Spice is a powerful tool for circuit analysis. But it often surprises users with
. holes in its abilities and strange definitions
. lack of industry-wide standards
. the need for the user to model the physics of their circuit, not just draw the schematic

I hope this blog will educate users and promote discussion in these areas.

Buying a PC for simulation


If you are thinking about buying a new computer, the processor makes a huge difference in simulation speed. This is most noticable in Transient simulation, especially with circuits like switch mode power supplies.

The simulation speed difference between a 3.3 GHz mid-level desktop and an entry level laptop will be much greater than the 3:1 ratio of their processor speeds! Even a mid-level laptop prioritizes graphics performance and battery life over CPU crunch.

First a definition
   Floating point math unit = FPU
   Spice spends most of its time crunching numbers with the FPU.

What to look for
Look for 2 or more cores with the highest possible clock speed and an intermediate or advanced internal architecture. Don’t be overly impressed with recent AMD processor series core counts - the FX series has only one FPU for every two cores (haven't checked the FM series). Intel has one FPU per core in the i3, i5, i7 architectures. Low and possibly mid-level laptop processors may have only one FPU per processor. A Spice program that can use 3 cores, for example, will run fastest if there are no fewer than 3 FPUs.

Few PC based Spice programs use more than 2 or 3 cores because it is hard to efficiently partition the algorithm Spice uses to solve the non-linear circuit matrix. For example, 5Spice uses two cores.

Finally
don't buy the low cost processor option. Intel and AMD have low cost processors that have respectable clock speeds but less efficient internal architectures. They are designed to be cheap and to run real world apps significantly slower (so you will buy the more expensive ones).

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