CN108829963A - The extracting method of twisted pair parasitic capacitance and conductance in external conductive casing - Google Patents

Abstract

The method for extracting parasitic capacitance and conductance of twisted-pair wires in a conductive shell relates to the field of parasitic parameter extraction in transmission line crosstalk prediction and elimination, and specifically relates to a method for extracting parasitic capacitance and conductance of twisted-pair wires in a conductive shell. The method includes the following steps: S1, by establishing an approximate periodic alternating transmission model of twisted pair, it is obtained that the distance h between the single wire and the central axis of the twisted pair in the intersection part changes, and then the distance d _i from the wire to the conductive shell is changed; S2, by establishing a mirror image replacement Extract the schematic diagram of parasitic inductance to obtain the inductance matrix L(FS) per unit length in the free space of each layer of medium, the inductance matrix per unit length L(INSUL) in the insulating layer, the complex (real) capacitance matrix C(FS) per unit length in the free space, and the insulation matrix Unit length complex (real) capacitance matrix in the layer S3, the overall composite capacitance matrix is obtained from the series idea And get the parasitic net capacitance C and the net conductance matrix G. The present invention adopts the idea of medium layering to extract, and the extracted parasitic parameters are more accurate.

Description

Extraction Method of Parasitic Capacitance and Conductance of Twisted Pair in Conductive Enclosure

technical field

The invention relates to the field of parasitic parameter extraction in transmission line crosstalk prediction and elimination, in particular to a method for extracting parasitic capacitance and conductance of twisted pair wires in a conductive shell.

Background technique

The electromagnetic coupling of the transmission line is reflected in the form of parasitic parameters. In order to realize transmission line crosstalk prediction and crosstalk elimination, the parasitic parameters must be obtained first. The extraction of parasitic parameters per unit length of transmission line is the basis of transmission line crosstalk analysis. The extraction of parasitic parameters is difficult in the extraction of parasitic capacitance and parasitic conductance.

In practice, the electrical parameter per unit length of a classical transmission line is only a simple value, which can be obtained through mature formulas. The common electrical parameters per unit length are mainly extracted by numerical calculation methods such as the method of moments. Scholars represented by Professor Paul C.R use the method of moments (MoM) to systematically analyze the extraction of conductor electrical parameters, and propose many effective solutions, but the wiring structure is usually regarded as uniform and lossless, and usually Placed on ideal land. When analyzing the influence of insulating coating on crosstalk in non-uniform transmission lines, Sergio A.Pignari and Giordano Spadacini used MoM simulation, and did not obtain a direct solution method for parasitic parameters under non-uniform medium conditions. When Abdolhamid Shoory et al. studied twisted-pair near-end crosstalk (NEXT) and far-end crosstalk (FEXT), they regarded twisted-pair crossover distance as zero, and did not consider the non-uniformity of parasitic parameters caused by line distance changes, and Treating the medium as lossless and uniform means idealizing the extraction of parasitic parameters.

Many models are based on the assumption that the distance between twisted pair crossings is zero, the conductor is ideal, and the surrounding medium is lossless and uniform. However, in actual situations, these conditions are often not met. The extracted parasitic parameters Not precise enough to accurately predict and remove crosstalk. For twisted-pair cables, the distance between conductors at the crossing part varies approximately linearly with the position, and in the case of lossy and non-uniform media, the calculation of parasitic parameters is complicated and difficult, and the classic transmission line analysis method is also no longer applicable, while the method of moments, finite Numerical methods such as the element method cannot effectively solve the problem of non-uniform multi-conductor transmission lines because of the large amount of calculation. According to this situation, the present invention proposes a method for solving these problems. Can meet the requirements of the actual production situation. And it is applicable to any transmission line situation.

In summary, the existing literature reports have not studied the problem of direct extraction of lossy non-uniform twisted pair parasitic capacitance and conductance, and the extraction method still needs to be solved.

Contents of the invention

The purpose of the present invention is to provide a method for extracting the parasitic capacitance and conductance of the twisted pair in the conductive shell of the non-uniform medium.

