+ Post New Thread
Results 1 to 3 of 3
  1. #1
    Full Member level 3
    Points: 1,014, Level: 7

    Join Date
    Jan 2018
    Posts
    161
    Helped
    1 / 1
    Points
    1,014
    Level
    7

    Help in understanding the paper "Understanding Wide-band MOS transistors"

    Hi, I am reading this paper on MOSFET bandwidth https://www.ece.ucsb.edu/Faculty/rod...Steininger.pdf.

    I have few questions
    1. For figure 4, the small signal equivalent was drawn in Figure 5. I don't understand why the dependent current source of M3 is not included in figure 5 and why gm1/wT (Cgs of M1) is included two times (second time at the output).
    2. I know that in compared with single stage, gain increases and bandwidth decreases in a multi-stage. But here it was said that "To obtain an amplifier with the highest possible bandwidth, we would like to cascade stages of low gain" and "It is possible to show that there is an optimum stage gain for a cascade of identical amplifiers that maximizes the overall bandwidth". Can someone explain this clearly.

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 39,379, Level: 48

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,364
    Helped
    1855 / 1855
    Points
    39,379
    Level
    48

    Re: Help in understanding the paper "Understanding Wide-band MOS transistors"

    Re 2: There is always a technology gain-bandwidth product
    which is your ultimate limit, even if you've done your best
    with the rest of the circuit optimization.

    A lineup that uses (say) one A=100 amplifier in a fmax=100GHz
    technology will probably give you a 1GHz BW.

    A lineup that uses the same technology, cascaded A=10 stages
    (A=100) but each stage having 10GHz BW, will have a A=100,
    BW 10GHz (-ish) but a 2-pole rolloff rather than 1-pole. This
    could be good or bad, depending on what you wanted to
    happen to incoming and locally generated harmonics, but
    probably better than 1GHz BW (especially if you wanted 2GHz
    passband).



    •   AltAdvertisement

        
       

  3. #3
    Full Member level 3
    Points: 1,131, Level: 7

    Join Date
    Jan 2019
    Location
    Belgium
    Posts
    163
    Helped
    69 / 69
    Points
    1,131
    Level
    7

    Re: Help in understanding the paper "Understanding Wide-band MOS transistors"

    In addition to the answer from dick_freebird, cascading multiple stages will have stability issues and you need to use some form of compensation which will lower your BW.
    Edit: *can have stability issues



--[[ ]]--