Differential pair into PCB calculator. 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. > A good starting point is to ask you board house give you the widths and spacing for your stackup. for example, with a layer-height of 0. If trace width is increased for the metal losses reduction, the single end impedance will be reduces. g. 19mm) traces with 7. A PCB impedance table will provide the trace width required to have a target impedance value on a standard stackup. 5mm pitch. 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. Coaxial Line Impedance. 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. 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. But it lacks the differential impedance (impedance between these two tracks). D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. It is okay to specify the single-ended impedance for each differential pair member. To answer, Zac. 0. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. 03) it gives me almost 160 Ohm - and even if use 53mil conductor height or. 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. 24 mm. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. 5 mm = 4. g. The sections below describe these steps in more detail. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. D+ and D-) _P/_N (e. It consists of a pair of center conductors separated by ground planes on the same substrate. The crosshatch should be at 45 deg (as shown in the diagram) The trace alignment over the hatch is important; it should be placed over the crosshatch intersections. 4mils/35um of copper thickness. ALTIUM DESIGNER. For sample: 45-46 Ohm single end traces impedance can be used in diff. Several common impedance standards are used in PCB design to optimize performance. Fabricators give trace impedance tables as guides to designers that need to implement controlled impedance in their PCBs. Saturn PCB - Toolkit for Impedance Calculation. The controlled impedance lines should be marked in the PCB schematic drawing. You can use the differential impedance Calculator to find the differential impedance. 01) and dielectric constant (3. Placing a Differential Pair directive on each pair net applies a parameter to the net,. It works in parallel with the standard. At the receiver, the signal is recovered by taking the difference between the signal levels on. ISO 11898 requires a cable with a nominal impedance of 120 Ω; therefore, you should use 120 Ω resistors for. 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. 2. trace geometry, and use this to calculate. The guides says spacing under 0. Here it is already defined in the schematic that this is D+ and D-. Note that these differential. 0. The differential impedance. I am routing differential pairs in Altium 20 and using controlled impedance profiles. A coplanar waveguide calculator will operate in one of two ways. Atlas Si for TDR. Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. Not too tricky. The nice part about coax is that it can be bent and flexible unlike most pcb transmission lines. It could result 5 Ohm resistance. 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. 9dB) • Minimize differential return loss (typical -12dB) • Minimize mode conversion –Intra-pair skew matching (50 ps of t RX HBR3)PCB trace length matching is exactly as its name suggests: you are matching the lengths of two or more PCB traces as they are routed across a board. 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. You need to set up certain rules. It worked for a while, then it began destroying random devices, obviously because of other design errors. PCB Structures / Discrete Structures / Signal Management. 3. The same applies to common mode impedance, except that. Yes, that's right. Once the option is active, click on the shortest trace and move the mouse. This is the impedance between the two signal traces of a pair. Assuming the differential pair I am routing is requiring 90 ohm (this is what the hardware guideline say "Route the USB differential pair on the top layer with a trace width and differential spacing tuned to the PCB stack-up for 90Ω differential impedance "). png . P/N De-skew Strategy on Differential Pairs. The same in true for bottom layer. Updated formulas for all of the differential pair impedance models. Calculates the differential pair impedance of a balanced line. 0 and (t/h) less than 0. Step 1 Calculate singled ended impedance for each: Use "impedance + trace space" from top drop down box: Set Z=50R, click single ened, gives a result of track. Z 0 Differential impedance (Ω): Calculate. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. There are four different types of impedance used in characterizing differential trace impedances. Configuring the Design Rules. 8065. 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. Z0,air Z 0, a i r = characteristic impedance of air. Learn how to configure, define, and use your design’s impedance requirements for single-sided and differential on each layer, with Altium Designer’s Layer St. Understanding coax can be helpful when working with it. Formula: Applicability: w ÷ t ≤ 0. A differential stripline pair refers to two traces located between two reference plane layers, which are routed as a differential pair. ETA: USB 2. 