RU2568327C2 - Meander line with additional delay - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention refers to the sphere of electric engineering and may be used in meander lines of printed circuit boards. The meander line with additional delay consists of one base conductor, two signal tracks parallel to the base conductor and to each other and interconnected at one end, and dielectric medium, at that the product of sums of board delays per unit length of even and odd modes times line length is more or equal to the sum of rise time, flat top and tailing edge time, and value of board delays per unit length of odd mode for the line is more than difference between value of board delays per unit length of even and odd mode in case of their evenness and value of board delays per unit length of a single line.

EFFECT: additional pulse delay is provided with minimum pulse form distortion.

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Description

The invention relates to electrical engineering and can be used to transmit a pulse signal in the meander lines of printed circuit boards with an additional delay and minimal distortion of the pulse shape.

When designing high-speed digital electronics, synchronization of the clock signals at the receiving points is required. It is necessary that all paths brought to the points of reception provide the same signal delays. For this, meander lines are often used. However, a pulsed signal in a meander with a high density of conductors, which they strive to reduce the occupied area, arrives at the receiving point distorted due to pickups initiated from the front and the decay of the signal at the ends of the meander conductors. The result is an uncontrolled reduction in line delay and distortion in the shape of the pulse. In the case when the delay in the line is less than the required, it is necessary to increase its length, and at the same time, the area occupied on the surface of the printed circuit board. Thus, meander delay lines either do not provide the specified delay due to distortion, or occupy a large area on the printed circuit board.

The meander delay line from one turn is known [T. Gazizov Distortion of a pulse signal in simple meander lines / T.R. Gazizov, A.M. Zabolotsky // Infocommunication technologies. - 2006. - Volume 4, No. 3. - S.34-38], providing the passage of the pulse through the conductor without distortion of its shape.

The disadvantage of this device is the need for two reference planes and a uniform dielectric filling between them.

Closest to the claimed device is a meander line based on a connected microstrip line [Fusco B. microwave circuit. Analysis and computer aided design: Per. from English - M.: Radio and Communications, 1990. - 288 p.: Ill. ISBN 5-256-00663-0], consisting of one reference conductor, two signal conductors parallel to it and to each other, interconnected at one end, and a dielectric medium.

The disadvantages of the prototype device are an uncontrolled decrease in the delay in the line and the distortion of the pulse shape and the presence of distortion in the shape of the pulse passing along the line due to the strong mutual relations between the half-turns.

The inventive meander line with an additional delay, consisting of one reference conductor, two parallel signal conductors connected to each other at one end, and a dielectric medium, differs in that the product of the sum of the linear delays of the even and odd modes by the length of the line or equal to the sum of the durations of the front, flat top and pulse decay, and the value of the linear delay of the odd line mode is greater than the difference of the linear delay of the even mode and the difference between the values the linear delay of an even or odd mode, if they are equal, and the linear delay of a single line.

The advantage of the claimed meander line, in contrast to the prototype device, is to ensure the passage of the pulse with an additional delay and minimal distortion of its shape.

The technical result, the proposed meander delay line is aimed at achieving, is to provide additional pulse delay with minimal distortion of its shape.

The technical result is primarily achieved by choosing the line length so that the delay value in the meander line is greater than or equal to the sum of the durations of the front, flat peak and pulse decay. Under this condition, the shape of the pulse is not distorted, although a pulse appears in front of it in the form of a trapezoid of positive polarity, and after it - negative. The impulses that appear are, in the terminology of coupled lines, a tip at the near end of the passive line, whose amplitude is proportional to a quarter of the sum of capacitive and inductive coupling. But this tip does not distort the shape of the pulse. Also, to achieve a technical result, it is necessary that the value of the linear delay of the odd mode of the line is greater than the difference between the linear delay of the even mode and the difference between the linear delay of the even or odd mode, if they are equal, and the linear delay of a single line. Under this condition, a negative polarity pickup is applied to the front and the back of the pulse, which in the terminology of coupled lines is a far crosstalk, and its amplitude is proportional to a quarter of the difference between the capacitive and inductive connections between the signal conductors. An additional delay is observed due to the summation of the pulse of the signal of positive polarity and the pickup of negative polarity at the end of the meander line. In this case, the front and decay of the pulse signal are distorted, but these distortions are insignificant.

