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Plotting Vth

Shahnaf
Hi, I am designing rectifier for very low power applications using gate cross coupled architecture of MOSFETs. So, My input is ac voltage which is around 500mV and less. In order to simulate my design, I am trying to look around the ways to lower the Vth. To do so, I want to check how Vth is varying w.r.t Width of NMOS, PMOS and Length of NMOS, PMOS. How should I plot Vth vs L or W in case of ac input? Suppose, i give some biasing to gate voltage by using some voltage source, at that time, how should I plot Vth? Please help me out as I am very confused. Thanks, Shahnaz.
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  • Not sure what analysis you're doing, but if you want to plot the Vth from anything other than a DC operating point, you'll need to get the simulator to save the vth. You can do this with:

    save M1:vth

    or

    save M1:oppoint

    where M1 is the name of the transistor. This would need to go into the spectre netlist - if you're using spectre from the Analog Design Environment, you can create a file called (say) "mysave.scs" with the above contents, and then include it by referencing it from Setup->Model Libraries.

    Having done that, you can access the vth for whichever analysis you're using by using the Results Browser in ADE.

    Regards,

    Andrew.

Reply

  • Not sure what analysis you're doing, but if you want to plot the Vth from anything other than a DC operating point, you'll need to get the simulator to save the vth. You can do this with:

    save M1:vth

    or

    save M1:oppoint

    where M1 is the name of the transistor. This would need to go into the spectre netlist - if you're using spectre from the Analog Design Environment, you can create a file called (say) "mysave.scs" with the above contents, and then include it by referencing it from Setup->Model Libraries.

    Having done that, you can access the vth for whichever analysis you're using by using the Results Browser in ADE.

    Regards,

    Andrew.

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