Questions tagged [low-pass]

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

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1 answer
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RC differentiator / RC integrator explanation (input waveform is square wave, triangular wave, sine wave)

The circuit below is an RC differentiator (RC high pass filter.) The input and output waveforms: I can understand this. Mainly due to capictor charging and discharging. How about an RC integrator (...
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-1 votes
1 answer
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Second-order LPF not filtering correctly

I am trying to implement a 2nd-order Butterworth low-pass filter with a cut-off frequency of 9 kHz. As an input I was using a square wave of 12 kHz. My op-amp rails are 0 and 5 V. The sqaure wave has ...
4 votes
3 answers
127 views

Find RC values of a second-order low-pass filter

I have a low-pass filter of second order. The transfer function is: $$\small G(s) = \frac{1}{R^2C^2s^2+(3CR - CR)s + 1}$$ And the amplitude function is: $$\small A(s) = \frac{1}{\sqrt{(R^2C^2s^2)^2 + ...
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6 votes
5 answers
463 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 ...
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0 votes
2 answers
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Resistor in series with capacitor or inductor

Why do we put resistors in series with capacitors or inductors in single time constant circuits? In this diagram we see a resistor connected in series with a capacitor. This could act as a low-pass ...
-1 votes
1 answer
40 views

Block RF in DC line, SMA

I have a coaxial line delivering DC to a bunch of RF amplifiers. The amplifiers are connected all in parallel in a chain in this way: This is a chain of SMA cables and tees going into each amp. As I ...
0 votes
1 answer
25 views

What is the dimension of Attenuation in the LC-EMI filter design formula?

the following formula is presented in the paper titled "guideline for a simplified differential mode EMI filter design". This is the amount of attenuation, the LC filter with L and C values ...
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Distributed element low-pass filter simulation with microstrip lines in QUCS

I want to simulate the resulting circuit of "EXAMPLE 8.5 LOW-PASS FILTER DESIGN USING STUBS" from Microwave Engineering (4th edition) by David M. Pozar. Here is the targeted circuit: 4GHz ...
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-1 votes
1 answer
42 views

Filtering out high frequency from my input graph

I have an input whose waveform looks something like this: It repeats over and over again until the source if turned off. It is composed of waves of 2 frequencies (16kHz and 1kHz). The final source ...
0 votes
2 answers
105 views

Resistive current sensor shows reading when I connect it in series with a battery while no current is flowing through it

I need to monitor the charge and discharge current of two 12V lead-acid batteries in series using an INA219 current sensor, and a 0.75 mOhm shunt. At first, I placed the current shunt in the low side ...
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0 answers
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Pi Filter Design

I'm new to design, all the help is appreciated. I'm drawing VCC12V from a external board for this application. I'm facing issues of EMI/EMC and voltage level of VCC5V is not that stable as expected to ...
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0 answers
50 views

Current measurements for a DC motor being rectified when in reverse direction (differential low pass filter implementation)

Recently for a project I've been trying to capture voltage and current characteristics for a DC motor. To measure current, I'm using a single resistor (R1) in series with the motor, and feeding the ...
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Current & BEMF Measurement with LP Filter - Determining Cut-Off Frequency

I am analyzing the BEMF and current sensing circuits of the ST Microelectronics demo board STEVAL-ESC001V1 as I am creating my own ESC based in part on this design. My application will use a 4S lipo ...
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2 votes
1 answer
80 views

Second order low pass filter: two 1st order filters not-immediately cascaded

A second order low pass filter (LPF) can be made by cascading two active LPF (an RC network + opamp.) What happens if, instead of immediately cascaded, an active LPF acts at the input (buffer) of a ...
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2 answers
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Smoothing potentiometer output

I am building a paddle controller for my Commodore C64. Basically all you need is a 470k (or 500k) potentiometer connected to two of the joystick wires. Internally, the C64 has capacitors through ...
-1 votes
1 answer
130 views

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 ...
4 votes
0 answers
73 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 ...
1 vote
1 answer
149 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 ...
3 votes
4 answers
210 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 ...
0 votes
1 answer
79 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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0 answers
74 views

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 ...
-1 votes
1 answer
73 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
327 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 ...
1 vote
2 answers
159 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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241 views

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
287 views

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 ...
0 votes
2 answers
52 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 ...
0 votes
4 answers
1k 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?
0 votes
1 answer
66 views

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 ...
1 vote
2 answers
101 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 ...
0 votes
3 answers
941 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
65 views

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 ...
0 votes
1 answer
124 views

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
128 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?
1 vote
0 answers
115 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
85 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 ...
3 votes
2 answers
437 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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0 answers
61 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 ...
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0 votes
3 answers
143 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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0 votes
2 answers
245 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 ...
-1 votes
2 answers
134 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 ...
4 votes
1 answer
202 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&...
0 votes
1 answer
49 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 votes
0 answers
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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 ...
1 vote
1 answer
144 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
127 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 ...
1 vote
2 answers
208 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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0 votes
1 answer
77 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?
1 vote
3 answers
104 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 ...
1 vote
4 answers
236 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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