Spectrum Software
Industrial Strength Simulation




Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.




Periodic Steady State


Periodic steady state is a feature that is new to MC10. It computes steady state waveforms, eliminating the transient part of the solution. Very often the steady state is the desired portion and the transient portion merely a nuisance. Consider this voltage quadrupler circuit.

Voltage quadrupler

Here is its transient run over 10mSec. It's clear that the transient response will require hundreds of 1ms periods to dissipate the initial transient to reach a steady state. In fact more than 1000 1mS periods will be needed to achieve a steady state accurate to less than 100uV.

Transient run without PSS

Now consider this run using Periodic Steady State.

Transient run using PSS

Here PSS has computed the steady state. It shows a ripple of about 200uV riding on a DC level of about 398 volts. The original run using 1000 1mS periods took about 10 seconds. The PSS run took about 1 second.

Now consider this circuit.

FFT test circuit

Here is its FFT without using PSS.

FFT without PSS

Here is its FFT with PSS.

FFT with PSS

You can see from the last FFT window plot that the circuit has a noise floor of about 175 dB and contains mainly odd harmonics. Without PSS the odd harmonics are completely lost. This is due to the fact that without PSS the waveform being analyzed is not really periodic. There are still initial transients present. With PSS the initial transient error is reduced to about 1nV and with this small error it is possible for the FFT window to more accurately see smaller harmonics.

Here are some guidelines for using PSS:

Periodicity: The circuit response must be periodic. If it is driven by multiple sources, tmax must be an integer multiple of the periods of those sources.

Linearity: The relationship between the initial and final points over the shooting interval must be near linear. With perfect linearity, convergence usually occurs within 1-3 iterations. If the relationship is highly nonlinear many more iterations may be required or PSS may not converge at all.

Non-chaotic Circuits: PSS cannot handle oscillators (unless the period is known) nor circuits that respond chaotically, such as delta-sigma modulators and some SMPS circuits.

Limitations: PSS does not work with circuits containing digital components, transmission lines, Laplace sources, Z-transform sources, or N-ports.

Download Winter 2013 Circuit Files
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