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# Derivation of Diode Models for Analog Simulation

IP.com Disclosure Number: IPCOM000111264D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 8 page(s) / 209K

IBM

## Related People

Snyder, CH: AUTHOR

## Abstract

One of the impediments facing engineers engaged in computer aided circuit analysis and design is obtaining circuit models for vendor components. For example, manufacturer's datasheets for Schottky diodes typically do not explicitly provide the physical device constants necessary to construct analog simulation models of their products. However, this information can be extracted from the manufacturer's data by the disclosed method. Additionally, the method is suitable for imbedding in a larger software framework to allow interactive or automatic model generation.

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Derivation of Diode Models for Analog Simulation

One of the impediments facing engineers engaged in computer
aided circuit analysis and design is obtaining circuit models for
vendor components.  For example, manufacturer's datasheets for
Schottky diodes typically do not explicitly provide the physical
device constants necessary to construct analog simulation models of
their products.  However, this information can be extracted from the
manufacturer's data by the disclosed method.  Additionally, the
method is suitable for imbedding in a larger software framework to
allow interactive or automatic model generation.

Mathematical Backgroud - The theoretical behavior of an ideal
Schottky diode is given by Eqn.  1 [1]  as:

I = I sub s lparen e sup <V/V sub T> - 1 rparen
[1]
where

I = diode current, Amperes
I sub s = diode current, Amperes
V = voltage across the diode terminals, volts
V sub T = kT over q, the volt-equivalent of
temperature
k = Boltzmann constant, 1.381X10 sup <-23>
Joules/º  Kelvin
T = temperature, º  Kelvin
q = electronic charge, 1.602X10 sup <-19> Coulombs

At room temperature (app 300 º  Kelvin), V sub T = 0.026
Volts.

Equation 1 does not consider the effects of a nonideal
parameter, series resistance, denoted R sub s, which is present in
all physical Schottky diodes.  For practical applications, Eqn.  1
must be modified to include this parameter in order to obtain an
accurate representation of the device behavior.  The result is given
by Eqn.  2 [2].

I = I sub s lparen e sup <lparen V - IR sub s
rparen / V sub T> - 1 rparen                           [2]

R sub s = diode series resistance, Ohms

Note that V is the voltage measured at the diode terminals, IRsub s
is the voltage drop across the equivalent series resistance, and V -
IR sub s is the voltage drop across the metal-semiconductor
(Schottky) junction.  For the values of diode voltage and current
typically given in manufacturer's data books, I is typically much
larger than I sub s lparen I gt gt I sub s or equivalently V gt gt V
sub T rparen so that Eqn.2 becomes:

I app I sub s lparen e sup <lparen V - IR sub s
rparen/V sub T> rparen                                 [3]

The model to be derived here is based on Eqn.3, and so it is
necssary to determine I sub s and R sub s.  Manufacturer's data books
typically do not specify either quantity; instead, curves of device
current versus device voltage are given.  Also, in char...