# Questions tagged [filter]

A filter selectively processes input signals in frequency- or time-domain.

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### Passive LC low pass in combination with series resonant/ band stop stage

I found this crossover circuit in a construction set and it puzzled me a while. I have absolutely no idea, why I should combine a 2nd order low pass with half a band stop. The low pass alone has a ...
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### What's wrong in my low pass filter design?

I use the magnitude of the transfer fuction |H(ω)|=1/sqrt(1+(ωRC)^2) to calculate the wanted output/input ratio at 0.1. I use R=1kohms, C=0.5uF for a 20kHz noise input. Why do I get nearly nothing for ...
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### Implementing a filter with an LDI integrator why this phase jumps

So I have a continuous time filter that I implemented in discrete time using an LDI Integrator. This what I obtained for the filter phase: In green there is the phase for the continuous time filter ...
36 views

### LTC 1060 switched capacitor filter in mode 3: why this output forms:

So I'm simulating a switched capacitor filter using LTC in mode 3. Here is my schematics: Now I'm performing a transient analysis with a 3V sinusoidal voltage with frequency 1.4 kHz and a 3V square ...
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### Find the transfer function and determine the type of this filter

I am learning basic circuits and I got stuck at this question: This is what I got: $$V_{o}=(\frac{sC_{1}V_{o}R_{2}+V_{o}-V_{in}}{R_{1}}-sC_{1}V_{o})\cdot \frac{-1}{sC_{2}}+sC_{1}V_{o}R_{2}+V_{o}$$ ...
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### How is the filter response affected by the sampling rate?

At this filter, the sampling frequency is changing the output bode plot. I have never thought this before. What is the explanation of this? edit: will be updated soon!
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### Calculating transfer function for complicated circuit

I have a circuit with many components for which I need to find the transfer function. More precisely, the circuit I am looking at looks something like that: Please don't go into the trouble of ...
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### Which power combiner should I use?

I have two microwave signals (0.2 and 2.3 GHz) and I have to join these signals in a common channel (microstrip TXline). I've decided to use two BP filters and a power combiner hybrid. I've already ...
104 views

### Is an inductor in a necessary ground loop useful for limiting noise in ground loops?

I am looking to ground several devices together that all ground to a common PC, and want to at least eliminate any HF noise between the grounds. It occurs to me an appropriately sized inductor series ...
55 views

### R-Cd parallel damping during power on

I am researching the PI filter. There're a number of great articles on how to calculate values for inductor and capacitors, the response curves and frequencies. Examples are: Input Filter Design for ...
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### What kind of power supply filter is this?

I found this filter in an inherited design. It is supposed to filter some noisy input (around 13V) coming from a generator. I'm new to designing filters and coils but something feels off here - I kind ...
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### Capacitance detection circuit in LTspice

I have designed a circuit to detect ice in software LTSpice. When I did ac analysis, it shows the gain is constant from 10KHZ to 10MHZ. That means, I can detect ice during operationg the sensor with ...
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### distortion on transition of bits in FSK

I have a question regarding the distortion I see at the transition of bit '0' and '1' in an FSK, I have the receiver connected to a sensing circuit at two frequencies, because my input is current ...
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### Can someone explain the workings of this Filter Board?

I'm trying to understand how the power supply of an analog synthesizer (Roland Jupiter-6) works. It was built around 1983 so some of the part numbers don't yield any relevant Google results. In ...
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### Bandpass filter obtained by complementary transformation of lowpass Sallen & Key: what went wrong?

I am considering the following lowpass Sallen & Key filter: My components are the following $R_1=10 k\Omega$ $R_2=10 k\Omega$ $C_1=150 nF$ $C_2=1.65 nF$ Now I have performed a ...
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### Sensitivity analysis of a filter

I have a question about sensitivity calculations. I have a lowpass Sallen & Key filter. I calculated: the relative error of the pole frequency due to the relative error of passive components and ...
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### Suppress noise on digital signal

Tasked with improving on an existing design, I need to read pulses using a reed sensor excited with a magnet, placed on the front wheels of motorbikes. The system's core has changed, moving from a PIC ...
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### DC/DC converter inductor makes annoying buzzing sound

I am using a PT4110E DC/DC converter to drive an LCD backlight. It operates at a frequency of 1.2 MHz. Electrically, everything is working fine. Voltages are stable and the inductor isn't heating. ...
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### DC/DC Pi output filter inductor gets hot and causes voltage drop

On my PCB I have a pi-filter as shown below at the output of a DC/DC converter. The DC/DC has an output voltage of 19.5V and will supply a max current of 1.3A. The switching freuqency of the converter ...
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### Impedance inverter transformation from series lumped resonators to lambda/2 resonators

Suppose I have the following series of filter transformations beginning with a lumped element bandpass filter and concluding with shunt susceptances- The transformation from step (a) to step (b), and ...
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### Sallen Key Lowpass Filter stops rolling off in simulation

I unfortunately have no pictures of my spice simulation since it's on a different computer, but I am attempting to create a Sallen Key lowpass filter with fc~=555Hz. I used the lowpass filter design ...
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### Question about local NFB in a transistor

I've seen this a few times and I can't seem to find documentation so maybe I'm not understanding what's happening here. My interpretation is that the transistor is configured as a common emitter and ...
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### Draw block diagram of equation

