I'm facing a problem about the Calibre LVS/PEX, I will describe it using this simple current mirror shown below, X and Y are same MOSFETs with width=16, nfing=2, m=1:
When I just do the layout with only one finger for both X and Y (w=16, nfing=1, m=1), and do the post-layout simulation, I injected 100uA to node
Vb, it has no problem seen from the post-layout schematic: X will absorb 100uA and Y will source 100uA.
But when I use 2 fingers, the problem comes. The layout is:
In this layout, the X and Y are in a single transistor which has w=32 and nfing=4, that means, X/Y are w=16, nfing=2 which is the same with the schematic above. ------ This is in my mind what is correct.
But when we do the LVS, it failed and showed property errors that X/Y has 2 fingers in the schematic but has 4 fingers in the layout:
If change some MOS properties in the schematic, nfing is changed from 2 to 4 (layout doesn't change), then hen the LVS passes, which we think is not correct (but it passes!). I used this extracted CalibreView file to do the post-layout simulation, the current reduced to a half as seen the comparison below:
Pre-simulation, both X and Y have 100uA current:
Post-simulation, the current reduced to only 50uA:
Does anybody know what would be the problem is and give some help? Thank you SO MUCH for any suggestions cuz I've been on this problem for days. Thank you!