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Questions tagged [sallen-key]

For questions about the Sallen-Key filter topology. Use in conjunction with related tags such as "filter", "active-filter", "high-pass-filter", and/or "operational-amplifier", as applicable.

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Band Pass Filter Design Simulation

I'm trying to simulate a bandpass filter in ltspice. bandpass filter should be in the 2-5 Hz frequency range I calculated the capacitor and resistor value for this range. However, the simulation ...
AEY's user avatar
  • 51
0 votes
3 answers
79 views

2nd-order Sallen-key low pass filter with unity gain outputs rail voltage when input is 0V

I was designing an active low pass filter for simple sigma-delta modulation signals. I found that the op-amp will output 3V when the input is 0V given that the power supply is 0~3.3V. I simulate the ...
ONLYA's user avatar
  • 163
0 votes
1 answer
133 views

Differential amplifier op-amp schematic connection and DC biasing

I have a differential IF (intermediate frequency) signal generated by an ADL5801 RF mixer. Stage 1: the signal is amplified before active filtering and it has LC LPF in the beginning for filtering ...
Cenk's user avatar
  • 75
0 votes
1 answer
67 views

My Sallen Key Butterworth high pass filter's frequency response graph is not responding

I tried to make a cutoff frequency of interface in partial discharge but the response frequency graph is not responding. I already changed (Amplitude= & frequency= 50Hz) in the sine generator ...
ADORINA's user avatar
1 vote
1 answer
447 views

Creating third order butterworth filter with Sallen–Key topology

I am trying to design a third order Butterworth filter with Sallen–Key topology. I am quite new to this and there is not much only about third order variations.I have the following requirements: Gain:...
confusionpersonified's user avatar
1 vote
1 answer
86 views

Incorrect cutoff frequency using two Sallen-Key filters to build a bandstop filter

I'm currently having trouble troubleshooting my answer. I have to make a bandstop filter that has a cutoff frequency of 100 rad/s, and 10^6 rad/s using two Sallen-Key filters. I made the low and high ...
doedoe's user avatar
  • 11
1 vote
0 answers
47 views

Sallen-Key filter with input signal attenuation

I want to reduce input signal amplitude before it gets to the low pass filter by 6dB. I could use MFB topology for K<1, but that would invert the phase. Is there a solution that keeps the phase? ...
bkxp's user avatar
  • 181
2 votes
2 answers
195 views

2nd Order Butterworth filter design. How to find "m" and "n" values

I was reading this article Active-Low Passfilter design from Texas Instruments, and I've been racking my brain all day trying to find how they determine the values for "m" and "n" ...
belmont Dubois's user avatar
0 votes
1 answer
115 views

Problems with output signal of a 2nd order low pass Sallen Key filter for an electret microphone

I'm having problems with a small circuit based on the amplification of a audio signal received by an electret microphone. It goes to a 2nd order Sallen Key low pass filter circuit with an ...
Zlmanuel87's user avatar
0 votes
3 answers
286 views

Why isn't the output of this Sallen-Key bandpass filter made with transistors like the output of the op amp version?

I made a transistor Sallen-Key Butterworth bandpass filter using two filter sections for each high-pass and low-pass stage. The output is different from the op amp version. I know it is possible to ...
Michael Weaser's user avatar
0 votes
1 answer
232 views

What is the difference between the Sallen-Key and VCVS topologies?

According to Wikipedia, the Sallen-Key is a special case of the VCVS (voltage-controlled voltage-source) filter topology in which the gain is unitary. The topology is: The VCVS refers to the non-...
Rubem Pacelli's user avatar
2 votes
0 answers
61 views

How to design a Deliyannis-Friend biquadratic section?

I have opened a question yesterday regarding a mistake I am not finding in my Deliyannis and Friend design algorithm: Deliyannis-Friend design: where is my mistake? Although I am still trying to find ...
Granger Obliviate's user avatar
1 vote
5 answers
303 views

Sallen-Key LP design algorithm

I am facing this design from Analog Devices: Image source: Analog Devices - Mini Tutorial MT-222, Sallen-Key Filters I don't understand how they reach the value for the coefficient m. I did a sanity ...
Granger Obliviate's user avatar
0 votes
0 answers
458 views

Narrow band band-pass filter design with LM358 op-amp

I am trying to design a narrowband band-pass filter with an LM358 op-amp, single supply 0-5 V. My requirement is a gain of 30 dB at center frequency 4 kHz and 20 dB attenuation at 3 kHz and 5 kHz. I ...
Sreya Ghosh's user avatar
0 votes
5 answers
337 views

TPA3116D2 amplifier with Sallen-Key low-pass filter on TDA2030

I have a 2 x 50 W TPA3116D2 (VHM-302) amplifier and a Pioneer TS-G1345R 35 W, 4 Ω speaker. When connecting them, there is no problem and the sound is good. However, I wanted to build a low-pass filter ...
Ozkan lV's user avatar
2 votes
3 answers
429 views

4th-order Butterworth filter - strange oscillation in output

I have created a 4th-order filter based on the result of calculations and simulation. Bellow is schematic: In simulation the filter works fine (I also checked the transfer function using this online ...
grandzello's user avatar
0 votes
4 answers
903 views

Designing Sallen-Key second-order bandpass filter

I am trying to design a Sallen-Key bandpass filter with a center frequency of 64 Hz, k = 1, Q = 1.8, and H0BP = 1. How do I approach finding the resistor values that will produce these results? So ...
the_circuit's user avatar
5 votes
2 answers
216 views

Did I design this filter correctly?

