Passive and Active (Sallen-Key) RC Filter Operation and Design
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- čas přidán 6. 07. 2024
- An introduction to passive and active low pass filters, filter requirements and design concerns, and the evolution from a simple single-pole RC filter to a multi-stage Sallen-Key topology.
Links and references at: www.analogzoo.com/?p=1090 - Věda a technologie
This is one of the best electronics videos I have seen. Fantastic explanation and the design tool you showed is definitely going in my bookmarks.
The best filter tutorial I have ever seen - thanks.
+emcgon Thanks! Be sure to check out the videos Matt Duff (from Analog Devices) did; there's a bunch of them, all very good.
I second that. Very well explained and thought out. Will check out Matt Duff as well. Thank you!
I suppose you had to filter through a lot of tutorials to get here eh?
@@magerehenk7579 i see wht u did there :)
I wish ..you made more of these filter topics...thank you
Perfectly explained! You sir have my gratitude.
Incredible video you did here. So easy to follow even though it's very complicated. tells a lot about your skill level.
I learn do much from your stuff. Please make more videos 😉
One of the best videos I have seen in a while 👍
Great presentation! Thank you.
Thanks Craig for a great tutorial!
excellent! keep them coming.
Thanks for the clear explain and the examples ! ... keep it up mate
You are genius in teaching! Thank you!!!
Thank you so much for this video.
Excellent! thank you very much. Very clearly explained.
Excellent!! Great!!
Thank you!!
BRILLIANT video!!! The ONLY possible thing missing is that you never showed an FFT scope plot of the 10kHz sine wave. SUBSCRIBED!
Nice, thanks a bunch. Would appreciate a similar guide for multi stage passive filters if you ever felt like it.
Nice video!
Great tutorial, thanks a lot! :D
Loved this video, its very well explained and easy to understand. I wonder if you would be able to do a voltage control filter based on OTA LM13600/13700 ? I'd be very interested. thank you again and keep up the excellent work.
nice video! Thank you
nice! thanks!
Very good video. Thank you for sharing. May i ask a question: why the magnitude do not go lower than -60 when frequency continuously increases?
thank u very much sir.pls suggest for power supply filter for 100hz cuttoff
Great anal llysis my frend
Great presentation. Thank you. What about slew rate at 14 Mhz ? What do I use for an op-amp ?
A narrow band pass filter could do this in a single stage. The possible disadvantage is matching the peak frequency to 10 kHz, but it is also necessary to match the cutoff frequency in your design.
Did you just connect the filter directly to the SA? I am asking because the filter does not have 50 ohm input/output impedance. The input impedance is in kohm range and out put must be a few ohm only. How did you calibrate the SA and TG?
Question here: on a S-K filter "cell", the op amp is working just as a buffer? COuld it be exchanged for a transistor buffer o even a tube buffer?
Can I ask a question? What price are we paying when adding capacitors to make the frequency response more even? Is it more ringing effect. right?
Nice tutorial. Thanks. Suppose I have a non-sinusoidal periodic input and am interested in filtering out the Fourier dc(average) component of the input through hardware, kindly suggest how I should go about the design
If you just want the DC value of a signal, you'll want to remove all signal components whose frequencies are above zero hertz, so you'd want a low-pass filter. What cut-off frequency you choose for your low-pass filter will depend on the frequency components of your input signal, as you want to attenuate all those components as much as possible. Note also that a low-pass filter is effectively an integrator in the time domain (think of a simple RC filter), so generally the lower your cut-off frequency, the longer it will take for the filter to settle on the DC value of the signal.
My understanding is that in a low-pass filter, when dc and lower
frequencies are passed from input to output, the capacitor facilitates
this by slowly getting charged. In order to meet a very low cut-off
frequency requirement, let me assume I use a very large time constant
(RC) which, let's say, is larger than the period T of the input
signal. During each positive excursion, the capacitor will try to
charge towards the peak value, though slowly, but will lose very
little charge before the next positive excursion arrives. Does this
not mean, the capacitor will not average out over time but instead
keep riding on the peak . If on the other hand, I am restricted to use
a RC time constant which is lesser than T, I will have no freedom to
choose the theoretical maximum RC time constant. Kindly let me know
if my understanding is correct. Thanks.
You state that the capacitor "will lose very little charge before the next positive excursion". This suggests that the capacitor discharges more slowly than it charged. If you apply a signal, say a sine wave, to an RC low pass filter, why would the capacitor charge at a different rate than it discharges?
The charge and discharge time of the capacitor is assumed to be the same. I consider a saw-tooth wave where the sweep time from 0v - peak (say 10v) takes 7T/8 secs and the fly-back period lasts for T/8 secs. If the charge and discharge time constants (RC) is comparable to 7T/8 secs, the capacitor will have sufficient time to charge to the peak value while getting only T/8 secs to discharge, before the next cycle starts. So, while RC will give the rate at which the capacitor will charge or discharge, the actual level to which it has come down on discharging will be determined by the fly-back time, viz. T/8 secs. Assuming it has lost only 2v before the next cycle started, the average value will be (10v+8v)/2 = 9v. On the other hand if I had allowed the fly-back period period of T/4 secs for the capacitor to discharge, the average would have decreased further. My question is, without caring for such variable average values dictated by the time periods of the impressed signal, how do I recover the true Fourier dc component present in the impressed signal. To cite another case, I want to know how I can recover the Fourier average of a full wave rectified signal whose average is some finite quantity and not zero. The charge and discharge time constants are assumed same and equal to T/4 secs. Thanks.
An RC low pass filter is an integrator, thus with the correctly selected R and C values it will give you the average of your input signal. In your example of a 0-10v sawtooth wave, the center of that sawtooth is 5v. Being a symmetrical, periodic waveform, the sawtooth spends just as much time above 5v as it does below 5v, hence the average of that signal is 5v, which is the DC component of that waveform. If you generate a 0-10v sawtooth signal with a function generator and feed it into an appropriate RC low pass filter, that's exactly what you'll see. Change the signal to a square, triangle, or sine wave, the average remains the same.
When you say "without caring for such variable average values dictated by the time periods of the impressed signal, how do I recover the true Fourier dc component", I assume you mean that you want to get the average voltage of the signal without caring about the frequency of the signal. The answer is, I don't think you can. Integrating a function over some period of time gives you the average, but different frequency signals necessarily complete their cycles over different time periods. For example, the period of a 10MHz signal is 100nS, so 1mS would be more than enough time to see many periods of the signal and determine its average value very accurately. A 1Hz signal on the other hand wouldn't complete even one cycle in that same 1mS time frame, so you wouldn't be able to accurately determine its average value.
So, if you know that your input signal is of a higher frequency, then you can make your R and C values smaller, and thus obtain your average DC voltage faster. But if you must accommodate very low frequency signals, then your R and C values will have to be larger, and it will necessarily take more time to get the average DC value that you're looking for.
Do Sallen-Key active filters work at HF frequencies 3-30Mhz ?