004” line/0. Details: In the list below, [1] is the reference design stackup information; [2] and [3] are the processes to get the result close enough to the reference design target so as to know the tool is valid; and [4] is the calculation in question because it is either 5. 1. The concept of driving the conductors as a differential pair implies the presence of a zero voltage ground. Thus, for optimal performance the resistors and MOSFETs must be matched. look at a differential source driving a twisted pair to the FDA. PCB Structures / Discrete Structures / Signal Management. 3. The impedance between the tracks is the differential impedance, (1. The most commonly used instrumentation. The questions are mostly on the inner layer differential impedance item [4] below. An example of this calculation using the Si8000m Quick Solver is shown below in figure 4. Coplanar Waveguide Calculator. This calculator finds both odd and even transmission line impedance. CSI-2 interface data pairs require a 100 ohm differential impedance. Note: If this post answers your question, please click the Correct Answer button. The latter for embedded dual stripline layers only. 331 1 2 5. The Coplanar Differential Pair Impedance Calculator is a tool that helps you calculate the characteristic impedance of a coplanar waveguide (CPW). The following are typical line widths and spacings for the more common impedance values when using ½ OZ copper: 50 Ohm Single Ended: 0. 4 Comments. This can vary, make sure you calculate it using an online impedance calculator or similar tool. Still, as you correctly analyzed it is much better to think of the individual lines in a differential pair as two length-matched single-ended lines, both with the half impedance. best to use a stackup calculator to provide quick ‘what if’ analysis of the possibilities. Some differential impedance requirement for differential pairs, where the signals must be routed together Just as an example, consider a 2-layer board on standard thickness 62 mil core (Dk = 4. 331 1 2 5. 75 m A = 9333 ohms. But I am not able to match this impedance. Most of the dedicated TL tools doesn't have this option, only if you use a full EM simulator. This means the slope resistance is 7 V 0. If you need to use differential pairs, you simply define traces in each layer as differential pairs and the impedance calculator will determine the correct spacing between traces. A PCB impedance calculator is necessary to set the constraints for trace structures during fabrication; they can vary in complexity, speed, and accuracy. Instant online PCB quote, get PCBs for only $2. No matter what the case was, if you did not have an impedance calculator, you had to rely on measurements, or some other data set to get an accurate value for trace width in your PCB. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. Going through Saturn PCB Calculator - which is free and useful software for engineers. infinite mutual impedance. The receiver, which is on the motherboard, is a standard LVDS receiver, with 100Ω termination resistors. Differential Impedance Ω. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. Ideally the traces in the differential pair only interact with each other, as another answer said. Figure 4. g. At the receiver, the signal is recovered by taking the difference between the signal levels on. The same applies to common mode impedance, except that common mode impedance arises under common mode driving. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. We get a lot of questions about trace impedance and how to calculate the right trace size to hit a specific impedance in a manufacturable PCB. In case I reduce the width and the distance of tracks to 0. This form of microstrip is composed of two traces. Also, it has got. Differential pairs: even or common mode?PCB impedance calculator – Single ended / Differential pair. Grounded Differential Coplanar Wave Guide. With t = 35 um (typical for copper with plating on a pcb), Z odd drops to 44 ohms, according to LineCalc. 5) and 1. There are single end trace impedance and distance between traces in the pair. Click here to see the user guide of our impedance calculator. Just to give designers a starting point, take a look at these differential impedance calculators you can use to get an initial estimate of the differential impedance for microstrips and striplines. To explore the differential pair transmission line results, nominate the calculated variable - either the Trace Width or Trace Gap - by clicking the appropriate . The interactive routing and differential pair length matching features in Altium Designer® can be used alongside an integrated electromagnetic solver in the Layer Stack Manager. Note that the y-axis is on a logarithmic scale for clarity. 100 Ohm Differential Pair: 0. The same applies to common mode impedance, except that common mode impedance arises under common mode driving. 