators and generates two initial resonance modes at different positions, and the initial resonance modes are coupled to form an initial passband; the two bandwidth expansion modules are respectively connected with the two input ends and the two output ends of the filtering module in a one-to-one correspondence manner; the bandwidth expansion module interacts with the filtering module to generate two new resonance modes at the frequency lower than the initial passband frequency, and the new resonance modes and the initial resonance mode are coupled to expand the initial passband width; the two stop-band optimization modules are respectively connected in parallel with the two bandwidth expansion modules, transmission zero points are introduced at different stop-band frequencies, a stop-band filtering structure is constructed, the out-of-band rejection capability and the rectangularity of the filter are improved, and broadband and high-selectivity collaborative optimization of the FBAR balanced circuit structure is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of filters, and more particularly to a FBAR filter balanced circuit and a radio frequency filter. BACKGROUND

[0002] The rapid development of mobile communication devices has continuously improved information transmission rate and information capacity, and has continuously developed communication frequency to high frequency and large bandwidth. A general electromagnetic wave signal filter cannot meet such a demand. The wavelength of a sound wave is much smaller than that of an electromagnetic wave, and thus an acoustic filter using a sound wave signal can be better applied to high frequency.

[0003] Compared with a traditional surface acoustic wave (SAW) technology, a film bulk acoustic wave technology can realize high quality factor (Q), high integration, and higher frequency, and has good compatibility with a semiconductor technology process, facilitates the design of a radio frequency integrated circuit, and becomes a research hotspot of a high-performance filter.

[0004] Research on a large-bandwidth filter mainly involves materials and circuit structures. In the selection of a material of an FBAR filter, AlN material becomes a commonly used piezoelectric material due to good compatibility with a CMOS process and the realization of a Q value of 1000-2000. However, due to the fact that an electromechanical coupling coefficient of the AlN material is only about 6%, a filter based on the AlN material has a narrow bandwidth, and can usually only realize narrowband filtering of about 3%. Adding Sc elements to the AlN material is an effective way to improve the electromechanical coupling coefficient (k t 2 ). A 20% Sc scheme can realize device preparation, and can improve the k t 2 to 12.4%. However, this modification method can significantly reduce the Q value of the material compared with pure AlN material.

[0005] In terms of circuit structures, a traditional ladder structure has super-high rectangularity, but the relative bandwidth that can be realized is less than half of k 2 t . A traditional network topology structure has good symmetry, but its suppression ability is related to impedance and phase, which makes it have large out-of-band suppression and poor rectangularity. Since the ladder structure and the network topology structure cannot break through the limitation of the electromechanical coupling coefficient of the piezoelectric layer material, they are usually used in the design of narrowband filters. Research results in recent years show that a FBAR filter circuit structure designed by combining a single-ended ladder topology with an IPD passive inductor has realized a relative bandwidth of more than 25% by virtue of the optimization of the inductor to the electromechanical coupling coefficient and the synergistic effect of the structure.

[0006] However, there are currently no results on designing similar ultra-wide bandwidth circuit structures based on balanced network topologies. Generally, bandwidth extension using inductors only utilizes the effective electromechanical coupling coefficient (k) of the inductor to the resonator. 2 eff The improvement of ) is due to the material k t 2 Due to limitations, only a 12% relative bandwidth can be achieved. Furthermore, the unutilized newly generated resonant modes of the inductor will worsen out-of-band rejection below the passband frequency. Compared to the single-ended FBAR filter, the balanced network structure has stronger common-mode rejection capability and signal stability, which can effectively reduce electromagnetic interference and improve signal integrity. However, there is a certain contradiction between its own rectangularity and out-of-band rejection. Summary of the Invention

[0007] To address the shortcomings of related technologies, the present invention aims to provide a balanced FBAR filter circuit and an RF filter, which solves the problems of the limitation of the effective electromechanical coupling coefficient of the balanced FBAR filter by the material's inherent electromechanical coupling coefficient, and the conflicting limitations between out-of-band suppression and rectangularity, and in-band insertion loss.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a balanced FBAR filter circuit, comprising: a filtering module, a bandwidth extension module, and a stopband optimization module; The filtering module includes a first resonator and a second resonator, which are used to generate two initial resonant modes at different locations, and the initial resonant modes are coupled to form an initial passband. The bandwidth expansion module includes a first bandwidth expansion module and a second bandwidth expansion module. The two ends of the first bandwidth expansion module are connected to the two input terminals of the filter module, and the two ends of the second bandwidth expansion module are connected to the two output terminals of the filter module. The first bandwidth expansion module and the second bandwidth expansion module interact with the first resonator and the second resonator to generate two new resonant modes at frequencies below the initial passband frequency. The new resonant modes couple with the initial resonant mode to extend the initial passband width towards lower frequencies. The stopband optimization module includes an upper sideband stopband optimization module and a lower sideband stopband optimization module, which are connected sequentially to each other, along with a first bandwidth expansion module, a filtering module, a second bandwidth expansion module, and an upper sideband stopband optimization module. The lower sideband stopband optimization module is connected in parallel with the first bandwidth expansion module, and the upper sideband stopband optimization module is connected in parallel with the second bandwidth expansion module. The stopband optimization module is used to introduce transmission zeros at different passband frequencies to construct a stopband filtering structure, thereby improving out-of-band rejection and rectangularity.

