I have a circuit that involves monitoring the voltage across a 66k ohm resistor with a Schmitt trigger. I got the circuit working just fine in Spectre and then layed it out - however I needed to tweak the 66k resistor from the original series of 6 segments to a series of 4 segments to get LVS to pass. I subsequently resimmed the schematic with the reconfigured 4-segment 66k resistor and the sim failed :-/. I thought maybe I was on some crazy cliff edge so I started tweaking the resistor value but it wasn't until I had changed the 4 segment total resistance to about 64k before I got to the same place as the 6 segment 66k resistor! I'm guessing the schematic is calculating the resistance differently to the simulator, however the process I'm using is what I would have thought was a fully ironed out, highly mature, 20 year old TSMC 0.18um CMOS process. I'm not fully sure how to debug this. I've attached some screenshots that I hope can be of assistance.
In addition to the attached pictures, I noticed that if I enter an illegal value (I used xxx) into the total resistance field of the Property Editor in the schematic that a formula appears for the total length and segment length. Those formulas are:
Total length:
(1e-06-40.6n)*(xxx*1/6-2*0.17m/(1e-06-(-0.14u)))/335.0+0*6
Segment length
(1e-06-40.6n)*(xxx*1/6-2*0.17m/(1e-06-(-0.14u)))/335.0+0
