A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection

Abstract

The application provides a differential filter with differential ultra-wideband band-pass and ultra-wideband common-mode suppression, which comprises a dielectric substrate, a resonator, a U-shaped transmission line symmetrical along a transverse central axis of the dielectric substrate, a stub and a gap line structure, and the stub is close to the U-shaped transmission line and the resonator; the U-shaped transmission line serves as an input / output end, so that signals of different frequencies enter the resonator from multiple paths of the stub after entering the gap line from the stub or from the gap line. The application increases the stub, so that the remaining differential signals enter the resonator through coupling, improves the bandwidth of differential signal transmission, generates a transmission zero point and a transmission pole point, and improves the passband performance; the resonator brings four in-band transmission pole points and multiple out-of-band transmission zero points near the passband, thereby improving the out-of-band suppression.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of filter design, and particularly relates to a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression. BACKGROUND

[0002] At present, communication technology is developing rapidly, and the demand for efficient and high-speed transmission is more urgent. Chips are constantly pursuing high frequency, high speed and small size, so the crosstalk influence in transmission is more and more obvious, and higher requirements are put forward for chip layout and wiring. At present, the chip clock frequency has exceeded 1GHz, and the signal integrity problem cannot be avoided. The traditional single-line interconnection cannot cope with the crosstalk problem, so more and more circuits use differential transmission lines. The differential filter can well suppress the common-mode signal caused by external noise interference due to the natural anti-interference characteristics of the differential line, and the two lines of the differential line are mutual return paths, which can also significantly reduce the external electromagnetic radiation. At present, differential transmission has been applied to many high-speed interfaces, such as PCI-E, USB3.0. Some serial protocols also use differential transmission, such as RS485 and RS-422.

[0003] At present, it is a big difficulty for the differential filter to realize wider frequency band and smaller rectangular coefficient under the condition of maintaining high common-mode suppression. For example, in 2020, Khaled Aliqab and other scholars published a paper entitled "Wideband Differential-Mode Bandpass Filters With Stopband and Common-Mode Suppression" in "IEEE Microwave and Wireless Components Letters" (VOL. 30, NO. 3, MARCH 2020), which proposed a wideband differential-mode bandpass filter. The filter is based on the optimized branch line structure using extended transmission lines, and has 4 horizontal connection lines on one side of the symmetry plane, 3 short stubs perpendicular to the symmetry plane, and the length of each is one quarter of the wavelength, so that the signal transmission can generate multiple paths, and multiple transmission poles can be generated in the passband by adjusting. The measured differential 3dB-FBW of the filter reaches 58%, and the common-mode suppression in the passband can reach-38dB, but because the coupling introduces new transmission poles in the upper stopband, the suppression of the upper stopband is affected.

[0004] For example, in 2024, Shipeng Zhao, Zhongbao Wang, et al. published a compact high-performance balanced wideband BPF in "IEEE Microwave and Wireless Technology Letters" (VOL. 34, NO. 6, JUNE 2024). The filter is based on a double-sided parallel strip line (DSPSL) structure, composed of two inverters, a short-circuit stub, a short-coupled line and an asymmetric three-line coupling structure with a band-loaded stub. By setting the DM signal to propagate in different paths to produce different phase shifts, the differential passband and stopband are formed due to the phase difference after superposition. The differential 3dB-FBW of the filter reaches 23.3%, and the common-mode suppression in the band can reach-30dB, and has very excellent out-of-band suppression, while realizing a wide notch band of 2.64GHz-3.36GHz. SUMMARY

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] The present application provides a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression, comprising a dielectric substrate, a resonator, a U-shaped transmission line symmetrical along the transverse central axis of the dielectric substrate, a stub and a gap line structure, and the stub is close to the U-shaped transmission line and the resonator; the U-shaped transmission line serves as the input / output end, so that signals of different frequencies enter the U-shaped transmission line and then enter the resonator from the stub or the gap line.

[0007] Specifically, the stub is a half-wavelength stub symmetrical along the transverse central axis of the dielectric substrate.

[0008] Specifically, the length of the part of the U-shaped transmission line perpendicular to the transverse central axis of the dielectric substrate is less than one-quarter wavelength of the upper limit cutoff frequency.

[0009] The design of the length of the perpendicular part being less than one-quarter wavelength of the upper limit cutoff frequency can effectively avoid unnecessary resonance phenomenon in this frequency band, ensure the stability and linearity of signal transmission, prevent abnormal frequency response of signals in this part, and thus maintain the quality of signal transmission on the entire transmission line.

[0010] Specifically, the resonator is a stepped impedance resonator with an added stub; the two arms of the resonator are provided with L-shaped open stubs at the ends.