[0009] The filter module includes four nodes, with the first and second nodes serving as input terminals, and the third and fourth nodes serving as output terminals; the filter module includes two first resonators and two second resonators; One of the first resonators is connected to the first node and the third node in a one-to-one correspondence, and the other first resonator is connected to the second node and the fourth node in a one-to-one correspondence; One second resonator is connected to the first node and the fourth node in a one-to-one correspondence, and another second resonator is connected to the second node and the third node in a one-to-one correspondence.

[0010] Optionally, the area ratio of the first resonator to the second resonator is in the range of 1 to 1.5, which is used to balance out-of-band suppression and rectangularity in filtering.

[0011] Optionally, the first bandwidth expansion module includes a first inductor, and the second bandwidth expansion module includes a second inductor; The two ends of the first inductor are respectively connected to the first node and the second node in a one-to-one correspondence; The two ends of the second inductor are connected to the third node and the fourth node respectively; The first and second inductors are used to form a new resonant mode at a position below the initial passband frequency.

[0012] Optionally, the upper sideband stopband optimization module includes two third resonators, two fourth resonators, and a third inductor; the two third resonators are connected in series with the two first resonators respectively; one fourth resonator is connected between the input terminals of the two third resonators, and the other fourth resonator is connected in series with the third inductor and then connected between the output terminals of the two third resonators; the third and fourth resonators in the upper sideband stopband optimization module have different resonant frequencies, which are used to introduce different transmission zeros and suppress them at positions higher than the initial passband frequency to form an upper sideband stopband; the third inductor is used to extend the stopband width. The lower sideband stopband optimization module includes a fifth resonator, which is used to introduce a transmission zero and suppress it at a position below the initial passband frequency to form a lower sideband stopband.

[0013] Optionally, the values ​​of the first inductor and the second inductor are in the range of 0~1.5nH, so as to form a new resonant mode at low frequency; The value of the third inductor is in the range of 0~10nH, and it is used to construct a band-stop filter structure over the entire frequency band covered by the FBAR filter.

[0014] Optionally, the first, second, third, fourth, and fifth resonators are all thin-film bulk acoustic resonators.

[0015] In a second aspect, the present invention also provides a radio frequency filter comprising a balanced FBAR filter circuit as described in any one of the first aspects.

