+ Post New Thread
Results 1 to 5 of 5
  1. #1
    Member level 5
    Points: 984, Level: 7

    Join Date
    Jul 2016
    Posts
    89
    Helped
    1 / 1
    Points
    984
    Level
    7

    Bypass dc signal which is accompanied with a low frequency sinusoidal signal

    Hi,
    I have two signals that I need to block one of them (DC signal). The input signal is something like this:

    Vin=VDC+Vac*Sin(2*pi*5*t)

    1 millivolt
    I wanted to use a series capacitor for blocking but based on the low ac input frequency (5 Hz) it makes my capacitor very big. what is your suggestion for rejecting the VDC?

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 258,488, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,127
    Helped
    13718 / 13718
    Points
    258,488
    Level
    100

    Re: Bypass dc signal which is accompanied with a low frequency sinusoidal signal

    Strictly speaking you need large time constant, not necessarily large capacitor. You should talk about circuit impedance first. What's the load receiving the AC signal?



    •   AltAdvertisement

        
       

  3. #3
    Member level 5
    Points: 984, Level: 7

    Join Date
    Jul 2016
    Posts
    89
    Helped
    1 / 1
    Points
    984
    Level
    7

    Re: Bypass dc signal which is accompanied with a low frequency sinusoidal signal

    Thank you for your response. This signal is output of a mixer which is going to connect to an op-amp( in buffer configuration)



    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 4
    Points: 7,327, Level: 20

    Join Date
    Dec 2015
    Location
    Madrid, Spain
    Posts
    1,275
    Helped
    314 / 314
    Points
    7,327
    Level
    20

    Re: Bypass dc signal which is accompanied with a low frequency sinusoidal signal

    Now depends on the settling time you need. For settling time = 0.5 seconds, a 16nF cap and 10 Meg resistor. Do not push too much the settling time, otherwise you will attenuate your AC signal.



  5. #5
    Advanced Member level 4
    Points: 6,247, Level: 18
    kripacharya's Avatar
    Join Date
    Dec 2012
    Location
    New Delhi
    Posts
    1,209
    Helped
    182 / 182
    Points
    6,247
    Level
    18

    Re: Bypass dc signal which is accompanied with a low frequency sinusoidal signal

    Since you are feeding into an opamp buffer config, then presumably the input impedance is >> 1Mohm even for a non-FET input opamp.
    Here even a 5uF capacitor should provide you a decent DC block with less than 1% attenuation of your signal.

    Of course if there are other elements in your circuit which you have not mentioned, then this result could be different.



--[[ ]]--