SAMPLED-DATA SIMULATION OF PERIODICALLY SWITCHED NONLINEAR CIRCUITS - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 137

Chapter 7
SAMPLED-DATA SIMULATION OF
PERIODICALLY SWITCHED
NONLINEAR CIRCUITS
Due to the aggressive reduction in both the feature size of devices and
the supply voltage of modern CMOS technologies, mixed-mode switching
circuits exhibit increasingly nonlinear characteristics. These nonlinear
characteristics include junction capacitances, nonlinear channel current
of MOSFET devices due to velocity saturation and mobility degradation
[58], the finite slew rate, clock feed-through and charge injection [59],
to name a few. To analyze the nonlinear behavior of these circuits,
general-purpose analog simulators, such as PSPICE and Spectre [60]
that use linear multi-step predictor-corrector algorithms [60, 61] as their
simulation engines, can be used. These algorithms, however, exhibit
the following deficiencies when analyzing periodically switched nonlinear
circuits, particularly when switches are modeled as an ideal device :
Inability to handle inconsistent initial conditions arising from ideal
switching [60]. Inconsistent initial conditions that may occur at
switching instants not only generate current or voltage impulses but
also cause network variables to exhibit discontinuous characteristics.
Both can not be handled by LMS-PC algorithms.
Reliance on Newton-Raphson iterations in every time step of inte-
gration to find the correct solution. Not only the cost of Newton-
Raphson is normally high, the step size used in these algorithms has