CN114639932B - Microstrip differential band-pass filter - Google Patents
Microstrip differential band-pass filter Download PDFInfo
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- CN114639932B CN114639932B CN202210305403.1A CN202210305403A CN114639932B CN 114639932 B CN114639932 B CN 114639932B CN 202210305403 A CN202210305403 A CN 202210305403A CN 114639932 B CN114639932 B CN 114639932B
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Abstract
The invention provides a microstrip differential band-pass filter, which belongs to the technical field of radio frequency microwave filters and comprises a PCB top layer, a dielectric substrate and a PCB bottom layer in sequence, wherein the PCB top layer and the PCB bottom layer are correspondingly provided with microstrip structures, and the microstrip differential band-pass filter and the dielectric substrate positioned between the two microstrip structures jointly form a microstrip differential circuit; the microstrip differential circuit comprises a fourth capacitor, a first differential transformer, a fifth capacitor, a second differential transformer and a sixth capacitor in sequence; the first differential transformer and the second differential transformer are formed by sequentially connecting a plurality of microstrip lines alternately positioned on the top layer and the bottom layer of the PCB in series through metalized through holes penetrating through the dielectric substrate. The invention utilizes the differential transformer to convert the inductive coupling differential band-pass filter into the differential band-pass filter with simpler and symmetrical structure, is suitable for being realized on a PCB board through the design of a microstrip line, and has the advantages of convenient debugging and large adjustable range of the frequency band of the filter.
Description
Technical Field
The invention belongs to the technical field of radio frequency microwave filters, and particularly relates to a microstrip differential band-pass filter.
Background
The filter is a basic device in electronics and is one of key components in a wireless communication transceiver, and the performance of the filter directly affects the performance of a system in which the filter is located. The primary function of the filter is to pass certain frequency components of the signal while significantly attenuating other frequency components. By using the frequency selection function of the filter, interference noise can be filtered out or spectrum analysis can be carried out. When referring to a communication system, differential circuits always provide superior performance compared to single-ended circuits. For example, higher signal amplitudes can be achieved with differential circuits than with single-ended circuits. Differential signals can provide twice the amplitude of single-ended signals, and better linearity and SNR (signal-to-noise ratio) performance at the same supply voltage. In recent years, with the research of differential circuits, effective suppression of harmful signals in a system has been achieved. Differential circuits have an intrinsic suppression of ambient noise and electromagnetic interference in the system compared to single-ended circuits. More and more microwave devices are designed in a differential structure, such as power amplifiers, mixers, low noise amplifiers and the like. The differential filter plays a very important role, and not only needs to have good differential mode response and common mode rejection in a required frequency band, but also has good frequency selectivity, transmission zeros appear on both sides of a differential mode passband as much as possible, and in addition, wide and good out-of-band rejection is also a necessary characteristic. Therefore, the differential filter has been widely regarded and studied.
An inductively coupled differential band-pass filter is a common differential filter, and has a circuit structure as shown in fig. 1, including a first inductor L 1 A second inductor L 2 A third inductor L 3 A fourth inductor L 4 A fifth inductor L 5 A sixth inductor L 6 A seventh inductor L 7 A first capacitor C 1 A second capacitor C 2 And a third capacitance C 3 (ii) a Wherein, the first inductance L 1 And a second inductance L 2 The differential positive line is connected in series; third inductance L 3 And a fourth inductance L 4 The differential negative line is connected in series; fifth inductance L 5 And a first capacitor C 1 Forming a first resonant circuit connected in parallel to the differential input terminal; sixth inductance L 6 And a second capacitor C 2 A second resonant circuit having two ends respectively connected to the first inductor L 1 A second inductor L 2 And a third inductance L 3 A fourth inductor L 4 To (c) to (d); seventh inductor L 7 And a third capacitance C 3 A third resonant circuit is formed in parallel with the differential output. Ideally the above parameters should be satisfied: l is a radical of an alcohol 1 ＝L 2 ＝L 3 ＝L 4 ，L 5 ＝L 6 ＝L 7 ，C 1 ＝C 3 。
In recent years, the development of microstrip differential filters has been extremely rapid. Scholars at home and abroad research and provide various microstrip-based differential filter design methods, and the development of the microwave differential filter is powerfully promoted. At present, the microstrip differential filter structure mainly comprises a double-sided parallel strip line structure, a coupling-based microstrip stepped impedance line structure, a cross resonator and a microstrip-slot line structure.
For an inductively coupled differential band-pass filter composed of a plurality of inductors and capacitors, a microstrip line is adopted on a PCB (printed circuit board) to design the inductively coupled differential band-pass filter into a microstrip differential band-pass filter, and the microstrip differential band-pass filter has the defects of complex structure, narrow bandwidth, difficulty in debugging and the like and is limited in application.