[0011] The resonator can further fine-tune the resonant characteristics of the resonator at a specific frequency by adding an L-shaped stub at the end of the two arms. By changing the length, width, and other parameters of the stub, the equivalent impedance, resonant frequency, and other parameters of the resonator can be adjusted to achieve more fine optimization of the performance of the resonator, so that it can better adapt to the specific circuit application requirements.

[0012] Through the above technical means, the adoption of the stepped impedance resonator can provide multiple different impedance steps. By reasonably designing the values and intervals of these impedance steps, selective resonance of signals at specific frequencies can be achieved. Specifically, the gap line structure is composed of a first gap line, a second gap line, and a third gap line; the first gap line is located below the U-shaped transmission line, and the third gap line is located inside the resonator; the second gap line connects the first gap line and the third gap line.

[0013] Through the above technical means, by printing the gap line on the lower surface of the dielectric substrate and using specific Lg0, Lg1, and Lg2 structures, the precise planning and control of the signal transmission path can be achieved. Different structural parts have functions such as adjusting signal impedance and controlling signal propagation speed, thereby laying the foundation for the signal transmission characteristics of the entire circuit system, so that the signal can be transmitted in the expected manner under the dielectric substrate, and the overall electromagnetic performance can be optimized through reasonable design of the three structures, such as reducing transmission loss and reducing signal reflection. Specifically, two L-shaped short-circuit stubs are symmetrically added to the end of the gap line along the transverse center axis of the dielectric substrate.

[0014] Through the above technical means, a pair of L-shaped short-circuit stubs is added at the end of the Lg2 structure of the gap line. First, the short-circuit characteristic of the short-circuit stub changes the equivalent impedance at this position, causing the electromagnetic characteristics of the gap line at this point to change significantly.

[0015] Specifically, the distance between the stub and the U-shaped transmission line and the resonator is the same, and the length of the stub is half the wavelength of 6GHz.

[0016] Specifically, the resonator also has a load stub, and the load stub is located inside the resonator and perpendicular to the transverse center axis of the dielectric substrate.

[0017] Specifically, the load stub has a stepped impedance with a length ratio of 1:1.

[0018] Through the above technical means, the transition between different impedance steps during signal transmission is smoother, which helps to reduce signal reflection and energy loss caused by impedance discontinuity.

[0019] Specifically, the second gap line is aligned with the inside of the two arms of the resonator perpendicular to the transverse center axis of the dielectric substrate.

[0020] Through the technical means, in the signal transmission process, the signal in the gap line structure can more effectively interact with the resonator and transmit the signal, through the coupling effect, the electromagnetic characteristics of the whole circuit system can be adjusted, such as the resonant frequency, impedance and other parameters of the circuit, so as to optimize the signal transmission and processing capability of the circuit in a specific frequency range, and improve the performance consistency and stability of the whole circuit. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and serve the purpose of explaining principles of the application. Other embodiments and many of the intended advantages of the embodiments will be readily appreciated as the same becomes better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

[0022] Figure 1 is a whole structure schematic diagram of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression according to an embodiment of the application;

[0023] Figure 2 is a top view of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression according to an embodiment of the application;

[0024] Figure 3 is a bottom view of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression according to an embodiment of the application;

[0025] Figure 4 is a mutual relationship diagram of upper and lower layer structure relationship of a dielectric substrate of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression according to an embodiment of the application;

[0026] Figure 5 is a differential signal transmission characteristic curve simulation diagram of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression according to an embodiment of the application;

[0027] Figure 6 is a common-mode signal transmission characteristic curve simulation diagram of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression according to an embodiment of the application. BRIEF DESCRIPTION OF DRAWINGS:

[0029] 1, U-shaped transmission line; 2, stub; 3, resonator; 4, gap line structure; 5, dielectric substrate. DETAILED DESCRIPTION

[0030] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration illustrative embodiments in which the application can be practiced. For purposes of explanation and illustration, directional terms are used with reference to the orientation of the described figures. However, it is to be understood that the embodiments can be practiced in other orientations than those presented in the figures. The directional terms, such as "top," "bottom," "left," "right," "upper," "lower," and the like are used to aid in describing the embodiments and are not to be construed as limiting. It is to be understood that other embodiments can be utilized and structural or logical changes can be made without departing from the scope of the present application. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present application is defined by the appended claims.

