Designing a Second Order Passive LPF: Tips and Insights

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In summary, the individual is seeking information on the design of a second-order passive low pass filter for a report. They have tried cascading two RC circuits but the simulated cutoff frequency does not match the desired cutoff. They ask for any insights but are advised to use an active filter instead. The person recommends a book on digital signal processing for more information and guidance on designing analog filters. However, the individual is required to design a second-order passive LPF for their assignment. Unfortunately, there was no answer provided in the forum for this specific question.
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ACLerok
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This isn't really an exact homework problem since it's for a report I'm doing. Basically, I was wondering what the design for a second order passive low pass filter looks like. I know how to design a regular first order circuit but I have no clue about a second-order PASSIVE LPF. I tried just cascading two RC circuits and using 1/(2pi(RC)) to define the cutoff frequency but after simulating it on my computer, the actual cutoff is quite off. Anyone have any insight into this?? Thanks in advance.
 
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  • #2
Why do you want to make a passive filter? Take my advice and use an active filter. The techniques for making active filters using op amps is very mature and you can get whatever gain you wish. Look for the book on the web (its free!): "Digital Signal Processing" by Steven Smith. Look on page 50 for a good discussion on analog filters and a simple design table.
 
  • #3
Believe me, I would, but it tells me to make a 2nd order passive LPF in the assignment. Thanks though.
 
  • #4
Shame there was no answer to this forum :( I am stuck now too I have to do a 3rd order high pass RC active filter though
 

1. What is a 2nd order passive LPF?

A 2nd order passive LPF (low-pass filter) is a type of electronic circuit that attenuates or filters out higher frequencies from an input signal, allowing only lower frequencies to pass through. It is called "passive" because it does not require an external power source to function.

2. How does a 2nd order passive LPF work?

A 2nd order passive LPF works by using two passive components, typically resistors and capacitors, to create a low-pass filter. The resistors and capacitors are arranged in a specific configuration, such as a Butterworth or Chebyshev filter, to attenuate higher frequencies while allowing lower frequencies to pass through.

3. What are the benefits of using a 2nd order passive LPF?

There are several benefits of using a 2nd order passive LPF, including simple circuit design, low cost, and low power consumption. It also has a steeper roll-off slope compared to a 1st order LPF, meaning it can more effectively filter out unwanted frequencies.

4. What are the applications of a 2nd order passive LPF?

A 2nd order passive LPF is commonly used in audio equipment to remove high-frequency noise from signals. It is also utilized in communication systems, such as radio and television, to filter out unwanted interference. Additionally, it can be used in power supplies to smooth out fluctuations in voltage.

5. Are there any limitations to using a 2nd order passive LPF?

One limitation of a 2nd order passive LPF is that it can only attenuate frequencies above a certain cut-off frequency, and cannot completely eliminate them. Additionally, the components used in the circuit may introduce some distortion to the output signal. It is also important to choose the correct filter type and component values to achieve the desired frequency response.

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