increasing frequency of ramp generator

Discussion in 'Analog & Mixed-Signal Design' started by Chandler Timm Doloriel, Apr 6, 2018.

  1. Chandler Timm Doloriel

    Thread Starter Member

    Apr 5, 2018
    Hello everyone!

    In my simulation of ramp generator, I only get small frequency below 100kHz. How should I increase the frequency to 250kHz? I tried changing Io, Ct and Rt but it only results to bad output.

    Here are my values that I get a 33kHz triangular output:
    Io = 33uA
    Ct = 1nF (0.55V)
    Rt = 5k
    Vdd = 1.2V

    In any of these parameters, Io is the most valuable I think? What value should I increase it to result to better output?

    Thank you for your time reading this [​IMG]
  2. Papabravo


    Feb 24, 2006
    Apparently the dvices are not capable of operating at higher frequency. Why do you think they will?
  3. Chandler Timm Doloriel

    Thread Starter Member

    Apr 5, 2018
    What is the maximum frequency this circuit can run? In my reference paper, it ran at 700kHz at vdd= 2. How can I calculate the max frequency it can run?
  4. Papabravo


    Feb 24, 2006
    It depends on the characteristics of the devices as defined in the simulation.
  5. danadak

    Distinguished Member

    Mar 10, 2018
    Depends on -

    1) MN2 Rdson limits speed of discharge of cap.
    2) MN2 gate driver speed handling MN2's input C.
    3) Speed of hysteresis driver in MN2s gate drive path.
    4) Speed MN2 can be turned off.
    5) Parasitics associated with ramp cap.

    Regards, Dana.
  6. ebp

    Well-Known Member

    Feb 8, 2018
    Look for clues, such as by reducing the capacitance by a factor of 10 and the output current by a factor of two. What would you expect? What does the simulation show?

    Showing a sim for a whole bunch of apparently identical cycles just obscures the details. If nothing is shifting with successive cycles, showing 2 or 3 is far better.
  7. RichardO

    Late Member

    May 4, 2013
    If you use LTspice for your simulation others will be able to see better exactly what you are doing. Please post the .asc file if you use LTspice.