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

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LTspice giving incorrect voltage value for simple first order low pass RC filter

I drew this low pass filter circuit to have a output voltage of 5v across capacitor at a frequency of 100Hz sine wave of amplitude 10v. But I am only getting 4.5 volt as output in steady state. I am ...
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1answer
35 views

Applying 1st order filter [on hold]

I have a 1st order continuous filter T * y'(t) + y(t) = u(t) . I discretized the equation by hand and applied filter and I used ...
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2answers
95 views

How do I get output impedence of ICs?

I am teaching electronics a few people as a hobby. I wanted to show them that as the frequency increases output voltage of low pass filter(simple first order RC filter) decreases. I don't have a ...
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2answers
37 views

high frequency noise from multiple feedback op amp

I've built a multiple-feedback low-pass filter with a TL084IN op amp. I've simulated the filter for the chosen R and C values using LTSpice and it looks like I was expecting: . I've also assembled ...
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1answer
28 views

Can I use barrier rectifier as a diode in bulk converter circuit?

I have this LC circuit which will work under 12V and quite high load (10-20A): The diode D1 must be a shottky diode but the only similar thing I have at the moment is actually 3-leg MBR3045CT ...
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0answers
21 views

Low pass filter for differential signals

I'm building an adc and amplifier circuit for sensing a differential signal out of a pressure sensor. My plan is to use a circuit very similar to what is seen below: The total differential output ...
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1answer
35 views

Narrow bandpass filter using maximally flat LPF prototype design

I'm doing a project involving wireless power transfer, where an LED will be turned on via 2 induction coils (tx and rx). The interfacing power circuitry for this has already been figured out (an ...
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4answers
190 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 ...
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2answers
64 views

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
45 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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26 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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27 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
37 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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1answer
42 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
45 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
69 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
62 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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463 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
44 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
95 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
120 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
46 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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646 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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69 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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60 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
70 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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51 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
111 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
72 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
63 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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155 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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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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143 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
99 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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49 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
244 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
93 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
269 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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156 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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91 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
314 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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105 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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122 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
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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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2answers
493 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
229 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
245 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
661 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 ...