Figure 1 shows an example of a cross sectional claimed line when the meander conductor is covered from above by one dielectric layer. Cross section parameters: w and t are the width and thickness of the conductor, s is the distance between the conductors, d is the distance from the edge of the structure to the conductor, hC is the thickness of the substrate layer, hV is the thickness of the coating layer, and ε _rC and ε _rV are relative, respectively dielectric constant of the substrate and the coating layer. On figb shows the equivalent circuit of the inventive meander line with a half-turn length l. The line consists of two parallel conductors 4, 5 in dielectric filling, interconnected at one end. One of the line conductors is connected to a pulse signal source, represented on the circuit as an ideal emf source 1 and internal resistance R _Г 2. Another conductor of the line is connected to the receiving device shown in the diagram with resistance R _Н 3.

The positive effect of the invention is shown in the graphs of figure 3 obtained in the simulation. The values of R _Г and R _{Н are} taken at modeling equal to 50 Ohms, and the duration of the front, flat top and pulse drop is 100 ps each. It is also important to note that the dielectric filling of the line under consideration will change only due to a change in ε _rV , while the remaining geometric and electrical parameters of the structure are unchanged.

The parameters of the cross section in figure 2 _a and the length of the meander line are selected so that the conditions

$$\left({\tau }_e+{\tau }_o\right)\cdot l\ge t_r+t_d+t_f,\left(\mathrm{one}\right)$$

$${\tau }_o>{\tau }_e-{\tau }^{\text{'}\text{'}},\left(2\right)$$

where τ _e and τ _о are the values of the running delays of the even and odd modes, l is the half-turn length, t _r ,

t _d and t _f are the durations of the front, flat top, and pulse decay, respectively, and r ′ is calculated by the formula

$$\tau \text{'}\text{'}={\tau }_{e=o}-{\tau }_{\mathrm{one}},\left(3\right)$$

where τ _{e = o} is the linear delay of an even or odd line mode, provided that they are equal, and τ ₁ is the linear delay of a single line, determined by the formula

$${\tau }_{\mathrm{one}}=\sqrt{L\cdot C},\left(\mathrm{four}\right)$$

where L is the linear inductance of a single line, and C is the linear capacitance of a single line.

The linear delays of the even and odd modes for the structure of coupled transmission lines symmetrical with respect to the reference conductor are calculated as [Malyutin ND Multiply connected strip structures and devices based on them / N.D. Malyutin. - Tomsk: Publishing house Tom. University, 1990. - 164 p.]

$${\tau }_e=\sqrt{\left(L_{\mathrm{eleven}}\cdot C_{\mathrm{eleven}}+L_{12}\cdot C_{12}\right)+\left(L_{12}\cdot C_{\mathrm{eleven}}+L_{\mathrm{eleven}}\cdot C_{12}\right)},\left(5\right)$$

$${\tau }_o=\sqrt{\left(L_{\mathrm{eleven}}\cdot C_{\mathrm{eleven}}+L_{12}\cdot C_{12}\right)+\left(L_{12}\cdot C_{\mathrm{eleven}}+L_{\mathrm{eleven}}\cdot C_{12}\right)},\left(6\right)$$

where C ₁₁ and C ₁₂ , L ₁₁ and L ₁₂ are the corresponding elements of the matrices (electrostatic and electromagnetic induction coefficients) L and C.

