Note the differential pairs above that look like a strand of intestine have a constant gap between the pairs. This will be specified in your controller's datasheet in the DDR4 interface specifications. The types of traces where impedance control is applied are: Single-ended and differential pairs of microstrip lines. The concept of driving the conductors as a differential pair implies the presence of a zero voltage ground. In addition to the characteristic impedance of a transmission line, the tool also calculates: This calculator is designed to calculate the characteristic impedance of an edge coupled stripline. Altium Designer makes it easy to calculate geometry when you need to calculate impedance for differential pairs. This is a tool that has been designed to determine the characteristic impedance (Z 0) of a twisted-pair cable. I did my research on what the differential impedance is and how should I approach it. Dielectric Constant The. Disc Air Capacitor Calculator; Impedance Calculator : XL, XC; Inductors, Transformers. The impedance of the surface microstrip shown is 50 ohms, so the impedance of the broadside coupled differential pair will be twice 50. Differential Pairs can be defined as an Electrical CSet or a Physical CSet. The questions are mostly on the inner layer differential impedance item [4] below. Z 0 now meets your requirements. If we want to hit the standard 50 Ohms impedance target, then we need to have a trace width of almost 110 mils!Differential microstrip and stripline pairs have common-mode noise immunity if they are routed symmetrically, but they also need to have controlled differential impedance to ensure impedance matching and consistent propagation delay throughout an interconnect. ; Apply the values to the differential calculation, e. g. This makes the problem of determining impedance much more complex, and building an initial lossless model requires a larger set of formulas from Wadell. When you are creating your schematic, you must use one of the following suffixes when naming your differential pair nets: +/- (e. 5 (FR-4) ! even for Conductor/Plane layers. From it, apart from making all traces the same length from camera sensor to cable connector, I believe the rules I need to follow are: Differential impedance of 100 Ohm. This 100 Ohm has no ground connection. 6 mm board that I want to create a 90 Ohm profile on. Just as important as determining an. There are a lot of online trace impedance calculators specifically designed for differential traces. Critical Signals (continued) Signal Name Description HDMI_DATA1x High-Definition Multimedia Interface (HDMI) differential data pair, positive or negativeFor example, the equation for the trace impedance in a differential pair of asymmetric striplines includes an approximation on the dielectric constant and geometry. 2. Critical Signals (continued) Signal Name Description HDMI_DATA1x High-Definition Multimedia Interface (HDMI) differential data pair, positive or negativeFor example, the equation for the trace impedance in a differential pair of asymmetric striplines includes an approximation on the dielectric constant and geometry. Agilent's LineCalc tool calculates Z odd = 50. Modeling approximation can be used to understand the impedance of. Notes: 1) Calculation assumes traces are centered vertically. Although there are plenty of free impedance calculators out there, I'm struggling to find one that can solve impedances for a differential pair using coplanar waveguide. . The resistance value chosen for the two resistors will be referred to as R D (for d rain resistance). USB traces must be 90 Ohms differential. Z diff equals Ra||(2Rb) (p model) or 2R 1 (T model). input signals, the half circuit can be used to calculate. Figure 2. Yes, that's right. beammy. Differential pairs are defined on the schematic by placing a Differential Pair directive (Place » Directive) on each of the nets in the pair. Note: If this post answers your question, please click the Correct Answer button. Details: In the list below, [1] is the reference design stackup information; [2] and [3] are the processes to get the result close enough to the reference design target so as to know the tool is valid; and [4] is the calculation in question because it is either 5. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. Two single-ended transmission lines with coupling are also known as a differential pair, as shown in Figure 5. 004” line/0. 8). EEWeb offers a free online broadside coupled stripline impedance calculator. While the edge couple differential symmetric stripline transmission line is a common technique for routing differential traces. The two most common impedances. net Forum comes closest to the proper track width. As you route your board, the built-in trace length calculator will check your routing against your design rules and flag errors for correction. It is defined as the ratio of powers of the differential gain to the common-mode gain found in equations (2) and (3). 