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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Filtering out high frequency from my input graph

I have an input whose waveform looks something like this: It repeats over and over again until the source if turned off. It is composed of waves of 2 frequencies (16kHz and 1kHz). The final source ...
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Do active filters exist that don't cause a voltage drop?

Pretty much all filters I have come across always cause some sort of voltage drop. A passive example is the classic RC filter, an active example is the capacitance multiplier (which is basically just ...
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What all circuits can be considered as LC ladder filter?

I'm new to filter design. I read that the sensitivity of lc ladder circuits to component variation is less. The IEEE paper titled "Class-J SiGe X-Band Power Amplifier Using a Ladder Filter-Based ...
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replace attenuators in filters with changing gain of each filters?

I have multiple filters that are all the same gain that are all attenuated differently with the same attenuator circuit. Is it possible to replace the attenuators with just changing the gain of each ...
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Do active filters count as amplifers?

Can we consider active filters to be amplifers? If we use the folowing active filter design, and adjust R1 and R2 correctly that the gain is set to 10 for example, does the output signal comes out ...
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How to set this switched capacitor filter's cut off frequency?

I have never used one and if I'm not wrong, this low pass switched capacitor filter is supposed to have tunable roll-off frequency. If we use the above configuration with a particular clock frequency,...
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What could cause an active filter (multiple feedback) to self oscillate?

I'm looking for a general description of what could cause a (multiple feedback) active filter to self-oscillate, what parameters as well as practical circuit construction principles affect it (...
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Second order low pass filter: two 1st order filters not-immediately cascaded

A second order low pass filter (LPF) can be made by cascading two active LPF (an RC network + opamp.) What happens if, instead of immediately cascaded, an active LPF acts at the input (buffer) of a ...
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Help Understanding Opamp Topology (Infinite Gain Multiple feedback with Resistor to Gnd?)

I ran across the following band-pass circuit and I'm not entirely sure what R14 is doing here. The following is a screenshot: For some context, the supply is a ...
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4th order low pass Butterworth filter with very low Q factor [closed]

I have designed a 4th order low-pass Butterworth filter with a 0.707 Q factor. However, what I am getting is almost no flatness in the pass band region and my frequency response looks like a half of a ...
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RC filters in JFET negative feedback

I saw a useful answer about JEFT negative feedback here and so I thought I'd ask for some help too!! I'm attempting to create a JFET gain stage that uses a filter in a negative feedback loop to boost ...
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Sanity check on this DAC reconstruction filter design

I've altered a reconstruction filter circuit to use the LTC728XT instead of the AD8608 op-amp used in the example circuit below. Is anyone able to see any issues with my attempt? This is being used as ...
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Unknown amplifier circuit Analysis

Does anyone know what this kind of amplifier circuit is? I am trying to analyze it by calculating its gain, cut-off frequency, and frequency response. I am not sure how to break this circuit into ...
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Calculate capacitance from cascade low pass filters

The task is to make a 2:degree filter with a slope of 40 dB/decade. I have this circuit. R1=R2=10kΩ, f=1kHz I also have this formula What I think (probably wrong). Is that that because 40 dB/decade, ...
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Butterworth Filter attenuates noticeably in pass-band

The Issue: I am using a Maxim MAX7480 8th order Butterworth low-pass filter to counter any aliasing from a sensor that measures signals up to 3kHz, but I only want up to 1kHz. Thus a critical ...
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Cut-off frequency and -3dB frequency of Butterworth filter

I am in the process of designing a Butterworth low pass filter in Sallen-Key topology. I use the Analogue Devices Filter design tool. After reading the TI application report I have calculated all the ...
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Bandpass filter test results not same as simulated results

I am designing a 40 kHz bandpass filter for a university project involving a portable ultrasonic device. I have designed a 40 kHz filter using the Linear Technology Filter Design Tool with a single ...
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Gain and phase margin of multiple feedback bandpass filter

