6. The differential impedance will be a bit less than 2x the single-ended impedance. Impedance Calculators. These equations are relatively simple compared to other transmission line geometries, comprising only 2 interrelated equations for the microstrip impedance. Where: Z is the characteristic impedance of the stripline (in ohms). EEWeb offers a free online twisted pair impedance (transmission line) calculator. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). 1. Common Mode Impedance (Zc) is the impedance when signals. The HIGH level is brought up to a logic level (5 V, 3. (Not reasonable in general, but sometimes used for test and measurement purposes). Then the low-impedance termination resistors, connectingDifferential pairs are very simple: they are composed of two traces, routed side-by-side, and that carry equal magnitude and opposite polarity signals on each trace. Multiply the result by the square root of the ratio of (1 + (2 * h / w)) to (1 – (2 * h / w)). Using Saturn's PCB Toolkit, it seems to be extremely difficult to achieve 100R. In the above equation, we’ve ignored losses (R and G in the transmission line impedance equation), but that’s okay, the point here is to pay attention. e. If the width of the trace is two times the height of the dielectric (for FR4, Dk from 4 to 4. This technique doesn’t work for wide band requirements, but is a simple way to achieve this at a specific. Broadside Coupled Stripline Transmission Line Models. 25Distance units: Substrate Height, H Trace Width, W Thickness, TThe differential impedance depends upon the D/H ratio. It consists of a pair of center conductors separated by ground planes on the same substrate. What’s more, these calculators return an accurate impedance value when as per. 28Ω. In the special situation for which there is no coupling to ground, Differential impedance equals the Characteristic. For example, if u = 1 and ε r = 10, then from the figure, Z 0 ε e = 126 Ω and ε e / ε r = 0. The factors that influence differential pair via impedance will affect the input impedance seen at the vias. 006” spacing. It has been correlated many times. Just as was the case with microstrip impedance calculators, stripline impedance calculators tend to rely on either the IPC-2141 formulas or on Wadell’s equations. ) and the LOW level is defined as zero. This definition effectively makes it equal to twice the odd mode impedance. W/H. The impedance calculator in the Allegro stack-up editor uses a static 2D field solver by default (bem2d). By inputting the known values. But in your differential pair, each line will have its own characteristic impedance, lower than 100 Ohms but higher than 50 Ohms (for instance a quick computing in Saturn PCB give me 77. Reset. , 10. That's why the numbers Mikrocontroller. When you click on the track, you can see the length of skew. (Sorry guys, I live and I have grown up in a metric world ) With these values, Saturn PCB's off-line calculator gives 57 Ohm differential impedance. You will see the Differential Impedance Calculator interface with input fields for Characteristic Impedance (Z0) and Common Mode Impedance (Zc). Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. The following impedance calculators are free to utilize. These are defined as the ratio of the sine wave voltage leaving a port to the sine wave voltage entering the port. The stripline impedance calculator provided below is useful for gaining an initial estimate of trace impedance for striplines. 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. However, during a handover of bus access from one node to another, or during a transmission pause, the bus idles. Trace Thickness (T) 2. 5mm, T=0. Coplanar Waveguide Calculator. The Microstrip Differential Impedance Calculator simplifies the process of determining the differential impedance of a microstrip transmission line. Most often, the only specified requirement of a differential pair is its differential impedance. Our free impedance calculator for coplanar waveguide can help you with your design features to ensure your PCB is working as you intend. If there is an insulator around the wire then this calculator will be an estimate. Unfortunately Online Calculators are deceiving unless you actually draw the numbers and understand the ratios and tolerance effects. The TDR module provides a polarity. So now you have the impedance looking into an infitely long line of cable. The IPC-2141 trace Impedance calculator will help make initial design easier by allowing the user to input basic parameters and get a. Press Analyze to see the results. 