[0031] Figure 1 is a schematic diagram of a whole structure of a differential filter with differential ultra-wideband passband and ultra-wideband common-mode rejection according to an embodiment of the present application, as shown in Figure 1 A differential filter with differential ultra-wideband passband and ultra-wideband common-mode rejection includes a dielectric substrate 5, a resonator 3, a U-shaped transmission line 1 symmetrical along a transverse middle axis of the dielectric substrate 5, a stub 2 and a slot line structure 4, and the stub 2 is close to the U-shaped transmission line 1 and the resonator 3; the U-shaped transmission line 1 is an input / output terminal, so that signals of different frequencies enter the resonator 3 from multiple paths of the stub 2 after entering the slot line from the stub 2 or from the slot line.

[0032] Specifically, the stub 2 is a half-wavelength stub 2 symmetrical along a transverse middle axis of the dielectric substrate 5. A length of the U-shaped transmission line 1 perpendicular to the transverse middle axis of the dielectric substrate 5 is less than one quarter of a wavelength of an upper limit cutoff frequency. The resonator 3 is a stepped impedance resonator 3 increasing the stub 2; two arm ends of the resonator 3 are increased with L-shaped open stubs. The slot line structure 4 is composed of a first slot line, a second slot line and a third slot line; the first slot line is located below the U-shaped transmission line 1, the third slot line is located inside the resonator 3, and the second slot line connects the first slot line and the third slot line. Two L-shaped short stubs are added to the end of the third slot line along the transverse middle axis of the dielectric substrate 5. The stub 2 has the same distance from the U-shaped transmission line 1 and the resonator 3, and the length of the stub 2 is a half-wavelength of 6GHz. The resonator 3 also has a load stub, which is located inside the resonator 3 and perpendicular to the transverse middle axis of the dielectric substrate 5. The load stub is a stepped impedance with a length ratio of 1:1. The second slot line is aligned with the inside of the two arms of the resonator 3 perpendicular to the transverse middle axis of the dielectric substrate 5.

[0033] In a specific embodiment, the present application includes a metal layer printed on the front of the dielectric substrate 5 and a ground layer on the bottom of the substrate, the dielectric substrate has a relative dielectric constant of 4.4, a loss angle of 0.02, a size of 40mm 40mm, thickness of 0.767mm FR4_epoxy material, BB' is the lateral axis of the dielectric substrate 5.

[0034] Figure 2 is a top view of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection according to an embodiment of the present application, Figure 3 is a bottom view of a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection according to an embodiment of the present application, as shown in Figures 2-3 A pair of U-shaped transmission lines 1 on both sides of the front surface of the substrate, as signal input or output ports, are connected to the horizontal part of the lateral axis BB' with a length and width of L0, W0, and the vertical part of the lateral axis BB' with a length of half wavelength about 10GHz and a length and width of L01, W01, which can effectively suppress differential signals above 10GHz. When the input signal of the U-shaped transmission line 1 is a common-mode signal, the lateral axis BB' generates an equivalent magnetic wall to hinder the transmission of the common-mode signal, and at this time the electric field generated by the common-mode signal is parallel to the magnetic wall, which is inconsistent with the gap line transmission mode, so it cannot enter the gap line to propagate. When the input signal of the U-shaped transmission line 1 is a differential signal, it can be converted to a gap line mode through strong magnetic coupling.

[0035] Lg0 in the gap line structure 4 is located below the U-shaped transmission line 1, and Lg2 is located inside the resonator 3. Two L-shaped short-circuit stubs are added at the end of the Lg2 structure along the lateral axis BB' to suppress Sdd21 above 15GHz.

[0036] (Parameters: W0=2.05mm, L0=11.46mm, W01=4.46mm, L01=12.40mm, S1=0.10mm, W02=1.46mm, L02=14.10mm, W03=1.60mm, L03=13.70mm, L04=11.62mm, W05=2.55mm, L05=6mm, W06_1=0.92mm, W06_2=0.5mm, L06=4.02mm, W07=0.5mm, L07=2.8mm, Wg0=4.48mm, Lg0=6.78mm, Wg01=0.5mm, Lg01=4.72mm, Wg02=3.5mm, Lg02=4.5mm, Wg03=0.3mm, Lg03=2.56mm.)

[0037] Further combined with Figure 1, the resonator 3 receives signals from different paths and filters, and four transmission poles are generated in the differential passband by adjusting the length and width ratio of the stepped impedance; the microstrip line with the length and width of L05 and W05 at the ends of the two arms of the resonator 3 is folded to form a new coupling path to suppress the high-frequency part of Scc21; here, L05 is one-quarter wavelength of 6GHz, used to suppress the Scc21 pole at 12GHz; the L-shaped open stub with the length and width of L07 and W07 at the end is used to suppress the high-frequency part of Sdd21; here, L07 is one-quarter wavelength of 15GHz, used to suppress the Sdd21 at 15GHz.

