+ Post New Thread
Results 1 to 6 of 6
  1. #1
    Full Member level 4
    Points: 3,696, Level: 14

    Join Date
    Jul 2005
    Location
    South Korea
    Posts
    232
    Helped
    13 / 13
    Points
    3,696
    Level
    14

    output swing

    Hi everybody?
    I'm new in this forum
    I have a question about opamp
    I designed fully differential folded cascode opamp using hspice
    and i want to measure output swing and input range
    how can I measure it using Hspice?

    please tell me how to do it

    thanks
    have a good day

    •   AltAdvertisment

        
       

  2. #2
    Member level 1
    Points: 1,562, Level: 9

    Join Date
    May 2005
    Posts
    36
    Helped
    8 / 8
    Points
    1,562
    Level
    9

    output swing

    For output swing, you need to sweep the inputs differentially. For ICMR, you need to sweep both inputs at the same time.



    •   AltAdvertisment

        
       

  3. #3
    Full Member level 1
    Points: 2,245, Level: 10

    Join Date
    Jul 2005
    Posts
    119
    Helped
    6 / 6
    Points
    2,245
    Level
    10

    icmr differential

    so if i want to find wether the CMFB can work properly in the output range,then i how i should do?sweep the input common mode voltage and then watch the output voltage wether is the expected value?
    Quote Originally Posted by kienhuy
    For output swing, you need to sweep the inputs differentially. For ICMR, you need to sweep both inputs at the same time.



    •   AltAdvertisment

        
       

  4. #4
    Full Member level 4
    Points: 3,696, Level: 14

    Join Date
    Jul 2005
    Location
    South Korea
    Posts
    232
    Helped
    13 / 13
    Points
    3,696
    Level
    14

    how to measure the output swing

    thanks for your answer.
    but i don't understand what does it mean
    for single ended I can measure ICMR with negative
    feedback. But how can for fully differential??
    DC sweep both input?
    Please tell me more easily~



  5. #5
    Member level 1
    Points: 1,562, Level: 9

    Join Date
    May 2005
    Posts
    36
    Helped
    8 / 8
    Points
    1,562
    Level
    9

    icmr input

    ljy4468,
    To sweep the inputs differentially, you need to have a common mode source and differential source at each input. For example, at the positive input, there is Vcm and 0.5*Vac. At the negative input, there is Vcm and a voltage-controlled voltage source with value -0.5*Vac. For your sweep, you simply need to sweep the 0.5*Vac source at the positive input.

    winsonpku,
    For CMFB, you should also check the stability of the CMFB loop, since you are also interested in the ac characteristics of the CM voltage. See the Gray and Meyer book for a better analysis.



    •   AltAdvertisment

        
       

  6. #6
    Full Member level 1
    Points: 2,245, Level: 10

    Join Date
    Jul 2005
    Posts
    119
    Helped
    6 / 6
    Points
    2,245
    Level
    10

    outp you

    for output swing,you should give differentiat sigal.which keinhuy said the most thing.you should set a named vid voltage,and then give 0.5vid and -0.5vid give two input ports,then you just sweep vid.
    for differential output,meaure the ICMR is the same as single-ended output.
    fully differental amp,you have inn and inp two input ports,then outn and outp two corresponding ports.you must sure that be the relationship between the output ports and input ports.you can increase the inn,then the output node volatge increase is outn,the other is outp.you can sweep any one of the two input ports.
    if you want sweep the inn,then you must short outn with inp.then the overlaped region(outn=inn) is the ICMR.
    is it clear?
    Quote Originally Posted by ljy4468
    thanks for your answer.
    but i don't understand what does it mean
    for single ended I can measure ICMR with negative
    feedback. But how can for fully differential??
    DC sweep both input?
    Please tell me more easily~



--[[ ]]--