To avoid microstrip modes, have h >> (w+2g) and extend component side ground away from the trace by > (w+2g). Inputs Trace Thickness Substrate Height Trace Width Trace Spacing Substrate Dielectric Outputs. Using this calculator, you can find the resonant frequency, which means that you can disregard the reactive impedance (reactance) and only pay attention to the resistive impedance (resistance). dBm to Watt converter Stripline Impedance calculator Microstrip line impedance Antenna G/T Noise temp. So move to your left, use Omni's Cable impedance calculator and enjoy. An example of this calculation using the Si8000m Quick Solver is shown below in figure 4. The differential via design shown in Figure 2 was built. Saturn to Allegro differ more than 10%, which would result in huge trace width and spacing. pairs. Differential impedance: 90 ohms (tolerance: +/- 15%) On a typical 1. Choose a calculator to tune your PCB design. Development Kits. 1. A coaxial cable is designed with 50-Ω or 75-Ω characteristic impedance. The calculator is set up to handle an asymmetric arrangement, where traces are not centrally located in the PCB layer stack. Incidentally, the trace thickness parameter does have a significant effect. Estimate the impedance of a symmetric differential stripline pair using Wadell's equations and a simple calculator. Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method. When selecting trace geometry, priority should be given to matching the differential impedance over the single ended impedance. 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. e. The Impedance Calculator is a tool which allows a quick pre-layout estimation of several kinds of line impedances between different layers. 3mm, as shown below: This increases the impedance slightly to 91. Ask the board manufacturer for the values. A 3-D EM simulator is used to design a differential via with the desired impedance and bandwidth. Another example of using large distances to separate out unwanted components might be to calculate the impedance of a. This calculator is designed to calculate the characteristic impedance of an embedded microstrip - a flat conductor suspended over a ground plane with a dielectric between it and another dielectric material above the conductor (see diagram below). Incidentally, the trace thickness parameter does have a significant effect. Differential input impedance is the ratio between the change in voltage between V1 and V2 to the change in current. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. ’. Figure 1. **Note: Like our stripline impedance calculator, all of our RF. So, I presume, that means the input resistance is simply the resistor on the inverting node. , 10. Impedance matching is important to reduce reflections and pre-serve signal integrity. Use several of them and compare. φ = 0° if 1/2πfC = 2πfL and R = 0. The default units for all given values, except the subtrate. 0 differential insertion loss test to 43. differential impedance data (Tables or Graphs) is very important when hand calculating (calculator) impedance matching options. 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. 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. Quarter Wave Transformer Impedance Calculator. In the ZL box, type 50 Ω. The bottom line is, study carefully, and take PCB trace impedance equations with a proper dose of. Vias (plated holes) are used to route electrical signals among different layers of a multilayer layer PCB. Just enter the given values for trace thickness, substrate heights, trace width, and substrate dielectric. 8 Ω. Print - Advertisement - This calculator helps you compute the characteristic impedance of an asymmetric stripline Inputs. This calculator finds both odd and even transmission line impedance. One of the features of this type of microstrip is the coupling between lines. Differential Impedance Ω. EEWeb offers a free online broadside coupled stripline impedance calculator. 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. Two conductors can create a transmission line. The efficiency of transmission of the embedded microstrip greatly depends on its characteristic impedance. Or we can input them within the RLC circuit calculator all at once and quickly get what we need without relying. Setting up the impedance calculator for differential pairs in Altium Designer. You only need to know the resistance, the inductance, and the capacitance values connected in series or parallel. The following formula is used to calculate the differential impedance of a microstrip: To calculate the differential impedance of a microstrip, divide the characteristic impedance of the microstrip by 2. 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. I found that a W of 0. Another example of using large distances to separate out unwanted components might be to calculate the impedance of a. Edge Coupled Microstrip Impedance Calculator. The greater the mismatch. Z 0 Differential impedance (Ω): Calculate. 