Questions tagged [characteristic-impedance]

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Transmission Line Step Response

This question seeks a canonical answer to a question regarding the transient response of a transmission line. Suppose one has a transmission line, long enough to be considered "infinite" for ...
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2answers
48 views

Thevenin equivalent of open ended transmission line Clarifications required

I am going through the below link for understanding about transmission line reflections. The below figure is an equivalent circuit of an open-ended transmission line. For finding the the voltage at V+ ...
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1answer
42 views

Via fence distance to the trace?

We have a board design with four layers that uses coplanar waveguide with ground plane: The trace has via fences. Originally, the design was: W=0.35mm, S=0.2mm, and H approximately 0.2mm (for one of ...
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1answer
59 views

Differential Impedance Matching

Below is a small portion of a schematic which I have seen It mentions that the transmission line will have a differential impedance of 100ohms between them. In case of Single ended it would be 50 ...
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2answers
79 views

Practical formula/method to predict the necessity of termination resistor

I am not into high frequency much and just know about ringing caused by reflections due to impedance mismatching in transmission lines. So I recently saw some non-engineer researchers in a lab that ...
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3answers
620 views

Using a miniature BNC connector on a PCB to measure high-frequency content with an oscilloscope

I am a power electronics engineer in R&D and often measure fast switching waveforms, specifically high bandwidth MOSFET gate signals. When connecting oscilloscope probes in the past I have found ...
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1answer
35 views

Calculating lengths of single-stub transmission line when all 3 characteristic impedances differ

Consider a transmission line circuit like the following but where \$Z_{o2}\$ was also unique (say \$Z_{o2}=7\,\Omega\$): I know how I would find \$l_1\$ and \$l_2\$ using smith charts: $$Re\left\{Y_n(...
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0answers
58 views

Transmission lines in paralell for RS485

I have a system with two RS485 transceivers connected by a 300 meters long cable, with 6 wires inside it. In this case, 3 paralell wires of this cable are being used for the "A" signal and ...
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3answers
283 views

Deriving the S-parameters, different Matched Loads possible?

I guess this is more of a conceptual question but for the problem below Im having trouble getting started on how to derive the S parameters for the network. I noticed that the network at 28.025 GHz ...
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1answer
22 views

J-Y(ST)Y..LG cable's charachteristic impedance

First: How to find out (e.g. calculate) the characteristic impedance for the cable mentioned? Id like to know how to model that cable in e.g. Ltspice, so I would like to know either Z or L' and C'. ...
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67 views

Characteristic Impedance vs Frequency

I am reading this paper and I see that characteristic impedance does not take frequency into account. I am surprised by this as I figured different rise time signals would have different frequency ...
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2answers
1k views

Impedance/Termination of Marvell PHY

I'm trying to understand the proper way to design a PCB to interface a Xilinx 7-series FPGA with a Marvell 88E1512 Ethernet PHY, without simply copying the design from an existing schematic. The ...
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1answer
40 views

Matching line driver output impedance over wideband

I'm designing a high impedance line tap for 10-10GBASE-T ethernet signaling. In the AFE I have a JFET LNA for high input Z which goes to a var. gain amplifier that is a fully differential ADC driver. ...
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1answer
81 views

How does wiring two LNAs in parallel affect charactaristic impedance?

It appears that wiring amplifiers in parallel improves the signal to noise ratio. I thought I would experiment with two SAV-541+ LNAs in parallel and see how they perform: How does wiring an LNA in ...
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1answer
66 views

Coax Cable Wave Impedance, Capacitive Load

I am studying the behaviour of cables over frequency, especially what a source sees, and have 2 Questions, as I did some simulations in LtSpice. As a model for the cable I used the "Lossy ...
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1answer
26 views

Load to Source impedance match for non-constant load impedance

i have a rf-system that is working in frequency range of 100 MHz and try to match the impedance of the load to the source system (50 Ohm). So, in general, i know that a network (P- or T-Network) has ...
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1answer
64 views

Impedance Matching of an Antenna

I am reading about antenna design and have a few questions which I could not get clarified. I read about "Stubs". I got to know that Stubs are used for impedance matching of an Antenna either by ...
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1answer
203 views

Stripline (with target impedance) between ground and power planes?

