frequency capabilities. 22 mm; trace distance: 0. 0 which can operate from 12 megahertz to around 240 megahertz. Either the desired impedance at a specific frequency is used to determine the waveguide width, or the width is entered and the impedance is calculated. 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). beammy. The vias on these differential pairs have their own impedance, which can create signal integrity problems on long interconnects. Once the option is active, click on the shortest trace and move the mouse. For now. $egingroup$ Note that it is possible to get 'free' impedance test coupons (the PCB fabricator will charge you for them). 81. This will give a 50ohm impedance from each trace to ground. 3. Using the KiCad Impedance Calculator. 6mm pcb thickness ) with 8 mil trace width, 8 mil trace spacing , 1. Calculates the outer and inner layer diameters of a padstack given the drill size. For a differential pair, the available layers, the Preferred Width and the Preferred Gap are controlled by the selected profile. In order to maintain the impedance, I would like to use a power plane as reference beneath the signals, instead of the GND plane, as it provides better dimensions for routing (width and spacing) in the PCB toolkit calculator. > A good starting point is to ask you board house give you the widths and spacing for your stackup. . We can summarize that, theoretically, in differential pairs, there are two return paths: the adjacent trace (trace 2) running parallel to trace 1 and the ground plane. ) You need a ground plane right below the impedance-controlled pair. If you have placed Differential Pair directives on nets in the schematic, the default project options settings will result in the differential pairs members being created on the PCB. As explained in Part 1 of this series ( Circuit Cellar 367, February 2021 [3]), PCB manufacturers can propose different PCB stack-ups, and specifying a low thickness for the so-called “top prepreg” will help to reduce the trace width. Grounded Differential Coplanar Wave Guide. If T R = 100pS. 5. The crosstalk coupling calculation requires information for the driver source as well as the PCB physical characteristics. High speed PCBs and signaling standards almost entirely use differential pairs with precise impedance. Value of Zo calculated by impedance calculator is not relevant here. There are a lot of online trace impedance calculators specifically designed for differential traces. The edge couple differential symmetric stripline transmission line is a common technique for routing differential traces. 1kOhm, 1% tolerance: Brown Black Black Brown Brown. For example, when two traces with Z =50 W are well separated (uncoupled), the differential impedance between them should be precisely Z DIFF = 2. 2 inches)!! On a board with signals switching at these speeds, most routes will be transmission lines. 8). You must estimate the differential trace insertion loss in dB/inch for the trace loss budget based on the selected PCB materials and stackup. Placing a Differential Pair directive on each pair net applies a parameter to the net,. I use Microstrip & Stripline calculator developed by Jean Nicolle. It always defaults to 10mil. Impedance captures the real. 29 mm width traces to obtain 100 Ohms ZDiff while using 0. 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. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. NOTE: The formulas used in the program are valid for 0. Only one trace width or pair geometry can meet a particular target impedance per layer. g. The targeted impedance for diff pair is 100 ohms, which is dependent on the width/space between conductors and hight to the reference plane. By running a mating ref trace through the crosshatch you emulate a solid plane and can use a standard impedance. I understand how routing a matched impedance differential pair works but I've never encountered the need for a specific resistance value for the traces. There are 3 types of single-ended models: single-ended non-coplanar, coplanar single. The correction can be done with the menu option: Route → Tune Differential Pair Length Skew/Phase. Si TRC – Track Resistance Calculator calculates DC. High speed digital designers should. I used a calculator embedded in Saturn PCB and an online calculator on JLCPCB and PCBWay web side. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. High speed PCBs and signaling standards almost entirely use differential pairs with precise impedance. Going to route the following signals: 100R differential pair (Zo = 50R) 90R differential pair (Zo = 45R) Planning to use the stack up JLC7628, with a 4 layer PCB, in total 1. This note describes some of the practical difficulties you'll sometimes run into when testing a controlled impedance PCB. The edge couple differential microstrip transmission line is a common technique for routing differential traces. This calculator finds both odd and even transmission line impedance, including four different types of impedance used in characterizing differential trace impedances, for microwave antennas, couplers and filters applications. 1mils. Defining the Differential Pairs on the Schematic. trace width: 0. Any net defined with ending as ‘+‘ and ‘–‘ are considered as differential pairs. The characteristic impedance Z 0, or the load impedance Z L, can be calculated with the value of ρ. Based on Zo Equation Per: IPC-D-317A:. I would use a stackup like. . Zachariah Peterson | Created: November 22, 2021 | Updated: June 25, 2023 Table of Contents Differential Impedance Defined Formulas for Differential Impedance Should You Use Characteristic or. Twisted pairs are used with balanced signals. is the impedance between two differential pair signal traces. Figure 5. 