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. The characteristic impedance is given by: Eq. Signal layer. Calculate the differential microstrip impedance and characteristic impedance of a differential microstrip line using dielectric constant, trace width, separation, thickness,. Z0 = (60 / √εr) * ln ( (8h) / (w + s)) Where εr is the dielectric constant of the substrate material, h is the substrate height, w is the trace width, and s is the spacing between traces. Following is the list of useful converters and calculators. 5. Unfortunately Online Calculators are deceiving unless you actually draw the numbers and understand the ratios and tolerance effects. The following formula is used to calculate the differential impedance of a microstrip: To calculate the differential impedance of a microstrip, divide the characteristic impedance of the microstrip by 2. 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. ) and the LOW level is defined as zero. 15 mm spacing. Z diff equals Ra||(2Rb) (p model) or 2R 1 (T model). It works in parallel with the standard PCBS layer stackup manager and gets the default setting from it. 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). The desired behavior of the differential amplifier is to amplify the differential mode voltage and attenuate the common mode voltage. This calculator finds both odd and even transmission line impedance. This 26 mil clearance between copper pour and the 13 mil trace is sufficient to ensure 50 Ohm impedance. . Differential impedance values are normally specified for impedance matching of differential pairs, rather than odd mode impedance. 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. It consists of a pair of center conductors separated by ground planes on the same substrate. p = (Zi - Zo) / (Zi + Zo) Let us consider the case Zi = Zo. 75 mA corresponds to a CE range of 1V to 8V. Differential impedance is the double of odd mode. Simons, "Coplanar Waveguide Circuits, Components, and Systems", Wiley. H1. This, by definition, gives a target of an odd mode impedance of 45 Ohms and an even mode of 60 Ohms. Before, working with a trace impedance calculator, one should be aware of which equations the calculation uses. Capacitance (C) = pF/ cm. These values depend upon the geometry. The Calculator Calculates the values of the Characteristic Impedance, Capacitance per unit length and propogation speed. This calculator finds both odd and even transmission line impedance. 1 Effective Permittivity and Characteristic Impedance of CPW. The microstrip is a very simple yet useful way to create a transmission line with a PCB. Mutual inductance and capacitance exist between the two traces in a differential pair. 1. 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. These impedance values thus determined can be. It uses the lan9512 reference schematic. 5) and 1. 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 . When it comes to the equations, you simply need to use the following: W = frac {A} {1. $endgroup$ – The Photon. Power. I agree. Create a new impedance profile, then select Single-Coplanar or Differential-Coplanar from the Impedance Profile Type drop-down list. εeff is the calculated effective dielectric constant of the microstrip line due to the nonhomogeneous nature of the structure (i. Figure 5. The desired behavior of the differential amplifier is to amplify the differential mode voltage and attenuate the common mode voltage. Single-ended signals are fairly straightforward. These transmission line arrangements are standard trace geometries implemented in PCB design software. 0mm (4L-02) When using our free Defined layer buildup 4L-02, you will reach the desired impedances e. e. Overview. 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. 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. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. W is the Width of the stripline. 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. November 14, 2022. Impedance Calculation for PCB Designers - Altium. In addition, the termination resistor value used should take into account the input impedance of the amplifier circuit. 8. Or the odd mode impedance is half of the differential impedance. ’. The PCB Impedance Calculator in Altium Designer. The impedance always represented by Z. Often when working with wires it is easy to create large return path loops if one is not paying close attention. Go to this 100-ohm class and select the nets which are there in this. Broadside-coupled Asymmetric Stripline. R is the resistance in ohms (Ω), . The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. 3. A typical 4 Layer Stackup looks as follows. The tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. Let’s start new project together!. If you select non-inverting op-amp, the calculator will show 11. Relative dielectric constant (er) mm. *Strictly, a loss quantity when expressed in dB should be positive. The calculation looks correct, but the tracks are too wide. Linkedin. 1. