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

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Decoupling a Microcontroller/Development Board Design

Im trying to design a broad purpose microcontroller board (developement board?) to send off to a fab house to then use in future projects. The micro being used is an ATtiny861A. Referring to the ...
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1answer
43 views

Best values for an RC low-pass filter

I have a sonic sensor which outputs analog voltage in 0-10V range with some noise on it. The sensor will measure the distance changes so I'm interested in an output signal not more than 40Hz. The ...
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25 views

Bandpass attenuation does not fit from lowpass transformation

I got a small problem and which I can't solve. I am designing a bandpass filter for use in a compressor, I am using the method of transforming a lowpass filter into a bandpass filter. I First design ...
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25 views

In communication, why is tr-signal's power a half of equiv. low-pass signal's?

The transmitted signal's model is like the following: \begin{align} s(t) &= \Re\{u(t)e^{j2\pi f_ct}\} \\&=\Re\{u(t)\}\cos(2\pi f_ct) - \Im\{u(t)\}\sin(2\pi f_ct) \\&=s_I(t)\cos(2\pi ...
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1answer
35 views

Given input voltage and a set of output voltages of a second order low pass filter, how to calculate the gain of the filter?

I know that voltage gain = 20 log (Vout/Vin) dB, but the slope of the Bode s plot of second order low pass filter is -40dB/decade compared to the first order low pass filter with -20dB/decade. So ...
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32 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!
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2answers
43 views

What is a good capacitance to use for a low pass and high pass filter?

First, I am using the minimum components circuit for the LM386 I am going to use the first circuit on this page. I am going to use a potentiometer in series with the circuit to give me variable ...
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2answers
62 views

Adding Low Pass Filter to Open Collector Hall Sensor

I'm using a gear tooth sensor to create pulses when a metal object passes the sensor. There's a lot of noise on the signal so I decided a simple low pass filter would suffice(f-cutoff = appx.400hz). ...
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2answers
61 views

Given the system function, how can i tell if it is a lowpass or a highpass filter? [duplicate]

If i am given the system function of a FIR digital filter obtained by recursive frequency sampling design procedure., how can i tell if it is a lowpass, highpass, or bandpass filter?
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450 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 ...
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1answer
41 views

How to determine RC filter cutoff of an ADC reading?

I'm making a circuit where I'm voltage splitting a variable resistor and then sending the input to an ADC pin on an Arduino. My question is, what frequency should I set a low pass filter for? How do ...
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3answers
79 views

Is there an equation for the cutoff frequency of a chebyshev filter?

I have this circuit here which is a low pass chebyshev filter, I have been asked to find it's cutoff frequency. I have used matlab to plot an output response against angular frequency graph here. But ...
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1answer
114 views

Low Pass Filter Impedances

I want to design a passive 4-pole low-pass RLC filter for my subwoofer amplifier. So far I found this page: http://sim.okawa-denshi.jp/en/RLClowkeisan.htm But it seems that changing the value of R ...
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1answer
44 views

Simulating a transmissive photo interrupter sensor with Arduino

First of all hello. I find myself in trouble while trying to simulate the behaviour of a photo interrupter sensor by using Arduino Uno R3. The idea is to get rid of the sensor and use Arduino to send ...
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2answers
76 views

Is it possible to convert a low frequency signal into a higher frequency signal?

I have a signal generator that has an adjustable frequency range that is below the required frequency that I need. Is it possible to input a signal from my generator into a passive series RLC filter ...
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636 views

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?
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53 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,
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46 views

a question about gain equation of low pass filter

This webpage says: For a passive low pass filter, The gain equation is the RC potential divider equation: Here, They say: The frequency response of the circuit will be the same as that for the ...
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1answer
64 views

How to design a suitable low pass filter for different waveform

I want to realize a DDS signal generator based on FPGA,which is composed of FPGA,DAC and low pass filter,and the FPGA control a DAC to output different kind of signal. Here are the system performance ...
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2answers
49 views

Anti-aliasing filter as notch and lowpass

In order to reach a steep attenuation for an analog antialiasing filter, there are issues if a high Q notch filter is followed by a low order lowpass filter (or vice versa)? The notch resonance could ...
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3answers
105 views

Help with low-pass filter and TTL logic interface

I am working with a motor control board which controls a DC motor (speed and direction). This board uses two SPDT relays for direction, and some sort of PWM for speed. Here's an abbreviated ...
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1answer
68 views

Low pass filter in the input of ADC supply

Attached figure shows a LPF connected to the input of an ADC preset in the microcontroller. Can anyone please explain why an inductor is connected in parallel with the resistor. Regards Hari
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1answer
56 views

Low pass filter on PSU and target amplifier

we are designing a LLC resonator PSU to feed a class D amp The switching frequency of the LLC PSU is 80-140Khz. At the end of the PSU we are thinking to add a LPF ( PI filter ) with a cutoff ...
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135 views

What sort of graph of Vout/Vin vs frequency will a low-pass and high pass filters have?

The graphic is in log (Vout/Vin) vs log (f). I think that, for the first one, would be something like this: http://www.sosmath.com/algebra/logs/log4/log42/gl02.gif and for the second one will be the ...
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1answer
53 views

Measuring the electrical performance of a low pass filter

I built a portion of a loudspeaker crossover circuit. Specifically, a simple 1-st order RC low pass filter. The filter is designed as shown on this page here. The Resistor is 15.5 Ohms The capacitor ...
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2answers
123 views

Does a sound card low pass filter input?

