GEGCalculators. Ask the board manufacturer for the values. ’. 1,235. There are a lot of online trace impedance calculators specifically designed for differential traces. H 1 (Dielectric thickness) : mm mils. Single Ended Impedance Ω. 75 inches without impedance control; Keep the differential pair length mismatch within 0. I see that Dielectric Constant is 4. which is the characteristic impedance of the system. The trace width is important as it determines the single-ended and differential impedance, capacitance, and inductance. Broadside-coupled Asymmetric Stripline. 01) and dielectric constant (3. Mutual inductance and capacitance exist between the two traces in a differential pair. Given the defaults (1. The differential impedance is measured across the two lines with the pair driven differentially. Impedance captures the real. Ohm’s Law provides the framework for solving network analysis problems; when the curtain gets pulled back, Ohm’s Law updates to become the relationship between voltage, current, and impedance, not resistance. Zo (diff) is calculated to be 244 ohms, so dividing by two yields a value of 122 ohms for the semi-coplanar structure. Advertise with us;. 3 shall be used. Board Setup. Differential impedance changes with coupling, which changes with trace separation. With both wires at the same potential there is no capacitance between them so the reference plane (return path) is less clear. 5. GDCPW is known for its balanced configuration, which helps reduce common-mode noise and interference in high-frequency signal. Learn the limitations and advantages of this tool and how to use a field solver for more accurate results. 1. where g m can be calculated as follows:The differential impedance depends upon the D/H ratio. Create a new impedance profile, then select Single-Coplanar or Differential-Coplanar from the Impedance Profile Type drop-down list. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. 35,851. Also, I tried the differential tools in KiCad, and I matched both pairs to the same length (otherwise, one track is about 6 mm longer). The stripline impedance calculator provided below is useful for gaining an initial estimate of trace impedance for striplines. The characteristic impedance is given by: Eq. 9. Doing this results in a gain change. 25mm between the differential pair with a width of 0. 68 mils. This is an approximate critical ratio. The surface finish is neglected. If the width of the trace is two times the height of the dielectric (for FR4, Dk from 4 to 4. Figure 4. Figure 4. 6mm spacing with a trace width of 0. When selecting trace geometry, priority should be given to matching the differential impedance over the single ended impedance. Power. Differential impedance is defined as impedance between the two lines when the line pair is driven differentially. The bottom line is: check with your fabricator when planning a 4-layer PCB stackup with 50 Ohm impedance. There are four types of impedance used in. 1. Coplanar Wave Guides 5. Impedance Calculation 5. Enter the values of Z0 and Zc into their respective input fields. Or we can input them within the RLC circuit calculator all at once and quickly get what we need without relying. 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. Figure 2. Consider Q 1 and Q 2 as current sources controlled by their base voltages. Trophy points. This is to avoid unwanted data signal reflections. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. Capacitance (C) = pF/ cm. I used some online calculator to calculate parameters of trace so it has 50 Ohm impedance. Click the “Calculate Differential Impedance” button. This calculator will convert voltage or power gains into decibels. 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). Table 1. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. Routing Diff Pairs with a Differential Line Impedance Calculator for Optimal Signal Transmission Twisted pair: \qquad \footnotesize \text {Impedance} = \frac {120 \times \ln (2s/d)} {\sqrt {\varepsilon_r}} Impedance = εr120 × ln(2s/d) As you can see, it is not overly complicated to calculate by hand, but it will definitely take longer than using our calculator. When it comes to the equations, you simply need to use the following: W = frac {A} {1. . may be positive (inductive) orFor instance, when IB I B = 40 uA, I estimate that a collector current range of 8 mA to 8. The Coplanar Differential Pair Impedance Calculator is a tool that helps you calculate the characteristic impedance of a coplanar waveguide (CPW). t. and thats the first time iam doing ethernet things. I used the KiCAD PCB calculator, asked the PCB manufacturer about the tangent loss (0. For R D, the value of 25 Ω is inserted, which is the differential output impedance of a typical NFC IC with respect to the ground signal. Multiply the result by the square root of the ratio of (1 + (2 * h / w)) to (1 – (2 * h / w)). The user only needs to enter the attenuation in decibels (dB) and the given characteristic impedance of the transmission lines to be matched. ”7. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). The PCB designer must ensure that its characteristic impedance has the desired value. L is the inductance in henries (H), and . PCB Structures / Discrete Structures / Signal Management. This impedance profile shows how differential impedance can stay flat over frequency while common-mode impedance can vary. Saturn to Allegro differ more than 10%, which would result in huge trace width and spacing. Twisted pairs are used with balanced signals. Asymmetric Stripline. 