I designed a multiple feedback bandpass filter using the Analog filter wizard. The design is purely education therefore I used ideal op-amp. Fc = 50KHz; DC gain = 6dB; Q = 5; I followed the ...
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1 answer
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Multiple Feedback Band Pass Filter Noise

I designed a multiple feedback filter using the analogue devices filter wizard. I have never designed this type of filter therefore I followed up by reading about it and manually calculating the ...
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1 answer
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Active filter for low capacitance AC coupled input

I need to interface an AC coupled sensor with rest of my system. The sensor I am working with produces approx. 10V peak with 10V of DC offset but it has a very small series resistance about 50fento. ...
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Review butterworth high pass filter design

Could anyone review my 2nd order Butterworth HPF design? I have mentioned design details along with schematics and initial results. Design specifications for 2nd HPF: Cutoff frequency= 100Mhz, ...
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1 answer
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Transfer Function for active filter

Not too sure why, but I can’t seem to figure out the transfer function for the filter in question below. Can’t isolate Vout/Vin fully, there’s a straggling Vin that I can’t move over. Any thoughts?
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Microphone active low pass filter doesn't work

I am trying to make an active low pass filter for my school project. I need to design a filter with 2000 Hz cut off freq and 20-25 gain. I tried to use TI filter design tool and analog devices filter ...
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Op-amp first-order low-pass filters, capacitor placement in inverting circuit

In the picture below the lag circuits at the input decide cutoff frequency by making the input voltage at the op-amp vanish at frequencies much higher than the cut-off frequency. I understand the ...
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Question about filter

I'm studying filter. I saw the filter in book. Therefore, I designed the circuit in the LTSpice for understanding the circuit. However, I do not clearly understand whether the filter is bandpass or ...
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2 votes
1 answer
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Transient response of active filter attenuation

I simulated a 5th order active high pass filter on LTSpice. However I find that the output voltage does not have same attenuation as the magnitude response plot. At 10Hz it is expected to have a 100dB ...
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1 answer
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Add Voltage Bias/Offset to 2nd-Order Sallen-Key Highpass

I need to add a highpass filter between a signal source and an ADC to get rid of high-amplitude low-frequency signals that would cause clipping. I built a second-order Sallen-Key filter and the ...
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What is this circuit called, and what is it used for?

I analyzed this circuit and found that it's an inverting amplifier and that the impedance of the circuit goes to zero when the frequency of the input voltage goes to infinity. Does anyone know the ...
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1 answer
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Butterworth Active Low Pass Filter Design

I'm designing a low pass active filter with a Butterworth response. The passband is DC to 1.5 kHz, so the -3 dB cut off frequency should be around 2-5 kHz to be safe. The topology I've decided to use ...
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How to choose digital potentiometer bandwidth for filter?

We want to use a Digital potentiometer for an active bandpass filter. But we do not know how to choose the bandwidth of the potentiometer. The center frequency of the filter will be 90MHz. Should I ...
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Single-ended to differential ADC driver with one pole active low pass filter

I have this ADC driver circuit: There is a passive filter downstream of the driver which works as desired. I'm focused here on the active filter. When I run AC analysis on this circuit configured for ...
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PSpice and calculations don't add up for an active band pass filter

I designed a basic active band pass filter and used these equations to come up with a center frequency of 29.9 kHz: $$f_0 = \frac{1}{2\pi\sqrt{(R_1||R_2)*R_2*R_3*C_1*C_2}}$$ In PSpice, it looks like ...
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how to calculate the transfer function of a differential active loop filter

When I was deriving the transfer function of a differential active loop filter provided by ADIsimPLL, I had some problems. The circuit diagram is shown below. First, for a differential active loop ...
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1 answer
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Frequency response of a low-pass, band-pass, and high-pass adder circuit

I'm doing a project and one of the steps consists of filtering a signal through a low-pass, band-pass and high-pass filter. All the filters are Sallen-Key with a passband gain of 1. The pass-band ...
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3 answers
191 views

What happens to high frequency noise in an op amp low pass filter?