I ask this question just because I'm curious to find out. As far as I understand, the Nyquist theorem says that the sampling frequency must be at least twice the bandwidth of the signal to be ...
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1answer
93 views

Lowpass LC filter

Here is my task: Lowpass filter circuit is given: Input signal to this circuit is: (it's periodic signal) L=36.4mH, C=85.4nF. Calculate and draw output signal. My idea is to: 1) Represent ...
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1answer
47 views

LC Filter Attenuation

Hi I built a simple LC low pass filter and I supply it with a 1 volt peak to peak ac voltage at 200 Hz from a function generator. My cutoff is set at 700 Hz and I have selected my circuit components ...
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1answer
207 views

Practical Opamp integrator problem

The opamp has an unity gain of 1 MHz.So when the resistor in parallel acts a feedback to bias the opamp stable.So if not for the capacitor,the circuit would have been a inverting amplifier with ...
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2answers
82 views

Inverse Filter Circuit

I have calculated the inverse transfer function of a low pass filter, and was wanting to design a circuit so that the original filters effect will be cancelled by its inverse. What would be the most ...
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1answer
240 views

PWM (Pulse Width Modulation) vs DAC (Digital Analog Convertor)

I am working on a project where I take over the control of a Nintendo 3DS Touch Screen. The touch screen is a 4 pin system. I have it all wired up and working, however I cannot get the screen to ...
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60 views

Inverter with low pass filter?

Is this low pass filter (see the part marked in red below)? If yes, why author used low pass filter in this place?
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151 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 ...
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83 views

Need help increasing rolloff for low pass voltage controlled filter

I am doing an LTspice simulation of this circuit (using LM13700) but with one difference. The power supply is +-5V. Also, by varying the control voltage, the cut-off needs to be able to be varied. The ...
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3answers
269 views

Second order RLC filter and load resistance choice

In this 2nd order, low-pass filter circuit simulate this circuit – Schematic created using CircuitLab I am interested in the transfer function $$ H(s) = V_L (s) / V_g (s) $$ which is ...
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96 views

Guidance designing low-pass filter for audio circuit power supply

I'm developing a BeagleBone Black cape that has, among other things, and audio CODEC and 10 W amplifier. The “other things” include a connection to WS2812 LEDs, which generate a lot of PWM switching ...
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113 views

Remove power line hum and noise from DC source

We are testing our device in a local RF compliance center next week. I spoke with them on the phone and they suggested using a car battery instead of an AC powered DC supply. The reason they gave ...
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4answers
1k 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 ...
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0answers
99 views

Trouble with decoupling capacitor on simple low-pass circuit

I'm trying to filter all signals above ~350Hz from an electret condenser microphone's output and amplify what's left for analog input / DSP. I'm a beginner, so I cobbled together the design from a few ...
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2answers
431 views

How to measure cutoff frequency of a low pass audio filter?

I've built a low pass filter for use in a synthesizer and would like to measure the cutoff frequency compared with various different control voltages to profile its characteristic. I have access to a ...
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1answer
221 views

Low Pass Filter For Square Wave Through An Optoisolator

I've got a higher voltage square wave input that I'm feeding through FOD817B Optoisolator. The square wave frequency is in the range of 30 to 300 Hz. The Circuit is like this: simulate this ...
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2answers
224 views

Matlab low pass filter design -removing noise

I am designing a low pass filter in matlab to remove the noises shown in the image. The original signal of interest lasts only for about 80 ms and rest of the signal are noises from probe tip. In ...
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3answers
595 views

DSP Cutoff vs Sampling frequency question on low pass filter

Is it unrealistic to have a 125 MHz sampling rate with a cutoff frequency of 5 Hz? I downloaded a few filter programs and used their methods and it seems that even with thousands of taps it still ...
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1answer
48 views

What are these things called in a bode plot

Here is a low pass filter bode plot: In the bode plot theory, what is K called? What is ω0 called? What do these two represent for a low pass filter? Does K not represent an amplification or ...
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1answer
391 views

Low-Pass filter on AVcc pin for ATtiny

The datasheet for the ATtiny861a states that "If the ADC is used AVCC should be connected to VCC through a low-pass filter". The datasheet doesn't specify what values I should use or what style of ...
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1answer
101 views

What to do with the Balance and NC pins?

For a course project, we are to use an LF356 operational amplifier What does the Balance and NC do? and I do not think I need it for my project(Sallen-kay filter 4-pole). Do I just ground it?
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669 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 ...
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1answer
51 views

Dual passive low-pass filter

I am building a class D amplifier and need to design passive low-pass filters for H-bridge with cut off frequencies at about 400 Hz. However, I am unsure about few things, this is the simplified ...
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1answer
137 views

Digital Low-Pass Filter When Oversampling Audio

The human ear can hear sounds up to ~ 20KHz. Some ADC's oversample. For example, to capture frequencies up to 20KHz, an ADC converter might sample at 160KHz. The steps are: 1. Filter the audio with ...
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1answer
72 views

Current regulator with controller?

I want to implement a circuit which allows to regulate the current flowing to the load. I have two use cases: Case 1 is the normal case where I would set the max. allowed current with a ...