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Accepted

Active low-pass filters --- good to what frequencies?

I believe your analysis to be good. I've made sallen-key 4th order filters that cut-off around 3 MHz with absolutely no worry about performance. I don't see that 10 MHz is unachievable. It's all ...
• 396k
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What is the advantage of a Sallen-Key filter over a normal second order filter?

What you call "normal" is a simple two-stage RC filter with very bad selectivity (two real poles only). In contrast. the Sallen-Key topology is capable of producing a second-order lowpass response ...
• 23k
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It is always good practices to use anti-aliasing filter before digitizing a signal. Although your target signal does not contain frequency components above the Nyquist rate, there might be other ...
• 601
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What is this circuit called, and what is it used for?

This is a capacitance multiplier: It behaves like a capacitor to ground with a capacitance of C*(1+R2/R1). This means you can use it to "simulate" very large capacitors without actually ...
• 7,238
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Unknown amplifier circuit Analysis

Theory What are the effective tools people use nowadays? The first, most effective, and primary tool to use is your brain. I first see is a high-pass passive RC filter leading into an active filter....
• 73k
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Cathode to cathode diodes in schematics

In my opinion this is not a well designed circuit, especially I have my doubts about the buck converter part. Also it isn't very well drawn either, for example around the LEDs D6, D8 and D9: there is ...
• 79.1k

Active filter with series inductor and resistor - do these exist?

Inductors are generally more expensive, more bulky and less ideal than capacitors so you'll usually see a strong preference for capacitors over inductors. Only very tiny values can be put into an IC, ...
• 343k

Do I need to worry about anti-aliasing filters before the ADC Unless your ADC has a built-in anti-aliasing filter, then yes, you should take care about it even if you're only interested in ...
• 4,997

• 3,613

Completely different circuit response with 1000kΩ than with 1MΩ resistance

In PSpice m and M are thousandths. You need to use Meg.
• 13.6k

How was the design of active filter topologies arrived at, invented or discovered?

A filter topology, whether it's a passive one like a pi-section or an active one like the Sallen-Key circuit, is just a way to produce some poles and zeros. Generally, you can tune the circuit values (...
• 122k

Active low-pass filters --- good to what frequencies?

My first question: really? A mere 100kHz is already too high for active filters to be practical? No, 100kHz is nothing, but it all depends on the opamp. At some point the Gain Bandwidth Product is ...
• 65.5k
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Why am I measuring such high THD+N on my active high-pass filter?

The number one suspects are the ceramic capacitors. Here is a SE link that shows the severe voltage dependence that ceramics have. The X5Rs are some of the worst, especially in the small SMD sizes. ...
• 3,694

How can I improve the response time of a low pass filter?

You cannot greatly change response time of a low-pass filter by changing its' order. What you have to do is change its cutoff frequency - the higher the cutoff frequency, the faster the response. ...
• 58.9k

What is wrong with this butterworth filter, how can it be improved?

The standard Sallen-Key design assumes you use perfect opamps. An LM324 is pretty slow as opamps go, I'm surprised it shows the filter working as well as it does. Perform a few more simulations, ...
• 145k

How to make perfboard circuits more compact

The ultimate answer is to use SMD components on a PCB - the parts are smaller, and using traces instead of wires will reduce stray capacitance; this can have a large effect in sensitive circuits. I ...
• 920
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Strange Distortion from Second Order Active Low Pass Filter

The LM324, while a brilliant achievement with 1970s transistors, has one well known bug - actually documented in its datasheet. This answer is based on a guess that you are running into this bug. ...
• 66.1k
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Unexpected plots for active low pass filter response in LTspice

In the first circuit the active Low Pass filter is a 2nd order filter while the passive Low Pass filter is a 1st order filter so I totally expect the curves to be different and they are what they ...
• 79.1k
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• 23k

How to design a band-pass filter with 2.4GHz center frequency?

Have someone stand there and request each electron's paperwork which should include a inter-circuit migration paperwork, quantum state, energy level details ect. On page 3 of the Feynman documents, ...
• 4,509
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Does Q-Factor matter for low pass and high pass filters?

Here's a picture (I drag out now and then) that explains the effect of Q on a 2nd order low pass filter: - The top three pictures show you the effect of varying the Q-factor. Q-factor can also be ...
• 396k
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Why does my electret microphone amplifying and filtering circuit output so much noise?

There are a number of problems with this circuit: The input to the reference is not filtered. R5 and R4 make half the supply voltage, but also transfer half of whatever noise is on the supply. ...
• 307k

Active filter with series inductor and resistor - do these exist?

To add to Spehro Pefhany's reasons, the circuit as shown has a gain at DC, which may cause issues with the following circuitry because of any DC offset voltage in the amplifier. Also, if the power ...
• 1,090
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