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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Removing output of low pass filter when turning off power

I'm constructing a presence detect circuit using a pulse modulated signal of 5 kHz and an infrared transmitter and receiver. The 5 kHz signal drives an infrared transmitter through a 3904 NPN ...
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67 views

What is the different bewteen the minimum attenation in butterworth and Chebyshev filter?

I have desgined n of a low-pass butterworth whose specification are fc=1khz , fs=2khz, Amax = 1 db and Amin=40 db. I found that I need to make sure the n gives me larger Amin which = 40db. So I ...
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52 views

How to design a low pass filter for Fourier Square Wave

I am trying to create a low pass filter with a cut-off frequency of 100Hz to retrieve a sine wave from a Fourier Square Wave. I am only able to achieve a sine wave with transients. How can I edit my ...
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I need to design a second order active filter low-pass Rauch structure of Bessel. Design data: f-cut = 15 Hz; C1 = 50 pF. More info in img [closed]

How can I find the values requierd? I tried using the formulas my teacher gave me but c2 is 0 when i use them. Am i doing something wrong? should i use other formulas? I tried to ask the teacher but ...
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An all-pass filter with 0 degrees to +180 degrees shift

I need an (for audio bandwidth) all-pass filter that has 0 degrees shift in low frequency and +180 degrees shift at high frequency. The ones here https://sound-au.com/articles/active-filters.htm (...
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Realisation conditions for impedances

Given a frequency function, which conditions should it fulfill to be realisable and implemented as a one-port impedance? I know that for it to be realisable with passive RLC components, the frequency ...
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61 views

Design an active bandpass filter to get 1.5MHz peak frequency and 300KHz band

I have this question in Linear Circuit Analysis course where I need to find the values of R1, R2, C1, C2, of the given bandpass filter circuit in order to get a peak frequency wp = 1.5 MHz and a ...
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Second order all-pass filter input impedance

I have a question about the second order all-pass filter input impedance when ω = ∞ and ω = 0 and I would appreciate if you could help me to understand the logic. When ω = 0, all capacitors can be ...
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Capacitors on DC power rails / voltage divider - analyzing a circuit

beginner here, please be nice :) I'm interested in the following DI-style box for my guitar, which I'm going to build, and I'm working on analyzing it. http://www.generalguitargadgets.com/pdf/...
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Why is my non-inverting band-pass filter not working properly?

I need to design a band-pass filter with the cutoff frequencies of f1=16384 Hz and f2=32768 Hz. I calculated the values of the components and it seems right, but when I run the simulation f1=9kHz ...
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Why is my low pass filter attenuating everything so much?

I have a car stereo with low level outputs from an RCA connector. I wired one channel into a simple RC LPF, then into a TPA3116-based amplifier (this one), then to a single 4 ohm woofer. Using a ...
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Trying to find a spec sheet on an old Toko active filter

I'm trying to find the pin-out of an old low-pass filter I have. I must have lost my docs for it decades ago. I've tried googling, but didn't turn up anything. It's Toko part-number TK5429. I got it ...
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Why isn't my the LTspice cutoff frequency for my multiple feedback low pass filter not matching?

I am designing a 6th order multiple feedback lowpass filter with cutoff frequency at 1000 Hz. I wrote a matlab script that calculated the capacitor and restore values. I combined all transfer ...
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how the comparator amp works as integrated amplifier [closed]

I need some explain how does comparator work as zero cross detection and integrated amp
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How to fix incorrect cutoff frequency using multiple feedback butterworth lowpass filter

I designed a 6th order low pass Butterworth filter using multiple feedback topology (Fc = 500 Hz). But when I run it in LTSpice, the cutoff frequency is seen shifted far below to around 10Hz. Why is ...
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44 views

Understanding time constant of high pass filter at op amp input

In the circuit attached R17 is the burden resistor for a CT which measures 50/60 Hz currents. The switch is a CMOS analog one, not electromechanical. When the switch is closed, the gain is about R16/...
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33 views

Feedback Loop Filters?

In the pictured schematic, is there a band pass filter in place? I’m having trouble understanding the function of R4, R6, C3 & C4. Any help or resources would be appreciated.
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More equations than unkowns in amplifier circuit

I am trying to find the Magnitude Response of the gain of this amplifier circuit. The gain formula is: $$ H(\omega) = \frac{\tilde{V_{out}}}{\tilde{V_{in}}}$$ My amplifier circuit is as follows:...
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Converting an analog Butterworth filter into a discrete filter

Here again to ask about another question. This time asking how to convert an analog transfer function to a discrete transfer function using standard continuous to discrete methods. The application ...
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26 views

Order of bandpass / bandstop filter?

I am unsure if a bandpass with one zero at 0 Hz and two poles above would be called a first order or a second order filter. The amplitude is rising and falling with 20 dB / decade and the phase ...
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42 views

How to measure a signal that uses a virtual ground using Arduino

I've created an EEG system that measures the potential difference between: 1) The differential amplification between EEG voltages. 2) a virtual ground between two 9V batteries. I'm trying to measure ...
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Do you need multiple instrumental amplifiers and filters for multichannel EEG systems?

I've created a 1 channel EEG using the AD620 instrumental amplifier and various active band filters. To add more channels, would I need one instrumental amp and series of filters per channel? or can I ...
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Multisim LF357N Op Amp Unity Gain - Questions

Im working on a junior project in which we need to buffer an input signal from a RX antenna, pass the signal through 3 filters in parallel, and pipe the outputted signal into a RTL-SDR. It serves very ...
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47 views

Effect of Source and Load Resistances on a Filter

suppose I want to design a low pass filter (for instance a Chebyshev filter) by using the low pass prototype method: The upper circuit is the Low pass prototype filter, while the lower one is the ...
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100 views

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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269 views

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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4answers
190 views

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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67 views

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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138 views

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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154 views

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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168 views

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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58 views

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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57 views

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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39 views

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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106 views

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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70 views

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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426 views

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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4answers
156 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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71 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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148 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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