Broadband balun based on capacitance and resistance loading

Abstract

The invention discloses a broadband balun based on capacitance and resistance loading, the broadband balun comprises a first coupling line and a second coupling line, the first coupling line and the second coupling line each comprise N sub-coupling lines, and N is a positive integer greater than or equal to 2; one end of the first coupling line is connected with the first input / output end of the balanced end, and the other end is connected with the output / input end of the unbalanced end; one end of the second coupling line is connected with the second input / output end of the balance end, and the other end is grounded; wherein in at least one coupling line, a grounded first resistor / a second resistor and a first capacitor which are connected in series are arranged between two adjacent sub coupling lines so as to carry out frequency compensation. The broadband balun provided by the invention has the characteristics of small size, low insertion loss, high port isolation and good port matching in a relatively wide frequency range.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radio frequency and microwave passive devices, and particularly relates to a wideband balun based on capacitor-resistor loading. BACKGROUND

[0002] Balun (Balance-Unbalance Transformer) is a kind of passive device for realizing conversion between balanced signal and unbalanced signal. In radio frequency and microwave circuits, end signal (unbalanced) exists widely in feeding, measurement and interface of some active devices, and electromagnetic compatibility is always a problem that needs to be considered in radio frequency front end. Differential signal has stronger common mode rejection capability and better anti-interference characteristics than traditional single-ended signal, and using differential signal transmission is the only choice for solving electromagnetic compatibility problem. Therefore, balun is widely used in antenna feeding network, differential amplifier input and output, filter and mixer interface and the like to complete impedance matching and signal mode conversion between single-ended and differential circuits. As a converter from unbalanced to balanced port, the performance of balun will directly affect the quality of radio frequency front end signal, and is a basic passive device for ensuring signal integrity and system stability. At present, with the development of devices towards miniaturization and portability, higher requirements are put forward for balun, and miniaturization, wide frequency band, high integration and low insertion loss will become important research directions of balun.

[0003] Therefore, there is an urgent need for a balun with good performance parameters such as working bandwidth, insertion loss and isolation. SUMMARY

[0004] The embodiment of the application provides a wideband balun based on capacitor-resistor loading, which can solve the above problems.

[0005] In a first aspect, the embodiment of the application provides a wideband balun based on capacitor-resistor loading, which comprises a first coupling line and a second coupling line, and the first and second coupling lines each comprise N sub-coupling lines, and N is a positive integer greater than or equal to 2. One end of the first coupling line is connected to a first input / output end of a balanced end, and the other end is connected to an output / input end of an unbalanced end. One end of the second coupling line is connected to a second input / output end of the balanced end, and the other end is grounded. At least one coupling line has a first resistor / series second resistor and a first capacitor arranged between two adjacent sub-coupling lines for frequency compensation.

[0006] In a second aspect, the embodiment of the application provides a design method of a wideband balun based on capacitor-resistor loading, which is used for designing the wideband balun provided in the first aspect, and the method comprises the following steps. Determine the impedance of each sub-coupling line according to the impedance ratio, single-ended input impedance and differential load impedance of the wideband balun; Determine the impedance of the second resistance and the capacitance value of the first capacitance according to the impedance of the sub-coupling line and the differential load impedance. Determine the impedance of the first resistance according to the impedance of the sub-coupling line.

[0007] Compared with the prior art, the beneficial effects of the embodiment of the present application are: by introducing the frequency compensation structure of resistance and capacitance combination, the signal response contradiction of the wideband balun at different frequency bands can be coordinated from the physical level. When the signal is at a low frequency band, the resistance arranged between the coupling lines can effectively absorb the common mode energy, and establish a stable load environment for the differential mode signal, thereby significantly improving the amplitude and phase balance at the low frequency band; as the signal frequency rises to a certain design threshold, the series capacitance is turned on due to the reduction of the capacity resistance, so that the resistance-capacitance network works together, and this structure can accurately compensate the energy loss and phase distortion of the high frequency signal caused by parasitic parameters. This frequency adaptive composite compensation mechanism enables the balun to automatically enable the matching optimization strategy at different frequency bands without relying on multi-stage cascading or complex structure in the whole wide frequency band, thereby realizing the coordinated improvement of the working bandwidth, amplitude consistency and phase balance degree under the premise of compact structure, for example, the overall size is only 1.138x2.046mm 2 . BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A structure schematic diagram of a wideband balun based on capacitance and resistance loading is provided for the embodiment of the present application. Figure 2 A specific structure schematic diagram of a wideband balun based on capacitance and resistance loading is provided for the embodiment of the present application. Figure 3 An implementation flowchart of a design method of a wideband balun based on capacitance and resistance loading is provided for the embodiment of the present application. Figures 4a-4e The schematic diagrams of the insertion loss, amplitude balance degree, phase balance degree, balanced output isolation degree and S parameter of the wideband balun provided by the embodiment of the present application are respectively shown. DETAILED DESCRIPTION

