A common-mode absorption electric field probe and its design method

Abstract

The present invention discloses a common-mode absorption electric field probe and a design method thereof, which are used to test horizontal electric field components. The present invention adds a common-mode absorbing structure to the horizontal electric field probe, which can effectively absorb the common-mode noise generated by the external vertical electric field component at the output end of the probe, thereby improving the accuracy of the probe in detecting the horizontal electric field component to be measured. The common-mode absorbing structure includes a balun and an absorbing resistor: the balun reflects the common-mode noise; the absorbing resistor absorbs the common-mode noise, and the common-mode absorbing structure has no effect on the differential-mode signal generated by the horizontal electric field component to be measured. The present invention overcomes the defect of unstable measurement of the horizontal electric field probe in certain frequency bands caused by the addition of a balun to the traditional horizontal electric field probe. Since the present invention reduces the problem of the narrow operating frequency band of the horizontal electric field probe caused by multiple reflections of common-mode noise, the probe can operate within a wide frequency band. Since the common-mode noise is absorbed rather than reflected, the test accuracy of the probe is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of common-mode noise suppression and electric field probe design, and in particular to a common-mode absorbing electric field probe and a design method thereof. Background Art

[0002] With the continuous advancement of electronic information, electronic devices are becoming increasingly miniaturized. The confined space has exacerbated electromagnetic compatibility issues between electronic devices. Electric field probes, which can measure the electric field distribution in unknown areas, play a crucial role in analyzing and remediating electromagnetic interference (EMI) issues. Horizontal electric field probes primarily measure radiated electric field signals parallel to the component under test. A horizontal electric field probe contains a differential line. The horizontal electric field under test induces a differential signal on the differential line. The voltage of the differential signal is then measured and converted to the value of the horizontal electric field under test. However, the differential signal line not only transmits the differential signal but also common-mode current. This common-mode current is primarily generated by the vertical electric field component perpendicular to the component under test within the test area, resulting in common-mode noise during testing. Effectively suppressing this common-mode noise is crucial to the accuracy of horizontal electric field measurements using horizontal electric field probes.

[0003] Research on suppressing common-mode noise in horizontal electric field probes is increasing annually. Some researchers are adding multiple active operational amplifiers to horizontal electric field probes to suppress common-mode noise. However, the introduction of active structures incurs additional overhead and can also make the probe bulky. Furthermore, many studies have investigated balun filters as a common-mode noise suppressor for horizontal electric field probes. Balun filters are traditional components for suppressing common-mode noise. They use differential inputs and a single line as an output. They can suppress common-mode noise within the operating frequency band by reflecting it without affecting the transmission of differential-mode signals. However, traditional balun filters suppress common-mode noise by reflecting it. Adding a reflective balun to the probe results in multiple reflections of the common-mode noise, causing instability in certain frequency bands. Consequently, horizontal electric field probes that use traditional balun filters to suppress common-mode noise have a relatively narrow operating frequency band.

[0004] The present invention mainly designs a common-mode absorption electric field probe, which absorbs common-mode noise through impedance matching and reduces the impact of noise reflection. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a common-mode absorption electric field probe and a design method thereof. A common-mode absorbing resistor is introduced into the balun. The balun reflects common-mode noise, and the common-mode absorbing resistor absorbs the common-mode noise. The common-mode absorbing structure has no effect on the differential-mode signal generated by the horizontal electric field component to be measured.

[0006] The technical solutions proposed by the present invention are as follows:

[0007] The first object of the present invention is to provide a common-mode absorption electric field probe, including a horizontal electric field probe and a common-mode absorbing structure. The horizontal electric field probe is composed of a probe transmission part and a probe detection part, and the common-mode absorbing structure is composed of a balun filter and a common-mode absorbing resistor; the balun filter is connected to the horizontal electric field probe, and the common-mode absorbing resistor is installed between the differential input port of the balun filter and the probe detection part.

[0008] Preferably, the balun filter is connected to the horizontal electric field probe in the following ways:

[0009] The differential input port of the balun filter is connected to the differential line of the probe detection part, and the single-ended output port of the balun filter is connected to the probe transmission part (from top to bottom: probe transmission part -> balun -> probe detection part); or one end of the differential line of the probe transmission part is connected to the differential line of the probe detection part, and the other end of the differential line of the probe transmission part is connected to the differential input port of the balun filter, and the single-ended output port of the balun filter is connected to the probe output part (from top to bottom: probe output part -> balun -> probe transmission part -> probe detection part).

