+ Post New Thread
Page 3 of 3 FirstFirst 1 2 3
Results 41 to 43 of 43
  1. #41
    Member level 3
    Points: 253, Level: 3

    Join Date
    Feb 2018
    Posts
    57
    Helped
    0 / 0
    Points
    253
    Level
    3

    Re: Balanced OTA-C cascode IC design

    If the filter's response is as follow what could possibly be the problem? the ideal response is to be flat between 1 and 3MHz with a 0dB gain and -3dB at both 1 and 3MHz, I understand the non ideal filter would differ slightly than the ideal one but it seems like there is a problem.



    •   AltYesterday, 15:07

      advertising

        
       

  2. #42
    Super Moderator
    Points: 241,298, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    41,879
    Helped
    12747 / 12747
    Points
    241,298
    Level
    100

    Re: Balanced OTA-C cascode IC design

    Lack of information to answer the question. You don't show the designed gm and capacitor values, thus we can't see if the measured filter gain is expectable or not.

    Secondly you would determine the actual gm and ro of differential OTAs.

    Finally, when paralleling differential OTA outputs, either G2 and G3 or G2a, G2b and G3, you must take care that the CMFB circuits don't saturate, either provide limited gain or use a common CMFB for all OTAs in parallel.



  3. #43
    Member level 3
    Points: 253, Level: 3

    Join Date
    Feb 2018
    Posts
    57
    Helped
    0 / 0
    Points
    253
    Level
    3

    Re: Balanced OTA-C cascode IC design

    Quote Originally Posted by FvM View Post
    Lack of information to answer the question. You don't show the designed gm and capacitor values, thus we can't see if the measured filter gain is expectable or not.

    Secondly you would determine the actual gm and ro of differential OTAs.

    Finally, when paralleling differential OTA outputs, either G2 and G3 or G2a, G2b and G3, you must take care that the CMFB circuits don't saturate, either provide limited gain or use a common CMFB for all OTAs in parallel.
    Quote Originally Posted by FvM View Post
    Lack of information to answer the question. You don't show the designed gm and capacitor values, thus we can't see if the measured filter gain is expectable or not.

    Secondly you would determine the actual gm and ro of differential OTAs.

    Finally, when paralleling differential OTA outputs, either G2 and G3 or G2a, G2b and G3, you must take care that the CMFB circuits don't saturate, either provide limited gain or use a common CMFB for all OTAs in parallel.
    -The ideal circuit with the ideal gm values and the capacitor values are in the first attachment, the second attachment is the response of the ideal circuit using the same architecture but with vccs instead of the OTAs the response is as designed in the ideal circuit as you can see, so I reckon the problem won't be with the gm values or capacitance but something to do with the non ideal circuit.
    - The OTA gm values and routs are as follows:
    Ideal gm value Non ideal value
    47.08u 47.087u rout equals to 26.45K
    62.882u 62.91u rout equals to 25.73K
    127.23u, 127.26u rout equals to 18.8K
    45.9u 45.93u rout equals to 26.4K
    17.42u 17.423u rout equals to 179.24K
    16.99u 17.004u rout equals to 179.27K

    -what do you mean by the CMFB circuits do not saturate? shouldn't they saturate in order to have a vout of my reference voltage ? as if they do not saturate the voltage won't be equal to the reference voltage and biasing of the second stage transistors in the differential OTA would be affected



--[[ ]]--