0mm (4L-02) When using our free Defined layer buildup 4L-02, you will reach the desired impedances e. Characteristic. Continuing on. characteristic impedance of the differential mode is Zd, common mode is Zc. You want to select “Microstrip Zdiff”. It is admittedly small, but it is non-zero. Using this calculator, I found 100 Ohms by giving 9 mils of track width, 5 mils of track separation, 8 mils of dielectric. Differential impedance is the ratio of voltage to current on a pair of transmission lines when driven in the differential. Use the following guidelines. Differential Trace Impedance . Both LM and CM converge to zero as spacing goes to infinity. You will need to know the thickness of the dielectric you will be using as well as the relative permittivity (dielectric constant). Dual Stripline Trace. 96D/H). 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. • Intra-pair trace should be matched to within 5-mils. Field solvers. W is calculated to achieve a trace impedance (Z0) of ~50W and S is calculated to achieve a differential trace impedance of 90W. If you do something else with the. • Trace width of any un-coupled section of a differential trace greater than 100-mils, should be increased to maintain target impedanceLength-tuning structures and their effects on impedance. The width of each track should be as per the requirements. Backwards crosstalk creates a pulse width that is twice that of the propagation time of the pulse traveling the coupling distance. Try TNT or TxLine. 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. Explore our high-quality products. Use the following guidelines. Microstrip Trace Impedance Calculator; Stripline Trace Impedance Calculator; Differential Trace Microstrip Impedance Calculator; Differential Trace Stripline Impedance Calculator; The. The guides says spacing under 0. 5 mil as the thickness of 3313 prepreg when the controlled impedance tracks are on top/bottom, use 5. 6) ; TanD = 0. Using 0. 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. The tool also calculates signal losses of any given trace. Note 1: The impedance tolerance after manufacturing may be around +/-20% on outer layers and +/-10% on inner layers. 03) it gives me almost 160 Ohm - and even if use 53mil conductor height or. Just as important as determining an appropriate trace width for a single-ended trace is. Click on Setup -> Constraints > Electrical Constraints Set - > Differential Pair Value - > Calculator >. Try it now for free. 15 mm. The equations in the MeasEqn block shown in Figure 14 are used to calculate the power delivered to the 50 Ω load on the balun output. Commonly, you calculate. When a single trace is considered in isolation, its impedance will have a well-defined value. This will also provide the time delay the cable provides for a signal and also the capacitance and inductance per. "Saturn PCB Toolkit" is also good for this. All the best. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. Best Regards, David LambeUnderstanding Coplanar Waveguide with Ground. Getting the Most Accurate Impedance Calculations. 6. What we have on these differential traces is a taper section, which RF engineers often use to match impedances. Copper. The KiCadPCB calculator is apparently assuming a rectangular trace profile which isn’t quite realistic, particularly with minimal trace clearance values. Differential Trace Routing. KB: Fail to use evaluation license with a dialog "You can use this license only on a single PC". Click here to see the user guide of our impedance calculator. This calculator is designed to find the characteristic impedance of an asymmetric stripline - a flat conductor between two ground planes. Tuning for your traces to the desired impedance value occurs by adjusting trace width and distance from the reference plane. Using a power plane as signal reference. 0. There are four different types of impedance used in characterizing differential trace impedances. Example, If Z 0 = 55 Ω, d = 6 mils. 4mm. I found that a W of 0. 2mm from the ground plane below. Wavelength/10 is the max trace length before you need to worry about impedance control So if you keep your traces under 15mm in length, then it doesn't matter. Differential Trace Routing. (unloaded trace impedance, Ohms) = Tpd (unloaded propagation delay, ps/unit len) =. Make sure that the matching or the pair lengths is maintained. 25mm trace. I've used 7 mil trace width with 5 mil spacing, top and bottom layers (35um copper) are 0. Embedded Microstrip. How do cheap Raspberry CSI-2 cables get around differential impedance matching. 