CN101470765A - Length compensation method for differential mode line pair, length calculation method and storage medium - Google Patents

Abstract

The present invention discloses a method for compensating the length of a differential mode line pair and a method for calculating the compensation length of a meandering delay line. The method for calculating the compensation length includes: counting the number of hypotenuses A and the number of corners B of the meandering delay line; measuring the line width W of the meandering delay line; measuring the height S ₁ of the parallel line segments of the meandering delay line; and calculating equation I to obtain the compensation length L _diff of the meandering delay line.

Description

Length Compensation Method of Differential Mode Line Pair, Length Calculation Method and Storage Medium

technical field

The present invention relates to a circuit layout, and in particular to a method for compensating the length of a differential mode line pair and a method for calculating the compensation length of a meandering delay line.

Background technique

With the advancement of technology, the operating frequency of digital circuits is getting higher and higher, resulting in many undesirable electromagnetic effects. Taking the Printed Circuit Board (PCB) as an example, when the signal is transmitted on the transmission line, electromagnetic radiation will be generated because the electromagnetic wave will be transmitted outward through the medium. This electromagnetic radiation will affect the normal operation of other electronic components, which is called Electromagnetic Interference (EMI). In today's digital circuits, the unit density of components continues to increase, which makes the circuit design of the PCB face many challenges. In actual wiring, paths of key line pairs (such as differential mode line pairs) may be unequal in length due to various factors such as corners.

FIG. 1 is a diagram illustrating a circuit layout for configuring a differential mode line pair. P11 and P12 in FIG. 1 represent two lines of the differential mode line pair respectively. When the differential mode line pair P11 and P12 pass through the corner, it is obvious that the signal path length of the outer circuit P11 must be longer than the signal path length of the inner circuit P12. The phase skew caused by the different path lengths will generate common mode noise, which will affect the signal integrity and generate the source of electromagnetic interference. Therefore, in order to ensure that the path lengths of the critical lines are the same, generally a "serpentine" line design technique is used to compensate the path length of the inner loop line P12.

For the serpentine lines designed by the traditional technology, the center line of the line (as shown by the dotted line in FIG. 1 ) is used to estimate the path length of the line. This approach seems reasonable, but the actual current does not necessarily flow along the neutral line of the circuit. This common technique will cause the circuit layout to fail to meet the requirement of equal length of the actual signal path, resulting in common-mode noise that cannot be ignored.

Contents of the invention

The invention provides a method for calculating the compensation length of the meandering delay line to more accurately calculate the compensation length of the actual signal path in the meandering delay line.

The invention provides a method for compensating the length of a differential mode line pair to more accurately design a differential mode line pair with the same length as the actual signal path.

The invention proposes a compensation length calculation method of a meandering delay line. The compensation length calculation method includes: counting the number of hypotenuses A of the meandering delay line; counting the number of corners B of the meandering delay line; measuring the line width W of the meandering delay line; measuring the parallel line segments of the meandering delay line height S ₁ ; and the calculation equation $L_{\mathrm{diff}}=A(\sqrt{2}-1)(S_1-(5W/6))+B\{\sqrt{{\left[\frac{W}{5}(1+\sqrt{2})\right]}^2+{\left[\frac{W}{5}\right]}^2}-\left[\frac{W}{5}(1+\sqrt{2})\right]\},$ In order to obtain the compensation length L _diff of the meandering delay line.

The invention proposes a method for compensating the length of a differential mode line pair. This length compensation method includes: setting the number of hypotenuses A of the meandering delay line; setting the number of corners B of the meandering delay line; setting the line width W of the meandering delay line; calculating the equation $A(\sqrt{2}-1)(S_1-(5W/6))+B\{\sqrt{{\left[\frac{W}{5}(1+\sqrt{2})\right]}^2+{\left[\frac{W}{5}\right]}^2}-\left[\frac{W}{5}(1+\sqrt{2})\right]\}=0$ In order to obtain the height S ₁ of the parallel line segment of the meandering delay line; set the height S ₁ of the parallel line segment of the meandering delay line; and match the meandering delay line to the differential mode line near the corner of the differential mode line pair in the inside line of the pair.

The invention further provides a computer-readable storage medium for storing computer programs. The computer program is used for loading into a computer system and causing the computer system to execute the above method.

The present invention uses the physical geometry structure of the meandering delay line to analyze the actual current trend, and then derives a more accurate length compensation method and its compensation length calculation method, so that the actual signal path can be more accurately calculated during the meandering delay time. The compensation length in the line can more accurately design the differential mode line pair with the same length as the actual signal path.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a diagram illustrating a circuit layout for configuring a differential mode line pair.