1< W/H < 3. Using the Impedance Calculator one can calculate the eigen modes as characteristic line impedance and the characteristic propagation constant gamma of available signals in a given cable segment. Sig± Differential input-signal source Z 0 Characteristic impedance of the balanced transmission line from the source to the amplifier input FDA circuit overview FDAs are broadband, DC-coupled amplifiers for balanced differential signals and have a unique ability to convert broadband, DC-coupled, single-ended signals into balanced differential. 62 Ohms. Tech Consultant Zach Peterson is talking Signal Integrity again today with a deep dive into Differential Impedance. Inputs Trace Thickness Substrate Height Trace Width Trace Spacing Substrate Dielectric Outputs Odd: Ohms Even: Ohms Common: Ohms Differential: Ohms Overview Differential Stripline Impedance Calculator. Example. Finally, use the equation below to convert the differential measurement to a single-ended result. This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). 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). Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. The microstrip calculator determines the width and length of a microstrip line for a given characteristic impedance (Zo) and electrical length or. I checked out TNT, but couldn't seem to be able to do the same with that either. The calculator shows 90 ohms can be achieved using. This is to accommodate users who found the original ranges too limiting. There are four different types of impedance used in characterizing differential trace impedances. f is the frequency in hertz (Hz), . Commonly fabricated with printed circuit board (PCB) technology, a microstrip antenna calculator tool is an electrical transmission line that is. PCB Impedance-Calculation: Help with the dimensioning of the impedances of your circuit board. 4: Normalized even-mode and odd-mode effective. To measure S-parameters, the preferred test equipment is a vector network analyzer (VNA). Hi, I am working on my board Stack-up to tune Single/Differential impedances of my board in Allegro PCB 16. it will not trip). The characteristic impedance (Z o) of a microstrip transmission line can be calculated using the active calculator or the equations at the bottom of the page. When you want to determine the width and length of a microstrip line for any given characteristic impedance and electrical length, or vice versa, a microstrip calculator is the right tool to do so. 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. Standard 4-Layer Stackup. High-quality circuit boards as prototype and series at reasonable prices. Schematic of a Typical Power Line EMI Filter. Include both the pcb dielectric thickness as well as the wire insulation in the height calculation. Surface microstrip lines are formed by etching one surface of a double-sided material. Microstrip allows for thinner flexible. pairs for aciving 85 Ohm diff. 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. A microstrip width calculator can calculate the width of a microstrip. Ask the board manufacturer for the values. The user only needs to enter the attenuation in decibels (dB) and the given characteristic impedance of the transmission lines to. The cloder the two traces, the smaller is the differential impedance Following is the formula for differential impedance for a Microstrip. A transmission line always features a differential microstrip impedance. Output ⊕. e. Build a model from experimental data of impedance vs. For example, with microstrip, you can specify the substrate parameters (primarily thickness and dielectric constant) and use Linecalc to calculate the impedance for a given line width; this is the “analysis” mode. “Total” noise levels measured separately in L1 and L2 5. Where. Example. A commonly-encountered form of parallel wire transmission line is 300 Ω 300 Ω twin-lead. (Line 1 and Line 2) In a typical IC based non-isolatedDC-DCSMPS, only two lines connect to the input port. This is 1. The default units for all given values, except the subtrate. The following formulas are used for the calculation: φ 90° if 1/2πfC < 2πfL and R = 0. Notice the increased amplitude at the receiving end. Edge-coupled Asymmetric Stripline. 4: Normalized even-mode and odd-mode effective. Most often, the only specified requirement of a differential pair is its differential impedance. Board thickness (h) = 50 micron. 1. The twisted pair helps create a more uniform inductance and capacitance per unit length of wire to ensure a constant impedance, by keeping the return path as close to the signal as possible. This transmission line calculator. 