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Subject: A question on result non-consistent between OP and Transient
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sz5g
Posts: 10
Online: User is Offline
8/13/2007 8:55 PM  
There is a small circuit I simulated and found inconsistent. In the spectre.out, the value on a
 transistor is :  gate 1.95651 V, drain 5.59709 uV, source 4.00421 uV, Ids = 159.733 pA.

However, the direct plots of transient results shown in waveform are totally different, as shown
 in the figure.  So what will cause the inconsistence, and which one are the correct results ?

I think this is actually a common question as I encounted similar things before, which touches
fundamentally how the simulation works.

Best regards,

Sz5g





adbeckett
Posts: 248
Online: User is Offline
8/13/2007 10:48 PM  
The question cannot possibly be answered, since you've not explained how the values in the spectre.out were simulated (was it from a DC simulation, an info analysis or what?). You've not explained what the transient was doing - are the conditions the same as DC? I notice there's a step at the start of your simulation results above. Also, the net names above and current measurement give no indication of which signal is which.

Remember that people don't have extrasensory perception in general - and it's hard to debug something without complete information.

This is most likely to be a setup mistake or a mistake in interpreting what you've done - but without seeing the full picture I can't pinpoint what is wrong.

Regards,

Andrew.
sz5g
Posts: 10
Online: User is Offline
8/16/2007 7:56 PM  
Andrew:

Thank you very much for your questions, which lead to the solution finally. An initial condition causes
the difference.

A related question will be: after " oppoint" calculated by using initial condition, will later on the "oppoint"
values be changed based on changing node values ? so that all calculations based on "oppoint" will be
updated accordingly ? Guess it should be.

sz5g
adbeckett
Posts: 248
Online: User is Offline
8/16/2007 11:26 PM  
Sorry, I don't understand your question...

Regards,

Andrew.
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Forums > Custom IC > Custom IC Electrical Design > A question on result non-consistent between OP and Transient


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