Question about design active filter

In summary, you designed an active low-pass filter, but you don't know if it is the correct method. You use this method: by let C=100 nF and use this equation "fc=1/(2*pi*C*R1)" and get R1= 8 Kohm,R2=R1. To get a filter of 4 order, you repeat that stage 4 times.
  • #1
samaaa
48
0
hi:

i designed an active low-pass filter,but i don't know if it correct method or not

i want fc=200 Hz and n(order)=4. i use this method:

Active_lowpass_filter.png

by let C=100 nF and use this equation "fc=1/(2*pi*C*R1)"
i get R1= 8 Kohm,R2=R1
this is for one stage

to get filter of 4 order,i repeat that stage 4 times
http://uploadpic.org/storage/2011/M3Oveluhfm4grO0dEPhZiUv.png


so is this method correct?
 
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  • #2
You show four stages, each of 1st order. That will work for an overdamped system (low Q), but if you are designing for a sharp Q (lower damping and with overshoot in its step response), then you'll have to use 2nd order stages. Each comprises 2 capacitors and 2 resistors (at least), and can provide a high Q response (i.e., Q greater than 0.707). In practice, the professional designer faces a bewildering choice, each offering its own set of pros and cons. But for an introduction to the topic there are a few well-tried classics. Any general second-order filter stage will do the job nicely; you'll need two stages.
 
  • #3
samaaa said:
i want fc=200 Hz and n(order)=4. i use this method:
...
so is this method correct?

No, because your first order filter has a gain of 0.5 at fc=200 Hz.

When you put the four filters in series, the gain at 200 Hz will be ##0.5^4## = 0.0625.

We don't know how much you already know about filter design, so it's hard to give much advice beyond "get a textbook and study it".

You could try Google for "design a low-pass Butterworth filter" (which seems to be what you were trying to do) but you might need to study some more basic ideas first.
 
  • #4
NascentOxygen & AlephZero thank you very much
 
  • #5

1. What is an active filter?

An active filter is an electronic circuit that uses active components, such as transistors and operational amplifiers, to filter out specific frequencies from an input signal. It is used to remove unwanted noise or to amplify desired signals.

2. How does an active filter differ from a passive filter?

An active filter uses active components, while a passive filter uses only passive components such as resistors, capacitors, and inductors. Active filters have the advantage of higher gain and lower output impedance, but they require a power supply.

3. What are the advantages of using an active filter?

Active filters have the advantage of being able to amplify desired signals while filtering out unwanted noise. They also have a higher bandwidth and can be easily adjusted or tuned for specific filter requirements.

4. What are the different types of active filters?

There are four main types of active filters: low-pass, high-pass, band-pass, and band-stop. Low-pass filters allow low frequencies to pass through while attenuating high frequencies. High-pass filters do the opposite, allowing high frequencies to pass through while attenuating low frequencies. Band-pass filters only allow a specific range of frequencies to pass through, while band-stop filters attenuate a specific range of frequencies.

5. How do I design an active filter?

To design an active filter, you will need to determine the desired cutoff frequency, gain, and filter type. Then, you can use a filter design tool or software to calculate the values of the components needed for the filter. It is also important to consider the power supply and operational amplifier specifications when designing an active filter.

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