Disclosure of Invention
The invention provides a micro-strip differential band-pass filter aiming at the problems of the inductive coupling differential band-pass filter in the background technology, and compared with a micro-strip circuit based on the inductive coupling differential band-pass filter, the micro-strip differential band-pass filter has the advantages of simple and symmetrical structure and easiness in implementation.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a microstrip differential band-pass filter is characterized by comprising a PCB top layer, a dielectric substrate and a PCB bottom layer which are sequentially arranged, wherein the PCB top layer and the PCB bottom layer comprise two correspondingly arranged floor boards and a microstrip structure positioned between the two floor boards, and the microstrip structures of the PCB top layer and the PCB bottom layer and the dielectric substrate positioned between the two floor boards jointly form a microstrip differential circuit;
the microstrip differential circuit is of a symmetrical structure and comprises fourth capacitors C which are sequentially arranged 4 A first differential transformer, a fifth capacitor C 5 A second differential transformer and a sixth capacitor C 6 (ii) a The first differential transformer and the second differential transformer are formed by sequentially connecting a plurality of microstrip lines alternately positioned on the top layer and the bottom layer of the PCB in series through metalized through holes penetrating through the dielectric substrate; the fourth capacitor C 4 A sixth capacitor C connected to the differential input terminal 6 Connected with the differential output terminal.
Further, the fourth capacitor C 4 And a sixth capacitance C 6 Is equal to the first capacitance C of the corresponding inductively coupled differential band-pass filter under ideal conditions 1 And a third capacitance C 3 The capacitance value of (c).
Further, the parameters of the first differential transformer and the second differential transformer are the same, and the self-inductance L is a 、L b And the mutual inductance M satisfies:
wherein Z is 1 、Z 5 And Z 6 First inductors L respectively corresponding to the inductively coupled differential band-pass filters in an ideal state 1 A fifth inductor L 5 And a sixth inductance L 6 The impedance of (a);
because the inductive coupling differential band-pass filter satisfies under the ideal condition: z is a linear or branched member 5 ＝Z 6 Therefore, it is
Where ω is the angular frequency of the transmitted signal and j is the imaginary unit.
Further, self-inductance L at the first and second differential transformers a 、L b And mutual inductance M, and a fourth capacitance C 4 And a sixth capacitance C 6 Is determined, a fifth capacitance C is obtained by simulation optimization 5 The capacitance value of (c).
Further, the fourth capacitor C 4 A first differential transformer, a second differential transformer and a third differential transformerSix capacitors C 6 With respect to the fifth capacitance C 5 And (4) symmetry.
Further, the fourth capacitor C 4 A fifth capacitor C 5 And a sixth capacitance C 6 The capacitor is a flat capacitor and consists of a microstrip line positioned on the top layer of the PCB, a dielectric substrate and a microstrip line positioned on the bottom layer of the PCB.
Furthermore, the two floor boards on the top layer of the PCB are connected with the corresponding floor boards on the bottom layer of the PCB through the metalized through holes penetrating through the dielectric substrate.
Further, the self-inductance and mutual inductance of the first differential transformer and the second differential transformer are adjusted by controlling the line width of the microstrip line, the geometric shape of the microstrip line and the position and size of the metalized via hole.
The invention has the beneficial effects that:
the invention provides a novel microstrip differential band-pass filter, which utilizes a differential transformer to convert an inductively coupled differential band-pass filter into a differential band-pass filter with simpler and more symmetrical structure. The structure is suitable for being realized on a PCB board through the design of the microstrip line, and has the advantages of simple and symmetrical structure, convenience in debugging and large adjustable range of the frequency band of the filter.
Drawings
FIG. 1 is a schematic diagram of a circuit configuration of an inductively coupled differential bandpass filter;
FIG. 2 is a simulation of an inductively coupled differential bandpass filter in a comparative example;
fig. 3 is a schematic circuit structure diagram of a microstrip differential bandpass filter according to an embodiment of the present invention;
fig. 4 is a simulation diagram of a microstrip differential bandpass filter according to an embodiment of the invention;
FIG. 5 shows a fourth capacitor C according to an embodiment of the present invention 4 A fifth capacitor C 5 And a sixth capacitance C 6 A schematic diagram of the plate capacitor is adopted;
fig. 6 is a schematic structural diagram of a first differential transformer and a second differential transformer in the embodiment of the present invention;
fig. 7 is a top perspective structural view of the microstrip differential bandpass filter according to the embodiment of the invention;
fig. 8 is a bottom perspective structure diagram of the microstrip differential bandpass filter according to the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Comparative example
The comparison example provides an inductively coupled differential bandpass filter, which has a structure shown in FIG. 1 and includes a first inductor LL 1 A second inductor L 2 A third inductor L 3 A fourth inductor L 4 A fifth inductor L 5 And a sixth inductor L 6 A seventh inductor L 7 A first capacitor C 1 A second capacitor C 2 And a third capacitance C 3 (ii) a Wherein, the first inductance L 1 And a second inductance L 2 The differential positive lines are connected in series; third inductance L 3 And a fourth inductance L 4 The differential negative line is connected in series; fifth inductance L 5 And a first capacitor C 1 Forming a first resonant circuit connected in parallel to the differential input terminal; sixth inductance L 6 And a second capacitor C 2 A second resonant circuit having two ends respectively connected to the first inductor L 1 A second inductor L 2 And a third inductance L 3 A fourth inductor L 4 To (c) to (d); seventh inductor L 7 And a third capacitance C 3 A third resonant circuit is formed in parallel with the differential output.
