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Questions tagged [low-pass]

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

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4answers
35 views

Is there a standard definition of LPF stop band starting point in terms of dB attenuation

Below illustrates a LP filter bands: I can say that the transition band starts at -3dB. But the transition band ends at some point and there the stop band starts. In this example it is -70dB they ...
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1answer
72 views

Are my op amp nodal voltages correct?

I am wondering if my assumptions are correct. For the circuit attached I assumed that Va is equal to Vb and which will be equal to Vc since the difference input voltage must be equal to zero.
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2answers
44 views

Nth order Butterworth filter transfer function for a given roll-off frequency

I want to plot a fourth order low pass Butterworth for any given cut off freq. But I'm lacking the correct transfer function. I saw some polynomial transfer functions in s domain. But their cutoff is ...
2
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1answer
144 views

Does a low-pass filter average the higher-order frequencies into a “DC offset”?

In a Pound-Drever-Hall lock, an electronic signal is produced of the form: We are interested in electronically isolating the term: My question is: how can we filter to get exactly this term (listed ...
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2answers
80 views

How can implement a low pass filter with this PWM signal? (Deadstop Fan won't start error)

I want to low pass the signal to the fans in this circuit. PWM frequency is 35khz and I calculated that I would need C = 10 µF and R = 10 Ω But no matter how I place my capacitor and resistor, ...
4
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1answer
102 views

How to generate this kind of filter?

I've been trying to understand this exercise proposed by my teacher. He asked us to find a combination of 2 ideal filters to generate a filter within the conditions of the image below. (That means, ...
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0answers
25 views

how to use the Vpp in this case?

in this exercise i thought i would approach it by finding the transfer function and i did find the transfer function by using a voltage divider equation, the problem im facing is that i don't have ...
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2answers
62 views

Amplifier and Low Pass filter not responding after few minutes of correct output?

I am trying to design an amplifier and low pass filter circuit for a piezo sensor. My frequency of interest is .3 Hz to 5 Hz, for first stage I have used charge amplifier and the subsequent 3 stages ...
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1answer
72 views

RLC Low-Pass Filter with MATLAB

I'm trying to refresh my knowledge on RLC filters, and I'm using MATLAB to model it. Given an RLC circuit with the elements in series, taking the output at the capacitor should result in a 2nd-order ...
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1answer
60 views

Moving summing block before integrator

I wanted to move the summing operation (+10) that I perform before the integrator block as shown below: (MODEL-1) I check in this wikibook page - https://en.wikibooks.org/wiki/Control_Systems/...
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1answer
45 views

Low Pass filter

I am making a Sallen-Key topology second order low pass filter with 10Hx cutoff frequency: I am using the LM248 op amp. The resistor and capacitor values are specified in the drawing. However, when I ...
2
votes
1answer
130 views

Why did C2 fail?

I'm trying to run a Raspberry Pi as a remote controller and timer for a diesel water pump but it keeps rebooting when the engine cranks. I checked and the supply doesn't drop below 10.5V during ...
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0answers
58 views

PWM to sinusoid with LC filter

I am studying a three-phase inverter with output LC filter (as shown). I want to get 12VAC 50Hz sinusoidal wave at output of LC filter (at load) Vdc=48V fs=10kHz switching freq. Load=13.8 ohm ...
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1answer
60 views

Converting a high frequency ac signal into square wave without creating a low pass filter by accident

I've been building an induction heater for a while now and wanted to get the frequency tracking to work properly. I need to convert the up to 600V ~100khz sine wave signal into a square wave, I've ...
1
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2answers
79 views

Cut-off frequency in coaxial cable

The cut-off frequency of an RL circuit is described by the following equation: $$f = \frac{R}{2\pi L}$$ where R is the resistance of the circuit and L is the inductance. Applying this equation to a ...
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1answer
57 views

Low pass filtering effect on accuracy of power measurement

I'm planning on measuring consumed power (for an e-bike) by sampling current and voltage with an ADC and digitally approximating the power based on the obtained values. I need to pick a sampling rate ...
1
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1answer
55 views

Topology for 1st order active low-pass filter

I have seen two different designs for a low-pass filter: 1) A resistor and capacitor in parallel in the feedback loop, combined with an input resistor on the - input, + tied to ground. 2) An input ...
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1answer
32 views

Clliptic lowpass filter IC

While checking old audio equipment, I stumbled upon the RF5609A filter IC. The only resources I found about this IC are: Looks like a 7-poles/6-zeros Elliptic LPF, used before and after AD/DA ...
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1answer
25 views

Can I use cumulative winding in common mode chokes?

