CN116054772A - A Balanced Bandpass Filter with Wide Common Mode Rejection - Google Patents

Abstract

The invention discloses a wide common mode rejection balanced band-pass filter, wherein a pair of balanced input ports P1/P1 'are led out from a first series-parallel resonance circuit, a pair of balanced output ports P2/P2' are led out from a second series-parallel resonance circuit, two groups of differential input/output port networks are formed, a differential mode passband is formed, and four resonance points are formed by adjusting lumped element parameters in two series-parallel resonance circuit structures; and connecting the two groups of series-parallel resonant circuits in series and then connecting the series-parallel resonant circuits in parallel to form a transmission zero point. The invention realizes the excellent performances of simple structure, easy integration, broadband common mode suppression, high frequency selectivity and ultra-wide high stop band suppression, and is an important radio frequency passive device which is favorable for improving the stability of a radio frequency system and the communication performance of a radio frequency front end.

Description

A Balanced Bandpass Filter with Wide Common Mode Rejection

technical field

The invention relates to a band-pass filter, in particular to a wide common-mode suppression balanced band-pass filter.

Background technique

With the rapid development of communication technology, filter, as a frequency selective device, plays a vital role in facing the increasingly crowded and extremely complex electromagnetic environment. Filters are widely used in various microwave communication systems, electronic countermeasures systems, and radar systems. They can not only reduce the attenuation of signals in the working frequency band, but also suppress the interference of signals outside the working frequency band. The quality of its performance is directly related to It affects the microwave transmission performance of the entire communication system. It can be said that in various modern communication systems, microwave filters are the most critical and important microwave passive components for a complete communication system.

Microwave filters generally contain two ports, which can combine and separate spectrum resources, and allow microwave signals required by the system to pass through without loss and distortion within the passband range. In actual communication systems, as the communication electromagnetic environment becomes more and more complex, circuit noise signals and environmental noise signals will interfere with the microwave signals received by the system. Therefore, a balanced circuit with a common-mode signal suppression function is widely used in microwave filters, and then a four-port balanced filter is formed.

In recent years, various research institutions have proposed a series of balanced filters that can achieve better anti-noise ability and more compact system structure. Common balanced filters are mainly based on half-wave stub transmission line structures, coupled resonator structures with staggered passbands, dual-path signal interference structures, microstrip-slot line conversion structures, and special coupling line structures. Therefore, the size is large, the integration level is low, and due to the periodic change of the insertion loss phase, there are high-order modes outside the working frequency band, which has the disadvantages of common-mode signal suppression and narrow bandwidth of high-stop band suppression.

The balanced filter loaded with lumped elements has the advantages of compact structure and easy integration. There are few reports on differential filters based on lumped components. The few reported lumped parameter balanced filters are mainly composed of multiple T-shaped circuit structures, cross-shaped circuit structures combined with series and parallel capacitor structures, and the number of components There are many, and there are also problems such as narrow common-mode rejection bandwidth, poor frequency selectivity of some designs, high-order modes and complex structures.

Contents of the invention

Purpose of the invention: Aiming at the above-mentioned prior art, a wide common-mode rejection balanced bandpass filter is proposed, which is based on lumped elements, has high frequency selectivity and ultra-wide high stopband rejection, and is simple in structure, easy to integrate and miniaturize .

Technical solution: A wide common-mode rejection balanced bandpass filter, including a pair of balanced input ports P1/P1', a pair of balanced output ports P2/P2', and two series-parallel resonator circuits with upper and lower mirror images , a series resonant circuit;

A pair of balanced input ports P1/P1' are drawn from the first series-parallel resonant circuit, and a pair of balanced output ports P2/P2' are drawn from the second series-parallel resonant circuit to form two sets of differential input/output port networks. A differential mode passband is formed, and four resonance points are formed by adjusting the parameters of the lumped components in the two series-parallel resonant circuit structures; two sets of series-parallel resonant circuits are connected in series and connected in parallel with the series resonant circuit to form a transmission zero point.

Further, the first series-parallel resonant circuit includes first to fourth inductors, first to sixth capacitors, and a grounding structure, wherein the third inductor, the fourth inductor, the first inductor, the first capacitor, and the second inductor are connected end to end in sequence , the other end of the third inductor is connected to one end of the sixth capacitor, and the other end of the sixth capacitor leads to a balanced input port P1; a fourth capacitor is connected in parallel between the third inductor and the fourth inductor, and the other end of the fourth capacitor is grounded; A second capacitor is connected in parallel between the fourth inductor and the first capacitor, and the other end of the second capacitor leads to a balanced input port P1'; a second capacitor is connected in parallel between the first inductor and the first capacitor, and the other end of the second capacitor is grounded ; A third capacitor is connected in parallel between the first capacitor and the second inductor, and the other end of the third capacitor is grounded.

