CN117613529B - 5G balance filter with high common mode rejection - Google Patents

5G balance filter with high common mode rejection Download PDF

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CN117613529B
CN117613529B CN202410092042.6A CN202410092042A CN117613529B CN 117613529 B CN117613529 B CN 117613529B CN 202410092042 A CN202410092042 A CN 202410092042A CN 117613529 B CN117613529 B CN 117613529B
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CN117613529A (en
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刘望
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Nanjing Digitgate Technology Co ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00Auxiliary devices
    • H01P1/20Frequency-selective devices, e.g. filters
    • H01P1/212Frequency-selective devices, e.g. filters suppressing or attenuating harmonic frequencies
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00Auxiliary devices
    • H01P1/20Frequency-selective devices, e.g. filters
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00Auxiliary devices
    • H01P1/20Frequency-selective devices, e.g. filters
    • H01P1/201Filters for transverse electromagnetic waves
    • H01P1/203Strip line filters

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  • Electromagnetism (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)

Abstract

The invention discloses a 5G balance filter with high common mode rejection, which belongs to the technical field of communication and comprises a dielectric substrate, wherein an input feeder line and an output feeder line are arranged on the upper surface of the dielectric substrate, a stepped impedance coupling line, a J converter, a branch 1 loaded at the tail end of the J converter, a branch 2 loaded at the tail end of the J converter, a uniform impedance resonator and a middle short circuit point of the uniform impedance resonator are arranged on the upper surface of the dielectric substrate, and the stepped impedance coupling line is positioned between the input feeder line and the output feeder line and has a negative coupling effect. One end of the J converter is connected with an input feeder, and the other end of the J converter performs tap feed on the branch 1 and the branch 2 which are connected in parallel. And the uniform impedance resonator and the J-type converter are subjected to gap coupling feed, and a short circuit point is loaded on the position of a horizontal symmetrical plane of the uniform impedance resonator. The coupling between the uniform impedance resonators is slot coupling; the balance filter provided by the invention realizes good differential mode passband filter characteristics and excellent common mode rejection ratio in a differential mode passband.

