Questions tagged [impedance]

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

Filter by
Sorted by
Tagged with
61
votes
5answers
13k views

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 ...
58
votes
8answers
159k views

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?
49
votes
5answers
44k 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 ...
40
votes
2answers
145k views

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/...
30
votes
4answers
5k views

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 ...
25
votes
2answers
33k views

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 ...
25
votes
6answers
13k views

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 ...
22
votes
3answers
14k views

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 ...
20
votes
2answers
5k views

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 ...
19
votes
9answers
6k views

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 ...
18
votes
2answers
39k views

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 ...
18
votes
5answers
13k views

Op-Amp Input Resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is of course an instrumentation amplifier that apparently uses an inverting amplifier's output instead of ...
18
votes
2answers
36k views

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 ...
16
votes
4answers
3k views

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 ...
15
votes
4answers
9k views

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 ...
14
votes
5answers
46k views

How are speakers matched with audio amplifiers? (avoiding overloading either)

I know a similar question title has been asked, but I believe that does not answer my question (and I couldn't think of a better way to phrase the question). I'm a bit confused by how exactly an amp ...
14
votes
2answers
4k views

How do you calculate the noise of an op-amp circuit?

I think I know how to do this, but you can find a lot of different instructions and calculators online that contradict each other. I have yet to find a clear, concise procedure for calculating the ...
13
votes
7answers
36k views

What is a load resistor?

I am not able to understand what a load resistor is and how does it relate with a load. Can anyone explain how the load resistor works and how is it different from the general resistor.
13
votes
5answers
13k views

ADC input impedance on MCUs

What is the input impedance of a typical MCU ADC? In this case I'm working with a PIC24FJ64GA004. I don't need high speed sampling - a maximum of 100 samples per second. I wish to connect a resistive ...
13
votes
2answers
2k views

Differential Signals - Why is having an equal impedance an advantage?

I lately heard in a course that a main advantage of differential signals is that both signals show the same impedance, whereas a single-ended signal, which is measured against ground, has a high ...
13
votes
3answers
27k views

Electronic aspects of iPhone 3.5mm audio output

I am working for a while now on a small project of building an external mic for the iPhone to be hooked in parallel to headphones (via the 3.5 mm jack). Basically, I want to replace the iPhone's ...
13
votes
4answers
3k views

How is it possible to have a 5W transmitter driving 50 ohms with a 12V supply?

So let's say you have a circuit, which generates a carrier wave at some frequency (let's say 27MHz) and it's connected to a 50 ohm dummy load (which I gather is equivalent to an antenna for circuit ...
13
votes
4answers
36k views

What does it mean for reactive power to be delivered / consumed?

Real power makes sense since there is actual consumption, but regarding reactive power; what is consumed / delivered? And how does the circuit change once this happens?
13
votes
2answers
3k views

Is paying extra for “Controlled Impedance” boards necessary?

I'm doing a bit of RF PCB design, and one of the things that caught my eye is the "Controlled Impedance" option. Checking more boxes always costs more, so I want to know if this is worth the extra ...
12
votes
2answers
2k views

Should each trace carrying RF be 50Ohm in characteristic impedance? How?

I have to translate a VHF (160MHz) receiver schematic into a PCB. After looking here and there, I am a bit confused. It seems like the main issues with RF are to avoid stray inductors and ...
12
votes
2answers
9k views

Output impedance of voltage divider?

When connecting a 10S LiPo (42V) to my ADC via a voltage divider, I began wondering how to calculate the output impedance of the divider. simulate this circuit – Schematic created using ...
11
votes
4answers
10k views

Required output impedance for ADC input?