Further, the second series-parallel resonant circuit is symmetrically mirrored up and down from the first series-parallel resonant circuit, and the second series-parallel resonant circuit includes fifth to eighth inductors, seventh to twelfth capacitors, and a grounding structure, wherein the first The seventh inductance, the eighth inductance, the fifth inductance, the seventh capacitor and the sixth inductance are connected end to end in sequence, the other end of the seventh inductance is connected to one end of the eleventh capacitor 603, and the other end of the eleventh capacitor leads to a balanced output port P2 ; The tenth capacitor is connected in parallel between the seventh inductance and the eighth inductance, and the other end of the tenth capacitor is grounded; the twelfth capacitor is connected in parallel between the eighth inductance and the fifth inductance, and the other end of the twelfth capacitor leads to a balanced The output port P2'; the eighth capacitor is connected in parallel between the fifth inductor and the seventh capacitor, and the other end of the eighth capacitor is grounded; the ninth capacitor is connected in parallel between the seventh capacitor and the sixth capacitor, and the other end of the ninth capacitor is grounded.

Further, the series resonant circuit is composed of the ninth inductance and the thirteenth capacitor connected in series, and the other end of the thirteenth capacitor is grounded; connect the other end of the second inductance in the first series-parallel resonant circuit with the second inductance in the second series-parallel resonant circuit The other end of the sixth inductance is connected, and a series resonant circuit is connected in parallel at the connection, that is, it is connected with the other end of the ninth inductance in the series resonant circuit to form a complete wide common mode suppression balanced bandpass filter circuit structure.

Beneficial effects: the existing balanced microwave filter has problems such as complex structure, large volume, poor frequency selectivity, narrow common-mode suppression bandwidth, and high-order modes. A few reported lumped parameter balanced filters have problems such as a large number of lumped elements, complex structures, and poor common-mode rejection. The present invention designs a lumped element wide common-mode rejection balanced bandpass filter, which realizes the excellent performance of simple structure, easy integration, broadband common-mode rejection, high frequency selectivity and ultra-wide high stopband rejection. It is an important radio frequency passive device that is conducive to improving the stability of the radio frequency system and the communication performance of the radio frequency front end. specific:

1. The present invention uses lumped elements to construct a wide common-mode rejection, high-frequency selective bandpass filter, and utilizes lumped parameters to destroy the phase periodicity of the insertion loss signal, thereby realizing ultra-wide and high-stopband suppression characteristics.

2. One end of capacitors 601 and 602 in the first series-parallel resonant circuit leads to a pair of balanced input ports P1/P1', and one end of capacitors 601 and 602 in the second series-parallel resonant circuit leads to a pair of balanced output ports P2/ P2' constitutes two sets of differential input/output port networks, forms a differential mode passband, and effectively suppresses common mode signals.

3. Two sets of series-parallel resonant circuits are connected in series to form four reflection poles, which improves the utilization of the lumped components of the balanced filter and reduces the number of components required for each order of filter power division response.

4. A series resonator circuit structure is connected in parallel at the connection of two sets of series-parallel resonant circuits to form a transmission zero point to achieve strong frequency selection characteristics.

Description of drawings

Fig. 1 is the circuit structural diagram of wide common mode rejection balanced type bandpass filter of the present invention;

Fig. 2 is a schematic diagram of parameters of a wide common mode rejection balanced bandpass filter of the present invention;

Fig. 3 is the graph of differential mode signal reflection coefficient S _dd11 and transmission coefficient S _dd21 with frequency response in the embodiment;

FIG. 4 is a graph showing the frequency response of the common mode signal transmission coefficient S _cc21 in the embodiment.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

A wide common-mode rejection balanced bandpass filter based on lumped components suitable for radio frequency front-end systems, as shown in Figure 1, includes a pair of balanced input ports P1/P1', a pair of balanced output ports P2/ P2' is composed of two series-parallel resonator circuits with upper and lower mirror images, and a series resonant circuit.