Description

5G balance filter with high common mode rejection
Technical Field
The invention relates to the technical field of communication, in particular to a high common mode rejection balance filter.
Background
With the rapid development of high-speed electronic systems, balanced/differential circuits have excellent performance in terms of environmental noise resistance and electromagnetic interference resistance as compared with single-ended circuits, and thus have been increasingly used and have attracted attention.
A filter is a commonly used circuit component that selects a specific frequency in the frequency domain and suppresses other frequencies. An excellent filter can remarkably improve the signal-to-noise ratio of the whole circuit system and reduce the interference of out-of-band useless signals on in-band useful signals. Since many communication systems employ differential routing to reduce common mode signals generated by ambient noise in the system, differential filters suitable for differential routing have been developed. Since the balanced filter can exhibit the same filtering characteristics as the normal filter in the corresponding operating frequency band in the case of differential mode excitation. In the case of common mode excitation, the high stopband rejection characteristic is exhibited in the operating frequency band.
(Compact microstrip balanced FILTER WITH adjustable transmission zeros) an electron lett 55) a schematic structural diagram and a parity-mode equivalent circuit diagram of a balanced filter with an adjustable transmission zero. The whole balance filter consists of an input feeder line, an output feeder line and two pi-type resonators. The resonance condition of the corresponding odd-even mode can be obtained by analyzing the odd-even mode equivalent circuit and the input impedance of the pi-type resonator, and theoretical support is provided for constructing the filter. By using the hybrid electromagnetic coupling technology, an adjustable transmission zero point is respectively generated at two sides of the differential mode working frequency band of the filter, and the filtering effect of the differential mode response of the filter is improved. Meanwhile, the common mode rejection can achieve a rejection effect of 20dB in the differential mode working frequency range.
(High-selectivity balanced filter with mixed electric and magnetic coupling,IEEE Microwave Wireless Compon Lett 26) The basic structure, the odd-even mode equivalent circuit and the coupling topological structure diagram of the high-selectivity balance filter are provided. From the coupling topology, there are two transmission paths for the signal: one is directly from S to L, the other is from S sequentially through resonator 1, resonator 2 and finally to L. In an equivalent differential mode circuit, two quarter-wave short-circuit resonators provide two resonant modes that constitute a differential mode operating band. Excellent band-pass filter characteristics of three transmission zeros and two transmission poles of the differential mode can be obtained through reasonable circuit parameter optimization. And simultaneously has a common mode rejection level of better than 35dB in the range of a differential mode operating frequency band.
(Wideband balanced filters with high selectivity and common-mode suppression,IEEE Microwave Wireless Compon Lett 63) A balanced filter structure with high selectivity and high common mode rejection of broadband designed based on a mode of loading branches by coupled lines is provided. The band-pass characteristic under the differential mode and the band-stop characteristic under the common mode are realized by adopting the improved coupling feeder line and the coupling line to load the branch resonator. In the 0.5-11GHz range, there is a common mode rejection of more than 20 dB. However, the near-end out-of-band rejection of this balanced filter in the differential mode is not better, only around 38 dB. And the common mode suppression degree in the differential mode working frequency band is only about 50 dB.
Some special english explanations will be mentioned here:
J-converter: inverting the converter; frequency: a frequency; s dd 21 |: differential mode transmission coefficients;
S dd 11 |: a differential mode reflection coefficient; s cc 21 |: common mode transmission coefficients; s: a source; l: a load;
Disclosure of Invention
The purpose of the invention is that: A5G balance filter with high common mode rejection is provided, so that the balance filter can show a band-pass filter characteristic with a fourth order and a relative bandwidth (3 dB) of 13.4% at 2.6GHz under differential mode excitation, and has a stop band rejection effect of 65dB near 2.6GHz under common mode excitation.
In order to achieve the above object, the design idea of the present invention is to design a balance filter having both high common mode rejection and excellent differential mode filtering characteristics, and specifically adopts the following technical scheme: the 5G balance filter with high common mode rejection comprises a medium substrate, wherein a circuit is arranged on the upper surface of the medium substrate, and comprises an input feeder line, an output feeder line, a stepped impedance coupling line, a J-converter, a first branch loaded at the tail end of the J-converter, a second branch loaded at the tail end of the J-converter, a uniform impedance resonator, a middle short circuit point of the uniform impedance resonator, differential pair input end ports (1, 1 ') of the balance filter and differential pair output end ports (2, 2') of the balance filter; the step impedance coupling line is positioned between the input feeder line and the output feeder line and has a negative coupling effect; one end of the J converter is connected with an input feeder, and the other end of the J converter performs tap feed on the first branch joint and the second branch joint which are connected in parallel; the uniform impedance resonator and the J-converter are subjected to gap coupling feed; the uniform impedance resonator is provided with a short circuit point at the horizontal symmetrical plane; the J-type transformer is coupled with the uniform impedance resonators through gap coupling, and the uniform impedance resonators are coupled through gaps.
Further, an equivalent differential mode circuit and an equivalent common mode circuit of the balance filter are obtained by using a parity mode analysis method.
Further, the resonance condition of the resonator is obtained by analyzing the input impedance of the first branch and the second branch connected in parallel in the equivalent differential mode and common mode circuit.
