eldo_user

Setting Up An Analysis
Transient Noise Analysis
Influence of .NOISETRAN Parameters on Simulation Performance and
Accuracy
The following guidelines describe the effect of the .NOISETRAN parameters FMIN, FMAX
and MRUN on simulation performance and accuracy, and provide guidance on how best to set
them.
• The FMAX parameter directly affects the time step size (through HMAX). Therefore,
this parameter has to be set large enough to accurately represent the noise sources but
not so large that simulation time is penalized. This parameter should correspond to the
circuit noise bandwidth. The appropriate value depends on the highest frequency in the
circuit.
• The FMIN parameter should be set to 0 (the algorithm to generate noise sources will be
faster and more accurate) unless you want to analyze the effect of the noise generated in
a specific narrow bandwidth.
• The MRUN flag should not be set except for some specific classes of circuits (PLLs,
Sigma-Delta converters) or when the simulator experiences a convergence problem and
reports that the MRUN flag should be used. With appropriate cases the .NOISETRAN
simulation runs much faster without the MRUN flag.
Related Topics
Tip
See “.NOISETRAN” and “.OPTION NOISETRAN_TUNING” in the Eldo
Reference Manual.
Generation of Time Domain Noise Sources
Speeding Up Transient Noise Analysis
Transient Noise Analysis Results
Transient Noise Analysis Algorithms
Two methods exist to generate transient noise signals, depending on the value of FMIN:
• When FMIN ≠ 0, the algorithm uses a sum of sine waves with random phases.
• When FMIN = 0, the algorithm uses gaussian random variables to generate noise
sources.
A noise source, with given frequency characteristics, will produce two different noise signals
depending on the method used to generate them. These signals will have different instantaneous
values but will have the same power and same frequency content.
During transient noise analysis, Eldo generates noise sources in the time domain for each noisy
component. These noise sources are generated as a sum of NBF sinusoids distributed between
Eldo® User's Manual, 15.3 245