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. Single ended. This sets the single-ended impedance AND differential impedance to the target value, even if there is no. An example of this calculation using the Si8000m Quick Solver is shown below in figure 4. A calculator for computing the impedance of an edge coupled stripline. Differential Impedance of Microstrip. The user only needs to enter the attenuation in decibels (dB) and the given characteristic impedance of the transmission lines to be matched. ; Er is the relative permittivity (dielectric constant) of the substrate material. Multiple Differential Pairs Insert multiple Differential Pair definitions per layer. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. 3 kΩ resistor and a 47 nF capacitor (which are standard resistor and capacitor values). Both gives me only 20 Ohm differential impedance. Routing Diff Pairs with a Differential Line Impedance Calculator for Optimal Signal Transmission Twisted pair: \qquad \footnotesize \text {Impedance} = \frac {120 \times \ln (2s/d)} {\sqrt {\varepsilon_r}} Impedance = εr120 × ln(2s/d) As you can see, it is not overly complicated to calculate by hand, but it will definitely take longer than using our calculator. Signal 1. t. Z diff equals Ra||(2Rb) (p model) or 2R 1 (T model). beammy. Where Z 0 is the characteristic impedance of the asymmetric stripline in ohms (Ω). First, calculate the amplifier input impedance R. Lo: inductance per unit length. (Differential Impedance, Ohms) = Note: 1oz = 1. It is now a major exercise to evaluate the impedance using a calculator or spreadsheet. Differential microstrip impedance calculator is an online electronic tool to measure the opposition to alternating current. 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. 3: Normalized characteristic impedance and normalized effective permittivity of a microstrip line as a function of u = w / h. when i use Saturn PCB design to match the differential impedance to 100ohms i get 0. No, the single-ended impedance provided in differential line calculators does not matter. They will give very similar. 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. This calculator is designed to calculate the characteristic impedance of a broadside couple stripline (see diagram below). Dielectric Thickness: mm. 75 m A = 9333 ohms. Embedded Microstrip. They will give very similar answers. Class creation for controlled impedance routing using Altium Designer. Given a value for impedance, it will (in most cases) calculate. Ask the board manufacturer for the values. For example, if you wish to input. Actually the "odd impedance" is the correct impedance to look at for the USB requirement of 90 Ohms differential impedance. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. The same applies to common mode impedance, except that. 75 inches without impedance control; Keep the differential pair length mismatch within 0. This will leave the rest of the signals which are rather non-critical like I2C, power good signals, etc. The equipment can be an impedance meter such as the E4991A from Agilent technology, working up to 3 GHz. As the signals are also referenced to ground, each differential pair signal also has a single ended impedance. FWIW, the calculator I've used in the past is called Polar SI8000 which apparently has been superceded by Speedstack PCB. Using an online differential impedance calculator, the height of the dielectric layer, h, is needed. 6), the impedance will be approximately 50 Ohms. IPC 2141 Trace Impedance Calculator. Twisted Pair Impedance (Transmission Line) Calculator. Notes: 1) Calculation assumes traces are centered vertically. This calculator helps calculate the values of the output voltage and the inverting and non-inverting gains of an operational amplifier. Rewrote the PDN Impedance calculator, old formula was too confusing. 25mm trace. Assuming both are accurate enough. Dual Stripline. g. They will give very similar answers. where . Then enter the values of the impedances as complex. H 2 is the subtrate h2. A coplanar waveguide calculator will operate in one of two ways. I see that Dielectric Constant is 4. Single-ENDED to Mixed-Mode S-Parameter Conversion Equations. Open the PCB layout tool (pcbnew) and go to File > Board Setup. Figure 1 New techniques for pc-board-layer-interconnect design provide predictable path impedance and improved signal integrity. 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. INPUT DATA. 3 Answers. This is an iterative process that repeatedly adjusts the via dimensions and runs EM simulations until achieving the desired impedance and bandwidth. 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. Description. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. 96D/H). 331 1 2 5. 254mm. Differential impedance, Z diff, is the impedance between the two conductors. A A is the cross section area, in mils 2; and. ; 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. For R D, the value of 25 Ω is inserted, which is the differential output impedance of a typical NFC IC with respect to the ground signal. Ground. A variant of coplanar waveguide is formed when a ground plane is provided on the opposite side of the dielectric, which is called finite ground-plane coplanar waveguide (FGCPW), or more simply, grounded coplanar waveguide (GCPW). 