[0009] In the following description, specific details such as specific system structures, techniques, etc. are presented in order to illustrate, but not to limit, the embodiments of the present application. However, it should be clear to those skilled in the art that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits and methods are omitted to avoid unnecessary details that hinder the description of the present application.

[0010] It will be understood that, when used in the specification and the appended claims, the terms "comprise", "comprising", "comprises" and "comprising" mean that the described features, integers, steps, operations, elements, and / or components are present, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0011] It will also be understood that the term "and / or", where used in the specification and in the claims, means any one or more of the associated listed items can be present or can be combined with any one or more of the associated listed items.

[0012] As used in the specification and the appended claims, the term "if' can be interpreted as meaning "when" or "once" or "in response to a determination" or "in response to a detection" depending on the context. Similarly, the phrase "if determined" or "if detected [the described condition or event]" can be interpreted as meaning "once determined" or "in response to a determination" or "once detected [the described condition or event]" or "in response to a detection [the described condition or event]" depending on the context.

[0013] In addition, the terms "first", "second", "third", etc. as used in the description of the specification and the appended claims are only used to distinguish descriptions and cannot be understood as indicating or implying relative importance.

[0014] Reference in the specification to "one embodiment" or "some embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" or "in some embodiments" in various places in the specification are not necessarily all referring to the same embodiment, although it can. The terms "comprise", "comprising", "have", "having", "include", "including", and "contain", "containing" as used in the specification and in the claims are meant to be interpreted as "including but not limited to", unless otherwise specifically noted.

[0015] The application will be further described below with reference to specific embodiments, but the embodiments of the application are not limited thereto.

[0016] Embodiment 1 Figure 1 A structure schematic diagram of a wideband balun based on capacitance resistance loading provided by an embodiment of the application is shown. As an example but not limitation, the wideband balun can include a first coupling line 11, a second coupling line 12, a frequency adjusting component 2.

[0017] In some embodiments, referring to Figure 1The first and second coupling lines can each include N sub-coupling lines, where N is a positive integer greater than or equal to 2. One end of the first coupling line 11 can be connected to a first input / output terminal of the balanced end, and the other end can be connected to an output / input terminal of the unbalanced end. One end of the second coupling line 12 can be connected to a second input / output terminal of the balanced end, and the other end can be grounded. In at least one of the coupling lines between the first and second coupling lines, a frequency adjustment component 2 is arranged between two adjacent sub-coupling lines, i.e., the wideband balun includes at least one frequency adjustment component 2 arranged between two adjacent sub-coupling lines.

[0018] For example, when one end of each of the first and second coupling lines is connected to a first and second input terminal of the balanced end, and the other end is connected to an output terminal of the unbalanced end and grounded, the first and second coupling lines can be used to convert a balanced signal output by the balanced end into an unbalanced signal and output the unbalanced signal to the unbalanced end. When one end of each of the first and second coupling lines is connected to a first and second output terminal of the balanced end, and the other end is connected to an input terminal of the unbalanced end and grounded, the first and second coupling lines can be used to convert an unbalanced signal output by the unbalanced end into a balanced signal and output the balanced signal to the balanced end.

[0019] For example, the frequency adjustment component is used to perform frequency compensation, so that the wideband balun has a wideband characteristic. For example, when the input signal is greater than the operating center frequency f0 of the wideband balun, compensation is provided for high-frequency loss. When the frequency of the input signal is less than the operating center frequency f0 of the wideband balun, common-mode energy is absorbed to provide a relatively stable load for the differential-mode signal, so that the wideband balun can operate within a wide range around f0.

[0020] In one possible implementation, referring to Figure 1 The frequency adjustment component 2 can be a first resistor or a second resistor and a first capacitor connected in series.

[0021] In one example, the first resistor is used to absorb common-mode energy.

