Differential filter with differential ultra-wideband band-pass and ultra-wideband common-mode rejection

Abstract

The invention provides a differential filter with differential ultra-wideband band-pass and ultra-wideband common-mode rejection, which comprises a dielectric substrate, a resonator, a U-shaped transmission line, a stub line and a slot line structure, the U-shaped transmission line, the stub line and the slot line structure are symmetrical along the transverse central axis of the dielectric substrate, and the stub line is close to the U-shaped transmission line and the resonator; and the U-shaped transmission line is used as an input / output end, so that signals with different frequencies enter the slot line from the stub line or the slot line and then enter the resonator from multiple paths of the stub line. By adding the stub line, other differential signals enter the resonator through coupling, the transmission bandwidth of the differential signals is improved, a transmission zero point and a transmission pole are generated, and the passband performance is improved; the resonator brings four in-band transmission poles, and brings a plurality of transmission zero points outside the band near the passband, thereby improving out-of-band rejection.

Description

Technical Field

[0001] The present application relates to the technical field of filter design, and in particular to a differential filter with differential ultra-wideband passband and ultra-wideband common-mode suppression. Background Art

[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. Therefore, the crosstalk effect in transmission is becoming 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 can no longer be avoided. The traditional single-line interconnection cannot cope with the crosstalk problem, so more and more circuits use differential transmission lines. Due to the natural anti-interference characteristics of differential lines, differential filters can well suppress common-mode signals caused by external noise interference, and the two lines of differential lines are return paths for each other, which can also significantly reduce external electromagnetic radiation. At present, differential transmission has been applied to many high-speed interfaces, such as PCI-E and USB3.0. Some serial port protocols also use differential transmission, such as RS485 and RS-422.

[0003] At present, it is a major difficulty for differential filters to achieve a wider differential bandpass and a smaller rectangular coefficient while maintaining high common-mode suppression. For example, in 2020, Khaled Aliqab and other scholars published "Wideband Differential-Mode Bandpass Filters With Stopband and Common-Mode Suppression" in "IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS" (VOL.30, NO.3, MARCH 2020). The wideband differential-mode bandpass filter is based on the optimized branch line structure using extended transmission lines. On one side of the symmetry plane, there are 4 connecting lines horizontal to the symmetry plane and 3 short stubs perpendicular to the symmetry plane, each with a length of one quarter of a wavelength, so that signal transmission can generate multiple paths, and multiple transmission poles can be generated in the passband through adjustment. The measured differential 3dB-FBW of the filter reaches 58%, and the common-mode rejection in the band can reach -38dB. However, due to the coupling in the upper stopband, a new transmission pole is introduced, which affects the rejection of the upper stopband.

[0004] Another example is the compact high-performance balanced wideband BPF proposed by Shipeng Zhao, Zhongbao Wang and other scholars in the "Compact High-Performance Balanced Wideband BPF With a Notch Band and Multiple Transmission Zeros" published in "IEEE MICROWAVEANDWIRELESS TECHNOLOGY LETTERS" (VOL.34, NO.6, JUNE 2024). The filter is based on a double-sided parallel stripline (DSPSL) structure and consists of an asymmetric three-line coupling structure with two inverters, a short-circuited stub, a short coupling line and a loaded stub. By setting the DM signal to propagate in different paths to produce different phase shifts, differential passbands and stopbands are formed due to the phase difference after superposition. The filter has a differential 3dB-FBW of 23.3%, and the in-band common mode suppression can reach -30dB, and has excellent out-of-band suppression, while achieving a wide notch band of 2.64GHz-3.36GHz. Summary of the invention

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] The present application provides a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression, including a dielectric substrate, a resonator, a U-shaped transmission line symmetrical along the transverse center axis of the dielectric substrate, a short stub and a slot line structure, and the short 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 U-shaped transmission line and then enter the resonator from the short stub or the slot line.

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

[0008] Specifically, the length of a portion of the U-shaped transmission line that is perpendicular to the transverse center axis of the dielectric substrate is less than one quarter of the wavelength of the upper cut-off frequency.

