Differential Trace Microstrip Impedance Calculator; Differential Trace Stripline Impedance Calculator; The standard geometries that are supported by these trace impedance calculators. In this worst-vase scenario, the via would. 062. Such a microstrip is constructed with two traces referenced to the same reference plane with a dielectric material between them. To add the impedance models, click on ⊕ under the impedance calculator section and provide the following. 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. The JLCPCB results are more reliable than (some of) the simple formula-based approaches. The capacitor value may be traded off to. Yes, solder mask can lower the single line impedance by 1 - 2 ohms and the differential impedance by 3 - 4 ohms for thin traces. Check here: UltraCAD's new Differential Impedance calculator will calculate single-ended and differential impedance for the common configurations we all deal with: Microstrip. ALGEBRAIC EQUATIONS Single Track For the stripline of Figure 2 with a symmetrically centredIf your design has controlled impedance traces, you can use our built-in impedance calculator. This is why in most cases the differential impedance of a pair of traces is a little less than twice the single ended impedance of each trace. Equation 2. That trace has an impedance, which is referred to as the characteristic impedance. There are a lot of online trace impedance calculators specifically designed for differential traces. Impedance vs. To use this tool, enter the values for. Tuning for your traces to the desired impedance value occurs by adjusting trace width and distance from the reference plane. 4. Single Ended Impedance Ω. Agilent's LineCalc tool calculates Z odd = 50. Either the desired impedance at a specific frequency is used to determine the waveguide width, or the width is entered and the impedance is calculated. Microstrip Trace Impedance vs. They are very simple to read, and the values in. The datasheet mentions that the LVSTL is tuneable, but what is the nominal differential and single ended impedance for these PCB traces? I have also checked the TN-53-06: LPDDR4/LPDDR4X Point-to-Point Design Guidelines from micron and it says this: Standard characteristic impedance (Z0) of no more than 50Ω, nominally, is. Controlled Impedance; PrePreg Chart. 5 mil (2116 prepreg) or 8. g. Dual Stripline. No, the single-ended impedance provided in differential line calculators does not matter. Instructions are below the calculator and don’t forget we can make and test your controlled impedance printed circuit boards too. When selecting trace geometry, priority should be given to matching the differential impedance over the single ended impedance. I suggest interested parties find an online trace impedance calculator and play around with some geometries. 2H, the formula for the non-embedded. The extracted model includes distributed parameters for resistance, capacitance, and inductance, as shown in Figure. Z 0 = Single Ended Impedance. Single ended impedance is the trace impedance with reference to ground. The calculation looks correct, but the tracks are too wide. The trace width (0. 6mm 4 layer PCB, 1oz outer copper, 0. Figure 8. • 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. Disc Air Capacitor Calculator; Impedance Calculator : XL, XC; Inductors, Transformers. Need to consider this if the data rate is 5 Gbps and above. AC Termination: AC Termination of a line results in the lowest power drain, but also requires two parts. Instead, field solvers normally focus on impedance and calculating the current distribution around the trace. There are a lot of online trace impedance calculators specifically designed for differential traces. Use 3. It supports both balanced and unbalanced lines. When a single trace is considered in isolation, its impedance will have a well-defined value. The DC resistance is determined by the trace's conductivity and the cross-sectional area. KB: Fail to install possibly due to lack of admin privilege or virus protection software. That means each trace would be a 50-ohm trace, if there were no coupling between the traces. View All Tools. Class creation for controlled impedance routing using Altium Designer. If you put 10 in the Line Width, the calculator calculates the single ended as well as differential impedance. What we have on these differential traces is a taper section, which RF engineers often use to match impedances. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. Every trace has capacitance between the trace and the return path of the signal on. Using an online differential impedance calculator, the height of the dielectric layer, h, is needed. 94 mil) is nominal thickness of 3313 prepreg. 1. 1. 2-side PCB, one side with signals, the other with GND. 8. Impedance calculations must account for the two distinct configurations of even (both traces at the same voltage as measured from ground) and odd (traces at the same voltage magnitude but opposite signs relative to ground) impedance. The PCB Impedance Calculator in Altium Designer. Chrome 92. Hello! I'm trying to calculate the trace width for a differential pair (carrying MIPI CSI-2 signals), using JLC's impedance calculator. 1 to 2. The factors that influence differential pair via impedance will affect the input impedance seen at the vias. Signal traces of high-speed differential pairs must be routed parallel to one another with a fixed distance between them. You simply need to select both ends of the pair to ensure the differential impedance remains consistent throughout the board. The Si8000m assumes negligible insertion loss in the transmission line; should you wish to model insertion loss the Si9000e adds. Try TNT or TxLine. Vias (plated holes) are used to route electrical signals among different layers of a multilayer. 