# Questions tagged [characteristic-impedance]

Characteristic impedance is the ratio of the amplitudes of voltage and current of a single wave propagating along a transmission line (i.e. without reflections traveling in the other direction). Its SI unit is the ohm.

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### PCB trace impedance infinite equivalent impedance of RLC model

I am trying to understand the PCB trace impedance model. Although not exactly, if we take a very small section of a PCB trace as an example, let's assume that it is in the form of series R, series L ...
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### How to match multiple impedance discontinuities?

I am trying to design a circuit to transmit various digital high frequency signals over cables, connectors and pcb to an oscilloscope. The simplified circuit looks like this: simulate this circuit &...
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### coplanar waveguide impedance calculation and tolerance

The Ublox Sara R5 System Integration Guide I am following states that a 50 Ohm antenna waveguide design is recommended and provides a couple example designs that achieve this using FR4 dielectric. ...
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### PCB interconnect trace characteristic impedance (Z0) at low frequencies

In high frequency signals, we generally set the trace characteristic impedance between 50-120 Ω. Calculation tools, for example, use the impedance calculation tool designed by Altium Simbeor, and it ...
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### PCB trace impedances of integrated circuits with high input impedance

There is an ADC front end IC (opamp) at the input of my ADC card and it has high input impedance, What should I set the differential trace impedance to when drawing the PCB? Does this matter much?
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### CAN Protocol traced routed with 90 ohm characteristic impedance

I am using ISO1042BDWV in my board. The schematic is given below. I know that the characteristic impedance of the CAN bus is 120 ohm. The layout team routed CANH and CANL as 90 Ω differential. The CAN ...
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### Characteristic impedance of a BNC jack to jack adapter

I have this BNC jack to jack adapter. I want to measure its impedance but I am reading around 1mΩ. The datasheet says that it is a 50Ω adapter. Why am I measuring such a low resistance?
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### Coax cables, impedance matching and BNC extensions

I'm trying to understand how to do proper measurements with a Voltage Differential Probe ( TT-SI 9010. This probe has an output impedance of 50ohm and has a BNC (It doesn't specify it in the data ...
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### Balun converting 100ohm single-ended trace to 50ohm single ended for spectrum analyzer

On my board, I have 100ohm differential pair traces connected to a 1:1 balun, so the signal impedance becomes 100ohm single ended. I would like to measure the signal spectrum with spectrum analyzer. ...
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### Confusion About Impedance Matching For Single-Ended and Differential Lines

I understand that for single ended RF signals I must ensure that the characteristic impedance of the transmission line matches the load impedance (say 50 ohm). I am a bit confused for differential RF ...
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### Does coiling a transmission line affect its characteristic impedance?

If I take an advertised 50 ohm impedance cable and turn it into a coil will this change its characteristic impedance from 50 ohm to something else? My intuition tells me it should as if we look at one ...
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### From the perspective of a progressive wave, what is lumped impedance? [closed]

This question asks about the meaning of lumped impedance in traveling wave theory. Should lumped impedance be viewed as something like a point charge, a point mass, or a direct delta function? When a ...
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### Connector impedance matching

The importance of termination matching the cable is emphasized all the time. But before the wires reach the termination resistor they usually pass the connector. I've only seen the impedance specified ...
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### How to do impedance matching when when all 3 characteristic impedances differ? [closed]

If we have a circuit like this and we need to do impedance matching on smith chart. How would we go about doing it? I think you would have to first normalize with the Zo1 and go to the 1+jX circle and ...
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### Derivation of input admittance of a lossless T-Junction Power Divider that is matched at the input port

I'm trying to understand how the equation for the input admittance for a lossless T-Junction power divider was derived, which is only matched at the input. Let $Z_0$, $Z_1$, $Z_2$ be the ...
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### How does the characteristic impedence of a lumped network work?

I'll take a textbook example to explain my problem. Find the scattering parameters of the 3 dB attenuator circuit shown in the figure: The solution reads: From (4.41), S11 can be found as the ...
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### PCB impedance calc and clearance

I am using Altium Designer and it has a nice impedance calculator which tells you the required track width for a desired impedance given the layer stack you have configured. So if layer 1 and layer 3 ...
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### Which stackup to choose for JLPCB FR4 up to ~10GHz

I am aware that 10GHz on FR4 is not ideal, but this is an hobby project and I can tolerate some losses. The 10GHz on the PCB is minimal (probably only a short coplanar waveguide or microstrip with 2 ...
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### Series resistor vs PCB track impedance

I want to understand the below question: There are digital interface for example, MII/RMII lines. It requires a PCB characteristic impedance of 50 Ω. Also, better EMC flexibility, it is said to place ...
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### General guidelines to avoid damaging RF components

So, I am a young researcher in physics and use RF components like splitters, mixers, couplers, amplifiers, etc. These are not high voltage amplitudes at all - at most a few volts - often hundreds of ...
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### Must the characteristic cable impedance match the series output impedance?

I have been working on a communication link between an FPGA and a SPI slave. The electrical connection between the two is done via a 2 metre cable composed of 42AWG wires with the following ...
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### Unexpected low characteristic impedance using the JLCPCB impedance calculator

I'm currently designing a PCB that is intended to fan out the 38 pins of a MICTOR connector to every other conductor of an 80-conductor ribbon cable (The PATA type one, that is AWG30 wires with a 0....
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### Signal wave form change as it travels down the transmission line

This question is not about reflections that will distort the signal which contains many high frequency components. I would like to know what the signal looks like (changes in shape, attenuation, etc.) ...
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### Analytical solution for the characteristic impedance along vertical wire over PEC ground plane (at given point h)?

For the purpose of TL transformer simulation I need a solution for the characteristic impedance of vertical wire, with radius a, at the infinitesimally short segment - not point, at the height h above ...
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### Stripline with coplanar ground plane?

I can't seem to find any impedance calculator that offers this configuration — not sure if it has a different name; I'm referring to a trace on an inner layer, sandwiched between ground planes on the ...
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### What's the cable configuration of a ribbon cable when aiming for a balanced characteristic impedance?

The ribbon cable in reference 1 states a balanced characteristic impedance of 122 Ω. For which configuration of the wires is this value valid? From reference 2, it becomes evident that the ...
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### Impedance matching and termination on a flexible PCB carrying a 4.8 MHz clock signal, need stack up recommendations

I need some expert advice and I trust I can get it here. I am in the process of designing a system that uses a PDM microphone connected to the the microcontroller via a flexible PCB (4.8 MHz clock ...
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### Appropriate current sink for measuring the impedance of transmission line

I am creating a current sink that can draw a step current from the Vnode of the circuitry in blue. The reason to draw a step current from Vnode is that I need to measure the characteristic impedance ...
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### Characteristic impedance when routing differential

Can the characteristic impedance value of a single-ended transmissions line be omitted when the two transmissions lines of a differential pair are routed differentially (not two isolated lines)? I ask ...
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### 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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### 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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### 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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### 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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### 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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