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Simulators >> Circuit Simulators >> New thought about simulation SC circuit by transient with ac analysis
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Message started by hspice on Aug 7^th, 2009, 8:39pm

Title: New thought about simulation SC circuit by transient with ac analysis
Post by hspice on Aug 7^th, 2009, 8:39pm

Hi, there:

I'm wondering if possible using transient with ac analysis instead of PSS or seperated test bench for SC curcuit evaluation.
There is a feature at IC61x, that we can insert ac analysis to transient analysis after specified time points for ac. Then we can pick, say a sampling & hold circuit as test bench, after picked up the point desired, just to break the feedback, and maintain op for ac analysis. In this way, we can evaluate the opamp within real application environment, better than seperated AC test bench!
However, I found there were two issues within this idea, the first, I have add a ac source at the input terminals of opamp, but at SH mode, those terminals are always high impedense point. The second one, I have to make a component which break at AC analysis and short at transient mode. By verilogA model, I did have one with flaw.
By using "analysis" command, it can be turned to open mode(large resistor) , but can't be turned back, loooks like spectre did not initialize simulation mode back to transient after AC analysis points.

Does anyone can commend my idea and solve my questions regarding to this method? I do think this way should work, unless something inside spectre bars

THX

vincent

Title: Re: New thought about simulation SC circuit by transient with ac analysis
Post by nobody on Aug 9^th, 2009, 7:53pm

That is one way I want to do the simulation in SC ckts because what I have now is HSPICE.

Title: Re: New thought about simulation SC circuit by transient with ac analysis
Post by Andrew Beckett on Aug 15^th, 2009, 12:48am

Note that this approach will not evaluate the response of the switch capacitor circuit - it would merely allow you to look at the AC response at a particular snapshot in time. In many circuits there would be no direct path from input to output at any single time - for example, the input switches would be open when the switches for the next stage are closed, and vice versa. So I'm not sure how useful it would be.

Spectre already has a component "switch" (which is in analogLib as spt1switch, spt2switch etc) which allows you to have an ideal switch which is in different positions during different analyses.

Regards,

Andrew.