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SPICE HELP

Discussion in 'Circuit Simulation & PCB Design' started by ANALA, Aug 14, 2017.

  1. ANALA

    ANALA New Member

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    DELAY= exp[(Vth2-Vth1)/n*Vth]
    Is there any way so that i can input this equation to the SPICE tool and plot Delay Vs supply voltage?
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Welcome to ETO!
    You can use the DELAY function to characterise a Behavioral Voltage or Behavioral Current source.
     
  3. ANALA

    ANALA New Member

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    My first step would be to implement and simulate an inverter using a particular technology node and plot delay vs supply voltage graph for different values of Vth.

    Next i want to validate my model against the simulated one using my proposed equation and compare the 2 graphs...since i m knew to SPICE i dont know how to go ahead with the second step..

    I basically want to know how can i enter the mentioned equation n plot the graph for different values of Vth,Vth1, Vth2 and supply voltage?
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Here how the Delay() function works in an Behavioral Voltage Source expression:

    51.png

    I delay V(in) by 200us, and multiply it by 2. Read the LTSpice Help file for circuit element B.
     

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    Last edited: Aug 15, 2017
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Here is how you vary the delay timing: 51a.png


    You can make either argument to Delay() a function of various things. Either argument can be an arbitrarily complex expression which is a function of some node voltage, branch current, or a varying parameter as I show above.
     
  7. Mosaic

    Mosaic Well-Known Member

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    To get a power graph (rather than a voltage y-axis) from a Behavioral Voltage component 'power expression', use a 1A current source on the output of the B component and Alt-click the Current source to display dissipated Watts on the graph.
     
  8. ANALA

    ANALA New Member

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    I don't wish to introduce delay in my waveform but rather i want to calculate the delay of the inverter using my proposed equation. The simulated circuit can be used to calculate delay..this i m aware of..but in the second step i want to validate my proposed model against the simulated one...so how do i do this?
     
  9. ci139

    ci139 Active Member

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    the eq. at #1 is quite simplistic - that is - it means it's more likely to "match" (loosely) a huge amount of experiment data (with systematic errors -- not shown in your formula) why don't you show us the part of the grid with test points on the signal path & everything in between

    the Spice is likely evt.-wise driven "quanted computation table" that hopefully preserves the energy conservation law e.g. all it's timing data is questionable or requires a sophisticated simulation setup . . .

    + your formulas dimensional (unit-wise) analysis makes me wonder how you get DELAY dimensioned by (SI) second considering the cap formula for example
     

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    Last edited: Aug 16, 2017

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