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. Single ended. The tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. 5. To calculate the values, the designer needs to know the following information: Number of board layers• As shown in Figure 1, traces should be 100-Ω(±5%) differential impedance of differential microstrip or differential stripline. 5mm pitch has about 100 ohm differential impedance in the configuration where a differential data pair wires are between ground. Impedance Calculator - Sierra Circuits. 254mm. This calculator computes the characteristic impedance of a twisted-pair cable based on its dimensions. This is typically used when golfers play only a partial round or when a full 18-hole round isn’t completed. To use this tool, enter the values for. 0037” line/0. Mutual inductance and capacitance exist between the two traces in a differential pair. This is a lot of terms to calculate in a simulation!Hi, I am working on my board Stack-up to tune Single/Differential impedances of my board in Allegro PCB 16. g. Visit to learn more about our other electrical engineering tools and resources. But I am not able to match this impedance. Yet I got a ZDiff CPW with ground capable calculator: Differential surface coplanar waveguide with ground calculations: *0. Vias (plated holes) are used to route electrical signals among different layers of a multilayer. Thus, for optimal performance the resistors and MOSFETs must be matched. Edge coupled differential pair Edge coupled internal symmetric differential pair Edge coupled internal. To calculate this, you need some values. $egingroup$ So basically your answer shows that the JLCPCB impedance calculator results are generally in the same ballpark as the proven field simulators. 4 Comments. If you are using differential pairs, think about trace coupling. . P/N De-skew Strategy on Differential Pairs. High-speed differential pair signal traces need to be routed parallel to each other with a constant spacing between them. 5 – Calculation of Differential Impedance using online Calculator Notice that in the above case we get 100 Ohms for 18 mils separation between the + and – traces and 10 mils separation from the ground trace. Differential Stripline Impedance Calculator. The bus impedance of the RS485 is approximately 100-120 Ohms differential and control trace impedance as ~50 Ohms. Microstrip Impedance Calculator. 75 mA corresponds to a CE range of 1V to 8V. 1. It can't be used with differential pairs, which are dominantly used with impedance-controlled high-speed signals;. Zo (diff) is calculated to be 244 ohms, so dividing by two yields a value of 122 ohms for the semi-coplanar structure. Cross-hatched copper plane in a flex stack-up for controlled impedance. This calculator. If R G = 402 W, we then need R T to be 114. microstrip Zo vs Edge Cpld Ext Zo). The Signal Integrity tool is examining the series termination needed based on the line's characteristic impedance If you are examining a trace in a differential pair, the Signal Integrity tool is still only used the characteristic impedance, not the odd-mode impedance. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. We recommend the software from Polar Instruments if you want to get exact impedance calculation. This rule maintains the desired signal impedance. The characteristic impedance (Z o) of coplanar waveguide with ground or microstrip lines with signal side ground plane can be calculated using the active calculator or the equations at the bottom of the page. It's true that generally the impedance value is determined by the following parameters; trace layer (microstrip or stripline), trace width, distance. Figure 6-1: Basic Differential Pair The most common application for a differential pair is the differential amplifier. The values you get from an online differential pair impedance calculator corresponds to an isolated differential pair, they do not consider the load component and they are not calculating the input impedance. A twisted-pair cable is simply two wires that are twisted together so as to reduce radiated EMI (electromagneticinterference) and mitigate the effects of received EMI. A twisted-pair cable is simply two wires that are twisted together so as to reduce radiated EMI (electromagnetic interference) and mitigate the effects of received EMI. g. 100 ohm differential pairs that are tightly coupled have a typical single ended impedance of around 65 ohms. For sample: 45-46 Ohm single end traces impedance can be used in diff. ; To. The designer needs to create a stackup for the board and then calculate the trace values for differential pairs and single-ended nets. 29 mm width traces to obtain 100 Ohms ZDiff while using 0. The same applies to differential pairs. Following equation or formula is used for Differential Microstrip Impedance Calculator. But in your differential pair, each line will have its own characteristic impedance, lower than 100 Ohms but higher than 50 Ohms (for instance a quick computing in Saturn PCB give me 77. 