3 V, etc. Capacitance – the impedance calculator uses the Impedance value to calculate the capacitance per unit length. KiCad has a built-in impedance calculator!The common-mode rejection ratio is a key figure of merit of any differential system because its primary role is to reject undesired common-mode currents with minimal impact on the desired differential-mode currents. 6mm) That should give the traces around 90 Ohms differential impedance according to the PDF, but when I try to input it to my impedance calculator (Saturn PCB toolkit V7. 3 Answers. 1 mm, therefore very small. It refers to the impedance that a pair of differential (opposite phase) signals will see in a microstrip transmission line configuration. Return loss Return loss is another way to look at impedance in the frequency domain. The differential impedance of MIPI tracks should be 100 Ohms, not 90 (USB requires 90). The total length of the signal path is about 1,330mils. There are four different types of impedance used in characterizing differential trace impedances. 9-Hole Score Differential Calculator. Unfortunately, TxLine doesn't do coplanar waveguide for differential traces. The most common examples of transmission lines that require controlled impedance are single-ended microstrip, single-ended stripline, microstrip differential pair, and stripline differential pair. 5 mil as the thickness of 3313 prepreg when the controlled impedance tracks are on top/bottom, use 5. This rule maintains the desired signal impedance. Differential pairs with vias and right-angle bends are acceptable. In case you need to calculate single ended or differential pair impedance on your PCB, try following links: I use Microstrip & Stripline calculator developed by Jean Nicolle. . Broadband Impedance Matching with Transformer; Ferrite Toroidal Coil (Amidon) Helical Coil Calculator; Impedance Calculator : XL, XC; Iron Powder Toroidal Coil (Amidon)They has confirmed me, that the used formulas are very simple formulas. The amplitude of this crosstalk is what this tool calculates. To access the differential calculator, in the Primary Gap, Neck Gap, or +/- Tolerance cells, do the following steps: 4. 1 Answer. 0 and (t/h) less than 0. It uses the lan9512 reference schematic. Given the defaults (1. • Differential pairs should be routed away from all other traces. I need to route 100ohm differential pair without GNd I can't find any PCB calculator for parallel routing on one layer. is the impedance between two differential pair signal traces. There are some signal integrity issues with de-skewing in traces: Impedance. Tightly coupled pairs (within a pair) are quite common and this has the advantage of having a somewhat higher single ended impedance on a per track basis within a differential pair which is often easier to implement. Capacitance (C) = pF/ cm. The same applies to differential pairs. To be honest, I am no idea of the impedance on. Jan 31, 2016 #2 FvM Super Moderator. 3mm, as shown below: This increases the impedance slightly to 91. #PCB #KiCad #HowtoIn this video, we show you how to create a deferential pair in KiCad. To achieve this, you may have to put small sections of trace tuning into the shorter line to equalize them. Edge coupled differential pair Edge coupled internal symmetric differential pair Edge coupled internal. For better impedance control, use PCB design software you can trust. , the via is electrically short). Polar or rectangular grids only allow direct reading of S11. I use the software a lot to calculate impedance, maximum current for t. The distance between the differential pair should be decided as per the stack-up design. Single-ended signals are fairly straightforward. Si9000e – PCB insertion loss field solver. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. 08mm - this is the border of manufacturability, I don't think it is practical to go there but for the calculation it is just fun - and I get some 31Ohms. Impedance examples 4 layers 1. If R G = 402 W, we then need R T to be 114. As discussed in the first section of The MOSFET Differential Pair with Active Load, the magnitude of this amplifier’s gain is the MOSFET’s transconductance multiplied by the drain resistance: AV = gm ×RD A V = g m × R D. Unfortunately, stating “should match the input impedance of the differential vias/pads” in Point #3 is easier said than done. 4mils = 0. 6mm 4 layer PCB, 1oz outer copper, 0. Hence, without loss of generality, one. The controlled impedance method applies to any trace that handles high-speed or high-frequency signals. Differential Pairs 101. You can calculate it with the following equation: Z (z) = V (z)/I (z). Use 3. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. 05 that is free software and very. The Impedance Calculator is a tool which allows a quick pre-layout estimation of several kinds of line impedances between different layers. The designer needs to create a stackup for the board and then calculate the trace values for differential pairs and single-ended nets. As discussed previously, the lengths of the two lines in the pair must be the same length. (Differential Impedance, Ohms) = Note: 1oz = 1. 