[0016] Compared with the prior art, the beneficial effects achieved by the above-described technical solution conceived in this invention include: employing a balanced network structure filter module, with a bandwidth extension module and a stopband optimization module added to both sides; the filter module includes a first resonator and a second resonator, generating two different resonant modes within the network structure and forming a passband through mode coupling; the bandwidth extension module generates a new resonant mode at a lower frequency than the original passband; based on this, by utilizing the coupling between the new resonant modes and the interaction between the new resonant modes and the original resonant modes, the filter passband width is effectively extended to lower frequencies. This method is not specific to the k-frequency response of a single resonator. 2 eff Improvement, therefore unaffected by k t 2 Overcoming limitations, the structure of this invention has a higher bandwidth extension capability. Furthermore, by adding a stopband optimization module, transmission zeros are introduced at different passband frequencies, significantly improving the rectangularity and out-of-band rejection of the extended-band filter without increasing insertion loss. This achieves synergistic optimization of the FBAR balanced circuit structure in terms of wide bandwidth and high selectivity, comprehensively improving the overall circuit performance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a balanced FBAR filter circuit provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the filter module circuit structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the circuit structure after bandwidth expansion according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the stopband optimized circuit structure according to an embodiment of the present invention; Figure 5 These are the amplitude-frequency characteristic curves and impedance characteristic curves corresponding to the filtering module provided in this embodiment of the invention; Figure 6 These are the amplitude-frequency characteristic curve and impedance characteristic curve after bandwidth expansion provided in the embodiments of the present invention; Figure 7 These are the final amplitude-frequency response curve and impedance response curve after stopband optimization provided in this embodiment of the invention. In the above figures, the same reference numerals are used, and the reference numerals are: 1. Filtering module; 2. First bandwidth expansion module; 3. Second bandwidth expansion module; 4. Upper sideband stopband optimization module; 5. Lower sideband stopband optimization module; 101. First resonator; 201. Second resonator; 301. First inductor; 302. Second inductor; 102. Third resonator; 202. Fourth resonator; 203. Fifth resonator; 303. Third inductor. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0019] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0020] like Figure 1 As shown, the present invention provides a balanced FBAR filter circuit, including: a filtering module 1, a bandwidth extension module, and a stopband optimization module; The filtering module 1 includes a first resonator 101 and a second resonator 201, which are used to generate two different initial resonant modes, and the initial resonant modes are coupled to form an initial passband. The bandwidth expansion module includes a first bandwidth expansion module 2 and a second bandwidth expansion module 3. The two ends of the first bandwidth expansion module 2 are connected to the two input terminals of the filter module 1, and the two ends of the second bandwidth expansion module 3 are connected to the two output terminals of the filter module 1, respectively. The first bandwidth expansion module 2 and the second bandwidth expansion module 3 interact with the first resonator 101 and the second resonator 201 to generate two new resonant modes at frequencies below the initial passband frequency. The new resonant modes couple with the initial resonant modes to extend the initial passband width towards lower frequencies. The stopband optimization module includes an upper sideband stopband optimization module 4 and a lower sideband stopband optimization module 5. The lower sideband stopband optimization module 5, the first bandwidth expansion module 2, the filtering module 1, the second bandwidth expansion module 3, and the upper sideband stopband optimization module 4 are connected in sequence. The lower sideband stopband optimization module 5 is connected in parallel with the first bandwidth expansion module 2, and the upper sideband stopband optimization module 4 is connected in parallel with the second bandwidth expansion module 3. The stopband optimization module is used to introduce transmission zeros at different passband frequencies to construct a stopband filtering structure, thereby improving out-of-band rejection and rectangularity. Filter module 1 is a balanced network structure. The first and second resonators generate two different initial resonant modes, forming an initial passband through mode coupling. A bandwidth extension module is added to each side of filter module 1, generating two new usable resonant modes at frequencies lower than the initial passband. Based on this, the filter passband width is effectively extended to lower frequencies through coupling between the new resonant modes similar to that generated by the first / second resonators, and through the interaction between the new and initial resonant modes. The upper sideband stopband optimization module 4 and the lower sideband stopband optimization module 5 design stopband filter structures within the out-of-band suppression frequency band required by filter module 1. They introduce transmission zeros at different passband frequencies to suppress specific frequencies, achieving out-of-band suppression and rectangularity optimization for both the upper and lower sidebands.

[0021] like Figure 2 As shown, optionally, the filter module 1 includes four nodes, with the first and second nodes serving as input terminals, and the third and fourth nodes serving as output terminals; the filter module includes two first resonators 101 and two second resonators 201. One of the first resonators is connected to the first node and the third node in a one-to-one correspondence, and the other first resonator is connected to the second node and the fourth node in a one-to-one correspondence; One second resonator is connected to the first node and the fourth node in a one-to-one correspondence, and another second resonator is connected to the second node and the third node in a one-to-one correspondence.

[0022] Optionally, the area ratio of the first resonator 101 to the second resonator 201 is in the range of 1 to 1.5, which is used to balance out-of-band suppression and rectangularity in filtering.

[0023] like Figure 3 As shown, optionally, the first bandwidth expansion module 2 includes a first inductor 301, and the second bandwidth expansion module 3 includes a second inductor 302. The two ends of the first inductor 301 are respectively connected to the first node and the second node in a one-to-one correspondence; The two ends of the second inductor 302 are respectively connected to the third node and the fourth node; The first inductor 301 and the second inductor 302 are used to form a new resonant mode at a position below the initial passband frequency.

[0024] This method is not affected by material k t 2 Due to limitations, therefore, relative to the inductance of the resonator, k... 2 eff It has enhanced bandwidth expansion capabilities.