The inductive coupling differential band-pass filter has the following parameters in an ideal state: l is 1 ＝L 2 ＝L 3 ＝L 4 ＝4.034nH，L 5 ＝L 6 ＝L 7 ＝4.216nH，C 1 ＝C 3 ＝1.525pF，C 2 ＝2.048pF。
The inductively coupled differential band-pass filter proposed by the comparative example is introduced into ADS (advanced design System) software for simulation, and the simulation result is shown in FIG. 2, which shows that the pass band range is about 1.8 GHz-2.9 GHz and the bandwidth is about 1.1GHz.
Examples
The structure of the microstrip differential band-pass filter is shown in fig. 3 and comprises a PCB top layer, a dielectric substrate and a PCB bottom layer which are sequentially arranged, the PCB top layer and the PCB bottom layer comprise two floors which are correspondingly arranged and a microstrip structure which is positioned between the two floors, and the two microstrip structures and the dielectric substrate which is positioned between the two microstrip structures form a microstrip differential circuit together.
The floor of the PCB top layer and the floor of the PCB bottom layer are made of large copper sheets, and the two floor of the PCB top layer are connected with the corresponding floor of the PCB bottom layer through metallized through holes penetrating through the dielectric substrate.
The microstrip differential circuit comprises a fourth capacitor C which is arranged in sequence 4 A first differential transformer, a fifth capacitor C 5 A second differential transformer and a sixth capacitor C 6 Fourth capacitor C 4 A first differential transformer, a second differential transformer, and a sixth capacitor C 6 With respect to the fifth capacitance C 5 And (4) symmetry. Differential signals are input from the differential input end and sequentially pass through a fourth capacitor C 4 A first differential transformer, a fifth capacitor C 5 A second differential transformer and a sixth capacitor C 6 And then output from the differential output terminal.
The fourth capacitor C 4 A fifth capacitor C 5 And a sixth capacitance C 6 All of which are flat capacitors, and the structure of which is shown in fig. 5 is composed of a microstrip line positioned on the top layer of the PCB, a dielectric substrate and a microstrip line positioned on the bottom layer of the PCB. The medium substrate is made of FR4 material, the dielectric constant is 9.6, and the medium thickness is 0.508mm; fourth capacitor C in this embodiment 4 And a sixth capacitance C 6 Is equal to the first capacitor C of the inductively coupled differential bandpass filter of the comparative example 1 And a third capacitance C 3 The capacitance value of (1.525 pF); the size C of the plate capacitor is controlled to be a littleThe area and the shape of the strip line are determined, and the calculation formula is as follows:
wherein d is the plate interval, and the plate interval is the thickness of the medium substrate; epsilon 0 A dielectric constant in vacuum of 8.85X 10 12 (F/m)；ε r Relative dielectric constant, here 9.6; when the capacitance value is 1.525pF, microstrip line area S is:
namely, a square microstrip line with a side length of about 3mm can be equivalent to the required plate capacitor. The above calculation is only for the case of ideal capacitance, and the shape and size of the microstrip line need to be adjusted in practice.
As shown in fig. 6, the first differential transformer and the second differential transformer are formed by sequentially connecting a plurality of microstrip lines alternately located on the top layer and the bottom layer of the PCB in series through metalized via holes penetrating through the dielectric substrate. FIG. 7 is a top perspective structural view of the microstrip differential bandpass filter, i.e. a structural view from the top layer of the PCB to the bottom layer of the PCB; fig. 8 is a bottom perspective structural view of the microstrip differential bandpass filter, i.e. a structural view from the bottom layer of the PCB to the top layer of the PCB.
