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. The guides says spacing under 0. 50 - 55 ohms). Differential Stripline Impedance Calculator. Surface microstrip lines are formed by etching one surface of a double-sided material. Visit to learn more about our other electrical engineering tools and resources. Supports Anritsu ShockLine™ MS46524B and VectorStar™ MS4647B. where L is the inductance per meter and C is the capacitance per meter. This 26 mil clearance between copper pour and the 13 mil trace is sufficient to ensure 50 Ohm impedance. I checked out TNT, but couldn't seem to be able to do the same with that either. Both LM and CM converge to zero as spacing goes to infinity. There are four different types of impedance used in characterizing differential trace impedances. This calculator will convert voltage or power gains into decibels. Depending on the configuration of the components you can construct a low pass or high pass filter. Multiply the result by the square root of the ratio of (1 + (2 * h / w)) to (1 – (2 * h / w)). 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. 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. Twisted pairs are used with balanced signals. By understanding the microstrip transmission line, designers can. s. Differential Impedance is the impedance between two differential pair signal traces. For these reasons, it is difficult to calculate optimum component values for a fully differential amplifier design whose input is single ended and terminated . Email. 8 substrates of various thicknesses. The top surface and the sides of the traces are exposed to air and are referenced to a power or ground plane. If the return path of a single wire is freespace then the impedance is quite high. Check here: UltraCAD's new Differential Impedance calculator will calculate single-ended and differential impedance for the common configurations we all deal with: Microstrip. For a single-ended differential amplifier, the gain is. 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. Input Impedance of Differential Vias. I use FR-4, so H=1. Turning over to the digital logic side of things, our favorite way to spew ones and zeros is to calculate the difference between two matching lines rather than trying to read a single line that is subject to momentary instances of noise as a voltage spikes across the landscape. INPUT DATA. Broadband Impedance Matching with Transformer; Ferrite Toroidal Coil (Amidon) Helical Coil Calculator; Impedance Calculator : XL, XC; Iron Powder Toroidal Coil (Amidon)Where: Z is the characteristic impedance of the stripline (in ohms). Differential input impedance is the ratio between the change in voltage between V1 and V2 to the change in current. This is to avoid unwanted data signal reflections. WhatsApp. For example, if you wish to input "25000000", just type "25M" instead. 1. Going to route the following signals: 100R differential pair (Zo = 50R) 90R differential pair (Zo = 45R) Planning to use the stack up JLC7628, with a 4 layer PCB, in total 1. When i put "Factory" cable dimensions in calculator i don"t come close to 90 ohms. The calculator will process the values and display the calculated Differential Impedance (Zd) in Ohms in the designated input field. This is an iterative process that repeatedly adjusts the via dimensions and runs EM simulations until achieving the desired impedance and bandwidth. 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. 9 Ohms). Differential impedance is the ratio of voltage to current on a pair of transmission lines when driven in the differential mode (one signal positive and the other negative). Spacing and width value pairs that will give a differential impedance of 100 Ohms on Dk = 4. Use several of them and compare. This calculator is designed to calculate the characteristic impedance of an edge coupled stripline. You can calculate it with the following equation: Z (z) = V (z)/I (z). 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. A coaxial cable is designed with 50-Ω or 75-Ω characteristic impedance. The range of accepted values is 20 to 90 Ω for single-ended and 50 to 150 Ω for differential signals. Z diff equals Ra||(2Rb) (p model) or 2R 1 (T model). All About Circuits is the largest online electrical engineering communities in the world with over 700K engineers, who collaborate every day to innovate, design, and create. The characteristic impedance is given by: Eq. 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). so i have had a look at a App-Note of the PHY chip: it. Keep the spacing between the pair consistent. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. 6mm thick. Using a differential pair to avoid common mode noise is common in audio circuits. This value is often given the name “differential impedance. (Differential Impedance, Ohms) = Note: 1oz = 1. and 31. This 50% margin is to ensure some noise immunity. 0. PCB Structures / Discrete Structures / Signal Management. 2. Common-mode impedance occurs with the pair driven in parallel from a common-source. Both differential and common mode impedances have been measured against frequencies up to 1 GHz, as shown in figure 4 below. Relative dielectric constant (er) mm. Classes for 50 and 100-ohm traces. Sorted by: 1. 