eldo_user

Speed and Accuracy
One Step Relaxation (OSR) Algorithm
This first partitioning method is automatic, based on the degree of coupling between
devices. A global option is set (.OPTION BLOCKS=NEWTON). Eldo will identify the
blocks consisting of tightly coupled devices and place them in partitions that will be
solved using the Newton method. The loosely coupled nodes are placed in the OSR
partition. The global circuit is solved using a relaxation loop. Simply, the relaxation loop
operates with individual nodes and also groups of tightly coupled nodes (the Newton
partitions). Note that the identification of tightly coupled devices is not based on the
netlist hierarchy (.SUBCKT, and so on).
• Flag (ANALOG) given on SUBCKT definition
This partitioning methods ‘tags’ the subcircuit definitions. The subcircuit definitions
tagged with (ANALOG) will be solved using the Newton method. This is useful when
the netlist hierarchy reflects the nature and coupling level of the blocks. All nodes that
are not inside a user-defined (ANALOG) SUBCKT, and which are connected only to
MOSFET, grounded capacitances, or low-value floating capacitances (the threshold
value for floating capacitance is set with .OPTION CAPANW= ) will be solved by OSR,
with all other nodes being solved by Newton. See the subcircuit definition syntax in the
.SUBCKT command in the Eldo Reference Manual.
• .NWBLOCK [RELTOL=val] [VNTOL=val]
This method is the most ‘manual’ one. Each Newton block is defined explicitly, with a
list of nodes. Hierarchical names and wildcards in such names are allowed. Optionally
the required Newton accuracy can be redefined for each block, using the RELTOL and
VNTOL parameters.
With any of the partitioning methods described above, OSR is implicitly activated. OSR
becomes the default method, and Eldo (or the user) defines what still has to be simulated with
Newton.
Whenever OSR and Newton are activated simultaneously, the OSR and Newton rules for
accuracy control apply to the OSR and Newton partitions respectively. For example the
RELTOL and VNTOL parameters still define the accuracy of the nodes inside the Newton
partitions, whereas EPS defines the accuracy of the OSR nodes.
Related Topics
Integral Equation Method (IEM) Algorithm
Tips for Improving Simulation Performance
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Eldo® User's Manual, 15.3