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. Use an online differential stripline impedance calculator Calculating Differential vs. Coplanar waveguides are open quasi-TEM waveguide geometries that use copper pour and a ground plane to provide shielding along the length of. Using this calculator, I found 100 Ohms by giving 9 mils of track width, 5 mils of track separation, 8 mils of dielectric (prepregs usually have a dielectric constant of 3. Ideally you'd need 2 lines with Zo =45 Ohms. The Saturn PCB software. You will want to control impedance with smaller variations in gap. 3. Impedance Calculators. By controlling the PCB impedance, unexpected damages or errors can be limited to some extent. Unfortunately, TxLine doesn't do coplanar waveguide for differential traces. Ls =. And this leads to our third rule: The separation between the two traces (of the differential pair) must remain constant over the entire length. This will create the differential pair. (Differential Impedance, Ohms) = Note: 1oz = 1. 6mm spacing with a trace width of 0. 3 * 1. . To access the differential calculator, in the Primary Gap, Neck Gap, or +/- Tolerance cells, do the following steps: 4. 0175mm of Copper (1/2 oz), gives me a best estimate of 9mil trace, 4mil space for a 90R differential microstrip impedance. For example, ECL logic has a 50 Ω characteristic impedance, and TTL has a source impedance range of 70 to 100 Ω. Added edge coupled embedded differential pair to calculator. For FR4, the route length at which transmission line effects need to be considered can be calculated as: L R ≥ T R × 49. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. I am using Altium Designer and it has a nice impedance calculator which tells you the required track width for a desired impedance given the layer stack you have configured. Differential impedance: 90 ohms (tolerance: +/- 15%) On a typical 1. This is good for routing space, but not so good for power delivery if there is a need for interplane capacitance. 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. PCB Trace Impedance Calculator Calculates the characteristic impedance and per-unit-length parameters of typical printed circuit board trace geometries. Select a configuration: Microstrip Trace. different differential pairs must have at least 30 mils of separation between the pairs. 1. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. Differential pairs with vias and right-angle bends are acceptable. Calculates the differential pair impedance of a balanced line. 1 mm. 254mm. On an impedance controlled layer (for example, with 100 diff), find an unused area and run a differential pair and expose at each end to the surface with test pads. PCB Padstack Calculator. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. Spread the loveA Grounded Differential Coplanar Waveguide (GDCPW) is a transmission line structure used in RF and microwave circuits. 52mm fr-4, 1oz cooper) and a target of 90ohm differential impedance, i calculated a value of about. 9. 6 mm;. The amplitude of this crosstalk is what this tool calculates. PCB Impedance-Calculation: Help with the dimensioning of the impedances of your circuit board. net Forum. The screenshot is as shown in the picture q1-pro-pcb. 1. e. The trace separation is varied from 1. A coplanar waveguide calculator will operate in one of two ways. They will give very similar answers. You can define various routing constraints such as length matching for differential pair, controlled impedance, and crosstalk prevention. Differential Pair Impedance Calculator Calculates the differential pair impedance of a balanced line. D+ and D-) _P/_N (e. D+ and D-) _P/_N (e. 0 differential insertion loss test to 43. However, PCBWay's calculator also reports a single-ended impedance along with the differential impedance. These are precisely the characteristics of a pair of lines to be designated as a differential pair. Calculates the outer and inner layer diameters of a padstack given the drill size. 006” space to be 100 Ohms differential” please make sure that the specified geometry is present on ALL the signal layers. Our impedance calculator features two main types of impedance models, single-ended and differential, within each trace structure. This microstrip impedance calculator gives you a good start for estimating the trace width and PCB dielectric thickness that will produce a target impedance value. Differential pairs are becoming common place in high speed design reducing. Given the defaults (1. 3. 6mm FR4 PCB with 7628 type stackup (4 layers), the above specifications usually result in 4. 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. Tech Consultant Zach Peterson di. It was very hard to achieve a differential impedance of 100R with such a thin dielectric, so it was suggested that I used a hatched ground. 3. 3mm, as shown below: This increases the impedance slightly to 91. It uses the lan9512 reference schematic. 8. The USB interface is a differential signal, so it requires a medium with defined differential impedance, to prevent signal reflections at discontinuities. NOTE: The formulas used in the program are valid for 0. Hi all, I would like to ask about the correct differential impedance calculation in the USB 2. I have one differential pair in the transmission line. 