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Information on dc_pivot_check option

Dmitry Babin

Hi all,

I'm simulating a circuit and get the following notice from Spectre: 

Bad pivoting is found during DC analysis. Option dc_pivot_check=yes is recommended for possible improvement of convergence

However, I can't find any reference to this option in the documentation. Can someone expand on it a bit?

 

Some background:

I'm simulating power-up of a circuit with two supplies. Initially, one supply is on, while another one is at 0V, and most of the nets in the 2nd part of the circuit are actually floating (no MOSFET conducts). Neverthless, I would expect the DC solution for them to be 0V (due to gmin conductors installed by Spectre at each floating net). However, that's not the case: DC solution assigns voltages of up to several hundred mV to some of the nets in the powered-down part! Moreover, the voltage values change strongly and inconsistently when I switch corners or change gmin value.

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