Questions tagged [sallen-key]
The sallen-key tag has no usage guidance.
14
questions
6
votes
6answers
2k views
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 ...
0
votes
1answer
65 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 ...
14
votes
4answers
2k 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 ...
1
vote
2answers
76 views
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 ...
0
votes
2answers
101 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 ...
6
votes
5answers
827 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 ...
1
vote
2answers
80 views
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 ...
0
votes
1answer
208 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 ...
0
votes
2answers
124 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.
0
votes
1answer
202 views
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 ...
0
votes
1answer
69 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 ...
2
votes
0answers
163 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 ...
2
votes
2answers
205 views
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 ...
2
votes
5answers
346 views
Does the Sallen-key filter require a buffer for low power applications?
I am designing a circuit which takes an 3uV at 10-10kHz input that filters, applies gain and integrates the analogue signal. I'm thinking of using the circuit below for the topology using two stages ...
