Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [impedance]

Impedance defines the voltage/current characteristic of any dipole circuit.

Impedance defines the voltage/current characteristic of any dipole circuit (a circuit with two terminals).

It's a complex number in that it relates both the magnitude and the phase of the voltage in relation to the current: Z = V/I

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Why is high input impedance good?

Naive perhaps, but Why is high input impedance a good thing? Is high input impedance always a good thing?
Everyone
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What is impedance?

This is presented as both a resource for the community and a learning experience for myself. I have just enough knowledge of the subject to get myself into trouble, but I don't have the best grasp of the subject's details. Some helpful responses…
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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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What is input and output impedance of an opamp?

I have never understood input and output impedances of an op-amp. If anyone can explain what these two terms mean in an op-amp I'd highly appreciate it. Thank you! http://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps5.html
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Why do characteristic impedances matter only when traces are longer than half a wavelength?

Why are characteristic impedances of traces not considered when the traces are shorter than half a wavelength? I've had the same issue with light diffraction, which happens when pinholes are smaller than half a wavelength - it sort of makes sense…
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Frequency dependence of electrolytic capacitors

It's said that electrolytic capacitors behave as inductors at high frequencies, which is why we put small ceramic caps in parallel with them: Electrolytic, paper, or plastic film capacitors are a poor choice for decoupling at high frequencies;…
endolith
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Resistance Vs Impedance?

What is the difference between the Resistance and Impedance? When we will say it is an Impedance and when we will say it as an Resistance? Can you explain it with diagram (If possible) and real time example. And how the reactances will form in…
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Why are high impedance circuits more sensitive to noise?

Why are high impedance circuits being more sensitive to the noise? They have less current flowing through them, but how is that related to noise, since external noise becomes voltage on the wires, and then current proportional to resistance?
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How is xΩ impedance cable defined?

This is probably a really simple question, but I can't seem to find a definite answer anywhere. I'm guessing 50Ω cable means 50Ω per unit length. What unit length is this? If this is not how its defined, how is it?
midnightBlue
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Why does ST recommend 100 nF decoupling capacitors for a 72 MHz MCU? (And not 10 nF.)

I've been reading about decoupling capacitors, and I can't seem to understand why ST recommends 100 nF decoupling capacitors on a 72 MHz ARM microcontroller. Usually 100 nF decoupling capacitors are only effective up to about 20-40 MHz due to…
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Why is impedance represented as a complex number rather than a vector?

I am trying to understand why impedance is not represented using vectors. I assume it is due to complex numbers having the property that $$j = \sqrt {-1}$$ but with my limited knowledge I can't see how this relates to impedance or why this property…
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Input impedance of Arduino Uno analog pins?

I'm using the ACS712 hall-effect based current sensing chip on some small robotic arm motors, and reading in the analog voltage with an Arduino Uno. I've had reasonably good results, but only after putting in an RC filter on the output. However,…
dustynrobots
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Constant current, constant power and constant impedance loads

Ive been looking for information on constant power, constant current and constant impedance/resistance loads, there's some information about the constant current loads, but very little that really explain constant power and constant impedance. So…
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Op-amp input resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is an instrumentation amplifier that apparently uses an inverting amplifier's output instead of a ground in the lower-right corner of the above figure, but…
In silico
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When laying out circuit board traces, what impedances do I need to consider?

I do low-speed circuit design for microcontrollers and such (usually at less than 20 MHz), and now I'm getting started on some more high-speed circuits. What I want to know is: What considerations need to be made for traces in high-speed…
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