16 mm. Target impedance and tolerance analysis for a particular trace . While this calculator will provide a baseline, any final design considerations should be made towards loss, dispersion. While every trace has an impedance, we don't care about the trace reactance if the trace is only carrying DC current. The total length of the signal path is about 1,330mils. In other words, if you are designing to hit a differential impedance target. Using an online calculator [4], a microstrip trace of 1oz, 120mil-wide copper on 0. Impedance changes significantly with a top ground plane. 35mm gives 50Ω, far easier to use. The amplitude increases as the coupling length increases up to a point. Trace Height (H) Figure 4. KB: Route traces between flex and rigid regions. 1 Effective Permittivity and Characteristic Impedance of CPW. 3 shall be used. 96D/H) Zo. The stripline impedance calculator provided below is useful for gaining an initial estimate of trace impedance for striplines. differential trace impedance for USB (90 Ohms) on 2-layer FR4 board. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). Speedstack Si – Insertion loss & impedance PCB stackup design including Si9000e. 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. Create a differential trace with KiCad - Schematic. Stripline Impedance. Before the length-tuning section, the odd-mode impedance of the traces in each pair is 50 Ohms, so the differential impedance of each pair is 100. 35mm gives 50Ω, far easier to use. It is admittedly small, but it is non-zero. To obtain a particular value of differential impedance, the two signal tracks are usually assumed to have the same cross-section — the balanced track case, used in most impedance calculation software. Expect a large variation of manufactured PCB impedance with 0. Finally, calculate the differential impedance (Zdiff) using the formula Zdiff = Z0 / √(1 – (W / (2 * H))^2). To the extent that the differential impedance is less than 100 Ohms, it is due to mutual coupling. Geometric Parameter Definitions: 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. Notes: 1) Calculation assumes traces are centered vertically. Is there any reason not to use these values? If you can fit a design with larger gaps and wider traces, then the differential impedance will be less sensitive to over-etching or under-etching during pcb fabrication. How to calculate differential impedance: Notes. For example, if you design a pwb with two traces, each one of which has a single ended impedance of 50 ohms, then the differential impedance of those two traces ends by being approximately 90 ohms. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. When selecting trace geometry, priority should be given to matching the differential impedance over the single ended impedance. This calculator finds both odd and even transmission line impedance. Then. Differential Impedance is the impedance between two differential pair signal traces. 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. The differential impedance of MIPI tracks should be 100 Ohms, not 90 (USB requires 90). I've used 7 mil trace width with 5 mil spacing, top and bottom layers (35um copper) are 0. Every trace has series inductance. Different board materials, the dielectric layer thicknesses and constant (Dk), and the thickness of the metal traces all need to be part of the calculations. Includes information on how trace width is calculated. Calculate the effective dielectric constant. In both cases, you’ll need to enter your stackup information into the calculator to get accurate results. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. The board contains two inner layers of GND and a ground plane around the RF track: To decide the thickness of the RF track, I used an online calculator:. Using typical values of W= 9 mil, H= 24 mil, T = 1. Go to this 100-ohm class and select the nets which are there in this. As seen from the formula when D decreases, while keeping B. 100 Ohm diferential impedance microstrip PCB traces geometries in. calculate the resulting differential impedance, and check that it matches the selected media (cable) differential mode characteristic impedance. Another example of using large distances to separate out unwanted components might be to calculate the impedance of a. There are a number of pcb transmission line typologies. This permits higher differential trace impedance and wider, lower loss traces. EEWeb offers a free online twisted pair impedance (transmission line) calculator. Differential Stripline Impedance Calculator. 2. trace width and thickness, distance from other copper features, dielectric constant, and dielectric thickness or distance to reference plane of the board material all contribute to the impedance of a. Atlas Si for VNA – Insertion loss test system – Delta-L 4. At some point the amplitude will stay constant. Notes: 1) Calculation assumes traces are centered vertically. 2) S/T > 5. 