Chapter 4 Behavioral modeling

Gnucap behavioral modeling is in a state of transition, so this is subject to change in a future release.

All simple components can have a behavioral description, with syntax designed as an extension of the Spice time dependent sources. They are not necessarily physically realizeable. Some only work on particular types of analysis, or over a small range of values. Some can be used together, some cannot.

All simple components are considered to have simple transformations. A function returns one parameter as a function of one other, as an extension of their linear behavior.

Linear behavior:

Capacitor: q = C v
Inductor: ϕ = L i
Resistor: v = I r
Admittance: i = Y v
VCVS: v_o = E v_i
VCCS: i_o = G v_i
CCVS: v_o = E i_i
CCCS: i_o = G i_i

Sources are defined as functions of time:

Voltage source: v = f(t)
Current source: i = f(t)

For behavioral modeling / nonlinear values, replace the constant times input by an arbitrary function:

Capacitor: q = f(v)
Inductor: ϕ = f(i)
Resistor: v = f(r)
Admittance: i = f(v)
VCVS: v_o = f(v_i)
VCCS: i_o = f(v_i)
CCVS: v_o = f(i_i)
CCCS: i_o = f(i_i)

Conditionals

AC: AC analysis only.
DC: DC (steady state) value.
OP: OP analysis.
TRAN: Transient analysis.
FOUR: Fourier analysis only.
ELSE: Anything not listed.
ALL: All modes.

Functions

COMPLEX: Complex (re, im) value.
EXP: Spice Exp source. (time dependent value).
FIT: Fit a curve with splines.
GENERATOR: Value from Generator command.
POLY: Polynomial (Spice style).
POSY: Posynomial (Like poly, non-integer powers).
PULSE: Spice Pulse source. (time dependent value).
PWL: Piece-wise linear.
SFFM: Spice Frequency Modulation (time dependent value).
SIN: Spice Sin source. (time dependent value).
TANH: Hyperbolic tangent xfer function.

Model Functions

TABLE: Fit a curve with splines.
Cap: Spice semiconductor “capacitor” model.
Res: Spice semiconductor “resistor” model.