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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Circuit to Convert Line Level to Mic Level

How would I design a circuit that converts a line level signal to be able to be fed into a microphone input? The input impedance of the microphone jack is 2 kohms.
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Impedance matching

What is impedance matching? Why it is used?
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Can the characteristic impedance Z0 of a conductor be measured?

We have a custom made data cable at my work, is there any good way to measure \$Z_0\$ of a cable, or must the formulas be used? Trying to work out what value termination resistor to use.
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Complex Impedances

What does it mean to have a complex impedance? For example, the impedance of a capacitor (in the Laplace domain?) is given by 1/sC (I believe) which equates to \$ \dfrac{1}{j \cdot 2 \pi \cdot f \cdot C}\$ where transients are neglected. What does…
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50-ohm trace impedance

I've just calculated trace parameters so that it would have 50 Ohm impedance on PCB. Then I've noticed, that its impedance does not change when I make line longer or shorter as long as I leave trace width & distance to ground plane intact. Is that…
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Why doesn't the real part of the impedance always equal to the resistor in an ideal parallel RC circuit?

A little confused when doing a quite simple AC simulation in ADS with a parallel RC circuit. 2 kΩ in parallel with a 12 pF. See the picture: My question is that why the real part of the impedance changes with frequency. Doesn't the real part…
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How does the conversion between admittance and impedance affect phase angle?

Wikipedia tells me that admittance \$Y\$ is the reciprocal of impedance \$Z\$: \$ Y = Z^{-1} = \dfrac{1}{R+jX}\$ which makes plain enough sense to me, except that I've forgotten how complex numbers work from high-school math. If someone gives me an…
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When do you need impedance matching?

Would anyone please explain why you don't need a controlled impedance board when you produce a PCB dealing with 50Mhz digital signal? I thought you might need a controlled impedance board, since 10Mhz is already fast enough to make problems 'in…
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What does impedance in datasheets mean?

Can anyone explain impedance in a datasheet? What does this mean: (50 uH + 5 ohm) || 50 ohm Line impedance stabilization network (LISN). Like this one : schwarzbeck.de/Datenblatt/k8124.pdf.
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How to measure headphone impedance for a target cut off frequency?

Lets say I have an audio signal with a DC offset and I want to use my earplugs to listen it clearly. Since I'm a human my hearing range is 20Hz to 20kHz. It means I need to filter very low frequency components i.e where f<20Hz. It means the cutoff…
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Output Impedance of a Digital Output

In High-Speed Digital Design, Dr. Johnson illustrates an example of calculating the output impedance of an IC (page 48.). He uses VOL of 0.15 V and VOH of 4.32 V (@ Vcc = 4.5 V) with an Io of 4 mA to compute a typical low state output resistance of…
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Impedance of headphones

This is probably the best article for a beginner about impedance with respect to headphones. I haven't managed to find an explanation of why the impedance of headphones is just a single, real number (like 250 Ohm). I thought impedance is a complex…
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Meaning of "impedance looking into..."?

I know that this is a very basic question. While learning electronics, I see the phrase "the impedance looking into X" very often (e.g. in The Art of Electronics, 3rd edition), but I haven't seen a clear definition. As someone with good background…
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How to build a 75 ohm to 50 ohm converter

I need help to build a simple converter to match a 75 ohm feed line to a 50 ohm antenna. Please help :-(
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