This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). Where: L is the gapped core inductance in henries (H) µ 0 is the permeability of free space (approximately 4π × 10-7 H/m); µ r is the relative permeability of the magnetic core material; N is the number of turns in the inductor; A is the cross-sectional area of the magnetic core in square meters (m 2); l eff is the effective magnetic path length in meters (m); g is the. The efficiency of transmission of the embedded microstrip greatly depends on its characteristic impedance. PCB Structures / Discrete Structures / Signal Management. Figure 1. Unfortunately, TxLine doesn't do coplanar waveguide for differential traces. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. 5mm, T=0. Reaction score. Reference: R. Locally hatched ground plane to increase differential impedance. Facebook. | Created: November 22, 2021 | Updated: June 25, 2023 Table of Contents Differential Impedance Defined Formulas for Differential Impedance Should You Use Characteristic or Odd-mode Impedance? Calculating. 75 mA 7 V 0. Enter the number n n of impedances in parallel as a whole number and press "Enter". The differential gain ADM of an amplifier with a differential output is defined as: # ½ Æ 8 È ½ 8 ½ Æ where VOD is the differential output voltage. ’. The differential impedance of MIPI tracks should be 100 Ohms, not 90 (USB requires 90). For an embedded (internal) microstrip, the formulas provided in paragraph 4. This tool calculates the matching network necessary to terminate a line of the specified characteristic impedence (Z o) in a specific complex load impedence (R L + jX L) at a specified frequency. Most often, the only specified requirement of a differential pair is its differential impedance. One of the features of this type of microstrip is the coupling between lines. Actually the "odd impedance" is the correct impedance to look at for the USB requirement of 90 Ohms differential impedance. Edge Coupled Stripline Differential Impedance Calculator Broadside Coupled Stripline Impedance Calculator Symmetric Stripline Impedance Calculator Asymmetric Stripline. Though this is an "imaginary" or "virtual" ground its influence is the same as a real copper wall. The default units for all given values, except the subtrate. All calculations use a frequency of 1 GHz. An example of this calculation using the Si8000m Quick Solver is shown below in figure 4. Since it is always important that the trace impedance remain constant over the entire length, this means that the coupling must remain constant over the entire length. 1,235. Thus, the TDR method is use-ful for measuring Z 0 and changes in Z 0 of a transmission line. Impedance Control. Calculates the differential impedance of a microstrip pair. ; Z 0 is the characteristic impedance of free space (approximately 377 ohms). Our impedance calculator features two main types of impedance models, single-ended and differential, within each trace structure. Remember that you can't. Click the “Calculate Differential Impedance” button. The bottom line is, study carefully, and take PCB trace impedance equations with a proper dose of. Is this a good practice for Ethernet? This is a capture of the PCB right now: This is the schematic that I am using. Enter the values of Z0 and Zc into their respective input fields. Conceptual overview of LISN-based measurement of differential-mode and common-mode conducted EMI of a switch-mode supply. USB 2 e. H1. One thing is for sure: When you are routing a high-speed PCB design you are going to be working with impedance-controlled routing and. t. This 50% margin is to ensure some noise immunity. Relative dielectric constant (er) mm. It also explains the factors that affect the impedance, such as trace width, dielectric constant, and frequency. Zo (diff) is calculated to be 244 ohms, so dividing by two yields a value of 122 ohms for the semi-coplanar structure. 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. Correct track impedance is the first point usually made in various online sources I've found on the subject, so I tried to get the microstrip impedance calculator to get as close the desired 100 Ohm. So, I presume, that means the input resistance is simply the resistor on the inverting node. JLCPCB Impedance Calculator. This calculator finds both odd and even transmission line impedance. The microstrip is a very simple yet useful way to create a transmission line with a PCB. 68 mils. When driven in differential mode by two identical amplifiers, this impedance change will be the same for both lines. In order to quantify this impact, we calculate the CMRR using Equation 9. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. 9. Differential Microstrip Impedance Formula or Equation. 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. Such a circuit will deliver an exact cutoff frequency of. Signal 2. Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method. 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). 