How Can I Modify The Existing Simulation Models In SPICE To Accurately Represent The Non-ideal Behavior Of Real-world Diodes, Specifically In Terms Of Incorporating Temperature-dependent Reverse Saturation Currents And Voltage-dependent Junction Capacitance, Without Compromising The Overall Computational Efficiency Of The Simulation?

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To modify the SPICE simulation models to accurately represent real-world diodes, focusing on temperature-dependent reverse saturation currents and voltage-dependent junction capacitance, follow these steps:

  1. Understand the Standard Diode Model: The standard SPICE diode model includes parameters such as IS (reverse saturation current), CJO (zero-bias junction capacitance), and MJ (grading coefficient). These can be adjusted to incorporate real-world behavior.

  2. Incorporate Temperature Dependence:

    • Reverse Saturation Current (Is): Use the built-in temperature scaling in SPICE. Set the TNOM parameter to the nominal temperature (usually 27°C). The instance parameter can then scale IS based on the operating temperature using the .TEMP command. The formula Is = IS*(T/Tnom)^(EG/(k*Vt)) is internally handled by SPICE when temperature is specified.

  3. Model Voltage-Dependent Junction Capacitance:

    • Utilize the CJO and MJ parameters in the standard diode model. CJO sets the zero-bias capacitance, and MJ defines the grading coefficient. These parameters allow the capacitance to vary with the reverse voltage according to the formula Cj = Cj0*(1 + Vr/Vj)^(-M).

  4. Set Simulation Temperature: Use the .TEMP command to specify the operating temperature, ensuring that SPICE adjusts IS and other temperature-dependent parameters correctly.

  5. Verify Model Accuracy: Run simulations at different temperatures and voltages to confirm that Is scales appropriately with temperature and capacitance changes with voltage as expected.

  6. Check for Efficiency: Using the standard model with these parameters maintains computational efficiency. Avoid complex subcircuits unless necessary, as they can slow down simulations.

By adjusting these parameters and commands, you can create a more accurate diode model in SPICE without compromising computational efficiency.