Foil 14.9 : VHDL-AMS frequential domain

Modeling and simulation in frequential domain

(spectral & noise sources, current source model)

Spectral and noise sources:

VHDL-AMS supports simulations in the noise and in alternative regime in a Spice-compatible manner, based on a small signal model derived from equations

F(x,dx/dt,t)

the small signal model is defined as the linear term of the Taylor expansion, with respect to all quantities,of F(x,dx/dt,t) system obtained when the value of the DOMAIN signal is FREQUENCY_DOMAIN, with the partial derived at the quiescent point
the small model signal is an incremental linear model described by a system of linear equations with increments of quantities of the unknowns
the system of equations describing the small signal model is homogenous unless the model specifies some specific stimuli in the frequential domain
the language provides two specific source quantities: the spectral source that defines the stimuli for frequential simulation and the noise source that specifies the noise characteristics

A model of current source:
A simple example below shows a model of a source of current. Its value is composed from a constant current (dcurr) and a spectral source q_ac combined with noise source q_ns :

entity complex_current_source is

generic (dcurr, ac_amplit, ac_phase, noise_amplit: real:=0.0);

port (terminal tplus, tminus: electrical);

end complex_current_source;

architecture example of current_source is

quantity i through tplus to tminus;

quantity quant_ac: real spectrum ac_amplit, ac_phase;

quantity quant_noise: real noise ns_amplit;

begin

i == dcurr + quant_ac + quant_noise;

end example;

expressions defining the amplitude for a source quantity or the phase for a spectral source are VHDL expressions
they can include names others quantities, that allow, for example, to define sources of bias dependent noise
these expressions can include calls to the function FREQUENCY that returns the frequency of current simulation

The language supports the stimuli in the frequential domain but does not support the frequential simulation behavior