# Questions tagged [filter]

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

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### My linear voltage regulator is overheating very fast

I'm using a 5 V / 2 A voltage regulator (L78S05) without a heatsink. I'm testing the circuit with a microcontroller (PIC18FXXXX), a few LEDs and a 1 mA piezzo buzzer. The input voltage is aprox. 24 ...
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### My understanding of RC circuits is broken

I asked a relatively simple question. Unfortunately, the answers provoke far more questions! :-( It seems that I don't actually understand RC circuits at all. In particular, why there's an R in there....
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### What is impedance?

This is presented as both a resource for the community and a learning experience for myself. I have just enough knowledge of the subject to get myself into trouble, but I don't have the best grasp of ...
68k views

### What is the purpose of a capacitor to ground?

I have here a filtering circuit from a microwave. What is the point of the capacitors to ground. Another answer in a previous question of mine said they were used for filtering however I don't ...
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### Why would you stack a resistor and capacitor on top of each other?

I've inherited an charge amplifier/shaping circuit from my predecessor. When he wanted to make a low-pass filter with current-to-voltage conversion, he had a standard circuit like: simulate this ...
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### How to combat noise from my circuit polluting my 12V rail?

I made a controller for 12V DC fan. It is basically a buck DC-DC converter controlled by voltage. It regulates voltage for fan from 3V (lowest speed, fan draws 60mA @ 3V) to 12V (full speed, fan draws ...
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### Why should I use digital filters rather than simply manipulate signals in the frequency domain and then recover them into the time domain?

I'm quite a novice in signal processing and I know this question may be too broad. But I would still like to hear hints from experts. I was taught to use butter (...
30k views

### How do I choose component values when designing a Low/High pass RC filter?

The cut-off frequency of a RC filter is obtained from the well known equation, $$1\over(2 \pi RC)$$ This is one equation with two variables. For example, R=100, C=10 has the same result as R=10, C=100....
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### I think I found an error in an electronics book. Are my equations correct here?

I'm reading Practical Electronics for Inventors, 4th edition, to freshen up my long forgotten knowledge of electronics. I love the book so far, but I just came across an equation there which seems ...
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### Why are there so many vias on this board?

I was looking at the MMZ09312BT1 development board layout, and I was curious about all the holes they have on the board. Are these vias? What is their purpose (I heard somewhere that they are meant as ...
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### Why use a resistor in filter circuits

Since capacitors and inductors can filter on their own. Why are separate resistors needed? For example in a RC circuit, using only a capacitor would be different in what manner?
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### Is a capacitor a high-pass filter or a band-pass filter?

This has been bugging me for a while now... Does a single capacitor, on its own, behave as a high-pass filter or a band-pass filter? In a crystal radio set, you use a single capacitor as the tuning ...
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### How to identify filter behaviour without memorizing different topologies

Is there a way to tell if a circuit is high or low pass without memorizing different topologies?
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### Why are caps configured this way in EMC filters?

Every EMC filter I've seen has capacitors between the AC lines and earth, configured like this: simulate this circuit – Schematic created using CircuitLab Why are the caps not configured like ...
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### What does this schematic symbol marked SG1 looking like two arrows pointing to each other represent?

I know the symbol at the bottom is ground, but I can't get what the other symbol is. It can be a single symbol of two arrows pointing at each other, or two symbols each one a arrow. I also have the ...
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### Analyzing Accelerometer data characteristics and designing a filter

I have about 32 seconds worth of accelerometer data of a basic driving scenario 25MPH normal roads along with hitting about 7 potholes and a rough patch of road. The accelerometer is mounted on the ...
4k views

### Why does increasing the sampling rate make implementing an anti-aliasing filter easier?

From an answer to a question regarding sampling rate and anti-aliasing filter I read the following: The closer you get to the theoretical minimum sample rate, the more difficult the analog filter ...
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### TVS diode before or behind resistor

The best way to protect AVR pin for me is RC filter and TVS diode but I don't know one thing. I've seen schematics where TVS diode was before RC filter like in first schematics. simulate this ...
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### Understanding bootstrapping in analog active filters

"Bootstrapping" is a common technique in (analog) active filters, where the output of the filter is fed back to a node that would otherwise be connected to ground. For example, the Sallen ...
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### What's the sharpest frequency response for a non-causal low-pass filter whose step response doesn't overshoot?

Butterworth, Bessel, Chebychev, and sinc low-pass filters are used in various cases where there are different tradeoffs between having a uniformly-decreasing frequency response, a uniform phase ...
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### Design a filter that allows frequencies below 5 kHz to pass freely, but all frequencies above 5.2 kHz must be undetectable

My biggest challenge with this question is its ridiculously steep roll-off rate. I am assuming that the signal is undetectable if its gain is -20 dB. This means that, within the transition band of ...
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### Why too many capacitors in parallel for Vdd supply net? Can't we just add all to replace with one big capacitor?

Here is a schematic of a Basys-2 board's power regulator IC and filters. It is just an example but this is fairly similar to many designs I've seen. Why are there so many capacitors added in parallel ...
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### Why have a 0.1 uF capacitor in parallel with 2500 uF in a power supply filter?

I'm troubleshooting an old solid-state bass amplifier (Ampeg B-15). The power supply has a 56 VAC transformer tap into a 4-diode full bridge rectifier circuit. One side of the bridge goes to ground. ...
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### What is the advantage of a Sallen-Key filter over a normal second order filter?