FIG. 2 illustrates a layout of a differential mode line pair according to an embodiment of the present invention.

FIG. 3A illustrates the layout of verification circuits according to an embodiment of the present invention.

FIG. 3B is a cross-section illustrating FIG. 3A.

FIG. 3C is a diagram illustrating the layout of the 45-degree differential mode rotation angle in FIG. 3A.

FIG. 4 illustrates simulation results of common-mode noise with uncompensated lengths and serpentine delay lines in differential-mode line pairs according to an embodiment of the present invention.

FIG. 5 is a flow chart illustrating a method for length compensation of a differential mode line pair according to an embodiment of the present invention.

FIG. 6 illustrates simulation results of common-mode noise with uncompensated lengths and serpentine delay lines in differential-mode line pairs according to an embodiment of the present invention.

FIG. 7 is a simulation result illustrating the frequency-domain differential-to-common-mode response of an uncompensated length and a serpentine delay line in a differential-mode line pair according to an embodiment of the present invention.

FIG. 8 illustrates a method for calculating the compensation length of a meander delay line according to an embodiment of the present invention.

Detailed ways

The following examples will be presented to illustrate the present invention, in order to enable those with common knowledge in the field to better understand the present invention and implement it accordingly. Of course, the following embodiments can also be implemented in the form of a computer program, and a computer-readable storage medium is used to store the computer program, so that the computer can execute the following methods.

In the following embodiments, a "serpentine" is used to implement a serpentine delay line. This embodiment analyzes the actual current trend to derive a more accurate formula, so the compensation length of the actual signal path in the meander delay line can be calculated more accurately, and then the difference between the actual signal path equal length can be more accurately designed. Die line pair.

FIG. 2 illustrates a layout of a differential mode line pair according to an embodiment of the present invention, wherein a meandering delay line is configured in one of the lines of the differential mode line pair. When the differential mode signal encounters a corner during transmission in the line, differential mode reflection noise will be generated at the drive end due to the discontinuity of the corner structure. Moreover, due to the unequal lengths of the wires, there will be a time difference between the two signals, so common mode noise will be generated at the receiving end. In order not to seriously deteriorate the differential mode reflection caused by the whole, in this embodiment, the height S ₁ of parallel line segments in the meandering delay line is set approximately equal to the spacing S of the differential mode line pairs. In addition, L ₁ in FIG. 2 represents the length of the parallel line segment, and W represents the line width of the differential mode line pair (also the line width of the meandering delay line).

Under this condition, this embodiment will compensate each differential mode rotation angle with a halved meandering delay line. FIG. 3A illustrates the layout of verification circuits according to an embodiment of the present invention. FIG. 3B is a cross-section illustrating FIG. 3A. Assume here that the distance between the differential mode line pair in Figure 3B is S=9mil, the line width W=4mil, the line thickness T=1.2mil, the distance between the differential mode line pair and the lower metal layer is H1=4mil, and the distance between the differential mode line pair and the upper metal layer The layer distance H2 = 13.2 mil, and the dielectric coefficient ε _r of the printed circuit board = 3.7. Time-domain analysis is performed on the layout of the verification circuit in FIG. 3A to observe how the receiving end suppresses common-mode noise. In FIG. 3A , the driving terminal transmits a positive voltage signal through one of the lines P42 , and transmits a negative voltage signal through the other line P41 . The aforementioned voltage amplitude is about 1 volt, the signal rise time is 50 ps, and the parallel segment length L ₁ of each meandering delay line is 3 W (three times the line width).

FIG. 3C is a diagram illustrating the layout of the 45-degree differential mode rotation angle in FIG. 3A. By geometrically analyzing Figure 3C, it can be known that the length difference of the 45-degree differential mode corner of this verification circuit is

2ΔL＝2(W+S)tan(θ/2)＝10.7696mil Formula (1)

, where θ is 45 degrees. It can be known from the above formula that when the length difference of the 45° differential mode rotation angle is known, under the condition of length matching (the length is calculated by the midline), the height S ₁ of the parallel segment of the two-fold meandering delay line is

$10.7696=4(\sqrt{2}-1){\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A200710307303E00111.png,A200710307303E00141.png"\; state="\{\{state\}\}">S</figure-callout>}}_1$ Formula (2)

, so S ₁ =6.5mil.