2. In order to quantify this impact, we calculate the CMRR using Equation 9. Overview. Single ended impedance is the trace impedance with reference to ground. Create a differential trace with KiCad - Schematic. There are a lot of online trace impedance calculators specifically designed for differential traces. Several Web sites such as the examples listed below contain additional reference information. 1. Edge Coupled Stripline Impedance Calculator. 01) and dielectric constant (3. This is an approximate critical ratio. Controlled differential impedance starts with characteristic 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. 08mm - this is the border of manufacturability, I don't think it is practical to go there but for the calculation it is just fun - and I get some 31Ohms. The designer selects the desired gain and the impedance of the signal source (default value of 50 Ω). Probe with the oscilloscope where the function generator feeds into the PCB. 25 Dimensional units: mm milsloop of the amplifier, which tends to drive the impedance at the output terminals, VO– and VO+, to zero, depending on the loop gain. 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. 29 mm width traces to obtain 100 Ohms ZDiff while using 0. Example. to NF The differential impedance calculator supports an asymmetric stripline structure. 0 specs requires a differential impedance of 90 Ohms and a common mode impedance of 30 Ohms (with some tolerance). Coplanar Waveguide With Ground Characteristic Impedance Calculator. This is to avoid unwanted data signal reflections. Figure 3 shows the respective p and T models used to calculate the differential impedance (Z diff). These equations are. Also, intuitively, from an examination of the field pattern, the even mode impedance Z 0e is likely to be high because the. Agilent's LineCalc tool calculates Z odd = 50. Figure 7. The tool implements numerical solutions of Maxwell’s equations to render accurate and consistent results. Design Rule 3. This calculator assumes the distance between the two reference planes to be an equal distance. Choose a calculator to tune your PCB design. Calculate Coplanar impedance for given PCB parameters. 6mm FR4 PCB with 7628 type stackup (4 layers), the above specifications usually result in 4. This calculator is designed to calculate the characteristic impedance of a symmetric stripline - a flat conductor between two ground planes whose distance between the conductor and the planes is the same for both reference planes. A twisted-pair cable is simply two wires that are twisted together so as to reduce radiated EMI (electromagnetic interference) and mitigate the effects of received EMI. We can calculate the differential voltage gain as follows. If there is an insulator around the wire then this. 8. The Si8000 Quick Solver is convenient to use for this purpose, as shown in Figure 4. 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. Z 0 = ( Z 0o * Z 0e )^0. with the following layout parameters (width|space|width): Ohm. mm mils. If JLCPCB's 4-layer PCB is. s + JX s (1) The “+“ implies “in series”. 3 kΩ × 47 nF) = 1. Differential Microstrip Impedance Calculator (Using Zo) Embedded Microstrip Impedance Calculator. It would be higher than the differential impedance but that doesn't sound right to me. This will also provide the time delay the cable provides for a signal and also the capacitance and inductance per. Tpd: propagation delay. PCB Impedance and Capacitance Calculator: Asymmetric. Figure 2 shows a typical EMI noise plot of a switch-mode, step-down buck supply without an input EMI filter. As seen here:On an impedance controlled layer (for example, with 100 diff), find an unused area and run a differential pair and expose at each end to the surface with test pads. Figure 25 shows a differential pair using the microstrip layout. This calculator will convert voltage or power gains into decibels. Zdiff. 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. differential amplifier is accomplished in four steps. where g m can be calculated as follows:The differential impedance depends upon the D/H ratio. Common-mode impedance occurs with the pair driven in parallel from a common-source. 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. For an embedded (internal) microstrip, the formulas provided in paragraph 4. Learn how to design. 9. Differential impedance is the ratio of voltage to current on a pair of transmission lines when driven in the differential. T. This slope resistance, in parallel with the collector resistor (Rc) dictates what the output resistance of the amplifier is. Let’s Get Digital - Differential Pairs in the Real World. t. The calculator shows 90 ohms can be achieved using. Figure 8. 25mm between the differential pair with a width of 0. 01 Mar 1998. 