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. Differential Impedance Differential Impedance: the impedance the difference signal sees ( ) ( ) 2 2( ) Z 0 small I V I V diff Z diff one one = = ≈ − Differential impedance decreases as coupling increases +1v -1v I one x I two How will the capacitance matrix elements be affected by spacing? C 12 C 11 C 22 Eric Bogatin 2000 Slide -18. A Pi Attenuator uses a single series resistor, and two shunts to ground (input and output) to attenuate a signal. 0; 1 < ε r < 15 ) Select the units for all dimensions: mm mils. Overview. Rebalance the amplifier gain paths, by adding R. You can build an RC low-pass filter with a cutoff frequency of 1 kHz using a 3. Their hardware design guideline said the traces between the USB and the termination resistors should have a differential impedance of 90 ohms. 3. (Differential Impedance, Ohms) = Note: 1oz = 1. Thus a "differential pair" any long distance apart will have an impedance of 98 ohms, without any coupling between the lines, i. W is the Width of the stripline. Suggested Solution: for 100 Ohm Differential, use half the board thickness and make the tracks equal to the board thickness. Simultaneous Switching Noise Guidelines. 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. Asymmetric Stripline Impedance Calculator. The Impedance Calculator is a tool which allows a quick pre-layout estimation of several kinds of line impedances between different layers. 77 mm gave me a differential impedance very close to 90 Ω. This means the slope resistance is 7 V 0. Figure 25. Parallel Wire Impedance (Zo) = Ohms. Embedded Microstrip. Power Divider Calculator. The intermediary nodes that attach to the main network bus should be short in order NOT to disrupt the end-to-end characteristic impedance of the main network bus cable. When designing the trace configuration for your differential pairs, you are typically targeting 100 ohms differential. Matching Differential Impedances. Now you're done with your resistors! The values should be R₁ = 76. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. JX. Even mode impedance is less clear to me. Track Thickness: mm. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. I tried to use the tool “PCB calculator” to determine the size of mi USB tracks. ; Er is the relative permittivity (dielectric constant) of the substrate material. Even mode impedance for commonly-driven transmission lines . Each transmission line has a Capacitance per unit length, inductance per unit length and resistance per unit length. Learn how to use a differential impedance calculator to design your PCB for high-speed digital data transfer. This calculator is designed to calculate the characteristic impedance of a symmetric stripline - a flat conductor between two ground planes whose distance between the conductor and the planes is the same for both reference planes. 08mm - this is the border of manufacturability, I don't think it is practical to go there but for the calculation it is just fun - and I get some 31Ohms. The impedance of a differential via pair cannot be treated with a single via impedance calculator unless the vias are spaced far apart. To improve calculation speeds, impedance profiles are calculated in separate threads (when available). where. Differential Impedance The impedance measured between the two lines when they are driven with opposite polarity signals. The grounded differential coplanar wave guide is the differential version of the grounded coplanar wave guide and is used in high-speed digital systems that require maximum noise immunity. In differential pairs, each trace in the pair carries the same magnitude, but opposite polarity. In addition, the termination resistor value used should take into account the input impedance of the amplifier circuit. For coupled surface microstrip, Wadell[1] gives 7 pages of equations to evaluate the impedance. Here is a plot with V IN1 and the differential output voltage: Here we have an output amplitude of 10 mV and an input amplitude of 1 mV; hence, our simulated differential gain is 10. The differential signals have a differential characteristic impedance. Multiple Differential Pairs Insert multiple Differential Pair definitions per layer. However, convention and some literature quote return loss as a negative value akin to an S (1,1) measurement on a Network. In stripline specifically, the trace width (w), the trace thickness (t), the distance between ground plates (b), and the relative permittivity (better known as DK). The op-amp calculator will display the voltage gain of the op-amp, e. November 14, 2022. 8 Ω. The calculation looks correct, but the tracks are too wide. 48 e-0. A calculator for computing the impedance of an edge coupled stripline. The process for impedance matching in high speed PCB designs depends on the signaling standard, supply voltage levels, and signal levels. This is an iterative process that repeatedly adjusts the via dimensions and runs EM simulations until achieving the desired impedance and bandwidth. The values L 0 and C 0 must be substituted into equation (11) to calculate the complex filter impedance. 4mils = 0. Just enter the given values for trace thickness, substrate heights, trace width, and substrate dielectric. 3 kΩ × 47 nF) = 1. Choose from different surface finishes,. 1< W/H < 3. 