On the Atmel ATmega328P on the Arduino Uno, the ADC RAIN value is 100 MΩ - which I assume is the ADC input impedance. However, in the datasheet it says "The ADC is optimized for analog signals ...
11
votes
5answers
5k views

Impedance Matching and Large Trace Widths

I am currently working on a design in which one of my ICs specifies the use of a 50 ohm trace. The answer to this question, Characteristic impedance of a trace, shows that a 120 mil trace is required ...
11
votes
2answers
4k views

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.
11
votes
4answers
25k views

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.
11
votes
4answers
2k views

Setting audio output impedance for output protection

I'm building a module for a modular synthesizer, according to the Eurorack standard. So this is a module intended to be connected to other modules via patch cables. While the above standard page does ...
11
votes
5answers
2k views

Art of Electronics: Emitter-Follower Zout

I am a growing frustrated with the Art of Electronics. It is such an approachable book in Chapter 1, and then in Chapter 2 it seems like the authors wanted to make it more textbook-like and they ...
11
votes
3answers
1k views

Measuring impedance

I am designing and building circuits which use 100Mb/s on a Low Voltage Differential Signaling (LVDS) bus. Some of these signals need to travel between PCBs on hand made cables. The problem is that I ...
10
votes
7answers
4k views

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 \...
10
votes
1answer
2k views

Why does this circuit oscillate?

The circuit below is an oscillator. When I simulate it with ltspice, it does indeed generate a waveform (although it doesn't seem to be a very pure sine wave). What I fail to understand is why it ...
10
votes
3answers
22k views

Input impedance of inverting amplifier clarification

Take a standard inverting amplifier: I'm unclear on what the input impedance is. At first I thought it was the equivalent resistance from the inverting input to the ground, which would be Rin || Rf, ...
10
votes
2answers
1k views

Impedance matching

What is impedance matching? Why it is used?
10
votes
4answers
432 views

Contact a very small area (impedance matched)

In my current project, I want to apply a voltage to a capacitor (top electrode on a thin film heterostructure) very rapidly. Since capacitors have their own charging rate \$(\tau = R \cdot t = R \cdot ...
9
votes
4answers
2k views

Why does the cable resistance jump from a low value to high value at a particular frequency?

I am not well versed with transmission line theory so if you can redirect me to relevant material I'd be grateful. So I used Agilent 4294A to find resistance of a 2 metre long shielded twisted pair ...
9
votes
6answers
10k views

Why do different value capacitors and resistors sound different in same amplifier circuit?

I have two questions... I have seen that different value capacitors in an amplifier circuit, sound different... For example, an amplifier circuit with a 470uf capacitor, has more bass, and treble... ...
9
votes
4answers
3k views

Why do cables have multiple grounds?

Many cables have multiple grounds. Why? For example, according to Wikipedia: The SATA standard defines a data cable with seven conductors (3 grounds and 4 active data lines in two pairs) and 8 mm ...
9
votes
1answer
3k views

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 ...
9
votes
2answers
4k views

Is this resistor needed in this opamp circuit?

I'm looking at the datasheet of the MCP6241. There's this schematic: The op-amp has a input bias current of 1 pA, and \$ 10^{ 13}\Omega\$ input impedance. Is resistor Rz still needed then?
9
votes
1answer
1k views

Impedance of differential inputs on AD converters

I'm currently trying to attach a rather fast ADC/DAC-converter chip to an FPGA to receive and transmit RF in the future, but getting the converter to run and attaching a signal generator and an ...
9
votes
0answers
762 views

Input Impedance calculation [closed]

I am trying to calculate input impedence of a MFB low pass filter. What I need is the symbolic expression as simple as possible so that later I fill in the values and get the impedence itself: I am ...
8
votes
5answers
7k views

How to compute input impedance?

I use a Sallen-Key filter for a project at university and I need to know its input impedance. Is there a way to compute it theoretically ? Here is my circuit:
8
votes
4answers
2k views

Does the impedance of a PCB track matter if the length of the track is far smaller than the wavelength of the signal?

I have a PCB with tracks of no controlled impedance. The longest track is shorter than 1/5000 of a wavelength. Does the impedance of the track even matter? If not, then at what length would I need ...
8
votes
1answer
6k views

Why are loudspeakers manufactured in various impedance values?

I'm acquainted with the concept of impedance matching in audio applications, but there's something that eludes me. First, a snippet from a home theater site: Loudspeakers have impedances of 8 ohms, ...
8
votes
2answers
2k views

Standard 2.54/1.27mm pinheader impedance

Note I turned my answer into something of a collection of free impedance calculators.. I was thinking of using one of the most ubiquitous connectors in the world - 2.54mm pin header. The snag here is ...
8
votes
2answers
16k 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 ...

1
2 3 4 5
22