004” line/0. Coaxial Cable Impedance Calculator. This calculator assumes the distance between the two reference planes to be an equal distance. Loss is calculated as a combination of dielectric loss and conductor loss at the analyzed/synthesized length. Learn how to design. We are now ready to calculate the microstrip characteristics. Equation Source: Ulaby "Fundamentals of Applied. The terminationPCIe: From PCI-SIG standards, PCIe Gen1 has 100 Ohms differential impedance, and Gen2 and higher have 85 Ohms differential impedance. Most online calculators do not account for copper roughness. To add the impedance models, click on ⊕ under the impedance calculator section and provide the following. Characteristic impedance is the ratio of voltage to current for a wave that is propagating in single direction on a transmission line. As we’ve seen above, the S-parameters and input impedance of a transmission line are the correct tools for describing signal reflection at the load end of a transmission line. Vias (plated holes) are used to route electrical signals among different layers of a multilayer. 5oz inner copper, 8 mil trace spacing) and a target differential impedance of 100 ohms, JLC's calculator suggests a trace width of 8. 0 specs requires a differential impedance of 90 Ohms and a common mode impedance of 30 Ohms (with some tolerance). Enter the new tool by Sierra Circuits. Dielectric Thickness: mm. 4. I used some online calculator to calculate parameters of trace so it has 50 Ohm impedance. (Differential Impedance, Ohms) = Note: 1oz = 1. Also note that your best bet may actually be VERY SHORT (few mm) traces, a thinner board or a 4 layer board :-) Thanks for your suggestions. Z diff equals Ra||(2Rb) (p model) or 2R 1 (T model). The difference between the total length of the data lines should be no more than 0. Try TNT or TxLine. Differential Stripline Impedance Calculator. Figure 5. In contrast, differential mode interference is a noise signal which exists between the line and return conductors. Figure 5. Incidentally, the trace thickness parameter does have a. ε r = Relative Dielectric Constant. calculate the impedance and capacitance of PCB traces. Equivalent impedance aroused by via parasitic inductance can be figured out by the following formula: Rising time of test signals is 500ps and its equivalent impedance is 4. Suggested Solution: for 100 Ohm Differential, use half the board thickness and make the tracks equal to the board thickness. This is an approximate critical ratio. Notes:. atlc. beammy. When dealing with differential pairs, thi. To make an effect transmission line with two wires it is best to create a twisted pair. Given the defaults (1. The original idea of USB physical drivers was a 18-mA current source into a transmission line terminated with 45Ω on both ends. Due to the parasitic capacitance provided by the PCB substrate and the mutual inductance between. 2. Distance between tracks (s) = 254 micron. The calculator is available in the Electrical Domain in Constraint Manager, from the Differential signaling in flex circuits follows the design method of surface microstrip transmission lines. A classic example of an impedance mismatched circuitA two part calculator which gives ideal and preferred value resistors, showing most formulas used and a link to the others. Typical values for most common differential signal types are 90 ohms differential, 100 ohms differential or 120 ohms differential. 7. Saturn PCB - Toolkit for Impedance Calculation. The differential impedance depends upon the D/H ratio. Thermal Noise Power Calculator. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. These parameters include:No, the single-ended impedance provided in differential line calculators does not matter. Z 0 = ( Z 0o * Z 0e )^0. PCB Structures / Discrete Structures / Signal Management. L is the inductance in henries (H),. Impedance Calculators used by Mantaro engineers and provided here for your use freely. Single ended impedance is the trace impedance with reference to ground. For now let us focus on the single ended impedance. 6. 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. The figure-1 above depicts differential microstrip line. you need to make sure all of your data reaches the receiver before the clock triggers. The input impedance of a line is a function not only of its characteristic impedance, but also of its loading impedance and electrical length (or physical length and frequency). This calculator requires symmetry in the trace widths and location between plane. Z d = Differential Impedance. Differential Pair Calculator The Differential Pair Calculator is used to perform what-if analysis to determine what values of Primary gap and width are needed to get specific differential and single line impedance. safety ground. When you use a line calculator with a proper 'diff pair' mode, it will take account of the geometry and the correct driving conditions, and provide you with a pair of lines that has 100 ohms differential impedance, and two lines