Differential filter

Abstract

The utility model aims to provide a differential filter. The differential filter comprises a bottom layer and a top layer which are arranged on a dielectric substrate, the bottom layer comprises two pairs of coplanar strip line resonators I and a phase inverter J, the two pairs of coplanar strip line resonators I are parallel to each other, and the two pairs of coplanar strip line resonators I are separated by the phase inverter J; the coplanar strip line resonator I is a quarter-wavelength resonator; the top layer comprises two metal wires I, and the two groups of metal wires I are aligned in parallel and are equally divided into two pairs of coplanar strip line resonators II by an inverter K; the metal wire I is a half-wavelength resonator, and the coplanar strip line resonator II is a quarter-wavelength resonator. The filter provided by the utility model can effectively improve the working bandwidth and better meet the broadband requirement.

Description

Technical Field

[0001] The utility model relates to the technical field of radio frequency circuit front-end communication devices, in particular to a differential filter. Background Art

[0002] Differential filters are very important components in RF systems. Their main function is to allow signals in a specific frequency band to pass through, filter signals in other frequency bands, and solve the interference problem between signals in different frequency bands. Therefore, the performance of the filter will directly affect the communication quality of the system. At present, two general trends in modern microwave wireless systems include broadbandization and hardware miniaturization. One is that in order to cope with the growing demand for data rates, wider frequency bands are needed to operate more and more frequency bands at the same time. The second is that stronger anti-interference capabilities are needed to cope with today's more severe electromagnetic environment.

[0003] At present, the existing filters can generally be divided into single-ended filters and differential filters. Traditional single-ended filters are easily interfered by external noise, and require additional balance when connected to differential circuits, which increases the cost of the system. Differential filters can suppress the interference of external noise, and have the advantages of good common-mode noise suppression, low electromagnetic interference, and small crosstalk. In this context, a large number of differential filters have been widely studied and developed, and their main focus is not only on the required differential mode filter response, but also on the ability to suppress unwanted common-mode signals. In this way, various differential filters are proposed based on branch line structures, coupled line structures, and signal elimination techniques. In addition, various types of resonators in coupling topologies are used as another alternative method, including T-shaped resonators, ring resonators, magnetically coupled resonators, etc. In order to construct a balanced filter with desired differential and common mode performance. However, the common-mode suppression of the above filters is achieved under specific technology, does not have the ability of inherent common-mode suppression, and is not achievable by the transmission line itself, resulting in the need to consider the influence of common-mode signals in the design, which increases the difficulty of design.

[0004] At present, the design of differential filters is mainly divided into double-sided parallel microstrip line structure, coupled microstrip line structure, branch line structure, etc. Based on the double-sided parallel microstrip line structure, an identical microstrip line is placed on the upper and lower surfaces of the dielectric substrate, and then the two microstrip lines are allowed to transmit signals with the same amplitude and opposite phase. This structure only allows differential mode signals to pass through and suppresses common mode signals, so it effectively suppresses the transmission of common mode signals. However, filters designed based on this structure generally have a large size, which is not conducive to the miniaturization of communication systems. On the other hand, since there is no actual ground plane in this structure, it is not conducive to connection and integration with other planar circuits. The differential filter based on coupled microstrip lines mainly uses step impedance lines and T-type input points to form a series of resonant modes, and achieves the required frequency response under differential mode excitation by parallel line coupling. However, this structure is mainly suitable for the design of narrowband differential filters, and it is difficult to apply to broadband and ultra-wideband differential filters. In this case, the coplanar stripline (CPS) structure can be used because it is a balanced transmission line that has been recognized to have inherent common mode suppression characteristics. Such differential filters have significant benefits in simplifying the overall filter design, as they only need to focus on differential-mode performance and can ignore common-mode effects. Summary of the invention

[0005] The utility model aims to provide a differential filter, which has an inherent common-mode rejection characteristic. Therefore, in the filter design process, only the differential-mode response needs to be considered without considering the influence of the common-mode signal, thereby simplifying the design process and being able to effectively improve the working bandwidth to better meet the needs of broadbandization.

[0006] The differential filter comprises a bottom layer and a top layer arranged on a dielectric substrate;

[0007] The bottom layer comprises two pairs of coplanar stripline resonators I and an inverter J, the two pairs of coplanar stripline resonators I are parallel to each other, and the two pairs of coplanar stripline resonators I are separated by the inverter J; the coplanar stripline resonator I is a quarter-wavelength resonator;

[0008] The top layer comprises two metal lines I. Two groups of metal lines I are arranged in parallel and aligned, and are evenly separated into two pairs of coplanar stripline resonators II by an inverter K. The coplanar stripline resonator II is a quarter-wavelength resonator.

[0009] The width of the coplanar stripline resonator I is the same as the width of the metal line I.

[0010] The length of the metal line I is 2-3 times the length of the coplanar stripline resonator I.

[0011] Feeder lines are arranged on both sides of the metal line I on the top layer, and ports are arranged at both ends of each group of feeder lines.

[0012] The characteristic impedance of the port is 50Ω.

[0013] The inverter K is a strip line with a width of 1 / 5-1 / 4 of the width of the coplanar strip line resonator I.

[0014] The inverter J is a gap strip, and the width of the gap strip is 8-9 times the width of the inverter K.

[0015] The dielectric substrate is Rogers 6010LM, with a dielectric constant of 10.9 and a thickness of 0.635 mm.