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. High-speed PCB design goals • Tight impedance control (eg 100Ω ±5%) • Minimize impedance mis-match (eg 100Ω ±10%) • Minimize use of via and via stub • Minimize insertion loss (typical -1. The geometry of the traces, the permittivity of the PCB material and the layers. Use several of them and compare. This sheet has the FTDI chip which converts the input serial signal into a USB differential signal. When routing differential signals across common PCB materials, each trace of the pair will experience different dielectric constants and corresponding signal velocities due to the differences in static permittivity (Ɛr) of the There are single end trace impedance and distance between traces in the pair. , D+ and D- (TSKEW)) must be less than 100 ps and is measured as described in. Using the KiCad Impedance Calculator. L R ≈ 50mm (2 inches). PCB Stackup Impedance Calculator Calculates the characteristic impedance per unit length parameters of typical Some of the common Dielectrics & their values: Relative. If you have copper fill on other layers, you can tie them to. In PCB design software with a built-in impedance calculator function, you can calculate impedance quickly. Preferably, the length of the clock trace should be somewhere in between. The impedance of a differential pair depends on the self capacitance and self inductance of each trace, and the mutual capacitance and mutual inductance between each trace. Fabricators give trace impedance tables as guides to designers that need to implement controlled impedance in their PCBs. The same figures put into pcbway's calculator give me 115R, and the same. 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. I checked out TNT, but couldn't seem to be able to do the same with that either. The following are typical line widths and spacings for the more common impedance values when using ½ OZ copper: 50 Ohm Single Ended: 0. And that they have the same separation from each other along the entire length of the line. If trace width is increased for the metal losses reduction, the single end impedance will be reduces. This calculator finds both odd and even transmission line impedance. 6 mm board that I want to create a 90 Ohm profile on. g. Most high speed signal protocols, such as PCIe or Ethernet, use differential pair routing, so you need to design to a specific differential impedance by calculating trace width and spacing. H 2 H 2 = subtrate height 2. The signal is 264MHz. 1. In tab “TransLine” i chose “Coupled Microstrip Line” and i can calculate the impedance of only one track. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. The two points at the beginning of the pair might be weakly coupled, but adding or removing some copper at the source end allows you to match pair lengths while ensuring common. Instant online PCB quote, get PCBs for only $2. ’ Give a name to this rule (100 ohms in this case) and double-click. Now to tuning the impedance of your diffpair’s PCB traces. 0 interface. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. Microstrip construction consists of a differential pair and a single reference layer (typically ground). Cross-section geometry of a stripline trace. 2 PCB Stack-Up and Board Layout. This rule maintains the desired signal impedance. If trace width is increased for the metal losses reduction, the single end impedance will be reduces. Here, we have set the differential tracks and spacing as 8 mils. 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. 035 mm. The test sample consists of a pair of differential traces at the top layer, followed by a differential via to the inner traces, then a second differential via connects to the BGA landing pads at the top layer again. It seems I could largely do without any impedance matching considerations, given what the trace lengths are. The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. This video will cover how to create, setup rules, and route differential pairs. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. Remember, the lower the impedance the greater the current drain, the higher the. The IPC Formulas and Wadell’s Method. Try TNT or TxLine. As most designers know, the impedance control in FR4 PCBs and PTFE PCBs are easy since the surface are almost absolutely flat, and there are many impedance calculating tools for choice. The via transitions start to really matter above 5 GHz. Select the Calculator button. Impedance Calculators. The sections below describe these steps in more detail. When you have a USB you need to create differential pairs and KiCad ma. This calculator finds both odd and even transmission line impedance. The stackup on the left side of Figure 2. PCB Impedance and Capacitance Calculator: Asymmetric Differential Stripline. A PCB's trace impedance depends on its geometry, core and prepreg material, and layers. From here, we can see that there are specific stack-ups where a CPW and a microstrip/stripline will have 50 Ohm impedance and the same trace width, even though the ground clearance is quite close clearance to the trace in the CPW. Ethernet cables can be unshielded so obviously just two wires without a ground plane can work. If the goal is to adjust the characteristic impedance, then you can likely do it by changing both width and spacing (keeping center-to-center the same) just as well as by changing the width without changing the spacing. 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. 5 mil as the thickness of 3313 prepreg when the controlled impedance tracks are on top/bottom, use 5. The i. You need to set up certain rules. The idea here is to determine the spacing required for a given width with the goal of hitting a specific differential impedance value. But I'm unsure if the Height I entered is. Yes, that's right. The other yellow rectangle is the USB connector. PCB Coplanar Waveguide Calculator RF PCBs can be complex boards that need careful interconnect design and layout. 