eldo_user

IEM Alone (.OPTION IEM)
Speed and Accuracy
One Step Relaxation (OSR) Algorithm
As discussed in “IEM Tolerance Parameters” on page 1263, this setup enables IEM to simulate
the whole circuit in a single block. This is required for all-analog designs, or at least when the
analog part of the circuit is much larger than the logic circuitry (in other words, approximately
75% of devices or more). This option is particularly recommended for circuits requiring high
precision and/or those manifesting stability problems. IEM intrinsically gives very good
accuracy and doesn’t require tightening of accuracy parameters. Hence, the default EPS value is
usually enough to achieve high quality simulation results. Lowering EPS will give even higher
precision, but at the expense of CPU time.
IEM + OSR (.OPTION BLOCKS=IEM)
This setup enables Eldo to partition the circuit, assigning tightly coupled blocks to IEM, the
remaining part being simulated with OSR. By default, MOS and grounded capacitors are
assigned to OSR, hence it is recommended to use this setup in conjunction with a correct
imposition of the attribute (ANALOG) for relevant circuits. This way, BJTs, resistors, and all
MOS analog subcircuits will be simulated by IEM while other MOS blocks will be considered
as logic ones and efficiently simulated by OSR (whenever possible).
As usual, it is possible to increase accuracy by reducing EPS, however, as in all-IEM simulation
this is not particularly recommended.
Note
The combination of IEM (a highly precise algorithm) with OSR (a fast but less precise
algorithm) may not be justified in some cases.
Related Topics
Integral Equation Method (IEM) Algorithm
One Step Relaxation (OSR) Algorithm
IEM Tolerance Parameters
One Step Relaxation (OSR) Algorithm
The OSR algorithm of Eldo is dedicated to the simulation of large MOS circuits showing weak
local couplings (large-scale feedback loops are not a problem). It is a unique algorithm to Eldo.
Its primary usage is the fast transistor-level simulation of large digital CMOS circuits, for which
the weak local coupling assumption is generally valid.
Caution
OSR is applicable to legacy processes only, typically 0.5μm or larger, and does not perform
efficiently with state-of-the-art processes. This is because OSR is based on fundamental
assumptions about the signal flow and weak electrical couplings between gates, drains, and
sources in MOS devices. These assumptions are no longer true with short-channel processes,
Eldo® User's Manual, 15.3 1265