eldo_user

Specifying Simulation Output
Defining Waveforms
Defining Waveforms
Use the .DEFWAVE command to define a new waveform by relating previously defined
waveforms and nodes. Some usage notes follow:
• Combining the .PLOT command with the .DEFWAVE command can be used to
generate so-called template waveforms, that is, piece-wise-linear waveforms defined by
a series of arbitrary (x,y) coordinates. Using .PLOT, these templates can be displayed
together with the simulation results (this is very useful when verifying whether a filter
response passes or not specifications such as cutoff frequencies, minimum attenuation,
and so on). For example:
.DEFWAVE FILTERSPEC=PWL(1e-3,0,100k,0,500k,-60,100G,-60)
.PLOT AC VDB(OUT) W(FILTERSPEC)
• Waveform definitions can be specified inside subcircuit definitions. Identical complex
calculations can be performed for each instance of the subcircuit. Typically the
subcircuit is declared once and instanced many times. This means there is no need to
have many instances of the same subcircuit with definitions of .DEFWAVE and .PLOT
for each. Eldo only calculates the .DEFWAVE statements that are called, not all
.DEFWAVE statements declared.
• Waveform names cannot contain arithmetic operators.
• Waveform names cannot contain the hierarchical separator: the period character “.”.
• Only one waveform may be defined per .DEFWAVE statement.
• It is not possible to use functions which expect at least one waveform as input.
• Built-in PPL functions that act on a waveform cannot be used in Tcl procs that are called
from .DEFWAVE statements. This is because .DEFWAVE expressions represent a
numerical value, and not a waveform.
• A wave is instantiated by preceding the wave name w, which can be followed by a
format suffix for complex waveforms, for example: wm, wdb, wp, wi, wr are enclosed
in parentheses ().
• A waveform expression cannot contain a division by zero. If this is the case, 1.0×10 -15 is
automatically assigned to a value.
• The .DEFWAVE command is order dependent in that all components of the waveform
expression must have already been defined earlier in the netlist. The following is illegal:
.defwave power_vdd=i(v1)*v(v1)
*...
v1 in out ...
However, the following is allowed:
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Eldo® User's Manual, 15.3