I am about to place/route and order my PCB for this subcomponent. It essentially takes in a low-amplitude analog signal from a 1/4" jack, adds a 1.65V bias, amplifies, and filters off any high ...
Rydberg's user avatar
  • 251
1 vote
3 answers
129 views

What type of filter did I accidentally create here?

I was trying to make a low-pass Sallen-Key filter, but I messed it up and made something else. I already have my PCB, so no going back now! I need to tune the cut-off frequency, but I don't know how ...
Rydberg's user avatar
  • 251
3 votes
1 answer
231 views

Why am I measuring such high THD+N on my active high-pass filter?

I have designed a 2nd-order active Sallen-Key high-pass filter for use in an audio circuit. An LTspice schematic is shown below, where VDD is 5 V. I have also breadboarded the circuit using low ...
zigzidane's user avatar
  • 115
2 votes
2 answers
864 views

Converting two cascaded first-order high-pass filters circuit to a second-order high-pass filter using Sallen-key configuration

Below is the transfer function of the two cascaded first-order high-pass filters (each with 20.6 Hz cut-off frequency) and their circuit: And then there is the transfer function of the second-order ...
Scipio's user avatar
  • 803
2 votes
3 answers
573 views

Second order active high pass filter

I am trying to design an active filter, which I assume is an active high pass filter according to what I see from the Bode plot. I can get the transfer function from this plot and then I need to ...
Jing Hao Siet's user avatar
1 vote
1 answer
857 views

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 ...
Johannes's user avatar
  • 279
0 votes
1 answer
337 views

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 ...
RM429's user avatar
  • 37
3 votes
0 answers
372 views

Which of these three op amps should I choose for my low frequency filter? [closed]

I want to design a lowpass filter-4th order Bessel, so two Sallen-Key low-pass circuits in cascade with a cutoff frequency of 200Hz. I need to choose the op amps for it. I have these 3 op amps to ...
Scipio's user avatar
  • 803
0 votes
2 answers
236 views

How to pass from a double-supply filter circuit to a single supply filter circuit?

So here is the main circuit, it's a lowpass filter-4th order bessel, so 2 sallen-key low-pass circuits in cascade. I already have all the components and transfer functions figured out but i would like ...
Scipio's user avatar
  • 803
1 vote
3 answers
964 views

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 ...
HandlerOne's user avatar
2 votes
2 answers
906 views

High pass filter: Overshooting before attenuation

Working with a 2nd order Sallen-Key high pass Butterworth filter with a cutoff frequency of \$f_c=0.5\$ Hz I am having difficulties making sense of a result that I got: After applying at its input a ...
Javier TG's user avatar
  • 123
1 vote
1 answer
1k views

Q of Sallen key low pass filter

During i study Sallen-key active low pass filter, i wondered why formula of Q is 1/(3-A). A is Voltage Gain. So i searched from web, and i found this. When R1=R2 and C1=C2, the Q be 1/(3-A). OK. But, ...
J.H's user avatar
  • 13
9 votes
4 answers
779 views

Cut-off frequency, gain and quality factor calculation of complex 2nd order low pass filter

I'm building a full analog chorus-effect pedal. My schematic is based on that of a Rockman X100 headphone amp, designed by Tom Sholz. In this schematic, there is a 2nd order low pass filter that looks ...
Linus Tielemans's user avatar
0 votes
0 answers
272 views

LTspice, Sallen & Key low pass filter + Low pass filter order 1

First of all, sorry for my English, it isn't my native language. I want to cascade a first order low pass filter and a low pass Sallen and Key structure in order to get my bandwidth at 30 Hz (Fc = 30 ...
Benjamin M's user avatar
0 votes
1 answer
518 views

Active low pass filter with cut-off frequency ~4250 Hz lets a 20 kHz signal through

I needed an active low pass filter for my project that can produce an output voltage within the required settling time and ripple voltage ranges. Although I managed to get a good enough output voltage ...
Curious Student's user avatar
0 votes
0 answers
83 views

Why is the output of my opamp mV?

I would like to use an Si514 as a tuneable oscillator driving later stages with 50 ohm impedance. So I put an opamp on it and attempted to configure it as a saleen-key low pass filter (to round the ...
foreverska's user avatar
1 vote
1 answer
400 views

Why does adding a gain to a Sallen-key second order HPF change the amplitude response?

