Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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.

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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How can PCB trace have 50 ohm impedance regardless of length and signal frequency?

Hmm, this seems to be just another question on line impedances. I understand that when we say "transmission line" effects we talk about things like cross talk, reflections and ringing (I guess that is just about it). These effects are not present at…
quantum231
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Transmission line reflection. I would like a non-mathematical explanation

I am a licensed radio amateur, and find bewildering the many different explanations, which range from folksy urban myth to Maxwell-Heaviside Equations, of what happens at the termination of a transmission line or feeder. I realise that they all come…
Harry Weston
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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 the signal travels, then reflection will occur, but…
Vignesh C
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Terminating shielded/screened twisted pair correctly

Theoretically, I can't see a problem if the twisted pair has an end of cable termination that is: - A single resistor (R) that matches the characteristic impedance of the cable placed across the two ends of the pair or, Two resistors…
Andy aka
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GPS Design Review (RF Input)

I've designed a PCB in Eagle to host a GPS Receiver module and a GPS patch antenna. The RF input to the module is specified as a 50Ω unbalanced (coaxial) RF input. I used this calculator to calculate the required width and spacing for a co-planar…
vicatcu
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Do USB Data Wires (D+/D-) have 90 ohm differential impedance and single ended 45 ohm impedance to ground and if so how is this made?

I understand that USB data transmission is done over various speeds where transmission line effects could come into play(max 480Mbps which means a max frequency that is much higher considering the square wave harmonics/edge rate, perhaps 5th…
scuba
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A transmission line with continuously varying impedance, how would reflection occur in this case?

Alright folks here it is, another transmission line question that has been bothering me. I understand the case where there is an abrupt change in impedance along a transmission line that leads to reflection of portion (or even all) of the…
quantum231
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Why Characteristic Impedance must be 50 ohms?

Where does this number come from? For single ended it must be 50 ohm and for differential pairs 100 ohm. Why? For PCB with controlled-impedance these are that common numbers. Outside of the PCB you can find others numbers for characteristic…
Jesus Castane
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Impedance of an Edge-Coupled Coplanar Waveguide With Ground

How can I compute the differential impedance of an Edge-Coupled Coplanar Waveguide With Ground? I couldn't find any free calculator online, so I wrote a small program which computes the the impedances of an Edge-Coupled CPWG and compared the result…
someonr
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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 passive components to an SMA connector). I am…
Waldorf
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Transmission Line Transient Response To Step Voltage Prior To Any Reflections

This question seeks a definitive and precise answer to a question regarding the transient response of a transmission line. Figure 10 of TI Application Note snla026a contains a graph showing (among other things) the current into transmission lines of…
Math Keeps Me Busy
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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 that the ground clip often induces unwanted HF content…
Jono Moran
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Are I/O buffers of ICs design to have 50ohm impedance?

Is it true that 50ohm characteristic impedance is a convention followed for signal carrying PCB tracks? Also, are the IC I/O buffers also designed to have a close to 50ohm impedance to match this?
quantum231
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How can I guarantee 50 ohm impedance on PCB trace?

I have a question. Imagine that I need to have a 50 ohms impedance in a PCB trace. For simple cases it's just applying the formula found all over the internet or use one of the online calculators While looking for this information online I came…
morcillo
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Controlled impedance in presence of vias and through-hole components (PTHs)

We have some controlled impedance traces on layer 4 of a board. Layer 3 is a GND plane. Layer 5 is a 3.3V plane. Both planes are unbroken (they occupy the entire layer), with the exception of vias and holes. There are a lot of holes on this PCB,…
SomethingBetter
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