FIG. 4 illustrates simulation results of common-mode noise with uncompensated lengths and serpentine delay lines in differential-mode line pairs according to an embodiment of the present invention. The verification circuit of the differential mode line pair shown in FIG. 3A and FIG. 3B has two differential mode corners. If the length difference of this differential mode line pair is not compensated (that is, the line layout similar to Figure 3A but without a meandering delay line), the simulation results show that there is a considerable common mode noise (the solid line in Figure 4 curve). And if the differential mode line pair is configured with a meandering delay line (such as the circuit layout of FIG. 3A ) to compensate for the length difference, the simulation results show that the common mode noise is greatly reduced (as shown in the dotted line curve of FIG. 4 ). Please note that here the compensation length is calculated based on the midline of the meandering delay line. According to the settings of the above verification conditions, it can be calculated that when the compensation length is calculated using the midline, the height of the parallel segment of the meandering delay line S ₁ needs to be 6.5mil. It can be seen from the dotted curve in Figure 4 that if the height S ₁ of the parallel segment of the meandering delay line is 6.5mil, although the common mode noise has been greatly reduced, there is still a non-negligible amount of common mode noise.

In other words, from the simulation results in Figure 4, it can be seen that the method of calculating the compensation length of the meandering delay line based on the neutral line, after compensation, cannot minimize the amount of common-mode noise (as can be seen from Figure 4 There are still some components that are not fully suppressed due to the amount of common mode noise). Therefore, the compensation length required for the meandering delay line is calculated by taking the middle line, which is still far from the actual required compensation length.

Therefore, this embodiment analyzes the actual current direction to derive an approximate correction formula, so the compensation length of the actual signal path in the meandering delay line can be calculated more accurately, and the actual signal path equal length can be designed more accurately differential mode line pair.

FIG. 5 is a flowchart illustrating a method for length compensation of a differential mode line pair according to an embodiment of the present invention. Referring to FIG. 5 , firstly, the user sets the number of hypotenuses A of the meandering delay line (step S510 ), the number of corners B (step S520 ), and the line width W (step S530 ). The above steps S510-S530 can also be automatically set by default values of the application program.

In step S540 , the line pair length difference L _diff formed by the differential mode lines for a certain corner (or certain corners) is calculated. In this embodiment, step S540 can apply the aforementioned formula (1) to calculate and obtain the line pair length difference L _diff , that is, calculate L _diff =2(W+S)tan(θ/2). For example, if the aforementioned verification conditions (W=4mil, S=9mil, θ=45 degrees) are used, a 45-degree rotation angle will cause the differential mode line pair to form a line pair length difference L _diff =10.7696 mil. Next, step S550 is carried out to calculate the equation

$L_{\mathrm{diff}}=A(\sqrt{2}-1)(S_1-(5W/6))+B\{\sqrt{{\left[\frac{W}{5}(1+\sqrt{2})\right]}^2+{\left[\frac{W}{5}\right]}^2}-\left[\frac{W}{5}(1+\sqrt{2})\right]\},$ Formula (3)

, to obtain the height S ₁ of the parallel segment of the meandering delay line. From the foregoing formula (1) and FIG. 3C , it can be known that the length difference L _diff between the differential mode line pairs passing through a 45-degree turning angle. Under the condition of length matching, and considering that the current will flow according to the "shortest path", it is assumed that the parameters set in steps S510-S530 of Fig. 5 are A=4, B=8, W=4mil, then step S550 The calculated result is S ₁ =9.1 mil. Then, according to the calculation result of step S550, the height _S1 of the parallel segment of the meandering delay line is set (step S560). Finally, step S570 is performed, according to the above parameter settings, a meandering delay line is arranged on the inner line P42 of the differential mode line pair near the corner of the differential mode line pair (as shown in FIG. 3A ).

In order to verify whether this embodiment can improve the original method of calculating the compensation length based on the center line, the aforementioned formula (2) and formula (3) are respectively applied to the verification circuit shown in FIGS. 3A and 3B . That is to say, the height S ₁ of the parallel segment obtained by calculating the compensation length from the midline = 6.5 mil, and the height S ₁ = 9.1 mil of the parallel segment obtained by calculating the compensation length in this embodiment, respectively, for the serpentine delay formed by the two Lines are verified to compare the difference in common-mode noise suppression between the two.

FIG. 6 illustrates simulation results of common-mode noise with uncompensated lengths and serpentine delay lines in differential-mode line pairs according to an embodiment of the present invention. Here, the simulation is performed with the verification circuit of the differential mode line pair shown in FIG. 3A and FIG. 3B . If the length difference of this differential mode line pair is not compensated (i.e. similar to the line layout shown in Figure 3A but without a meandering delay line), the simulation results show considerable common mode noise (as shown in the solid line in Figure 6 curve). And if the differential mode line pair is configured with a meandering delay line (as shown in the circuit layout of Figure 3A) to compensate for the length difference, the simulation results show that the common mode noise is greatly reduced (as shown in the dotted line curve and the dotted line curve in Figure 6 ). Please note that the dotted curve in Fig. 6 is the simulation result of common mode noise obtained by calculating the parallel line segment height S ₁ =6.5mil from the midline of the meandering delay line; while the dotted curve is based on the present embodiment and The method illustrated in FIG. 5 is used to calculate the parallel line segment height S ₁ =9.1 mil, and the obtained common mode noise simulation results. It can be seen from the dotted curve in FIG. 6 that if the height S ₁ of the parallel segment of the meandering delay line is 6.5mil, although the common mode noise has been greatly reduced, there is still a non-negligible amount of common mode noise. In contrast to the dotted curve in Figure 6, if the height S ₁ of the parallel segment of the meandering delay line is 9.1mil, the amount of common-mode noise will be minimized, and the so-called "line equal length" can be more accurately achieved.

