Hi t4_v,thank you for your reply.
First of all, your transistors are big thus their matching should be improved just by that. The problem can be the length that I guess is the minimum length and is equal to 0.7 um, thus it can be a little problematic in Monte Carlo and the matching can worsen.[/QUOTE]
My technology is 0.35um, I choose 0.7u to improve matching,i understand that for better matching length have to be as large as possible(even when width is already large),but I don't know is there some kind of rule of thumb what is minimal length for good matching?
Secondly, your example ABBAABBA is, using Baker book, rather common centroid. Interdigitated layout is ABABABAB.
Take a look also here: **broken link removed** .
About ABABABAB,how much can this type of layout be good for marching,since it does not have same common centre for both mosfets.[/QUOTE]
Also,is multi-finger layout of common centroid (like in pdf you send,section Common Centroid Layout with Multi-Fingered Gates) good technique for matching,can I just take my mosfets A and B ,divide each of them in two smaller mosfets with multfinger and make common centroid layout?or is it much better to make interdigitated common centroid layout?
Thirdly, as BigBoss pointed out parasitic capacitances are not so important. The currents that flow through transistors depends on their dimensions (width W and length L). The most important is that the two transistors dimensions are the same, thus in layout is usually means bigger than minimum sizes and the same surroundings for both transistors.[/QUOTE]
I am making full differential opamp,in which i need current mirrors and diff pair of mosfet,I made some initial simulations and I noticed that when I tried patterns which don't have same parasitic capacitances, I dont have symmetrical outputs,so I think that for my circuit I need to have as much as possible symmetrical parasitic capacitances.