Questions tagged [low-pass]

A low-pass filter lets lower frequencies through and blocks or reduces higher frequencies.

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How do I choose component values when designing a Low/High pass RC filter?

The cut-off frequency of a RC filter is obtained from the well known equation, $$1\over(2 \pi RC)$$ This is one equation with two variables. For example, R=100, C=10 has the same result as R=10, C=100....
Aug's user avatar
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16 votes
2 answers
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How to identify filter behaviour without memorizing different topologies

Is there a way to tell if a circuit is high or low pass without memorizing different topologies?
DragonDude's user avatar
13 votes
4 answers
4k views

Why don't decoupling/bypass capacitors need resistors to perform their function, like regular filters?

Why don't decoupling/bypass capacitors need resistors to perform their function, like regular filters? Is it because the stray resistance of copper traces is enough to filter, along with the ...
Rafael's user avatar
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12 votes
3 answers
19k views

What is the advantage of a Sallen-Key filter over a normal second order filter?

Wikipedia links to a Sallen-Key filter as a active low pass, so I tried it out with LTSpice. The frequency response and phase response are not linear, instead frequency response even gets higher ...
Christian's user avatar
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12 votes
4 answers
4k views

Is a 100 Ω/1 nF RC low-pass filter enough to protect a microcontroller I/O pin from ESD?

While researching ESD protection on this site, I came across this question. The answer by Peter Smith contains a comment by @Ale..chenski: Just a nit pick: if you can afford 100R and 1nF to ground on ...
Unimportant's user avatar
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11 votes
3 answers
8k views

Understanding the AVCC pin wiring on ArduinoLeonardo (low-pass filter?)

The Arduino Leonardo has an interesting difference with previous boards: the AVCC pin of the ATMEGA32U4 is connected to +5V through a MH2029-300Y ferrite beads and to GND through a 1uF capacitor. In ...
sarfata's user avatar
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9 votes
4 answers
727 views

Cut-off frequency, gain and quality factor calculation of complex 2nd order low pass filter

I'm building a full analog chorus-effect pedal. My schematic is based on that of a Rockman X100 headphone amp, designed by Tom Sholz. In this schematic, there is a 2nd order low pass filter that looks ...
Linus Tielemans's user avatar
9 votes
5 answers
6k views

Difference: Low Pass Filter and Large Capacitor?

When working with microcontrollers it is recommended to place filter/decoupling capacitors between a supply pin and ground. I understand the purpose of this implementation, namely that voltage across ...
sherrellbc's user avatar
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9 votes
2 answers
3k views

Low pass filter with two capacitors?

I'm trying to drive a speaker from an ESP8266 for a project, and found an article suggesting (ab)using I2S as a 1-bit Pulse Density Modulation DAC. Apparently that's pretty noisy, so the article gives ...
Garth Kidd's user avatar
9 votes
2 answers
2k views

What is wrong with this butterworth filter, how can it be improved?

I have designed a 6th order butterworth low pass filter with 20KHz cut off frequency using Sallen Key topology (thanks Andy Aka). The filter is behaving as expected with the cut off frequency and roll-...
quantum231's user avatar
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9 votes
5 answers
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Why does my electret microphone amplifying and filtering circuit output so much noise?

Background information I'm currently designing an input conditioning circuit that amplifies and filters an electret microphone signal in preparation for the signal to be processed by an ADC (analogue ...
SIMPLY MARC's user avatar
9 votes
4 answers
15k views

Divider and lowpass combined

I am using the following circuit for two purposes: As a voltage divider, to reduce DC sensor output to a range suitable for my ADC. As a lowpass filter, to remove high frequency noise from the signal....
Jeremiah Rose's user avatar
9 votes
4 answers
37k views

Why a low-pass filter applied to a square wave gives a weird wave?

When a low-pass filter acts on a square wave, the output is something similar to this: My question is simple. If the filter is a low-pass filter, it should filter all frequencies that are above some ...
felipeek's user avatar
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9 votes
3 answers
530 views

Question about RC charge-discharge curve

I found the following image on electronics-tutorials.ws: Isn't this wrong? Shouldn't the voltage rise faster during the first 2T than that it decreases during the next half period? I think so ...
flup's user avatar
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9 votes
1 answer
1k views

Significance of cut-off frequency in a low-pass filter

My question is: why do we choose cut-off frequency to satisfy that the magnitude of transfer function \$ H(\omega) = \frac{1}{\sqrt{2}} \$? Therefore I am not asking how cut-off frequency is ...
Binary Yildirim's user avatar
8 votes
6 answers
4k views

Decoupling Capacitors: What happens to the DC on the cap once noise is introduced and it shorts?

simulate this circuit – Schematic created using CircuitLab I've been using decoupling caps for a while now and I understand their purpose in keeping DC signals clean since capacitors allow high ...
OhmerSimpson's user avatar
8 votes
3 answers
16k views

Trying to determine the output of a RC-filter with load

I have a low pass filter like this: simulate this circuit – Schematic created using CircuitLab \$V_{\text{out}}\$ is measured right after \$R_1\$, which I suppose means that it is measured ...
rablentain's user avatar
8 votes
5 answers
6k views

How to Calculate Complex Low Pass Passive RLC Filters?