1 to 2. pairs for aciving 85 Ohm diff. Ohm. Single ended. The stub length must. I wanted to use Altium to calculate the width of the trace automatically, so that it had a 50 Ohm impedance. To use this tool, enter the values for. The ground plane helps. Input the known values, and let the calculator determine the unknown. Finally, use the equation below to convert the differential measurement to a single-ended result. 77 mm gave me a differential impedance very close to 90 Ω. Here is an online PCB Differential Impedance Calculator to calculate the differential impedance of Printed Circuit Board. Stripline Trace. eu. When the two lines are far apart (say, more than 3 or 4 trace widths), then the lines are weakly coupled and the individual line impedance is about 1/2 the pair. In principle, you can calculate the inductance of a trace with a 3D field solver utility, but this is not the norm in transmission line design. Supports Anritsu ShockLine™ MS46524B and VectorStar™ MS4647B. As the driving frequency increases, mutual inductance between circuits in your board will cause the impedance of your power delivery network to increase. 0. It seems I could largely do without any impedance matching considerations, given what the trace lengths are. 3mm of the microcontroller), therefore i rounded the width to 0. Ask the board manufacturer for the values. When two ends of a differential pair or a group of signal nets are mismatched, there will be excess skew between signals. Edit: also, think ahead if you are going to use ground pours around the traces. Figure 3. To summarize, the common and differential. Place the MDI termination within 250 mils of the 82578. When designing the trace configuration for your differential pairs, you are typically targeting 100 ohms differential. 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. So, the trace width and distance to adjacent reference plane is determined by the desired. 5mil (7628 prepreg) when tracks are inside. Click on Setup -> Constraints > Electrical Constraints Set - > Differential Pair Value - > Calculator >. how to reach 120Ohm impedance on a 4 layer board? (I use JLCPCB standard 4 layer stack-up, and with their calculator I don't reach 120Ohm for single ended and for differential I only get close with 3. You must estimate the differential trace insertion loss in dB/inch for the trace loss budget based on the selected PCB materials and stackup. The PCB trace width and the spacing to the grounded copper regions need to be designed to set the designed impedance to the. 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. For this reason, the 50 ohms impedance traces should be 5. Atlas Si for TDR. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. While this calculator will provide a baseline, any final design considerations should be made towards loss, dispersion, copper roughness, phase shift, etc. Actual results may vary depending on application and conditions. This is because communication flows both ways on the CAN bus. Excite the other end of the trace with the function generator. 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. 3 CPW Structures; 3. Use the following equation to calculate the impedance of a stripline trace layout. Typical impedance tolerances are 10% and 7%, and can go as low as 5% or 2% in the extreme cases. 0. This calculator is designed to calculate the characteristic impedance of an edge coupled microstrip. Class creation for controlled impedance routing using Altium Designer. Equation 2. 4 Differential Line and Coplanar Strip; 3. Bandwidth Calculator & Max PCB Trace Length Calculator. View All Tools. Simulation Done with PCB Trace Differential Trace Impedance of 50 Ω and Trace Length of 50 psec. Look what happens to the impedance if we place a ground plane on the top layer that is close to our signal. Give this class a name (100 ohms in our case). Chrome 92. 1. 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. Z 0 = Single Ended Impedance. There are 3 types of single-ended models: single-ended non-coplanar, coplanar single-ended, and coplanar single-ended without ground. Edge Coupled Stripline Impedance Calculator. This has been a research topic for differential serial protocols over the last several years, and standards like USB 4 place specific requirements on broadband signal integrity metrics. I found that a W of 0. I am developing a 4-layer FR-4 board containing a GNSS receiver (L1 + L2). Since this is the flex board it is very thin 8 mills total thickness, those it is difficult to create required hight to the reference plane. Stripline. While this calculator will provide a baseline, any final design considerations should be made towards loss, dispersion, copper roughness, phase shift, etc. See how in your microstrip example the traces are 192 um wide while in the coplanar design they are 117. The idea here is to determine the spacing required for a given width with the goal of hitting a specific differential impedance value. Given these design specifications, lab measurements of this standard differential via are correlated with HFSS simulation results to first calibrate th e simulation setup. So, let’s finish this. There have been trace routing tools available for a long time that help with differential pair routing, and designers have had access to impedance calculators to determine their trace widths. don't change the any dielectrical contant. 