Jockey,

  From the available information it is a little difficult to guess what the
issue is. Since non Monte Carlo simulation runs properly, the first
question is how is the Monte Carlo model implemented. Next, why
are you using transient analysis to measure the difference in
base-emitter voltage? Isn't a dc sweep sufficient? Since it would
eliminate the issues with transient setup. Finally, iabstol is a simulator
option not an analysis options,  simulation --> options.

                                                                          Sheldon

Jockey,

  First you are using pnp transistors not npn transistors. Next,
a few questions:
1) Why do it this way?
   Why not two current sources of the same value and size
   one of the pnp transistors?

2) Next you are operating these transistors at very low
   current density, have you checked the p-channels models
   subthreshold characteristics?

3) Again, why are you performing transient analysis on this
   circuit? You are just looking at the temperature tracking,
   then dc analysis is all you need. For example, when
   performing a similar analysis of a bandgap reference, only
   need to run dc in order to verify trimming ranges.  

4) What other parameters are you tracking in your analysis? For
   example, how much head room do the current source have?
   Is there any reason that the circuit is might be having issues
   setting up? Looking at your schemtic, it does not seem like
   there should be any issue, but it might be worth checking.

                                                                  Sheldon

     

The question is, are the vertical pnp built with substrate as the collector.
If the vertical pnp transistors are substrate pnp transistors, then a
fourth terminal is not required since by definition the third terminal,
collector, and fourth terminal, substrate, are connected. Using
substrate pnp transistors for diodes is not an issue.

Dear sheldon adn rfidea,

Yes I am using GF 65nm technology with substrate vpnp, so the substrate serves as collector terminal.

I am not using vpnps with different area and same current density because the error introduced due to process spread will be many times more.

I have to keep the current density low to minimize the impact of emitter base series resistance which further introduces error.

Any way I am looking into suggestions and will keep updated.