1 to 2. High-quality circuit boards as prototype and series at reasonable prices. Figure 6-1: Basic Differential Pair The most common application for a differential pair is the differential amplifier. To examine impedance variations, select the Impedance Workflow option in the analysis toolbar. Now let’s incorporate the finite output resistance: And next we recall that the small-signal analysis technique. Defining the Differential Pairs on the Schematic. You can make your own spread sheet using formulas provided by Wedell's book "Transmission Line Design Handbook" page 196, 197, 198 (attached)Relative dielectric constant (er) mm. But, you usually want some decent coupling between the traces, so a good single-ended impedance target for each trace is between. Differential pairs should be tightly coupled throughout their entire length, so try to avoid variations due to pads, vias, or components along the routing path. 6 ohms and Z even = 110 ohms for your geometry, very close to your result. According to this guidelines, the differential pair (DP and DM signals of the USB) must have 90 ohm impedance to each other. It is widely used for data communications and telecommunications applications in structured cabling systems. with the following layout parameters (width|space|width): Ohm. P/N De-skew Strategy on Differential Pairs. Adding stitching vias adds distributed capacitance in. For a printed circuit board (PCB) this is a pair of traces, also known as a differential pair. Controlled impedance traces are determined by their physical dimensions and the property of the dielectric material used in the circuit board. e. The process for impedance matching in high speed PCB designs depends on the signaling standard, supply voltage levels, and signal levels. This is a tool that has been designed to determine the characteristic impedance (Z 0) of a twisted-pair cable. If, in addition to a differential impedance (Z Diff), you also need a defined Z 0, proceed as follows:. Common-mode impedance occurs with the pair driven in parallel from a. I use the software a lot to calculate impedance, maximum current for t. By Perrine Juillion / April 8, 2020. Single ended. In addition to the characteristic impedance of a transmission line, the tool also calculates: This calculator is designed to calculate the characteristic impedance of an edge coupled stripline. When these traces are routed together in close proximityDifferential Pairs. Differential Pair Calculator The Differential Pair Calculator is used to perform what-if analysis to determine what values of Primary gap and width are needed to get specific differential and single line impedance. 225m s = 2mm. The auto-router will add a trace to match the longest trace as shown in Figure 5. 1. The track widths should. 2 Calculating Impedance The following equations can be used to calculate the differential impedance of the board. To use this calculator, simply input your microstrip geometry and Dk value, and the tool will return the differential impedance value for a pair of microstrip traces. The differential skew is adjusted with a tiny blip on one line towards the bottom of this image. Differential pair impedance depends on a lot of variables in reality,. I believe the 100-ohm differential equates to 50-ohm single ended because you can think of the two 100-ohm impedances as being in parallel resulting in an effective 50-ohm single-ended equivalence. About Saturn PCB Toolkit (latest v8. width|space|width. Therefore i tried using this paper to calculate a characteristic impedance of 60Ohm for a coplanar strip attaching the CAN-Transceiver to a Twisted Pair cable, the CAN bus medium. Z 0 = 100 W is common for twisted-pair cables. 8). Altium Designer makes it easy to calculate geometry when you need to calculate impedance for differential pairs. The trace width and spacing for a certain impedance may be obtained using impedance calculators. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. Differential Pairs 101. The most commonly used twisted pair cable impedance is 100 ohms. 2 High-Speed Signal Trace Lengths As with all high-speed signals, keep total trace length for signal pairs to a minimum. Using the KiCad Impedance Calculator. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. 1 - Do I have to use differential traces with controlled impedance? I didn't find a note about this in the datasheet, but is it necessary to use 100 ohm or 120 ohm differential traces? 2 - In case controlled impedance traces are needed, using a calculator I get that for a basic 4 layer stackup, the traces are about 0. Comparator tab . Although there are plenty of free impedance calculators out there, I'm struggling to find one that can solve impedances for a differential pair using coplanar waveguide. D+ and D-) _P/_N (e. When you use a line calculator with a proper 'diff pair' mode, it will take account of the geometry and the correct driving conditions, and provide you with a pair of lines that has 100 ohms differential impedance, and two lines of 50 ohms impedance when the other line is driven with an inverted signal. The amplitude increases as the coupling length increases up to a point. As you can see, calculating the twisted pair characteristic impedance by hand using Eq. Keeping the final. If trace width is increased for the metal losses reduction, the single end impedance will be reduces. Following is the list of useful converters and calculators. Select the Calculator button. This is the same reason we have to consider spacing between traces in differential pairs: the two conductors interact with each other to determine the odd-mode (and differential) impedance . Ohm. PCB Impedance and Capacitance Calculator: Asymmetric Stripline. These tools allow you to calculate a highly accurate impedance and propagation delay model for your differential pairs, and you can use these results to specify delay. 