Wikipedia links to a Sallen-Key filter as a active low pass, so I tried it out with LTSpice. The frequency response and phase response are not linear, instead frequency response even gets higher ...
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### Why don't decoupling/bypass capacitors need resistors to perform their function, like regular filters?

Why don't decoupling/bypass capacitors need resistors to perform their function, like regular filters? Is it because the stray resistance of copper traces is enough to filter, along with the ...
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### Ripple voltage filtering capacitor

I'm an self-taught high schooler who's trying to understand how filtering capacitors work. I've searched and read multiple websites trying to understand how filtering works. At the point where I am, I'...
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### Good filter design software for Mac OS X/Unix?

I need to implement a simple lowpass filter for a data acquisition circuit (using stretch conductive fabric as a resistive sensor). Various sources have recommended that the best way to go about this ...
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### Audio Amplifier Op amp

I'm trying to design a circuit in which a microcontroller produces a signal and then using an amplifier drives an 8ohm speaker. I've so far used LM386, but it cannot go above 1W, which turned out to ...
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### Distribution of component values with a given tolerance?

Suppose I have a collection of parts with the same nominal value and some tolerance, say 50 Ohm 1% tolerance resistors. What distribution of actual component values can I expect? I can imagine ...
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### Twin-T Active Notch Filter Analysis

Could anyone give me a hint in analyzing the Twin-T Active Notch Filter? I tried a delta-star transform, followed by nodal analysis, but ended up with conflicting equations. For an example, look at ...
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### Troubleshooting a faulty filter circuit in a PAL CRT display

I have an old CRT monitor (Phillips CM8833) which I am attempting to repair. When displaying a composite PAL signal, it only shows a black and white image, but it is still able to display RGB signals ...
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### IIR filters what does infinite mean?

I am having difficulty understanding what "infinite" in IIR means in practice..In theory the impulse response is used for feedback..If this feedback never ends how output is generated?
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### How to analyze this circuit in the time and frequency domain?

I came across this circuit in another post and started looking at the op amp filter and how to apply traditional circuit analysis ( using 1/jwc for capacitors) and couldn't derive the transfer ...
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### Do I need a 50/60Hz notch filter for battery powered devices?

Given that battery powered devices are not plugged in the mains power, can I assume that there will be no 50/60 Hz frequency noise? This question came up while thinking about what the circuit for a ...
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### How to compute input impedance?

I use a Sallen-Key filter for a project at university and I need to know its input impedance. Is there a way to compute it theoretically ? Here is my circuit:
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I am designing a circuit that is intended to capture audio samples from multiple channels for sound source localisation. Each channel has the following 2 stage op-amp circuit, before going into a ...
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### Are there any quick way to tell if a filter is high-pass, low-pass, or band-pass, just by looking at the transfer function in the s domain?

How can I quicly determine if a given filter's transfer function like: $H(s)=\frac{k}{s^2+ks}$, or $H(s)=\frac{1}{s+k}$, is either a low-pass, high-pass, or band-pass ?
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### How to filter noise from ground?

I have an audio application scenario here. The Idea is to power a device (that later produces sound) with USB. Unfortunately, I have massive static and what sounds like pink (Brownian) noise on GND. ...
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### Why is the output of a filter considered 70.7% of input while determining the cutoff frequency?

I have seen in many books that while finding the cutoff frequency of a filter (from the transfer function) the output is considered 70.7% of the input. Why 70.7%? Why not 50% or 20%?
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### Bridge rectifier: What is the purpose of these two elements?

I found the following circuit in a random video (don't know what it's worth) and have two questions about it. I get that it's a full wave rectifier, and I think I have a decent idea on how it works. ...
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### How does an emitter follower work as an AM detector?

Can someone explain how an emitter follower used as an AM detector (shown below) actually works? I don't get how a (theoretically) linear system like an emitter follower would work as a detector when ...
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### 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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### Difference: Low Pass Filter and Large Capacitor?

When working with microcontrollers it is recommended to place filter/decoupling capacitors between a supply pin and ground. I understand the purpose of this implementation, namely that voltage across ...
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### Intuitive explanation for filters

Can anyone provide an intuitive explanation for the filtering action of RC or LC circuits? I know the mathematical treatment involving reactances but I was wondering if that could be explained ...
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### Gain in Sallen-Key filter

How can we increase the passband gain in a Sallen-Key type low pass / high pass filter, preferably without using additional op-amps.
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### Function of Specific Capacitor in Audio Amplifier's Negative Feedback

The audio amplifier that I am referring to here consists of three stages. Among others, the amplifier also includes negative feedback (NFB) that is made of two passive resistors. From the base of TR3 ...
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### Use of 100K ohm resistor along with 0.1uF capacitor?

In the circuit diagram below, why is there a 100KΩ resistor (NOT R2) connected to the capacitor? To my understanding the capacitor-resistor act as a high pass filter to block the DC offset of ...
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### Methods of filtering noise caused by DC brush motors

I am looking for any information that would help me reduce the power rail noise and EMI of DC brush motors. I am building a robot that is powered by 2 x 250 W 24V DC motors. Thank you in advance
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### Is it possible to make a weak analog low-pass filter with less than 20 dB/decade roll-off?

Part of Respawned Fluff's answer to this recent question on headphones got me thinking about low-pass filters: It seems they actually invert the transfer function of the dummy head/ears via ...
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