3mm, as shown below: This increases the impedance slightly to 91. Unfortunately Online Calculators are deceiving unless you actually draw the numbers and understand the ratios and tolerance effects. Surface microstrip lines are formed by etching one surface of a double-sided material. It also explains the factors that affect the impedance, such as trace width, dielectric constant, and frequency. 2. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. When i put "Factory" cable dimensions in calculator i don"t come close to 90 ohms. This will be increased if you have plated through vias, so you might want to calculate with a thickness of 2. If a. Saturn PCB - Toolkit for Impedance Calculation. Another example of using large distances to separate out unwanted components might be to calculate the impedance of a. t. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. Figure 3. Example. An FDA with equal-value resistors in each output to provide differential output termination is shown in Figure 1. The T match circuit gets its name because the circuit topology looks like the letter “T”. It consists of a pair of center conductors separated by ground planes on the same substrate. Relative dielectric constant (er) mm. Differential Impedance Calculator. The drawing below is a 3D electromagnetic model of stripline with perfect electrical conductors encasing all four sides along the z and y axes (created using Ansoft's. Differential Microstrip Impedance Formula or Equation. KiCad 5. p = (Zi - Zo) / (Zi + Zo) Let us consider the case Zi = Zo. Relative Dielectric Constant ( εr ): Track Width. 29 mm width traces to obtain 100 Ohms ZDiff while using 0. Differential impedance values are normally specified for impedance matching of differential pairs, rather than odd mode impedance. Learn how to design. 2. Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. 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. Differential Impedance Calculator - Stripline. The conductor and ground planes are separated with a dielectric. The differential impedance will be a bit less than 2x the single-ended impedance. This will leave the rest of the signals which are rather non-critical like I2C, power good signals, etc. These radio frequency calculators help with unit conversion, attenuator design, antenna design, radars, and various other basic calculators. 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 . 5) and 1. f c = 1 / (2π × 3. 8. 6 ohms and Z even = 110 ohms for your geometry, very close to your result. The cloder the two traces, the smaller is the differential impedance. This will also provide the time delay the cable provides for a signal and also the capacitance and inductance per. What is the characteristic impedance of twisted pair cables? 100 ohms. Re: Calculating Differential Impedance for USB Differential Pair. Following is the formula for differential impedance for a Stripline. Microstrip. So move to your left, use Omni's Cable impedance calculator and enjoy. Differential impedance: 90 ohms (tolerance: +/- 15%) On a typical 1. Use several of them and compare. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. There are a lot of online trace impedance calculators specifically designed for differential traces. Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. (Differential Impedance, Ohms) = Note: 1oz = 1. 0 and (t/h) less than 0. ω = 2πf is the angular frequency in rad/s,. Calculating the Differential impedance is a two-step process, first Calculate the single ended impedance Zo and then use this value to calculate the differential impedance. The ground plane helps keep the EMI localized and the trace impedance continuous. We want to follow the specification, selecting components and routing. Using this calculator, I found 100 Ohms by giving 9 mils of track width, 5 mils of track separation, 8 mils of dielectric (prepregs usually have a dielectric constant of 3. An example of a wire microstrip might most often be found in prototypes or reworked boards where a wire is used over the top of pcb or copper clad material. This 50% margin is to ensure some noise immunity. e. It uses the lan9512 reference schematic. I agree. Differential Impedance Differential Impedance: the impedance the difference signal sees ( ) ( ) 2 2( ) Z 0 small I V I V diff Z diff one one = = ≈ − Differential impedance decreases as coupling increases +1v -1v I one x I two How will the capacitance matrix elements be affected by spacing? C 12 C 11 C 22 Eric Bogatin 2000 Slide -18. Use several of them and compare. 7. 3. The Calculator Calculates the values of the Characteristic Impedance, Capacitance per unit length and propogation speed. The stripline impedance calculator provided below is useful for gaining an initial estimate of trace impedance for striplines. 4 Comments. 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. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. Some of them include Microstrip, Stripline and Coplanar Waveguide. It is widely used for data communications and telecommunications applications in structured cabling systems. The calculator will process the values and display the calculated Differential Impedance (Zd) in Ohms in the designated input field. There are a lot of online trace impedance calculators specifically designed for differential traces. To use this tool, enter the values for. Let’s illustrate how to calculate the impedance of a stripline using our calculator: Suppose you have the following parameters: εr = 4. We care about maintaining the same differential impedance for the same reason we. A variant of coplanar waveguide is formed when a ground plane is provided on the opposite side of the dielectric, which is called finite ground-plane coplanar waveguide (FGCPW), or more simply, grounded coplanar waveguide (GCPW). Also, be aware, 90 ohms is the differential impedance, the characteristic or single ended impedance will be more than half (ie. This calculator is designed to calculate the characteristic impedance of a microstrip - a flat conductor suspended over a ground plane with a dielectric between them (see diagram below). Email: [email protected] mil (0. There should be a solid ground in the layer underneath the trace. Impedance Control. Finally, calculate and adjust the feedback resistor for the correct gain. e. εr is the Relative Permittivity. The PCB internal/external trace resistance shall be calculated according to the following formula: R = (ρ * L / (T * W)) * (1 + α * (TAMB – 25 °C)) Where: R is the trace resistance [Ω] ρ is the resistivity parameter, whose value for copper is 1. This calculator is designed to calculate the characteristic impedance of an embedded microstrip - a flat conductor suspended over a ground plane with a dielectric between it and another dielectric material above the conductor (see diagram below). GDCPW is known for its balanced configuration, which helps reduce common-mode noise and interference in high. 2. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). Differential impedance at low frequency represents the sum of inductance resistances of the filter. Differential pair on a reference plane for differential mode (left picture) and common mode (right picture) line impedance In addition to the four line impedance types the Impedance Calculator is also able to calculate the Coupling Factor between two traces on either the same signal layer (horizontal coupling) or between two traces on different. 0. 6mm FR4 PCB with 7628 type stackup (4 layers), the above specifications usually result in 4. ; We can use each of these parameters separately in each equation to find the resonant frequency, the Q-factor, and the damping ratio. I checked out TNT, but couldn't seem to be able to do the same with that either. The equations quoted below are from Reference 1, and are offered here as a starting point for a design, subject to further analysis, testing and design verification. Edge-coupled Asymmetric Stripline. The closer you place the pairs together, the differential impedance gets smaller because LM and CM get larger. 3. Such a microstrip is constructed with two traces referenced to the same reference plane with a dielectric material between them. As discussed previously, the lengths of the two lines in the pair must be the same length. In case I reduce the width and the distance of tracks to 0. These impedance values thus determined can be. There are four different types of impedance used in characterizing differential trace impedances. Based on Zo Equation Per: IPC-D-317A:. There is also a dielectric material placed above the conductor. *Strictly, a loss quantity when expressed in dB should be positive. width|space|width. Twisted pairs are used with balanced signals. Distance units: Substrate Height, H Trace Width, W Thickness, TChapter 3: Capacitors, Inductors, and Complex Impedance - 21 - To study a constant supply voltage on an RC circuit, we set the left side of equation 3. You can calculate it with the following equation: Z (z) = V (z)/I (z). The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. Or the odd mode impedance is half of the differential impedance. Impedance (Ω): The desired impedance. Reaction score. 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. , 10. Figure 1. If you like this tutorial, you may like to buy the book . Choose a calculator to tune your PCB design. 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. The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. 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. All calculations use a frequency of 1 GHz. If you select non-inverting op-amp, the calculator will show 11. 4 Differential Line and Coplanar Strip; 3. The characteristic impedance is given by: Eq. This assumes ~0 trace thickness. In the limit of a very long transmission line (such as when the line length is many multiples of the wavelength), then the tanh function eventually converges to 1. T represents trace thickness. So, I presume, that means the input resistance is simply the resistor on the inverting node. Dielectric Thickness: mm. Enter the values of Z0 and Zc into their respective input fields. In the ZL box, type 50 Ω. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. 3 Answers. This passive filter calculator has you pick your composition (RC – Resistance/Capacitive, RL – Resistance/Inductance, or LC – Inductance/Capacitive) and enter your values to calculate the cutoff/-3dB frequency. Before, working with a trace impedance calculator, one should be aware of which equations the calculation uses. net Forum comes closest to the proper track width. Z diff = 2* Z o (1 - 0. 