Track width of the Ethernet pairs is 0. 72 mil. The Saturn PCB software. 5 mm = 4. In many application notes how to make an Ethernet interface, the wiring. 22 mm; trace distance: 0. On a 1. Defining the Differential Pairs on the Schematic. GDCPW is known for its balanced configuration, which helps reduce common-mode noise and interference in. 1. pH nH uH mH H kH. If you can - Use a 0. Differential Microstrip Impedance Calculator (Using Zo) Embedded Microstrip Impedance Calculator. Differential pair PCB design basics, covering differential signalling benefits, references, impedance control, inter- and intra-pair matching, and terminatio. PCB Assembly Quotes. The designer needs to create a stackup for the board and then calculate the trace values for differential pairs and single-ended nets. The process for impedance matching in high speed PCB designs depends on the signaling standard, supply voltage levels, and signal levels. 3mm, as shown below: This increases the impedance slightly to 91. 3) to calculate trace width and. Note: Units do not matter for this calculation as long as they are consistent. 29 mm width traces to obtain 100 Ohms ZDiff while using 0. 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 default units for all given values, except the subtrate. Using the KiCad Impedance Calculator. 5 to 4. The typical impedance should be a 100 Ohm differential with a +/- 10% control. This routing width rule targets a class of DRAM nets. Broadside coupled non-shielded differential pair; PCB Padstack Calculator. 3 Answers. If you’re designing an RF PCB for. 2 inches)!! On a board with signals switching at these speeds, most routes will be transmission lines. Note: The results are only for approximation and rough estimation, the final values and the. It is only equal to double the characteristic impedance in certain cases. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. This becomes more. 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. To calculate geometry for 90OHMs Differential pairs routed on 2 layer PCB (Differential impedance of Microstrips) you need to know: width of the traces, space (gap) between the traces, height of dielectric above return plane, trace thickness and relative permittivity of the dielectric. Changed how the wire gauge calculator works, added max amps in air. Figure 5. The signal is 264MHz. 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. 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. . e. Rule setup for differential pair (100 ohms) routing using Altium Designer. 5; w, t, s, h > 0;Made in Europe. 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. The impedance calculator in the Layer Stack Manager supports single and differential coplanar structures. Re: Differential impedance calculation. The accuracy of a controlled impedance trace on a PCB is usually critical to the correct performance of the PCB. 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. frequency capabilities. The vias on these differential pairs have their own impedance, which can create signal integrity problems on long interconnects. 0 and (t/h) less than 0. This calculator determines the impedance of a symmetric differential stripline pair. NEW Methodical Method to Hardware & PCB Design - you can calculate single-ended impedance. Several Web sites such as the examples listed below contain additional reference information. > There are a lot of impedance calculators on the web but none seem to match each other. Microstrip Impedance Calculator. 22 mm; trace distance: 0. is the impedance between two differential pair signal traces. KiCad has a built-in impedance calculator!$egingroup$ To avoid crosstalk from neigbouring signals - including its own, you should apply the 3W rule of thumb - traces should be at least 3 times their width apart. The differential micro strip calculator requires some parameters. For example, when two traces with Z =50 W are well separated (uncoupled), the differential impedance between them should be precisely Z DIFF = 2. 5mm pitch has about 100 ohm differential impedance in the configuration where a differential data pair wires are between ground. So, the trace width and distance to adjacent reference plane is determined by the desired. A coplanar waveguide calculator will operate in one of two ways. PCB Trace Impedance Calculator. For context, as I understand it, the Ethernet pairs between the PHY and magnetics need to be impedance controlled to 100ohm and they need to be routed (ideally) in parallel, and the trace space and trace width are important variables in the impedance control. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. One of the features of this type of microstrip is the coupling between lines. NOTE: The formulas used in the program are valid for 0. Take account, the internal used formulas sometimes don't equal on Conductor Impedance tab and on Differential pairs tab (e. 4mils/35um of copper thickness. 6 mm;. They are very simple to read, and the values in. There are 3 types of single-ended models: single-ended non-coplanar, coplanar single-ended, and coplanar single-ended without ground. 5 and I took 3. The targeted impedance for diff pair is 100 ohms, which is dependent on the width/space between conductors and hight to the reference plane. 