I have been designing a common mode choke for common mode noise filtering at the input of my SMPS. I have chosen the capacitance value to be 6.6nF on both Line to Ground and Neutral to Ground. I am ...
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1answer
28 views

How is Phase Shift of an Op-Amp calculated using Polar Coordinates

I have a textbook (Op-Amp: Characteristics & Applications by Robert G. Irvine, 1981) and its Frequency response chapter started by discussing the Internal LP filters between the Input Differential ...
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3answers
184 views

How to calculate the transfer function?

I have The following circuit network (link to multisim) and i am asked to find the transfer function, the max and min value, the cutoff frequency, angle and the type of the filter. [the actual ...
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1answer
90 views

Is the author wrong about this RC low pass filter circuit? [closed]

When reducing an RC low pass filter, the author of a text book makes the following statement: “Let us assume the application is such that, so that the voltage across RL is negligible.” Is the book ...
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1answer
24 views

Ltspice ac anlysis with dc offset

I am doing ac analysis of a simple passive RC low pass filter. The input is a 2 V peak to peak sinusoidal signal. R=1.2k and c=12nF. I want to add a 2.5 V dc offset to the input signal. When I change ...
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1answer
58 views

Designing a Band Pass Filter

I need a band pass filter that only accepts frequencies from 1000 to 1400 Hz and then toggles the transistor. It has to work from .1 Vpp to 1 Vpp and rejects anything else. I have been testing this ...
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2answers
197 views

Low Pass Filter Wrong Pole Location

I wanted to understand and derive an equation of simple low pass filter that shows the location of pole in frequency response graph (Bode plot). So, here is the derivation: $$V_{OUT}=\frac{V_{IN}*...
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1answer
193 views

How to get 50 Hz sine wave from inverter bridge driving PWM pins of MCU

I am using this circuit to see the sine wave coming from a DsPIC Pins to check the shape of sine wave created from my sine table. PWM frequency is 18 kHz But the sine wave does not seem to be ...
2
votes
1answer
62 views

Lowpass Filter and Attenuator

I am designing a circuit to power a brushed DC motor. The motor will be given 24VDC, modulated with PWM. I would like to have an analog voltage sense capability for use with my Atmel ATmega328P @ 3.3 ...
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1answer
72 views

Problem related to the transfer function of RC low pass filter

I have the following question: For the passive RC low pass filter shown below: $$V_S(t)=\cos(t)+\cos(100t)$$ $$V_0(t)=\alpha\cos(t+\theta)+\beta\cos(100t+\phi)$$ (where \$\alpha\$, \$\beta\...
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2answers
563 views

Cutoff frequency of a second order low pass RLC circuit

L = 25 mH, R =1 kOhm, C = 10nF and Vs(t)=sin(wt)V, freq = 500 Hz I am trying to calculate the cutoff frequency of a second order low pass RLC circuit I don't know if I can still apply the formula of ...
2
votes
4answers
905 views

Detect ring signal using a low pass filter

I created 2 boards communicating each other like an intercom system. One of them has a button to send a ring signal to the other. The ring signal consists of PWM signals created by an MCU. I want to ...
1
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2answers
430 views

High Pass vs Low Pass simple Circuit (RC vs CR)

In an RC circuit, where the resistor comes before the capacitor, the circuit acts like a low pass filter. Whereas in a CR (I don't know if that is how you say it) circuit, where the capacitor comes ...
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1answer
66 views

Calculating the transfer function of this op-amp circuit

The first op-amp is a differential, second one is a follower and third one is a second order low pass filter. I've been struggling with the low pass and the final output of the circuit and I am not ...
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0answers
63 views

Physical significance of positive group delay with negative phase delay

This question is an addendum to: Is group delay the same as the delay of a certain frequency? Lately, I've been going back to basics to better understand the concepts of group and phase delay, so I ...
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3answers
136 views

