Questions tagged [low-pass]

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

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45 views

Low pass filter calculation for H-bridge output

I'm controlling a motor through an H-bridge, and want to low-pass filter the output of the bridge before the signal going into the motor. The purpose is to remove high-frequency noise that might ...
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48 views

What's the purpose of the applied "buffer networks" between each level?

The following simulation is performed to analyze the Nyquist diagram of a 3 pole RC low pass filter. I don't understand why the highlighted networks are required. How does it work? With buffer: ...
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Rene Schmitz MOSFET filter having problems, or the simulator

Simulating Rene Schmitz's MOSFET filter seems to have erratic behavior. Simulated version From what I understood, you have to make the sure that the gain level after the first opamp is within 600 mV. ...
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111 views

What's wrong with my diode low pass filter?

I'm trying to build this circuit and took the exponential converter from the 24 dB ladder from haraldswerk.de which is pretty equal to Scott Bernardi's exponential converter, ladder The ladder filter ...
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70 views

A voltage controlled diode ladder filter for a modular synthesizer by Moritz Klein

Designing a diode ladder filter from scratch: Designing a diode ladder filter from scratch "Complete project on falstad: ..." Turning my diode ladder filter into a eurorack module "...
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1answer
33 views

How to calculate RC filter time constant of parallel battery cell filters

I am working on cell balancing circuit for a stack of LiIon cells. The filters are used in front of and ADC input to filter the cell voltage. The datasheet claims that with given values the cutoff ...
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2answers
70 views

Finding the correct low-pass filter audio input cutoff frequency

This low-pass filter, taken from the Synthesizer Arturia Minibrute is rated at 15 MHz. $$\frac{1}{2\pi RC} = \frac{1}{2\pi \times 100\Omega \times 100\text{ pF}} = 15,915,494.3092$$ Why would you aim ...
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109 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 ...
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4answers
85 views

Why do diplexer low-pass filter output have more inductors than capacitors and vice versa?

I am reading "Practical Radio Frequency Test & Measurement A Technician's Handbook" by Joseph J. Carr. On page 41, it has a diagram (figure 2.29 shown below). In that figure, why do ...
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1answer
75 views

Envelope detector followed by a low pass filter

What are the advantages of adding an RC low pass filter after an envelope detector? I am asking this because I often notice (in multiple studies) that this type of circuit logic (in the figure below) ...
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3answers
134 views

How do you choose the cut off frequency of a low pass filter for analog input

I would like to read an analog input from temperature sensor or pressure sensor that measure the value from a slow process with let's say 1s of rise time. I know that using a low pass filter is a ...
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54 views

Low pass filter symmetry

I wanted to know which one of these circuits would be better to protect the transformer. The low pass filters are used as protection to block the high high frequency from the resonant circuit as the ...
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159 views

Removing noise from the speed sensor of a motorcycle

I am trying to make a digital dashboard for a motorcycle using a Raspberry Pi, a display and some sensors. I am using this speed sensor. When I put the sensor on the axis of the motor wheel and run ...
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86 views

Why is this NIC (Negative Impedance Converter) circuit simulation working in LTSpice, but not in an actual circuit?

I've been trying to invert the phase response of a non-inverting low pass filter by using a "negative resistor" (-5000 ohms), which is achieved by the simulation below (bode plot + circuit): ...
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2answers
64 views

what's the use of this passive RC filter

I was looking through the design of this board, which uses ADS1299 for measuring EEG signals. EEG signals have a freq band of usually about 5-100Hz and they are low in their SNR as well. Before the ...
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33 views

Measurement system [duplicate]

My question is what the purpose of components in the red marked, blue marked and black marked area?.
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74 views

Help understanding combined High/Low Pass filter circuit

I am a newbie and trying to understand the operation of this White Noise Coloration Filter - I have contacted the original author but at time of writing have bot received a response. The circuit is as ...
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2answers
87 views

Best practice for anti-aliasing very low sample rates?

I'm looking to sample a signal using an ADC at very low rates - perhaps once every minute. What's the best practice for anti-aliasing filtering in this situation? Obviously, trying to construct a ...
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1answer
97 views

Low-pass filter LC for PWM

In the following application I want to control a DC motor powered in 24 V and about 50 W. For that I use a microcontroller of the STM32 range which will be able to provide me a PWM signal of 200 kHz. ...
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80 views

low-pass filter

Why in a low-pass filter, the higher the input frequency, the lower the frequency passed by the capacitor? I know that there is a formula Z(c) = 1/omegajC. The higher the omega, the higher the ...
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1answer
47 views

Q of Sallen key low pass filter

During i study Sallen-key active low pass filter, i wondered why formula of Q is 1/(3-A). A is Voltage Gain. So i searched from web, and i found this. When R1=R2 and C1=C2, the Q be 1/(3-A). OK. But, ...
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310 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 ...
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130 views

Second Order Low Pass Filter Proteus Simulation

I am trying to simulate the following circuit on proteus but on the oscilloscope I see the signal has no change in between input and output. In accordance with the data sheet (LM348) I am supplying ...
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2answers
60 views

Tow Thomas biquad filter output amplitude is increasing as I increase frequency

I was trying to simulate the Tow Thomas biquad filter and measure the output amplitudes of the second order low pass filter output. The input is 100mv peak at 100Hz and I varied it gradually till ...
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27 views