1. Calculate the Differential Microstrip Impedance of a transmission line based on the the distance between the strips, height of the substrate, trace thickness and dielectric constant of the substrate. The vias on these differential pairs have their own impedance, which can create signal integrity problems on long interconnects. Understanding Coplanar Waveguide with Ground. If you're trying to get your own pcb design project , you should use this tool. Every trace has series inductance. Re: Calculating Differential Impedance for USB Differential Pair. Differential impedance, Z diff, is the impedance between the two conductors. PCB Trace Width Calculator. Reference layer. To calculate the impedance, I use Saturn PCB impedance calculator software, Inc - PCB Toolkit V8. Z0 = (60 / √εr) * ln ( (8h) / (w + s)) Where εr is the dielectric constant of the substrate material, h is the substrate height, w is the trace width, and s is the spacing between traces. calculate the impedance and capacitance of PCB traces. 1 Answer. PCB Impedance-Calculation: Help with the dimensioning of the impedances of your circuit board. The characteristic impedance of your microstrips is determined by the trace width for a given layer stackup. If you are using differential pairs, think about trace coupling. The efficiency of transmission of the embedded microstrip greatly depends on its characteristic impedance. Depend-ing on the logic family used, trace length difference of 500 mil can be tolerated. There are many demands placed on PCB stackup design. Altium Designer includes a PCB trace impedance calculator, PCB trace width calculator under IPC 2152, and a plethora of other important design tools. External Copper Thickness: Copper weight for the top and bottom layers. 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. Calculate the Differential Microstrip Impedance of a transmission line based on the the distance between the. 2. Controlled differential impedance starts with characteristic impedance. It is good practice to match differential trace length and to keep the distances between the traces consistent. This is for 75 Ohm impedance source (terminated with corresponding. FWIW, the calculator I've used in the past is called Polar SI8000 which apparently has been superceded by Speedstack PCB. Use the following guidelines. 3mm, as shown below: This increases the impedance slightly to 91. The guides says spacing under 0. For microstrip traces, a solid ground plane is needed under the signal traces. In PCB design software with a built-in impedance calculator function, you can calculate impedance quickly. The total length of the signal path is about 1,330mils. While commonly constructed using printed circuit boards, this structure can also be built using other materials as long as there is a conductor separated from. Click on Net -> All Layers -> Line under the Spacing Constraint Set. - Since you have 2 layer board, use a ground polygon beneath the RS485 communication (Both Control and Bus circuitry) - Several points in the layout as shown in the attached. Instead, field solvers normally focus on impedance and calculating the current distribution around the trace. Place your components, vias, coupling capacitors. Single ended traces impedance control is less important in review perspective. Given the defaults (1. Microstrip Differential Impedance Formula. 8. (unloaded trace impedance, Ohms) = Tpd (unloaded propagation delay, ps/unit len) =. Z diff = 2* Z o (1 - 0. High speed PCBs and signaling standards almost entirely use differential pairs with precise impedance. Bus line impedance (Z Bus) Differential Mode line impedance (Z Differential) Common Mode line impedance (Z Common) The Single Line impedance is based on the inductance L and capacitance C per unit length of the trace and can be calculated by the following formula: Below there a few examples where the single line impedance is of interest: Coplanar Waveguide Calculator. Before we can start routing the PCB, we need to define Design Rules for our differential traces. The IPC-2141 trace Impedance calculator will help make initial design easier by allowing the user to input basic parameters and get a calculated impedance according to the IPC-2141 standard. This assumes ~0 trace thickness. 