2. At some point the amplitude will stay constant. The differential skew is adjusted with a tiny blip on one line towards the bottom of this image. Example, If Z 0 = 55 Ω, d = 6 mils. 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). Regarding the impedance of USB signal traces the layout guidelines state: DP, DM Differential trace impedance = [DP(45ohm) + DM(45ohm)] = 90 ohm, and do not jump the DP DM signals that cause impedance miss match. The amplitude of this crosstalk is what this tool calculates. CAN_L is pin 2 and CAN_H is pin 7 on the standard 9-pin D-SUB connector. Use several of them and compare. Z diff = 2* Zo (1 - 0. 6mm thick. This assumes ~0 trace thickness. Impedance control in flex stack-ups is essential to reduce signal reflections and achieve dependable signal integrity. Thus a "differential pair" any long distance apart will have an impedance of 98 ohms, without any coupling between the lines, i. Just a clean step. Mitch Morey, San Diego, CA: I'm working on a board with 100-ohm differential signaling that I would like to design for microstrip routing. Best Regards, David LambeUnderstanding Coplanar Waveguide with Ground. ’. Once you know the characteristic impedance, the differential. W is calculated to achieve a trace impedance (Z0) of ~50W and S is calculated to achieve a differential trace impedance of 90W. Edge Coupled Microstrip Impedance Calculator. Calculate the Differential Microstrip Impedance of a transmission line based on the the distance between the. calculate the impedance and capacitance of PCB traces. Free Trace Line Impedance Calculators that utilize the #3 approach. Several online tools can calculate the required trace width to carry rated current while keeping the trace temperature below a specified limit. 063” FR4 PCB has about 52Ω impedance. My board house can do 5/5 mil trace/space. Embedded Microstrip. Equation 2 is the most commonly used equation for surface microstrip transmission line impedance calculations. 5ohms and the fact that it’s nearly flat above about 800kHz). 2) S/T > 5. I would like to know how to calculate trace width and gap to route differential pair in this situation. Modeling approximation can be used to design the microstrip trace. Advanced differential impedance calculator facilitates design and production of latest-generation PCBs. pair impedance with predifined traces’ gap. 0. Impedance in your traces becomes a critical parameter to consider during stackup design for high-speed PCBs, but the. Two 50 Ohm traces next to each other have a differential impedance of around 100 Ohms, or maybe a bit less. It is only equal to double the characteristic impedance in certain cases. calculate the resulting differential impedance, and check that it matches the selected media (cable) differential mode characteristic impedance. Some calculators opt for Wadell's results, yet they simply state they are "based on Wheeler’s method" without providing references. The accuracy of a controlled impedance trace on a PCB is usually critical to the correct performance of the PCB. Once you know the characteristic impedance, the differential impedance. 15 mm. This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). Controlled impedance (CI) is the characteristic impedance of a transmission line in a PCB conductor and its related reference planes. Differential impedance is the ratio of voltage to current on a pair of transmission lines when driven in the differential. Using this data in a frequency-dependent solver, the impedance of the trace looks like this (note the additional 1. 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. 1. There are some advantages to using a. It is admittedly small, but it is non-zero. Actual results may vary depending on application and conditions. 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. Atlas Si for VNA – Insertion loss test system – Delta-L 4. For differential pairs, there is also a spacing value given. The guides says spacing under 0. This calculator helps you calculate the characteristic impedance of a coaxial cable given its dimensions. The characteristic impedance of your microstrips is determined by the trace width for a given layer stackup. Ensuring impedance-controlled routing also requires knowledge of the substrate’s dielectric constant and your required trace width. The outputs impedances can be odd,. The required inputs are the Dk value for the dielectric constant of the PCB substrate, and the. 0 differential insertion loss test to 43. Obviously a stripline requires four or more layers, since at least three copper layers are needed. Assuming both are accurate enough. External Copper Thickness: Copper weight for the top and bottom layers. The article will not go into the details of these other aspects that indirectly are part of the impedance controlled traces challenge. Calculates the bandwidth of a digital signal and maximum trace length, using the IPC-2251 method or the frequency domain method, for transmission line effects. 19mm) traces with 7. KB: Prevent multiple license seats being used on one installation instance. THESE FORMULAS ARE APPROXIMATIONS! They should not be used when a high degree of accuracy is required. 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. For an embedded (internal) microstrip, the formulas provided in paragraph 4. 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. Coplanar waveguides are open quasi-TEM waveguide geometries that use copper pour and a ground plane to provide shielding along the length of a PCB trace. Design traces for 100 W differential impedance (± 15%). 