3mm of the microcontroller), therefore i rounded the width to 0. Differential pairs are very simple: they are composed of two traces, routed side-by-side, and that carry equal magnitude and opposite polarity signals on each trace. Both LM and CM converge to zero as spacing goes to infinity. Coax Impedance (Transmission Line) Calculator. Bog standard FR4, the type used as standard by PCB manufacturers is not really up to the task of Gen3 PCIe. If they aren't that high, then don't worry about matching on the PCB, but use. g. The image below tells a thousand words. differential impedance accurately In order to have maximum coupling of the magnetic field lines, the space between two conductors of a differential pair should be kept to a minimum. . 0: Conclusion. Note: The results are only for approximation and rough. 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. D+ and D-) _P/_N (e. PCB Trace Impedance Calculator. Development Kits. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. 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. Assuming both. Modeling approximation can be used to design the microstrip trace. different differential pairs must have at least 30 mils of separation between the pairs. Fabricators give trace impedance tables as guides to designers that need to implement controlled impedance in their PCBs. Finally, all calculators provide theoretical impedance values as they cannot take in to account the variables and. $egingroup$ Note that it is possible to get 'free' impedance test coupons (the PCB fabricator will charge you for them). , broadside coupled, embedded microstrips, symmetric or asymmetric stripline, or regular microstrips. 05 that is free software and very. 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. I tried to use the tool “PCB calculator” to determine the size of mi USB tracks. L R ≈ 50mm (2 inches). Differential Stripline Impedance Calculator. 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. Figure 81 shows the topology. Note: valid for (w/h) from 0. 1,481. With PCBWay impedance calculator, you can calculate the approximate impedance of your PCB / high frequency circuit board. Understanding coax can be helpful when working with it. Microstrip Impedance Calculator. 100 ohm differential pairs that are tightly coupled have a typical single ended impedance of around 65 ohms. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. PCB Impedance Calculation. This sets the single-ended impedance AND differential impedance to the target value, even if there is no. When enabled. To be precise, the current flows through the. The only unified PCB design package with an integrated trace length calculator and PCB trace length matching vs. The differential pair trace lengths should be matched with a tolerance of 20% of the signal rise/fall time. By understanding the microstrip transmission line, designers can. Speak to an Account Manager +1 (800) 763-7503. 2. Figure 5 shows the dimensions of a stripline and microstrip pair. However, PCBWay's calculator also reports a single-ended impedance along with the differential impedance. Ls =. With PCBWay impedance calculator, you can calculate the approximate impedance of your PCB / high frequency circuit board. 94 mil) is nominal thickness of 3313 prepreg. Unfortunately, stating “should match the input impedance of the differential vias/pads” in Point #3 is easier said than done. For a Dk = 4. The answer lies in the spacing between the traces in the pair. 5) and 1. The stackup on the left side of Figure 2. 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. It's true that generally the impedance value is determined by the following parameters; trace layer (microstrip or stripline), trace width, distance. 9. Atlas Si for TDR. 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. 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. 331 1 2 5. When you try to calculate track geometry (track width and spacing) for specific impedance on 2 layer PCB, usually you end up with very weird numbers - means you may give up on trying to use that width. Remember, the lower the impedance the greater the current drain, the higher the. microstrip Zo vs Edge Cpld Ext Zo). Follow the 8W spacing for differential clocks (or explore other rules) Even greater spacing is needed for high-speed differential signals. 5mm pitch. ; To. KiCad has a built-in impedance calculator!The two traces comprising a differential pair, when routed close together, share a certain amount of cross-coupling. Differential impedance: This is the impedance of a pair of transmission lines. The differential impedance will be a bit less than 2x the single-ended impedance. 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 theThe impedance of a differential via pair cannot be treated with a single via impedance calculator unless the vias are spaced far apart. I am planning to manufacture the PCB at PCBWAY so I decided to use their calculator but as you can see in the photo when using the minimum allowed spacing , the width of the traces is so large for usual USB traces. 006” spacing. Value of Zo calculated by impedance calculator is not relevant here. > A good starting point is to ask you board house give you the widths and spacing for your stackup. PCB Traces. L R ≈ 5mm (0. The visual result (in the design editor window) of the cumulative filter is determined by the highlighting methods enabled (Mask/Dim/Normal, Select, Zoom). That option operates on a single trace. THESE FORMULAS ARE APPROXIMATIONS! They should not be used when a high degree of accuracy is required. Now select the two nets that you want to declare differential. • A single differential pair should be routed as close together as possible. Calculates the outer and inner layer diameters of a padstack given the drill size. 