Op amp integrator

Discussion in 'General Electronics Chat' started by Andrew1234, Mar 16, 2015.

  1. Andrew1234

    Thread Starter New Member

    Feb 16, 2015
    20
    1
    Hi,
    I would like to use an op amp configured as an integrator as a low pass filter. How to calculate the R and C to get the target corner frequency? If I want to use two successive integrators for a second order low pass filter, again, how to calculate the Rs and Cs for the two op amps. Thanks for the advice or pointer to where I can learn about this!
    Regards
    Andy
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  3. Papabravo

    Expert

    Feb 24, 2006
    10,179
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    The transfer function of an integrator is

    1 / jωRC

    Can you work out the corner frequency from that?
    BTW there are better ways to make filters.
     
  4. OBW0549

    Well-Known Member

    Mar 2, 2015
    1,328
    890
    Microchip offers a Windows app, FilterLab, with which you can synthesize 2nd- through 8th-order filters. Very handy.

    http://www.microchip.com/pagehandler/en_us/devtools/filterlab-filter-design-software.html
     
    Last edited: Mar 16, 2015
  5. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Two integrators will give a 2nd order filter with a low damping factor and poor characteristics around the corner frequency.
    Use some type of filter design software such as OBW0549 suggested to generate a proper Butterworth active filter or other 2nd order filter with good characteristics.
     
  6. Andrew1234

    Thread Starter New Member

    Feb 16, 2015
    20
    1
    thank you guys, this is all helpful. I am building a Class D amplifier. I was thinking of using a couple of integrators for the loop filter. This is common in Class D amps I have studied, and an integrator also provides a convenient way to create a triangle reference needed to generate the PWM signal. But possibly integrators are used for the filter for cost reasons in integrated circuits (and these are ones I have studied). Since I will be doing a discrete design, I can probably be more flexible in the approach to the loop filter.
     
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