Second order low pass filter with unity gain

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Discussion Overview

The discussion revolves around the design of a second order low pass filter with unity gain, specifically in the context of a homework assignment. Participants explore different approaches to achieving this design while considering constraints such as power supply limitations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks confirmation on their method for creating a second order low pass filter with unity gain.
  • Another participant acknowledges the proposed method as a candidate but questions its representativeness as a good filter.
  • A participant describes their specific application involving a transimpedance amplifier followed by the filter, noting a power supply constraint of 5V for the op-amps.
  • Concerns are raised about the performance of the proposed filter, with one participant indicating that it behaves like a passive two-stage filter, leading to a Bode plot that does not maintain a flat response.
  • Questions are posed about how to improve the filter's response and whether a different design is necessary.
  • One participant suggests researching active filters for potentially better performance.
  • A later reply indicates that the original question was not very specific, implying that the proposed design may be acceptable as is.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of the proposed filter design, with some suggesting improvements while others believe the current design may suffice given the lack of specificity in the assignment.

Contextual Notes

Participants discuss the limitations of the proposed filter design, including its passive nature and the implications for the Bode plot, but do not resolve the mathematical or technical details involved in improving the design.

Who May Find This Useful

Students and practitioners interested in filter design, particularly in the context of low pass filters and operational amplifier constraints.

Henry
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Homework Statement


I need to design a second order filter with unity gain.

Homework Equations


None - not taking component values into account for now.

The Attempt at a Solution


Is this a correct method of creating a 2nd order low pass filter with unity gain?
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That is one such candidate; not what I'd consider a good representative of such a filter, but it certainly fits.

What is the application you need it for?
 
I had to design a two part system with a transimpedance amplifier then a second order low pass filter for a piece of coursework. It's specified that we cannot use a power supply larger than 5v for the opamps though, so I designed the system to take care of all of the gain during the transimpedance stage.

Sorry if that sounds confusing, I'm still getting my head around this a little bit.
 
What you have there is basically a passive two-stage filter, so its Bode plot is not nice and level over any range, it begins drooping right from DC.
 
How would I go about changing that?
 
Henry said:
How would I go about changing that?
Do you need it to be any different, though?

For flatter responses, google: active filters.
 
Probably not, the question wasn't particulary specific, it just asked for a second order low pass filter so that's probably fine. Thank you for your help! :smile:
 

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