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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Using active BPF to convert a square wave into a sine

I have an inverter that converts 24 V DC to a 48 VAC peak-to-peak square wave with a frequency of 55 Hz. I am then going to use a step-up transformer to output 120 VAC to power some rocket valves that ...
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How to design BJT active filters

In High school and University courses, I have only seen active filters made around OpAmps. I'd like to know something about active filters built with BJT amplifiers. Figure: Example of BJT filter ...
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BJT high frequency analysis

I have a little bit of confusion on how the textbook author is determining the high frequency cutoffs for the parasitic capacitance parameters for a common emitter amplifier. This is Boylestad ...
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negative miller capacitance

I'm learning about the Miller capacitance effect when a capacitor is tied to both the output and input of an amplifier. This is specifically about learning to deal with the parasitic capacitances of a ...
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Is it possible to sweep 20 Hz to 20 kHz with one potentiometer?

I'm designing a resonant filter based on a state variable filter topology with sweepable frequency and variable resonance. The filter is designed to sweep from roughly 20 Hz up to 20 kHz (50 kohm ...
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Filters in cascade

Let´s say that in order to avoid having a filter of too large of a degree, I use multiple filters in cascade: Low frequency gain of 8dB Cut-off frequency of 4Hz Chebyshev of order 2 Would the ...
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Which resistors control the gain of this filter?

Update2: Nevermind the update1, question went far beyond its scope. Accepted answer was my expectation. Update1: I have the filter(bandpass) design below, created using texas instruments filter ...
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Active RC filters

I was reading paragraph 4.2 of this book about Active RC filters. It says that if we want to get a band pass filter with high selectivity (i.e. high quality factor Q) we should use resonant circuits (...
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Low-pass cutoff frequency definition (-3dB vs. filter design)

For low-pass filters, we usually define the cutoff frequency as the frequency at which the gain drops by -3dB. Another definition, however, comes up in filter design as one of the parameters that ...
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Design of second order low pass filter using passive RC components and opamp

I have an RC low pass filter connected to the non inverting terminal of the opamp. There is a feedback resistor from output of opamp to its inverting pin.Then an RC low pass filter is placed at the ...
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Noisy output on active bandpass filter PCB Design

I'm trying to design a 40dB active bandpass filter with a centre frequency of 130KHz and a passband of 80KHz. I don't really know much about filter design so I used the TI filter design tool to design ...
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Preferred resistor (E series) value optimiser

Is there a tool to find the closest optimum preferred resistor values given a list of constraints? For example I'm designing a filter but only have a few odd resistor and capacitor values to choose ...
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Trouble designing a low pass filter

I was trying to design a simple 3rd order low pass filter by cascading 3 first order low pass filters along with an amplifier at the end. The transfer function is straightforward: $$ H(j\omega )=4\...
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sallen-key bpf giving low gain after coupled to differential input

I designed a Sallen-key band pass filter where the gain at center frequency is 45.6dB. After feeding it with a sine wave at the center frequency, it amplifies the signal by 45.6dB. However, after ...
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Choosing RC values for Active LPF to match signal input impedance

I am design a basic 1st order Active LPF with unity gain and am new to this field. How do I make sure that I choose my R and C values to match the input signal impedance or does this not matter? What ...
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Second Order Filter with DC offset

The circuit below takes the signal from a current transformer, depicted as I1, convert it to voltage through R9 and go to the second order filter U1. I want to add an offset to the current transformer ...
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PWM to analog converter

In many applications, when a PWM signal is converted to an analog signal, they use a second order low pass active filter cascaded with a low pass passive filter, like the one shown below, (from ...
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Low Pass Filter requirements

I've got a variable pulse wave (that looks like a square wave) ranging from 5Hz to 60Hz. The peak voltage is 5V. I'm trying to design a low pass filter that effectively gives the average voltage as a ...
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DC ripple stabilizer. 3rd order low pass filter. How to supply op-amps properly

I have a cheap ac-dc adapter, but it outputs DC with a ripple. It has variable output, so it can output 12, 14, 17, and so on up to 32V. I measured output of ac-dc adapter with an Agilent multimeter, ...
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Why is the transfer function of this non-inverting low-pass filter wrong?

I came across this block in a larger circuit: With a transfer function (in pole-zero form) of; $$ H(s) = \frac{s+30000}{s+5000} $$ which was found using KCL on the inverting terminal of the op-amp. ...
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Self Oscillating INA with Multiple Feedback filter

I'm working on a circuit to receive a signal in the 220Hz range. The signal is created from a small loop transmitter emitting a 50% duty cycle DC square wave of about 4.8 Watts. The receiver is a ...
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142 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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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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139 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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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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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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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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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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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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133 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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81 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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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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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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63 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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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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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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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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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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135 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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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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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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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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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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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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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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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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