CN111010141A

CN111010141A - Filter, radio frequency front-end circuit and communication device

Info

Publication number: CN111010141A
Application number: CN201911118982.3A
Authority: CN
Inventors: 庞慰; 刘胜杰
Original assignee: Tianjin University; ROFS Microsystem Tianjin Co Ltd
Current assignee: Tianjin University; ROFS Microsystem Tianjin Co Ltd
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2020-04-14

Abstract

The invention provides a filter, a radio frequency front-end circuit and a communication device, which realize high-impedance band suppression; the filter includes: a silicon substrate; a first filter and a second filter disposed on the silicon substrate; and a signal transmission line for electrically connecting the first filter and the second filter; one end of the first filter is connected with the signal input end, the other end of the first filter is connected with the signal transmission line, the other end of the signal transmission line is connected with the second filter, and the other end of the second filter is connected with the signal output end, so that the first filter and the second filter are connected in series.

Description

Filter, radio frequency front-end circuit and communication device

Technical Field

The invention relates to the technical field of semiconductors and MEMS (micro-electromechanical systems), in particular to a filter, a radio frequency front-end circuit and a communication device which use a bulk acoustic wave resonator to realize higher stop band rejection.

Background

With the development of wireless communication applications, the demand for data transmission rate is higher and higher, and the data transmission rate corresponds to high utilization rate of spectrum resources and spectrum complexity. The complexity of the communication protocol imposes stringent requirements on the various performances of the rf system, and the rf filter plays a crucial role in the rf front-end module, which can filter out-of-band interference and noise to meet the signal-to-noise ratio requirements of the rf system and the communication protocol.

Rf filters are mainly used in wireless communication systems, such as rf front-ends of base stations, mobile phones, computers, satellite communication, radar, electronic countermeasure systems, and the like. The main performance indicators of the rf filter are insertion loss, out-of-band rejection, power capacity, linearity, device size and cost. The good filter performance can improve the data transmission rate, the service life and the reliability of the communication system to a certain extent. Especially, under the condition that the current spectrum resources are in shortage, two adjacent spectrum resources are very close to each other, and in order to realize simultaneous operation of the two adjacent spectrum resources without mutual influence, two communication systems must adopt filters to perform mutual isolation, so that the out-band rejection index of the filters is very important for the performance of a radio frequency receiving system, and the high roll-off and high out-band rejection level basically becomes the 'standard configuration' of an FBAR/SMR filter. Therefore, how to design a high out-of-band rejection filter to achieve high performance of a wireless communication system is still a technical problem to be solved.

Disclosure of Invention

In view of the above, the present invention provides a filter, a radio frequency front end circuit and a communication apparatus, which implement high-impedance band rejection.

The technical scheme of the filter provided by the first aspect of the invention is as follows:

a filter, comprising:

a silicon substrate;

a first filter and a second filter disposed on the silicon substrate;

and a signal transmission line for electrically connecting the first filter and the second filter;

one end of the first filter is connected with the signal input end, the other end of the first filter is connected with the signal transmission line, the other end of the signal transmission line is connected with the second filter, and the other end of the second filter is connected with the signal output end, so that the first filter and the second filter are connected in series.

A technical solution of a radio frequency front-end circuit provided in a second aspect of the present invention is:

a radio frequency front end circuit comprising:

a filter; and

and the amplifying circuit is connected with the filter.

The third aspect of the present invention provides a communication apparatus, wherein:

a communication device, comprising:

an RF signal processing circuit for processing a radio frequency signal transmitted and received by the antenna element; and

a frequency front end circuit that transmits the radio frequency signal between the antenna element and the RF signal processing circuitry.

The filter framework provided by the invention integrates and arranges two filter structures on a silicon substrate, but the two filter structures are different from the filters in series, the two filters are processed at one time during production, one filter can realize higher stop band rejection level, and the out-of-band rejection level of the FBAR/SMR filter is greatly improved on the premise of not increasing the size of the filter in a large scale, thereby not only meeting the requirement of a customer on the miniaturization of the filter, but also leading the FBAR/SMR filter to reach and exceed the out-of-band rejection level of a cavity/dielectric filter.

Drawings

The drawings are included to provide a better understanding of the invention and are not to be construed as unduly limiting the invention. Wherein:

FIG. 1 is a diagram of a prior art single filter topology;

fig. 2 is a structural diagram of a conventional FBAR filter;

FIG. 3 is a diagram of a prior art single filter assembly;

FIG. 4 is a graph of S21 for a prior art single filter;

FIG. 5 is a block diagram of an assembly of the proposed filter according to one embodiment;

FIG. 6 is a block diagram of a topology of a proposed filter according to one embodiment;

fig. 7 is a graph of S21 for the proposed filter of one embodiment.

Detailed Description

The invention is further described with reference to the following figures and examples.

