30
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How to identify filter behaviour without memorizing different topologies
Look at the extremes. DC and very high frequencies. For DC you can remove the capacitors and short the inductors. For high frequencies you can short the capacitors and remove the inductors. By looking ...
- 8,155
29
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Why are there so many vias on this board?
This is generally referred to as via stitching, and it's generally used to reduce either the high-frequency electrical impedance or the thermal resistance between layers. It can also be used to ...
- 3,379
28
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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 ...
- 25.7k
25
votes
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Why have a 0.1 uF capacitor in parallel with 2500 uF in a power supply filter?
What you have there isn't two capacitors in parallel. It's more like this:
simulate this circuit – Schematic created using CircuitLab
The small cap is a ceramic type, it has a low series ...
- 14k
24
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Why does increasing the sampling rate make implementing an anti-aliasing filter easier?
As you decrease the sampling frequency there is less separation between the images in the frequency domain.
source
Remember that the repetition of the spectrum occurs at the sampling frequency. When ...
- 6,097
24
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Bridge rectifier: What is the purpose of these two elements?
That is a de facto circuit for cheap generic mains powered LED lamps.
The capacitor is an essential part, the circuit is called a "capacitive dropper" which is used to bring down the voltage ...
- 138k
23
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How to combat noise from my circuit polluting my 12V rail?
The 1000uF capacitors C1 and C3 might not be able to handle such high frequency switching transients very well. Large value caps always have very bad high frequency response.
I suggest trying to ...
- 80.5k
21
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Design a filter that allows frequencies below 5 kHz to pass freely, but all frequencies above 5.2 kHz must be undetectable
You have assumed a 20dB/dec per filter order roll-off for your filter. This is not true for all filter types.
Let \$f_0 = 5 \mathrm{kHz}\$ and \$f_{\mathrm{stop}} = 5.2 \mathrm{kHz}\$. Then $$\frac{...
- 6,097
21
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Design a filter that allows frequencies below 5 kHz to pass freely, but all frequencies above 5.2 kHz must be undetectable
This kind of sharp rolloff requires a digital filter. Don't even think about analog. You need to convolve the input with a sinc function. The width of the sinc function (the number of kernel points)...
- 312k
20
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Do I need a 50/60Hz notch filter for battery powered devices?
An ECG circuit picks up 60Hz "common mode" signal from both probes then inverts it and feeds it to the patient's foot to cancel it. The heart does not produce a common mode signal so its output is not ...
- 1,218
18
votes
Why are there so many vias on this board?
It's a high-frequency RF part. 900MHz = 30cm wavelength. So even a board that's a few cm across is a significant proportion of a wavelength. The vias are to make sure that the top copper is really ...
- 45.4k
18
votes
How to make a 1 H, 10 A inductor
Here's a 0.1H 10A inductor. It weighs 35lbs.
There is a limit to the magnetic flux the magnetic core can handle. Above that it will saturate and inductance will decrease. Large value inductors require ...
- 72.1k
17
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Why would you stack a resistor and capacitor on top of each other?
Forget the 40kHz- this kind circuit really likes to oscillate at very high frequency- the feedback resistor is almost open (1M) at high frequencies in comparison to a few pF and the amplifier has a ...
- 384k
17
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I think I found an error in an electronics book. Are my equations correct here?
Standard Form
Over some time, standard forms have been developed for these equations. There's a reason why. But I'll get to that in a moment.
The usual 1st order low-pass standard forms for your case ...
- 77.4k
17
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Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?
is there any disadvantage of using a high-value resistor with a low-value capacitor or vice versa?
Yes.
High impedance brings to mind:
High-value resistors create high-impedance nodes. That wouldn't ...
16
votes
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TVS diode before or behind resistor
You have three components there that are all there for protecting the AVR, but all are doing a different job.
The resistor is there to stop steady state high voltages.
The capacitor is to remove ...
- 1,114
16
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Purpose of capacitors and extra resistors in the feedback of the inverting op amp?
It is a fairly standard ADC driver topology.
Modern ADCs often have switched capacitor architectures that need a fairly large cap local to the input to provide the very fast current pulses that the ...
- 17.4k
16
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Ripple voltage filtering capacitor
I've included a snapshot, of sorts, so that you can see what's happening better:
On the main diagram, I expanded out a rectangle and placed it over to the right side so that you might see a little ...
- 77.4k
15
votes
Why would you need an op amp for reference voltage when the voltage divider does the trick?
Is there a reason this schematic uses an op amp (AD8031) for the reference voltage of the op amp (AD8544) filter when the voltage divider already brings down the voltage anyways?
The usual reason to ...
- 128k
15
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How to remove aliasing effects?
The whole problem with aliasing is that after sampling, you can't tell the difference between a signal at some frequency \$f\$, and some other frequency \$f + F_s\$. This is actually the definition ...
- 45.4k
15
votes
How to make a 1 H, 10 A inductor
I think your only option to get a small footprint 1H, 10A inductor is to redefine the word "small" to mean "humongous."
This is a 1H, 240mA inductor
It is a box an inch and a half ...
- 69.2k
14
votes
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Using LC filter instead of RC filter in mains powered circuits
Ideal capacitors and inductors don't dissipate any power, whereas resistors do. One advantage is therefore that L-C filters are more efficient than R-C or R-L filters. Often it's not the actual ...
- 312k
14
votes
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Do I need a 50/60Hz notch filter for battery powered devices?
Assuming you're talking about the input signal, you may still want the filter because the long leads running to the chest pads (or wherever your detection location is) could pick up a 50/60Hz signal ...
- 773
14
votes
How does an emitter follower work as an AM detector?
With no input signal, the bias network sets the base voltage to be about 3.4V. The emitter voltage is set to around 2.8V (depending on temperature) from a small amount of current coming from the ...
- 442
14
votes
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How are RF filters constructed?
As you've discovered, once you are up in the 100MHz+ range, little is "simple".
When using discrete capacitors and inductors, you have to consider their parasitic complements. Even basic ...
- 6,246
13
votes
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What is the practical reason for associating cut-off frequency to %50 power attenuation?
First, calling it the "cutoff frequency" leads to misconceptions. "Rolloff frequency" is a better name that gives you a more accurate mental picture of what is really happening.
Using the -3 dB ...
- 312k
13
votes
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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 ...
- 80.5k
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