8. Rule 2 consequence. Figure 3. For a given differential impedance specification , a change in spacing and substrate thickness forces a change in the trace width in order to maintain the same odd-mode impedance value. Depend-ing on the logic family used, trace length difference of 500 mil can be tolerated. There are a number of pcb transmission line typologies. 0 Dimensional units: mm milsDifferential Impedance Ω. A circuit trace routed on the inside layer of the PCB with two low-voltage reference planes (i. 5. Single-ended signals are fairly straightforward. This makes the problem of determining impedance much more complex, and building an initial lossless model requires a larger set of formulas from Wadell. Let's match the impedance of the same signal since differential pair routing is completed when the impedance is matched properly. Use a Numerical Field Solver for Impedance and Return Path Calculations. Single ended impedance is the trace impedance with reference to ground. - 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. Note: Units do not matter for this calculation as long as they are consistent. So I need to choose the correct trace width/spacing, am I right? Previously I was used 5mils width and 6mils spacing differential traces. 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. 16 mm. The characteristic impedance is given by: Eq. Please bear in mind the copper trace, minimum etch, manufacturing capability etc of the pcb supplier. Getting the Most Accurate Impedance Calculations. Mode Pattern for Identical Traces Hyperlynx simulation +1v -1v +1v +1v Mode: odd, or 1, or a Mode: even, or 2, or b Corresponds to differential driven Corresponds to common driven I odd x I. We recommend the software from Polar Instruments if you want to get exact impedance calculation. Trace stubs must be avoided. The article will not go into the details of these other aspects that indirectly are part of the impedance controlled traces challenge. Differential Stripline Impedance Calculator. 30967mm) is slightly larger the size of the smallest pad (0. The default units for all given values, except the subtrate. Make sure that the matching or the pair lengths is maintained. Sorted by: 1. 9D/B) Zo = Single Ended impedance. Differential Stripline Impedance Calculator. A 3D view of a complex impedance controlled PCB in Altium Designer. Therefore, for fast enough rise times, the impedance it offers can be significant. trace geometry, and use this to calculate impedance. . 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. Since it is always important that the trace impedance. 5x would be best, but 2x is acceptable. 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. I used some online calculator to calculate parameters of trace so it has 50 Ohm impedance. Sierra Circuits can: Help you with your controlled impedance stack-up. 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. It is admittedly small, but it is non-zero. Following is the formula for differential impedance for a Microstrip. This will give us the appropriate trace width and trace separation for the desired differential impedance. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. 0 specs requires a differential impedance of 90 Ohms and a common mode impedance of 30 Ohms (with some tolerance). infinite mutual. Yet I got a ZDiff CPW with ground capable calculator: Differential surface coplanar waveguide with ground calculations: *0. Performing PCB trace length matching vs frequency correctly requires considering the entire bandwidth of a propagating signal on a trace. But make sure you get the spacing between the diff pairs and their thickness (copper weight) correct. Incidentally, the trace thickness parameter does have a significant effect. Insertion Loss. The closer you place the pairs together, the differential impedance gets smaller because LM and CM get larger. The surface finish is neglected. USB traces must be 90 Ohms differential. This calculator is designed to calculate the characteristic impedance of an edge coupled microstrip. This note describes some. The trace impedance or PCB impedance damages the integrity of both analog and digital signals. FYI, I followed 2nd option and values were quite similar. of typical printed circuit board trace geometries. Every trace has series inductance. 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. This is for 75 Ohm impedance source (terminated with corresponding. In this design there is a coplanar ground plane a controlled distance away from the trace that is close enough that it significantly affects the impedance of the trace. 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. width|space|width. Back to Resources Use our free impedance calculator to ensure your design is error-free! Impedance Calculator Structure Type Single Ended. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. Using this calculator, I found 100 Ohms by giving 9 mils of track width, 5 mils of track separation, 8 mils of dielectric. This, by definition, gives a target of an odd mode impedance of 45 Ohms and an even mode of 60 Ohms. The signal is now too slow and there will be no reflections due to impedance mismatch. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. 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. 