[0025] like Figure 4As shown, optionally, the upper sideband stopband optimization module 4 is located to the right of the second inductor 302, and the lower sideband stopband optimization module 5 is located to the left of the first inductor 301; The upper sideband stopband optimization module 4 includes two third resonators 102, two fourth resonators 202, and a third inductor 303. The two third resonators 102 are connected in series with the two first resonators 101 respectively. One fourth resonator 202 is connected between the input terminals of the two third resonators 102, and the other fourth resonator 202, after being connected in series with the third inductor 303, is connected between the output terminals of the two third resonators 102. The third resonators 102 and fourth resonators 202 in the upper sideband stopband optimization module 4 have different resonant frequencies, used to introduce different transmission zeros, improving out-of-band rejection and rectangularity at positions higher than the initial passband frequency. The third inductor 303 interacts with the fourth resonator 202, improving the k-frequency response of the fourth resonator. 2 eff This expands the stopband width and improves the suppression capability of the stopband optimization module 4. In addition, the introduction of the third inductor 303 will also introduce a new resonant mode below the passband frequency. The transmission zero generated by the new resonant mode will improve the lower sideband stopband suppression capability and rectangularity. The lower sideband stopband optimization module 5 includes a fifth resonator 203, the two ends of which are connected to the first node and the second node in a one-to-one correspondence; the lower sideband stopband optimization module 5 is used to introduce another transmission zero point to further improve the lower sideband stopband suppression capability and rectangularity.

[0026] Based on the above embodiments, optionally, the values ​​of the first inductor and the second inductor are in the range of 0~1.5nH; The value of the third inductor is in the range of 0~10nH, and it is used to construct a band-stop filter structure over the entire frequency band covered by the FBAR filter.

[0027] In the embodiments of the present invention, the first inductor 301, the second inductor 302, and the third inductor 303 are on-chip inductors or surface mount inductors implemented using a high-resistivity silicon substrate or a ceramic sheet.

[0028] Optionally, the first resonator 101, the second resonator 201, the third resonator 102, the fourth resonator 202, and the fifth resonator 203 are all thin-film bulk acoustic wave resonators. All of the above resonators adopt an air gap type or solid-state assembly type structure.

[0029] In one specific embodiment, the area of ​​the first resonator 101 in the filter module 1 is 7550 μm. 2 The area of ​​the second resonator 201 is 6240um. 2The bandwidth extension module, composed of the first inductor 301 and the second inductor 302, and the filter module, composed of the first resonator 101 and the second resonator 201, are integrated as a whole. By adjusting the values ​​of the first inductor 301 and the second inductor 302, the bandwidth is extended, as shown below. Figure 6 As shown, the first inductor 301 has a capacitance of 0.53nH, and the second inductor 302 has a capacitance of 0.4nH. After introducing the inductors, the original impedance maxima of the series path (the first series path from the first node to the third node, and the second series path from the second node to the fourth node) shifts from 4.2GHz to 4.42GHz, and a new resonant mode is generated at 3.13GHz. Similarly, the original impedance maxima of the parallel path (the first parallel path from the first node to the fourth node, and the second parallel path from the second node to the third node) shifts from 3.44GHz to 4.05GHz, and a new resonant mode is generated at 3.33GHz. Coupling effects occur between these modes, and... Figure 5 In comparison, notch filtering is significantly improved, with bandwidth extending to lower frequencies, ultimately achieving an optimized effect of -3dB bandwidth of 1.004GHz.

[0030] Based on this, the upper and lower sidebands of the FBAR filter are optimized using the upper sideband stopband optimization module 4 and the lower sideband stopband optimization module 5, such as... Figure 7 As shown, the upper sideband stopband optimization module 4 introduces transmission zeros at 4.93GHz, 4.52GHz, and 2GHz by adjusting the parameter values ​​of the third resonator 102, the fourth resonator 202, and the value of the third inductor 303 within the module; the lower sideband stopband optimization module 5 introduces a transmission zero at 3.02GHz by adjusting the parameters of its internal fifth resonator 203, at which point the area of ​​the third resonator 102 is 6300um. 2 The area of ​​the fourth resonator 202 is 4240um. 2 The third inductor 303 has a size of 3nH, and the fifth resonator 203 has an area of ​​12800um. 2 Through the above operations, the out-of-band rejection and rectangularity of the filter were effectively optimized, increasing the out-of-band rejection from over 25dB to over 35dB, and the rectangularity performance reached 85%, achieving a relative bandwidth of 26.4%.

[0031] Based on the above embodiments, the present invention also provides a radio frequency filter, comprising a balanced FBAR filter circuit as described in any one of the above embodiments.