[0016] The working principle of the utility model is as follows:

[0017] The present invention forms a 4th-order differential bandpass filter through the coplanar stripline resonator I and the coplanar stripline resonator II, in combination with an inverter k equivalent to an inductor and an inverter J equivalent to a capacitor, thereby achieving a good filtering effect.

[0018] The present invention adopts a coplanar stripline structure to design a differential filter. Since the coplanar stripline itself has the ability to suppress common-mode signals, the influence of common-mode signals does not need to be considered. Therefore, only differential-mode response is required in the design, thereby simplifying the design process.

[0019] The utility model adopts wide-side coupling, so that the working bandwidth of the filter is improved, which can better meet the demand for broadbandization, and makes the filter size very compact, adapting to the trend of miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a simulation principle diagram of the differential filter of Example 1;

[0021] Figure 2 is a schematic structural diagram of a differential filter of Example 1;

[0022] Figure 3 It is a differential mode S parameter diagram of the simulation filter of the method of embodiment 1;

[0023] Figure 4 It is a common-mode S parameter diagram of the simulation filter of the method of embodiment 1;

[0024] The serial numbers and names in the figure are as follows:

[0025] 11-bottom layer, 22-top layer; 1-coplanar stripline resonator I, 2-inverter J, 3-metal line I, 4-inverter K, 5-feed line, 6-port. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the accompanying drawings and embodiments. Example 1

[0027] like Figure 1-2 As shown, the differential filter comprises a bottom layer 11 and a top layer 22 arranged on a dielectric substrate;

[0028] The bottom layer 11 includes two pairs of coplanar stripline resonators Ⅰ1 and an inverter J2. The two pairs of coplanar stripline resonators Ⅰ1 are parallel to each other and separated by the inverter J2. The coplanar stripline resonators Ⅰ1 are quarter-wavelength resonators.

[0029] The top layer 22 includes two metal wires Ⅰ3. Two groups of metal wires Ⅰ3 are arranged in parallel and aligned, and are evenly separated into two pairs of coplanar stripline resonators Ⅱ by an inverter K4. The coplanar stripline resonator Ⅱ is a quarter-wavelength resonator.

[0030] The width of the coplanar stripline resonator Ⅰ1 is the same as the width of the metal line Ⅰ3.

[0031] The length of the metal line Ⅰ3 is twice the length of the coplanar stripline resonator Ⅰ1.

[0032] Feeder lines 5 are provided on both sides of the metal line I 3 on the top layer 22 , and ports 6 are provided at both ends of each group of feeder lines.

[0033] The characteristic impedance of the port 6 is 50Ω.

[0034] The inverter K4 is a stripline whose width is 1 / 4 of the width of the coplanar stripline resonator Ⅰ1.

[0035] The inverter J2 is a gap strip, and the width of the gap strip is 8 times the width of the inverter K4.

[0036] The dielectric substrate is Rogers 6010LM, with a dielectric constant of 10.9 and a thickness of 0.635 mm. Example 2

[0037] Simulation experiment

[0038] like Figure 3 and 4 As shown, according to the filter structure of Example 1, the design index of the required differential filter is determined, requiring a differential filter with a bandwidth of more than 40%, a return loss better than 16dB, an insertion loss within 1dB, and a common mode attenuation of 50db. Then, a suitable substrate is selected in SONNET 15, modeled and simulated in SONNET 15 simulation software, and the desired filtering effect can be achieved by adjusting the distance and geometric dimensions between the microstrip lines. Figure 3 and Figure 4 They are the simulation results of the differential mode and common mode S parameters of the proposed filter. Figure 3and Figure 4 It can be seen that in the frequency range of 4.35-6.7GHz, the fractional bandwidth is 42.5%, the minimum return loss is better than 16.93dB, and the insertion loss is less than 0.57dB. In the wide frequency range of 4-7GHz, the common mode suppression effect is better than 69dB.

Claims

1. A differential filter, comprising a bottom layer (11) and a top layer (22) arranged on a dielectric substrate; characterized in that: The bottom layer (11) comprises two pairs of coplanar stripline resonators I (1) and inverters J (2), the two pairs of coplanar stripline resonators I (1) are parallel to each other, and the two pairs of coplanar stripline resonators I (1) are separated by the inverter J (2); Coplanar stripline resonator I (1) is a quarter-wavelength resonator; The top layer (22) comprises two metal lines I (3), the two groups of metal lines I (3) are arranged in parallel and aligned, and are evenly separated by an inverter K (4) into two pairs of coplanar stripline resonators II; the coplanar stripline resonator II is a quarter-wavelength resonator.

2. The differential filter according to claim 1, wherein: The width of the coplanar stripline resonator I (1) is the same as the width of the metal line I (3).

3. The differential filter according to claim 1, wherein: The length of the metal line I (3) is 2-3 times the length of the coplanar stripline resonator I (1).

4. The differential filter according to claim 1, wherein: Feeder lines (5) are respectively arranged on both sides of the metal line I (3) on the top layer (22), and ports (6) are respectively arranged at both ends of each group of feeder lines.

5. The differential filter according to claim 4, characterized in that: The characteristic impedance of the port (6) is 50Ω.

6. The differential filter according to claim 1, wherein: The inverter K (4) is a metal line with a width of 1 / 5-1 / 4 of the width of the coplanar stripline resonator I (1).

7. The differential filter according to claim 6, wherein: The inverter J (2) is a gap strip, and the width of the gap strip is 8-9 times the width of the inverter K (4).

8. The differential filter according to claim 1, wherein: The dielectric substrate is Rogers 6010LM, with a dielectric constant of 10.9 and a thickness of 0.635 mm.

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