Questions tagged [noise]

Noise is an unwanted disturbance in an electrical signal. This tag is for questions about sources of noise, noise types, issues caused by electrical noise, or improving the signal-to-noise ratio of an analog circuit.

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Noise and what does V/√Hz actually mean?

Noise figures in (op-amp) datasheets are expressed in V/√Hz, but Where does this unit come from? Why the square root? How should I pronounce it? How should I interpret it? I know lower is better, but ...
jippie's user avatar
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50 votes
4 answers
14k views

Loud pop noise while plugging to a headphones jack

I have a Panasonic RX-ES29 boombox with a type C plug (ungrounded). I sometimes hear a relatively loud snap/pop sound in the right speaker of my headphones while I completely plug them into the ...
Sepp A's user avatar
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41 votes
9 answers
11k views

How can "purely" electrical circuits emit sound?

Moving membranes or piezoelectric materials obviously produce sound waves, but how can "purely" electrical circuits such as transformers or DCDC choppers (and others) often have an audible noise? Is ...
Mister Mystère's user avatar
41 votes
6 answers
55k views

What is "common-mode" noise?

Can someone explain what "common-mode" noise is, and how it can be problematic? I understand "noise" on a signal in general. If I have a "noisy" +5V rail on a circuit board, I'm not going to be ...
Adam Head's user avatar
  • 1,436
38 votes
4 answers
2k views

Identifying Source of Periodic Artifact at Op-Amp Output

My MAX44251 dual op-amp has a very small unwanted 131KHz periodic artifact at the output, seemingly regardless of how it's configured. My assumption was EMI, but I can't see this 131KHz signal on any ...
Keegan Jay's user avatar
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33 votes
7 answers
27k views

Why does GSM cause speakers to buzz?

Based on numerous internet resources, speaker wire acts like an antenna which picks up the transmitted signal of nearby cellphones and causes the speakers to buzz. But I'm not really buying that... A ...
JSideris's user avatar
  • 599
31 votes
6 answers
7k views

Why do some EMI/RF shields have holes on the top and some don't?

I am not talking about cutouts for tall components. I don't think they are for ventilation as they are often covered with manufacturer labels.
Dojo's user avatar
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31 votes
6 answers
14k views

Noise reduction strategies in electrophysiology

When recording electrical signals from cells (in a dish or inside a living human or animal body), one major problem is to increase the signal to noise ratio. These signals are usually in the 10uV to ...
Ali's user avatar
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30 votes
4 answers
10k views

Why is it good to slow down digital lines with resistors?

I've heard that sometimes it is recommended to "slow down" a digital line by putting a resistor on it, let's say a 100 ohm resistor between the output of one chip and the input of another chip (...
Alex I's user avatar
  • 3,401
29 votes
2 answers
5k views

How to disable a single op-amp in dual packaging?

I am using a dual op-amp package in a circuit, however I only need to use one. Is there anyway to disable the other op-amp so it doesn't inject electrical noise in my circuitboard? I think grounding ...
user1207381's user avatar
26 votes
8 answers
9k views

Is it possible to receive information if the received power is below the noise floor?

This relates to my previous question, which I think I have asked in the wrong way: How to insert background EM noise into pathloss equation? I wasn't really interested in detectability of the signal,...
David K.'s user avatar
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26 votes
3 answers
3k views

Is twisting a single ended signal with its own GND really useful?

I know that the most robust way of transferring an analog signal over long distances is via differential pairs which are twisted together and then shielded (shield grounded at one end only). But ...
user42875's user avatar
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25 votes
3 answers
18k 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 ...
1p2r3k4t's user avatar
  • 706
24 votes
2 answers
13k views

Via fences for noise reduction of a chip antenna?

I'm working on a 4-layer PCB that has a wifi module and a chip antenna, the antenna is placed at the corner of the PCB and the copper beneath it is removed, I see that via fences are used on the ...
mux's user avatar
  • 1,886
22 votes
7 answers
40k views

Ferrite bead position

I wish to use some extra power supply filtering for my DAC, ADC, CPLD and OpAmp devices. In this question I got the point about the global locations for ferrite beads. If I understood correctly, the ...
Nazar's user avatar
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22 votes
4 answers
17k views

How to clean up a noisy signal?

I'm controlling a 4-pin PWM PC fan from a PIC16F684 with the fan speed driven from an ADC reading of a proximity sensor. This all works ok. I wasn't originally planning to use the tachometer output ...
Roger Rowland's user avatar
21 votes
6 answers
5k views

How to combat noise from my circuit polluting my 12V rail?