The common idea for a stripline is that the trace is sandwiched between two ground planes. My question: is it the same, for the purpose of characteristic impedance, to have a ground plane or a power (...
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1answer
280 views

Why is 50ohm sometimes used as a differential impedance?

I'm creating a design where I convert an RF single-ended signal to a differential signal with a 5400BL15B050E RF balun that is then fed to a ADL5802 RF mixer. The balun datasheet specifies the single ...
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1answer
345 views

The explanation about why do we define the formula of Characteristic impedance,propagation constant and Velocity propagation

There is a long transmission line 1.Characteristic impedance \$Z_C=\sqrt{\frac{z}{y}}=\sqrt{\frac{impedance}{admittance}}\$,and in the lossless line,\$Z_C=\sqrt{\frac{L}{C}}\$ 2.propagation ...
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5answers
3k views

Physics behind signal reflections and series termination

I have been looking for cause of signal reflections in transmission lines. Everywhere it is concluded that the reason is impedance mismatch. I can understand if the impedance changes in the path of ...
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67 views

Transmission Line Impedance 3 phase

I have the following question that I can't seem to figure out. The question ask to solve for the impedance of a 3ph transmission line. I've found the De (distance relative distance) and XL using the ...
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1answer
77 views

Confusion in understanding characteristic impedance and input impedance of an open circuited transmission line

The characteristic impedance Zo can be derived by considering LC sections throughout the line with open circuit at the end of the line, and this value is independent of length of the transmission line ...
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52 views

Impedance matching to minimize VSWR

I was trying to determine what the impact of impedance mismatching would be to an RF output and I came across this. About half way down the page, the author makes this claim. In general, if the ...
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2answers
160 views

Ringing problems on the output of inverter/comparator

I'm trying to drive some RF switches that need 0 to -5 V control logic with a 0 to 3.3 V signal. I found 2 topologies for this level shifting effect, one using a comparator and one using an inverter. ...
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3answers
632 views

How to estimate characteristic impedance for a random cable and tolerance of the termination resistor?

When we have a source with 50 Ohm output impedance we use a coaxial cable with a 50 Ohm characteristic impedance. And if we don’t know the output impedance then we use a 50 Ohm termination resistor at ...
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0answers
283 views

Twisted pair with shield and drain wire

Ive been posed with a problem regarding calculating the characteristic impedance of a shielded twisted pair with a drain wire. While I understand how to calculate this for a "normal" shielded twisted ...
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3answers
425 views

Characteristic Impedance of a port

I thought that the characteristic impedance was a parameter defined only for transmission lines. But now I have this question: is it defined also for a port? And, eventually, what does it represent ...
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3answers
234 views

LC Filter Design with coaxial input and output

I was trying to design a Chebychev high pass filter of 400MHz corner bandwidth, 0.2db ripple and 5 poles. I am confused with the proposed design in this filter design calculator. This calculator asks ...
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3answers
1k views

Velocity Factor in Transmission Line

For a lossless line, you have \$Z_0=\sqrt{\frac{L}{C}}\$ and \$VF=\frac{1}{c\sqrt{LC}}\$. For a line with R, L, G and C parameters, we have \$Z_0=\sqrt{\frac{R+j\omega L}{G+j\omega C}}\$. But how ...
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1answer
83 views

Why this evaluation board use different track impedance than the right one? Ethernet PHY, routing

Im doing a design with a implementation of 1Gb ethernet switch, for that I bought a evaluation board to do it well. The problem is that in the layout of the ev board I can check that the track ...
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2answers
117 views

What does line impedance stabilization mean?