I have designed a FPGA based DDS and now I want to add a low pass filter to its output. Previously I was working on a project based on AD9850 DDS(0-50MHz) and I had a commercial module for it that had ...
Aug's user avatar
  • 1,571
7 votes
3 answers
3k views

Why is inverting op-amp behaving like a low pass filter?

can anyone explain why this circuit behaves like a low pass filter despite having no capacitor in the feedback loop?
mwilliams25's user avatar
7 votes
3 answers
2k views

Strange Distortion from Second Order Active Low Pass Filter

I'm feeding a 250KHz PWM audio signal from an ATtiny85 into a second order active low pass filter: The output is then fed into a decoupling capacitor and then into an LM324 amplifier. The output of ...
mbmast's user avatar
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6 votes
4 answers
9k views

Bypass capacitor vs low-pass filter

i'm trying to get my head round two intermingling factors relating primarily to an rc low pass filter and bypass capacitors for providing a low impedance path for high frequency AC signals, ...
ConfusedCheese's user avatar
6 votes
5 answers
2k views

Transfer function of second-order Butterworth filter

I'm trying to understand the second order Butterworth filter and build a transfer function of it for analysing in the frequency plane. I have my second order Butterworth filter. Then I specify the ...
euraad's user avatar
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6 votes
5 answers
4k views

How to recognize the type of analog filter given its topology?

Having trouble to tell what kind of filter (Low-Pass, High-Pass, Band-Pass, Band-Reject(Notch) are present given a topology in cascade. In the following picture I see 3 stages, is this ok? (2 active ...
mongoose85's user avatar
6 votes
5 answers
5k views

How to calculate the frequency of oscillation of this low-pass phase shift oscillator?

In the following phase-shift oscillator a low pass network is used instead of a high-pass network. simulate this circuit – Schematic created using CircuitLab Usually the frequency of ...
Physco111's user avatar
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6 votes
2 answers
487 views

Trying to implement a digital IIR filter why is this happening?

hope everyone is staying safe. I am trying to implement a digital filter that I made from a continuous transfer function onto a STM32 microcontroller. Using the CMSIS DSP functions found here ...
Leoc's user avatar
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6 votes
4 answers
866 views

Simple low pass digital filter implementation for non-uniform sampling?

I have a system sampling an analog input and I want to filter that value using a simple, first order filter. EG something of the form: Yn = A*Xn + B*Yn-1 However I have no control over the ...
Peter M's user avatar
  • 298
6 votes
2 answers
351 views

3dB Cutoff Measurement vs (Calculated + Simulated)

I am stumbling upon a very strange situation unless I did something totally wrong in my measurement setup. Speaking of it, I've installed an acoustic measurement tool (REW) and measured for testing ...
abg1984's user avatar
  • 121
6 votes
2 answers
3k views

100W Low Pass Filter

Currently I have a 60W amplifier for the 400-500MHZ band with a 50Ω impedance. In order to prevent jamming other frequencies I will need a low pass filter to block any frequencies above 500MHZ. I just ...
Mykson's user avatar
  • 61
6 votes
2 answers
13k views

What is the transfer function of n-cascaded RC filters?

Is there an explicit formulation for n-cascaded RC filters? The resistor and capacitor values are not necessarily same. Assume that: \$ R_i \neq R_j \$ and \$ C_i \neq C_j \$ for \$ i \neq j\$ and \$ ...
hkBattousai's user avatar
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5 votes
5 answers
938 views

Will a low-pass filter make zero-crossing detection less precise?

In my application I need to sample a number of bipolar signals coming from piezo sensors, and detect their relative time difference (for multilateration based on difference time of arrival). I expect ...
ris8_allo_zen0's user avatar
5 votes
1 answer
307 views

Why do my high and low pass filters look like high pass filters in LTSpice plot?

I am new to this and trying to learn about designing analogue audio filters. I looked at a couple of tutorials online that gave examples about how to implement and simulate high and low pass filters. ...
Rob Hinchliff's user avatar
5 votes
2 answers
12k views

Should I always put a low-pass filter on an ADC input?

I'm a recent hobbyist EE and new to micro controllers. I've built a test circuit to make measurements with a type K thermocouple, a PT1000 as well as an oxygen sensor. The weak signals go through a ...
Torsten Römer's user avatar
5 votes
2 answers
703 views

What is the steepest roll-off achievable for an analogue low-pass constructed with a single op-amp?

I was wondering about this question. What if the only design requirement is having the highest steepness of the roll-off but using only one op-amp? I know it's possible to construct approximations of ...
Sanuuu's user avatar
  • 387
5 votes
2 answers
13k views

How to design a 4th/6th/8th passive low pass filter?