Furthermore, the coupling line with the ladder impedance resonance shape is adopted to couple the input feeder line and the output feeder line, and the negative coupling effect is generated.
Furthermore, according to the equivalent differential mode circuit, an equivalent topological structure of the balance filter under differential mode excitation is provided.
Further, the short circuit branch is loaded at the symmetrical plane of the uniform impedance resonator, and the result is obtained by analyzing an equivalent common mode circuit: independently adjusting the electrical length of the shorting stub enables independent adjustment of the common mode response.
Further, the working frequency band of the microstrip filter covers 2.515GHz-2.675GHz (mobile 5G frequency band).
Further, the overall volume of the circuit is 0.34 lambda g×0.52λgg which is the guided wave wavelength corresponding to 2.6 GHz).
Compared with the prior art, the invention has the beneficial effects that:
1. The balance filter designed by the invention has a novel differential mode coupling topological structure, and the high-selectivity band-pass filter characteristics of four-order in-band and four transmission zero points out-of-band under differential mode excitation are realized by using a novel resonator coupling mode of loading parallel short circuit and open circuit branches by using novel input and output coupling lines and a source negative coupling technology.
2. The open-circuit branch and the short-circuit branch which are connected in parallel can be connected in parallel for resonance under a specific condition, and can be equivalent to a quarter-wavelength resonator; under differential mode excitation, the middle two-stage resonator is equivalent to a short-circuit quarter-wave resonator, and a signal transmission path is added by adding the step impedance source negative coupling between the source and the load, so that a plurality of transmission zeros can be formed on differential mode and common mode response, and the filter characteristic of a differential mode working frequency band is greatly improved.
3. The step impedance ratio of the source negative coupling line is adjusted, so that the out-of-band rejection characteristic of the differential mode response is improved, the high-frequency stop band rejection reaches 45dB, and the low-frequency stop band rejection reaches 66dB. The common mode response is independently adjusted by loading short circuit branches on the symmetry plane of the filter intermediate uniform impedance resonator, so that the common mode rejection in the differential mode working frequency band reaches 65dB. And meanwhile, excellent differential mode filtering characteristics and common mode rejection in a differential mode working frequency band exceeding 65dB are realized.
Drawings
Fig. 1 is a schematic diagram of a balanced filter with high common mode rejection in an embodiment.
Fig. 2 is an ideal transmission line model of a high common mode rejection balanced filter in an embodiment.
Fig. 3 (a) shows an equivalent differential mode circuit schematic diagram of a high common mode rejection balanced filter according to an embodiment, and (b) shows an equivalent common mode circuit schematic diagram of a high common mode rejection balanced filter according to an embodiment.
Fig. 4 is a diagram of an equivalent coupling topology of a balanced filter under differential mode excitation in an embodiment.
Fig. 5 is an illustration of the effect of the source negative coupling ladder impedance ratio α on the out-of-differential-mode rejection and common-mode transmission zero (unloaded uniform-impedance resonator short-circuit stub) in an embodiment.
FIG. 6 is an illustration of the effect of center-loaded short-circuit stub width w 9 on the differential-mode, common-mode response of a balanced filter in an embodiment.
FIG. 7 is an illustration of the effect of center-loaded short-circuit stub length l 14 on the differential-mode, common-mode response of the balanced filter in an embodiment.
Fig. 8 is a diagram of the actual circuit processing of a balanced filter with high common mode rejection in an embodiment.
Fig. 9 is a differential mode, common mode simulation and test curve of the high common mode rejection balanced filter in the embodiment.
Detailed Description
The present invention will now be explained more fully with reference to the accompanying drawings and examples.
The design idea of the present embodiment is to design a balance filter having both high common mode rejection and excellent differential mode filter characteristics. The specific implementation mode is as follows:
Fig. 1 is a high common mode rejection balanced filter structure proposed in this embodiment. The circuit structure is vertically symmetrical about a horizontal central axis of the circuit. The circuit specifically comprises an input coupling line terminal loading open-circuit short-circuit resonator, an output coupling line terminal loading open-circuit short-circuit resonator, a ladder impedance-shaped source and load coupling line, and two intermediate-order coupling lines. The specific circuit dimension parameter (i represents the length of the microstrip line, w represents the width of the microstrip line, r represents the radius of the ground hole) is ,l1=4.2,l2=8.3,l3=6.6,l4=9.4,l5=4.5,l6=1.25,l7=3.5,l8=2,l9=3.15,l10=2.5,l11=1.85,l12=1.9,l13=5.95,l14=1.5,w1=1.75,w2=0.8,w3=0.8,w4=2.05,w5=0.8,w6=0.6,wf=1.9,w9=0.6,c1=0.3,c2=1.35,c3=0.3,r=0.1;, the unit of the above parameter is unified as mm, and the source negative coupling step impedance ratio α=5. For ease of analysis, fig. 2 models the ideal transmission line equivalent of the balanced filter. It is apparent from fig. 2 that the filter as a whole is symmetrical about the axis AA'.
The equivalent differential mode circuit shown in fig. 3 (a) and the equivalent common mode circuit shown in fig. 3 (b) of the balance filter can be obtained by the odd-even mode analysis theory. Wherein the equivalent common mode circuit can be regarded as an equivalent circuit of the balanced filter under common mode excitation. The equivalent differential mode circuit can be regarded as an equivalent circuit of the balance filter under differential mode excitation.
The method for loading open circuit and short circuit branches on the terminals of input and output coupled lines is novel in the coupling mode between resonators by independently analyzing the equivalent differential mode circuit, and the method has the great advantage that the circuit can be miniaturized to a certain extent due to the adoption of a better coupling structure. The parallel open branch and short branch can be equivalent to a quarter-wavelength resonator when resonating. The input impedance of the parallel open branch and short branch is:
Where Z is the characteristic impedance of the ideal transmission line, θ is the electrical length of the ideal transmission line, j is the imaginary unit, Z 1 is the open-circuit branch characteristic impedance in FIG. 3 (a), Z 2 is the short-circuit branch characteristic impedance in FIG. 3 (a), θ 1 is the open-circuit branch electrical length in FIG. 3 (a), and θ 2 is the short-circuit branch electrical length in FIG. 3 (a).
When Z in1DM = infinity, the open branch and the short branch resonate in parallel, providing a resonant mode. The middle two-order resonator is a quarter-wavelength resonator.
The coupled line terminal can be obtained by independently analyzing the equivalent common mode circuit to load two parallel open-circuit branches. When two parallel open branches resonate, the equivalent is a half-wavelength resonator, and the input impedance is as follows:
Where j is an imaginary unit, Z 1 is the open circuit branch characteristic impedance in fig. 3 (b), Z 2 is the open circuit branch characteristic impedance in fig. 3 (b), θ 1 is the open circuit branch electrical length of fig. 3 (b), and θ 2 is the open circuit branch electrical length of fig. 3 (b).
When Z in1CM = infinity, the two open branches resonate in parallel, equivalent to a half-wavelength resonator. The middle two-order resonator is a quarter-wavelength resonator.
By comparing and analyzing the equivalent differential mode and the common mode circuit, the equivalent common mode circuit is found to be more than the equivalent differential mode circuit by a truncated branch (the impedance is 2Z 7, and the electrical length is theta 7) on the intermediate-order resonator. The characteristics of the common mode circuit can be individually adjusted by adjusting the circuit parameters Z 7 and θ 7 while not affecting the characteristics of the differential mode circuit. This feature can play an important role in the subsequent optimization of the common mode rejection ratio.
In order to further study the differential mode operating band characteristics of the balanced filter, an equivalent coupling topology of the balanced filter under differential mode excitation as in fig. 4 is proposed according to the equivalent differential mode circuit in fig. 3 (b). The novel coupling structure mode and the equivalent of a quarter-wavelength resonator when the short circuit branch and the open circuit branch are in parallel resonance can be clearly obtained from fig. 4, and two resonance modes are provided. Wherein the solid lines between the open branch, the short branch and the source and the load represent the way the microstrip line is connected. There are two paths for energy transfer between the source and the load: one is a resonator passing through two quarter wavelengths; and secondly, the microstrip line solid line source is negatively coupled through a ladder impedance shape. The number of transmission zeros under differential mode excitation can be increased, and thus the differential mode filter characteristic can be improved. Resonance mode 2 and resonance mode 3 are provided by a quarter wave resonator. The dashed lines between the resonators, between the source and the load represent gap couplings. The balanced filter will therefore exhibit the characteristics of a bandpass filter under differential mode excitation, which has four resonant modes and has multiple transmission zeros.
The specific effect of source negative coupling on the filter differential common mode response is explored next. Fig. 5 shows the effect of the source negative coupled microstrip line impedance ratio α=w 8/w7 on the differential mode transmission response (|s dd 21 |) and the common mode transmission response (|s cc 21 |). The out-of-band rejection of the differential mode transmission response band-pass filter becomes significantly higher when the impedance ratio α varies from 1 to 5 with other parameters in the circuit unchanged. At the same time, the common mode transmission response is suppressed to be gradually deteriorated in the range of the band-pass filter operating frequency band.
After knowing the out-of-band rejection method for improving the differential mode transmission response, the common mode rejection of the common mode transmission response in the band-pass filter operating frequency range can be independently optimized by adjusting the physical dimensions corresponding to Z 7 and theta 7, namely w 9 and l 14. Fig. 6 and 7 explore the specific effect of the width and length w 9 and l 14 of the center-loaded short-circuit stub on |s dd 21|、|Scc 21 |. From fig. 6, it is known that when w 9 is changed from 0.3mm to 0.9mm, |s dd 21 | is unchanged, |s cc 21 | common mode rejection in the range of |s dd 21 | operating frequency band is slowly increasing. From fig. 7, it is clear that when l 14 is changed from 0.5mm to 2.5mm, |s dd 21 | is unchanged, |s cc 21 | is significantly improved in common mode rejection in the range of |s dd 21 | operating frequency band. Therefore, the out-of-band rejection of the differential mode response and the common mode rejection in the differential mode working frequency band can be simultaneously achieved to be designed optimally by reasonably adjusting l 14 and alpha.
And after the simulation result is optimized, processing the balance filter with high common mode rejection by using an FR4 dielectric plate with the thickness of 1mm to obtain a circuit object. The whole size of the circuit is 0.34 lambda g×0.52λgg which is the guided wave wavelength of the FR4 dielectric board at 2.6 GHz.
Finally, the differential mode and common mode simulation and test results of the balanced filter with high common mode rejection are summarized in fig. 9. Firstly, the response of a differential mode or a common mode can be obtained, and the simulation curve and the test curve are well matched. In the differential mode response, the center frequency of the fourth-order band-pass filter is 2.65GHz, the 3dB bandwidth is 13.4%, the maximum insertion loss in the working frequency band is 3.1dB, and the minimum in-band return loss is 13dB. Having four transmission zeroes makes the out-of-band rejection of the band-pass filter better than 45dB. In addition, in the common-mode response, the common-mode rejection effect of 65dB is achieved in the operating frequency band range of the band-pass filter.
The preferred embodiments of the present application have been described in detail, but the application is not limited to the examples. Various equivalent changes and substitutions can be made by those skilled in the art without departing from the spirit of the application, and such equivalent changes and substitutions are intended to be included within the scope of the application as defined in the claims.

