Questions tagged [noise]

About issues caused by electrical noise, or improving the Signal/Noise ratio of an analog circuit.

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7
votes
1answer
6k 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 ...
30
votes
5answers
41k 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 ...
29
votes
7answers
20k 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 ...
19
votes
2answers
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 ...
19
votes
3answers
12k 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 ...
19
votes
3answers
12k 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 ...
42
votes
3answers
50k views

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, ...
21
votes
2answers
8k 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 ...
12
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2answers
3k 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 ...
27
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2answers
4k 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 ...
9
votes
1answer
2k views

Ground noise and voltage drop problem

I have an RC device powered by a 3.7V poly battery, which includes a motor and a 40KHz sonar. The voltage across the sonar sensor is amplified and then adc-ed. The motor is driven by a 2KHz PWM. When ...
6
votes
2answers
3k views

Triac spurious triggering issue

I have a circuit where I am using triacs to switch home appliances like fan, tube light etc. This is the circuit I am using: (TRIAC1, TRIAC2, TRIAC3 come from arduino GPIO pins) First load is a fan ...
6
votes
1answer
1k 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 ...
15
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3answers
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 ...
7
votes
6answers
37k views

What causes old power supplies to start humming?

I have a number of mains-powered devices that have begun humming (I assume at 50Hz, though I haven't measured it). These include clock radios, a speaker system, a lamp (20W halogen with a transformer ...
1
vote
1answer
734 views

Strange noise on DDS

I have built an FPGA based DDS (fc=200MHz. out: 0-50 or 0-80 MHz) . I have a decent DAC output wave and now trying to build an appropriate filter for it ( Fig-1 ). The filter works rather fine but ...
1
vote
2answers
178 views

Power supply noise problem in a measurement system

This might be a bit long to explain but actually a power supply noise is affecting a system's measurements. I will briefly try to explain the system and the noise issue with several pics. This is ...
0
votes
0answers
138 views

Where might the noise be coming from in this speaker driver circuit?

Well, it will be a broad schematic. To summarize, there my approach is: Yellow part is for oscilations at three different freqs(around 0.8 - 2 kHz, different for each of the three signals), ...
29
votes
6answers
12k 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 ...
46
votes
3answers
9k 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 ...
11
votes
3answers
19k 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 ...
39
votes
9answers
10k 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 ...
26
votes
4answers
7k 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 (...
11
votes
4answers
15k 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 ...
11
votes
4answers
24k 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 ...
18
votes
2answers
20k 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 ...
17
votes
3answers
7k 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,...
10
votes
7answers
22k views

LM386 audio amplifier not amplifying

This is my first attempt at making a really simple audio amplifier. The schematics are below:- First I tried connecting the circuit to a 9V battery. (Multimeter reads around 8.3 Volts, which is in ...
15
votes
6answers
22k 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 ...
7
votes
2answers
4k views

Accelerometer double integration error

I wanted to use an accelerometer or IMU to measure speed and displacement over a period of about 1 minute or 400m. From this answer I found at stackoverflow, the error propagates at a rate of \$t^2\$ (...
5
votes
3answers
10k views

Ground loop? Switch mode power supply noise

I have a single 12V supply powering a 12V class D audio amplifier (Tripath TA2020 based, model 'SMSL SA-36') (C) and a very cheap 12V to 5V 2A rated switch mode converter (A). The 5V is used to power ...
4
votes
2answers
11k views

Best way to filter DC-DC output noise

This question has arisen due to the below issue, where a analog design board was scrapped due to too much noise from switching regulators. eliminating-those-unwanted-op-amptia-outputs The design ...
4
votes
2answers
8k views

Zener Noise Generator - NPN BJT Amplifier Analysis

I'm interested in creating a low voltage white noise generator by means of a zener diode, as detailed here: Zener & BJT Noise Generator. Specifically, I want to use the circuit here, in order to ...
7
votes
1answer
3k views

What component of my phone charger produces chirps and how does it do that?

My Nokia cell phone is charged with a very lightweight compact charger similar to this AC-15 (can't find the one I actually use). While the battery is close to empty the charger works silently - just ...
6
votes
5answers
2k views

What kind of DC power supply has least noise

I operate an MEG system (extremely sensitive magnetic sensors for measuring brain activity) and I recently found that the DC power source that feeds into our magnetic shielded room (power used for ...
2
votes
1answer
341 views

Noise can be Differential or Common!

I have a basic understanding on this topic but i still have some doubts, my text books says Differential means it will have impact on one of the 2 signal nodes. and Common will have a common impact on ...
12
votes
4answers
2k 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 ...
7
votes
5answers
7k views

Why does my electret microphone amplifying and filtering circuit output so much noise?

Background information I'm currently designing a input conditioning circuit that amplifies and filters a electret microphone signal in preparation for the signal to be processed by an ADC (analogue ...
5
votes
2answers
1k views

Noise Gain of Op Amp

Why is the noise gain of an op amp always constant at $$1+\frac{R_1}{R_2}$$ and independent of configuration, unlike signal gain?
3
votes
2answers
343 views

Trouble with Schimtt trigger settings for varying sinusoidal inputs

To make my problem easier to describe, I drew the above figures (abbreviated as Fig.). The sinusoidal input comes from a rotating device, from a small alternator(a permanent magnet AC generator). ...
1
vote
1answer
325 views

Microcontroller GPIO in audio circuits

I'm designing an analog synthesizer, which is controlled by an STM32 -microcontroller. In several parts of the circuit, I intend to use a GPIO pin to control switches in the circuit, and in two ...
9
votes
2answers
8k views

Power supply noise in audio

I have what is surely a classic problem with regard to power supply switching noise and audio but I am unable to sort myth from reality with regard to what I found so far on the topic. Setup: I have ...
8
votes
1answer
3k views

How do I choose a ferite bead for power supply filtering?

I want to put a ferite bead on positive SMPS supply rail that goes to analog part of the mixed digital/analog circuit. Now on parametric search at Digikey I can see several parameters: Current ...
5
votes
1answer
629 views

Why are there two sets of ENBW correction factors?

For calculating the equivalent noise bandwidth of a non-brickwall filter, I can find two different sets of numbers, both of which claim they are similar things: ...
0
votes
1answer
456 views

What could be causing this interference and how to eliminate it?

(update: Please also see the major edit at the end) A sensitive electronic equipment Device 1 below is basically composed of a power line EMI filter at the mains entry, an SMPS power supply which ...
0
votes
0answers
213 views

How to do switching noise analysis of dcdc on LTSpice

Background : In one of my board i have used LT8471 as DCDC , as my cards being analog cards, i tried maximum to seperate the power network and analog chain from noise, my initial problems with dc-dc ...
15
votes
5answers
28k 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 ...
19
votes
4answers
11k 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 ...
14
votes
1answer
1k 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 ...
9
votes
3answers
16k views

How to filter noise from ground?

I have an audio application scenario here. The Idea is to power a device (that later produces sound) with USB. Unfortunately, I have massive static and what sounds like pink (Brownian) noise on GND. ...