MUX Pulldown resistor Questions

I have a precision application where I am demodulating two sine waves using an analog mux (ADG613) and then Low pass filter to measure it's amplitude. The ADG613 is a 1:4 MUX made into a DPDT (chosen ...
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66 views

second order low pass filter simulation and configuration

Can someone explain what the sets of resistors and capacitors do? im a student in my second year in EE we were asked to simulate this circuit for various sinusoidal frequency inputs and record the ...
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182 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 ...
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28 views

unsure how to calculate power spectral density after passing through low pass filter

Unsure how to answer this question any help would be greatly appreciated i have uploaded my attempt at an answer however i feel that i have done the conversion from dBm to Watts incorrectly Im also ...
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71 views

How Can I Get a Stable Triangle Wave With Adjustable Frequency

I am trying to make a wave generator. It will have switch modes for frequency between 1.6kHz to 1.6Hz with x10 increments. Everything is set except the triangle wave. I use a wien birdge oscillator to ...
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2answers
61 views

Cirrus Logic CS4334 DAC Low Pass Filter?

I have a Cirrus Logic CS4334 audio DAC chip working (datasheet here). One thing that confuses me is the "typical connection diagram" circuitry from the datasheet shown below. In my ...
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266 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 ...
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1answer
118 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. ...
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269 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 ...
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37 views

LTspice, Sallen & Key low pass filter + Low pass filter order 1

First of all, sorry for my English, it isn't my native language. I want to cascade a first order low pass filter and a low pass Sallen and Key structure in order to get my bandwidth at 30 Hz (Fc = 30 ...
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83 views

Why does the dynamic error of a low pass filter decrease when adding a load at the output?

I have this anti-aliasing low pass filter where R = 100Ω and C = 3.62μF. When the input has a frequency of 50Hz, Vin(t) = sin(2π*50t), I have worked out the dynamic error and found that the maximum ...
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43 views

VSB AM and Complex envelope

I'm trying to solve a problem below. I've already solved (1), but not (2) yet. The term 'lowpass equivalent' means 'complex envelop' in this textbook. And this is solution of problem(2) Where does ...
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2answers
288 views

Converting PWM to DC voltage

I am trying to convert an Arduino PWM signal into variable DC voltage source. This will be done by varying the duty cycle output from the Arduino. My question arises when I consider building higher ...
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1answer
58 views

Low Pass filter using Parrallel components

I have a PCB design that I need to add a low pass filter. However I can only add components in parallel. It is going to be very difficult to cut the tracks or add components in series. Is there any ...
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66 views

Series variable resistance with NPN transistor

i'm trying to build a symple voltage controlled low pass filter and in the design they ask for a transconductance amplifier (which works as a series resistance in the R C pair for the passive low pass)...
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1answer
77 views

Confused about the gain effect over cutoff frequency

I am a bit confused regarding the gain effect over the cutoff of the active low pass filter. While I was checking the AC sweep ...
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1answer
46 views

Exercise relating to FIR filter [closed]

I was trying to resolve a problem from "Understanding Digital Signal Processing". I have some questions about it. Why do we need to redesign the filter if we find out that the sample rate is ...
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1answer
58 views

How to use same low pass filter for square and sine wave

I'm trying to desing simple DDS waveform generator using DDS IC, but I'm a bit lost about designing output filter for it. My requirements are 1 Hz - 25 MHz sine, square and triangle/ramp wave. Using ...
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2answers
78 views

DC accurate low pass filter [closed]

I need to make an dc accurate low pass filter. Actually, I need to measure the dc/average value of a waveform. Suggest me some good and practical 0hz low pass filters. That is, the filter that can ...
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1answer
106 views

Cut off frequency in simulation does not match in calculation

I am an engineering student currently learning how to design low-pass active filters. Currently, I am having trouble matching my calculations with the simulation values. My design has the following ...
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73 views

Analog low pass filter noise versus anti-aliasing effect

I am designing a nano-volt-sensitive, 32-bit ADC system for research. The signal of interest is 10~100 uV and DC to 100Hz the goal is 10nV sensitive system. The signal will be amplified by a pre-...
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66 views

LPF 12dB/octave design

I'm designing a diode limiter for audio use where the signal is high passed through a discrete transistor circuit. After the diode stage the signal would need its low end restored and I'm struggling ...
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22 views

Feed-through termination to vary bandwidth and signal power

I'm currently facing an interesting problem regarding RC low-pass filters. In my experimental setup, I have a reverse-biased photodetector (DET01CFC from Thorlabs). To amplify this signal, I make use ...
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158 views

Converting PDM Data to analog

I have researched about PDM Data and I have seen this sentences on wikipedia: In section of Digital-to-analog conversion "The process of decoding a PDM signal into an analog one is simple: one ...
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149 views

RC filter impulse response is exponential decaying but inverse Fourier is Sinc function

As we all know that the inverse Fourier transform of a frequency domain unit pulse/rectangular function (which looks like low pass filter) is Sinc function. So, I was under the impression that any low ...
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58 views

How to build a low pass filter with limited resources?

I need to build a low pass filter, to filter frequencies that are over 550Hz. By the cutoff frequency formula fc = 1/2piRC, RC has to be around 1/3500 so that fc is approximately 550Hz. I have a lot ...

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