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.
63
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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 ...
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0
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34
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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? ...
- 181
2
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2
answers
131
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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" ...
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1
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66
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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 ...
0
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3
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140
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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 ...
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1
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118
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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-...
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2
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0
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52
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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 ...
- 1,403
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5
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239
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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 ...
- 1,403
0
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0
answers
312
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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 ...
0
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5
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222
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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 ...
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2
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3
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306
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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 ...
- 61
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4
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420
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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 ...
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5
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2
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197
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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 ...
- 253
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3
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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 ...
- 253
3
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1
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178
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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 ...
- 115
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2
answers
607
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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 ...
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2
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3
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474
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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 ...
1
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1
answer
598
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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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1
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243
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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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3
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0
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309
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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 ...
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2
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197
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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 ...
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3
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814
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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 ...
- 115
2
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2
answers
719
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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 ...
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1
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811
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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, ...
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9
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4
answers
692
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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 ...
0
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0
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244
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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 ...
0
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1
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419
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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 ...
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181
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Is the system linear, time-invariant and causal? Does the decomposition property hold? Sallen Key bandpass filter
I have this ordinary Sallen Key bandpass filter: -
simulate this circuit – Schematic created using CircuitLab
I'm being asked, if the system is linear and/or time-invariant and/or causal. ...
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0
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80
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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 ...
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312
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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 ...
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2
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974
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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 ...
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2
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102
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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 ...
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3
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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?
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80
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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 ...
- 1,403
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1
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142
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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
$$R_1=10 k\Omega$...
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1
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110
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Bode is plot despite of high quality factor
I'm trying to simulate the following circuit in LTSpice:
As can be seen, the Gain
$$ 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 ...
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275
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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 ...
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2
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2
answers
604
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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 ...
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67
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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 ...
- 1,403
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3
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431
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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 ...
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137
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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 ...
0
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3
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286
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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 ...
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3
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2k
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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 ...
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3
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201
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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 ...
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1k
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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. ...
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3
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558
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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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162
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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 ...
0
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1
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218
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Is this transfer function impossible with a low-pass Sallen-key filter?
I was given this transfer function and instructed to use a Sallen-key cascaded with a 1st order filter to achieve it.
$$H(s)=\frac{628^3}{(s+628)(s^2+628s+628^2)}$$
The first order transfer function ...
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6
answers
5k
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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 ...
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717
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Sallen-Key Low Pass Oscillator
How to design a Sallen-key Low pass Oscillator that gives undamped oscillations? I've grounded the input of the Sallen-key low pass filter but still can't get any oscillation at the output. I've ...