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. The IPC-2141 trace Impedance calculator will help make initial design easier by allowing the user to input basic parameters and get a. Figure 4. Mutual inductance and capacitance exist between the two traces in a differential pair. 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 impedance calculations. It is important to determine the characteristic impedance of a twisted-pair cable because this impedance should match the impedance. KiCad has a built-in impedance calculator!The common-mode rejection ratio is a key figure of merit of any differential system because its primary role is to reject undesired common-mode currents with minimal impact on the desired differential-mode currents. Compatible with Flex PCBs and Turnkey PRO service. manufactures will have a preferred tool that PCB designers can use to calculate the Impedance but there are also many available online. transmitted across a twisted pair cable by a differential line driver and sensed at the far end by a. 331 1 2 5. To get the correct parameters, we have to use the specifications from our PCB house and the provided calculator. Careful differential pair routing, impedance control, grounding, and noise reduction techniques are key factors for performance optimization. But for extreme geometries and for many differential pair structures, these approximations can. Formula: Applicability: w ÷ t ≤ 0. I checked out TNT, but couldn't seem to be able to do the same with that either. The differential amplifier can be implemented with BJTs or MOSFETs. is the impedance between two differential pair signal traces. Stripline is another type of transmission line that can be easily built on a pcb. Coaxial Line Impedance. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. , USB. Edge-Coupled Microstrip. 1. DP, DM Differential trace impedance = [DP(45ohm) + DM(45ohm)] = 90 ohm, and do not jump the DP DM signals that cause impedance miss match To meet those requirements I used some online impedance calculators to estimate the required trace properties for a 2-layer FR4 PCB. Both LM and CM converge to zero as spacing goes to infinity. Layers: Total number of copper layers in. Impedance Calculator - Sierra Circuits. For instance, I want a 100 Ω controlled impedance pair, and have used "differential" before which seemed to work fine. 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. The following are typical line widths and spacings for the more common impedance values when using ½ OZ copper: 50 Ohm Single Ended: 0. Skin Depth Calculator. If you viewed the via impedance calculator article linked above, then you likely noticed that. Enter the number n n of impedances in parallel as a whole number and press "Enter". Single-ended and differential pairs of coplanar waveguides. Another example of using large distances to separate out unwanted components might be to calculate the impedance of a. 25, but gives me nice trace from the module to the stub then to microcontroller. A printed circuit board (PCB) mechanically supports and electrically connects electronic components on a circuit board. To use these to design for a target impedance, simply cycle through various geometric values for the trace width until the calculator returns the target. the odd mode inductance and capacitance per unit length. In some cases, we can also use 75-ohm differential impedance. Now I'd like to get into this topic and the first task would be to create a ~ 10cm board to board interconnect flex PCB with 90 ohm (USB) and 100 ohm (LVDS) controlled impedance traces on it. Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method. You can use all the calculators you want if you don't know the exact board make up. 0. 75 mA 7 V 0. One of the features of this type of microstrip is the coupling between lines. The allegro calculator gives a value of 56. This calculator finds both odd and even transmission line impedance. The return path is defined by the reference plane near the pairs and the distance between the two pairs. Details: In the list below, [1] is the reference design stackup information; [2] and. The single 50 Ohms is the impedance of a single-ended transmission line that has a ground connection. An example of this calculation using the Si8000m Quick Solver is shown below in figure 4. Controlled impedance is typically applied in single-ended microstrip, embedded microstrip, stripline differential pair, and planar PCB transmission lines. But there's a ground between R7 and R8!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. 6mm thick. No, the single-ended impedance provided in differential line calculators does not matter. Although widely applied to coaxial cables against EMI susceptibility problems, the Zt parameter can be easily extended to coaxial cables EMI emissions. Differential pairs with vias and right-angle bends are acceptable. A common approach is to create a net class or differential pair class that includes these nets, then create a routing rule that targets this class, as shown in the images below. I have no luck finding an asymmetric differential stripline impedance calculator online. 