[0009] The design of the vertical part length being less than one-quarter wavelength of the upper cutoff frequency can effectively avoid unnecessary resonance in this frequency band, ensure the stability and linearity of signal transmission, and prevent the signal from having abnormal frequency response in this part, thereby maintaining the quality of signal transmission on the entire transmission line.

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

[0011] Adding L-shaped stubs at the end of the two arms of the resonator can further fine-tune the resonant characteristics of the resonator at a specific frequency. By changing the length, width and other parameters of the stubs, the equivalent impedance, resonant frequency and other parameters of the resonator can be adjusted, thereby achieving more precise optimization of the resonator performance and enabling it to better adapt to specific circuit application requirements.

[0012] Through the above technical means, the use of the stepped impedance resonator can provide multiple different impedance steps, and by reasonably designing the values ​​and spacing of these impedance steps, selective resonance of specific frequency signals can be achieved. Specifically, the slot line structure 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, the third slot line is located inside the resonator, and the second slot line connects the first slot line and the third slot line.

[0013] By means of the above-mentioned technical means, the slot line is printed on the lower surface of the dielectric substrate and three specific structures of Lg0, Lg1 and Lg2 are adopted, which helps to realize the precise planning and control of the signal transmission path. Different structural parts respectively undertake 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 under the dielectric substrate in the expected manner, and the overall electromagnetic performance can be optimized by the reasonable design of these three structures, such as reducing transmission loss and signal reflection. Specifically, two L-shaped short-circuit stubs are symmetrically added at the end of the slot line along the transverse center axis of the dielectric substrate.

[0014] By using the above technical means, a pair of L-shaped short-circuit stubs are added at the end of the Lg2 structure of the slot line. First, the equivalent impedance at this position can be changed by the short-circuit characteristics of the short-circuit stubs, so that the electromagnetic characteristics of the slot line at this point change significantly.

[0015] Specifically, the short stub has the same spacing as the U-shaped transmission line and the resonator, and the length of the short stub is half the wavelength of 6 GHz.

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

[0017] Specifically, the load stub is a step 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 mutation.

[0019] Specifically, the second slot line is aligned with the inner sides of two arms of the resonator that are perpendicular to the horizontal center axis of the dielectric substrate.

[0020] Through the above-mentioned technical means, during the signal transmission process, the signal in the slot line structure can more effectively interact with the resonator for energy and signal transmission. Through this coupling effect, the electromagnetic characteristics of the entire circuit system can be coordinated and adjusted, such as jointly affecting the circuit's resonant frequency, impedance and other parameters, thereby optimizing the circuit's signal transmission and processing capabilities within a specific frequency range, and improving the overall circuit performance consistency and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated into and constitute a part of this specification. The accompanying drawings illustrate the embodiments and are used together with the description to explain the principles of the present application. It will be easy to recognize other embodiments and many expected advantages of the embodiments because they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale with each other. The same reference numerals refer to corresponding similar parts.

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

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

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

[0025] Figure 4 It is a diagram showing the relationship between the upper and lower structure layers of a dielectric substrate of a differential filter having differential ultra-wideband bandpass and ultra-wideband common mode suppression according to an embodiment of the present application;

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

[0027] Figure 6 It is a simulation diagram of a common-mode signal transmission characteristic curve of a differential filter with differential ultra-wideband passband and ultra-wideband common-mode suppression according to an embodiment of the present application.

[0029] 1. U-shaped transmission line; 2. Short stub; 3. Resonator; 4. Slot line structure; 5. Dielectric substrate. DETAILED DESCRIPTION

