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Questions tagged [active-filter]

An active filter is a type of analog electronic filter that uses active components such as an amplifier.

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Multiple feedback single supply

I've been trying to get a multiple feedback lowpass filter to work. With this schematic. The filter works in the simulation but when i try to build it, it gives no output. The op amp used to build ...
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2answers
70 views

Does this Sallen and Key filter work on a single supply and does the input offset matter?

This is the schematic for a Sallen and Key from the Doepfer Musikelektronik website: simulate this circuit – Schematic created using CircuitLab I intend to run this in a synth, the oscillators ...
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66 views

Can the OpAmp be safely removed from the Twin-T notch filter?

This is a very typical (text-book) example of an active Twin-T notch filter with adjustable Q. However, after having posted THIS question, one of the commenters pointed out that there is a design ...
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Why use an opamp for the variable Q feedback in a Twin-T notch filter?

In the following circuit, for a Twin-T notch filter, the author is using an additional inverting op-amp for the T-filter "feedback", that is connected to a potentiometer (pot). Image credit: here ...
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81 views

Band pass filter implementation using 741 op amp

My assignment for a school project on Circuit Theory, is to construct a Band Pass Filter at least 3rd order with a stop band around 20kHz. First things first, I need to design the circuit. I have to ...
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1960's video showing early computer design & simulation of a low-pass filter circuit?

I ran across this IBM computer aided design and simulation software demonstration from the 1960's in the video The Incredible Machine (1968) The gain vs frequency plot shows what looks like the ...
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55 views

Calculating cutoff frequency of a second order active filter

I'm trying to calculate cutoff frequency of the low pass filter that schematic is shown below. I obtained this circuit from Analog Filter Wizard and it's cutoff frequency is 170kHz at -3 dB, but when ...
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3answers
986 views

Active filter with series inductor and resistor - do these exist?

I have seen (online) and in books basic active filters (involving an op-amp) with a series R C branch at the input side. This series R C branch at the input side would make the circuit a high-pass ...
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4answers
46 views

Tradeoffs for creating higher order butterworth filters

I am working on a bandpass filter to filter the output from a hydrophone. This is my first time designing a filter and using a cookbook from TI, I built a 4th order Butterworth filter with two partial ...
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1answer
30 views

Designing a network to fit specific amplitude and phase response curves

If we are given a frequency response curve made up of the amplitude (magnitude) and phase (angle) responses, is it possible to design an electronic network with a transfer function identical to the ...
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1answer
44 views

Differential (Subtractor) op amp with low pass filter

is it possible to have a subtractor circuit with a low pass filter in it? My thought is that I would have the possibility of doing that if I add a capacitor in parallel with R3. Is it actually ...
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What effect do R5,R6,R7,R8 have on the following DSBSC Modulator?

I know that the first 741 essentially adds m(t) and c(t).The gain should be 1 so why do we have 3.9kohms resistance ? What use is it ? The second 741 circuit is a band pass filter . I think there is a ...
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2answers
49 views

Is the Roll-Off of Butterworth Filter of degree N always N*20db/dec?

I am trying to implement a fourth order Butterworth high pass filter under a Sallen-Key topology. Two frequencies, one at the passband and another for the stopband, are set to be at some specific gain/...
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3answers
83 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 ...
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1answer
33 views

Estimating response of a filter given its order and roll off frequency

As far as I know, for any filter we if we know that filter has 1kHz bandwidth we can infer that the 3dB point is at 1kHz. In some cases I only have the limited data for the filter. For example this ...
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1answer
49 views

Active filter - oscillation and incorrect operation

I have a noisy and low amplitude (0-50mV amplitude) signal from a hall effect sensor (TI DRV5053) that has a ~1V DC offset. The signal will be in the range of 95-105 Hz and is used to determine the ...
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1answer
103 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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1answer
98 views

LTspice 60 Hz notch filter simulation

I am trying to build an EEG circuit based on the description here: https://www.instructables.com/id/DIY-EEG-and-ECG-Circuit/. I would like to simulate the behavior of certain sections of the circuit ...
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2answers
72 views

Purpose of a resistor in active filter circuit

I am currently analysing this circuit, and even though its purpose is clear to me I am unable to tell what is R17 supposed to do. Is it there just to set gain? I would be grateful for any explanation, ...
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Differential bandpass filter Audio application

I am developing an Audio project which is required to output a signal between 10kHz - 40kHz at ±1V. The sound is produced from an AD9106 chip which is interfaced to the following circuit: When ...
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1answer
84 views

Twin notch filter working

Can someone please explain to me in depth as to how this twin notch circuit is working. Also is what is the formula for finding the notch frequency because some sites give the answer as (1/2×pi×RC) ...
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1answer
64 views

Would an 8 order analog filter be enough for creating a bandpass filter of 8-40 hz?

I am creating a project in which I need to an analog active bandpass filter. The opamps used in the active filters do need any feedback hence are more like comparators. There is a power line noise of ...
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Building a Shunt Active Power Filiter Using

I am trying to built an experimental setup of a shunt active power filter to validate some Matlab simulations, I am using a SEMITEACH B6U+E1CIF+B6CI. (Here is the datasheet) and picture of the device :...
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1answer
107 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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2answers
835 views

Cathode to cathode diodes in schematics

I'm trying to understand the following circuits for an MPPT, and I do have some questions: Why there is a capacitor C6 in parallel with R2 for the voltage divider for analog reading, and how was the ...
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1answer
182 views

Input impedance of low pass filter on LTspice must be constant in it's pass band?