1. For this calculation, the units of d and h can be ignored as long as they have the same unit. Coplanar Waveguide With Ground Characteristic Impedance Calculator. In tab “TransLine” i chose “Coupled Microstrip Line” and i can calculate the impedance of only one track. To find the impedance of a capacitor (Zc) and an inductor (Zl) in an AC circuit, you use the following formulas: For the capacitor: Zc = 1 / (2πfC) For the inductor: Zl = 2πfL Where f is the frequency, C is the capacitance, and L is the inductance. Typical values for most common differential signal types are 90 ohms differential, 100 ohms differential or 120 ohms differential. If driven from a transformer or other floating source the differential impedance of 50kohm makes sense. With this combination of powerful impedance modeling you can quickly determine the manufacturing variations for each of your designs and model resin-rich areas between differential traces to achieve the highest yields from yourThe characteristic impedance Z 0, or the load impedance Z L, can be calculated with the value of ρ. If your structure has two microstrip feed lines, you can extract even and odd modes by creating weak coupling between main resonator and feed lines. Series Equivalent Differential Impedance (SEDZ) Model Details The SEDZ format schematic is represented by Figure 55. Figure 1 New techniques for pc-board-layer-interconnect design provide predictable path impedance and improved signal integrity. 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 . Here are some tips for measuring differential impedance. If there is an insulator around the wire then this. Twisted Pair Impedance (Transmission Line) Calculator. 2. 5x would be best, but 2x is acceptable. 4mils = 0. Try TNT or TxLine. 01 Mar 1998. Following is the formula for differential impedance for a Microstrip. Microstrip Impedance Calculator. 3 shall be used. R is the resistance in ohms (Ω),. 96s/h )The Microstrip Differential Impedance Calculator simplifies the process of determining the differential impedance of a microstrip transmission line. You can interpret the name 'RLC circuit' to mean. This PDF document provides a comprehensive guide on how to calculate the impedance of various PCB structures, such as microstrip, stripline, and differential pairs. Use several of them and compare. I checked out TNT, but couldn't seem to be able to do the same with that either. The characteristic impedance is generally defined to. 3 CPW Structures; 3. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. So, I am trying to figure out how to use Kicad’s PCB Calculator for “Coupled Microstrip Lines”:A Grounded Differential Coplanar Waveguide (GDCPW) is a transmission line structure used in RF and microwave circuits. Enter the values of trace width (w), trace thickness (t), trace dielectric thickness (h), overall dielectric thickness (h1), and the dielectric constant (er). Thinking about the problem as the impedance the differential signal sees (the thing we care about) compared to the impedance the common mode signal sees (the part of the signal we typically try to eliminate in a difference amplifier) is probably more appropriate for most practical signals, and gives us a nice simple expression. Integrated differential impedance deviations; By “integrated,” we mean that the particular aspect of signal integrity applies throughout the relevant matching frequency range. Pasternack PCB Microstrip Calculator is an online calculation tool that lets you compute a microstrip's height/width ratio, impedance and relative dielectric constant for a microstrip transmission line. Facebook. Quarter Wave Transformer Impedance Calculator. Differential-mode (DM) noise current flows in power lines with opposite directions 2. 3. 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. WhatsApp. in series with the inverting input gain resistor. 1. pairs. The iCD Stackup Planner offers unprecedented simulation speed, ease of use and industry leading impedance accuracy at an affordable. With hundreds of coaxial RF cables in-stock and ready to ship worldwide immediately, our coax capacitance calculator lets you calculate the impedance of a coax by allowing you to enter the outer diameter dielectric width and inner conductor diameter. The edge couple differential microstrip transmission line is a common technique for routing differential traces. Quartz Crystal Parameter Calculator. The differential via design shown in Figure 2 was built. 17mm FR408 - 17um. PCB Impedance and Capacitance Calculator: Asymmetric Stripline. Often when working with wires it is easy to create large return path loops if one is not paying close attention. Track and gap widths are of concern in controlled impedance, but unless your speaker and mic connections (I assume audio frequencies) are going a long way you should not have any particular requirement for controlled impedance. The impedance between one differential trace and the ground. Notes: 1) Calculation assumes traces are centered vertically. You can see. It helps you practice by showing you the full working (step by step differentiation). T. Relative Dielectric Constant ( εr ): Track Width: mm. Open the PCB layout tool (pcbnew) and go to File > Board Setup. Impedance in your traces becomes a critical parameter to consider during stackup. Instead, field solvers normally focus on impedance and calculating the current distribution around the trace. $endgroup$ – The Photon. , equal in magnitude but opposite in polarity). It works in parallel with the standard PCBS layer stackup manager and gets the default setting from it. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. Note that Zdiff (differential impedance) is equal to 2 * Zodd, so a Zodd of 45 Ω gives us a Zdiff of 90 Ω. Hi, I am working on my board Stack-up to tune Single/Differential impedances of my board in Allegro PCB 16. It consists of a pair of center conductors separated by ground planes on the same substrate.