FIG. 7 is a simulation result illustrating the frequency-domain differential-to-common-mode response of an uncompensated length and a serpentine delay line in a differential-mode line pair according to an embodiment of the present invention. It can be seen from the simulation results that the compensation length of the meandering delay line is generally calculated based on the neutral line, which cannot minimize the amount of common-mode noise after compensation (some components of the amount of common-mode noise are not fully suppressed) . The present embodiment and the method illustrated in FIG. 5 calculate the height S ₁ of the parallel line segment, regardless of the performance in the time domain or the frequency domain, the so-called "line equal length" can be more accurately achieved.

FIG. 8 illustrates a method for calculating the compensation length of a meander delay line according to an embodiment of the present invention. The compensation length required by the meandering delay line generally needs to correspond to the length difference L _diff of the differential mode line pair. The length difference L _diff may be caused by a 45-degree corner or other reasons. The compensation length is here regarded as the length difference L _diff . First count the number of hypotenuses A of the meandering delay line (step S810) and the number of corners B (step S820), and measure the line width W of the meandering delay line (step S830) and the height _S1 of the parallel line segment (step S840 ). Then proceed to step S850 to calculate the above equation (3) to obtain the compensation length L _diff of the meandering delay line. For example, as shown in Figure 2, the number of hypotenuses A=4 and the number of corners B=8 of the meander delay line; if the line width W=4mil and the height S ₁ of the parallel line segment =9.1mil, the The compensation length L _diff is about 10.7696mil.

To sum up, in the above-mentioned embodiment, due to the analysis of the actual current direction, a more accurate length compensation method and its compensation length calculation method can be derived, so the actual signal path in the meandering delay line can be more accurately calculated. Compensate the length, so that the differential mode line pair with the same length as the actual signal path can be designed more accurately.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention, and anyone with ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the claims.

Claims (6)

1. A method for calculating the compensation length of a meandering delay line, comprising: Count the number of hypotenuses A of the meandering delay line; Count the number of corners B of the meandering delay line; Measuring the line width W of the meandering delay line; measuring the height S ₁ of the parallel segment of the meandering delay line; and Calculation equation $L_{\mathrm{diff}}=A(\sqrt{2}-1)(S_1-(5W/6))+B\{\sqrt{{\left[\frac{W}{5}(1+\sqrt{2})\right]}^2+{\left[\frac{W}{5}\right]}^2}-[\frac{W}{5}(l+\sqrt{2})\left]\right\},$ In order to obtain the compensation length L _diff of the meandering delay line. 2. The method for calculating the compensation length of a meandering delay line according to claim 1, wherein the meandering delay line comprises a meandering line. 3. A computer-readable storage medium for storing a computer program, the computer program is used to load into a computer system and make the computer system execute the compensation length of the meandering delay line as claimed in claim 1 Calculation method. 4. A length compensation method for a differential mode line pair, comprising: Set the number of hypotenuses A of a meandering delay line; Set the number of turns B of the meandering delay line; Setting the line width W of the meandering delay line; Calculating the line pair length difference L _diff formed by the differential mode line for a corner; Calculation equation $L_{\mathrm{diff}}=A(\sqrt{2}-1)(S_1-(5W/6))+B\{\sqrt{{\left[\frac{W}{5}(1+\sqrt{2})\right]}^2+{\left[\frac{W}{5}\right]}^2}-[\frac{W}{5}(l+\sqrt{2})\left]\right\},$ To obtain the height S ₁ of the parallel segment of the meandering delay line; Set the height S ₁ of the parallel segment of the meandering delay line; and Near the corner, the serpentine delay line is arranged in the inner line of the differential mode line pair. 5 . The method for compensating the length of a differential mode line pair according to claim 4 , wherein the meandering delay line comprises a meandering line. 6 . 6. A computer readable storage medium for storing a computer program, the computer program is used to load into a computer system and make the computer system execute the method for length compensation of the differential mode line pair as claimed in claim 4 .

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