0. Click on Setup -> Constraints > Electrical Constraints Set - > Differential Pair Value - > Calculator >. Example Problem: Use the following variables as an example problem to. This is assuming that you have a Design Rule in place which links the impedance profile to a. Can I / should I add extra components to the bus traces, to reach. Use the following guidelines. This calculator finds both odd and even transmission line impedance. This will give us the appropriate trace width and trace separation for the desired differential impedance. impedance to rise. 5. Surface microstrip lines are formed by etching one surface of a double-sided material. required trace geometries to meet a nominal differential impedance target of 100 Ω with ±10% tolerances. you need to get trace widht and trace thickness,impedance value for your trace (single and Differential). 68 mils. Copper thickness (t) = 18 micron. 5mil clearance on a 63 mil board (1. 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. I have already some experience on single ended controlled impedance but this is my first. Radio Frequency Engineering Calculator. The second link seems to hint that some calculators take some extra parameters into consideration. KB: Route traces between flex and rigid regions. Having never routed differential signals the size difference these calculators are coming up with is a little alarming but perhaps this is normal? Parameters: Trace Separation: 4mil; Trace thickness: 1. This will also provide the time delay the cable provides for a signal and also the capacitance and inductance per. Standard 4-Layer Stackup. The impedance calculator in the Allegro stack-up editor uses a static 2D field solver by default (bem2d). Route your single-ended and differential pair traces. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. Speedstack is the stackup design tool of choice for professional PCB Designers fabricators and brokers who have a requirement to document and design stackups drill plans and material requirements complete with high. This is more than the to times trace width which is recommended (also read as close as possibly). I'm designing a custom PCB around the Raspberry Pi RP2040 MCU. Next step is to check the via count of each single trace. 3mm, as shown below: This increases the impedance slightly to 91. To find what a given trace width will have a single ended or differential impedance, we can use a built in calculator from Allegro. • When using an impedance calculator, the outer layers of the PCB contain less glass than. There should be a solid ground in the layer underneath the trace. 254mm. The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. Copper. Create a new impedance profile, then select Single-Coplanar or Differential-Coplanar from the Impedance Profile Type drop-down list. Ensuring impedance-controlled routing also requires knowledge of the substrate’s dielectric constant and your required trace width. 347 e -2. 2-0. e. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. In PCB design software with a built-in impedance calculator function, you can calculate impedance quickly. you need to get all the details from Manufacturer. 1. which simplifies the process of determining the characteristic impedance of a microstrip trace. Differential Impedance: Single-ended Impedance: Significant field collisions (bad design--will be too much crosstalk): In short, do not put much faith in the single calculators you find online. 254mm. Note that Zdiff (differential impedance) is equal to 2 * Zodd, so a Zodd of 45 Ω gives us a Zdiff of 90 Ω. Asymmetric Stripline. A coplanar waveguide calculator will operate in one of two ways. 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 . Microstrip Impedance -Differential Stripline Impedance -Differential W = Width of the trace H = Height of dielectric above theThe trace width is important as it determines the single-ended and differential impedance, capacitance, and inductance. Microstrip Trace Impedance Calculator; Stripline Trace Impedance Calculator; Differential Trace Microstrip Impedance Calculator; Differential Trace Stripline Impedance Calculator; The. The track widths should. Using typical values of W= 9 mil, H= 24 mil, T = 1. altium. See full list on resources. I found that a W of 0. This note describes some. 05 that is free software and very famous among designers. Differential Trace Routing. Speedstack is the stackup design tool of choice for professional PCB Designers fabricators and brokers who have a requirement to document and design stackups drill plans and material requirements complete with high speed transmissionline information. Since PIe edge connector’s character impedance is 85Ω, the traces between the connector and I should be 85Ω -- the rest is usually set to 100Ω. The idea here is to determine the spacing required for a given width with the goal of hitting a specific differential impedance value. 2 Ω impedance. Before we can start routing the PCB, we need to define Design Rules for our differential traces. Differential signaling will produce a voltage effect between the traces similar to odd-mode. Field solvers. We care about maintaining the same differential impedance for. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. 48 e -0. If you use your layer stackup calculator with a thick 2 layer board to calculate the differential impedance for microstrips, you’ll find that the actual trace width needed is much smaller and is a function of spacing. This sets the single-ended impedance AND differential impedance to the target value, even if there is no. (unloaded trace impedance, Ohms) = Tpd (unloaded propagation delay, ps/unit len) =. Just as important as determining an appropriate trace width for a. How to calculate differential impedance: Notes. 2) S/T > 5. Example (PageIndex{1}): CPW; 3. Get latest updates and offers. e. 5. Hello! I'm trying to calculate the trace width for a differential pair (carrying MIPI CSI-2 signals), using JLC's impedance calculator. 