19mm) traces with 7. These differential amplifiers are optimized for DC signals and are typically characterized by high gain, high input impedance, and high common mode rejection ratio (CMRR). NOTE: The formulas used in the program are valid for 0. The ICD Stackup Planner calculates characteristic impedance plus edge coupled and broadside coupled differential impedance. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. To calculate this, you need some values. If we want to hit the standard 50 Ohms impedance target, then we need to have a trace width of almost 110 mils!Differential microstrip and stripline pairs have common-mode noise immunity if they are routed symmetrically, but they also need to have controlled differential impedance to ensure impedance matching and consistent propagation delay throughout an interconnect. g. 50 - 55 ohms). Question #1: How to determine the required spacing between length-matched signals or differential pairs and the adjacent layers? If you are length matching that implies that the interface is probably fast enough to require controlled impedance. I am trying to design a CAN bus node. This kind of functionality is present in only some PCB design programs, and those with it have varying degrees of accuracy in their output. The differential via design shown in Figure 2 was built and tested. 6mm thick. Incidentally, the trace thickness parameter does have a significant effect. If a different frequency is required, pick. Visit to learn more about our other electrical engineering tools and resources. This is more than the to times trace width which is recommended (also read as close as possibly). Vias (plated holes) are used to route electrical signals among different layers of a multilayer. They will give very similar answers. Thus, for optimal performance the resistors and MOSFETs must be matched. The ratio of cross-hatch conductor width (HW) to cross-hatch pitch (HP) plays an. We’ll go over how differential pairs can. This 8W rule also applies to ground planes on the same layer. 6 inches - this is very easy to do; If you can access a differential impedance calculator, then use differential. There’s an actual free 2D impedance calculator out there (arbitrary transmission line calculator, or ATLC). Anyone have suggestion of one? Thanks Alan . The best differential coplanar waveguide calculator can account for all of these effects simultaneously and without a complex 3D field solver. The required Impedance Profile is selected in the applicable Routing Width design rule (for individual nets), or Differential Pairs Routing design rule. The impedance calculator in the Allegro stack-up editor uses a static 2D field solver by default (bem2d). GEGCalculators. Zo (diff) is calculated to be 244 ohms, so dividing by two yields a value of 122 ohms for the semi-coplanar structure. Reaction score. $egingroup$ So basically your answer shows that the JLCPCB impedance calculator results are generally in the same ballpark as the proven field simulators. Differential Stripline Impedance Calculator. 0. It incorporates many features that PCB designers and engineers are in regular need of like current capacity of a PCB trace, via current, differential pairs and much more. Your relay is single line with characteristic impedance of 50 Ohms. g. This curve defines. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. In Altium Designer you can easily change the width of both of the differential pair tracks, but if you do so the gap of the diff pair changes depending on the change of the width. Email: info@multi-circuit-boards. Also, be aware, 90 ohms is the differential impedance, the characteristic or single ended impedance will be more than half (ie. Follow the 8W spacing for differential clocks (or explore other rules) Even greater spacing is needed for high-speed differential signals. Figure 1. This assumes ~0 trace thickness. Use an impedance calculator to determine the trace width (W) and spacing (S) required for the specific board stack-up being used. There are a lot of online trace impedance calculators specifically designed for differential traces. To set the rules for the classes we created above, we will follow these steps: Go to ‘Design’ >> ‘Rules. Adjust the distance "s". Differential and Common-Mode Impedance 2. This is a calculator used for determining the characteristic impedance of a microstrip. . e. The differential pair impedance depends on the characteristic impedance and the spacing between each end of the differential pair. 6), the impedance will be approximately 50 Ohms. The main takeaway for me: To get to around 80 ohms, I should not pull ground on the signal. In. You will want to control impedance with smaller variations in gap. RS485 uses differential signaling for the cable of 100Ω or 120Ω, the terminating resistance should match the cable. