[SOLVED] LVS Device Mismatch Error with Multiple Gate Devices (AMS Hit Kit 0.35u)

[ashwatik]

I have a problem with LVS errors, I am not able to figure out what might be wrong here. I have split a 16 gate transistor into 8 + * (in the AMS process, you don't have multiplicity, only number of gates). For some reason, there are 4 transistors that do not get recognized in the layout. I am not sure why at all. I have attached the LVS error report here:

View attachment ams-lvs-error.txt

I use Layout XL and I have tried "Update Nets and Components", I have deleted those four parts and created them again. The schematic is 4 transistors in parallel with each transistor having 4 gates (I needed to use a common centroid layout).

I would really appreciate some insight into the problem, as soon as possible.

 

[Jushoraj]

can yo please attach a snapshot of that particular part of layout and schematic....
Have you check whether all source connections are OK or not???

 

[ashwatik]

I have checked as much as I can. For some reason, Assura does not recognize 5 nets that I have, where I have attached the transistors in parallel. Is there anyway I can re-extract the layout. I have attached the schematic and the main layout blocks. I have attached the images.


FYI: I have used "vd" and "vs" as my vdd and gnd.

Thank you for your reply.

 

[ashwatik]

There were two issues that lead to this error:
1. To make life easier, I learnt that I could even name transistors with the bus expansion format for multiple dievces, instead of adding new instances in parallel, I thought this was only valid for well, buses (wires). This format made locating the error easier.
2. If I enabled 'Substrate' in the cascoded devices, there is a metal1 short to the source of the transistor, which is not supposed to happen for a cascode. The substrate is connected to the lowest potential and the source is connected to the drain of the transistor it is cascoding to. Therefore, these cascoded transistors were not identified by LVS because the net connections were not matched. Hence, the net mismatch and device mismatch errors.

That one issue solved almost all my LVS errors.

General Tip: if the LVS debugger identifies less gates, check for shorts.