8. There are many demands placed on PCB stackup design. The bus impedance of the RS485 is approximately 100-120 Ohms differential and control trace impedance as ~50 Ohms. ZL =. mils: Distance between planes (B) mils: Relative Dielectric constant (Er) Differential. When enabled. Differential Pair Routing. Dielectric constant = 3. Back to Resources Use our free impedance calculator to ensure your design is error-free! Impedance Calculator Structure Type Single Ended Differential Trace width (W) mils Trace. 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. Trace thickness is 0. Thank you. The standard 4-layer stackup uses two inner layers for power and ground, and the two outer layers are for components and trace. 2. PCB Structures / Discrete Structures / Signal Management. Activate the mixer to its normal operating conditions. To update trace width, select the traces of interest and use the "Route > Retrace Selected" command. Now also calculates DC resistance with temperature compensation. To meet those requirements I used some online impedance calculators to estimate the required trace properties for a 2-layer FR4 PCB. If it is off substantially, the PCB trace dimensions should be adjusted to provide a match. Pick a signal frequency for your taper. To prevent reflections the PCB trace pair’s impedance should be matched to the interconnect/media. don't change the any dielectrical contant. To add the impedance models, click on ⊕ under the impedance calculator section and provide the following. To get the correct parameters, we have to use the specifications from our PCB house and the provided calculator. This would be more manageable. 100 Ohm diferential impedance microstrip PCB traces geometries in. The total length of the signal path is about 1,330mils. 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 tool also calculates signal losses of any given trace. Differential impedance. Simulation Done with PCB Trace Differential Trace Impedance of 50 Ω and Trace Length of 50 psec. This means that the actual trace width for a 50 ohm line could vary from design to design. 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. Edge-coupled Asymmetric Stripline. Microstrip. This impedance is dominated by the physical separation between your power rails, traces, and internal planes in your board. From this equation, calculate the real and imaginary components to. 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. As these proximity effects are proportional to the field strength of neighbouring traces they can be substantially reduced by increasing trace-to-trace spacing. 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. 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. 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. 020. Create a differential trace with KiCad - Schematic. 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. Continuing on. 159 OS X 10_15_7 EasyEDA. and thats the first time iam doing ethernet things. Unfortunately Online Calculators are deceiving unless you actually draw the numbers and understand the ratios and tolerance effects. There are four different types of impedance. 1 to 3. Just enter the given values for trace thickness, substrate heights, trace width, and substrate dielectric. A PCB impedance calculator uses field solvers to accurately approximate impedance values. h = Dielectric Thickness. The stub length must. when two coupled tracks are used to give a differential impedance. 6mm spacing with a trace width of 0. See how in your microstrip example the traces are 192 um wide while in the coplanar design they are 117. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. pairs for aciving 85 Ohm diff. The default units for all given values, except the subtrate dielectric, is in millimetres. High-quality circuit boards as prototype and series at reasonable prices. x allows an easy way to make differential pairs and keep control of the trace length, thus the phase or skew between the traces. 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. Build a model from experimental data of impedance vs. Using a differential pair to avoid common mode noise is common in audio circuits. 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. 2. Stack Symmetry – enable to add layers in matching pairs, centered around the mid-dielectric layer. Differential pairs are commonly found in high-speed data communication systems, such as those used in computer interfaces (e. Assign the trace width and spacing that will make the impedance of the differential traces - the desired impedance. Using a power plane as signal reference. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). In fab notes, give the expected impedance (100ohm differential), the acceptable tolerance (often +/-10% or 20%), and which traces are. The accuracy of a controlled impedance trace on a PCB is usually critical to the correct performance of the PCB. 3 shall be used. B = separation between reference planes. com To use this tool, enter the values for trace thickness, substrate height, trace width, trace spacing and subtrate dielectric in the calculator above and press the "calculate" button. Most often, the only specified requirement of a differential pair is its differential impedance. 1 mm trace spacing chosen in your design. This calculator allows you to add the impedance model and compute the desired trace geometry and spacing for a target impedance. The differential 100 Ohms line has width 0. Note that the y-axis is on a logarithmic scale for clarity. 77 mm gave me a differential impedance very close to 90 Ω.