# Questions tagged [sallen-key]

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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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### 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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### 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 ...
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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 ...
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### Active LPF 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 ...
55 views

### 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. ...
74 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 ...
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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 ...
801 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 ...
74 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 ...
714 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?
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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 ...
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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 ...
352 views

### 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 ...
3k views

### 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 ...
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### Why is the cutoff frequency of this highpass filter with formula different from LTspice?

I used this online tool to play around and design a Sallen-Key low pass filter with a cutoff frequency of 0.3Hz. When I now put the resulting values for R1, R2, C1 and C2 in the formula I get exactly ...
388 views

### Does this Sallen and Key filter work on a single supply and does the input offset matter?

This is the schematic for a Sallen and Key from the Doepfer Musikelektronik website: simulate this circuit – Schematic created using CircuitLab I intend to run this in a synth, the oscillators ...
2k views

### 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 ...
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### Sallen-Key - how opamp input bias current changes cutoff frequency?

As in the title: what exactly is the impact of input bias current in Sallen-Key topology, for example the one below: I read that it can matter significantly, however I did not find anything more on ...
415 views

### Input impedance of low pass filter on LTspice must be constant in it's pass band?

I have single supplied sallen-key filter more that have nice 3MHz flat LPF response. I tried to compute the resistance directly by dividing the input voltage by input current which is the voltage and ...
296 views

### What is the difference between a Sallen-Key Band pass filter and a band pass filter?

Am currently doing an assignment on sine wave generation and am using a sallen key band pass filter - i am unsure what the difference between the band pass filter and the sallen-key band pass.
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### Sallen-Key filter for PT100 RTD measurement

I am going to build temperature sensing system using PT100 sensor (and later Raspberry PI 3). I refer my work to Microchip note AN687 Precision Temperature-Sensing With RTD Circuits. On the page 4 is ...
208 views

### LTC1966 Sallen-Key post-filtering application question

Just a quick question about an application circuit in the LTC1966 datasheet. Figure 13 on page 18 shows a third order (when considering output resistance of the LTC1966) Sallen-Key filter, with a ...
263 views

### Does Sallen-Key filter need a high impedance load?

I am using the circuit below to monitor the output of a piezoelectric diaphragm, represented by a sine wave generator and capacitor C3. The circuit is powered from a split supply (+5V/-5V) derived ...