Understanding Fast SPICE Simulators

SPICE (Simulation Program with Integrated Circuit Emphasis) is used today by IC designers and students for custom and analog IC designs who need the highest accuracy. Without SPICE we could never see the world that we see today!

Fast SPICE is like SPICE by reading a transistor-level netilst however it runs much faster by making assumptions about your circuit netlist and will partition the netlist automatically into smaller pieces which can then be solved more quickly. Fast SPICE simulators can be flat or hierarchical tools. Without the Fast SPICE Simulators Verification Engineer would have been launching one test case out of 100 and then would have gone for a month long vacation. After that also there is no surety that the simulation results are there or crashed!!


Other than partitioning a netlist for a faster simulation run with Fast SPICE simulation tools we can replace the modules in the design that a particular test case is not targeting to a model written in C, Verilog-AMS etc. This further increases the speed of the simulation and thus decreases the product's time to market.


Today, there are many tools in the market that help AMS Verification Engineers to do their job :


1. XA , latest tool from Synopsys
2. Nanosim, years old and still going strong tool from Synopsys
3. Ultrasim from Cadence
4. Finesim from Magma
5. HSIM from Synopsys


In SNUG 2009, a paper was presented (link given below) that shows that XA (which is acronym for Extreme Accuracy) is much faster and more accurate in co-simulations/ Mixed Signal Simulations than Nanosim. 


http://www.synopsys.com.cn/information/snug/2009/accelerated-mixed-signal-full-chip-verification-with-xa-vcs




But to understand how these Fast SPICE Simulators work there is an excellent paper from Springer - "A Perspective on Fast SPICE Simulation Technology".
To read the article Click here .


You can find here the answers for these questions - 


1. How SPICE is different from Fast SPICE?
2. How Fast SPICE simulators are able to make changes in the netlist so as to complete a simulation 100 to 1000 times faster than SPICE?
3. What algorithms or numerical analysis is used by Fast SPICE Technology?
4. How is partitioning done in the netlist by Fast SPICE Tools and how it is getting improved in the market?
5. How memories are run faster with the help of Fast SPICE Technology?