Questions tagged [low-pass]

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

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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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1 vote
2 answers
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Low Pass Filter Wrong Pole Location

I wanted to understand and derive an equation of simple low pass filter that shows the location of pole in frequency response graph (Bode plot). So, here is the derivation: $$V_{OUT}=\frac{V_{IN}*...
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8 votes
3 answers
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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
0 votes
2 answers
3k views

Low pass filter not working properly

This is the pass band that I'm using to filter some EMG signals through electrodes. When I test it with multisim it works really well as you can see, but when I test it with real equipment (...
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0 votes
2 answers
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How to find Vout for the following band pass filter

I have a problem finding the following Vout for this circuit. Is it possible to just use the following formulas that i have shown. I am just unsure due to the resistors. I assume that what i have ...
Student's user avatar
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12 votes
4 answers
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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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9 votes
3 answers
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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
5 answers
12k views

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
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
3 votes
4 answers
2k views

Tool to calculate cascaded but independent single-pole RC hi-pass filters

I frequently use a single op-amp stage for both gain and hi-pass filtering. I normally implement 2 independent single-pole low-pass filters: the input to the op-amp and the ground end of the negative-...
Dwayne Reid's user avatar
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2 votes
1 answer
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Designing a Chebyshev filter: am I getting the order wrong?

I'm solving the following problem: Consider the design of a Chebyshev lowpass filter with 3 dB DC gain, a passband limited to 1 kHz with a maximum ripple of 3 dB, and a stopband characterized by AS = ...
Granger Obliviate's user avatar
2 votes
4 answers
1k views

Detect ring signal using a low pass filter

I created 2 boards communicating each other like an intercom system. One of them has a button to send a ring signal to the other. The ring signal consists of PWM signals created by an MCU. I want to ...
abdullah cinar's user avatar
1 vote
1 answer
126 views

Loss of 2nd order behavior on 2nd order low-pass filter

I have a 2nd order Sallen-Key Low-pass filter, cut-off frequency of 170Hz. When attached to a perfect source, this is the bode plot. As expected, 40dB/decade response. The low-pass filter is used as ...
HFOrangefish's user avatar
0 votes
3 answers
11k views

cutoff frequency of low pass filter with two resistors (differential signal)

How do I calculate the cutoff frequency for this design? simulate this circuit – Schematic created using CircuitLab Or simply,
rumman's user avatar
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1 answer
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Low pass filter target frequency for a mixed signal frequency synthesizer

I'm building a frequency synthesized local oscillator with coarse and fine tuning to span 30.5 to 32MHz. The design follows the following block diagram (bits not essential to this question removed ...
Buck8pe's user avatar
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0 votes
3 answers
4k views

How to calculate the transfer function?

I have The following circuit network (link to multisim) and i am asked to find the transfer function, the max and min value, the cutoff frequency, angle and the type of the filter. [the actual ...
Reddevil's user avatar
-3 votes
2 answers
478 views

RC circuit charging and discharging by square wave not giving a square wave across input on oscilloscope [closed]

question shifted to Input across RC circuit is not showing a square wave though the input is a square wave as it was unclear
Syed Mohammad Asjad's user avatar
20 votes
2 answers
30k views

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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8 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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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
2 answers
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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
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
4 votes
1 answer
1k views

Noise problems in current sensing

I have the following circuit: simulate this circuit – Schematic created using CircuitLab I am using a motor from an electric bike, as a generator and I am rotating it using a drill, to test ...
NickG's user avatar
  • 391
3 votes
1 answer
9k views

Passive Pi Low Pass Filter LC

I'm trying to use a simple pi low pass filter using two capacitors and one inductor. I've found the formula to calculate the value of the capacitance and of the inductance using the cut off frequency,...
Luca Daidone's user avatar
3 votes
3 answers
1k views

Can someone explain how this RFI filter works?

This is an RFI filter from a 12V automotive DC motor. This motor design is over 20 years old and currently in "service" production. We just learned that the capacitor we're using is now in short ...
gtetil's user avatar
  • 401
3 votes
2 answers
1k views

High frequency noise filtering in audio

I power a DAC from SMPS. After the SMPS I use a LDO. My problem is that most LDOs only have a good PSRR around 100 kHz or lower, while my SMPS has a switching frequency of about 1 MHz (thus noise). 1 ...
Johan B.'s user avatar
  • 359
3 votes
2 answers
3k views

Obtain an accurate DC value in an AC+DC signal

Background: My goal is to use an Arduino with two proximity probe sensors to achieve some output. It is worth mentioning that the output of the proximity probe has two components: DC output that ...
Sabir Moglad's user avatar
3 votes
4 answers
2k views

Finding the bandwidth of second order lowpass filter

I have a lowpass filter with the transfer function \$H(s) = -\frac{3}{3s^2+s+3} \$. Converting it to standard form yields $$H(s) = -\frac{1}{s^2+\frac{1}{3}s+1} $$ Comparing this to the standard ...
Carl's user avatar
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2 votes
1 answer
266 views

Attenuation - two stage RC low‐pass filter

I am having trouble with finding the attenuation and bode diagrams for this circuit below. This circuit is two stage RC low-pass filters. I have been trying to find resources on how to do them with ...
Jorge Juarez's user avatar
2 votes
3 answers
6k views

How to calculate phase shift of a low-pass filter's output?