[0010] Preferably, the common-mode absorbing resistor is located at the differential input port of the balun filter, or is located at a distance from the balun input port.

[0011] Preferably, the common-mode absorbing resistor is composed of two or more single resistors connected in parallel, one end of the common-mode absorbing resistor is connected to the differential input port of the balun filter, and the other end is connected to the ground plane.

[0012] Preferably, the common-mode absorbing resistor is composed of two or more single resistors connected in series, and both ends of the common-mode absorbing resistor are connected in series in the differential line of the probe transmission part, or both ends of the common-mode absorbing resistor are connected in series in the ground plane close to the probe transmission part; and the common-mode absorbing resistor is at a certain distance from the differential input port of the balun filter.

[0013] Preferably, the common-mode absorbing resistor and the differential line of the probe transmission part achieve common-mode impedance matching.

[0014] A second object of the present invention is to provide a design method for the common-mode absorption electric field probe, comprising:

[0015] 1) One end of the differential line of the probe transmission part is connected to the differential line of the probe detection part, and the other end of the differential line of the probe transmission part is connected to the differential input port of the balun filter;

[0016] 2) A common-mode absorbing resistor formed by two or more single resistors connected in parallel is connected to the differential input port of the balun filter, one end of the common-mode absorbing resistor is connected to the differential input port of the balun filter, and the other end is connected to the ground plane;

[0017] 3) Adjust the size of the common-mode absorbing resistor to achieve common-mode impedance matching with the differential line of the probe transmission part, thereby absorbing the common-mode noise reaching the differential input port of the balun filter and reducing the common-mode noise reflected back to the probe detection part.

[0018] Furthermore, step 1) is replaced by: the differential input port of the balun filter is connected to the differential line of the detection part of the probe, and the single-ended output port of the balun filter is connected to the transmission part of the probe.

[0019] Furthermore, step 2) is replaced by: connecting a common-mode absorbing resistor in series on the differential line of the probe transmission part, wherein the common-mode absorbing resistor is composed of two or more single resistors connected in series.

[0020] Furthermore, step 2) is replaced by: etching the ground plane adjacent to the transmission part of the probe into two separate parts, and then connecting a common-mode absorbing resistor in series between the two separate ground planes, wherein the common-mode absorbing resistor is composed of two or more single resistors connected in series.

[0021] Compared with traditional common mode reflection probes (such as Figure 4 As shown), the advantages of the present invention 1) and 2) are as follows.

[0022] The balun is added to the transmission section of a horizontal electric field probe. Its primary purpose is to combine differential signals into a single-port output and suppress the common-mode noise of the vertical electric field component measured by the probe. To facilitate probe use, the probe's electrical length is typically very long. If there is no absorber structure behind the balun, the impedance at the balun input port is open circuit (taking a quarter balun as an example), and the common-mode noise transmitted from the probe is fully reflected. On the other hand, the detection section of a horizontal electric field probe is open circuit, which causes the reflected common-mode noise to fully reflect again, ultimately resulting in multiple total reflections. In particular, at certain frequencies, common-mode noise can resonate in the probe's transmission section, causing it to couple to the balun's output or the probe's output, affecting probe performance and resulting in a narrow operating frequency band.

[0023] As shown in the present invention, adding the two common-mode absorbing resistors described above after the balun of the horizontal electric field probe can absorb common-mode noise transmitted from the probe, eliminating resonance of common-mode noise and effectively resolving the narrow operating frequency band problem caused by total reflection of common-mode noise. Furthermore, because the common-mode absorbing resistors absorb rather than reflect common-mode noise, the probe's test accuracy is also improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the common-mode absorbing resistor added to the balun input terminal of the present invention.

[0025] Figure 2It is a schematic diagram of the common-mode absorbing resistor added in the present invention being added to the ground plane which is a quarter wavelength away from the balun input end.

[0026] Figure 3 It is a schematic diagram of the common-mode absorbing resistor of the present invention added to the transmission line at a distance of one quarter wavelength from the input end of the balun.

[0027] Figure 4 It is a traditional common-mode reflection type horizontal electric field probe.

[0028] Figure 5 Schematic diagram of the common-mode absorption horizontal electric field probe of the present invention with a parallel resistor added to the balun input port, (a) PCB routing diagram, and (b) simulation model diagram.