I made a controller for 12V DC fan. It is basically a buck DC-DC converter controlled by voltage. It regulates voltage for fan from 3V (lowest speed, fan draws 60mA @ 3V) to 12V (full speed, fan draws ...
Chupacabras's user avatar
  • 5,434
21 votes
8 answers
32k views

Reduction of DC motor noise

I am designing a circuit with a DC motor 12V DC Reversible Gearhead Motors - 70RPM and some other stuff including a MCU and a LASER, all driven from a single 12V source and am concerned about big HF ...
ElecEnthusiast's user avatar
21 votes
2 answers
25k views

What might be the cause of high pitch sound coming from a switching regulator circuit?

We designed a switching regulator circuit using a 1.5MHz, internal-switch, switching regulator (semtech.com/images/datasheet/sc185.pdf). Vin is 5V, Vout is 3V3. We have an input capacitor (47uf), an ...
SomethingBetter's user avatar
19 votes
2 answers
2k views

Why does connecting a high-current device to my digital circuit cause weird behavior?

I have a arduino microcontroller other digital thing and when I connect a motor pump heater other high current thing I experience weird ADC measurements reboots crashes errors in digital ...
Phil Frost's user avatar
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19 votes
3 answers
14k views

How do you choose an inductor for connecting separate ground planes?

On a board with separate analog and digital ground planes connected at one place, the connection is often made with an inductor. How is this inductor chosen? Obviously it has to be able to handle ...
Jeanne Pindar's user avatar
18 votes
3 answers
8k views

What problems could occur when chaining 40 shift registers?

I'm planning on chaining together 40 x 74HC595 shift registers. The whole chain of 74HC595s will be controlled by a 5 V microcontroller, which will generate the SDI,...
m.Alin's user avatar
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18 votes
1 answer
2k views

What is the purpose of the fenced-off area on this board?

I saw a recent video on YouTube where the presenter describes a commercial micro-current measurement product. What purpose does this tinned fence serve? I'm guessing its for noise suppression but I'd ...
user3418620's user avatar
  • 1,330
18 votes
3 answers
3k views

Why doesn't aliasing of broad band noise 'pile up' in the sample band?

I recently built a simulation to study sampling, the effects of aliasing and the effects of anti-aliasing filters on the sampled signal. For fundamental frequencies above the sample band it's obvious ...
docscience's user avatar
17 votes
6 answers
11k views

Why use the fast Fourier transform for noise reduction instead of a classical electronic filter?

I'd like to know how to remove environmental noise from a speech recording. I've made some research and I've noticed that most of the methods proposed use the fast Fourier transform. But why can't ...
Jazis's user avatar
  • 173
16 votes
7 answers
5k views

How to filter out the switching noise from a DC/DC converter

I've set up a power supply using a MAX632 DC/DC Boost converter to bring up voltage from a small 4.5V battery, then I'm using a LM2940CT-5.0 linear regulator to bring it back to 5V, which the voltage ...
jmgonet's user avatar
  • 1,073
16 votes
5 answers
3k views

Cable shielding adequate for video, but not audio frequencies

I am no expert in audio equipment, but to educate myself I have been studying. In the process, I came across a video which tests the audio frequency shielding of a purported shielded video cable. (I ...
Math Keeps Me Busy's user avatar
16 votes
5 answers
2k views

1/f noise, is it limited?

Basically my question is: I doubt noise density goes to infinity because we can reach the limit f→0 in any DC circuit in contrast to the limit f→∞ (which is an idealization because all circuit ...
user171780's user avatar
16 votes
3 answers
2k views

Why use LNAs in a noise generator?

In this Maxim appnote the avalanche noise of a zener diode is amplified by two cascaded LNAs (Low-Noise Amplifiers): You can guess what my question is: why use low-noise amplifiers if you want ...
Federico Russo's user avatar
15 votes
3 answers
490 views

Is it sensible to always use larger diameter conductors for carrying smaller signals?

This question as originally written sounds a little bit insane: it was originally asked to me by a colleague as a joke. I am an experimental NMR physicist. I frequently want to perform physical ...
Landak's user avatar
  • 655
15 votes
2 answers
5k 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 ...
endolith's user avatar
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14 votes
7 answers
15k views

Is there any downside to using a larger than needed smoothing capacitor?

I work with low-power DC voltage regulators. I am already aware of the formula to calculate the size of smoothing capacitor(s). This can be an iterative process of testing one size with a scope and ...
PhilM's user avatar
  • 291
14 votes
1 answer
8k views

Analog & Power Ground Planes Doubts

Working on a new board, I have to face some requirements to ensure the performance of the whole system once is manufactured. PCB is a 4-layer one, and it has both analog and digital components. But ...
Yolco's user avatar
  • 367
14 votes
1 answer
2k views

What's with all this noise?