[0022] For example, if it is desired to expand the operating bandwidth of the wideband balun downward, a first resistor connected to ground can be arranged between two sub-coupling lines of the wideband balun.

[0023] In one example, the second resistor and the first capacitor connected in series are used to provide compensation for high-frequency loss, to expand the frequency band and to flatten the group delay.

[0024] For example, if it is desired to expand the operating bandwidth of the wideband balun upward, a second resistor and a first capacitor connected in series can be arranged between two sub-coupling lines of the wideband balun.

[0025] Specifically, one end of the second resistor can be connected between two adjacent sub-coupling lines, and the other end can be connected to one end of the first capacitor. The other end of the first capacitor can be grounded.

[0026] In some embodiments, referring to Figure 1 , the wideband balun can further include a matching network 3.

[0027] The exemplary matching network 3 can be arranged between the first and second coupling lines and the input / output end of the balanced end, for improving the matching characteristics of the port.

[0028] In a possible implementation, the matching network can include one inductance and two second capacitances arranged symmetrically and respectively on the first and second coupling lines.

[0029] Exemplarily, referring to Figure 1 , one end of each of the two second capacitances is connected to one end of the first and second coupling lines respectively, and the other end is grounded; one end of the inductance can be connected to one end of the first coupling line 11, and the other end is grounded.

[0030] The present application can coordinate the signal response contradictions of the wideband balun at different frequency bands from the physical level by introducing the frequency compensation structure of the combination of resistance and capacitance. When the signal is at a low frequency band, the resistance arranged between the coupling lines can effectively absorb the common-mode energy, and establish a stable load environment for the differential-mode signal, thereby significantly improving the amplitude and phase balance at the low frequency band; as the signal frequency rises to a certain design threshold, the series capacitance is turned on due to the reduction of the capacity resistance, so that the resistance-capacitance network works together, and this structure can precisely compensate the energy loss and phase distortion of the high-frequency signal caused by parasitic parameters. This frequency-adaptive composite compensation mechanism enables the balun to automatically enable the matching optimization strategy at different frequency bands without relying on multi-stage cascading or complex structure in the entire wideband, so as to realize the coordinated improvement of the working bandwidth, amplitude consistency and phase balance degree on the premise of compact structure, for example, the overall size is only 1.138x2.046mm 2 .

[0031] Embodiment 2 On the basis of embodiment 1, Figure 2 The specific structure diagram of a wideband balun based on capacitance and resistance loading provided by the embodiment of the present application is shown. As an example but not limitation, when N=4 and the working bandwidth is designed as 2~18GHz, the wideband balun can include four frequency adjustment components.

[0032] In one example, a frequency adjustment component can be arranged between the 1st sub-coupling line and the 2nd sub-coupling line of the 1st coupling line 11, including the 2nd resistor R1 and the 1st capacitor C1; a frequency adjustment component can be arranged between the 2nd sub-coupling line and the 3rd sub-coupling line, including the 1st resistor R3. A frequency adjustment component can be arranged between the 2nd sub-coupling line and the 3rd sub-coupling line of the 2nd coupling line 12, including the 2nd resistor R2 and the 2nd capacitor C2; a frequency adjustment component can be arranged between the 3rd sub-coupling line and the 4th sub-coupling line, including the 1st resistor R4.

[0033] For example, the sub-coupling lines can be arranged in a first direction (see Figure 2 the direction indicated by the arrow 201), and the closer to the balance end, the smaller the serial number; that is, compared to the n+1th sub-coupling line, the nth sub-coupling line is closer to the balance end, n is a positive integer less than or equal to N.

[0034] In one example, referring to Figure 2 , the matching network M1 can include the 2nd capacitor C3, the 2nd capacitor C4 and the inductor L1.

[0035] One end of the 2nd capacitor C3 and the 2nd capacitor C4 is grounded, and the other end is connected to one end of the 1st coupling line 11 and one end of the 2nd coupling line 12 respectively. One end of the inductor L1 is grounded, and the other end is connected to one end of the 1st coupling line 11.

[0036] Through the joint action of the capacitors and inductors in the matching network, in the differential mode, the voltage at the node connected by the inductor L1 and the 1st coupling line is about 0, which has no effect on the signal; in the common mode, the matching network presents high resistance, which improves the common-mode rejection ratio (CMRR).