I'm kind of new to this and was wondering how I would go to draw a block diagram for a differential equation that I've recently calculated?: y[n] = y[n-1]+ [1/4] ([x[n]-x[n-4]]) There is no problem ...
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### Issues with a Sallen-Key low pass filter for turning a PWM into a DC voltage

I need to turn a 490Hz PWM into a DC voltage using a Sallen Key low pass filter. In the picture, you can see my bode plot and there is -60dB attenuation at 490Hz. The passband has 0dB of gain. The ...
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### Doubt about an exercise on leapfrog filter

I'm asked to find the order, type, number of poles and zeroes and the dc gain of the following filter: Since the output of each integrator is the input both of the following and the preceding ...
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I am designing a stripline filter with ADS and I am interested into the interdigital structure. It seems that ADS only has SCLIN component for coupled edge structure, which is thought for parallel ...
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### Finding upper cutoff and lower cutoff frequencies on notch circuit

I need to find upper cutoff (UCF) and lower cutoff (LCF) frequencies based on formulas of a notch circuit, but I'm getting a quadratic equation (as expected) with an imaginary number (IN; not expected....
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### GPS antenna reference design

I have to put a GPS antenna on a PCB layout, but not sure how to calculate a matching network, and how to check that it will work correctly. I've chosen components with desired features (radiation ...
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### Opamp creating a DC offset at high frequencies

I am measuring a 4th order filter that consists in the cascade connection of two biquadratic Rauch sections. All my measurements went well except when I try to measure signals with high frequency (4 ...
102 views

### Matlab Digital filter not working, how come?

Before reading any further, to give you on some insight on the output level of the oscilloscope picture's the ~340mV green signal is normal. If you know me I posted a question as to why its 340mV but ...
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### Output signal is being attenuated after the Biquad filter direct Form 1, why?

Thought this would deserve a separate post on its own. What's going on is that I finally got my low pass digital filter working on the STM32H753ZI using the PMODI2S2 peripheral and I noticed the ...
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### RF Antenna 50 ohm controlled impedance design

this is my first time doing RF design and I'm currently using ThingMagic Nano M6E RFID module and in the process of designing a 50ohm impedance circuit/trace from the IC to the antenna. On their ...
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### LC power filter, big L or big C?

I was reading a datasheet for a Murata DC-DC converter Murata DC-DC converter. It has the following LC filter recommendation to reduce output ripple: As the output voltage of the DC-DC converter goes ...
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### Designing a filter: does the order i which we cascade the sections matter?

So I am designing a 4th order lowpass filter using two biquadratic sections. I decided to split the gain evenly between both sections. After some calculations, one of the sections has a quality factor ...
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### PWM square wave to DC voltage simple conversion

How do I convert a PWM square signal into a stable DC voltage (0V - 3.3V) in easiest and reliable way possible? (preferably in programming- microcontroller)
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### Full wave bridge rectifier design

I am asked to design a full bridge rectifier with the following parameters: Vin = 230 VAC Vout = 18 VDC Iout = 1 A ΔVout = 500 mV Efficiency at least 70% The frequency of the voltage in the primary ...
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### Chebyshev filter design (lowpass to highpass with specifications)

I have been trying to solve the following problem: Design a band pass filter with 2nd order Chebyshev filters: Low-pass to high-pass (both 2nd order in cascade.) Find the component values (resistors ...
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### Cutoff frequency of stacked low pass RC filters

How can I determine the cutoff frequency of a filter between V1 and the output marked with the red arrow? All resistors and capacitors have the same value. In the picture is a stack of battery cells (...
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### Power over coax filter selection

TL;DR - How do I determine the appropriate inductor size to filter out signals at 115.2 kHz? Is the channel frequency determined by the baud rate or the signal rise time? Edit -10/5/2020 Looks like ...
28 views

### Do time contant vary with the order of filter?

I have this doubt whether time constant varies with order of filter or not.If not, when/what (type of) circuit has more than one time constants?
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### Difference between EMI filter and RFI filter

I always see EMI filters on power entereing of machines. They have generally circuit something like a below: The machine that I investigad has noise limitter filter that called RFI filters on ...
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### Experimental tips RC second order circuit

I'm implementing a RC second order filter in the lab. My results were quite good, but of course not exactly equal to the simulation and theoretical prediction. I'm trying to understand why this is ...
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### What is the formula for cutoff frequency for LCL filter?

I have an assignment for school and one of the questions is asking me to find the "bandwidth" of a "pi filter." This teacher miss words things sometimes and I know it's actually a ...
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### When designing a second-order RLC band pass filter, how can we choose whether to use the series form or parallel form?

Second order RLC filter can be realized in series and parallel forms. Suppose we need a high Q factor, if we choose a series form, we need the inductor to have a larger value than the capacitor and ...
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### Cleaning power rail from switch mode power supply

In my circuit, I do not have control over what the power supply is used. Thus, I am preparing for the worst where a cheap noisy SMPS is used. I have some ADCs down the line that get their power from ...
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### Derivation of an RC Low Pass Filter's Cutoff Frequency

I can't seem to figure out how to derive an RC low pass filter's cutoff frequency. I'm doing so an exercise because I want to find out the cutoff frequency of a more complex low pass filter, because I ...