of 50 ohms impedance when the other line is driven with an inverted signal. You want to select “Microstrip Zdiff”. It has a common mode impedance of 25 ohm and and a differential impedance of 100 ohm. Edge Coupled Microstrip Differential Impedance Calculator. An example follows. Although implementations vary, the wire diameter is usually about 1 mm and and the wire spacing is usually about 6 mm. 6 Ω and ε e = 6. Because input impedance only depends on the. With the expressions for VO± from before and some algebra, an equation to calculate the output impedance of the circuit1 Answer. By inputting the known values and leaving one variable blank, you can quickly calculate the missing parameter. WE WANT UNCOUPLED FORM! Pay Attention to UNITS! Wave Equations for Transmission Line Impedance and Shunt Admittance of the line . 1 (a). Skin Depth Calculator. 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. LVDS pairs need 100 ohms differential impedance. You can interpret the name 'RLC circuit' to mean a circuit. Speedstack is the stackup design tool of choice for professional PCB Designers fabricators and brokers who have a requirement to document and design stackups drill plans and material requirements complete with high. The impedance of a balanced system is defined by the impedance between the two paths, whereas in an unbalanced system, one terminal is connected to ground. For a printed circuit board (PCB) this is a pair of traces, also known as a differential pair. Refer types of microstrip line and basics of microstrip line for more information. Imagine a differential pair made of two individually screened 50 ohm cables. Differential impedance, Z diff, is the impedance between the two conductors. Track Thickness: mm. The free on-line trace-impedance calculator tool[5] provided an estimate of the parasitic capacitance. THESE FORMULAS ARE APPROXIMATIONS! They should not be used when a high degree of accuracy is required. Just enter the given values for trace thickness, substrate heights, trace width, and substrate dielectric. For example, if u = 1 and ε r = 10, then from the figure, Z 0 ε e = 126 Ω and ε e / ε r = 0. This can be achieved by regulating the inner and outer diameter of the coaxial cable, along with the. Details: In the list below, [1] is the reference design stackup information; [2] and [3] are the processes to get the result close enough to the reference design target so as to know the tool is valid; and [4] is the calculation in question because it is either 5. For sample: 45-46 Ohm single end traces impedance can be used in diff. It is widely used for data communications and telecommunications applications in structured cabling systems. φ = 0° if 1/2πfC = 2πfL and R = 0. Phone: +44 (0)1425 489 111 / +49 (0) 8104 628 0. net Forum comes closest to the proper track width. As capacitance is added to a transmission line (example: periodic loads) the impedance goes down. I am using microstrips on external layers only. Differential Pair Calculator The Differential Pair Calculator is used to perform what-if analysis to determine what values of Primary gap and width are needed to get specific differential and single line impedance. Length of both tracks should be the same. 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. 150 inches (3. The pair of conductors can be wires in a twisted-pair. Figure 81 shows the topology. 1. 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. Most RF Coaxial Cables have an impedance of 50 ohms or 75 ohms. In terms of how these calculators work, the impedance of a transmission line in a PCB can be calculated in four ways: Use the R, L, C, G parameters from the Telegrapher’s equations to calculate the impedance of the transmission line. Also, be aware, 90 ohms is the differential impedance, the characteristic or single ended impedance will be more than half (ie. Impedance (Ω): The desired impedance. If your design has controlled impedance traces, you can use our built-in impedance calculator. The next graph investigates this further. Figure 3. 8. In the special situation for which there is no coupling to ground, Differential impedance equals the Characteristic. The range of accepted values is 20 to 90 Ω for single-ended and 50 to 150 Ω for differential signals. If you're trying to get your own pcb design project , you should use this tool. It mentions formula or equations used in this differential Microstrip Impedance Calculator. Controlled. The term “characteristic impedance. e. Thus a "differential pair" any long distance apart will have an impedance of 98 ohms, without any coupling between the lines, i. R is the resistance in ohms (Ω),. - Arbitrary Transmission Line Calculator (for transmission lines and directional couplers) Transmission lines, including directional couplers, of arbitrary cross section and an arbitrary number of dielectrics can be analysed with atlc. My design requires that the pairs travel over very thin flexible PCB, about 50mm total transmission length. Distance elements enhance selectivity further by being both directional and having a defined reach in terms of impedance. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. 6 Ω. 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. , inverting, from the drop-down menu. Differential signalling is a method for electrically transmitting information using two complementary signals. ε R. Receiver input impedance: If too low, this limits the number of receivers that the driver can handle. 7. It also explains the factors that affect the impedance, such as trace width, dielectric constant, and frequency. The PCB Impedance Calculator in Altium Designer. Picking from the CST Cable Studio Segments Navigation Tree. Note: Units do not matter for this calculation as long as they are consistent. If there is an insulator around the wire then this calculator will be an estimate. So move to your left, use Omni's Cable impedance calculator and enjoy. The twisted pair helps create a more. The odd mode impedance, Z 0,o, is given by the following equation: Eq. For an embedded (internal) microstrip, the formulas provided in paragraph 4. Differential pair routing is one of many aspects of high-speed design. • As shown in Figure 1, traces should be 100-Ω(±5%) differential impedance of differential microstrip or differential stripline. The characteristic impedance is given by: Eq. For this calculation, the units of d and h can be ignored as long as they have the same unit. This is lower than the impedance of the line on its own as the influence of the equal and opposite polarity of the two propagating signals make the structure behave as though an extra ground plane has been added vertically between the traces. Select the box with the geometry that you would like to calculate. ; W is the width of the conductor (in meters). There are a lot of online trace impedance calculators specifically designed for differential traces. 5. GDCPW is known for its balanced configuration, which helps reduce common-mode noise and interference in high-frequency signal. 4mils/35um of copper thickness. In principle, you can calculate the inductance of a trace with a 3D field solver utility, but this is not the norm in transmission line design. The differential impedance of MIPI tracks should be 100 Ohms, not 90 (USB requires 90). Broadside Coupled Stripline Transmission Line Models. Note: valid for (w/h) from 0. The ground plane helps keep the EMI localized and the trace impedance continuous. This planning tab is one of the most useful tabs as it enables you to calculate the optimal data when you need a specific target impedance for single and differential pair traces. 7. This calculator can calculate the impedance and propagation delay of any microstrip by taking its respective height, width, thickness & dielectric constant. The microstrip impedance calculator shown above uses Wadell’s equations for microstrip impedance, which can be found in the seminal textbook Transmission Line Design Handbook. To calculate the external resistor values, start by calculating Z IN. ALTIUM DESIGNER For. Try This New Tool. Select the units for all dimensions: mm mils. 1 where k is the solution of: Eq. To avoid microstrip modes, have h >> (w+2g) and extend component side ground away from the trace by > (w+2g). Skin effect: The skin effect in a PCB trace, including coplanar waveguides, adds additional AC and DC resistance to the total impedance. Field solvers. 671; thus Z 0 = 48. The trace width (0. 1. ; H is the height of the dielectric layer (in meters). The USB 2. You can use Equation 5 to calculate the impedance of aA typical test network for a single-ended line is shown below (note; this can be easily extended to a differential line). 331 1 2 5. 3 V, etc. exe, Power Distribution System Impedance CalculatorExamine Reflection Using S-parameters and Input Impedance. the impedance seen from the line with this architecture; the diagram is shown in Figure 5. 8mils) and the dielectric thickness is 63 mils (using FR-4 and dielectric constant. 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. The first type is differential mode noise which is conducted on the signal (VCC) line and GND line in the opposite direction to each othe. In some cases, we can also use 75-ohm. EXAMPLE: INPUTS: Er = 4. Don’t forget to check out our other. Specific Absorption Rate (SAR) Calculator. The generator and load impedances are G and ZL, respectively. Differential impedance is twice the odd mode impedance. This transmission line calculator. 