What exactly does line impedance stabilization mean? What parameters of line impedance are stabilized and how? How does line impedance / source impedance vary with frequency?
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3answers
86 views

What exactly is Characteristic impedence in transmission lines? [duplicate]

Please help me to understand what does a characteristic impedance mean. I am unable to get the exact idea of what does it actually mean and its physical significance.
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415 views

USB cable characteristic impedance

Does differential impedance between D+ and D- not only depends on separation between and wire gauge of D+ and D-, dielectric constant of the insulation, but also the GND wire and shielding? I want to ...
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1answer
314 views

analog signal generator output in Volts vs dBm

I am connecting a mixer to a microwave source and need to be careful of how much power I am giving to the LO and RF of the mixer. If I just stay in the unit of dBm, it would be ok but I became ...
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3answers
200 views

Equivalent Characteristic Impedance for Different Trace Widths

Suppose I have a PCB trace that needs to be impedance matched, but the trace width changes as it travels from its source to its destination. Something like this: The 5mil trace would have a certain ...
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1answer
176 views

RF layout bend over Component

We lay out the RF trace for below model. GSM 900MHz RF trace maintain at 50Ω impedance. As I know, the RF trace needs to be as short as possible for better signal. Do we need to bend RF trace ...
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1answer
1k views

Routing large RF trace to small SMD pad

I am designing an RF board in Altium where due to the dielectric selected and its thickness, the trace width for a 50 ohm characteristic impedance is thicker than some of the SMD component pads. What ...
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0answers
163 views

Some calculations on Transmission Lines

I have to do some (simple) calculations for a transmission line. I was given a power supply of \$11V\$/\$22\Omega\$, \$Z_0 = 50\Omega\$, \$v = 2.2 \times 10^8 m/s\$, a load capacitance of \$1.124nF\$ ...
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1answer
613 views

Impedence Matching of Antenna and Coaxial Cable

There is a scenario based question which is confusing for me Antenna had four rods each 15cm arranged as a plus sign. its brass shielding was cut and it had two 75 ohm coaxial cables in it. one 10 cm ...
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2answers
674 views

What is the definition of characteristic impedance of a lattice network?

We were being taught about Lattice networks in class, today, and our professor mentioned that the characteristic impedance of a symmetrical lattice network like is given by: $$Z_0=\sqrt{Z_aZ_b}$$ I'...
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1answer
137 views

Difference in the characteristic impedance of a low frequency signal

In one of my PCB design, for a RS 485 signal termination resistor of 120 ohm is there. But the differential characteristics impedance of the signal is taken as 100 ohm instead of 120 and the signal ...
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1answer
229 views

Calculating Characteristic Impedance of Jumper Wire

I'm conducting a test of the LTC490 driver/receiver (http://www.analog.com/media/en/technical-documentation/data-sheets/490fb.pdf), using a small incremental encoder. I'll make the connections using ...
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3answers
1k views

Impedance Matching for Helical Antenna

I'm building a helical antenna at 1.7 GHz from scratch. Theory says that its characteristic impedance is 140 Ohm. The RF transmission line is 50 Ohm so there has to be an impedance transformer in ...
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3answers
976 views

Influence of I/O impedance in Butterworth passive filter design

I'm using a simple online simulator tool to build a passive Butterworth filter. An affirmation made in this page confused me: Enter the filter characteristic impedance. In all cases, unless you ...
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2answers
280 views

Preferable pattern for differential length matching

When the positive and negative tracks of a differential signal are not equal in length, we add some bumpy patterns in the shorter track to make them equal. On the other hand, we usually have a rule ...
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1answer
1k views

cable spec: differential characteristic impedance

I am hunting around for a cable with twisted-shielded pair conductors with the correct differential characteristic impedance for RS-485 (120 ohm) Most of the cable spec sheets for cables with twisted ...
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1answer
599 views

Finding cable impedance, to determine RS485 line termination

We have some Belden 6341PC cable which will be used with some RS-485 communications equipment, which of I'm learning will need line terminators. I'm told the resistor values needed should match the ...
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3answers
2k views

50 Ohm Single Ended Signal Impedances on PCBs

I have a basic understanding of transmission line theory and how 50ohm traces are designed on a PCB. I was wondering what the origin of this 50ohm impedance is. Are single ended digital signals on ICs ...
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2answers
2k views

Why is the characteristic impedance usually purely resistive?

I know the characteristic impedance to be the square root of the ratio of the impedance (Z) and the conductance (G) of the line, both complex numbers. Hence, the characteristic impedance must be also ...