4 ohms; differential impedance: 90. 0. At the receiver, the signal is recovered by taking the difference between the signal levels on. 6mm thick, 1. 1. Coaxial Line Impedance. One should note that some routing and computer architecture standards (i. Follow the general stripline pair-to-pair spacing rule of 5H for TX-to-TX and RX-to-RX. Differential Pair Routing. RS485 uses differential signaling for the cable of 100Ω or 120Ω, the terminating resistance should match the cable. Z0,air Z 0, a i r = characteristic impedance of air. While you can get away with small impedance mismatches, some signal drivers will have an impedance that does not match the standard 50 Ohm value typically used with signal traces. Note: The results are only for approximation and rough. This calculator is designed to calculate the characteristic impedance of an edge-coupled microstrip. The main takeaway for me: To get to around 80 ohms, I should not pull ground on the signal. 5. The velocity factor is simply: 1 / sqrt (e_r*mu_r). 0055” spacing. AC coupling capacitors can be positioned anywhere throughout the differential pair’s length. Otherwise, keep shopping. To set the rules for the classes we created above, we will follow these steps: Go to ‘Design’ >> ‘Rules. While every trace has an impedance, we don't care about the trace reactance if the trace is only carrying DC current. 004” line. With today’s modern PCBs,. 0: Conclusion. Whenever there is an imbalance in a differential system, the fields no longer completely cancel and radiate in proportion. they normally use 7. Supports Anritsu ShockLine™ MS46524B and VectorStar™ MS4647B. The source for formulas used in this calculator (except where otherwise noted) is the Design Guide for Electronic Packaging Utilizing High-Speed Techniques (4th Working Draft, IPC-2251, February 2001. 4. Above 3-5 GHzThe stackup design is very crucial for the manufacturing of a controlled impedance PCB. The calculator shows 90 ohms can be achieved using. MX6 Design recommendations about 100 Ohms for differential pair is quite reasonable for FlexCAN. In case your board only routes differential pairs between two connectors, you may not even have ground connected via cable shield to connector metal frame. 2. The critical dimension that must also be taken into account is the distance between the signal pairs. Other calculators are like a black box; you have no idea which formulas they are using and no way to check the accuracy of these calculations. 1<S/H<3. There are four different types of impedance used in characterizing differential trace impedances. 6 mm. 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. trace geometry, and use this to calculate. The formula used in this calculator is an approximation for the characteristic impedance of a coplanar waveguide: scssCopy code. ISO 11898 requires a cable with a nominal impedance of 120 Ω; therefore, you should use 120 Ω resistors for. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. 6mm, that will make it easier to approximate the 90 Impedance - Use as thick traces as possible, and be aware that if you let the ground pour on the top layer get too close, it will also alter the impedance. 22 mm; trace distance: 0. For differential pairs, there is also a spacing value given. Polar or rectangular grids only allow direct reading of S11. PCB Impedance and Capacitance Calculator: Asymmetric Stripline. Best-in-Class PCB Fabrication, Assembly, & Components. Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method. With PCBWay impedance calculator, you can calculate the approximate impedance of your PCB / high frequency circuit board. Re: Calculating Differential Impedance for USB Differential Pair. PCB Traces. Added ability to include Er effective to the wavelength calculator. This makes the problem of determining impedance much more complex, and building an initial lossless model requires a larger set of formulas. 6 mm PCB; 1. 6 mm is used) can anybody help me how to calculate 100 ohm impedance. Altium Designer makes it easy to calculate geometry when you need to calculate impedance for differential pairs. As logic circuits developed, the need for faster interconnects increased, making impedance levels increasingly important. Probably the most common electrical uses for LVDS are as an physical layer for SerDes links, long-reach channels in backplanes, or board-to-board connections. One of the features of this type of microstrip is the coupling between lines. Assuming both. Also, be aware, 90 ohms is the differential impedance, the characteristic or single ended impedance will be more than half (ie. 1 ohms; In addition to those calculation I found some other resources with some sample trace properties: Mikrocontroller. Industry Leading PCB Designer's Tools. 1. But I am not able to match this impedance. The differential impedance. 1 to 2. Differential pairs are defined on the schematic by placing a Differential Pair directive (Place » Directive) on each of the nets in the pair. Sierra. Terminate far end of the pair with 90 Ohms resistor (it is odd mode. It is important to determine the characteristic impedance of a twisted-pair cable because this impedance should match the. Eq. In the PCB panel, as you click on an entry in a list, a filter will be applied based on that entry. Allegro offers several advanced routing features that help you build complex PCB designs. This is the impedance between the two signal traces of a pair. Have you noticed a marked difference between the results given by PCB impedance calculators? It turns out, you're not wrong. 00:11:15 | 18 SEP 2019. 