[0037] Embodiment 3 On the basis of Embodiment 1 / Embodiment 2, Figure 3 The present application provides a design method of a broadband balun based on capacitor-resistor loading. As an example but not limitation, the method can be used to design the broadband balun provided in Embodiment 1 / Embodiment 2. The method can include steps S301-S303, which will be described below.

[0038] S301, according to the impedance ratio, single-ended input impedance and differential load impedance of the broadband balun, the impedance of each sub-coupling line is determined.

[0039] In one example, when the impedance ratio of the broadband balun is 1:2, the impedance of the sub-coupling line can be calculated by the following formula:

[0040] wherein, Zc is the impedance of the sub-coupling line, Zin is the single-ended input impedance, ZL is the differential load impedance.

[0041] For example, referring to the wideband balun provided in Embodiment 2, if N = 4, ,Zc = 50Ω, ZL = 100Ω, the impedance of each sub-coupling line can be 50Ω, which can meet the impedance matching of 1:2. S302, determining the impedance of the second resistance and the capacitance value of the first capacitance according to the impedance of the sub-coupling line and the differential load impedance.

[0042] In one example, the impedance of the second resistance introduced for widening the frequency band and flattening the group delay

[0043] can be calculated by the formula The capacitance value of the first capacitance connected in series at the front end of the second resistance so that the damping only acts at high frequencies can be calculated by the formula wherein, C is the capacitance value of the first capacitance, f H is the high-frequency resonance frequency, and R is the differential load impedance. For example, continuing to refer to the above example, the impedance of the second resistance R1, R2 can be calculated to be about 50Ω. When

[0044] , the capacitance value of the first capacitance C1, C2 can be calculated to be about 2.1 pF. S303, determining the impedance of the first resistance according to the impedance of the sub-coupling line.

[0045] Generally, the first resistance for relieving the last-stage reflection and unbalanced symmetry has the same impedance as the sub-coupling line.

[0046] Optionally, the method can further include the following steps S304, S305.

[0047] S304, determining the capacitance value of the second capacitance according to the common-mode resonance frequency.

[0048] In one example, referring to Embodiments 1 and 2 above, when the matching network is composed of two second capacitances and one inductance, the capacitance value of the second capacitance can be calculated by the following formula:

[0049]

[0050] wherein,

[0051] wherein, fcm is the common-mode resonance frequency, is an inductance value of the inductor L1, , are respectively capacitance values of the second capacitors C3, C4.

[0052] For example, continuing to refer to the above example, if L1=10 nH, and let By calculation, C3=C4≈2.5 pF can be obtained.

[0053] S305, according to the simulation parameters of the wideband balun, adjusting the impedance of the first resistor and the second resistor, and the capacitance value of the first capacitor.

[0054] In one example, after designing the wideband balun, the performance of the wideband balun can be simulated, and then according to the simulation results, i.e. the values of each simulation parameter, the values of each element in the wideband balun are adjusted.

[0055] For example, when the common mode rejection ratio of the wideband balun is insufficient, the capacitance values of the second capacitors C3, C4 can be increased to make the common mode resonance frequency decrease; when the output phase deviation occurs, the capacitance values of the second capacitors C3 / C4 can be fine-tuned on one side to make the phase difference approach 180°; when the amplitude imbalance occurs, the capacitance value of the first capacitor on the channel with stronger amplitude can be reduced; when the high-frequency matching is poor, the capacitance value of the first capacitor can be increased or the impedance of the first resistor can be reduced; when the insertion loss is large, the impedance of the second resistor can be reduced or the capacitance value of the first capacitor can be slightly reduced; when the low-frequency reflection is high, the impedance of the first resistor can be appropriately increased.

[0056] Figures 4a-4e are respectively schematic diagrams of the insertion loss, the amplitude balance degree, the phase balance degree, the balanced output isolation degree, and the S parameter of the wideband balun provided by the embodiment of the present application.

[0057] Referring to Figure 4a It can be seen that the working bandwidth of the wideband balun provided by the embodiment 2 of the present application can include 2~18GHz, and the insertion loss in the working bandwidth is between -6dB and -8dB. Referring to Figure 4b It can be seen that in the frequency band of 2~20GHz, the amplitude balance degree of the wideband balun is less than ±0.5dB; referring to Figure 4c The phase balance degree of the wideband balun is less than 7°; referring to Figure 4d The port isolation degree of the wideband balun is less than -8. dB; referring to Figure 4e It can be seen that in the frequency band of 2~20GHz, the S11 parameter of the wideband balun is less than -10dB, and the S22, S33 parameters are less than -5dB.

