There is much material on older technologies and for differential pairs but for current domain circuits we need large-L and stacked devices, not so many devices in parallel. I wonder what is the "best" layout regarding area-efficiency and matching in technologies like FDSOI and FinFet? E.g. to form a precise W=10um and L=40um current mirror? Presentations, deep thoughts, device simulations or measurement results are highly welcome.
This question was asked almost 1 year ago. Maybe you no longer need any comments, but I will write some answers, anyway.
Matching of the transistors is important for both differential pair and current mirror. Therefore, the well-known methods (common-centroid, stacked, etc.) can be assumed to be good choices. The aim is not only to reflect equally the variations of the effects of process steps (e.g. different etching rates in different directions), but also to maintain a good thermal matching (Thermal gradients may cause other mismatches due to temperature effects).
On the other hand, using long channels helps to increase the current mirror's transfer accuracy (It's an issue of ID-VDS dependency, causing lower accuracy due to different VDS values of input and output transistors. It is also the main cause of a low output resistance). However, a long channel also dictates a wide channel (so to satisfy a W/L ratio), which automatically causes a large occupied area on the chip.
I need to add, however, that, large transistors match better (in terms of parameters) than small transistors (provided that the proper layout techniques are applied for good matching).
I don't know whether you had the option to use cascode connections for the transistors. This can increase the output resistance and can also set the VDS values of input and output transistors very close, without the need for long-channel devices. Thus, you can make economy from the area.
Unfortunately, classical cascode structures require larger voltage headroom. Nevertheless, there are some alternative cascode structures which don't require larger voltages to operate.
Best regards...
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