2. Differential Pair Impedance Calculator. These features become essential if you generally work on high-speed designs. 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. 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. 100 Ohm Differential Pair: 0. One of the features of this type of microstrip is the coupling between lines. PCB Impedance-Calculation: Help with the dimensioning of the impedances of your circuit board. trace width: 0. 25. As also noted in the picture, the subsequent calculations are on the: [2] top-layer single-end impedance; [3] top-layer differential impedance; [4] inner-layer differential impedance. For assistance, we provide our impedance calculator. 3. Follow the 8W spacing for differential clocks (or explore other rules) Even greater spacing is needed for high-speed differential signals. Some calculators will allow you to calculate trace impedance in a number of geometries, e. 1<W/H<3. They are very simple to read, and the. Select the Calculator button. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. Skin Depth Calculator. 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 tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. 5mil (7628 prepreg) when tracks are inside. Twisted pairs are used with balanced signals. This form of microstrip is composed of two traces. KiCad has a built-in impedance calculator!Signals on an FR4 PCB travel at approx half the speed of light, so you'd want to make your longest trace no more than 44 mm longer than the shortest trace. Although JLCPCB can produce boards with 2 oz external copper, the calculator only supports 1 oz because (1) the wider tolerance of 2 oz traces hinders impedance control, and (2) most signal traces only carries small currents. I am designing a flexible PCB to carry two types of differential signals. Differential pairs are commonly found in high-speed data communication systems, such as those used in computer interfaces (e. One rule of thumb for defining spacing between each trace in a differential pair is the “5S” rule, sometimes called the “5W” rule in application notes and other PCB design guidelines. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. Ls =. This becomes more. This is because communication flows both ways on the CAN bus. To achieve this, you may have to put small sections of trace tuning into the shorter line to equalize them. Use Saturn PCB's toolkit with the "Differential Pairs" tab. PCB Thickness is 1. For example, ECL logic has a 50 Ω characteristic impedance, and TTL has a source impedance range of 70 to 100 Ω. 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. or Differential Pairs Routing design rule. Re: Differential impedance calculation. Fig 2b Equivalent termination (showing Rc open circuit) in even mode. 10. The differential via design shown in Figure 2 was built and tested. 1. net Forum. I used the KiCAD PCB calculator, asked the PCB manufacturer about the tangent loss (0. Is this a good practice for Ethernet? This is a capture of the PCB right now: This is the schematic that I am using. PCB Coplanar Waveguide Calculator RF PCBs can be complex boards that need careful interconnect design and layout. I have one differential pair in the transmission line. 6 mm; resulting differential impedance: 100 Ohms; IBEX. In high-frequency systems using differential pairs, unbalanced currents, or ground currents, take the path with the least impedance. Thus, for optimal performance the resistors and MOSFETs must be matched. 1,481. 8mm PCB instead of 1. So unless you carefully design your routes within your PCB, the impedance would be uncontrolled, and its value. Given the defaults (1. . Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. In PCB design software with a built-in impedance calculator function, you can calculate impedance quickly. The characteristic impedance is generally defined to. The impedance calculator determines the signal properties and clearances (first image), use that clearance in the via shielding Distance setting. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. As the signals are also referenced to ground, each differential pair signal also has a single ended impedance. . Figure 1. I've seen from several. This interactive controlled impedance routing greatly simplifies the task of designing a controlled impedance PCB. Grounded Differential Coplanar Wave Guide. The distance between the differential pair should be decided as per the stack-up design. which is 0. 0 which can operate from 12 megahertz to around 240 megahertz. 5mm pitch has about 100 ohm differential impedance in the configuration where a differential data pair wires are between ground. This sets the single-ended impedance AND differential impedance to the target value, even if there is no. 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. Characteristic impedance or surge impedance is the impedance of a PCB transmission line without including the effect of other transmission lines. 