eldo_user

Setting Up An Analysis
Transient Noise Analysis
• .PART being used (for ADiT, and so on)
• .CHRSIM present
• Presence of DELAY operators, T elements, FNS elements
• Use of local truncation error algorithm (QTRUNC option active)
• Mixed-mode simulation (presence of .A2D/.D2A commands)
• Use of Verilog-A
The multiple-run MRUN scheme can also benefit from multi-processor machines to speed-up
simulations in the following ways:
• .NOISETRAN MRUN simulations can be distributed by the .MPRUN command
• .NOISETRAN can be accelerated by specifying multi-threading with eldo –use_proc N
As with many simulations, there is a compromise between accuracy and speed. The main
transient noise parameters controlling this are as follows:
• FMIN—setting to 0 uses a faster, more accurate algorithm.
• FMAX—main factor to increase accuracy, even much higher than circuit cutoff
frequency HMAX forced to 1/(2 × FMAX), thus CPU ~ FMAX. It is better to explicitly
set a lower value for HMAX than a high value for FMAX to achieve the best accuracy
possible.
• NBRUN—CPU time and accuracy increase with NBRUN.
• MRUN—single run algorithm is faster than multiple-run.
Transient noise analysis requires more accuracy by default, therefore the simulator accuracy
values (EPS, VNTOL, RELTOL) are overridden, see “Simulator Accuracy Considerations with
Transient Noise” on page 258.
Simulator Accuracy Considerations with Transient Noise
The default values of EPS, VNTOL, RELTOL, and HMAX are changed in transient noise
analysis from the values used in other analyses. For .NOISETRAN, the defaults are:
• EPS=1.0×10 −6
• VNTOL=1.0×10 −6
• RELTOL=1.0×10 −6
By default, Eldo is able to compute noise voltages down to approximately 1µV. As most of the
applications create higher levels of noise, this should be sufficient in most cases. In all other
cases, it is advisable to increase the simulator accuracy.
258
Eldo® User's Manual, 15.3