As the title suggests, I have done all the necessary calculations to implement a gain into my second order stage of my 6th order high pass filter but for some odd reason, it would change the amplitude ...
unity123's user avatar
3 votes
2 answers
1k views

Why is the output of a high-pass filter not 0 when the input is 0?

I'm trying to design a 5th order Butterworth high-pass filter built on the Sallen-key topology with a cut-off frequency at 100Hz. For some reason, the output has a DC offset of around 5mV when the ...
unity123's user avatar
0 votes
2 answers
105 views

Help for analog signal chain for 16bits ADC

I work on analog amplifier and filter chain for an internal STM32H753VI 16bits ADC. The signal chain is based on ultra-low noise opamp LT6237 and differential driver LT1994. The sample-rate of ADC ...
rom1nux's user avatar
  • 498
2 votes
3 answers
5k views

How to design a 2nd Order High Pass Butterworth filter with a cutoff frequency of 0.5 Hz? [closed]

c1=c2=10µf, R1? R2? using the unity-gain Sallen-key topology what should I do?
Cyrine Dridi's user avatar
0 votes
2 answers
89 views

Bandpass filter obtained by complementary transformation of lowpass Sallen & Key: what went wrong?

I am considering the following lowpass Sallen & Key filter: My components are the following \$R_1=10 k\Omega\$ \$R_2=10 k\Omega\$ \$C_1=150 nF\$ \$C_2=1.65 nF\$ Now I have performed a ...
Granger Obliviate's user avatar
0 votes
1 answer
168 views

Measuring experimentally the poles parameters

I have the following Sallen & Key lowpass filter: $$T(s)=\frac{\frac{1}{R_1R_2C_1C_2}}{s^2+(\frac{1}{C_1R_1}+\frac{1}{C_1R_2})s+\frac{1}{R_1R_2C_1C_2}}$$ The parameters values are $$R_1=10 k\Omega$...
Granger Obliviate's user avatar
0 votes
1 answer
118 views

Bode is plot despite of high quality factor

I'm trying to simulate the following circuit in LTSpice: As can be seen, the Gain $$ G = 1 + \dfrac{R_3}{R_4} = 1 + 1.6 = 2.6 \Rightarrow Q = 2.5$$ Which should give a peak, but I'm getting following ...
xrfxlp's user avatar
  • 121
1 vote
1 answer
328 views

2nd order Sallen-Key low pass filter frequency response

I am trying to implement the following circuit in LTspice for studying the frequency response of the 2nd order Sallen-Key low pass filter for a project. Why am I getting a negative peak in the ...
kodekuzuri's user avatar
2 votes
2 answers
713 views

Sallen Key Lowpass Filter stops rolling off in simulation

I unfortunately have no pictures of my spice simulation since it's on a different computer, but I am attempting to create a Sallen Key lowpass filter with fc~=555Hz. I used the lowpass filter design ...
Jaywalk's user avatar
  • 539
0 votes
0 answers
79 views

Is this circuit a Sallen & Key biquad?

So I came up with the following filter to analyze: My first thought was that this reminded me of a Sallen & Key biquadratic section. However I'm having trouble identifying each component. Taking ...
Granger Obliviate's user avatar
2 votes
3 answers
600 views

How to use Butterworth Polynomials to determine RC components of a n-th order filter

I am working on a project to design a 7th-order Butterworth filter Sallen-Key topology. I am not sure how to interpret the Butterworth polynomials correctly to calculate each component. I mean how is ...
Dom's user avatar
  • 21
0 votes
1 answer
165 views

Chebyshev filter - theoretical vs simulation gain

Question is about the gain peak (or maybe more suitable would be growth) ocurring in higher frequencies (>20kHz) in Chebyshev filter 4-th order in simulation (simulated using Bode Analyzer in NI ...
Krzysztof's user avatar
0 votes
3 answers
344 views

Verification of Sallen Key Design

I have designed this Sallen-Key to give a 2nd order low pass circuit with a cut-off frequency of 150Hz. Another design specification is that R1=R2 and C1=C2. The issue is when simulated on LT-Spice ...
madge2111's user avatar
-1 votes
3 answers
3k views

Sallen-Key LPF Q factor and gain

Welcome all. I need some advice with Sallen-Key topology. I used Analog Devices tool for my design and I admit it nice quick and easy. However, I am struggling with one detail. When studied control ...
Wintermute's user avatar
0 votes
3 answers
231 views

Sallen key topology choosing right op-amp

Welcome all. I designed Bessel low pas filter using Analogue Devices filter wizard. It is a fantastic toll saving loads of time. However, like any tool has its limitations. Upon completion my design I ...
Wintermute's user avatar
0 votes
3 answers
2k views

Differences between 2nd order low pass filters

I don’t know how to design filters, but I need a second order low pass filter. I searched them on the internet and found two schemes. One is Sallen-Key, and the other I don’t know what is called. ...
John Doe's user avatar
0 votes
3 answers
607 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 ...
Aami's user avatar
  • 109