$Revision:   1.2  $
$Author:   pwt  $
$Date:   29 May 1990 17:26:38  $

"Parts" on-line help file
Release 4.04, July 1990
(C) Copyright 1986-1990 MicroSim Corporation
DMOD 1
Diode - Forward Current

Device curve:

        Vfwd    forward voltage across junction for Ifwd
        Ifwd    forward current @ Vfwd

Model parameters:

        IS      saturation current
        N       emission coefficient
        RS      series resistance
        IKF     high-injection "knee" current
        XTI     IS temperature coefficient
        EG      activation energy

This screen estimates the parameters IS and RS from three voltage and current
values.  Try to include data from low current values (where the increase in
current is exponential), moderate current values, and high current value (where
the increase in current is clearly resistive).

The last two model parameters, XTI and EG, may be changed.  We have set them to
be normal values for silicon diodes.  For Schottky-barrier diodes these may be
changed to XTI = 2 and EG = 0.69, which will give better modeling over
temperature.

Also, it is sometimes helpful to set up traces for a few values of temperature
(use Trace command) for adjusting XTI.
DMOD 2
Diode - Junction Capacitance

Device curve:

        Vrev    reverse voltage across diode (junction) for Cj
        Cj      junction capacitance @ Vrev

Model parameters:

        CJO     zero-bias junction capacitance
        VJ      junction potential
        M       junction grading coefficient
        FC      coefficient for onset of forward-bias depletion capacitance

This screen estimates the parameters CJO and M from a capacitance values given
at non-zero reverse biases (a zero value for a Vj data point is OK).

The value for FC has been set to be normal for silicon diodes, but is
relatively unimportant, as forward capacitance is dominated by diffusion
capacitance (and modeled by transit time).

The data sheets for most switching and power diodes have little detail about
reverse bias capacitance, because it is not too important.  Varicap diodes
usually have better, more complete information.  Be aware that the diode
package adds some fixed amount of capacitance that is not included in the
device model, but may be included by the user with a small capacitor across the
diode.  Having determined the package capacitance, subtract that from the total
capacitance to model the diode junction.
DMOD 3
Diode - Reverse Leakage

Device curve:

        Vrev    reverse voltage for Irev
        Irev    reverse (leakage) current @ Vrev

Model parameters:

        ISR     recombination current saturation value
        NR      recombination current emission coefficient

This screen derives the generation-recombination current values for the device
which, with the capacitance modeling (previous screen), provides the primary
leakage mechanism of the diode junction.

Reverse current leakage is increased by imperfections in manufacturing which
are not modeled.  Breakdown also increases reverse current, but this is modeled
in the next screen.
DMOD 4
Diode - Reverse Breakdown

Device data:

        Vz      nominal Zener voltage @ Iz
        Iz      nominal Zener current for Vz
        Zz      Zener impedance (resistance) @ Vz,Iz

Model parameters:

        BV      reverse breakdown voltage (a positive value)
        IBV     reverse breakdown current (a positive value)

This screen estimates the parameters BV and IBV for reverse breakdown
operation, which is how voltage regulator (Zener or avalanche) diodes work. 
Enter the values for Vz, Iz, and Zz.

BV and IBV will nearly equal Vz and Iz.  As the breakdown effect is modeled by
an exponential function, the value of BV and IBV will adjust so that device
impedance, Zz (ratio of the change in voltage to the change in current) is
correct at Vz,Iz.
DMOD 5
Diode - Reverse Recovery

Device data:

        Trr     reverse recovery time
        Ifwd    forward current (before switching)
        Irev    initial reverse current
        Rl      load resistance (total load of test fixture)

Model parameters:

        TT      transit time

This screen estimates the parameter TT from switching time.  Enter values for
the upper list.  Be sure to include the test fixture resistance and pulse
generator resistance in Rl.

The screen does a transient simulation of the diode switching.  Some of the
parameters from earlier screens that have dynamic effects, for example, CJO,
are included in the simulation.  You may need to adjust the X-axis to see the
entire waveform.