[0029] Figure 6 The V of the horizontal electric field probe of the common mode absorption parallel resistor added to the balun input port of the present invention is d and V c Simulation result diagram.

[0030] Figure 7 Schematic diagram of the common-mode absorption horizontal electric field probe of the present invention, in which a series resistor is added at a distance of one-quarter wavelength from the balun input port, (a) PCB routing diagram, and (b) simulation model diagram.

[0031] Figure 8 The V of the horizontal electric field probe with the common mode absorption series resistor added to the balun input port at a quarter wavelength is d and V c Simulation result diagram. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings.

[0033] The common mode absorption resistor added in the present invention can be connected in parallel to the input end of the balun, or in series at a certain distance from the input end of the balun. The schematic diagrams are as follows: Figure 1 、 Figure 2 and Figure 3 As shown, the common mode wave absorption principle of the present invention is explained below using the commonly used Marchand balun as an example. The horizontal electric field probe includes three structures: Marchand balun, probe transmission part and probe detection part.

[0034] The structure of the Marchand balun is as follows Figure 1 、 Figure 2 and Figure 3As shown in the top dotted box in the figure, there are two short-circuited input transmission lines (the other ends of which are connected to the differential input of the balun) and one open-circuited output transmission line (the other end of which is connected to the output of the balun). When a differential-mode signal is transmitted on the input transmission line, the differential-mode signal will be coupled to the output transmission line, and the differential-mode signal reflected back to the balun input port and the probe detection part is very small; when a common-mode signal is transmitted on the input transmission line, the power of the common-mode signal coupled to the output transmission line is very small, and because the input transmission line terminal is short-circuited, most of the common-mode signal is reflected back to the balun input port and the probe detection part. To facilitate the explanation of the absorption principle and application examples of the present invention, it is assumed below that the input transmission line length is one-quarter wavelength λ / 4 (λ is the wavelength) at the center operating frequency of the balun. It should be noted that the probe proposed in the present invention is not limited to this assumption.

[0035] 1) The present invention connects two absorbing resistors R in parallel at the input end of the balun, and its structural diagram is shown as follows: Figure 1 As shown. Among them, one end of the two resistors is connected to the line of the differential input of the balun, and the other end is grounded. When the common-mode noise sensed by the probe is transmitted to the input of the balun, if there is no parallel resistor, the impedance seen from the input port of the balun is an open circuit (assuming that the input transmission line length of the balun is one-quarter wavelength λ / 4, according to the transmission line impedance transformation principle, the impedance of the balun input is infinite), and the common-mode noise generated by the external vertical electric field component is fully reflected back to the probe detection part. The probe detection part is two separate metal wires, such as Figure 1 As shown, it is equivalent to an open circuit, so the reflected common mode noise will be reflected again. When the distance from the probe detection part to the balun input end is an integer multiple of λ / 2, multiple reflections will form a resonance of the common mode noise, so that the common mode noise is sensed to the probe output end. In the present invention, after adding two parallel resistors R, the parallel resistors and the original open circuit form a parallel circuit structure as shown in FIG. Figure 1 As shown inside, the input impedance of the balun input port relative to common-mode noise is R / 2. By selecting an appropriate resistor R, the common-mode characteristic impedance of the probe transmission portion can be made equal to the input impedance R / 2 of the balun input port, thereby achieving impedance matching. This absorbs common-mode noise reaching the balun input and reduces the amount of common-mode noise reflected back to the probe detection portion.

[0036] 2) The present invention can also connect a wave absorbing resistor R in series at a distance of λ / 4 from the input end of the balun. Figure 2 As shown in the figure: At a distance of λ / 4 from the input end of the balun, the ground plane is etched into two separate parts, and then an absorbing resistor R is connected in series between the two separated ground planes, which is equivalent to connecting an absorbing resistor in series in the middle of the original complete ground plane; the absorbing resistor R can be connected in series in the middle of the two transmission lines, as shown in the figure. Figure 3As shown in Figure 1, the common-mode input impedance at the balun's input terminal at λ / 4 is zero (according to transmission line theory, the terminal short-circuit of the balun's input line passes through two λ / 4 terminals, forming a short-circuit input impedance). When an absorber resistor R is connected in series with the ground plane or transmission line at this point, the common-mode input impedance at the balun's input terminal at λ / 4 is R. By selecting an appropriate absorber resistor value, the common-mode characteristic impedance of the probe's transmission section can be matched with the input impedance at the balun's input terminal at λ / 4. When the probe's detection section senses common-mode noise, it absorbs the common-mode noise reaching the balun's input, reducing the amount of common-mode noise reflected back to the probe's detection section.

