Extended-precision cures Spice convergence issues

July 24, 2013 // By Mike Robbins
Extended-precision cures Spice convergence issues
Mike Robbins of CircuitLab explains how extended-precision simulation is able to cure SPICE convergence problems.

Convergence issues are a frustrating deterrent to the use of simulation in analog and power electronics design, and in the four decades of SPICE, millions of engineers have suffered from the failed, painfully slow, or incorrect simulations that result.  We found that a large class of convergence issues (especially in switching-dominated circuits) came from well-defined circuits that simply collided with the dynamic range of the IEEE 64-bit floating point “double” type.  We have now released the first extended-precision numerical core inside a circuit simulation engine.

Unsolvable Equations  
The CircuitLab community ran more than half a million simulations last month.  Each one involved constructing tens, hundreds, or even thousands of simultaneous, highly nonlinear, strongly coupled differential equations, which are repeatedly linearized and solved iteratively.  Last month alone, our software constructed and factored more than 600 million matrices, and solved those factored systems more than 1.6 billion times.

Some simulations were failing to converge even though the circuits were well defined, by which we mean that any proficient high school math student could have computed the correct solution.  But the numerical methods in the solver could not!  

For example, here’s a two-diode circuit in another simulation engine:

This simple circuit situation occurs many times within larger systems, often with one or both diodes implicitly hidden within a power MOSFET or a CMOS input.  It is easily analyzed by inspection and the current should be limited in both directions by the diode reverse saturation current plus any transient current charging the diode, but it faces serious convergence issues in simulation.  In another simulation engine, this takes hours and hours to even partially simulate, and displays noisy currents millions of times larger than would be seen in reality.  Does your software do this?

In CircuitLab, with the new extended-precision numerical core we’ll describe below, this circuit and others simulates quickly and correctly in milliseconds ( try it instantly -- no download required

Design category: 

Vous êtes certain ?

Si vous désactivez les cookies, vous ne pouvez plus naviguer sur le site.

Vous allez être rediriger vers Google.