0 of the transmission line and the impedance of the TDR. x. 3. Enter the values of Z0 and Zc into their respective input fields. The right figure shows the transfer characteristic of the differential amplifier. s. Make sure the correct Layer is selected before changing this option. 9 Ω, R₂ = 3,062 Ω, and R₃ = 50. Agilent's LineCalc tool calculates Z odd = 50. 1,235. Altium Designer’s differential line impedance calculator will set up your impedance-controlled differential pair routing widths for you. The cloder the two traces, the smaller is the differential impedance. net Forum comes closest to the proper track width. Note that Zdiff (differential impedance) is equal to 2 * Zodd, so a Zodd of 45 Ω gives us a Zdiff of 90 Ω. 10. Differential Impedance of. The USB 2. 5GHz. Modeling approximation can be used to understand the impedance of the edge couple differential stripline transmission line. The designer then has the option of selecting a seed. Sorted by: 1. Eurocircuits’ PCB DEFINED IMPEDANCE pool is a fast turnaround solution for PCB’s with a specific impedance requirements for certain tracks. 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. Both LM and CM converge to zero as spacing goes to infinity. It is widely used for data communications and telecommunications applications in structured cabling systems. Excite the other end of the trace with the function generator. 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. 6 ohms and Z even = 110 ohms for your geometry, very close to your result. 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. 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. Separation between Planes. The impedance between one differential trace and the ground. Use several of them and compare. ; B is the susceptance component of the admittance. There are 3 types of single-ended models: single-ended non-coplanar, coplanar single. If driven from a transformer or other floating source the differential impedance of 50kohm makes sense. This is the impedance between the two signal traces of a pair. g. Modeling approximation can be used to understand the impedance of. 5 Ohms higher than the formula method. they normally use 7. 12 equal to a constant voltage. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). Data entry is primarily made in the upper left pane, although the bottom middle pane contains some secondary entry fields. Signal 2. In differential pairs, each trace in the pair carries the same magnitude, but opposite polarity. Doing this results in a gain change. Power Added Efficiency (PAE) Calculator. 77 mm gave me a differential impedance very close to 90 Ω. Cohn, Seymour B. Other calculators will use different equations for the same system, depending on the relevant approximations used in the derivation of the formula. You can make your own spread sheet using formulas provided by Wedell's book "Transmission Line Design Handbook" page 196, 197, 198 (attached)Impedance Calculators. Press the Analyze button to calculate the electrical parameters. W. For the calculation, you can assume that the two vias are. There are four different types of impedance used in characterizing differential trace impedances. H is the Height of the stripline. RF Amplifier PAE Calculator. Microstrip Mitred Bend Calculator. Differential Microstrip Impedance Formula or Equation. This calculator helps you calculate the characteristic impedance of a coaxial cable given its dimensions. Reflection Coefficient Calculator. Terminate the trace at one end with a small SMT 50 Ohm resistor (49. Impedance in your traces becomes a critical parameter to consider during stackup. Differential impedance at low frequency represents the sum of inductance resistances of the filter. Modeling approximation can be used to understand the impedance of the edge couple differential stripline transmission line. High speed digital designers should. ZO *. 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 required values are trace thickness, substrate heights, trace width, and subtrate dielectric in the calculator above and press the "calculate" button. Open the PCB layout tool (pcbnew) and go to File > Board Setup. Microstrip is a single trace on the top layer, with no ground close to it on the same layer. 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. Edit: also, think ahead if you are going to use ground pours around the traces. 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. Edge-coupled Asymmetric Stripline. If it this PCB has many power islands AND there are controlled impedance traces, then it may be a better idea to keep all the controlled impedance traces on Signal 1 and Ground on Layer. ω = 2πf is the angular frequency in rad/s,. The op-amp calculator will display the voltage gain of the op-amp, e. 25, but gives me nice trace from the module to the stub then to microcontroller. 2. However, two reasons for this is to increase input impedance and to reduce distortion due to the nonlinearity of the BJTs. Impedance. The impedance of a differential via pair cannot be treated with a single via impedance calculator unless the vias are spaced far apart. 5.