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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131 views

Why is -12v connected to GND in this schematic?

A couple of questions: 1) It looks to me that the three-prong ground connection in the bottom right of this schematic is the only ground connection. I used the GNDPWR symbol in my KiCad schematic to ...
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1answer
64 views

transfer function of a op amp

how can I calculate the cut off frequency of the non inverting op amp circuit? I calculated the one for the inverting op amp so far. I calculated the unity gain bandwidth A0 = G1 + G2 / G2. should ...
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1answer
110 views

Active filter has unintended attenuation for lower frequencies

I have design an active filter with an online tool. The circuit looks as follows: It should be a low pass filter of 3rd order with a cut-off frequency at 50kHz. Unfortunately, it attenuatues DC ...
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61 views

How do I convert poles and zeros of a transfer function into a circuit / required circuit components?

I have been given a bode plot of a low pass filter, and tasked with essentially reversing the effects by using a high pass filter. I have solved for the transfer function which is the first equation, ...
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2answers
71 views

What are the differences between active bandpass filter topologies?

I want to use a narrow band active bandpass filter but I found generally 2 topologies as seen below. What are the differences between them?
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1answer
55 views

Buffer stage for audio filter

Can someone explain the purpose of this buffer stage? I understand how it works in the sense that I understand the cause of each reading on the oscilloscope but I don't understand why the buffer stage ...
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2answers
106 views

Transfer Function Derivation

Where did the following transfer function come from? \$H(s) = -H_o\frac{\frac{\omega_o}{Q}s}{s^2 +\frac{\omega_o}{Q}s + \omega_o^2}\$ \$H_o\$ is the gain at resonant frequency. I'm told it ...
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1answer
42 views

Multi-stage fully differential bandpass filters

I've recently been doing a bunch of research on analog filtering in preparation for a data acquisition system I'm building. For context, while I'm fairly comfortable with FPGAs and digital/computer ...
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2answers
51 views

Active band pass filter + offset

I'm trying to know the fr equation for the following op amp configuration: I have some capacitors values for specific fr frequencies: fr = 34Hz -> C = 33nF fr = 50Hz -> C = 22nF fr = 160Hz -> C = ...
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1answer
47 views

LTSpice - envelope detector LPF behaving like buffer

I have an issue with an LTSpice simulation and I'm not sure if the issue lies in the simulation setup or somewhere more basic. The simulation is as follows: The system is as follows: on the left, ...
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1answer
30 views

Can a 3 phase IGBT based front end converter work without line reactor?

I have been working on developing a 3 phase active power filter, which has a 3 phase IGBT bidirectional converter. I have been able to develop APFC (Active Power Filter Converter) with the line ...
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1answer
77 views

Filtering a Square Wave into a Sine Wave

I am trying to Filter a +-4V odd inverted square wave into a sine wave. How should I go about doing so? So far I have computed the Fourier series of my particular input signal to be: Which I ...
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1answer
54 views

Low pass to high pass filter conversion

Ripples from Mutable Instruments (open hardware) is a low pass 4th order filter. The schematic is found here https://mutable-instruments.net/modules/ripples/downloads/ripples_v40.pdf Can I swap ...
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Active low-pass filters — good to what frequencies?

Appendix E of The Art of Electronics, 3rd Edition (LC Butterworth filters) starts by saying that "active filters are convenient at low-frequencies but impractical at higher frequencies". They go and ...
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1answer
125 views

Is using passive anti-aliasing filter with its transfer function instead of an active filter common or reliable?

I need to ask this general question with an example for clarity. Imagine I have to measure a signal with BW of 5kHz and I need to make a unity gain active anti-aliasing filter with a steep roll off ...
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1answer
134 views

DC Filter for DC free transmitting

I have a sine signal with Vpp = 5V, DC Offset = 2.5V. Now I am asking myself how to remove this offset in order to have a DC free transmission.
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Some questions about an active filter design using a design tool

After a previous question I decided to make an active LP filter by using Analog Device's filter design tool. I found a +/-15V dual supply so I want to use it to power the filter. I'm quite new in ...
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1answer
44 views

Adjusting the gain on a 4th Order Butterworth Bandpass fIlter gain

I designed a bandpass filter with the TI filter designer tool but I initially designed with a gain of 40 dB. However, I'd like to reduce the gain to 20dB but I'm having issues doing trying to figure ...
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1answer
66 views

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
108 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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2answers
77 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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2answers
158 views

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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3answers
91 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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2answers
107 views

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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92 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
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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
54 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
34 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
67 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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44 views

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
57 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
146 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
38 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
64 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
104 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
200 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
76 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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0answers
86 views

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
152 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
67 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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0answers
38 views

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
148 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
851 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
218 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
120 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
37 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
456 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
63 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
109 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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2answers
370 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 ,...