[0037] In a specific implementation of the present invention, the single output line and the differential input line of the balun structure are on different layers of the PCB and are coupled by broadside.

[0038] Figure 5 (a) is a common-mode absorption horizontal electric field probe model of the present invention, where the absorbing resistor is connected in parallel to the balun input port. The PCB board of the probe includes four metal layers: the first and fourth layers are metal ground planes, and the second and third layers of PCB board wiring are respectively as follows: Figure 5 As shown in the left and right images in (a), the probe also has metal shielding on its sides, connected to the first and fourth ground planes. From top to bottom, the probe is divided into three sections: the transmission section (CPW trace structure), the balun, and the probing section (two separate metal traces). Figure 5 (a) The second and third layers within the dashed box together form the balun. To save space, the balun's output traces are designed in a U-shape. The second-layer balun's input traces are connected to the outer metal ground plane via ground vias. A 50-ohm resistor is connected in parallel at the balun's input port to absorb waves. At the balun's input, the second-layer trace is connected to the slotted first layer via a blind via. A resistor is connected in parallel between the blind via and the first-layer ground plane, and then between the balun's input and ground.

[0039] Figure 5 (b) shows a model of the probe and a microstrip test board. The probe is perpendicular to the microstrip line, with the bottom of the probe 1 mm from the line. The microstrip line is used to generate the electric field to be measured. The characteristic impedance of the microstrip line is designed to be 50 ohms. One end of the microstrip line is excited with a 1V voltage, and the other end is matched with a 50 ohm load. The microstrip line generates a vertical electric field component E above its midline. z , a horizontal electric field component E is generated at a certain distance away from the center line of the microstrip line along the x direction x ,like Figure 5 (b) As shown. By placing the probes in these two areas, the external electric field E can be detected separately. z and E x The voltage generated at the output of the probe is expressed as V c and V d Indicates. Vc and V d They represent the probe's response to common-mode noise and the signal to be measured, respectively.

[0040] Figure 6 V is the value of the conventional probe without absorbing resistor and the probe of the present invention. c and V d As can be seen from the figure, the traditional probe has no absorbing resistance, so the non-test electric field component E z Resonance occurs at 2.91 GHz and causes the noise voltage output by the probe to increase. At the same time, the electric field component E that needs to be tested x At 2.52GHz, the output voltage also fluctuates greatly. After the wave absorbing resistor is added, the non-test electric field component E is effectively eliminated. z The resonance generated at 2.91 GHz reduces the electric field component E that needs to be tested. x The resulting output voltage fluctuations.

[0041] Figure 7 (a) is the horizontal electric field probe model of the present invention with common mode absorption and absorbing resistor connected in series at λ / 4 from the balun input port. The PCB board of the probe consists of four metal layers: the first and fourth layers are metal ground planes, the second and third layers are PCB wiring, respectively. Figure 7 As shown in the left and right images in (a), the probe also has metal shielding on its sides, connected to the first and fourth ground planes. From top to bottom, the probe consists of three sections: a balun, a transmission section (differential line structure), and a probing section (two separate metal lines). Figure 7 (a) The second and third layers within the dashed box together form the balun. To save space, the balun's output traces are designed in a U-shape. The ground trace on the third layer is connected to the metal ground plane on the fourth layer via a via. A 50 ohm resistor is connected in series with the differential trace in the transmission section.

[0042] Figure 7 (b) shows a model of the probe and a microstrip test board. The probe is perpendicular to the microstrip line, with the bottom of the probe 1 mm from the line. The microstrip line is used to generate the electric field to be measured. The characteristic impedance of the microstrip line is designed to be 50 ohms. One end of the microstrip line is excited with a 1V voltage, and the other end is matched with a 50 ohm load. The microstrip line generates a vertical electric field component E above its midline. z , a horizontal electric field component E is generated at a certain distance away from the center line of the microstrip line along the x direction x ,like Figure 7 (b) As shown. By placing the probes in these two areas, the external electric field E can be detected separately. z and E x The voltage generated at the output of the probe is expressed as V c and V d Indicates. Vc and V d They represent the probe's response to common-mode noise and the signal to be measured, respectively.

