Diode model

The Multisim diode model is based on the original SPICE3 diode model. It contains a number of enhancements, including improved convergence and support for high-injection effects.

See below for details. 

Large signal model

In the following equations, V_d is the voltage across source Id. It does not include the drop across Rd. 

Static equations

The current through the diode is the sum of the forward current, I_fwd, and reverse current, I_rev: 

Forward current: 

The forward current is the sum of the normal and recombination currents: 

With the default parameter values, most of the terms drop out or the factors are set to 1. Therefore the forward current simply degenerates into the normal current, I_nrm. 

Reverse current: 

The reverse current is the sum of the high and low reverse currents: 

Capacitance equations

The diode's non-linear capacitance, C_d, is the sum of the diffusion capacitance:

and the junction capacitance.

Temperature dependent parameters 

The following parameters are functions of temperature. T is the operating temperate and TNOM is the nominal (or measured temperature). T and TNOM can be adjusted in a number of ways. 

Noise model 

The diode has a thermal noise generator, , as a result of the series ohmic resistance, and the shot and flicker noise generators, collectively , as a result of the PN junction. 

Ohmic resistance noise: 

Shot and flicker noise:

References 

1. G. Massobrio and P. Antognetti, Semiconductor Device Modeling with SPICE, 2nd edition, McGraw-Hill, 1993. 
   
2. A. Vladimirescu, The SPICE Book, Wiley, 1994.