30967mm) is slightly larger the size of the smallest pad (0. The trace width should also not exceed twice the dielectric thickness between the target signal layer and the nearest reference. Figure 1. The calculations are pretty standard and supported by many freely available calculators. Edge Coupled Microstrip Impedance Calculator. , power and/or GND) constitutes a stripline layout. Build a model from experimental data of impedance vs. If the characteristic impedance of the two single-ended lines is Z0, then Zd and Zc can easily be derived. The signal is now too slow and there will be no reflections due to impedance mismatch. Board. The article will not go into the details of these other aspects that indirectly are part of the impedance controlled traces challenge. In this worst-vase scenario, the via would. Use several of them and compare. The physical parameters of the trace i. In terms of how these calculators work, the impedance of a transmission line in a PCB can be calculated in four ways: Use the R, L, C, G parameters from the Telegrapher’s equations to calculate the impedance of the transmission line. There should be a solid ground in the layer underneath the trace. 25mm, a trace width of 0. 0 specs requires a differential impedance of 90 Ohms and a common mode impedance of 30 Ohms (with some tolerance). 0 Dimensional units: mm milsDifferential Impedance Ω. For this calculation, the units of d,h, t and w can be ignored as long as they have the same units (mils, mm, inches). Controlled differential impedance starts with characteristic impedance. 2-side PCB, one side with signals, the other with GND. To avoid microstrip modes, have h >> (w+2g) and extend component side ground away from the trace by > (w+2g). 4 mm dielectric leads to too thick PCB, even on 8 layers. Figure 4. While discontinuities might be unavoidable, they should be lumped together to keep their area small. For example, with a thickness of 0. To get the correct parameters, we have to use the specifications from our PCB house and the provided calculator. h = Dielectric Thickness. Use an impedance calculator to determine the trace width (W) and spacing (S) required for the specific board stack-up being used. In other words, if you are designing to hit a differential impedance target (such as. High speed measurement tools. To add the impedance models, click on ⊕ under the impedance calculator section and provide the following. Now also calculates DC resistance with temperature compensation. Impedance control in flex stack-ups is essential to reduce signal reflections and achieve dependable signal integrity. PCB stackup, signal integrity and controlled impedance: Signal integrity tools: Stackup design. 4 mil, εr. Board Setup. 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. 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. Select a configuration: Microstrip Trace. Design and stackup in altium, For ex: 8 layers and impedance control of 100 ohms on layer 2 and 7 and ask your fabricator to suggest a stackup for same 8 layers and trace impedance of 100 ohms for layer 2 and 7 and compare the values. Impedance captures the real and complex. of typical printed circuit board trace geometries. 2 Ω impedance. Most popular calculators don’t even have a box height parameter. Note: The 6-Layer board temporarily only provides JLC3313 Stackup. The differential impedance of MIPI tracks should be 100 Ohms, not 90 (USB requires 90). 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. One thing is for sure: When you are routing a high-speed PCB design you are going to be working with impedance-controlled routing and. Dual Stripline. The termination resistors on a cable should match the nominal impedance of the cable. Developed in direct response to industry demands for a means of evaluating the impedance of differential PCB trace structures, the new CITS 25 calculator tool is a true 32-bit application that runs under Windows 95, 98 and. 1. When calibrated,Differential Pair Routing. 25mm between the differential pair with a width of 0. We have upgraded our Impedance Calculator, a free 3D field solder, which now uses the 2D numerical solution of Maxwell’s equations for PCB transmission lines. The differential impedance between the positive and negative trace of the transmission line is slightly less than twice the impedance of the single ended impedance. Stripline. 3. Go to ‘ Design’ >> ‘Classes’ >> ‘Net classes. PCB Trace Impedance Calculator. For differential pairs, there is also a spacing value given. Using a differential pair to avoid common mode noise is common in audio circuits. IPC 2141 Trace Impedance Calculator. The trace width and spacing for a certain impedance may be obtained using impedance calculators. 