004” line. •One or two stage differential mode (line-to-line) low pass filter. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. INPUT DATA. 1 to 2. Change W (line width) to 3. Differential Microstrip Impedance Calculator. Grounded Differential Coplanar Wave Guide. Support for Coplanar Transmission Line Structures. 5 Ohms higher. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. Single-ended signals are fairly straightforward. There are four different types of impedance used in characterizing differential trace impedances. A Grounded Differential Coplanar Waveguide (GDCPW) is a transmission line structure used in RF and microwave circuits. Any line condition placing the impedance phasor tip outside this circle will cause the relay to be restrained (i. So, I am trying to figure out how to use Kicad’s PCB Calculator for “Coupled Microstrip Lines”: I’m unsure about what a couple of the parameters mean and can’t find. The rules shown below are a rough approximation, and you should always check the approximation using an impedance calculator or field solver. I see that Dielectric Constant is 4. 0; 1 < ε r < 15 ) Select the units for all dimensions: mm mils. g. Safe connection of measuring equipment 4. , USB. But impedance change as a result of vias reaches more than 12Ω and it indicates that measured value features extreme variation with theory-calculated value. The specifications of my PCB are- the conductor thickness is 2oz(2. 150 inches (3. The default units for all given values, except the subtrate. The other metrics used to describe transmission line impedance depend on the relative arrangement of two transmission lines. Spurious Free Dynamic Range Calculator. Calculates the resistance, inductance and capacitance per unit length of common low-loss transmission line configurations. The common mode impedance is defined as the impedance of the lines connected in parallel, which is half of the even mode impedance. 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. They are equal when the line is loaded in its characteristic impedance. The original source of formula is IPC-2141: Controlled Impedance Circuit Boards and High-Speed Logic Design, April 1996. Modeling approximation can be used to understand the impedance of. For example the impedance of a line with 1,5 mm width, conductor hight of 0,73 mm and. Characteristic impedance is purely a function of the capacitance and. You only need to know the resistance, the inductance, and the capacitance values connected in series or parallel. Edge Coupled Stripline Impedance Calculator. What is the characteristic impedance of twisted pair cables? 100 ohms. Question: The Zo in the matrix data: Zo mode 1 ==> Zcm(common mode) or Zoe(even mode). Click the button corresponding to the unknown parameter to calculate its value ( w/ (h-t) <0. Either the desired impedance at a specific frequency is used to determine the waveguide width, or the width is entered and the impedance is calculated. This calculator is designed to calculate the characteristic impedance of a microstrip - a flat conductor suspended over a ground plane with a dielectric between. Because the lines are symmetrical, the. The questions are mostly on the inner layer differential impedance item [4] below. For example, a single 0. e. 36 mm substrate, has an impedance to ground, unbalanced, of about 49 ohms. When considering differential traces, add the space between traces (s) to this list. 1. 1. Impedance (Z o ): 76. Differential impedance, Z diff, is the impedance between the two conductors. 5. Differential Impedance Calculator - Stripline. This calculator allows you to add the impedance model and compute the desired trace geometry and spacing for a target impedance. Determining trace impedance and propagation delay in PCB traces takes a trace length calculator and impedance profiler tool, and these features work best when they are integrated into your PCB design software. With high speed and high frequency controlled impedance design, you need design tools that allow you to define the proper impedance for your specific trace configuration on surface layers or on internal signal layers. Clemson Vehicular Electronics Laboratory: Transmission Line Impedance Calculator. It is only equal to double the characteristic impedance in certain cases. 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. 6 ohms and Z even = 110 ohms for your geometry, very close to your result. Provide values for four of the five parameters h, c, t, w, Z 0 and the relative permittivity of the dielectric. Or the odd mode impedance is half of the differential impedance. Alternatively, and equivalently, it can be. t = Trace Thickness. Ethernet lines are differential pairs with a differential impedance of 100 Ohms. Stable line source impedance 2.