The metalized via holes are adopted, so that the lines can be arranged back and forth between the top layer and the bottom layer of the PCB, the design of the first differential transformer and the second differential transformer is completed between the micro-strip lines of the top layer and the bottom layer of the PCB, and the self-inductance L of the first differential transformer and the self-inductance L of the second differential transformer are adjusted by controlling the line width, the geometric shape of the arranged lines and the positions and the sizes of the metalized via holes of the micro-strip lines of the top layer and the bottom layer of the PCB a 、L b And mutual inductance M.
In this embodiment, the first differential transformer and the second differential transformer have the same parameters and self-inductance L a 、L b And the mutual inductance M satisfies:
wherein Z is 1 、Z 5 And Z 6 First inductors L respectively corresponding to the inductively coupled differential band-pass filters in an ideal state 1 A fifth inductor L 5 And a sixth inductance L 6 The impedance of (2);
since the inductively coupled differential bandpass filter in the comparative example is ideally satisfied: l is a radical of an alcohol 5 ＝L 6 =4.216nH, the first differential transformer and the second differential transformer in this embodiment ideally satisfy:
where ω is the angular frequency of the transmitted signal and j is the imaginary unit.
Self-inductance L at first and second differential transformers a 、L b And mutual inductance M, and a fourth capacitance C 4 And a sixth capacitance C 6 In the case of a determined capacitance value, the fifth capacitance C 5 And as an adjustable variable, debugging the microstrip differential band-pass filter through simulation optimization. When the fifth capacitor C 5 When the capacitance value of (2.7902 pF), the simulation result is shown in FIG. 4, it can be seen that the pass band range is about 1.875GHz to 3.575GHz, the bandwidth is about 1.7GHz, and the comparison exampleCompared with a simulation structure of the medium-inductance coupling differential band-pass filter, the bandwidth is increased to a certain extent, and meanwhile, the simulation structure is simple and symmetrical and is convenient to debug.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (4)
1. A microstrip differential band-pass filter is characterized by comprising a PCB top layer, a dielectric substrate and a PCB bottom layer which are sequentially arranged, wherein the PCB top layer and the PCB bottom layer respectively comprise two correspondingly arranged floor boards and a microstrip structure positioned between the two floor boards, and the two microstrip structures and the dielectric substrate positioned between the two microstrip structures jointly form a microstrip differential circuit;
the microstrip differential circuit is of a symmetrical structure and comprises a fourth capacitor C which is arranged in sequence 4 A first differential transformer, a fifth capacitor C 5 A second differential transformer and a sixth capacitor C 6 (ii) a The first differential transformer and the second differential transformer are formed by sequentially connecting a plurality of microstrip lines alternately positioned on the top layer and the bottom layer of the PCB in series through metalized through holes penetrating through the dielectric substrate; the fourth capacitor C 4 A sixth capacitor C connected to the differential input terminal 6 Connected with the differential output terminal.
2. The microstrip differential bandpass filter according to claim 1, wherein the fourth capacitance C 4 A fifth capacitor C 5 And a sixth capacitance C 6 The capacitor is a flat capacitor and consists of a microstrip line positioned on the top layer of the PCB, a dielectric substrate and a microstrip line positioned on the bottom layer of the PCB.
3. The microstrip differential bandpass filter according to claim 1, wherein both of the floor boards of the top layer of the PCB board are connected to the corresponding floor board of the bottom layer of the PCB board through a metalized via hole penetrating the dielectric substrate.
4. The microstrip differential bandpass filter according to claim 1, wherein the self-inductance and the mutual inductance of the first differential transformer and the second differential transformer are adjusted by controlling the line width of the microstrip line, the geometry of the microstrip line, and the position and the size of the metalized via hole.
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| CN111641398A (en) * | 2020-04-23 | 2020-09-08 | 黄果池 | Numerical control passive microwave/millimeter wave band-pass filter based on-chip transformer |
| CN112904079A (en) * | 2021-01-22 | 2021-06-04 | 新郦璞科技(上海)有限公司 | Bidirectional radio frequency power detector, working method and system |
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| JP2001345601A (en) * | 2000-03-30 | 2001-12-14 | Toshiba Corp | Filter circuit |
| KR101119910B1 (en) * | 2010-05-03 | 2012-02-29 | 한국과학기술원 | Mobile RFID Reader Transceiver System |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111641398A (en) * | 2020-04-23 | 2020-09-08 | 黄果池 | Numerical control passive microwave/millimeter wave band-pass filter based on-chip transformer |
| CN112904079A (en) * | 2021-01-22 | 2021-06-04 | 新郦璞科技(上海)有限公司 | Bidirectional radio frequency power detector, working method and system |
Non-Patent Citations (1)
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| 《基于混合传输线结构的多层平面差分滤波器的研究》;郭欣;《中国优秀博硕士学位论文全文数据库(博士)》;20170615;全文 * |
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