Questions tagged [low-pass]

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

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4th order low pass Butterworth filter with very low Q factor [closed]

I have designed a 4th order low-pass Butterworth filter with a 0.707 Q factor. However, what I am getting is almost no flatness in the pass band region and my frequency response looks like a half of a ...
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4 votes
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51 views

Butterworth Filter attenuates noticeably in pass-band

The Issue: I am using a Maxim MAX7480 8th order Butterworth low-pass filter to counter any aliasing from a sensor that measures signals up to 3kHz, but I only want up to 1kHz. Thus a critical ...
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1 vote
1 answer
58 views

Cut-off frequency and -3dB frequency of Butterworth filter

I am in the process of designing a Butterworth low pass filter in Sallen-Key topology. I use the Analogue Devices Filter design tool. After reading the TI application report I have calculated all the ...
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3 votes
3 answers
168 views

Is there a big difference between different opamps?

I'm trying to build a lowpass filter for a line level signal (from the headphone jack of a phone or laptop) for sampling with an Arduino. I found this filter calculator and input the specifications ...
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1 answer
72 views

Transfer Function for active filter

Not too sure why, but I can’t seem to figure out the transfer function for the filter in question below. Can’t isolate Vout/Vin fully, there’s a straggling Vin that I can’t move over. Any thoughts?
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Microphone active low pass filter doesn't work

I am trying to make an active low pass filter for my school project. I need to design a filter with 2000 Hz cut off freq and 20-25 gain. I tried to use TI filter design tool and analog devices filter ...
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-1 votes
1 answer
53 views

Active Second Order Low Pass Filter Does Not Give Desired Output

I am creating a second order low pass active filter, with a cutoff of 140kHz and unity gain. However the filter does not give an output representative of a Low Pass Filter. I dont know where i am ...
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3 answers
151 views

Why do 1st order low-pass filters on a square wave look like this?

I know that low-pass filters only allow voltages at low frequencies to go through the circuit and block out voltages that come in at high frequencies. With this in mind, how does the graph display ...
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1 vote
2 answers
92 views

Any preferred sequence for low-pass filter and attenuator?

I have a 76 MHz (square wave) 12 dbm signal coming out of an Si5351 clock generator that I need to attenuate to -15 dbm, and pass through a 5th-order Chebyshev low-pass LC filter to remove the ...
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How to mathematically choose values for a pi filter without knowing the cutoff frequency?

I am trying to design an AC to DC converter. After the rectifier, I have a pi filter. I need to calculate my L and C values, but I don't know what the cutoff frequency is/how to find it! Any help is ...
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1 answer
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RC low pass filter for NTC

I want to measure temperature using an NTC resistor and ADC (of an MCU). A low pass input filter is required with a certain cutoff frequency. Here is the recommended schematic: So I replace ...
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2 answers
49 views

Loop Filter Bandpass Jitter Characteristic in PLL

I was watching some PLL video lectures by Professor Elad Alon, and he explains why intuitively the jitter transfer function of the loop filter to the PLL output has a bandpass characteristic. He says ...
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4 answers
329 views

LC Low pass filter in LTSpice

I would like to model a low pass filter in LTSpice, but my frequency response looks like a bandpass, similar to an RLC filter. Is LTSpice incapable of simulating LC filters with an RC one?
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1 answer
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First order low pass filter - Calculate capacitance change

I'm trying to calculate the relative change in permittivity of a capacitor. I have created a circuit that feeds a 80MHz square wave signal into a first order low pass filter. I don't know the ...
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1 vote
2 answers
77 views

Bubba Oscillator - Last filter not buffered

Let's say that we have the following circuit of a Bubba Oscillator The purpose of the four low pass filters is to achieve a 45 degrees phase shift in the oscillation frequency. Meanwhile, the three op ...
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0 votes
3 answers
229 views

Choose the cutoff frequency from the sampling rate

I want to use a low pass filter for the input of my ADC, and I would like to choose the most appropriate cut-off frequency based on the sampling rate of the ADC, which is 40 SPS. Is there a simple ...
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1 vote
1 answer
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How to LPF only one of the inputs to a voltage adder?

I'm taking voltages from two inputs, and I'd like to add them together using an op amp (this is actually a summing integrator). I would like to filter out the noise in V_DAC (which will not change ...
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0 votes
1 answer
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Butterworth Active Low Pass Filter Design

I'm designing a low pass active filter with a Butterworth response. The passband is DC to 1.5 kHz, so the -3 dB cut off frequency should be around 2-5 kHz to be safe. The topology I've decided to use ...
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-1 votes
3 answers
101 views

Frequency response of low pass filter

I have an ideal low pass filter having cutoff frequency 1kHz. If I provide an input having single frequency component at 1kHz, will there be any output or zero?
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1 vote
0 answers
84 views

Single-ended to differential ADC driver with one pole active low pass filter

I have this ADC driver circuit: There is a passive filter downstream of the driver which works as desired. I'm focused here on the active filter. When I run AC analysis on this circuit configured for ...
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2 votes
1 answer
68 views

RIN measurements of a laser

I want to measure the relative intensity noise between 0 and 1 MHz of a laser using a photodiode (20 MHz BW), a voltage amplifier (10 MHz BW), and a spectrum analyzer. Since I don't have so much ...
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3 votes
2 answers
406 views