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. 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. As discussed previously, the lengths of the two lines in the pair must be the same length. Differential impedance: 90 ohms (tolerance: +/- 15%) On a typical 1. Right-click and choose Change from the pop-up menu. Note: The 6-Layer board temporarily only provides JLC3313 Stackup. If T R = 100pS. PCB manufacturer generally verifies the impedances with impedance coupon (traces drown during design in a separate portion outside our. input values trace thickness: 1 oz/ft^2; substrate height: 1. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. common impedance: 19. except for W, the width of the signal trace. 0 which can operate from 12 megahertz to around 240 megahertz. 25mm trace. 2 Answers. 8 core of FR4 material, we would have a propagation delay of approximately 150 ps/inch, or approximately 6 inches/ns. The i. PCB manufacturer normally provides information about PCB stackup and track geometry. The differential impedance target, as well as the single-ended impedance of each trace, is maintained by keeping the spacing between the two traces constant. If trace width is increased for the metal losses reduction, the single end impedance will be reduces. 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. Differential pairs are commonly found in high-speed data communication systems, such as those used in computer interfaces (e. The resistance value chosen for the two resistors will be referred to as R D (for d rain resistance). . Sierra. 5) and 1. PCB Structures / Discrete Structures / Signal Management. 0 interface. See moreCalculate the impedance of PCB traces quickly and easilly using DigiKey's Trace Impedance Calculator. The design approach of controlled impedance routing is a key ingredient of high speed PCB design, in which effective methods and tools must be adopted to ensure the intended high speed performance for your PCBs. 1mm (3. 5 mil (2116 prepreg) or 8. Differential Pair Impedance Calculator. The standard specifies a two-wire differential bus; the characteristic line impedance is 120 Ohm. Click on Setup -> Constraints > Electrical Constraints Set - > Differential Pair Value - > Calculator > If you put 10 in the Line Width, the calculator calculates the single ended as well as differential impedance. 8 mm to 0. differences being that if you wish to change the track thickness and spacing as the differential pair changes layers in the PCB to control impedance then they should be defined as a Physical CSet. Yet I got a ZDiff CPW with ground capable calculator: Differential surface coplanar waveguide with ground calculations: *0. 5 mm). A pair of lines can be modeled as follows: Differential pair line. I am routing LVDS pair on a flex board. . ’ Give a name to this rule (100 ohms in this case) and double-click. 1. For FR4, the route length at which transmission line effects need to be considered can be calculated as: L R ≥ T R × 49. . This link also has a track maximum current calculator, crosstalk calculator and thermal via calculator. This is because communication flows both ways on the CAN bus. So move to your left, use Omni's Cable impedance calculator and enjoy. This is more than the to times trace width which is recommended (also read as close as possibly). For assistance, we provide our impedance calculator. With its fast, accurate, frequency-dependent transmission line modeling, the Si9000e is designed to model transmission line loss, impedance at given frequencies and extract full transmission line parameters over a wide range of popular PCB transmission lines (over 100 structures). 1 has six signal layers, but only has one pair of planes closely spaced. Remember, the lower the impedance the greater the current drain, the higher the. In the image below, I am comparing differential vias with merged. The PCB board also affects the circuit’s impedance. Dimensional units: mm mils. CSI-2 interface data pairs require a 100 ohm differential impedance. I am trying to design a USB circuit, where the signaling is over a differential pair D+ and D- and these two lines are required by the spec to have 90 ohms of differential impedance. Search Results for: pcb toolkit Saturn PCB Toolkit Help. Use several of them and compare. 48 mm FR4 thickness. I am routing differential pairs in Altium 20 and using controlled impedance profiles. 8mm PCB instead of 1. 1. png . Thus, for optimal performance the resistors and MOSFETs must be matched. For better impedance control, use PCB design software you can trust. Additionally, it only takes into account single-ended structures (not. This transmission line calculator. For complex impedance matching, the input impedance is important as this is the impedance seen by a. Fig 2b Equivalent termination (showing Rc open circuit) in even mode. So unless you carefully design your routes within your PCB, the impedance would be uncontrolled, and its value. Based on Zo Equation Per: IPC-D-317A:. Use stripline routing for better far end crosstalk performance and a tight impedance tolerance, and keep trace lengths shorter than the maximum allowed length limited by the full-channel IL and eye diagram simulation results. 