Using shielded audio cable for potentiometer sensor

I'm trying to measure a potentiometer from an Arduino's ADC. The potentiometer has a maximum value of 100k ohms and is located about 1 meter from the Arduino. The potentiometer's wiper is wired to the ...
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0answers
175 views

Non-inverting Lowpass Filter with Capacitor in Feedback

I am looking for a circuit that I expected to find everywhere but I don't. The "active" lowpass filter I often see in the web uses an RC filter with a buffer in series. simulate this circuit – ...
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2answers
245 views

Gibbs phenonemon in real life

If I feed a square wave into a first order, passive, low-pass filter (resistor and capacitor), I get the following results on an oscilloscope (sorry, I don't know how to scale and rotate images): Why ...
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3answers
218 views

Standard ways to make a variable low pass filter

I tried out a basic low pass filter on one of my analog synthesizers: simulate this circuit – Schematic created using CircuitLab and this seems to work. I was wondering how I can create a ...
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2answers
67 views

RC Waveform output signal confusion

I've been struggling to understand how filter capacitors specifically low pass filters achieve their output signal waveform. If I take the example from https://www.electronics-tutorials.ws/rc/rc_3....
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1answer
113 views

Lpf ramp response intution [closed]

How to intutively draw ramp response of low pass filter intutively . I am able to do it from laplace transform but i am unable to understand..
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0answers
57 views

How does the data rate of a CAN bus affect the value of the capacitor used in a split termination scheme?

I'm helping to redesign the CAN bus of an electric car, and we're interested in achieving higher data rates of up to 8 Mbit/s. We have a transceiver selected, a CMC to reduce inductively coupled ...
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3answers
826 views

How to make a low pass filter of current, instead of voltage?

Is there a way to low-pass filter current, rather than voltage? Let's suppose there is a circuit consisting of a current source and a load. The current source may have a little bit of current ...
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1answer
55 views

LPF and AMP for ADC with op amp not giving sufficient gain

I have a project where I need to have audio input into atmega168PA. I've decided to implement it by using an electret microphone which will feed into op amplifier for low-pass filtering and ...
1
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1answer
276 views

Noise problems in current sensing

I have the following circuit: simulate this circuit – Schematic created using CircuitLab I am using a motor from an electric bike, as a generator and I am rotating it using a drill, to test ...
9
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2answers
1k views

Low pass filter with two capacitors?

I'm trying to drive a speaker from an ESP8266 for a project, and found an article suggesting (ab)using I2S as a 1-bit Pulse Density Modulation DAC. Apparently that's pretty noisy, so the article gives ...
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3answers
127 views

What is the time derivative at t=0 for a second order low-pass step response?

For a first order system like an RC filter you have something like $$y(t)=1-e^{-\frac{t}{\tau}}\\ y'(t)=\frac{1}{\tau}e^{-\frac{t}{\tau}}\\ y'(0)=\frac{1}{\tau}$$ But for a second order system there ...
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1answer
94 views

How to determine the corner frequency needed?

I want to design a second order sallen key low pass filter. I want to attenuate a 100Hz signal to around 10%. I need to use a 2nd order low pass filter. How could I calculate the corner frequency ...
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1answer
636 views

Transfer function of high pass filter via impulse response function

I'm having a hard time computing the transfer function of a high pass RC filter, by taking the Fourier transform of its impulse response function: $$ H(\omega)=\int_{-\infty}^{\infty} h(t)e^{-i\omega ...
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1answer
308 views

How to design filter for inverter for following cases?

I am going to make two pure sine inverters for collage project. Both inverter uses 24V battery as DC voltage source. Switched to ~360Vdc and ~180Vd by boost converter accordingly. Both then switched ...
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2answers
87 views

RC Filter measured response differs from calculated transfer function

I've created a first-order RC filter with R = 68 Ohm, C = 5.0 uF, and I am studying the transfer function of this filter. I have calculated the transfer function to be 1/(1+jwRC), based on the ...
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1answer
149 views

Change in gain and cutoff frequency of 2nd order passive filters due to amplifier circuit

I'm designing an simple equalizer for a first course in Electric Circuits and having some problems. Circuit diagram and AC Sweep Simulation (Multisim 14): Circuit Diagram AC Sweep Simulation The ...