People often talk about noise in circuits. Cheap op-amps are noisy, running a motor can create noise on the supply, and a lot of analog circuits deal with the signal-to-noise ratio (ie: trying to keep ...
Greg d'Eon's user avatar
  • 3,827
14 votes
2 answers
7k views

IC power pin connection for noise immunity and decoupling

There's been much talk on other Q&A threads on how to connect decoupling capacitors to an IC, resulting in two completely opposite approaches to the problem: (a) Place decoupling capacitors as ...
andresgongora's user avatar
14 votes
3 answers
24k views

Physically, how does connecting a PCB to chassis ground reduce noise?

I realize this may seem to duplicate Should chassis ground be attached to digital ground? but the answers in that thread don't explain why one should connect the chassis to PCB ground, aside from ...
Paul L's user avatar
  • 1,262
14 votes
4 answers
2k views

Eliminating mains hum from frequency modulated RF LC oscillators

I'm trying to build a frequency modulated LC oscillator but all circuits I've tried have terrible mains hum after demodultaion. The oscillator is tuned by capacitive sensor but I'm using a fixed ...
hidefromkgb's user avatar
14 votes
1 answer
3k views

Noise problem with buck/boost switching regulator

I am designing a electrical device for a research project (I'm a PhD student, but unfortunately not EE!). More info on the device can be found at http://iridia.ulb.ac.be/supp/IridiaSupp2012-002/ The ...
arnuschky's user avatar
  • 435
13 votes
9 answers
12k views

Why Decibels are used to measure Signal to Noise Ratio?

We just started a communications course in college and we came across SN ratio. The following is an ambiguity I am facing which my professor is unable to resolve: Signal to Noise Ratio is the ratio ...
iluvthee07's user avatar
13 votes
5 answers
3k views

Can PCB test points be a source of noise?

If I want to design a PCB with as much noise immunity as possible, should I leave off test points? I'm concerned that TP4 and TP5 may be acting as antennas and picking up noise.
user256639's user avatar
13 votes
4 answers
25k views

What does "correlation" mean in signal processing?

What do the words "correlated" and "uncorrelated" mean in signal processing? E.g. - "uncorrelated white noise.."
Let It Be's user avatar
  • 169
13 votes
3 answers
13k views

Need help with eliminating LED-generated noise

I am very new to electronics, to electronics.SE.com and this is my very first project, so bear with me if my question misses some key-information (in such case, just leave a comment and I will try to ...
mac's user avatar
  • 315
13 votes
7 answers
1k views

Amplifying a nV signal across a small resistance

I am interested in the feasibility of amplifying/measuring a nV level (or otherwise assumed very small) signal across a small resistance. The SNR of this signal isn't so bad in itself because of the ...
Orhym's user avatar
  • 241
13 votes
4 answers
5k views

Should I ground the heatsink?

I am using an npn transistor in TO-220 package, and its collector is electrically connected to the metal part on it. I have checked it via a multimeter. I use a heatsink for that transistor, with ...
muyustan's user avatar
  • 2,066
13 votes
4 answers
29k views

Implementing guard trace/ring in PCB design

I have read here and there some articles about pcb guard trace/ring. But none of them discussed how to correctly implent it. What I could find were some pictures and comparison that cant help me at ...
Dumbo's user avatar
  • 3,274
13 votes
2 answers
2k views

Hobby oscilloscope based on AVR. How to remove op-amp noise?

I'm building a hobby oscilloscope on an ATmega16 microcontroller. The main problem is that I receive a large amount of noise while measuring the signal. I used LF353 amplifiers to shift voltage and I ...
Ashton H.'s user avatar
  • 801
13 votes
5 answers
3k views

Which is the preferred approach to PCB layout for signal vs power traces in analog circuits, and things to consider?

I have had to layout 2 layer PCBs several times now for analog signals, and am just beginning to learn the process. I often face a similar question in one form or another with regard to laying out ...
teeeeee's user avatar
  • 765
12 votes
4 answers
21k views

How do I eliminate PWM noise when driving a fan?

I'm driving a 12V 0.11A brushless DC fan with PWM using an MSP430Gxxxx --> TC427CPA FET driver --> BS170 N-FET. The fan is on the low side of the FET. Even with a duty cycle of 90% and a frequency of ...
Vincent Van Den Berghe's user avatar
12 votes
4 answers
3k views

Why exactly is it discouraged to gap the ground plane?

From time to time I hear (and read) that it is not good to make separate Gnd planes for digital and analog circuit parts. It's all summarized in this rule of thumb: "Don't split the Gnd plane, don't ...
K.Mulier's user avatar
  • 2,349
12 votes
1 answer
2k views

Are reverse biased transistors stable?

The usual circuit (found widely across the internet) for a true random number generator's (TRNG) entropy source is a reverse biased transistor like so: Q1 is typically a 2N3904 as it has been found ...
Paul Uszak's user avatar
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