75 mm track on a 0. Differential Pair Routing. Differential pairs: even or common mode? PCB impedance calculator – Single ended / Differential pair. To use this calculator, simply input your microstrip geometry and Dk value, and the tool will return the differential impedance value for a pair of microstrip traces. Use an online differential microstrip impedance calculator. Differential Impedance ($$Z_{0_{diff}}$$): The impedance between the two lines with opposite polarity signals. Jan 31, 2016 #2 FvM Super Moderator. To use this calculator, simply input your microstrip geometry and Dk value, and the tool will return the differential impedance value for a pair of microstrip traces. Using a differential pair to avoid common mode noise is common in audio circuits. 006” spacing. The differential pair impedance depends on the characteristic impedance and the spacing between each end of the differential pair. If you use two of those and operate them differentially !!! then the characteristic impedance can be treated as a 100 Ohms differential impedance. 1-11. Make sure to follow below for efficient RS485. 1. Note: The 6-Layer board temporarily only provides JLC3313 Stackup. It can't be used with differential pairs, which are dominantly used with impedance-controlled high-speed signals;. W is calculated to achieve a trace impedance (Z0) of ~50W and S is calculated to achieve a differential trace impedance of 90W. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. Modeling approximation can be used to understand the impedance of the edge couple differential stripline transmission line. That option operates on a single trace. Just as important as determining an appropriate trace width for a single-ended trace is determination of an appropriate spacing between two traces in a differential pair. Length of both tracks should be the same. Differential pair routing. 15 mm spacing. , equal in magnitude but opposite in polarity). 0 and 0. g. Calculating the impedance . In the image below, I am comparing differential vias with merged. In case you need to calculate single ended or differential pair impedance on your PCB, try following links: I use Microstrip & Stripline calculator developed by Jean Nicolle. A cross-hatch plane is shown in the image below. If your differential pair has 100 ohm (differential) characteristic impedance, you should just design the uncoupled parts of the lines to have 50 ohm (single-ended) characteristic impedance. The most commonly used instrumentation. 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. . Going through Saturn PCB Calculator - which is free and useful software for engineers. Hello Community, iam currently designing a board that contains an 100MBit Ethernet connection. 5 and I took 3. 94 mil) is nominal thickness of 3313 prepreg. So, to calculate the differential impedance of Figure 1, simply calculate the impedance of Figure 3, and double it. 6mm spacing with a trace width of 0. In the case where you are routing differential pairs, then the potential between the two pairs will always be opposing (i. Dr J Alan Staniforth. The program used to calculate the impedances, assumes that, in manufacture, the. 2. Go to Route > click tune differential pair skew/phase > click on any of the track. ”7. 0 high-speed. Give it better GND connection if possible. Twisted pairs are used with balanced signals. The closer you place the pairs together, the differential impedance gets smaller because LM and CM get larger. Use 3. 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. The JLCPCB Impedance Calculator computes track width values and recommended stack-ups from user-input values of board layer, thickness, copper weight, target impedance, trace spacing (for edge-coupled pairs), and impedance trace to copper gap (coplanar waveguides). 5 mil wide traces with about 6 mils of gap between the traces. i know that i can use. 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. Differential Stripline Impedance Calculator. 5. 62 Ohms. Differential Protocol: Select the desired protocol from the dropdown list, this list will autofill the Target ZDiff edit box. The ratio of cross-hatch conductor width (HW) to cross-hatch pitch (HP) plays an important role while characterizing the cross-hatch plane. Inductance (L) = nH/ cm. These equations delineate between single-ended and double-ended lines, with the latter used in differential pair setups. Actually the "odd impedance" is the correct impedance to look at for the USB requirement of 90 Ohms differential impedance. > A good starting point is to ask you board house give you the widths and spacing for your stackup. 