03556mm. Formula: Applicability: w ÷ t ≤ 0. The Layer Stack Manager in Altium Designer includes an impedance calculator that accounts for copper roughness. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. Right-click and choose Change from the pop-up menu. , USB. MX6 Design recommendations about 100 Ohms for differential pair is quite reasonable for FlexCAN. A mistake was made when designing a set of mother and daughter PCBs, resulting the daughter board to have its LVDS pairs at ~100Ω differential impedance, while the motherboard ~90Ω. Terminate far end of the pair with 90 Ohms resistor (it is odd mode. Based on Zo Equation Per: IPC-D-317A:. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. e. L1=Ground, L2=signal/transmission lines, L3=signal, L4=Power. The calculation looks correct, but the tracks are too wide. And this leads to our third rule: The separation between the two traces (of the differential pair) must remain constant over the entire length. Technical Consultant Zach Peterson explores a viewer question surrounding Coplanar Routing, specifically how to route on a single-layer board. 4 ohms; differential impedance: 90. Use the same trace widths throughout the length of the trace. trace width: 0. Against the two rows select the. (Sorry guys, I live and I have grown up in a metric world ) With these values, Saturn PCB's off-line calculator gives 57 Ohm differential impedance. If you require a controlled impedance PCB, you should discuss. The differential impedance of a PCB is simply the current to voltage ratio on pairs of transmission lines driven in differential mode. NOTE: In order to understand the PCB Toolkit version differences, I have added this brief description of the version series. 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. 13 mm; substrate thickness 1. Here, we are using a USB 2. Board. When you need to do trace length matching in PCB design, your goal is to minimize timing differences between traces in a length-matching differential pair in a serial protocol, multiple traces. This calculator finds both odd and even transmission line impedance. Not too tricky. For example, with a thickness of 0. 6mm spacing with a trace width of 0. This delay results in timing errors, data skew, clock, and data mismatches, and causes reliability issues. Note the differential pairs above that look like a strand of intestine have a constant gap between the pairs. 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. PCB Coplanar Waveguide Calculator RF PCBs can be complex boards that need careful interconnect design and layout. How is Microstrip Impedance calculated?When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. Si TRC – Track Resistance Calculator calculates DC. This 8W rule also applies to ground planes on the same layer. 1 - 48 Layers 1WD Express 30 Years experience. On the top layer and I have 50 ohm impedance for single ended signals with a trace width 7. It shows the minimum trace-to-ground spacing required to. The total length of the signal path is about 1,330mils. Capacitance – the impedance calculator uses the Impedance value to calculate the capacitance per unit length. TheIt does not work. PCB Impedance-Calculation: Help with the dimensioning of the impedances of your circuit board. This is the odd-mode impedance of the differential pair. It has been correlated many times. It worked for a while, then it began destroying random devices, obviously because of other design errors. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. There are two design rules that are obeyed during length tuning, the Matched Length rule and the Length rule, both are in the High Speed category in the PCB Rules and Constraints Editor. The single-ended impedance of a trace in a differential pair will depend on the distance to the other trace, and applying a length-tuning structure is equivalent to changing the distance between the traces while meandering. This calculator finds both odd and even transmission line impedance. – Microstrip lines are either on the top or bottom layer of a PCB. Modeling approximation can be used to design the microstrip trace. There is a slightly different, but tightly coupled question here with this impedance calculator: "stripline differential impedance": Stripline here seems to be placed in some inside layer. 5 mil (0. Such a microstrip is constructed with two traces referenced to the same reference plane with a dielectric material between them. While the distance between the differential signals is lower (for impedance), area two show that the differential pair makes turns to make it longer while not keeping the same signal wire. 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. The formula used in this calculator is an approximation for the characteristic impedance of a coplanar waveguide: scssCopy code. 35mm prepreg, 8mil track width, 8mil spacing → 100Ω impedance. To optimize the PCB trace impedance and stackup, you must follow the key notes below: If thin dielectric layers with high dielectric constant (Dk) cannot be. H 2 H 2 = subtrate height 2. 