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Design Languages >> Verilog-AMS >> Transition Filter DC operation
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Message started by s1s2kim on Apr 7^th, 2014, 7:59pm

Title: Transition Filter DC operation
Post by s1s2kim on Apr 7^th, 2014, 7:59pm

Hello
I have a question about DC operation of transition() function in Verilog-a. In the manual, the description about it is like :

"In DC analysis, transition() passes the value of the expr directly to its output. The transition filter is designed to smooth out piecewise constant waveforms. When applied to waveforms which vary smoothly, the simulation results are generally unsatisfactory. In
addition, applying the transition function to a continuously varying waveform can cause the simulator to run slowly. Use transition() for discrete signals and slew() (see Section 4.4.10) for continuous signals."

My question is, when transtion passes the value to output, is it smoothed? or still piecewise?

If it is piecewise, is there any option smoothing piecewise analog funciton in DC analysis?
I want to have continuous output in both DC and transient. Help me please

Title: Re: Transition Filter DC operation
Post by Ken Kundert on Apr 8^th, 2014, 12:25am

In DC analysis, the waveforms are assumed to be constant. A transition function cannot smooth a DC solution any smoother than it already is, because for the purpose of the analysis, the waveform is not changing. In other words, when a source voltage changes in a DC analysis, the analysis effectively waits forever for any transients to disperse, and then the analysis computes the result.

Thus, the transition function has absolutely no effect in DC analysis, except for the fact that it may not pass AC small signals.

In transient the argument to the transition function should be a piecewise constant waveform. The output will be continuous and piecewise linear.

In DC analysis, all waveforms are constant.

-Ken