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0
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1answer
37 views

Reflections on a differential transmission line

I understand why reflections occur when there is an impedance mismatch on a single-wire transmission line. However, when we introduce a differential line, I am having trouble picturing what would ...
1
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1answer
39 views

How much is the propagation velocity affected by the characteristic impedance?

Someone posted the (very educational!) video Similiarities of Wave Behavior from 1959 in another answer, and after watching the part about impedance mismatches, it strikes me that the propagation ...
4
votes
3answers
83 views

Characteristic impedance of a D-subminiature connector

I would like to know what the characteristic impedance of two adjacent pins of a D-subminiature connector is, or how I can go about calculating it. For example, see below 50-pin D-sub, if I were to ...
0
votes
1answer
83 views

IBIS Model Characteristic Impedance

I have tried to understand how to match my 50 ohm pcb trace, which is carrying a high-speed data signal, with a digital chip's input pin. The problem is that I don't understand why the calculations ...
0
votes
2answers
200 views

BNC cable's characteristic impedance and voltage drop

As far as I understand, the characteristic impedance matters when a signal is oscillating since the BNC coaxial cable can be modeled as having inductors and capacitors as in the figure: I have ...
1
vote
3answers
332 views

Height of the substrate in online PCB impedance calculators

Is the height of the substrate just the non conductive portion between copper layers ? Using this calculator as an example In a 4L board, if the top and bottom traces are of the same thickness and ...
0
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2answers
509 views

What is the 'characteristic frequency' of a certain impedance?

I'm not familiar with that term. Could somebody explain it to me? Is it the frequency at which the phase of the AC current running through the impedance goes to zero? Edit: Here is the context in ...
2
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2answers
151 views

Role of “HDMI Baluns”?

I understand that an HDMI cable contains essentially 4 shielded twisted pairs, along with additional control lines. Each of the twisted pairs is specified, to my understanding, to be a balanced ...
3
votes
3answers
549 views

How does a passive 1x Scope probe work?

I understand about input impedance and capacitance... My question relates to the cable: What is the characteristic impedance of the cable connecting the probe to the scope? It must be terminated in a ...
5
votes
1answer
157 views

How to minimize characteristic impedance mismatches caused by vias?

This question springs from an answer here. When using stripline configurations for rf signalling, the conductors are routed on an inner layer of the pcb, sandwiched between two ground planes. I ...
3
votes
2answers
263 views

Which of these Stripline Impedance Calculations is correct?

Different sources are giving me drastically different characteristic impedance values, and am hoping someone will verify them for me. Generally, with microstrip, I start with an online calculator to ...
4
votes
3answers
1k views

Can differential USB traces be routed relative to Power (not Ground) planes?

I would like to route my USB 2.0 (12MHz) signal on the bottom layer of a 4-layer PCB. However, the edge-coupled microstrips would then be referenced to the power plane, not the ground plane. The ...
0
votes
2answers
141 views

Characteristic impedance of a transmission line

characteristic impedance of a transmission line depends on frequency of transmission as can be seen by its expression. What will be the characteristic impedance of TL if my signal has two frequency ...
0
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1answer
86 views

Routing trace characterstic impedance determination based on interface

I have seen specifying routing impedance of interfaces from manufacturers like for USB Differential impedance of 90 ohms DDR2 Single ended impedance 50-60 Ohms, Differential impedance - 100-120 Ohms....
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3answers
207 views

Output impedance refers to open circuit o/p impedance or short circuit o/p impedance?

When we specify output impedance of a two port network, does it imply open circuit output impedance or short circuit output impedance? Wikipedia: output impedance ; Wikipedia: two-port network g22 (...
3
votes
3answers
154 views

Controlled Impedance Microstrip Frequency

Are you supposed to calculate the characteristic impedance for the frequency you are using or at 1GHz? I see pretty much everything calculated at 1GHz in all examples and papers. For example - for ...
4
votes
1answer
862 views

Calculating differential PCB traces - Edge-Coupled Microstrip

I finally have the microstrip characteristic impedance thing figured out. But now, of course, I need to learn about differential signalling on PCB traces. I've spent some time researching. Here is ...
5
votes
1answer
3k views

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 ...
2
votes
2answers
952 views

What types of signals should be considered to have a 50 Ω trace impedance?

Generally speaking, what time of signals should be designed to have a 50 Ω trace impedance ? Some datasheets I've read have specifically mentioned 50 Ω but others have not. Is it good practice to ...
3
votes
1answer
221 views

RF Circuit (what does capacitor do?)

I'm trying to work out why a 0.7pF capacitor was chosen. The circuit operates at 12GHz. At 12GHz, the capacitor has an impedance of about \$18\Omega\$. Also at 12GHz, ...
0
votes
1answer
93 views

RF Ground (Reflections?)

I'm trying to understand how someone can ground an RF signal (especially relating to microstrip lines). I think I'm missing something... Since the impedance of ground is supposed to be \$0\Omega\$, ...
3
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3answers
442 views

Consensus on microstrip trace impedance calculations?

I'm designing a PCB that has a 2.4GHz signal that I'm routing to an SMA jack. I'm trying to figure out the geometry of the necessary microstrip trace. This is the first rf PCB I've worked on. The ...
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votes
2answers
134 views

Stripline impedace ..?

i have a doubt in stripline impedance calculation. general strip line calculations are taking strip line as having 2 planes on top and bottom . in our case stackup is such that, on bottom side plane ...
14
votes
2answers
781 views

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 ...
3
votes
2answers
8k views

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 ...
7
votes
3answers
299 views

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 ...
3
votes
2answers
3k views

Derivation of Characteristic Impedance?

I start from the telegrapher's equation: \$-\frac{dV(z)}{dz}=(R'+j\omega L')I(z)\$, where \$V(z)\$ and \$I(z)\$ are the phasors of voltage and current respectively, in the transmission line model. \$R'...
2
votes
1answer
5k views

Reflecting impedance in a transformer

Please can anyone tell me what exactly is meant by reflecting of impedance in a transformer? I do not know much about transformers, but I want to know about its uses and phenomena behind it. I will ...
2
votes
0answers
225 views

Problem related to the compliance voltage

I have a question that I am using a stimulator to generate biphasic current source for stimulation. At the output of the stimulator, a 1K resistor is in series with 0.1uF capacitor. The I use two ...
2
votes
2answers
307 views

terminated cable capacitance

As much as I know, the input impedance of a coaxial cable with a characteristic impedance of 50 \$\Omega\$ which is terminated with a 50 \$\Omega\$ load resistor, should be 50 \$\Omega\$ as well. This ...
33
votes
4answers
18k views

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 ...
6
votes
2answers
7k views

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 ...
13
votes
1answer
2k views

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 ...
23
votes
3answers
731 views

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 ...
4
votes
2answers
1k views

Impedance Matching for Short-Low Frequency Traces

Is it necessary to have impedance matching for short PCB traces if the frequency is lower than say 100MHz ? I've read somewhere that for a trace to be considered a transmission line it should have a ...
1
vote
3answers
2k views

Why is impedance represented as a complex number?

Let me know one thing. Why is impedance represented by a complex number when considering loss? Usually it is said that imaginary part is because of loss. Is it True? If it is true then does that ...
6
votes
3answers
821 views

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 ...
2
votes
2answers
4k views

When does controlled impedance on a PCB matter?

Suppose I have a PCB that contains a microprocessor, or an FPGA (a "controller"). This "controller" drives a single-ended signal to an LVDS driver IC and a single-ended signal to a connector that goes ...