I'm simulating a basic low-pass RC filter in Proteus, and I need to find the phase shift of the output at varying frequencies. I've plotted a frequency response graph which shows the phase against ...
MendelumS's user avatar
  • 147
2 votes
1 answer
524 views

How to speed up charging of output capacitors of ADXL335?

Problem statement I need to obtain as fast as possible after power-up a reading from an accelerometer. The accelerometer is located in a car and is powered by the same rail of the rear braking lights,...
FarO's user avatar
  • 1,316
2 votes
1 answer
2k views

Flash an LED to music

Im trying to flash an LED to music. I have tried to follow this article and calculate values but cannot get it to go. Basically what i think i need is: audio in through a low pass filter (isolate ...
jme's user avatar
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1 vote
3 answers
1k views

Unexpected behavior of the Sallen-Key second order filter

I met an unexpected behavior when I simulated under Multisim (National Instruments) the Sallen-Key circuit given on the image below. The circuit is designed to receive a 1.8kHz modulated sin wave as ...
eldala07's user avatar
1 vote
2 answers
460 views

Is this correct for non-inverting op-amp?

Do 0.1 uf and 100 k ohm act as low-pass filter in here?
user30878's user avatar
  • 185
1 vote
1 answer
608 views

Frequency response of a low-pass, band-pass, and high-pass adder circuit

I'm doing a project and one of the steps consists of filtering a signal through a low-pass, band-pass and high-pass filter. All the filters are Sallen-Key with a passband gain of 1. The pass-band ...
João Marques's user avatar
1 vote
3 answers
5k views

Why do RC circuit voltages decay *slowly* rather than instantly?

Let's take the simplest RC circuit imaginable: simulate this circuit – Schematic created using CircuitLab Now I think I properly understand why the voltage rises slowly after the leading edge ...
0x24a537r9's user avatar
1 vote
1 answer
114 views

Butterworth and Chebyshev filter problem

Find the minimum order Butterworth lowpass filter whose attenuation isn't bigger than 2 dB at 5 rad/s and has 10 dB at 8 rad/s, 20 dB at 10 rad/s, and 40dB at 30 rad/s, then do it for Chebyshev filter....
Joe 's user avatar
  • 13
1 vote
1 answer
385 views

Getting rid of noises after RC low pass filter stage

I am outputting a 40kHz square wave from arduino and passing it through an RC circuit in order to get a clean 40kHz sinusoid out. However, the output wave I am getting is noisy.(see picture) Any ...
Bogdan Raspopin's user avatar
1 vote
3 answers
1k views

Resistor placement in filter circuits

Why does the placement of the resistor in a filter circuit matter? I've heard if you switch an inductor and a resistor in a series circuit it could change the type of filter you get. Ex: From a low ...
Bryansp's user avatar
  • 15
1 vote
1 answer
1k views

BJT Active low-pass filter frequency calculation

The left BJT of this circuit acts as a low-pass filter. According to Simple transistors Low Pass filter, where I found this schematic, its cut-off frequency is 150 Hz. How do we calculate this ...
raffs's user avatar
  • 55
1 vote
1 answer
3k views

lead high pass filter and lag low pass filter

I have a question regarding lead high pass filter and lag low pass filter. I do not quite understand the reasoning behind these two special case (when z=0) ? Thanks!
kevin's user avatar
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1 vote
1 answer
151 views

How much gain I am getting and with the 2 stage transistor amplifier attached with a Global NFB [duplicate]

This is just a direct manual solving directly subtituting values in a formula with disregard to temp etc. Sorry for the incomplete information here are the goals of this: "gain of 100≤Av≤130 and ...
Lumiere's user avatar
  • 23
0 votes
2 answers
313 views

Sallen-Key Low Pass filter

I was trying to do a project on LT spice for the frequency response for Sallen-Key low Pass filter. But when I tried the Following circuit, I am getting a roll off 20db / decade instead of 40db/decade....
Aryan's user avatar
  • 13
0 votes
1 answer
1k views

Low-pass LC filter on both sides of a motor

I'm building an H-bridge to control a load. The design is done, and all that's left is to filter out the switching frequency. The switching frequency is at 20 kHz, and since the current flowing ...
Helena Færch's user avatar
0 votes
0 answers
70 views

Output voltage at different output optical chopper frequencies

I have a circuit as shown in the figure and I am using it to extract output voltage of thermopile (to determine the time constant of thermopile ) at different output frequencies. The optical chopper ...
Pukhtun's user avatar
  • 11
0 votes
1 answer
89 views

Need help with pulse sensor design modification [closed]

So I've got the below pulse sensor design. I don't understand why they filter before they amplify. I'd like to modify it in a way that I amplify the signal first, LPF second, HPF last. For some reason ...
DribbleNibble's user avatar
0 votes
0 answers
59 views

Input across RC circuit is not showing a square wave though the input is a square wave [duplicate]

I wanted to observe the transient response of the capacitor so applied a square wave of 205mHz from a function generator as that would allow complete charging and discharging for the capacitor in the ...
Syed Mohammad Asjad's user avatar
0 votes
1 answer
163 views

Cascaded Filter Output Not Correct

I am simulating a speaker system with tweeter, woofer, and midrange speakers. I know my values for the components are all correct, but the output plot is a little off. The passbands should be a little ...
python_'s user avatar
  • 21
0 votes
2 answers
4k views

Multiple feedback low-pass filter design

I'm trying to design second order multiple feedback low-pass filter with cut-off frequency at 1500 Hz and Chebyshev approximation. Transfer function for this scheme is defined as: Where: And ...
Long Smith's user avatar