Example one

The traditional FBAR/SMR filter is composed of FBAR resonators, and a passband and a stopband of the filter are formed by a topological structure of series connection and parallel connection of the resonators. Fig. 1 is a topological architecture diagram of a conventional 4-3 filter. The 4-3 filter is composed of 4 series resonators and 3 parallel resonator branches, wherein the 4 series resonators are connected in series between an input end 101 and an output end 102 of the filter, and a first parallel grounding branch 103, a second parallel grounding branch 104 and a third parallel grounding branch 105 are sequentially connected between connection points of the 4 series resonators; in which the resonance frequency of the parallel arm and the resonance frequency of the series arm are not the same, typically differ by at least several tens of mega, and therefore the series resonator and the parallel resonator are represented by different symbols in fig. 1.

Fig. 2 is a physical diagram of a 4-3 filter. Fig. 1 and 2 are in a one-to-one correspondence, wherein 201 corresponds to 101 in the schematic diagram of fig. 1, i.e. the filter input; 202 corresponds to 102 in the schematic diagram of fig. 1, i.e. the filter output; 203 corresponds to 103 in the schematic diagram of fig. 1, i.e. the first parallel grounding branch of the filter; 204 corresponds to 104 in the schematic diagram of fig. 1, i.e. the second parallel ground branch of the filter; 205 corresponds to 105 in the schematic diagram of fig. 1, i.e. the third parallel ground branch of the filter; 206 is the functional area of the filter, in which the FBAR resonators are all located in the functional area 206 of the filter, and then connected to the input, output and ground terminals of the surface layer of the filter chip through VIA 207, in order to accurately test the performance of the filter, two sets of "GSG" test pads are made on the surface layer of the filter, as shown in fig. 2.

From the above figures, the use of a "GSG" probe has the advantage that the performance of the filter can be accurately tested, but the following problems still exist: the GSG probe limits the number of filter grounds, thereby limiting the complexity of the topology of the filter and making the out-of-band rejection index of a single filter very deep.

Fig. 3 shows an assembly structure of a single filter, in which an input terminal 301 and an output terminal 302 of the filter are respectively connected to an input terminal and an output terminal on a PCB (308), three parallel grounding branches 303/304/305 of the filter are all connected to a GND of the PCB, the assembly adopts a gold wire bonding manner, a PAD of the FBAR filter and a PAD of the PCB are connected by a gold wire 307, and an S21 curve of the single filter is as shown in fig. 4 by using the connection manner of fig. 3.

As can be seen from fig. 4, the single filter out-of-band rejection is a little more than-30 dBc, and it can be seen that the average level of out-of-band rejection is not high, which causes this problem: because the performance of the filter needs to be accurately measured, a GSG test structure is needed, and the GSG test structure can only support three GNDs, so that the GNDs of the filter are limited to three, the topological structure of the filter cannot be very complicated, even if the design complexity of the filter is slightly increased by adopting modes such as parallel branch combination and the like, the effect is not good through simulation analysis.

Therefore, the out-of-band rejection level that can be realized by a single filter is limited, and the rejection of-30 dBc is not enough for the current communication system, so in order to provide a higher out-of-band rejection level and meet the requirement of the communication system on the signal rejection level, the embodiment provides a new filter scheme, and 2 filters are integrated on one silicon chip for cascade connection, thereby improving the overall out-of-band rejection level of the filter.

Fig. 5 shows an assembly structure of the filter according to the present embodiment. As shown in fig. 5, the filter according to the present embodiment includes a silicon substrate 506, a first filter 503, a second filter 504, and a signal transmission line 505, wherein the first filter 503 and the second filter 504 are integrally disposed on the silicon substrate 506, and the first filter 503 and the second filter 504 are electrically connected by the signal transmission line; the input 501 of the filter is connected to the input of the PCB507, the output 502 of the filter is connected to the output of the PCB507, and the three parallel ground branches of the

filters

503 and 504 are all connected to the GND of the PCB 507.

Fig. 6 is a schematic diagram of the structures of the first filter 503 and the second filter 504 in fig. 5. The first filter 503 comprises a series resonator 5031-5034 and a parallel resonator 5035-5037, wherein the series resonator 5031-5034 is connected in series between the input end 501 and one end of the signal transmission line 505; the

parallel resonators

5035 and 5037 are connected in parallel between the connection points of the

series resonators

5031 and 5034 and the reference terminal (ground).

The series resonator 5031 and the

parallel resonator

5035 and 5037 respectively have: the piezoelectric element includes a silicon substrate, a lower electrode formed on the substrate, a piezoelectric film formed on the lower electrode, and an upper electrode provided on the piezoelectric film so as to face each other with the piezoelectric film and the lower electrode interposed therebetween.