Provided that the values of the linear delays of the even and odd line modes are equal, the term (L ₁₂ · C ₁₁ + L ₁₁ · C ₁₂ ) = 0, then

$${\tau }_{e=o}=\sqrt{\left(L_{\mathrm{eleven}}\cdot C_{\mathrm{eleven}}+L{}_{12}\cdot C_{12}\right)}.\left(7\right)$$

Thus, substituting (7) and (4) in (3), we obtain

$$\tau \text{'}\text{'}=\sqrt{\left(L_{\mathrm{eleven}}\cdot C_{\mathrm{eleven}}+L{}_{12}\cdot C_{12}\right)}-\sqrt{L\cdot C}.\left(8\right)$$

To fulfill the condition (1), consider the line shown in figure 1 a . Cross section parameters: w = 120 microns, t = 30 microns, s = 150 microns, d = 360 microns, hС = 100 microns, hV = 50 microns; ε _rC = 4.49; ε _rV = 9.2. Calculated matrices:

, $$L=\left[\begin{array}{cc}\mathrm{339,89}& \mathrm{57,57}\\ \mathrm{57,57}& \mathrm{339,89}\end{array}\right]нГн/м$$

. $$C=\left[\begin{array}{cc}141.97& -32.71\\ -32.71& 141.97\end{array}\right]PF/m$$

, $$L=\left[\begin{array}{cc}339.89& 57.57\\ 57.57& 339.89\end{array}\right]nGn/m$$

.

Using (5) and (6), we obtain τ _e = 6.59 ns / m, τ _o = 7.023 ns / m. With a line length l = 25 mm, the product of the sum of the linear delays of the even and odd signal modes by the line length is 340.3 ps. The sum of the durations of the front, flat top and decay of the pulse signal is 300 ps. Thus, condition (1) is satisfied.

To fulfill condition (2), we consider a similar meander line, but with ε _rV = 4.79. For such a line:

, $$L=\left[\begin{array}{cc}\mathrm{339,89}& \mathrm{57,57}\\ \mathrm{57,57}& \mathrm{339,89}\end{array}\right]нГн/м$$

. $$C=\left[\begin{array}{cc}119.42& -20.22\\ -20.22& 119.42\end{array}\right]PF/m$$

, $$L=\left[\begin{array}{cc}339.89& 57.57\\ 57.57& 339.89\end{array}\right]nGn/m$$

.

Using (5) and (6), we obtain τ _e = 6.2791 ns / m, τ _o = 6.2790 ns / m. Thus, the linear delays of the even and odd modes coincide up to the third sign.

To calculate τ _1, we consider a single transmission line with similar electrical and geometric parameters of the conductor and dielectrics (Fig. 1 a ). Linear capacitance and inductance, respectively, C = 114.49 pF / m and L = 342.29 nH / m.

Using the obtained matrices for the meander lines and the values of linear capacitances and inductances of a single line, from (8) we obtain τ ′ = 0.019 ns / m. Substituting the values of τ _e = 6.59 ns / m, τ _o = 7.023 ns / m and τ ′ = 0.019 ns / m in (2), we obtain 7.023> 6.40 (ns / m). Thus, condition (2) is satisfied.

Figure 3 shows the waveforms at the end of the meander (V3) and single (V2) lines (with the same total conductor length 2l) for equivalent line circuits in Figs. 1b and 2b. Forms V2 and V3 are given for two cases when τ _e = τ _o and τ _o > τ _e + τ ′. The delay difference between V3 and V2 for τ _e = τ _o related to l is τ ′. The value of τ ′ in the graph is 0.048 ns / m, and calculated analytically - 0.019 ns / m. The difference can be caused by inaccurate fulfillment of the condition τ _e = τ _o and incomplete matching of the lines with the loads. From Fig.3b it can be seen that the claimed meander line has an additional delay, the value of which is greater by Δt than the delay in a single line. Thus, the positive effect of the claimed line is shown.

Claims (1)

A meander line with an additional delay, consisting of one reference conductor, two signal conductors parallel to it and to each other, connected at one end, and a dielectric medium, characterized in that the product of the sum of the values of the running delays of the even and odd modes by the line length is greater than or is equal to the sum of the durations of the front, flat top and pulse decline, and the value of the linear delay of the odd line mode is greater than the difference between the linear delay of the even mode and the difference between the linear the delay of the even or odd mode, if they are equal, and the value of the linear delay of a single line.

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