1. εeff is the calculated effective dielectric constant of the microstrip line due to the nonhomogeneous nature of the structure (i. Ground. differential impedance data (Tables or Graphs) is very important when hand calculating (calculator) impedance matching options. The impedance calculator can also update the PCBS stackup with the current setup. Another example of using large distances to separate out unwanted components might be to calculate the impedance of a. Create a new impedance profile, then select Single-Coplanar or Differential-Coplanar from the Impedance Profile Type drop-down list. We care about maintaining the same differential impedance for the same reason we. However, due to manufacturing techniques and tolerances, the two tracks may have different cross-sections — the unbalanced track case. Differential. 3mm of the microcontroller), therefore i rounded the width to 0. Radio Frequency Engineering Calculator. Equation 9 For high gain, the CMRR of the 2-op amp instru mentation amplifier is similar to the CMRR of the differential amplifier. It works in parallel with the standard PCBS layer stackup manager and gets the default setting from it. IPC 2141 Trace Impedance Calculator. 96D/H). This is an iterative process that repeatedly adjusts the via dimensions and runs EM simulations until achieving the desired impedance and bandwidth. 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 . THESE FORMULAS ARE. View All Tools The edge coupled differential microstrip transmission line is a common technique for routing differential traces. Although widely applied to coaxial cables against EMI susceptibility problems, the Zt parameter can be easily extended to coaxial cables EMI emissions. Speedstack Si – Insertion loss & impedance PCB stackup design including Si9000e. The JLCPCB results are more reliable than (some of) the simple formula-based approaches. A typical 4 Layer Stackup looks as follows. There are a lot of online trace impedance calculators specifically designed for differential traces. Z LC is the LC circuit impedance in ohms (Ω),. φ is the phase difference between the total voltage V T and the total current I T in degrees (°). this type of termination. This will also provide the time delay the cable provides for a signal and also the capacitance and inductance per. H1. , 10. g. The INA134 has 25kohm resistors for the network and the datasheet specifies 50kohm for both common-mode and differential input resistances. Edit: also, think ahead if you are going to use ground pours around the traces. Differential impedance is defined as impedance between the two lines when the line pair is driven differentially. 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. Where: Y is the electrical admittance. Consider Q 1 and Q 2 as current sources controlled by their base voltages. f is the frequency in hertz (Hz), . 7, if that is what you were doing. Our pi attenuator calculator is designed to aid you in calculating the correct values of the resistors R1 and R2, according to the diagram below. Power Filtering/Distribution x. Also, intuitively, from an examination of the field pattern, the even mode impedance Z 0e is likely to be high because the. While commonly constructed using printed circuit boards, this structure can also be built using other materials as long as there is a conductor separated from. 75 mA 7 V 0. 3 V, etc. The Differential microstrip impedance calculator is used to compute the differential (Zd) and single-ended impedance (Zo) of an edge-coupled microstrip line just by entering the width, separation and thickness of the trace along with the dielectric thickness and constant of the coupled line. f is the frequency in hertz (Hz), . 9D/B) Zo = Single Ended impedance. Figure 4. The tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. The values L 0 and C 0 must be substituted into equation (11) to calculate the complex filter impedance. Because the lines are symmetrical, the. The calculator is available in the Electrical Domain in Constraint Manager, from theI'm designing a custom PCB around the Raspberry Pi RP2040 MCU. Reference layer. The iCD Stackup Planner offers unprecedented simulation speed, ease of use and industry leading impedance accuracy at an affordable. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. Impedance in your traces becomes a critical parameter to consider during stackup. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. Most often, the only specified requirement of a differential pair is its differential impedance. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. There are four different types of impedance used in characterizing differential trace impedances. I am routing differential pairs in Altium 20 and using controlled impedance profiles. 8 mm; W = 2 mm; Plug these values into the. The trace width is important as it determines the single-ended and differential impedance, capacitance, and inductance. Is this a good practice for Ethernet? This is a capture of the PCB right now: This is the schematic that I am using. 9. L is the inductance in henries (H),. The stripline impedance calculator provided below is useful for gaining an initial estimate of trace impedance for striplines. Creating and Configuring an Impedance Profile. 