The second filter 504 includes series resonators 5041-5044 and parallel resonators 5045-5047, the series resonators 5041-5044 being connected in series with each other between the other end of the signal transmission line 505 and the output terminal 502; the

parallel resonators

5045 and 5047 are connected in parallel between the respective connection points of the

series resonators

5041 and 5044 and the reference terminal (ground).

The series resonator 5041-5044 and the parallel resonator 5045-5047 described above have: the piezoelectric element includes a silicon substrate, a lower electrode formed on the substrate, a piezoelectric film formed on the lower electrode, and an upper electrode provided on the piezoelectric film so as to face each other with the piezoelectric film and the lower electrode interposed therebetween.

In this embodiment, the first filter 503 and the second filter 504 have the same filter structure, and the upper and lower electrodes are deposited on a silicon wafer at the same time, and the piezoelectric film is grown.

The filter proposed by the embodiment has the following beneficial effects:

(1) the higher stop band rejection level can be realized, and the requirement of a modern communication system on high out-of-band rejection can be met;

(2) under the condition of meeting the requirement of high out-of-band rejection, the silicon chip still has the advantage of miniaturization, and two filters are manufactured on one silicon chip, because a plurality of structural sizes can be shared, the series connection size of the two filters is smaller than that of the two filters;

(3) the use is more convenient, the work finished by the original two devices is realized by one device, and the working procedures and time are saved no matter in chip installation or routing

Fig. 7 is a S21 curve of the filter according to the embodiment, and as compared with fig. 4, it can be seen that the overall out-of-band rejection level of the filter according to the embodiment has reached more than 60dB, and this out-of-band rejection level can already satisfy the specification requirement of most communication systems for the filter, and in addition, the advantage of miniaturization is added, so that the FBAR/SMR filter device can satisfy the requirement of high rejection and miniaturization of most communication systems.

Example two

Here, a radio frequency front-end circuit and a communication device including the filter according to the above-described embodiments will be described.

The radio frequency front-end circuit, the RF signal processing circuit and the baseband signal processing circuit form a communication device.

The radio frequency front end circuit is provided with a filter, a power amplification circuit and a low noise amplifier circuit.

The power amplifier circuit is a transmission amplifier circuit that amplifies the radio frequency transmission signal output from the RF signal processing circuit and outputs the amplified radio frequency transmission signal to the antenna element via the filter.

The low noise amplifier circuit is a reception amplifier circuit that amplifies the radio frequency signal obtained through the filter and outputs the amplified radio frequency signal to the RF signal processing circuit.

The RF signal processing circuit performs signal processing on a radio frequency reception signal input from the antenna element via the reception signal path by frequency down conversion or the like, and outputs a reception signal generated by the signal processing to the baseband signal processing circuit. The RF signal processing circuit 3 performs signal processing on the transmission signal input from the baseband signal processing circuit by frequency up-conversion or the like, and outputs a high-frequency transmission signal generated by performing the signal processing to the power amplifier circuit. The RF signal processing Circuit 3 is, for example, an RFIC (Radio Frequency Integrated Circuit).

The signal processed by the baseband signal processing circuit is used for image display as an image signal or for speech communication as an audio signal, for example.

The rf front-end circuit may include other circuit elements between the filter, the power amplifier circuit, and the low noise amplifier circuit.

Further, the rf front-end circuit and the communication device are not limited to the configuration including the filter.

The communication device may further include a baseband signal processing circuit according to a radio frequency signal processing method.

The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A filter, comprising:

a silicon substrate;

a first filter and a second filter disposed on the silicon substrate;

2. The filter of claim 1, wherein the first filter comprises:

more than 4 series resonators connected in series between the signal input terminal and one end of the signal transmission line; and

and a parallel resonator connected between any one of the connection nodes of the 4 or more series resonators and a ground terminal.

3. The filter of claim 1, wherein the second filter comprises:

more than 4 series resonators connected in series between the other end of the signal transmission line and the signal output end; and

4. A filter according to claim 2 or 3, characterised in that the series resonators comprise: the piezoelectric element includes a substrate, a lower electrode formed on the substrate, a piezoelectric film formed on the lower electrode, and an upper electrode provided on the piezoelectric film so as to face each other with the piezoelectric film and the lower electrode interposed therebetween.

5. A filter according to claim 2 or 3, characterised in that the parallel resonators comprise: the piezoelectric element includes a substrate, a lower electrode formed on the substrate, a piezoelectric film formed on the lower electrode, and an upper electrode provided on the piezoelectric film so as to face each other with the piezoelectric film and the lower electrode interposed therebetween.

6. A radio frequency front end circuit, comprising:

the filter of any one of claims 1 to 5; and

and the amplifying circuit is connected with the filter.

7. A communications apparatus, comprising:

the radio frequency front end circuit of claim 7, transmitting the radio frequency signal between the antenna element and the RF signal processing circuitry.