3 Answers. Use a Numerical Field Solver for Impedance and Return Path Calculations. As a compromise, at least for surface microstrip configurations, the value of the dielectric constant can be increased by approximately 14% in differential impedance calculators[2] to average the effect of the layers. x allows an easy way to make differential pairs and keep control of the trace length, thus the phase or skew between the traces. The calculator by Spok consulting, for example, gave the following result: Problem. The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. Getting the Most Accurate Impedance Calculations. Such a microstrip is constructed with two traces referenced to the same reference plane with a dielectric material between them. 0 differential insertion loss test to 43. 8. H= Distance between signal trace and ground plane. Reference: R. 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 theCalculate Coplanar impedance for given PCB parameters. 5oz inner copper, 8 mil trace spacing) and a target differential impedance of 100 ohms, JLC's calculator suggests a trace width of 8. It is now a major exercise to evaluate the impedance using a calculator or spreadsheet. With differential pairs, you also need to examine. 6mm spacing with a trace width of 0. Mutual inductance and capacitance exist between the two traces in a differential pair. Just as important as determining an appropriate trace width for a. Description. Use the results from #3 to calculate the width profile with. with the following layout parameters (width|space|width): Ohm. This transmission line calculator was. KB: Fail to use evaluation license with a dialog "You can use this license only on a single PC". That means each trace would be a 50-ohm trace, if there were no coupling between the traces. The termination resistor [R] is still selected to match the trace impedance [Z o], while the capacitor is selected by: X c = [3 * T r] / Z o. However, to keep costs down, there are only two drill pairs, meaning that a high-speed signal may only need to travel 3 mil down a 23 mil via. Terminate the trace at one end with a small SMT 50 Ohm resistor (49. 5ohms and the fact that it’s nearly flat above about 800kHz). 1. This makes the problem of determining impedance much more complex, and building an initial lossless model requires a larger set of formulas. Impedance Calculator - Sierra Circuits. Gaps in signal traces impact the entire test waveform, and its single-point impedance is too high, making the entire waveform uneven. They are very simple to read, and the values in. traces ), and stripline traces, ( traces within the layer stack, typically sandwiched by two ground planes ). For an embedded (internal) microstrip, the formulas provided in paragraph 4. For example, a 4-mil differential trace should not have more than an 8-mil space. PCB Trace Impedance Calculator Calculates the characteristic impedance and per-unit-length parameters of typical printed circuit board trace geometries. Yes, solder mask can lower the single line impedance by 1 - 2 ohms and the differential impedance by 3 - 4 ohms for thin traces. (5mil prepreg) But in your case if using a 10 mil dielectric; Impedance is almost constant ratiometric to the conductor geometry ratios if <2:1 ratios for planar and < 3:1 for differential coplanar. This is assuming that you have a Design Rule in place which links the impedance profile to a. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. Differential Impedance Ω. Probe with the oscilloscope where the function generator feeds into the PCB. Re: Calculating Differential Impedance for USB Differential Pair. I checked out TNT, but couldn't seem to be able to do the same with that either. 1 mm trace spacing chosen in your design. TheseIt always defaults to 10mil. To prevent reflections the PCB trace pair’s impedance should be matched to the interconnect/media. We recommend the software from Polar Instruments if you want to get exact impedance calculation. 75 mm=30 mil). Differential impedance is a two-step process, first Calculate the single ended impedance Zo and then use this value. It is especially required when high-frequency signals propagate through a circuit board trace. Going to 100 ohms diff you would be looking at 15 mil parallel traces. The bus impedance of the RS485 is approximately 100-120 Ohms differential and control trace impedance as ~50 Ohms. The calculator below uses Wadell’s. The microstrip is a very simple yet useful way to create a transmission line with a PCB. 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. PCB Trace Width Calculator & PCB Trace Resistance Calculator per IPC-2152 .