100 Ohm diferential impedance microstrip PCB traces geometries in. You will need to know the thickness of the dielectric you will be using as well as the relative permittivity (dielectric constant). characteristic impedance, signal speed, crosstalk and differential impedance. Capacitance (C) = pF/ cm. Before i start to make my new one with bare wire I started with impedance calculation. In addition, the termination resistor value used should take into account the input impedance of the amplifier circuit. A 3-D EM simulator is used to design a differential via with the desired impedance and bandwidth. ’. The differential via design shown in Figure 2 was built and tested. Differential impedance at low frequency represents the sum of inductance resistances of the filter. H is the Height of the stripline. The differential impedance is defined as the. 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. 6 inches - this is very easy to do; If you can access a differential impedance calculator, then use. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. Edit: also, think ahead if you are going to use ground pours around the traces. 3. The impedance of the surface microstrip shown is 50 ohms, so the impedance of the broadside coupled differential pair will be twice 50. Integrated differential impedance deviations; By “integrated,” we mean that the particular aspect of signal integrity applies throughout the relevant matching frequency range. 1. Just enter the given values for trace thickness, substrate heights, trace width, and substrate dielectric. Suppose we have a system with the following parameters: R= 30 Ω;; L = 10 mH; and; C = 100 μF. As also noted in the picture, the subsequent calculations are on the: [2] top-layer single-end impedance; [3] top-layer differential impedance; [4] inner-layer differential impedance. Example. Overview. To improve calculation speeds, impedance profiles are calculated in separate threads (when available). 48 e -0. The Twisted Pair Impedance Calculator is able to compute the characteristic impedance Z 0(twisted pair) based on the dimensions of the twisted-pair cable. So, to calculate the differential impedance of Figure 1, simply calculate the impedance of Figure 3, and double it. The op-amp calculator will display the voltage gain of the op-amp, e. 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. ) and the LOW level is defined as zero. You could assist/improve the noise immunity by heavily loading the. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. Signal layer. Also differential pairs. Relative Dielectric Constant ( εr ): Track Width: mm. This, by definition, gives a target of an odd mode impedance of 45 Ohms and an even mode of 60 Ohms. Then calculate R T for impedance matching and the value of the R2 for differential balance. Polar or rectangular grids only allow direct reading of S11. SAVE & ACCEPT. For instance, I want a 100 Ω controlled impedance pair, and have used "differential" before which seemed to work fine. The two most common impedances. We want to follow the specification, selecting components and routing traces at the correct. We get a lot of questions about trace impedance and how to calculate the right trace size to hit a specific impedance in a manufacturable PCB. The user only needs to enter the attenuation in decibels (dB) and the given characteristic impedance of the transmission lines to be matched. If you select non-inverting op-amp, the calculator will show 11. Figure 5. 0 and (t/h) less than 0. It uses the lan9512 reference schematic. It is only equal to double the characteristic impedance in certain cases. The PCB designer must ensure that its characteristic impedance has the desired value. Acknowledgements: The source for formulas used in this calculator (except where otherwise noted) is the Design Guide for Electronic Packaging Utilizing High-Speed Techniques (4th Working Draft, IPC-2251, February 2001. 254mm. 77 mm gave me a differential impedance very close to 90 Ω. The microstrip impedance represents the characteristic impedance of the microstrip line, which is the uniform impedance provided by the uniform cross-sectional dimensions along the microstrip (flat copper conductor) length; to prevent signal reflection. Finally, all calculators provide theoretical impedance values as they cannot take in to account the variables. I used the KiCAD PCB calculator, asked the PCB manufacturer about the tangent loss (0. First, calculate the amplifier input impedance R. The calculation looks correct, but the tracks are too wide. 3. Units do not matter as long as they are consistent. When designing the trace configuration for your differential pairs, you are typically targeting 100 ohms differential. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. Rewrote the PDN Impedance calculator, old formula was too confusing. Telegram. 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. This impedance profile shows how differential impedance can stay flat over frequency while common-mode impedance can vary. Zo (diff) is calculated to be 244 ohms, so dividing by two yields a value of 122 ohms for the semi-coplanar structure. JLCPCB Impedance Calculator. This PDF document provides a comprehensive guide on how to calculate the impedance of various PCB structures, such as microstrip, stripline, and differential pairs. This will leave the rest of the signals which are rather non-critical like I2C, power good signals, etc. Using an online differential impedance calculator, the height of the dielectric layer, h, is needed. 