eldo_user

Integration Method
Speed and Accuracy
One Step Relaxation (OSR) Algorithm
When using OSR, the same integration methods as for the case of Newton (namely BE, TRAP,
and GEAR) can be used (using .OPTION METHOD=).
Time Step Control
When using OSR, the default time step control algorithm is the same as in the case of Newton
(LVLTIM=2), and thus it uses local truncation error (LTE) control. Only the LVLTIM=1,
LVLTIM=2 and LVLTIM=3 methods are selectable together with OSR. The other method
(LVLTIM=0 is meaningless in the context of OSR (there are no Newton iterations when using
OSR).
Accuracy Control
The accuracy control when using OSR is much simpler than with Newton. The global parameter
EPS is used to control everything. Furthermore, the actual value of EPS (in Volts) is directly
used for the convergence control.
Accuracy of the relaxation loop and the inner loop is directly controlled by EPS.
• Relaxation loop is stopped when:
|V(irelax) - V(irelax-1)| < EPS for all nodes
• Inner loop:
|V(iter) - V(iter-1)| < EPS/50 on the current node
Combined OSR/Newton Simulation
Eldo can partition a circuit so that some blocks are simulated using OSR and other blocks are
simulated using the standard Newton algorithm. Typical candidate examples would include
circuits with large digital CMOS blocks driving and/or driven by analog blocks such as voltage
regulators, bandgap references, high-gain operational amplifiers, and so on.
In these cases, the speed and capacity of OSR is used to handle the large weakly-coupled
sections of the circuits, and Newton, with its accuracy and ability to handle tightly coupled
devices, is used for the analog blocks.
The partitioning can be left entirely to the discretion of Eldo, or the user can try to help and
indicate which blocks (subcircuits) must be simulated with OSR or Newton. In the latter case,
the partitioning is always indicative only, and Eldo may choose to alter the boundaries of the
partitions to accommodate the requirements of the OSR algorithm.
There are several ways to trigger these mixed OSR/Newton simulations:
• .OPTION BLOCKS=NEWTON
Eldo® User's Manual, 15.3 1267