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Advanced Design System 2009 Update 1-AC Simulation
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Size:167.59 KB
Category:Agilent
Add Time: 2010-8-16 16:24:42
Updated:2010-8-16 16:24:42
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About:
When an AC small-signal simulation is run, the system first computes the DC operating
point of the circuit. Whenever a linear simulation such as a linear AC simulation requires a
single-point DC bias simulation to be run first, it is referred to as a bias-dependent linear
simulation. The most common example is the case of a linear amplifier that uses a biased
transistor as the active element. The DC bias simulation is executed automatically and
transparently (unless an error causes the DC simulation to fail to converge).
Following the DC bias simulation, the simulator linearizes all nonlinear devices about their
bias points. A linearized model captures the small incremental changes of current due to
small incremental changes of voltage. These are the derivatives of the transistor model
equations, which are evaluated at the DC bias point. Nonlinear resistors and current
sources are replaced by linear resistors whose values are set by the small signal
conductance dI/dV. Current sources that depend on voltages other than the voltage across
the source are replaced by linear dependent current sources dI1/dV2. Nonlinear capacitors
are replaced by linear capacitors of value dQ/dV.
The resulting linear circuit is then simulated over the specified frequency range. Small-
signal AC simulation is also performed before a harmonic-balance (spectral) simulation to
generate an initial guess at the final solution.
EMAIL: cadserv21@hotmail.com
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