03) it gives me almost 160 Ohm - and even if use 53mil conductor height or. Then we have a simple homogeneous differential equation with the simple solution for the current of a decaying exponential, I I e /(t RC) 0The iCD Design Integrity software incorporates the iCD Stackup Planner, iCD PDN Planner, iCD CPW Planner and SmartSolver software plus a myriad of functionality specifically developed for high-speed PCB design. 1. 5mil clearance on a 63 mil board (1. 6 inches - this is very easy to do; If you can access a differential impedance calculator, then use differential. H 1 (Dielectric thickness) : mm mils. PCB samples, finding that predicted accuracy varies according to target impedance. I found that a W of 0. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. STEVE: High speed systems today face many simultaneous impedance requirements that must be achieved in the same stack-up – differential impedances at 100 ohms for ethernet, USB at 90 ohms, PCIe at 85 ohms, and a myriad of single-ended DDR requirements. 2. Enter the values of Z0 and Zc into their respective input fields. 6mm spacing with a trace width of 0. Note that Zdiff (differential impedance) is equal to 2 * Zodd, so a Zodd of 45 Ω gives us a Zdiff of 90 Ω. This tool will help you create a matching circuit so that optimal power transfer occurs between unmatched loads. 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. The required inputs are the Dk value for the dielectric constant of the PCB substrate, and the. 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. You can calculate the capacitance and inductance formed by one ground via and the signal via with simple formulas (Reference 1). INPUT DATA. In both cases, you’ll need to enter your stackup information into the calculator to get accurate results. (Differential Impedance, Ohms) = Note: 1oz = 1. The differential impedance depends upon the D/H ratio. GDCPW is known for its balanced configuration, which helps reduce common-mode noise and interference in high. 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. To use this calculator, simply input your microstrip geometry and Dk value, and the tool will return the. 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. Twisted Pair Impedance (Transmission Line) Calculator. 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 efficiency of transmission of the embedded microstrip greatly depends on its characteristic impedance. An example of this calculation using the Si8000m Quick Solver is shown below in figure 4. Differential pair into PCB calculator. Eurocircuits’ PCB DEFINED IMPEDANCE pool is a fast turnaround solution for PCB’s with a specific impedance requirements for certain tracks. INPUT DATA. . Single-ended signals are fairly straightforward. Useful converters and calculators. 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). Impedance Control. The twisted pair helps create a more. 0 of the transmission line and the impedance of the TDR. Enter the values of input resistance (1 kΩ) and feedback resistance (10 kΩ). 5. For now let us focus on the single ended impedance. The required inputs are the Dk value for the dielectric constant of the PCB substrate, and the. Trophy points. 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. I found that a W of 0. 2 Calculating Impedance The following equations can be used to calculate the differential impedance of the board. In the next page we will see what factor effect the differential impedance and how to calculate it. We recommend the software from Polar Instruments if you want to get exact impedance calculation. 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. At the receiver, the signal is recovered by taking the difference between the signal levels on. For this calculation, the units of d and h can be ignored as long as they have the same unit. The calculator shown below uses Wadell’s equations for differential impedance, which can be found in the seminal textbook Transmission Line Design Handbook. 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. 347 e -2. calculate the impedance and capacitance of PCB traces. Modeling approximation can be used to understand the impedance of. 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. ; G is the conductance component of the admittance. The calculator shows 90 ohms can be achieved using. I am using microstrips on external layers only. Common-mode (CM) noise current flows in power lines with same direction CM noise behavior “Voltage driven”, dv/dt, electric field, high impedance DM noise behavior “Current driven”, di/dt, magnetic field, low impedance Buck Boost Vin Cin Cout Lf Q1. Print - Advertisement - This calculator helps you compute the characteristic impedance of an asymmetric stripline Inputs. I used the KiCAD PCB calculator, asked the PCB manufacturer about the tangent loss (0. The online menus contain a calculator to help you to define the correct track and gap values for your layout, for example for 50Ω characteristic and 90Ω differential impedance using material with a guaranteed. As also noted in the picture, the subsequent calculations are on the: [2] top-layer single-end impedance; [3] top-layer differential impedance; [4] inner-layer. 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. Enter one of the three values and the calculator will output the other two. Actually the "odd impedance" is the correct impedance to look at for the USB requirement of 90 Ohms differential impedance. Z diff = 2* Z o (1 - 0. 4mils/35um of copper thickness. 