A method for extracting the parasitic capacitance and conductance of twisted-pair wires in a conductive shell comprises the following steps:

(1) By establishing the approximate periodic alternating transmission model of the twisted pair, it is obtained that the distance h between the single wire and the central axis of the twisted pair at the intersection part changes, and then the distance di between the wire and the conductive shell is changed;

(2) By establishing a schematic diagram of parasitic inductance extracted by mirror image replacement, the self-inductance per unit length in free space lii(FS), the mutual inductance per unit length in free space l _ij (FS), and the self-inductance per unit length in insulating medium l _ii (INSUL ), the mutual inductance per unit length l _ij (INSUL) in the insulating medium, and obtain the inductance matrix per unit length L(FS) in the free space of each layer medium, the inductance matrix per unit length in the insulating layer L(INSUL), and the unit length in the free space Capacitance matrix C(FS), unit length capacitance matrix in the insulating layer

(3) The overall composite capacitance matrix is obtained from the idea of series connection And get the parasitic net capacitance C and the net conductance matrix G.

In described step (1), by

L(FS)C(FS)＝μ ₀ ε ₀ E(n)

The unit length capacitance matrix C(FS) in the free space of each layer and the unit length capacitance matrix in the insulating layer are obtained Where μ is the permeability of the insulating layer, μ ₀ is the permeability of the free space, is the complex permittivity of the insulating layer, ε ₀ is the permittivity of the free space, E(n) is the unit matrix of order n, L(FS) is the inductance matrix of unit length in free space, L(INSUL) is the unit length of the insulating layer Inductance matrix, C(FS) is the capacitance matrix of unit length in free space, is the capacitance matrix per unit length in the insulating layer.

In described step (3), by

The overall composite capacitance matrix is derived where C(FS) is the capacitance matrix of unit length in free space, is the capacitance matrix per unit length in the insulating layer.

In the step (2), the self-inductance per unit length in the insulating medium is:

Among them, l _ii (INSUL) is the self-inductance per unit length in the insulating medium, _rs is the inner radius of the conductive shell, μ ₀ is the magnetic permeability of the free space, r _w is the radius of the inner conductor of the twisted pair, r _m is the outer radius of the insulating layer, d _i is the distance between the center of the i-th wire and the central axis of the housing.

In the step (2), the mutual inductance per unit length in the insulating medium is:

Where l _ij (INSUL) is the mutual inductance per unit length in the insulating medium, s ₁ is the distance from the center of wire i to point A on the outer layer of the insulating layer of wire j, and s ₂ is the mirror image center of wire i to point A on the outer layer of the insulating layer of wire j s _ij is the distance from the center of wire i to the center of wire j, s″ is the distance from the mirror image center of wire i to the center of wire j, μ ₀ is the magnetic permeability of free space, and π is the circumference ratio.

In the step (2), the self-inductance per unit length in free space is:

Among them, l _ii (FS) is the self-inductance per unit length in free space, μ ₀ is the magnetic permeability of free space, π is the circumference ratio, _rs is the inner radius of the conductive shell, d _i is the distance between the center of the i-th wire and the central axis of the shell Distance, r _m is the outer radius of the insulating layer.

In the step (2), the unit length capacitance matrix C (FS) in free space is a real matrix when the permittivity is a real number, and is a complex matrix when the permittivity is a complex number; the unit length capacitance matrix in the insulating layer It is a real matrix when the permittivity is a real number, and a complex matrix when the permittivity is a complex number.

total complex capacitance The expressions can directly lead to the matrix of net capacitance and net conductance per unit length.

The beneficial effects of the present invention are:

For heterogeneous media, the extraction of parasitic parameters is complicated, and the present invention adopts the idea of medium layering to extract, and the extracted parasitic parameters are more accurate.