The first series-parallel resonant circuit located above is composed of inductors 101, 102, 301, 302, capacitors 103, 104, 105, 303, 602, 601 and grounding structures, wherein inductors 301, inductors 302, inductors 101, capacitors 103 and inductors 102 are connected end to end in turn, the other end of the inductor 301 is connected to one end of the capacitor 601, and the other end of the capacitor 601 leads to a balanced input port P1; a capacitor 303 is connected in parallel between the inductor 301 and the inductor 302, and the other end of the capacitor 303 is grounded; A capacitor 602 is connected in parallel with the inductor 101, and the other end of the capacitor 602 leads to a balanced input port P1'; a capacitor 104 is connected in parallel between the inductor 101 and the capacitor 103, and the other end of the capacitor 104 is grounded; a capacitor 105 is connected in parallel between the capacitor 103 and the inductor 102 , the other end of the capacitor 105 is grounded.

The second series-parallel resonant circuit located below is symmetrically mirrored up and down from the first series-parallel resonant circuit, and the second series-parallel resonant circuit is composed of inductors 201, 202, 401, 402, capacitors 203, 204, 205, 403, 603, 604 and a grounding structure, wherein the inductor 401, inductor 402, inductor 201, capacitor 203, and inductor 202 are connected end to end in sequence, the other end of the inductor 401 is connected to one end of the capacitor 603, and the other end of the capacitor 603 leads to a balanced output port P2; A capacitor 403 is connected in parallel between the inductor 401 and the inductor 402, and the other end of the capacitor 403 is grounded; a capacitor 604 is connected in parallel between the inductor 402 and the inductor 201, and the other end of the capacitor 604 leads to a balanced output port P2'; the inductor 201 and the capacitor 203 are connected in parallel A capacitor 204, the other end of the capacitor 204 is grounded; a capacitor 205 is connected in parallel between the capacitor 203 and the inductor 202, and the other end of the capacitor 205 is grounded.

The series resonant circuit is composed of an inductor 501 and a capacitor 502 connected in series, and the other end of the capacitor 502 is grounded.

Connect the other end of the inductance 102 in the first series-parallel resonant circuit to the other end of the inductance 202 in the second series-parallel resonant circuit, and connect the series resonant circuit in parallel at the connection, that is, the other end of the inductance 501 in the series resonant circuit One end is connected to form a complete wide common mode rejection balanced bandpass filter circuit structure.

As shown in Figure 2, it is a schematic diagram of the circuit parameters of the wide common mode suppression balanced bandpass filter of the present invention. When the differential mode signal of equal amplitude and antiphase is input into the circuit from the port P1/P1', adjust the inductance 301, 302 and the capacitance 303, The parameter values in 601 and 602 make the signals at both ends of the port P1/P1' in phase, and the differential signal is transmitted to the port P2/P2' output through the first series-parallel resonant circuit structure, the series resonator and the second series-parallel resonant circuit structure, Among them, four resonance points are formed by adjusting the parameters of the lumped components in the two series-parallel resonant circuit structures, and the series resonant structure generates a transmission zero point in the low frequency band, forming better frequency selection characteristics. When a common-mode signal with equal amplitude and same phase is input into the circuit from the port P1/P1', the signals at both ends of the port P1/P1' are reversed, and the common-mode signals cancel each other out, forming a good common-mode rejection. Performances such as high frequency selectivity, broadband common-mode rejection, and broadband high-stopband rejection can be achieved by reasonably selecting the parameter values of each lumped element, and the number of lumped elements is small and the structure is simple.

The present invention designs a balanced bandpass filter with wide common mode suppression lumped elements, which realizes the advantages of simple structure, easy integration, broadband common mode suppression, high frequency selectivity and ultra-wide high stop band suppression, and improves the Balanced filter lumped component utilization reduces the number of components required for each order of filter response. In order to better illustrate the technical effects of the present invention, the present embodiment designs a wide common mode suppression lumped element balanced bandpass filter with a center frequency of 2 GHz, and performs optimization simulation verification, and the specific parameters are: L1=9.4 nH, C1=0.48pF, C2=0.11pF, L2=4.53nH, C3=2.75nH, L3=2.75nH, C4=5.4pF, C5=1.976pF. Circuits in other frequency bands can be obtained by adjusting the parameter values in this embodiment.

FIG. 3 is a graph showing the frequency response of the differential mode signal reflection coefficient S _dd11 and transmission coefficient S _dd21 obtained through simulation in this embodiment. It can be seen from the figure that when working in differential mode, the reflection coefficient S _dd11 can be less than -20dB in the range of 1.848～2.227GHz, and there are four reflection poles, and a transmission zero point is generated at 1.31GHz; in the stop band range of 0-1.693GHz Inside, the transmission coefficient S _dd21 is less than -20dB, and the frequency range where the high-frequency stopband transmission coefficient S _dd21 is less than -20dB is greater than 10f ₀ , and f ₀ is the working center frequency, which has strong frequency selection characteristics and broadband high stopband characteristics.