331 1 2 5. For an embedded (internal) microstrip, the formulas provided in paragraph 4. I see that Dielectric Constant is 4. Figure 8. How field solvers such as the Si8000/9000 calculate impedance. The vias on these differential pairs have their own impedance, which can create signal integrity problems on long interconnects. , the via is electrically short). 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. TransCalc is an open-source impedance calculator of various transmission lines based on common closed-form approximations. (Differential Impedance, Ohms) = Note: 1oz = 1. look at driving a twisted pair differentially from the FDA. 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. eu. For Si engineers & PCB technologists. Return loss Return loss is another way to look at impedance in the frequency domain. Instrumentation amplifiers are analog subsystems that amplify low-level signals in the presence of high common mode noise. The topology pre-dates the solid-state era and is generally attributed to Alan Blumlein, when it appeared in one of his patents in 1936. It incorporates many features that PCB designers and engineers are in regular need of like current capacity of a PCB trace, via current, differential pairs and much more. The closer you place the pairs together, the differential impedance gets smaller because LM and CM get larger. Typical values for most common differential signal types are 90 ohms differential, 100 ohms differential or 120 ohms differential. See moreThe Differential Pair Impedance Calculator simplifies the process of designing PCBs and high-speed communication systems, ensuring that signals are transmitted efficiently and. Altium Designer’s rules-driven design engine allows you to define trace length tolerances in differential pairs and across signal nets. 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. KiCad has a built-in impedance calculator! Inductance – the impedance calculator uses the Impedance value to calculate the inductance per unit length. The controlled impedance method applies to any trace that handles high-speed or high-frequency signals. Coupling can, however, be used to advantage in the form of differential impedance. The signal is 264MHz. Adding Impedance Rules Many differential pairs also require to be routed to a specific width to meet an impedance-based. Differential Termination Techniques - • Textbook Reading Assignments 1. This assumes ~0 trace thickness. Given the defaults (1. As you can see, calculating the twisted pair characteristic impedance by hand using Eq. This assumes ~0 trace thickness. Impedance Control. I am trying to design a USB circuit, where the signaling is over a differential pair D+ and D- and these two lines are required by the spec to have 90 ohms of differential impedance. Our impedance calculator features two main types of impedance models, single-ended and differential, within each trace structure. The Si8000m adds enhanced modelling to predict the finished impedance of multiple dielectric PCB builds and also takes into account the local variations in dielectric constant on close spaced differential structures. To achieve impedance control, PCB design software with an integrated field solver can help in designing the right trace width for the HDI layer stack-up. 2In real high speed signal pairs (like USB3) the pins are swappable to avoid the need to cross the traces. 0. This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). Testing and modelling characteristic impedance of differential pairs without ground. Because the traces are together on the same layer (plane) I'm not sure how "coplanar". 293, 50% of the copper removal can be achieved. For better impedance control, use PCB design software you can trust. Still, as you correctly analyzed it is much better to think of the individual lines in a differential pair as two length-matched single-ended lines, both with the half impedance. The ICD Stackup Planner calculates characteristic impedance plus edge coupled and broadside coupled differential impedance. In case I reduce the width and the distance of tracks to 0. Typical values for most common differential signal types are 90 ohms differential, 100 ohms differential or 120 ohms differential. Other calculators will use different. 0mm (4L-02) When using our free Defined layer buildup 4L-02, you will reach the desired impedances e. The example below shows how adjusting the stitching via placement could affect a differential via. The differential pair is all about balance. - 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. A web-based tool to calculate the impedance of your PCB traces and vias. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. PCB manufacturer normally provides information about PCB stackup and track geometry. Sorted by: 1. Incidentally, the trace thickness parameter does have a significant effect. 