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. With both wires at the same potential there is no capacitance between them so the reference plane (return path) is less clear. 01 Mar 1998. Notes: 1) Calculation assumes traces are centered vertically. Differential Pair Impedance (Z_diff) = (2 × Z_single) / sqrt(1 + (2d / s)) Where: Differential Pair Impedance (Z_diff) represents the characteristic impedance of the differential. Asymmetric Stripline. x allows an easy way to make differential pairs and keep control of the trace length, thus the phase or skew between the traces. The vias for these high-speed traces will be backdrilled to be a total length of 23 mil, keeping the via stubs no longer than roughly 1/20th of a wavelength. Consider Q 1 and Q 2 as current sources controlled by their base voltages. These radio frequency calculators help with unit conversion, attenuator design, antenna design, radars, and various other basic calculators. T. 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. That's why the numbers Mikrocontroller. 1. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. L is the inductance in henries (H), and . 8. The main cable should be terminated at both physical ends and, the intermediary nodes that come from that cable. The T match circuit gets its name because the circuit topology looks like the letter “T”. 48 e -0. Trace Thickness. 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. 6mm 4 layer PCB, 1oz outer copper, 0. Just as important. Differential impedance, Z diff, is the impedance between the two conductors. 5 mil wide traces with about 6 mils of. e. 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. Figure 25. For a single-ended differential amplifier, the gain is. KiCad 5. Choose a calculator to tune your PCB design. No, the single-ended impedance provided in differential line calculators does not matter. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). 5. To avoid microstrip modes, have h >> (w+2g) and extend component side ground away from the trace by > (w+2g). 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. Embedded microstrips are commonly crafted using printed circuit boards, although other. 3: Normalized characteristic impedance and normalized effective permittivity of a microstrip line as a function of u = w / h. Note: The results are only for approximation and rough estimation, the final values and the. It is only equal to double the characteristic impedance in certain cases. Advertise with us;. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. If a. Creating and Configuring an Impedance Profile. Z = V I = Z0= 1 vC V 1 vC LV = vC Features of the impedance: looks like a resistor dependant on intrinsic properties only is an intrinsic property independent of length. This calculator assumes. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). Power Filtering/Distribution x. ; 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. This assumes ~0 trace thickness. This calculator is designed to help calculate the value of the resistors R1 and R2 to be used in T-pad attenuator. 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. And this leads to our third rule: The separation between the two traces (of the differential. 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). 5. When designing the trace configuration for your differential pairs, you are typically targeting 100 ohms differential. Click the button corresponding to the characteristic impedance to calculate its value. PCB samples, finding that predicted accuracy varies according to target impedance. 25mm trace. Z0 = (L/C)^0. USB traces must be 90 Ohms differential. They will give very similar answers. [m] width of the trace. Overview. Atlas Si for TDR. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. Coplanar Waveguide With Ground Characteristic Impedance Calculator. 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. It has been correlated many times. Multiply the result by the square root of the ratio of (1 + (2 * h / w)) to (1 – (2 * h / w)). The impedance is based on the cross-sectional geometry of the trace. 7, if that is what you were doing. Modeling approximation can be used to understand the impedance of. INPUT DATA. If you like this tutorial, you may like to buy the book . thanks to 6 layers I am now pretty confident that I can place all diff pairs on top and bottom layers, directly above the ground planes. Learn how to use a differential impedance calculator to design your PCB for high-speed digital data transfer. The op-amp calculator will display the voltage gain of the op-amp, e. The designer selects the desired gain and the impedance of the signal source (default value of 50 Ω). Make sure the correct Layer is selected before changing this option. 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). Rewrote the PDN Impedance calculator, old formula was too confusing. ; H. Disc Air Capacitor Calculator; Impedance Calculator : XL, XC; Inductors, Transformers. It is the ratio of voltage and current amplitudes of a single wave propagating along the line in the absence of reflections from other directions. Board Setup. 