TINA Bug? Simulating capacitors in series

Rahul Chander

I was getting unexpected simulation results from TINA and when I drew a really really simplified circuit, I narrowed the bug to following.

Circuit 1 and 2 are identical but the second one is considered an "irregular" circuit when AC node voltage simulation is turned on. The only difference is that two capacitors cannot be used in series in the way that I am doing. However, two resistors can be used in series without any issues.

This is extremely strange and I think it may be leading to incorrect simulation results in another circuit that I am interested in simulating.

TINA Version: 7 (free)

over 14 years ago

0 Rick Downs - WEBENCH Design Center over 14 years ago

TI__Expert 5515 points

Rahul,

This isn't so much a "bug" as it is a difference in the way TINA handles capacitors... if you double click on the capacitors, you'll see a parameter called RPar, which is a parallel resistance for the capacitor. TINA defaults this setting to Infinite, which means that when it runs a DC operating point (which it always does), there's no DC solution to two caps in series. Change RPar to someting like 1G, and your circuit will no longer be "irregular".

0 Rahul Chander over 14 years ago in reply to Rick Downs - WEBENCH Design Center

Prodigy 150 points

Rick,

Thanks for the explanation. Are you saying that TINA needs to resolve the voltage at each node and the node between the capacitors cannot be resolved as it sees infinite impedance left and right of it?

I wish that the error message was more descriptive.

Thanks

0 Rick Downs - WEBENCH Design Center over 14 years ago in reply to Rahul Chander

TI__Expert 5515 points

Yep, you got it right.

We've suggested changing the error message to TINA's developers.

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TINA Bug? Simulating capacitors in series