4 Comments. This sets the single-ended impedance AND differential impedance to the target value, even if there is no. These calculators ALL use wrong naming for "differential impedance". Technical Consultant Zach Peterson explores a viewer question surrounding Coplanar Routing, specifically how to route on a single-layer board. Ideally the traces in the differential pair only interact with each other, as another answer said. Voltage Divider Calculator 1 (Fixed) Voltage Divider Calculator 2 (Adjusteable) Capacitors. The Coplanar Differential Pair Impedance Calculator is a tool that helps you calculate the characteristic impedance of a coplanar waveguide (CPW). 1mm (3. The trace width (0. 3) to calculate trace width and. We’ll go over how differential pairs can hel. g. Stack Symmetry – enable to add layers in matching pairs, centered around the mid-dielectric layer. I tried using different line width (10mils,15mils,20mils,25mils,30mils) of the differential pair but it doesn’t help me. The even mode impedance is defined as the impedance measured by observing one line, while the other line is driven by an equivalent signal as the first. When the trace impedance is well-controlled, it indicates that it is constant along the whole PCB path. For a printed circuit board (PCB) this is a pair of traces, also known as a differential pair. It has been correlated many times. Enter your board parameters and get instant results. Common-mode impedance occurs with the pair driven in parallel from a. This means that the channel dimensions of both FETs must be the same and that R 1 must equal R 2. Download the file here. Impedance Calculation for PCB Designers - Altium. PCB Structures / Discrete Structures / Signal Management. Note that the driver output impedance may be configurable among various values. Just as. 03556mm. 94 mil) is nominal thickness of 3313 prepreg. Using the KiCad Impedance Calculator. PCB manufacturer normally provides information about PCB stackup and track geometry. Select the same nets to analyze and run the simulation. Then enter the values of the impedances as complex. Using the formula, you can calculate the Differential Impedance (Zd) as follows: Zd = 2 * 100 / sqrt (1 + (2 * 100 / 20)) Zd = 200 / sqrt (1 + 10) Zd = 200 / sqrt (11) Zd ≈ 60. In microstrip, this technique is ideal for routing differential pairs. The reason for this is that the input impedance is what matters, and the input impedance at the via transition will look like the trace impedance (i. Finally, all calculators provide theoretical impedance values as they cannot take in to account the variables and. Impedance examples 4 layers 1. In. e. The JLCPCB results are more reliable than (some of) the simple formula-based approaches. $egingroup$ @Bryce, whether the individual line's impedance is half the differential impedance depends on whether the pair is "strongly coupled" or "weakly coupled". They will give very similar answers. The via transitions start to really matter above 5 GHz. Microstrip construction consists of a differential pair and a single reference layer (typically ground). That means each trace would be a 50-ohm trace, if there were no coupling between the traces. INPUT DATA. Note that the y. on layer 3 from the top, between power and ground plane. In microstrip, this technique is ideal for routing differential pairs. The impedance calculators below are completely free to access and use. 11. Only a 2D field solver can accurately calculate the differential impedance. The even mode impedance is simply the impedance of a single line when the two lines are driven. High speed PCBs and signaling standards almost entirely use differential pairs with precise impedance. 4mils = 0. This will create the differential pair. So, strive to keep your traces short and far apart in high-speed design. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. Use 3. When dealing with differential pairs, thi. To make an effect transmission line with two wires it is best to create a twisted pair. For differential pairs, this meant that there was a differential pair impedance requirement, or rather an odd-mode impedance requirement. You can make your own spread sheet using formulas provided by Wedell's book "Transmission Line Design Handbook" page 196, 197, 198 (attached)Relative dielectric constant (er) mm. The 9-hole score differential allows golfers to maintain an up-to-date handicap index even when they only play a short. This video will cover how to create, setup rules, and route differential pairs. Parallel Wire Impedance (Zo) = Ohms. 75 inches without impedance control; Keep the differential pair length mismatch within 0. Twisted Pair Impedance Calculator . Ensure optimal signal integrity in high-speed communication systems with our Differential Pair Impedance Calculator. Spacing and width value pairs that will give a differential impedance of 100 Ohms on Dk = 4. The stackup design is very crucial for the manufacturing of a controlled impedance PCB. How to Use the Calculator. The board house achieves these tolerances by observing how their process affects impedance.