[0038] The distance between the stub 2, the U-shaped transmission line 1 and the resonator is S1, the length of the stub 2 is half of the wavelength of 6GHz, and the length and width are L02 and W02 respectively, which can make part of the signal directly pass through the three-line coupling into the resonator 3; at this time, the stub 2 will generate a transmission pole at 6GHz and a transmission zero at 6.6GHz, and the coupling with the U-shaped transmission line 1 will generate a transmission zero at 10GHz; another part of the signal enters the gap line and then couples into the resonator 3 after passing through the stub 2, which will generate two new transmission poles in the passband; another part of the signal enters the gap line and then directly enters the resonator 3 through magnetic coupling.

[0039] The simulation results of the present application are further illustrated by using electromagnetic field simulation software ANSYS Electronics Desktop 2017.1:

[0040] As shown in Figure 5 , the simulation of differential signal input is carried out, mainly for the simulation of differential signal return loss |Sdd11| and differential signal insertion loss |Sdd21|, the 3dB passband of Sdd21 is 1.4-6.0GHz, . The minimum insertion loss |Sdd21| in the passband is 0.9dB, the 20dB bandwidth is 1.26-6.6GHz, and the rectangular coefficient is 1.16, which reflects that the passband of the filter has good selectivity; the return loss |Sdd11| in the passband is mostly kept above 10dB, and the minimum value below 10dB is 7.5dB; the insertion loss |Sdd21| in the stopband is above 20dB in the range of 6.6-18.32GHz (3.17 )。

[0041] As shown in Figure 6As shown, the common mode signal input is simulated, mainly for the common mode signal insertion loss |Scc21| is simulated, in the differential passband, the common mode insertion loss |Scc21| is minimum for 32dB, embodying that the filter has enough common mode suppression ability in the passband. In the differential passband, the common mode insertion loss |Scc21| is above 20dB in the range of 6GHz to 20GHz.

[0042] Further, compared with other similar filters, it can be seen that the filter has certain advantages compared with other filters:

[0043]

[0044] Obviously, those skilled in the art can make various modifications and changes to the embodiments of the present application without departing from the spirit and scope of the present application. In this way, if these modifications and changes are within the scope of the claims of the present application and their equivalents, the present application also aims to cover these modifications and changes. The word "comprises" does not exclude the presence of other elements or steps not listed in the claims. The simple fact that certain measures are described in mutually different dependent claims does not mean that the combination of these measures cannot be used to advantage. Any reference signs in the claims should not be considered as limiting the scope.

Claims

1. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection, characterized in that, The device includes a dielectric substrate, a resonator, a U-shaped transmission line symmetrically arranged along the transverse central axis of the dielectric substrate, a stub line, and a slot line structure. The U-shaped transmission line and the stub line are disposed on the upper surface of the dielectric substrate, and the slot line is disposed on the lower surface of the dielectric substrate. The stub line is located close to the U-shaped transmission line and the resonator, between the U-shaped transmission line and the resonator, and is a half-wavelength stub line. The resonator is a stepped impedance resonator with the stub line added. L-shaped open-circuit stub lines are added to the ends of the two arms of the resonator. The slot line structure consists of a first slot line, a second slot line, and a third slot line. The first slot line is located below the U-shaped transmission line, the third slot line is located inside the resonator, and the second slot line connects the first slot line and the third slot line. The U-shaped transmission line serves as an input / output terminal; signals of different frequencies enter the U-shaped transmission line and then enter the resonator through the stub line or the slot line.

2. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 1, characterized in that, The stub is a half-wavelength stub that is symmetrical about the transverse central axis of the dielectric substrate.

3. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 1, characterized in that, The length of the portion of the U-shaped transmission line perpendicular to the transverse central axis of the dielectric substrate is less than one-quarter of the wavelength of the upper cutoff frequency.

4. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 3, characterized in that, Two L-shaped short-circuit stubs are added symmetrically along the transverse central axis of the dielectric substrate at the end of the third gap line.

5. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 1, characterized in that, The stub is spaced at the same distance from the U-shaped transmission line to the resonator, and the length of the stub is half a wavelength of 6 GHz.

6. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 2, characterized in that, The resonator also has a load stub located inside the resonator and perpendicular to the transverse central axis of the dielectric substrate.

7. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 6, characterized in that, The load stub has a stepped impedance with a length ratio of 1:

1.

8. A differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode rejection as described in claim 3, characterized in that, The second slot line is aligned with the inner sides of the two arms of the resonator perpendicular to the transverse axis of the dielectric substrate.

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