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. case of Figure 1, the mismatch occurs between the characteristic impedance of the twisted pair (typically 100Ω) and the 4 kΩinput resistance of the DS26LS32A. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. This is typically used when golfers play only a partial round or when a full 18-hole round isn’t completed. This definition effectively makes it equal. A web-based tool to calculate the impedance of your PCB traces and vias. If you control impedance, you place a tolerance in the fabrication notes. 0055” spacing. While it is not necessary or a requirement to match the PCB 'stubs' it's probably a good idea if the speeds of your RS485 bus are high (+50MHz). Note: The 6-Layer board temporarily only provides JLC3313 Stackup. g. Reference: R. This simple impedance calculator had a number of limitations, including requiring return paths to be implemented by plane layers, only supporting symmetrical stripline board structures, and no support for differential impedance calculations. It renders fairly accurate results suitable for use in circuit board manufacturing and engineering analysis. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). 2 of the Microstrip Calculator, h=H1 and b=H2-H1. Suggested Solution: for 100 Ohm Differential, use half the board thickness and make the tracks equal to the board thickness. It is important todetermine the characteristic impedance of a twisted-pair cable because this impedance should match the impedance. Anyone know of any free software that can do that? The only one I was able to find was Si9000 and Si8000m by Polar instruments, but they aren't free. Everywhere on this curve, the differential impedance of the pair is 100 Ohms. Differential impedance: 90 ohms (tolerance: +/- 15%) On a typical 1. Incidentally, analog signal integrity may be a bigger problem than digital in this design. PCB Structures / Discrete Structures / Signal Management. For double termination, we want the source to provide R S = 50 W on each side for 100-W differential output impedance, and we want the input of the FDA to present a 100-W dif-ferential load. So, the trace width and distance to adjacent reference plane is determined by the desired. A differential pair should have a significant mutual impedance, at least similar to or smaller than the impedance of each line to ground. Compatible with Flex PCBs and Turnkey PRO service. Formula: Applicability: w ÷ t ≤ 0. The impedance of a differential via pair cannot be treated with a single via impedance calculator unless the vias are spaced far apart. beammy. e. I did my research on what the differential impedance is and how should I approach it. User Interface. Differential pair routing. In case you need to calculate single ended or differential pair impedance on your PCB, try following links: I use Microstrip & Stripline calculator developed by Jean Nicolle. the odd mode inductance and capacitance per unit length. Disc Air Capacitor Calculator; Impedance Calculator : XL, XC; Inductors, Transformers. Differential impedance is twice the odd mode impedance. PCB Trace Impedance Calculator; Electromagnetic Compatibility Laboratory. The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. If your differential pair has 100 ohm (differential) characteristic impedance, you should just design the uncoupled parts of the lines to have 50 ohm (single-ended) characteristic impedance. The S50 Impedance. If R G = 402 W, we then need R T to be 114. There is only one method I am aware of that gives any level of accuracy for differential via impedance calculations, and it starts from a calculation of the propagation delay through a pair of differential vias. The concept of Shield Transfer Impedance (Zt), introduced by S. In the special situation for which there is no coupling to ground, Differential impedance equals the Characteristic. 5 and I took 3. 1. To use this calculator, simply input your microstrip geometry and Dk value, and the tool will return the differential impedance value for a pair of microstrip traces. i know that i can use. Speedstack Si – Insertion loss & impedance PCB stackup design including Si9000e. Also, I tried the differential tools in KiCad, and I matched both pairs to the same length (otherwise, one track is about 6 mm longer). The program used to calculate the impedances, assumes that, in manufacture, the. While the length and impedance are both important, 1mm of length differential will not affect your system's performance in any way, even for usb-2. Twisted pairs are used with balanced signals. The differential via design shown in Figure 2 was built and tested. pairs for aciving 85 Ohm diff. The grounded differential coplanar wave guide is the differential version of the grounded coplanar wave guide and is used in high-speed digital systems that require maximum noise immunity. 