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. There have been trace routing tools available for a long time that help with differential pair routing. You will need to know the thickness of the dielectric you will be using as well as the relative permittivity (dielectric constant). (to the next pair and to the ground plane. Such a stripline is constructed with two traces referenced to the same reference planes above and below the traces with a dielectric material between them. 4mils/35um of copper thickness. This calculator determines the impedance of a symmetric differential stripline pair. This transmission line calculator. eu. Note: The results are only for approximation and rough. To automatically select all traces that belong to a specific impedance profile, you can select Nets in the the PCB Panel and click the appropriate net class. Before we can start routing the PCB, we need to define Design Rules for our differential traces. You want to select “Microstrip Zdiff”. Single-ended signals are fairly straightforward. Earlier versions of the PCB editor included a simple impedance calculator, with limited support for unusual board structures. Calculates the outer and inner layer diameters of a padstack given the drill size. The calculator shows 90 ohms can be achieved using. L R ≈ 50mm (2 inches). too. W is calculated to achieve a trace impedance (Z0) of ~50W and S is calculated to achieve a differential trace impedance of 90W. 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. Dual Stripline Trace. Also, be aware, 90 ohms is the differential impedance, the characteristic or single ended impedance will be more than half (ie. With today’s modern PCBs,. The Layer Stack Manager in Altium Designer includes an impedance calculator that accounts for copper roughness. For differential signals on the top layer, I have 100 ohm impedance for trace width 5 mil and gap 5. Grounded Differential Coplanar Wave Guide. The High speed protocol that is being designed for determines what the single and differential trace Impedance the traces need to meet as well as the tolerance for the impedance (e. 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. The amplitude of this crosstalk is what this tool calculates. D_P and D_N) KiCad looks for these suffix pairs when using the differential pair routing tool during PCB layout. Build a model from experimental data of impedance vs. Now to tuning the impedance of your diffpair’s PCB traces. Differential pair length tuning. These are pure estimates to. 30967mm) is slightly larger the size of the smallest pad (0. Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method. Differential Impedance in Constraint Manager Advanced Constraints can be used to view the Differential Impedance in Constraint Manager. The differential pair is all about balance. 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. 34, 40, and 48 Ohms single-ended impedance are common, and each of these will have a specific corresponding differential pair impedance. D+ and D-) _P/_N (e. Dimensional units: mm mils. USB traces must be 90 Ohms differential. When designing high-speed boards, you need to worry about two things: length matching in parallel nets and differential pairs, and specified trace lengths to comply with specific routing standards. As an example, If I want to meet the 80Ω diff/ 40Ω single impedances, taking the first inner signal layer, and using the Saturn Edge Coupled asymmetric calculator, the input would be: H2= 180um H1= 176um w = 0. An impedance mismatch will. Altium Designer makes it easy to calculate geometry when you need to calculate impedance for differential pairs. of typical printed circuit board trace geometries. D+ and D-) _P/_N (e. , PCIe Gen 2 and Gen 3) also use a different value for differential pair. There are four different types of impedance used in characterizing differential trace impedances. 6mm 4 layer PCB, 1oz outer copper, 0. g. Coplanar Waveguide With Ground Characteristic Impedance Calculator. Trace width and spacing depend on your PCB stackup. Track width (w) = 137 micron. With PCBWay impedance calculator, you can calculate the approximate impedance of your PCB / high frequency circuit board. For example, a single 0. Stripline Trace. The surface finish is neglected. (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. 1mm (3. 6mm FR4 PCB with 7628 type stackup (4 layers), the above specifications usually result in 4. The answer lies in the spacing between the traces in the pair. ; Make sure D > 2S to minimize the crosstalk between the two differential pairs. Grounded Differential Coplanar Wave Guide. I don't know what do you mean with regular traces, as any regular trace on a ground plane is a microstrip. Above 3-5 GHzThe stackup design is very crucial for the manufacturing of a controlled impedance PCB. 006” spacing. Note: Use the following guidelines when using two differential pairs: D = Distance between two differential pair signals; W = Width of a trace in a differential pair; S = Distance between the trace in a differential pair; and H = Dielectric height above the group plane. Hi all, I would like to ask about the correct differential impedance calculation in the USB 2. There are a lot of online trace impedance calculators specifically designed for differential traces. Oct 29, 2021. Inductance – the impedance calculator uses the Impedance value to calculate the inductance per unit length. A differential stripline pair refers to two traces located between two reference plane. Either or both of these rules may be important in your design, it all. Note the differential pairs above that look like a strand of intestine have a constant gap between the pairs. The closer you place the pairs together, the differential impedance gets smaller because LM and CM get larger. g. . H1: Height of the dielectric between the trace and the reference plane. Right-click and choose Change from the pop-up menu. I would use a stackup like. THESE FORMULAS ARE APPROXIMATIONS! They should not be used when a high degree of accuracy is required. Single-Ended Impedance The trace impedance (single-ended) in an individual trace is normally calculated by ignoring any neighboring traces, so no coupling to other conductors in the design will be included. 