Low pass filter - cut off frequency

How do I find the cut off frequency of a low pass filter? Consider the following part: https://www.analog.com/media/en/technical-documentation/data-sheets/1062fd.pdf Edit: I have attached the ...
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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 ...
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3 answers
123 views

Gain at zero hertz

I have attached the figure of my circuit. I know that as the frequency rises the gain of the circuit decreases due to low pass filtering but what if I want to measure the DC output voltage ( 0 Hz) ? ...
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-1 votes
2 answers
139 views

Second Order Passive Low Pass Filter RC Circuit Design [closed]

I'm learning about Second Order Passive low Pass Filter RC Circuit for my homework. I need to create a circuit with a specification that has a 1 kHz cut off frequency. I quickly learned on how to ...
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-1 votes
2 answers
96 views

Transient simulation of low-pass filters

I am simulating two low-pass filters with different cut-off frequencies. The first image below shows the outputs -LPF1 and LPF2- and the input -V(z)- of the both low-pass filters. The second image ...
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4 votes
1 answer
187 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&...
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0 votes
1 answer
42 views

Low-pass filtering using an AD8630

I have a circuit that is used to amplify the incoming signal from a thermopile sensor. The AD8630 op-amp is connected to resistors to have a gain of 1000 but I am confused about the capacitor. Is it ...
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0 answers
73 views

What would the output waveform be in each of these cases?

In the second picture, the source is a step function from 0 to 1V. I feel like I solved them, but I am not convinced that my understanding is air-tight. Any help is appreciated. Edit: Adding my ...
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1 vote
1 answer
80 views

Removing noise generated by a servo from an audio signal

Background I'm working on an Arduino-based audio visualisation project where I run an audio signal into the Arduino, using an FFT to calculate the intensities at different frequencies and then using ...
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1 vote
1 answer
92 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 ...
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1 vote
2 answers
114 views

Connection of Cx capacitors to neutral in 3-Phase EMI filter

I'm working with a circuit which uses a common schematic for EMI filtering. I simulated the schematic and I added a 200 kHz AC signal to the main 50 Hz line, to model the differential mode noise. In ...
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1 answer
61 views

Why does the group delay change when I use a different values for this capacitor in this low pass filter?

Here's the circuit If C5 is 0.1F then the group delay plot is constant in the pass band: If C5 is 470uF then for the frequencies between 1 and 3 Hz it's not constant anymore: Why does that happen?
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1 vote
3 answers
97 views

I'm trying to modify this circuit to to operate with only one power supply and find the impact of the input offset voltages

So here's the circuit: And here's my attempt: V1, R6 and R7 form a voltage divider so half of V1 voltage goes to the output of U3. C4 ac-couples the filter, blocking any dc level in the signal ...
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1 vote
4 answers
158 views

Calculating the theoretical frequency response and static gain of a filter

I'm trying to calculate the theoretical frequency response and static gain of this low-pass filter. As far as my knowledge goes, calculating them using experimental means would be simple, but how ...
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0 votes
2 answers
212 views

Is this an RC low pass filter?

The D6 is a digital pin (input) of the Arduino Nano. Function of the circuit: If the button is not pressed the internal pull up pulls the input D6 up to 5 V (high). If the button is pressed the input ...
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3 votes
0 answers
125 views

Which of these three op amps should I choose for my low frequency filter? [closed]

I want to design a lowpass filter-4th order Bessel, so two Sallen-Key low-pass circuits in cascade with a cutoff frequency of 200Hz. I need to choose the op amps for it. I have these 3 op amps to ...
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0 votes
2 answers
67 views

How to pass from a double-supply filter circuit to a single supply filter circuit?

So here is the main circuit, it's a lowpass filter-4th order bessel, so 2 sallen-key low-pass circuits in cascade. I already have all the components and transfer functions figured out but i would like ...
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1 vote
1 answer
135 views

What is the effect of a low pass filter on a stepped signal?

I'm trying to smooth out the steps from a digitally-generated LFO signal which changes step-wise. The digital steps are small, but still audible when the LFO is hooked up to the circuit that uses it (...
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-1 votes
1 answer
62 views

Designing a bode diagram circuit

I have realized some low pass filters with a nominal cut off frequency around 10kHz, which I will use in combination with other filters to eliminate noise on DC and quasi-DC signals (around 30Hz). I ...
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0 votes
1 answer
69 views

Why does the RC corner frequency change when replacing the resistor with an equivalent diode?

This is slightly related to another question but actually a matter of its own: This is a simple analysis of the corner frequency of an RC lowpass formed by resistor R1 and capacitor C1, for various ...
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1 answer
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What is a proper circuit for a variable low pass filter that can be controlled with a potentiometer?

I have some 100k digipots (MCP41100) and I want to make a lowpass filter controlled with an ATmega328P. I want a variable cutoff between 20 Hz - 20 kHz with unity gain. 1st order is enough, but it can ...
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0 votes
0 answers
125 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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0 votes
1 answer
54 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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0 answers
50 views

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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0 answers
188 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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1 vote
2 answers
67 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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1 vote
2 answers
104 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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0 votes
1 answer
259 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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0 votes
4 answers
137 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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