Description of drawings

Figure 1 is the specific operation flow chart

Figure 2 Explanatory diagram for extracting parasitic inductance by image replacement

Figure 3 is the overall cross-sectional structure of two pairs of twisted pairs placed in a conductive shell (one pair connected by a dotted line) and the cross-sectional structure of a single twisted pair

Figure 4 is a twisted pair approximate period alternating transmission circuit model

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

In the accompanying drawing three, 1 is a conductive shell, 2 is a free space, 3 is an insulating layer, and 4 is a wire conductor.

The present invention is described in detail by taking the parasitic capacitance and conductance between two pairs of twisted pairs coupled in a conductive shell as an example, then n is 4, which constitutes a 4+1 non-uniform multi-conductor transmission line model. The cross-sectional structure of two pairs of twisted pairs placed in a conductive shell with an insulating layer is shown in Figure 4. Then in the parallel part of the twisted pair Intersection part tanβ=r _m /l', where (i=1,2,3,4). All twisted-pair conductors are made of copper, and the parameters are set as follows:

μ ₀ =4π×10 ^-7 , ε ₀ =8.854187817×10 ^-10 , ε=3.5ε ₀ , tanδ=0.02, l'=0.25cm, r _w =0.4064mm, r _s =1.778mm, r _m =0.889 mm

Utilize the method of the present invention to extract its parasitic capacitance and conductance below, shown in table 1 is the parasitic capacitance of different positions of twisted-pair crossing part, conductance extraction result (frequency f is fixed as 1MHz), x gets different values and promptly represents different lines Since the multi-conductor transmission line inductance matrix is a symmetrical matrix, only some items are given in the table, and other repeated items are omitted. It can be seen from the table that the method of the present invention can directly extract the parasitic capacitance and conductance matrix of any segment of the twisted pair under different frequencies, which is in line with the actual situation and has great reference value.

The following table shows the extraction results of parasitic capacitance and conductance at different positions of the twisted pair cross section (f=1MHz):

The object of the invention is to solve the problem of extracting the parasitic capacitance and conductance of the twisted pair surrounded by multi-layer lossy non-uniform medium in the conductive shell. Especially for inhomogeneous media, the extraction of parasitic parameters is particularly complicated, and the present invention adopts the idea of media layering to extract.

The parasitic inductance, capacitance, conductance parameter matrix extracted from the multiconductor transmission line equation is as follows:

Among them, n is the number of wires.

The parasitic parameters are mainly affected by two factors, one is the change of the distance from the center of the wire to the ideal conductive shell caused by the change of the wire spacing, and the other is the non-uniformity of the medium.

The establishment of the twisted-pair approximate cycle alternating reversal model is shown in Figure 1, including parallel parts and crossing parts, and half of the distance between the crossing parts is l'. The spacing between twisted-pair conductors is not constant. The distance between the wires in the crossing part varies linearly with the position, resulting in uneven parasitic parameters, and each parasitic parameter is related to its position in the crossing part. It can be seen from Fig. 1 that a pair of twisted-pair wires has a line spacing h=x tanβ.

Assuming that the inner radius of the conductive shell is r _s , the distance between the center of the i-th wire and the central axis of the shell is d _i , and the difference in h will lead to the difference in d _i . The wire is surrounded by two layers of different media, the first layer is an insulating layer, and the second layer is free space. The lossy inhomogeneous medium parameter of the wire is

Insulation layer: ε, μ, tanδ, r _w < r < r _m

Free space: ε ₀ , μ ₀ , r _m <r<r _s

Complex permittivity of insulating layer

Where ε and ε ₀ are the dielectric constants of the insulating layer and free space, respectively, μ and μ ₀ are the permeability of the insulating layer and free space, respectively, and δ is the loss angle of the lossy insulating layer. Let the inner conductor radius of the twisted pair be r _w , and the outer radius of the insulating layer be r _m . The angle between the wires is θ _ij , and the center of the cross-section wire circle is O _i .