FIG. 4 is a graph showing the frequency response of the common-mode signal transmission coefficient S _cc21 obtained by simulation in this embodiment. It can be seen from the figure that when the common mode works, the common mode rejection can reach 23.2dB in the range of 0-20GHz, and two common mode transmission zeros are generated at the frequency points of 1.31GHz and 2.23GHz respectively, with ultra-wide common-mode rejection characteristics.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (4)

1. A wide common-mode rejection balanced bandpass filter is characterized in that it comprises a pair of balanced input ports P1/P1 ', a pair of balanced output ports P2/P2 ', two series-parallel connections of upper and lower mirror image distribution a resonator circuit, a series resonant circuit; A pair of balanced input ports P1/P1' are drawn from the first series-parallel resonant circuit, and a pair of balanced output ports P2/P2' are drawn from the second series-parallel resonant circuit to form two sets of differential input/output port networks. A differential mode passband is formed, and four resonance points are formed by adjusting the parameters of the lumped components in the two series-parallel resonant circuit structures; two sets of series-parallel resonant circuits are connected in series and connected in parallel with the series resonant circuit to form a transmission zero point. 2. wide common mode rejection balanced type bandpass filter according to claim 1, is characterized in that, the first series-parallel resonant circuit comprises the first to the fourth inductance (101,102,301,302), the first to The sixth capacitor (103, 104, 105, 303, 602, 601) and the grounding structure, wherein the third inductor (301), the fourth inductor (302), the first inductor (101), the first capacitor (103) and the The two inductors (102) are connected end to end in turn, the other end of the third inductor (301) is connected to one end of the sixth capacitor (601), and the other end of the sixth capacitor (601) leads to the balanced input port P1; ) and the fourth inductance (302) in parallel with the fourth capacitor (303), the other end of the fourth capacitor (303) is grounded; between the fourth inductance (302) and the first inductance (101) in parallel with the second capacitor ( 602), the other end of the second capacitor (602) leads to the balanced input port P1'; the second capacitor (104) is connected in parallel between the first inductor (101) and the first capacitor (103), and the second capacitor (104) The other end is grounded; a third capacitor (105) is connected in parallel between the first capacitor (103) and the second inductance (102), and the other end of the third capacitor (105) is grounded. 3. wide common-mode suppression balanced bandpass filter according to claim 2, is characterized in that, the second series-parallel resonant circuit is by the first series-parallel resonant circuit symmetrical mirror image up and down, the second series-parallel resonant circuit Including fifth to eighth inductors (201, 202, 401, 402), seventh to twelfth capacitors (203, 204, 205, 403, 603, 604) and a grounding structure, wherein the seventh inductor (401), the Eight inductances (402), fifth inductances (201), seventh capacitors (203) and sixth inductances (202) are connected end-to-end in sequence, and the other end of the seventh inductance (401) is connected to one end of the eleventh capacitor 603, and the tenth inductance The other end of a capacitor (603) leads to a balanced output port P2; a tenth capacitor (403) is connected in parallel between the seventh inductance (401) and the eighth inductance (402), and the other end of the tenth capacitor (403) is grounded; A twelfth capacitor (604) is connected in parallel between the eighth inductor (402) and the fifth inductor (201), and the other end of the twelfth capacitor (604) leads to a balanced output port P2'; the fifth inductor (201) and An eighth capacitor (204) is connected in parallel between the seventh capacitor (203), and the other end of the eighth capacitor (204) is grounded; a ninth capacitor (205) is connected in parallel between the seventh capacitor (203) and the sixth inductor (202), The other end of the ninth capacitor (205) is grounded. 4. wide common-mode rejection balanced type bandpass filter according to claim 3 is characterized in that, series resonant circuit is made up of the 9th inductance (501) and the thirteenth electric capacity (502) series connection, the thirteenth electric capacity ( The other end of 502) is grounded; The other end of the second inductance (102) in the first series-parallel resonant circuit is connected with the other end of the sixth inductance (202) in the second series-parallel resonant circuit, and at the connection The parallel series resonant circuit is connected with the other end of the ninth inductance (501) in the series resonant circuit to form a complete circuit structure of wide common mode suppression balanced bandpass filter.

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