[0030] In the following detailed description, reference is made to the accompanying drawings, which form a part of the detailed description and are shown by illustrative specific embodiments in which the present application can be practiced. To this end, directional terms, such as "top", "bottom", "left", "right", "up", "down", etc., are used with reference to the orientation of the figures described. Because the components of the embodiments can be positioned in several different orientations, directional terms are used for the purpose of illustration and are by no means limiting. It should be understood that other embodiments may be utilized or logical changes may be made without departing from the scope of the present application. Therefore, the following detailed description should not be adopted 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 the overall structure of a differential filter with differential ultra-wideband passband and ultra-wideband common-mode suppression according to an embodiment of the present application, such as Figure 1 As shown, a differential filter with differential ultra-wideband bandpass and ultra-wideband common-mode suppression includes a dielectric substrate 5, a resonator 3, a U-shaped transmission line 1 symmetrical along the transverse center axis of the dielectric substrate 5, a short stub 2 and a slot line structure 4, and the short stub 2 is close to the U-shaped transmission line 1 and the resonator 3; the U-shaped transmission line 1 serves as an input / output end, so that signals of different frequencies enter the resonator 3 from the short stub 2 or from the slot line and then enter the slot line through multiple paths of the short stub 2.

[0032] Specifically, the stub 2 is a half-wavelength stub 2 symmetrical along the transverse center axis of the dielectric substrate 5. The length of the portion of the U-shaped transmission line 1 perpendicular to the transverse center axis of the dielectric substrate 5 is less than one-quarter wavelength of the upper cutoff frequency. The resonator 3 is a stepped impedance resonator 3 with a stub 2 added; L-shaped open-circuit stubs are added to the ends of the two arms of the resonator 3. 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-circuit stubs are added symmetrically at the end of the third slot line along the transverse center axis of the dielectric substrate 5. The stub 2 has the same spacing as the U-shaped transmission line 1 and the resonator 3, and the length of the stub 2 is half wavelength of 6 GHz. The resonator 3 also has a load stub, which is located inside the resonator 3 and perpendicular to the transverse center axis of the dielectric substrate 5. The load stub is a step impedance, and the length ratio is 1: 1. The second slot line is aligned with the inner sides of the two arms of the resonator 3 perpendicular to the horizontal axis of the dielectric substrate 5 .

[0033] In a specific embodiment, the present invention includes a metal layer printed on the front side of a dielectric substrate 5 and a ground layer at the bottom of the substrate. The dielectric substrate adopts FR4_epoxy material with a relative dielectric constant of 4.4, a loss angle of 0.02, a size of 40mm*40mm, and a thickness of 0.767mm. BB′ is the horizontal axis of the dielectric plate 5.

[0034] Figure 2 is a top view of an example of a differential filter with differential ultra-wideband passband and ultra-wideband common mode suppression according to an embodiment of the present application, Figure 3 is a bottom view of a differential filter with differential ultra-wideband passband and ultra-wideband common mode suppression according to an embodiment of the present application, such as Figure 2-3 As shown, a pair of U-shaped transmission lines 1 located on both sides of the front of the substrate serve as the input or output port of the signal respectively. The length and width of the 50Ω transmission line connected to the horizontal part of the horizontal axis BB′ are L0 and W0 respectively, and the length of the vertical part to the horizontal axis BB′ is half the wavelength of 10GHz, and the length and width are L01 and W01 respectively, 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 horizontal axis BB′ generates an equivalent magnetic wall to hinder the transmission of the common mode signal, and the electric field generated by the common mode signal at this time is parallel to the magnetic wall, which is inconsistent with the slot line transmission mode, so it cannot enter the slot line to propagate. When the input signal of the U-shaped transmission line 1 is a differential signal, it can be converted into the slot line mode through strong magnetic coupling.

[0035] In the slot line structure 4, Lg0 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 along the horizontal axis BB' at the end of the Lg2 structure to suppress Sdd21 above 15 GHz.

[0036] (Parameter values ​​are as follows: 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=6.78 mm, Wg01=0.5mm, Lg01=4.72mm, Wg02=3.5mm, Lg02=4.5mm, Wg03=0.3mm, Lg03=2.56mm. )

[0037] Further integration Figure 1Resonator 3 receives signals from different paths and filters them. By adjusting the ratio of the length and width of the step impedance, four transmission poles are generated in the differential passband. The microstrip lines at the ends of the two arms of resonator 3 with lengths of L05 and W05 are folded to form a new coupling path to suppress the high-frequency part of Scc21. Here, the length of L05 is one-quarter wavelength of 6 GHz, which is used to suppress the Scc21 pole at 12 GHz. The L-shaped short-circuit stub with lengths of L07 and W07 is added at the end to suppress the high-frequency part of Sdd21. Here, the length of L07 is one-quarter wavelength of 15 GHz, which is used to suppress Sdd21 at 15 GHz.