The main idea of the present invention is to use the parasitic inductance matrix of each layer of medium area in different sections of the twisted pair to extract the total net capacitance and conductance matrix, specifically as follows:

For the case where the wire is surrounded by a circular insulating medium, there is μ=μ ₀ , so the inductance per unit length is not affected by the inhomogeneous medium, that is, it is the same as in the case of being placed in a homogeneous medium (free space). Define the inductance matrix per unit length in free space and in the insulating layer as L(FS) and L(INSUL) respectively. Using the mirror image method to find the parasitic inductance between the wires, the conductive shell can be located in the radial direction of the shell center The mirror current at the place is replaced, as shown in Figure 3. The specific solution is as follows.

The self-inductance per unit length and mutual inductance per unit length in the insulating medium are:

Among them, s ₁ is the distance from the center of wire i to point A on the outer layer of the insulating layer of wire j, s ₂ is the distance from the mirror image center of wire i to point A on the outer layer of the insulating layer of wire j, s _ij is the center of wire i to the center of wire j , s″ is the distance from the center of the mirror image of wire i to the center of wire j.

The self-inductance per unit length and mutual inductance per unit length in free space are:

Among them, s'1 is the distance from the center _of the wire i to the point B of the ideal conductive shell, and s'1 is the distance from the center of the mirror image _of the wire i to the point B of the ideal conductive shell.

Then the unit length inductance matrices L(INSUL) and L(FS) in the insulating layer and in the free space are obtained.

The dielectric constant of the medium around the wire is non-uniform. Therefore, the capacitance and conductance per unit length are affected by the inhomogeneous medium. The unit length complex (real) capacitance matrix in the insulating layer and free space is defined as C(FS) (if the dielectric constant is real, the capacitance is real, otherwise, it is a complex number).

L(FS)C(FS)＝μ ₀ ε ₀ E(n)

Wherein, where E(n) is an n-order identity matrix.

Because there is an equipotential surface at the contact surface of two media, that is, the surface r= _rm , the total complex capacitance It can be regarded as power recovery in each area

capacity series.

total complex capacitance Expression (7) can directly obtain the matrix of net capacitance and net conductance per unit length.

From the above analysis, we can see that in view of the need to extract the net capacitance and net conductance per unit length, we must first obtain the complex capacitance matrix of each layer of dielectric, and then we must and only need to extract the parasitic inductance matrix of each layer of dielectric area.

Extraction method of parasitic capacitance and conductance of twisted-pair wire surrounded by lossy inhomogeneous medium in conductive enclosure.

Aiming at the practical problem that the parasitic parameters in the process of solving the crosstalk of non-uniform twisted-pair wires are complex and the wires can only be regarded as lossless and uniform, the present invention proposes the non-uniform parasitic capacitance of lossy non-uniform twisted-pair wires and Extraction method of conductance matrix.

The present invention establishes the approximate periodic alternate transmission model of the twisted pair, no longer approximates the intersecting part of the twisted pair to zero, and the distance between the wires changes due to different positions. The schematic diagram of the axial wire spacing of twisted-pair wires is further refined, and it is concluded that the distance h between the single wire and the central axis of the twisted-pair wires in the intersection part changes, resulting in the change of the distance d _i from the wires to the conductive shell.

Establish a schematic diagram of parasitic inductance extracted by mirror replacement, and obtain the parasitic inductance parameter matrices L(INSUL) and L(FS) of each layer of medium,

Depend on

L(FS)C(FS)＝μ ₀ ε ₀ E(n)

Get the capacitance matrix of each layer and C(FS), the overall composite capacitance matrix is obtained from the series idea

Depend on

Derive the parasitic net capacitance and net conductance matrices.

According to the twisted pair model in the given conductive shell, the specific operation is carried out according to the given parameters, and the parasitic capacitance and conductance matrix at different positions of the crossed parts of the twisted pair at a fixed frequency are obtained.