Claims (4)

1. A high common mode rejection 5G balanced filter, characterized by: the circuit comprises an input feeder line, an output feeder line, a stepped impedance coupling line, a J-converter, a first branch loaded at the tail end of the J-converter, a second branch loaded at the tail end of the J-converter, a uniform impedance resonator, a middle short circuit point of the uniform impedance resonator, differential pair input end ports (1, 1 ') of a balance filter and differential pair output end ports (2, 2') of the balance filter; the step impedance coupling line is positioned between the input feeder line and the output feeder line and has a negative coupling effect; one end of the J converter is connected with an input feeder, and the other end of the J converter performs tap feed on the first branch joint and the second branch joint which are connected in parallel; the uniform impedance resonator and the J-converter are subjected to gap coupling feed; the uniform impedance resonator is provided with a short circuit point at the horizontal symmetrical plane; the J-type converter is coupled with the uniform-impedance resonators through gap coupling, and the gap coupling is adopted as the coupling between the uniform-impedance resonators;
The filter uses a parity mode analysis method to obtain an equivalent differential mode circuit and an equivalent common mode circuit of the balance filter; analyzing input impedance of the first branch and the second branch which are connected in parallel in the equivalent differential mode circuit and the equivalent common mode circuit to obtain a resonance condition;
the equivalent differential mode circuit adopts a method of loading parallel open-circuit branches and short-circuit branches at the terminals of input and output coupling lines to couple resonators; when the parallel open branch and the short branch resonate, the equivalent is a quarter-wavelength resonator; the input impedance of the parallel open branch and short branch is:
Wherein j is an imaginary unit, Z1 and Z2 are branch characteristic impedance, and theta 1 and theta 2 are branch electricity lengths;
When Zin1DM is in an = infinity state, the open-circuit branch and the short-circuit branch are in parallel resonance, a resonance mode is provided, and the middle two-order resonator is a quarter-wavelength resonator;
the equivalent common mode circuit adopts a method of loading two parallel open-circuit branches at the terminal of an input coupling line to couple resonators; when two parallel open branches resonate, the equivalent is a half-wavelength resonator, and the input impedance is as follows:
Wherein j is an imaginary unit, Z1 and Z2 are branch characteristic impedance, and theta 1 and theta 2 are branch electricity lengths;
When Zin1 CM= infinity, two open branches are in parallel resonance, which is equivalent to a half-wavelength resonator, and the middle two-order resonator is a quarter-wavelength resonator;
According to an equivalent differential mode circuit, an equivalent coupling topological structure of the balance filter under differential mode excitation is provided, the equivalent coupling topological structure is a quarter-wavelength resonator when a short-circuit branch and an open-circuit branch are in parallel resonance, four resonance modes are provided, the open-circuit branch and the short-circuit branch in the first resonance mode are connected with a source through a microstrip line, and the open-circuit branch and the short-circuit branch in the fourth resonance mode are connected with a load through the microstrip line;
there are two paths for energy transfer between the source and the load: one is a resonator passing through two quarter wavelengths in the second and third resonance modes; secondly, realizing source negative coupling through a ladder impedance microstrip line;
In a first path of energy transfer between the source and the load, the coupling modes between the quarter-wave resonator in the second resonance mode and the quarter-wave resonator in the third resonance mode of the source and the load are slot coupling;
in a second path of energy transfer between the source and the load, the source is coupled to the load in a slot coupling.
2. A high common mode rejection 5G balanced filter according to claim 1, wherein: the circuit as a whole is vertically symmetrical about a horizontal central axis.
3. A high common mode rejection 5G balanced filter as in claim 1 wherein: the dielectric substrate is an FR4 board with a relative dielectric constant of 4.4 and a thickness of 1 mm; the input feeder and the output feeder are 50Ω feeders.
4. A high common mode rejection 5G balanced filter as in claim 2 or 3 wherein: the whole volume of the circuit is 0.34 lambdag multiplied by 0.52 lambdag, and lambdag is the guided wave wavelength corresponding to 2.6 GHz.
CN202410092042.6A 2024-01-23 2024-01-23 5G balance filter with high common mode rejection Active CN117613529B (en)

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