[0038] The spacing between the short stub 2 and the U-shaped transmission line 1 and the resonator is S1. The length of the short stub 2 is half the wavelength of 6 GHz, and the length and width are L02 and W02 respectively. A part of the signal can directly enter the resonator 3 through three-line coupling. At this time, the short stub 2 will generate a transmission pole at 6 GHz and a transmission zero at 6.6 GHz. At the same time, the coupling with the short stub 1 will generate a transmission zero at 10 GHz; another part of the signal enters the slot line and then enters the short stub 2 and then couples into the resonator 3. At this time, two new transmission poles will be generated in the passband; another part of the signal enters the slot line and then directly enters the resonator 3 through magnetic coupling.

[0039] The electromagnetic field simulation software ANSYS Electrons Desktop 2017.1 is used to simulate the present invention and further illustrate the results:

[0040] like Figure 5 As shown, the differential signal input is simulated, mainly the differential signal return loss |Sdd11| and the differential signal insertion loss |Sdd21|. The 3dB passband of Sdd21 is 1.4-6.0GHz, f0=3.7GHz. 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 shows that the filter has good selectivity in the passband; the in-band return loss |Sdd11| is mostly kept above 10dB, and the minimum value below 10dB is 7.5dB; the insertion loss |Sdd21| in the out-of-band stopband is above 20dB in the range of 6.6-18.32GHz (3.17f0).

[0041] like Figure 6As shown in the figure, the common-mode signal input is simulated, mainly the common-mode signal insertion loss |Scc21| is simulated. In the differential passband, the common-mode insertion loss |Scc21| is 32dB at the minimum, which shows that the filter has sufficient common-mode suppression capability in the passband. Outside the differential passband, the common-mode insertion loss |Scc21| is above 20dB in the range of 6GHz to 20GHz.

[0042] Furthermore, by comparing this application with other similar filters, it can be seen that this filter has certain advantages over 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 is also intended to cover these modifications and changes. The word "comprising" does not exclude the presence of other elements or steps not listed in the claims. The simple fact that certain measures are recorded in mutually different dependent claims does not indicate that the combination of these measures cannot be used to profit. Any figure mark in the claims should not be considered to limit the scope.

Claims

1. A differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection, characterized in that: The invention comprises a dielectric substrate, a resonator, a U-shaped transmission line, a stub and a slot line structure symmetrical along the transverse central axis of the dielectric substrate, wherein the stub is close to the U-shaped transmission line and the resonator; the U-shaped transmission line serves as an input / output end, and after signals of different frequencies enter the U-shaped transmission line, they enter the resonator from the stub or the slot line.

2. A differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 1, characterized in that: The short stub is a half-wavelength short stub symmetrical along the transverse central axis of the dielectric substrate.

3. The differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to 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 cut-off frequency.

4. The differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 1, characterized in that: The resonator is a stepped impedance resonator with the stub added; L-shaped open-circuit stubs are added to the ends of the two arms of the resonator.

5. The differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 1, characterized in that: 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.

6. A differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 5, characterized in that: Two L-shaped short-circuit stubs are symmetrically added at the end of the third slot line along the transverse center axis of the dielectric substrate.

7. The differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 1, characterized in that: The short stub is spaced the same as the distance between the U-shaped transmission line and the resonator, and the length of the short stub is half the wavelength of 6 GHz.

8. The differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 4, characterized in that: The resonator also has a load stub, which is located inside the resonator and perpendicular to the transverse center axis of the dielectric substrate.

9. A differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 8, characterized in that: The load stub is a step impedance with a length ratio of 1:

1.

10. The differential filter with differential ultra-wideband passband and ultra-wideband common mode rejection according to claim 5, characterized in that: The second slot line is aligned with the inner sides of two arms of the resonator that are perpendicular to the horizontal center axis of the dielectric substrate.

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