[0058] This can prove that the present application has the characteristics of small size, low insertion loss, high port isolation degree, and good port matching in the frequency range of 2~18GHz.

[0059] Therefore, the application can coordinate the signal response contradiction of the broadband balun at different frequency bands from the physical level by introducing the frequency compensation structure of the resistance-capacitance combination. When the signal is at a low frequency band, the resistance arranged between the coupling lines can effectively absorb the common-mode energy, establish a stable load environment for the differential-mode signal, and thus significantly improve the amplitude and phase balance at the low frequency band. As the signal frequency rises to a specific design threshold, the series capacitance is turned on due to the reduction of the capacitive reactance, so that the resistance-capacitance network works together. This structure can precisely compensate the energy loss and phase distortion of the high-frequency signal caused by the parasitic parameters. This frequency-adaptive composite compensation mechanism enables the balun to automatically enable the matching optimization strategy at different frequency bands without relying on multi-stage cascading or complex structure in the entire wide frequency band, so as to realize the coordinated improvement of the working bandwidth, amplitude consistency and phase balance degree on the premise of compact structure, for example, the overall size is only 1.138x2.046mm 2 .

[0060] In the above embodiments, the description of each embodiment has its own focus. The parts not described or recorded in detail in a certain embodiment can be referred to the related description of other embodiments.

Claims

1. A broadband balun based on capacitive-resistive loading, characterized in that, It includes a first coupling line and a second coupling line, and both the first and second coupling lines include N sub-coupling lines, where N is a positive integer greater than or equal to 2; One end of the first coupling line is connected to the first input / output terminal of the balanced end, and the other end is connected to the output / input terminal of the unbalanced end. One end of the second coupling line is connected to the second input / output terminal of the balanced terminal, and the other end is grounded; In at least one of the coupling lines, a grounded first resistor / a second resistor and a first capacitor are provided between two adjacent sub-coupling lines for frequency compensation.

2. The broadband balun according to claim 1, characterized in that, The first resistor is used to absorb common-mode energy.

3. The broadband balun according to claim 1, characterized in that, The second resistor and the first capacitor connected in series are used to compensate for high-frequency losses.

4. The broadband balun according to claim 1, characterized in that, A matching network is also provided between one end of the first coupling line and the second coupling line and the first input / output terminal and the second input / output terminal of the balance terminal to improve the matching characteristics.

5. The broadband balun according to claim 4, characterized in that, N=4, and the operating frequency of the broadband balun includes 2~18GHz.

6. The broadband balun according to claim 5, characterized in that, A second resistor R1 and a first capacitor C1 are connected in series between the first segment of the first coupling line and the second segment of the first coupling line, and a first resistor R3 is connected between the second segment of the coupling line and the third segment of the coupling line. The nth segment of the coupling line is closer to the balance end than the (n+1)th segment of the coupling line. A second resistor R2 and a first capacitor C2 are connected in series between the third and fourth segments of the second coupling line, and a first resistor R4 is connected between the third and fourth segments of the coupling line.

7. The broadband balun according to claim 6, characterized in that, A matching network M1 is also provided between the first segment of the first coupling line and the balanced end. The matching network M1 includes an inductor L1, a second capacitor C3, and a second capacitor C4. One end of the inductor L1 and the second capacitor C3 is grounded, and the other end is connected to one end of the first coupling line. One end of the second capacitor C4 is grounded, and the other end is connected to one end of the second coupling line.

8. A design method for a broadband balun based on capacitive-resistive loading, characterized in that, The method is used to design a broadband balun as described in any one of claims 1-7, the method comprising: The impedance of each sub-coupled line is determined based on the impedance ratio of the broadband balun, the single-ended input impedance, and the differential load impedance. The impedance of the second resistor and the capacitance value of the first capacitor are determined based on the impedance of the sub-coupled line and the differential load impedance. The impedance of the first resistor is determined based on the impedance of the sub-coupled line.

9. The method according to claim 8, characterized in that, The capacitance value of the first capacitor satisfies the following formula: Where C is the capacitance value of the first capacitor, f H R is the high-frequency resonant frequency, and R is the differential load impedance.

10. The method according to claim 8, characterized in that, The method further includes: Adjust the impedances of the first resistor and the second resistor, and the capacitance value of the first capacitor, according to the simulation parameters of the broadband balun.

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