Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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.

For questions about the Sallen-Key filter topology. Use in conjunction with related tags such as , , , and/or , as applicable.

See Wikipedia's article on the Sallen-Key topology for more information.

59 questions
14
votes
4 answers

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 say that "at frequencies of 100kHz and above, the…
Cal-linux
  • 2,029
  • 2
  • 20
  • 37
9
votes
4 answers

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 like a variant of a Sallen-Key low pass filter,…
Linus Tielemans
  • 91
  • 2
8
votes
5 answers

Circuit for small level voltage detection (microvolts)

I have been working on a project lately which help in the detection myogenic potentials (of the levels of micro-volts). After studying from several places, I finalized the following test circuit. The initial voltage dividers helps in generating the…
DodZi
  • 115
  • 1
  • 7
6
votes
6 answers

Why does this potentiometer in an op-amp feedback path cause noise when adjusted?

I have placed a dual-gang 100k potentiometer in the feedback path of two op-amps that work as a Sallen-Key filters. This controls gain but also the Q factor of the filter (somewhat demonstrated on wikipedia. However, when I move the knob, it makes…
loudnoises
  • 1,816
  • 16
  • 28
5
votes
2 answers

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 frequencies. I know that this circuit could have…
Rydberg
  • 201
  • 1
  • 5
3
votes
1 answer

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 quality components (X5R caps and 1/4 W, 5% resistors).…
zigzidane
  • 115
  • 5
3
votes
0 answers

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

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 choose from: MCP6004 TL084 LM324 A quick google…
Scipio
  • 773
  • 4
  • 8
3
votes
2 answers

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 frequency of the input is less than the cut-off…
unity123
  • 43
  • 4
3
votes
2 answers

Circuit for Inverse Chebyshev or Elliptic LPF

I know I came across a 2 op-amp, 2 capacitor circuit that can be used for a single section of an Inverse Chebyshev (a.k.a. "Chebyshev Type II) or an Elliptic (Cauer) filter. It has a pair of zeros on the \$j\omega\$-axis at \$\pm j\omega_z\$, and…
robert bristow-johnson
  • 1,645
  • 1
  • 12
  • 29
2
votes
0 answers

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 the problem it is starting to become clear for me…
Granger Obliviate
  • 1,391
  • 10
  • 29
2
votes
3 answers

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 tool) but in the real world, it doesn't. I use a…
grandzello
  • 61
  • 3
2
votes
2 answers

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 high-pass filter (with 20.6 Hz cut-off frequency)…
Scipio
  • 773
  • 4
  • 8
2
votes
3 answers

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 design an active filter . The transfer function…
Jing Hao Siet
  • 21
  • 2
2
votes
3 answers

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

c1=c2=10µf, R1? R2? using the unity-gain Sallen-key topology what should I do?
Cyrine Dridi
  • 37
  • 1
  • 3
2
votes
2 answers

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 on wikipedia's page on the topology with R1=2.26k,…
Jaywalk
  • 539
  • 3
  • 15
1
2 3 4