I am trying to design a 4th/6th/8th passive low pass filter. The filter is used after a DAC to generate a fixed frequency sine wave. The DAC will export a square wave at 1kHz. So the pass band of the ...
richieqianle's user avatar
  • 1,612
5 votes
2 answers
713 views

TI Application Report - What are those additional resistors in the low pass filter

I was searching some documents and tutorials online for filter design. Then I stumbled upon this TI application report. The following is referring to section 2, figure 7 and figure 8 of the paper. I ...
PetPaulsen's user avatar
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5 votes
3 answers
2k views

80's Cassette Line to Microphone Level for iPhone

This is a followup question to this one: Using an iPhone as a cassette recorder for 80's home computer I'm trying to record from an 80's home computer (a Microbee) into an iPhone. Although I ...
Brad Robinson's user avatar
5 votes
3 answers
379 views

Why is the output from my photodiode not linearly related to laser power?

I have some basic understanding of electronics but am having trouble optimizing our setup for laser intensity measurements. Currently, we are using a Thorlabs photodiode PDA100A with 50Ω terminators ...
Jordan Epstein's user avatar
5 votes
1 answer
282 views

RC low pass filter not working as expected

I have designed a high voltage power supply and I'm trying to filter out the switching noise. I'm using a transformer that is driving a basic Cockroft-Walton voltage multiplier to a 1200V DC signal. ...
bricechart's user avatar
5 votes
1 answer
327 views

Electrochemical Measurements Using Lock-In amplifier

I'm trying to measure small electrochemical signals using a trans-impedance amplifier fed into a lock-in amplifier. I have an electrochemical cell that poses a very high impedance (100s of MegaOhms) ...
zzlmes's user avatar
  • 53
5 votes
1 answer
427 views

on-chip low-pass filter with sub-Hertz cutoff frequency

Sometime ago I had to implement an on-chip (CMOS 65nm) low-pass filter (first order) with very low cutoff frequency (lower than 100mHz). I used PMOS pseudo resistors and momcap, and had to check all ...
Ali's user avatar
  • 220
5 votes
0 answers
387 views

Using a "noise eating" active low-pass filter

I'm trying to use a MAX281 low-pass IC to filter a DC signal I'm producing on-board. I'm yet to find other chips with the same features so, if you haven't come across them, they're designed to work by ...
CharlieB's user avatar
  • 229
4 votes
5 answers
5k views

What is the purpose of this simple 1 capacitor 2 resistor high pass filter?

I have seen the standard high pass filter with the -3dB cutoff frequency = \$ 1/2\pi RC\$. simulate this circuit – Schematic created using CircuitLab However I have seen this particular ...
midnightBlue's user avatar
  • 1,833
4 votes
1 answer
6k views

How to do low pass filtering on a differential signal

If I have a differential signal on a pair of wires then how would I do a simple RC low pass filter on this differential signal?
scico111's user avatar
  • 877
4 votes
3 answers
800 views

How can I calculate the total impedance of a second-order low-pass filter?

How can I calculate total impedance of this low-pass filter? Also, how can I measure the phase difference? For example: L = 12.73 mH C = 198 μF R = 8 Ω F = 100 Hz Simulators show a graph as top: ...
POPI's user avatar
  • 143
4 votes
1 answer
249 views

Problem with the simulation of two different low-pass filters

I am trying to simulate the circuit below. Why do both low-pass filters show the same behaviour, even though their component values are different? Edit: How stupid of me. I used the label "In&...
elektronik's user avatar
4 votes
2 answers
2k views

Where to ground low pass filter before dual supply operated op-amp?

The circuit below shows my setup. The resistor and capacitor act as passive low pass filter. In my setup the C1 is grounded to GND (0 V) but the op-amp operated with dual supply (+-5V). My question is ...
user30878's user avatar
  • 185
4 votes
2 answers
404 views

AC Op-amp integrator with DC Gain Control in LTspice

Our teacher explained to us that this set up allows us to produce the effect of a low pass filter: I have indeed found useful formulas to achieve this. The problem however is that when I simulate ...
c.leblanc's user avatar
  • 339
4 votes
1 answer
323 views

Digital control of electromechanical gauges

I have the exact same scenario as a previous question Digital Control of Analog Gauge but am still having trouble solving. I have two (fuel and temp) old (circa 1973) electromechanical analog gauges ...
jefflit's user avatar
  • 49
4 votes
1 answer
184 views

Delay for low-pass filter to give proper mean value of a periodic signal on LTspice

I noticed that I have a 4-5 seconds delay before the output of my low pass filter op amp gives the correct mean value of an input square wave. Is it normal for the delay to be that long and if so, are ...
c.leblanc's user avatar
  • 339
4 votes
2 answers
327 views

Dedicated digital filter

I have built a DDS (0-80MHz) with an FPGA (XC3S400) that I can program it for making almost any wave form (limited frequency by the wave form complexity). After weeks of struggling with making a ...
Aug's user avatar
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