My understanding is that in a simple passive RC low pass filter, the high frequency noise will just go to ground while the low frequency signal will go through the resistor only. My question is what ...
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Non-linear amplifier

An amplifier has a non-linear response given by Vo= aVin +bVin^2 at all frequencies. When a sine wave of amplitude 1V is input to the amplifier the output of the amplifier contains a harmonic at -80 ...
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What is the purpose of this extra capacitor in this opamp low pass filter?

I'm trying to follow along with this blog post reverse engineering the HC-SR04 ultrasonic distance sensor. The signal from the receiving transducer is amplified, filtered, and then amplified again. On ...
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3 answers
207 views

What is the transfer function of this bandpass filter?

I have this bandpass filter for which I'm trying to get the transfer function. The amplifier is not idead and has an open-loop gain of 100k and a gain-bandwidth product of 10MHz. I tried everything ...
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1 answer
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Multiple Feedback Filter

I built a Multiple Feedback low pass filter on the breadboard using an LM7171. Below is the schematics: While doing measurements, I noticed two things: Large DC bias at the input R3 and the output ...
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How to design a 2nd order LP active filter with differents responses?

I have been asked to design and simulate a 2nd order analog low pass filter having the responses of Butterworth, Chebyshev and Bessel. Im looking for guidance and suggestions,since I understand the ...
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Is there a method to convert a Butterworth response into Chebyshev and Bessel responses?

I wonder if once there is a completed/aproximated a design model of any of the responses mentionated, it can be operated mathematically (or there is a method/recipe) to generate the other responses? ...
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5 votes
2 answers
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How is the slope of the frequency response of an analog active filter defined?

I have seen different types of filters, and different slope values at -20 db, -40, etc. The literature says that the order define the slope, but how? How can it be mathematically justified? For ...
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Why is my active passband filter (LP and HP Butterworth filters in series) not working?

I did each filter alone and they work fine, but when they are made together to form a bandpass filter with the same components I used they don't work. The output on the oscilloscope is a very weak ...
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3 answers
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Active high pass filter experiment result

The pictures above are the circuit model and plot. uA741 of Texas Instrument was used as an op-amp on the circuit. 1 Vrms was used as an input voltage so that the output can be the voltage gain. The ...
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1 vote
1 answer
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How to find damping and the natural response in a system with a zero and complex pole pair

I want to know how to get damping and the natural response in a system with a zero and complex pole pair. I calculated the following transfer function: (from an active filter composed of 2 capacitors ...
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1 answer
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Why is my narrow bandwidth multiple feedback active bandpass filter oscillating?

When I put the following narrowband active bandpass circuit on a breadboard, using a MCP601 single-supply CMOS op-amp, it just oscillates at about 339 kHz with a Vpp of about 1.36 V at a supply of 5 V....
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Finding the correct low-pass filter audio input cutoff frequency

This low-pass filter, taken from the Synthesizer Arturia Minibrute is rated at 15 MHz. $$\frac{1}{2\pi RC} = \frac{1}{2\pi \times 100\Omega \times 100\text{ pF}} = 15,915,494.3092$$ Why would you aim ...
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1 vote
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What's the difference between these two Sallen-Key bandpass filters?

I am thinking about using a Sallen-Key bandpass filter for an audio project I am working on. While trying to understand the circuit, I came across two similar, but slightly different circuits. The ...
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2 votes
1 answer
139 views

A few questions regarding Op-amp filters and DC bias

I have a few questions in relation to the attached schematic.....the input signal is a sinusoid of F=1Hz and Vpeak=2mV. The signal passes through a band pass filter (BPF) with a gain of 143, and then ...
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Dual state variable filter HP24 output

So I've been playing with 4-stage state variable filter (SVF hereinafter) to get a voltage-controlled filter with Highpass 24db/octave (HP24), LP24 and BP12 outputs. Unfortunately, reading about these ...
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