Claims (7)

1. the extraction method of twisted-pair parasitic capacitance and conductance in the conductive shell, is characterized in that, comprises the following steps: (1) By establishing an approximate periodic alternating transmission model of the twisted pair, it is obtained that the distance h between the single wire and the central axis of the twisted pair in the cross section changes, and then the distance d _i from the wire to the conductive shell changes; (2) By establishing the schematic diagram of parasitic inductance extracted by mirror image replacement, the self-inductance per unit length in free space l _ii (FS), the mutual inductance per unit length in free space l _ij (FS), and the self-inductance per unit length in insulating medium l _ii ( INSUL), the unit length mutual inductance l _ij (INSUL) in the insulating medium, and the unit length inductance matrix L(FS) in the free space of each layer medium, the unit length inductance matrix L(INSUL) in the insulating layer, and the unit in the free space Length capacitance matrix C(FS), unit length capacitance matrix in the insulating layer (3) Obtain the overall composite capacitance matrix through the idea of series connection And get the parasitic net capacitance C and the net conductance matrix G. 2. the extraction method of twisted-pair parasitic capacitance and conductance in the conductive housing according to claim 1, is characterized in that: in described step (1), by L(FS)C(FS)＝μ ₀ ε ₀ E(n) The unit length capacitance matrix C(FS) in the free space of each layer and the unit length capacitance matrix in the insulating layer are obtained Where μ is the permeability of the insulating layer, μ ₀ is the permeability of the free space, is the complex permittivity of the insulating layer, ε ₀ is the permittivity of the free space, E(n) is the unit matrix of order n, L(FS) is the inductance matrix of unit length in free space, L(INSUL) is the unit length of the insulating layer Inductance matrix, C(FS) is the capacitance matrix of unit length in free space, is the capacitance matrix per unit length in the insulating layer. 3. the extraction method of twisted-pair parasitic capacitance and conductance in the conductive housing according to claim 1, is characterized in that: in described step (3), by The overall composite capacitance matrix is derived where C(FS) is the capacitance matrix of unit length in free space, is the capacitance matrix per unit length in the insulating layer. 4. the extraction method of twisted-pair parasitic capacitance and conductance in the conductive shell according to claim 1, is characterized in that: in described step (2), in the insulating medium, unit length self-inductance is: Among them, l _ii (INSUL) is the self-inductance per unit length in the insulating medium, _rs is the inner radius of the conductive shell, μ ₀ is the magnetic permeability of the free space, r _w is the radius of the inner conductor of the twisted pair, r _m is the outer radius of the insulating layer, d _i is the distance between the center of the i-th wire and the central axis of the housing. 5. the extraction method of twisted-pair parasitic capacitance and conductance in the conductive housing according to claim 1, is characterized in that: in described step (2), mutual inductance per unit length in the insulating medium is: Where l _ij (INSUL) is the mutual inductance per unit length in the insulating medium, s ₁ is the distance from the center of wire i to point A on the outer layer of the insulating layer of wire j, and s ₂ is the mirror image center of wire i to point A on the outer layer of the insulating layer of wire j s _ij is the distance from the center of wire i to the center of wire j, s″ is the distance from the mirror image center of wire i to the center of wire j, μ ₀ is the magnetic permeability of free space, and π is the circumference ratio. 6. the method for extracting twisted pair parasitic capacitance and conductance in the conductive housing according to claim 1, is characterized in that: in described step (2), in the free space, unit length self-inductance is: Among them, l _ii (FS) is the self-inductance per unit length in free space, μ ₀ is the magnetic permeability of free space, π is the circumference ratio, _rs is the inner radius of the conductive shell, d _i is the distance between the center of the i-th wire and the central axis of the shell Distance, r _m is the outer radius of the insulating layer. 7. the extraction method of twisted-pair parasitic capacitance and conductance in the conductive housing according to claim 1, is characterized in that: in described step (2), in free space, unit length capacitance matrix C (FS) is in dielectric constant It is a real matrix when it is a real number, and it is a complex matrix when the dielectric constant is a complex number; the capacitance matrix of unit length in the insulating layer It is a real matrix when the permittivity is a real number, and a complex matrix when the permittivity is a complex number.