[0043] Figure 8 V is the value of the conventional probe without absorbing resistor and the probe of the present invention. c and V d As can be seen from the figure, the traditional probe has no absorbing resistance, so the non-test electric field component E z Resonance occurs at 4.23 GHz and causes the noise voltage output by the probe to increase. At the same time, the electric field component E that needs to be tested x The present invention also produces a large output voltage fluctuation at 4.23GHz. After adding the absorbing resistor, the non-test electric field component E is effectively eliminated. z The resonance generated at 4.23 GHz reduces the electric field component E that needs to be tested. x The resulting output voltage fluctuations.

[0044] The above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and many variations are possible. All variations that can be directly derived or imagined by a person skilled in the art from the disclosure of the present invention should be considered to be within the scope of protection of the present invention.

Claims

1. A common-mode absorption electric field probe, characterized in that: It includes a horizontal electric field probe and a common-mode absorbing structure. The horizontal electric field probe is composed of a probe transmission part and a probe detection part, and the common-mode absorbing structure is composed of a balun filter and a common-mode absorbing resistor. The balun filter is connected to the horizontal electric field probe, and the common-mode absorbing resistor is installed between the differential input port of the balun filter and the probe detection part. The common-mode absorbing resistor is composed of two or more single resistors in parallel, one end of the common-mode absorbing resistor is connected to the differential input port of the balun filter, and the other end is connected to the ground plane.

2. A common-mode absorption electric field probe according to claim 1, characterized in that: The balun filter is connected to the horizontal electric field probe in the following ways: The differential input port of the balun filter is connected to the differential line of the probe detection part, and the single-ended output port of the balun filter is connected to the probe transmission part; or one end of the differential line of the probe transmission part is connected to the differential line of the probe detection part, and the other end of the differential line of the probe transmission part is connected to the differential input port of the balun filter, and the single-ended output port of the balun filter is connected to the output end of the probe.

3. The common-mode absorption electric field probe according to claim 1, characterized in that: The common-mode absorbing resistor is located at the differential input port of the balun filter, or is located at a distance from the balun input port.

4. The common-mode absorption electric field probe according to claim 3, characterized in that: The common-mode absorbing resistor is composed of two or more single resistors connected in series, and the two ends of the common-mode absorbing resistor are connected in series in the differential line of the probe transmission part, or the two ends of the common-mode absorbing resistor are connected in series in the ground plane close to the probe transmission part; and the common-mode absorbing resistor is at a certain distance from the differential input port of the balun filter.

5. A common-mode absorption electric field probe according to claim 1 or 4, characterized in that: The common-mode absorbing resistor and the differential line of the probe transmission part achieve common-mode impedance matching.

6. A design method for a common-mode absorption electric field probe according to claim 1, characterized in that: include: 1) One end of the differential line of the probe transmission part is connected to the differential line of the probe detection part, and the other end of the differential line of the probe transmission part is connected to the differential input port of the balun filter; 2) A common-mode absorbing resistor formed by connecting two or more single resistors in parallel is connected to the differential input port of the balun filter. One end of the common-mode absorbing resistor is connected to the differential input port of the balun filter, and the other end is connected to the ground plane. 3) Adjust the size of the common-mode absorbing resistor to achieve common-mode impedance matching with the differential line of the probe transmission part, thereby absorbing the common-mode noise reaching the differential input port of the balun filter and reducing the common-mode noise reflected back to the probe detection part.

7. The design method of the common-mode absorption electric field probe according to claim 6, characterized in that: Replace step 1) with the following: the differential input port of the balun filter is connected to the differential line of the probe detection part, and the single-ended output port of the balun filter is connected to the probe transmission part.

8. The design method of the common-mode absorption electric field probe according to claim 6, characterized in that: Replace step 2) with: connect a common-mode absorbing resistor in series on the differential line of the probe transmission part, wherein the common-mode absorbing resistor is composed of two or more single resistors connected in series.

9. The design method of the common-mode absorption electric field probe according to claim 6, characterized in that: Replace step 2) with the following: etch the ground plane adjacent to the transmission part of the probe into two separate parts, and then connect a common-mode absorbing resistor in series between the two separate ground planes. The common-mode absorbing resistor is composed of two or more single resistors in series.

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