4. Differential pair into PCB calculator. 4 Ethernet PHY PCB Design Layout Checklist SNLA387 – JUNE 2021 Submit Document FeedbackUnderstanding Coplanar Waveguide with Ground. Near 50 ohms, many of these approximations are within a few percent accurate. 5 mil (0. This controls the differential impedance. 1. We will assume here that both of the lines of the pair are identical and uniform. There are 3 types of single-ended models: single-ended non-coplanar, coplanar single. Search Results for: pcb toolkit Saturn PCB Toolkit Help. This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). • Differential pairs should be constructed as 100 ohm, controlled impedance pairs. Value of Zo calculated by impedance calculator is not relevant here. 1 to 2. Once you know the characteristic impedance, the differential. Also note that your best bet may actually be VERY SHORT (few mm) traces, a thinner board or a 4 layer board :-) Thanks for your suggestions. The idea here is to determine the spacing required for a given width with the goal of hitting a specific differential impedance value. Low-voltage differential signaling (LVDS) is codified in the TIA/EIA-644 standard and is a serial signaling protocol. H 2 H 2 = subtrate height 2. 0055” spacing. The following are typical line widths and spacings for the more common impedance values when using ½ OZ copper: 50 Ohm Single Ended: 0. The differential pairs should be loosely coupled. The characteristic impedance Z 0, or the load impedance Z L, can be calculated with the value of ρ. It is important to determine the characteristic impedance of a twisted-pair cable because this impedance should match the. The screenshot is as shown in the picture q1-pro-pcb. 6. Using the KiCad Impedance Calculator. Ready to give CircuitStudio a try? Click here to get started: and PCB Stacking The trace impedance is affected by many factors such as the width of the trace, th e thickness of the copper, the PCB material, the PCB stacking specification, and the spacing between the differential pairs. 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. Modeling approximation can be used to design the microstrip trace. Instant online PCB quote, get PCBs for only $2. Use the Series and Shunt Impedance Calculator: to try your own impedances; Change Grid: S11, (ZL normalized to source impedance Z0) Z_Load: Z_Load: Matching Network Calculator. Coplanar Waveguide Calculator. PCB Coplanar Waveguide Calculator RF PCBs can be complex boards that need careful interconnect design and. The termination resistors on a cable should match the nominal impedance of the cable. The trace impedance or PCB impedance damages the integrity of both analog and digital signals. You will need to know the thickness of the dielectric you will be using as well as the relative permittivity (dielectric constant). This routing width rule targets a class of DRAM nets. TheIt does not work. Calculates the characteristic impedance and per-unit-length parameters of typical printed circuit board trace geometries. 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. Differential Pair Impedance Calculator. The characteristic impedance (Z o) of coplanar waveguide with ground or microstrip lines with signal side ground plane can be. At that point the rest of the description is missing, which includes wire diameter, insulation thickness and dielectric constant, and the number of twists per inch or other unit of distance. 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. 81. The critical dimension that must also be taken into account is the distance between the signal pairs. – Microstrip lines are either on the top or bottom layer of a PCB. Any net defined with ending as ‘+‘ and ‘–‘ are considered as differential pairs. Step 1 Calculate singled ended impedance for each: Use "impedance + trace space" from top drop down box: Set Z=50R, click single ened, gives a result of track. 25mm trace. Preferably, the length of the clock trace should be somewhere in between. I am using microstrips on external layers only. For sample: 45-46 Ohm single end traces impedance can be used in diff. This is more than the to times trace width which is recommended (also read as close as possibly). This makes the problem of determining impedance much more complex, and building an initial lossless model requires a larger set of formulas. Added edge coupled embedded differential pair to calculator. Sample coupon — Gerber Data mpcd1345. 1. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. Right-click and choose Change from the pop-up menu. 127mm, or 127 μm for the calculator’s purposes. is the impedance between two differential pair signal traces. 