120 Ohm Differential Pair: 0. They are very simple to read, and the. The S50 Impedance Profile is defining the routing widths, which will change according. PCB Impedance Calculation. 90 Ohm Differential Pair: 0. P/N De-skew Strategy on Differential Pairs. The tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. The microstrip is a very simple yet useful way to create a transmission line with a PCB. On the top layer and I have 50 ohm impedance for single ended signals with a trace width 7. While commonly constructed using. 5mil (7628 prepreg) when tracks are inside. 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. Your PCB software should make it easy to work with high-speed design rules and constraints within a single interface. This form of microstrip is composed of two traces. Flexible PCB Quotes. 0. g. Several common impedance standards are used in PCB design to optimize performance. The same applies to differential pairs. USB traces must be 90 Ohms differential. High-speed data on differential links must be de-skewed to achieve the maximum eye opening and avoid mode conversion. 331 1 2 5. Impedance; Signal Loss; S Parameter; Crosstalk; Geometry Information . Skin Depth Calculator. On a reference plane, there is an edge coupled differential microstrip line with two traces. The Layer Stack Manager in Altium Designer includes an impedance calculator that accounts for copper roughness. This sets the single-ended impedance AND differential impedance to the target value, even if there is no. g. g. 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 DC resistance is determined by the trace's conductivity and the cross-sectional area. High-speed designs carry a requirement for controlled impedance, crosstalk control, and the need for interplane capacitance. To calculate the impedance, I use Saturn PCB impedance calculator software, Inc - PCB Toolkit V8. Not too tricky. BGA land calculator based on the IPC-7351A specification. I am routing LVDS pair on a flex board. • As shown in Figure 1, traces should be 100-Ω(±5%) differential impedance of differential microstrip or differential stripline. Insertion Loss. 4 mil trace thickness. for example, with a layer-height of 0. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. The differential via design shown in Figure 2 was built and tested. Using the wrong impedance will cause the signal to be reflected inside the track. CAN bus layout design. Development Kits. The process for impedance matching in high speed PCB designs depends on the signaling standard, supply voltage levels, and signal levels. KiCad has a built-in impedance calculator! For differential pairs of microstrips, the formulas involved are much more complicated because coupling between the traces in the differential pair must be included in the impedance calculation. BGA land calculator based on the IPC. We will assume here that both of the lines of the pair are identical and uniform. microstrip Zo vs Edge Cpld Ext Zo). You want to select “Microstrip Zdiff”. 100 ohm differential pairs that are tightly coupled have a typical single ended impedance of around 65 ohms. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. I tried to calculate differential impedance in three independent calculators and calculate manually from the formula. See moreCalculate the impedance of PCB traces quickly and easilly using DigiKey's Trace Impedance Calculator. So if layer 1 and layer 3 are ground planes and you place an RF signal track on layer 2 it will need to be x mm wide for 50. , the via is electrically short). Using the KiCad Impedance Calculator. Create a new impedance profile, then select Single. In a previous article, we have seen how to route a differential pair signal. Uncoated Microstrip Differential Pair Impedance Calculator . If we want to hit the standard 50 Ohms impedance target, then we need to have a trace width of almost 110 mils! Choose a calculator to tune your PCB design. Using the built-in Simbeor ® impedance calculator, the PCB editor's Layer Stack Manager calculates the trace width needed to deliver the specified impedance. Capacitance – the impedance calculator uses the Impedance value to calculate the capacitance per unit length. This will leave the rest of the signals which are rather non-critical like I2C, power good signals, etc. LVDS PCB layout guidelines aim to ensure optimal signal integrity and minimize noise interference by considering factors like impedance control, differential pair routing, grounding, etc. I used Saturn PCB design to calculate width and spacing between conductors. Differential Pair Impedance Calculator Calculates the differential pair impedance of a balanced line. 8mm PCB instead of 1. 3) to calculate trace width and. I am trying to design a CAN bus node. Color-Code. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. > There are a lot of impedance calculators on the web but none seem to match each other. ZL =. In “Eaglelake platform design guide”, Intel recommends 95Ω±15 % differentialThe Si8000m adds enhanced modelling to predict the finished impedance of multiple dielectric PCB builds and also takes into account the local variations in dielectric constant on close spaced differential structures. Added edge. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. 8). Single-ended and differential pair routing guidelines impedance will have defined geometry to ensure impedance goals are met. Modeling approximation can be used to understand the impedance of. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. If the track thickness and gap remain the same throughout the cross section of the PCB then it is recommended that the differential pair beI'm unsure if the reference plane would be the GND and the PWR layers.