6 ohms and Z even = 110 ohms for your geometry, very close to your result. φ = 0° if 1/2πfC = 2πfL and R = 0. Several Web sites such as the examples listed below contain additional reference information. USB traces must be 90 Ohms differential. 3 Answers. Saturn to Allegro differ more than 10%, which would result in huge trace width and spacing. 8. Table 1. 1 to 2. One of the features of this type of microstrip is the coupling between lines. RF Amplifier PAE Calculator. Dividing the differential impedance. 1,235. Each transmission line has a Capacitance per unit length, inductance per unit length and resistance per unit length. Z represents the Impedance of the stripline. Now, let’s go just a step further as we consider the behavior of odd mode and even mode impedances. has two length-matched 45 Ohm lines. Try TNT or TxLine. You may also check it on amazon. First, consider a microstrip. 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. Using a power plane as signal reference. The overall single-ended to differential gain (GAIN) must take into account the input attenuation of the R S and R T resistive divider and the effect of adding R2. 1. 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. 01) and dielectric constant (3. ; B is the susceptance component of the admittance. A typical 4 Layer stack up. Zdiff. when two coupled tracks are used to give a differential impedance. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. One of the features of this type of microstrip is the coupling between lines. Matching the differential trace length and keeping the distances properly, this calculator is used to calculate the characteristic impedance of an edge coupled microstrip. ( 0. Single and differential coplanar structures are supported by the Simbeor impedance calculator. How to verify performance. Edge Coupled Microstrip Impedance Calculator. Usually Microstrip separated from the ground by using dielectric substrate. Differential and common mode impedance measurement Figure 8 shows the variation of impedance versus frequency. Other calculators will use different equations for the same system, depending on the relevant approximations used in the derivation of the formula. You don’t need to care about the common impedance if there are no common signals on the twisted pair. Thus a "differential pair" any long distance apart will have an impedance of 98 ohms, without any coupling between the lines, i. And this leads to our third rule: The separation between the two traces (of the differential. 5 and I took 3. It has been correlated many times. 3 CPW Structures; 3. This calculator helps calculate the values of the output voltage and the inverting and non-inverting gains of an operational amplifier. Calculate the Differential Microstrip Impedance of a transmission line based on the the distance between the strips, height of the substrate, trace thickness and dielectric constant of the substrate. The T match circuit gets its name because the circuit topology looks like the letter “T”. ; Both the conductance (G) and susceptance (B) components of admittance are real numbers, and the complex term jB accounts for the phase relationship between them. The desired behavior of the differential amplifier is to amplify the differential mode voltage and attenuate the common mode voltage. 7 Keysight ADS schematic used to convert from 4-port single-ended to 2-port mixed-mode S-parameters using equations or 4-port Balun components. Finally, calculate and adjust the feedback resistor for the correct gain. PCB Structures / Discrete Structures / Signal Management. Or we can input them within the RLC circuit calculator all at once and quickly get what we need without relying. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. Note: Units do not matter for this calculation as long as they are consistent. Power Added Efficiency (PAE) Calculator. 1. We can calculate the differential voltage gain as follows. To calculate relative dielectric constant, this online differential microstrip impedance calculator can assist you to compute the opposition to alternating current based on the input values of trace width, thickness, dielectric thickness, trace separation and dielectric constant. Given a value for impedance, it will (in most cases) calculate. 15 mm spacing. The idea here is to determine the spacing required for a given width with the goal of hitting a specific differential impedance value. RF Transformer Calculator. Conceptual overview of LISN-based measurement of differential-mode and common-mode conducted EMI of a switch-mode supply. The differential via design shown in Figure 2 was built. 0 differential insertion loss test to 43. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. In the case where you are routing differential pairs, then the potential between the two pairs will always be opposing (i. As the signals are also referenced to ground, each differential pair signal also has a single ended impedance. 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. Choose from different surface finishes,. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). 6mm board, 100R microstrip differential impedance, they suggest 4/5 mil trace/space, which is a bit different than 9/4. Enter values for R1 and R2 to calculate attenuator loss and impedance. Multiply the result by the square root of the ratio of (1 + (2 * h / w)) to (1 – (2 * h / w)). To use this tool, enter the values for. Open the PCB layout tool (pcbnew) and go to File > Board Setup. , inverting, from the drop-down menu.