6mm thick. One should always check carefully whether a calculator implements these equations under the appropriate approximations. But I am afraid that, even an continuous power plane will not provide a proper reference for those Eth differential pairs. Added ability to include Er effective to the wavelength calculator. A coplanar differential raises the diff impedance while lowering Zo with adjacent grounds so it needs a thinner height of dielectric. « Reply #7 on: April 21, 2023, 03:42:36 pm ». Giving the PCB house the data can take one of two forms. Tech Consultant Zach Peterson is talking Signal Integrity again today with a deep dive into Differential Impedance. Impedance. The maximum skew introduced by the cable between the differential signaling pair (i. The targeted impedance for diff pair is 100 ohms, which is dependent on the width/space between conductors and hight to the reference plane. If you read many PCB design guidelines, particularly on parallel protocols and differential pair routing, you’ll see many mentions of trace length matching. 5. The Saturn PCB software. 1. Edge coupled differential pair Edge coupled internal symmetric differential pair Edge coupled internal asymmetric differential pair Edge coupled embedded differential pair Broadside coupled shielded differential pair Broadside coupled non. In the image below, I am comparing differential vias with merged. In differential pairs, each trace in the pair carries the same magnitude, but opposite polarity. Differential pairs are becoming common place in high speed design reducing. The auto-router will add a trace to match the longest trace as shown in Figure 5. High speed PCBs and signaling standards almost entirely use differential pairs with precise impedance. $egingroup$ So basically your answer shows that the JLCPCB impedance calculator results are generally in the same ballpark as the proven field simulators. 15 mm spacing. 1. Calculates the characteristic impedance and per-unit-length parameters. Note that the y-axis is on a logarithmic scale for clarity. The trace width (0. 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. In the case where you are routing differential pairs, then the potential between the two pairs will always be opposing (i. KiCAD doesn't have a calculator for differential coplanar waveguide. Technical Consultant Zach Peterson explores a viewer question surrounding Coplanar Routing, specifically how to route on a single-layer board. This means that the channel dimensions of both FETs must be the same and that R 1 must equal R 2. For the signal trace of width W and thickness T, separated by distance H from a ground (or power) plane by a PCB dielectric with dielectric constant εr, the characteristic impedance isEdge-coupled coated differential microstrip Edge coupled differential microstrip for flex PCB. D+ and D-) _P/_N (e. Note: If this post answers your question, please click the Correct Answer button. Our impedance calculator features two main types of impedance models, single-ended and differential, within each trace structure. Using the KiCad Impedance Calculator. Layout basics for USB designs. g. 50 - 55 ohms). The coax is a good way to create a transmission line. 3. 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. See moreCalculate the impedance of PCB traces quickly and easilly using DigiKey's Trace Impedance Calculator. Since it is always important that the trace impedance remain constant over the entire length, this means that the coupling must remain constant over the entire length. D+ and D-) _P/_N (e. This calculator is designed to calculate the characteristic impedance of an edge coupled stripline. The vias on these differential pairs have their own impedance, which can create signal integrity problems on long interconnects. 2 inches)!! On a board with signals switching at these speeds, most routes will be transmission lines. Use the same trace widths throughout the length of the trace. Rule setup for differential pair (100 ohms) routing using Altium Designer. e. Ohm’s Law provides the framework for solving network analysis problems; when the curtain gets pulled back, Ohm’s Law updates to become the relationship between voltage, current, and impedance, not resistance. 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. PCB Repair Quotes. NEW Methodical Method to Hardware & PCB Design - you can calculate single-ended impedance. There are single end trace impedance and distance between traces in the pair. 4mils = 0. Note that the driver output impedance may be configurable among various values. 1. Vias (plated holes) are used to route electrical signals among different layers of a multilayer layer PCB. The pair in PCB is not twisted. 1. The DC resistance is determined by the trace's conductivity and the cross-sectional area. is the impedance between two differential pair signal traces. Polar UK: Si9000e PCB transmission line modeling. . Figure 5 shows the dimensions of a stripline and microstrip pair. In general, it is double the odd-mode impedance, which is the value we care about for differential signaling, as it is used in high-speed PCB design. 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. A pair of lines can be modeled as follows: Differential pair line. (Differential Impedance, Ohms) = Note: 1oz = 1. 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.