0 and CAN-FD might be slow enough to get away without it (and I'm honestly not sure, the performance will depend on the specific configuration), but if I were reviewing a layout with diff pairs without a ground reference I would be very unhappy with it. Just as important as determining an appropriate trace width for a single-ended trace is determination of an appropriate spacing between two traces in a differential pair. USB traces must be 90 Ohms differential. The Si8000m assumes negligible insertion loss in the transmission line; should you wish to model insertion loss the Si9000e adds. IPC 2141 Trace Impedance Calculator. a BJT differential pair that voltage is infinite. 006” spacing. The calculator is available in the Electrical Domain in Constraint Manager, from theTable 1-1. High-speed data on differential links must be de-skewed to achieve the maximum eye opening and avoid mode conversion. The trace impedance calculators that design tools often provide can be used to. The return path between two pairs also creates some loop inductance, which can receive crosstalk as differential mode noise. But practically (especially in a dense design like your example), they also interact with surrounding conductors, and the coplanar ground, or ground beneath a differential microstrip will affect the characteristic impedance. The default units for all given values, except the subtrate. Coaxial Line Impedance. This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). 6. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. A differential amplifier multiplies the voltage difference between two inputs (Vin+ - Vin-) by some constant factor Ad, the differential gain. Let’s move onto another example. In the case where you are routing differential pairs, then the potential between the two pairs will always be opposing (i. Parallel Wire Impedance, Inductance, Capacitance and Propagation Delay Calculator Results. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. The stackup on the left side of Figure 2. When designing the trace configuration for your differential pairs, you are typically targeting 100 ohms differential. 05): Take account, the internal used formulas sometimes don't equal on Conductor Impedance tab and on Differential pairs tab (e. Twisted pairs are used with balanced signals. Use 3. INPUT DATA. 34, 40, and 48 Ohms single. In this study, Keysight’s Path Wave Advanced System Designer, ADS, which has an integrated 2D field solver, was used for the analysis of a virtual prototype. These values are trace width, substrate heights, substrate dielectric, and trace thickness. Agilent's LineCalc tool calculates Z odd = 50. g. Atlas Si for Touchstone – PCB Insertion loss processing with Delta-L 4. Even mode impedance for commonly-driven transmission lines . too. Using a differential pair to avoid common mode noise is common in audio circuits. Using the KiCad Impedance Calculator. But in your differential pair, each line will have its own characteristic impedance, lower than 100 Ohms but higher than 50 Ohms (for instance a quick computing in Saturn PCB give me 77. Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method. But I'm unsure if the Height I entered is. Twisted Pair Impedance Calculator . 2Distance units: Substrate Height, H Trace Width, W Thickness, TFigure 1. It can't be used with differential pairs, which are dominantly used with impedance-controlled high-speed signals;. This calculator computes the characteristic impedance of a twisted-pair cable based on its dimensions. The microstrip is a very simple yet useful way to create a transmission line with a PCB. The reason for this is that the input impedance is what matters, and the input impedance at the via transition will look like the trace impedance (i. So move to your left, use Omni's Cable impedance calculator and enjoy. The targeted impedance for diff pair is 100 ohms, which is dependent on the width/space between conductors and hight to the reference plane. trace geometry, and use this to calculate. 004” line/0. 3mm of the microcontroller), therefore i rounded the width to 0. You can see. The differential impedance will be a bit less than 2x the single-ended impedance. The Differential Pair Impedance Calculator is a specialized tool used in electrical engineering and signal integrity analysis to determine the characteristic impedance of a differential pair of transmission lines. Try TNT or TxLine. Based on Zo Equation Per: IPC-D-317A:. The resultant current is called common-mode current. 3. To calculate the values, the designer needs to know the following information: Number of board layers• As shown in Figure 1, traces should be 100-Ω(±5%) differential impedance of differential microstrip or differential stripline. Differential Impedance ($$Z_{0_{diff}}$$): The impedance between the two lines with opposite polarity signals. When you click on the track, you can see the length of skew.