03) it gives me almost 160 Ohm - and even if use 53mil conductor height or. Enter the values of Z0 and Zc into their respective input fields. Z RL is the RL circuit impedance in ohms (Ω), . Near 50 ohms, many of these approximations are within a few percent accurate. There are a lot of online trace impedance calculators specifically designed for differential traces. 1. 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. I see that Dielectric Constant is 4. Impedance examples 4 layers 1. Adiff = gm ×RD A d i f f = g m × R D. The designer then has the option of selecting a seed. For example, if you wish to input "25000000", just type "25M" instead. Estimate the impedance of a symmetric differential stripline pair using Wadell's equations and a simple calculator. φ = 0° if 1/2πfC = 2πfL and R = 0. You can calculate the capacitance and inductance formed by one ground via and the signal via with simple formulas (Reference 1). There are four different types of impedance used in characterizing differential trace impedances. Design Rule 3. 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. 864. Impedance Calculation 5. Differential impedance changes with coupling, which changes with trace separation. Here are some tips for measuring differential impedance. There is also a dielectric material placed above the conductor. Suppose we have a system with the following parameters: R= 30 Ω;; L = 10 mH; and; C = 100 μF. Saturn PCB - Toolkit for Impedance Calculation. To see how this works, consider the diagram below. Table 1. 25mm between the differential pair with a width of 0. Following is the formula for differential impedance for a Stripline. This calculator finds both odd and even transmission line impedance, including four different types of impedance used in characterizing differential trace impedances, for microwave antennas, couplers and filters applications. Differential Trace Microstrip Impedance Calculator; Differential Trace Stripline Impedance Calculator; The standard geometries that are supported by these trace impedance calculators are shown in the graphic below. (Differential Impedance, Ohms) = Note: 1oz = 1. As discussed previously, the lengths of the two lines in the pair must be the same length. Trace Width. In addition, the termination resistor value used should take into account the input impedance of the amplifier circuit. H 1 (Dielectric thickness) : mm mils. When the termination resistor matches the track impedance, there will be no reflections. High-quality circuit boards as prototype and series at reasonable prices. 6mm thick. 96s/h )The Microstrip Differential Impedance Calculator simplifies the process of determining the differential impedance of a microstrip transmission line. The characteristic impedance is given by: Eq. 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. ; B is the susceptance component of the admittance. 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. Also, intuitively, from an examination of the field pattern, the even mode impedance Z 0e is likely to be high because the. The impedance value you calculate is the transmission line impedance the signal sees as it reflects off the mismatched load and travels on the line. One of the features of this type of microstrip is the coupling between lines. The differential gain ADM of an amplifier with a differential output is defined as: # ½ Æ 8 È ½ 8 ½ Æ where VOD is the differential output voltage. Example. Their hardware design guideline said the traces between the USB and the termination resistors should have a differential impedance of 90 ohms. The impedance of the surface microstrip shown is 50 ohms, so the impedance of the broadside coupled differential pair will be twice 50. on layer 3 from the top, between power and ground plane. 96D/H). Differential Impedance The impedance measured between the two lines when they are driven with opposite polarity signals. The required inputs are the Dk value for the dielectric constant of the PCB substrate, and the. 035mm and Er = 4. Even mode impedance is less clear to me. Quartz Crystal Parameter Calculator. Separation between Planes. To maximize signal integrity, proper routing techniques for differential signals are important for high-speed designs. Figure 4. If I calculate it for embedded edge coupled differential pair, it is still only 39. If you're trying to get your own pcb design project , you should use this tool. The impedance of each trace of the differential pair references to ground. Newsletter. 