I have single supplied sallen-key filter more that have nice 3MHz flat LPF response. I tried to compute the resistance directly by dividing the input voltage by input current which is the voltage and ...
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1answer
83 views

Cut / Boost of this Shelving-Filter

Hello everybody This circuit is a high shelfing-Filter. I do have trouble calculating the maximum cut / boost. I know that the devider (R3 and R4) sets the maximum cut and boost but how do I ...
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1answer
32 views

Analog Devices Filter Wizard Schematic Question

I am using filter wizard to help me design an active multiple feedback bandpass filter. I understand the parts of the schematic that show the stages of the filter, like this: However, I am ...
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1answer
343 views

How do I create a working bandpass filter in LTSpice?

I am attempting to create a bandpass filter in LTSpice. I am fairly new to the program, which is probably contributing to my difficulties. The filter I am creating needs to have a center frequency of ...
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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
100 views

Deliyannis-type narrowband filter is oscillating when I apply GND to the input

TLTR: My Deliyannis-type narrowband filter is oscillating when I apply GND to the input Vin. I was expecting to get almost zero volts, but I am actually getting a sine wave at almost 20KHz. I´m trying ...
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1answer
299 views

Designing 4th order Butterworth Multiple feedback bandpass filter

I'm trying to design a 4th order Butterworth bandpass filter using Multiple feedback topology. The design requirements I am trying to achieve for this filter are; Q factor = 10, Av = 11, fc = 100kHz ,...
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1answer
82 views

What is the purpose of these capacitors in this State Variable Filter schematic?

I need some help understanding this schematic. It's a state variable filter based parametric equalizer. What are the capacitors C4, C5 and C6 for? Are those coupling capacitors like C1 and C7? Are ...
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2answers
207 views

Parametric Equalizer with State Variable Filter

I'm new to this forum but hope to get some answers to a project I'm working on. I'm trying to build an parametric equalizer with several bands (5 Bass-Bands, 3 Middle-Bands, 3 High-Bands). In the ...
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1answer
64 views

Options for 2 or 3 band active audio tone control circuits with quite steep frequency response

I'm trying to roughly replicate the sound of the per-stereo-channel 3 band equaliser conttols of an old Citronic Pro-8 / Pro-10 DJ mixer. If I'm correct had a fairly steep curve so bass and treble ...
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1answer
86 views

What kind of filtering does this op-amp perform?

I am using a heart rate sensor whose schematic is provided here. The circuit uses an operational amplifier (towards the right of the figure) which among other things, does a filtering operation. I ...
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1answer
81 views

Where is the dc component?

So a ac filter doesnt allow the dc component to pass through it, so the dc component would take a altetnative path where as the ac component would easily pass through it. My question is, where is dc ...
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1answer
51 views

4th order (active) filter, I want constant phase shift band

I'm needing to improve an existing fourth order active filter design. The filter amplifies 10-100 kHz signals as desired, however the phase shift is causing problems. 10 kHz signals are phase shifted ...
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79 views

Whats the effect of a resistor inside the feedback of an active low-pass filter?

I'm working on the bias driver of an EEG system to remove the common mode signals from the channels. The output stage consists in a active inverting low-pass filter (I used an AD8606). Due to ...
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1answer
362 views

Simple audio equalizer design: One filter is sending all the other signals to ground

I’m designing and building an audio equalizer with active frequency filters for my school project and I thought the base design was completely functional until I decided to simulate it on Proteus VSM. ...
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255 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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1answer
159 views

Audio Transformer output straight into an opamp?

Below is a circuit I'm working on. It's a guitar input buffer featuring transformer isolation. The transformer I'm using is pretty expensive and should be fairly linear, but I decided to add a graphic ...
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2answers
67 views

How to decide a Filter circuit and Cut-off frequency to my application?

I have to design a Gas sensor(SEN-09405) interfacing circuit with STM32F030CCT6 Controller ADC Pin through a filter circuit(To improve the Analog signal). Based on which parameter, I can decide Filter ...
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1answer
88 views

Inverting Second Order Filter

I am working on an audio filter, and my goal is to filter out noise below 90Hz and 20kHz (the range of my speakers). I will have some nearby circuits running at 25 to 30kHz, so I have decided to go ...
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1answer
71 views

Pre-Amplifier Question [duplicate]

back at it again with a problem that I am stuck on and need some clear explanation of. 1/2: I was wondering How those Bass controls work, for example the ones in the car you allow to change the bass ...
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2answers
198 views

Active band pass filter that looks like a sallen–Key topology filter

I was using the Analog Devices design Wizzard in order to design a band pass filter with theese characteristics: Gain : 23 dB Passband: -3dB at 15 KHz Stopband: -40dB at 40 KHz The filter has 4 ...
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1answer
181 views

Transfer function of Op-Amp-Twin-T Filter

I have the following circuit and wanted to find out the transfer function of the whole circuit (which includes the non-ideal op-amp as well - modelled as a VCVS - H(S) is DC gain with some poles). I ...
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4answers
866 views

Chosing R and C values for a given RC filter design

I'm currently into designing passive LP filters such as RC topology and active filters such as Sallen-Key topology. I'm fully aware that what matters in the choice of values for the resistors and the ...
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2answers
423 views

How to design a sharp 200kHz band pass filter

I have made an a fm communication system to send audio through power lines. The center frequency is 100khz or 200 khz and maximum frequency deviation is ±10khz(with no IF stage). The modulator and ...
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61 views

Frequency selective preamplifier at 10-20 kHz

I'm looking for a way to amplify microvolt AC signals generated in an induction coil. I want to use 5 V single supply rail-to-rail opamps to amplify the signal at least 100 times in the range of ...