1 ohms; In addition to those calculation I found some other resources with some sample trace properties: Mikrocontroller. High-speed data on differential links must be de-skewed to achieve the maximum eye opening and avoid mode conversion. 1<W/H<3. If you have a dense 16-layer board, and your note reads: “All signal layers: 0. Re: Calculating Differential Impedance for USB Differential Pair. 2. While, when it comes to flexible and. There are four different types of impedance used in characterizing differential trace impedances. The 5S rule states that the spacing between two lines in a differential pair should be a factor 5 larger than the width of each trace in the pair. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. Microstrip and Stripline Differential Pair DimensionsDifferential impedance values are normally specified for impedance matching of differential pairs, rather than odd mode impedance. For a differential pair, the available layers, the Preferred Width and the Preferred Gap are controlled by the selected profile. The auto-router will add a trace to match the longest trace as shown in Figure 5. Grounded Differential Coplanar Wave Guide. High speed PCBs and signaling standards almost entirely use differential pairs with precise impedance. The trace width (0. 0037” line/0. The surface finish is neglected. Differential pairs with vias and right-angle bends are acceptable. 25mm trace. One should note that some routing and computer architecture standards (i. The same applies to differential pairs. This coupling lowers the differential impedance between the traces. Now, let us see the routing of the differential pair. This is not usually a routing rule a designer might consider unless they are doing something very intentional with RF design, or they are routing differential pairs that require a specific impedance. 75 mm track on a 0. Complete the routing of a PCB design can be one of the most demanding PCB-related tasks. which is 0. Now to tuning the impedance of your diffpair’s PCB traces. You can use all the calculators you want if you don't know the exact board make up they're using; they should be able to help you. 24 mm. 5. Several common impedance standards are used in PCB design to optimize performance. 5mil (7628 prepreg) when tracks are inside. 1. The characteristic impedance Z 0, or the load impedance Z L, can be calculated with the value of ρ. 3. 6193. 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. 1. Supports Anritsu ShockLine™ MS46524B and VectorStar™ MS4647B. 0. 5 to 4. 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. Learn more about determining microstrip trace impedance; Learn more about determining symmetric stripline trace impedance; The fastest way to determine impedance is in PCB design software that. These parameters include:This is eight layer stackup. 004” line. Contents. This note describes some of the practical difficulties you'll sometimes run into when testing a controlled impedance PCB. When dealing with differential pairs, thi. Impedance calculators will help you to determine your line width and layer configurations while board layer stackup editors will help you to plug in the correct PCB materials and widths. It’s sufficient to minimize your diffpair coupling to unrelated copper. Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. The main takeaway for me: To get to around 80 ohms, I should not pull ground on the signal. 3mm of the microcontroller), therefore i rounded the width to 0. g. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. In PCB design software with a built-in impedance calculator function, you can calculate impedance quickly. g. Impedance Control. This is good for routing space, but not so good for power delivery if there is a need for interplane capacitance. Altium Designer makes it easy to calculate geometry when you need to calculate impedance for differential pairs. Characteristic. 30967mm) is slightly larger the size of the smallest pad (0. If you control impedance, you place a tolerance in the fabrication notes. W1: Width of the bottom surface of the trace. 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. 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. To get the correct parameters, we have to use the specifications from our PCB house and the provided calculator. e. I. 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. Note that the y-axis is on a logarithmic scale for clarity. When you calculate differential impedance you still need to have a ground reference. Is this a good practice for Ethernet? This is a capture of the PCB right now: This is the schematic that I am using. The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. 68 mils. L1=Ground, L2=signal/transmission lines, L3=Power, L4=signal or. The Differential microstrip impedance calculator is used to compute the differential (Zd) and single-ended impedance (Zo) of an edge-coupled microstrip line just by entering the width, separation and thickness of the trace along with the dielectric thickness and constant of the coupled line. The amplitude of this crosstalk is what this tool calculates. The trace width (0. Grounded Differential Coplanar Wave Guide. 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. These impedances depend in first approximation on the following PCB parameters. The screenshot is as shown in the picture q1-pro-pcb. Before we can start routing the PCB, we need to define Design Rules for our differential traces.