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. The surface finish is neglected. The allegro calculator gives a value of 56. The cloder the two traces, the smaller is the differential impedance Following is the formula for differential impedance for a. Finally, all calculators provide theoretical impedance values as they cannot take in to account the variables and. One of the features of this type of microstrip is the coupling between lines. Edge-coupled Asymmetric Stripline. The procedure for calculating the differential impedance of an interconnect with a differential via transition is iterative; you calculate the input impedance from the receiver end and work backwards to the load end. SEDZ = R. Differential impedance: 90 ohms (tolerance: +/- 15%) On a typical 1. Dielectric Thickness: mm. Agilent's LineCalc tool calculates Z odd = 50. It is important todetermine the characteristic impedance of a twisted-pair cable because this impedance should match the impedance. Edit: also, think ahead if you are going to use ground pours around the traces. For differential pairs of microstrips, the formulas involved are much more complicated because coupling between the traces in the differential pair must be included in the impedance calculation. In the case where you are routing differential pairs, then the potential between the two pairs will always be opposing (i. net Forum comes closest to the proper track width. Differential Impedance Ω. Dividing the differential impedance. Single ended. For example, the equation for the trace impedance in a differential pair of asymmetric striplines includes an approximation on the dielectric constant and geometry. It is now a major exercise to evaluate the impedance using a calculator or spreadsheet. The tool provides two networks that will have the desired impedence at that frequency, but their. Keep the spacing between the pair consistent. 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. calculate the impedance and capacitance of PCB traces. Press the Analyze button to calculate the electrical parameters. Moreover, this tool can also compute the signal propagation delay in inches per nanosecond (ns/in), the inductance per unit length in nano-Henrys per inch (nH/in), and. 1. Zo (diff) is calculated to be 244 ohms, so dividing by two yields a value of 122 ohms for the semi-coplanar structure. What is the characteristic impedance of twisted pair cables? 100 ohms. 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. 1. 3 CPW Structures; 3. Overview. 12 equal to a constant voltage. Example (PageIndex{1}): CPW; 3. Calculate the approximate impedance dimensioning of your PCB / high frequency circuit board with the Multi-CB impedance calculator. What this means to you is that at the resonant frequency, depending on whether the circuit is in parallel or series, the impedance is the highest or. For budgetting reasons I'm tied to a stock pooling layer stackup, so I went for OSHpark's 4-layer stackup (35um copper - 0. Using a power plane as signal reference. 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. 0 differential insertion loss test to 43. 5. What is a Microstrip Differential Impedance? Microstrip Differential Impedance. *The structure may propagate in 3 modes: coplanar waveguide, coupled slot lines and microstrip. THESE FORMULAS ARE. . 17mm FR408 - 17um. Differential pair into PCB calculator. impedance between paralel D+and D- wire should be 90ohms and also impedance Between D+ and GND and D- and gnd should be 45-50ohm. Try TNT or TxLine. The bottom line is: check with your fabricator when planning a 4-layer PCB stackup with 50 Ohm impedance. R is the resistance in ohms (Ω), . Tech Consultant Zach Peterson is talking Signal Integrity again today with a deep dive into Differential Impedance. Supports Anritsu ShockLine™ MS46524B and VectorStar™ MS4647B. Description. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. H. g. ’. 3. There are a number of pcb transmission line typologies. Impedance in your traces becomes a critical parameter to consider during stackup. Useful converters and calculators. 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. They can give you some stackup options, and they can tell you the trace width you will need to reach 50 Ohms for their stackup. 1 Answer. The PCB designer must ensure that its characteristic impedance has the desired value. Figure 81 shows the topology. Figure 4: Common and differential impedance of ACMS-Q3225E-201-Tcalculate the pcb impedabce and capacitance of asymmetric stripline. 3. Simultaneous Switching Noise Guidelines. Capacitance (C) = pF/ cm. Note: Units do not matter for this calculation as long as they are consistent. 50. 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. Si TRC – Track Resistance Calculator calculates DC. ”7. Differential pair routing is one of many aspects of high-speed design. This calculator helps you calculate the characteristic impedance of a coaxial cable given its dimensions. When you use a field solver to calculate differential crosstalk, you will be using time-domain results (showing pulses input into the victim interconnect) and S-parameters to quantify broadband differential crosstalk. Coplanar Wave Guides 5. 5. 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. Agilent's LineCalc tool calculates Z odd = 50. PCB Structures / Discrete Structures / Signal Management. If JLCPCB's 4-layer PCB is. USB traces must be 90 Ohms differential. Or we can input them within the RLC circuit calculator all at once and quickly get what we need without relying. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. This 26 mil clearance between copper pour and the 13 mil trace is sufficient to ensure 50 Ohm impedance. 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. This calculator assumes the distance between the two reference planes to be an equal distance. Also differential pairs. 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. Trace Thickness Substrate Height 1 Substrate Height 2 Trace Width. This calculator is designed to calculate the characteristic impedance of an edge-coupled microstrip. In some cases, we can also use 75-ohm differential. However, if the impedance of the transmission line changes for any reason, a part of the electromagnetic wave is reflected back towrds the source. 5GHz. The differential impedance depends upon the D/H ratio. The rules shown below are a rough approximation, and you should always check the approximation using an impedance calculator or field solver. Incidentally, the trace thickness parameter does have a significant effect. Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets. Activity points. With our handy calculator, you can choose from 50 Ohm, 75 Ohm, 93 Ohm and 95 Ohm coaxial cables. The Derivative Calculator supports computing first, second,. 2. Email. 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. The differential signals have a differential characteristic impedance. The values L 0 and C 0 must be substituted into equation (11) to calculate the complex filter impedance. I use FR-4, so H=1. Just enter the given values for trace thickness, substrate heights, trace width, and substrate dielectric. Zdiff. e. Mutual inductance and capacitance exist between the two traces in a differential pair. This calculator is designed to calculate the characteristic impedance of an edge coupled microstrip. Differential Impedance Calculator - Microstrip The differential impedance between the positive and negative trace of the transmission line is slightly less than twice the impedance of the single ended impedance. 8. differential impedance data (Tables or Graphs) is very important when hand calculating (calculator) impedance matching options. So move to your left, use Omni's Cable impedance calculator and enjoy. f is the frequency in hertz (Hz), . The tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. The differential via design shown in Figure 2 was built and tested. 347 e -2. Setting up the impedance calculator for differential pairs in Altium Designer. mils: Distance between planes (B) mils: Relative Dielectric constant (Er) Differential Trace Impedance: ohms: References. In this example, the. If you don't have access to a differential impedance calculator, or you don't know how to calculate it, then just keep trace lengths less than 0. where . There are a lot of online trace impedance calculators specifically designed for differential traces. Added 2 conductors thru-hole and BGA to the padstack calculator. Mutual inductance and capacitance exist between the two traces in a differential pair. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. Differential Pair Impedance. Typical values for most common differential signal types are 90 ohms differential, 100 ohms differential or 120 ohms differential. Even mode impedance is defined as impedance of a single transmission line when the two lines in a pair are driven with a common mode signal (the same amplitude and the same polarity). In the special situation for which there is no coupling to ground, Differential impedance equals the Characteristic. Edit: also, think ahead if you are going to use ground pours around the traces. In the next page we will see what factor effect the differential impedance and how to calculate it. How to Use the Calculator. 4mils = 0. **Note: Like our microstrip line impedance calculator, all of our RF calculators allow SI prefix input. Also does diff. $endgroup$ – The Photon. 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. 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. The required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. This value is often given the name “differential impedance. For better impedance control, use PCB design software you can trust. Learn the limitations and advantages of this tool and how to use a field solver for more. Enter the values of trace width (w), trace thickness (t), trace dielectric thickness (h), overall dielectric thickness (h1), and the dielectric constant (er). The peaks of S21 figure show even and odd modes. Altium Designer makes it easy to calculate geometry when you need to calculate impedance for differential pairs. You want to select “Microstrip Zdiff”. 6 inches - this is very easy to do; If you can access a differential impedance calculator, then use differential. 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. If the impedance of the TDR unit is known via proper calibration, then the Z 0 of the transmission line attached to the TDR unit may be determined. 4mils/35um of copper thickness.