[0032] This invention employs a balanced network-structured filter module with bandwidth extension and stopband optimization modules added to both sides. The filter module includes a first resonator and a second resonator, generating two different resonant modes within the network structure and forming a passband through mode coupling. The bandwidth extension module generates new resonant modes at lower frequencies relative to the original passband. Based on this, by utilizing the coupling between the new resonant modes and the interaction between the new and existing resonant modes, the filter passband width is effectively extended to lower frequencies. This method is not targeted at a single resonator k. 2 eff The improvement is therefore unaffected by the original electromechanical coupling coefficient (k). t 2 Overcoming the limitations of [previous invention], the structure of this invention has a higher bandwidth extension capability. Furthermore, by adding a stopband optimization module, the rectangularity and out-of-band rejection of the extended-band filter are significantly improved without increasing insertion loss. The balanced FBAR filter utilizes inductors to improve k... 2 eff Subject to the inherent k of the material 2 t The limitations of out-of-band suppression and the conflicting constraints between rectangularity and in-band insertion loss are addressed. A balanced FBAR circuit structure is achieved through synergistic optimization of wide bandwidth and high selectivity, comprehensively improving the overall circuit performance.

[0033] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A balanced FBAR filter circuit, characterized in that, include: Filtering module, bandwidth extension module, and stopband optimization module; The filtering module includes a first resonator and a second resonator, which are used to generate two initial resonant modes at different locations, and the initial resonant modes are coupled to form an initial passband. The bandwidth expansion module includes a first bandwidth expansion module and a second bandwidth expansion module. The two ends of the first bandwidth expansion module are connected to the two input terminals of the filter module, and the two ends of the second bandwidth expansion module are connected to the two output terminals of the filter module. The first bandwidth expansion module and the second bandwidth expansion module interact with the first resonator and the second resonator to generate two new resonant modes at frequencies below the initial passband frequency. The new resonant modes couple with the initial resonant mode to extend the initial passband width to lower frequencies. The stopband optimization module includes an upper sideband stopband optimization module and a lower sideband stopband optimization module, which are connected sequentially to each other, along with a first bandwidth expansion module, a filtering module, a second bandwidth expansion module, and an upper sideband stopband optimization module. The lower sideband stopband optimization module is connected in parallel with the first bandwidth expansion module, and the upper sideband stopband optimization module is connected in parallel with the second bandwidth expansion module. The stopband optimization module is used to introduce transmission zeros at different passband frequencies to construct a stopband filtering structure, thereby improving out-of-band rejection and rectangularity.

2. The circuit as described in claim 1, characterized in that, The filter module includes four nodes, with the first and second nodes serving as input terminals, and the third and fourth nodes serving as output terminals; the filter module includes two first resonators and two second resonators; One of the first resonators is connected to the first node and the third node in a one-to-one correspondence, and the other first resonator is connected to the second node and the fourth node in a one-to-one correspondence; One second resonator is connected to the first node and the fourth node in a one-to-one correspondence, and another second resonator is connected to the second node and the third node in a one-to-one correspondence.

3. The circuit as described in claim 2, characterized in that, The area ratio of the first resonator to the second resonator ranges from 1 to 1.5, and is used to balance out-of-band suppression and rectangularity in filtering.

4. The circuit as described in claim 2, characterized in that, The first bandwidth expansion module includes a first inductor, and the second bandwidth expansion module includes a second inductor; The two ends of the first inductor are respectively connected to the first node and the second node in a one-to-one correspondence; The two ends of the second inductor are connected to the third node and the fourth node respectively; The first and second inductors are used to form a new resonant mode at a position below the initial passband frequency.

5. The circuit as described in claim 4, characterized in that, The upper sideband stopband optimization module includes two third resonators, two fourth resonators, and one third inductor; the two third resonators are connected in series with the two first resonators respectively. A fourth resonator is connected between the input terminals of two third resonators, and another fourth resonator is connected in series with a third inductor between the output terminals of two third resonators. The third and fourth resonators in the upper sideband stopband optimization module have different resonant frequencies, which are used to introduce different transmission zeros and suppress them at positions higher than the initial passband frequency to form an upper sideband stopband. The third inductor is used to extend the stopband width. The lower sideband stopband optimization module includes a fifth resonator, which is used to introduce a transmission zero and suppress it at a position below the initial passband frequency to form a lower sideband stopband.

6. The circuit as described in claim 4 or 5, characterized in that, The values ​​of the first inductor and the second inductor are in the range of 0~1.5nH, so as to form a new resonant mode at low frequency; The value of the third inductor is in the range of 0~10nH, and it is used to construct a band-stop filter structure over the entire frequency band covered by the FBAR filter.

7. The circuit as described in claim 1, characterized in that, The first, second, third, fourth, and fifth resonators are all thin-film bulk acoustic resonators.

8. A radio frequency filter, characterized in that, It includes a balanced FBAR filter circuit as described in any one of claims 1-7.

Images