Re: why we use 1:1, 2:1, 4:1 and 8:1 devices for BJT matchin
I would say that the diference between CMOS matching and BJT matchins is dependent on two things:
Size of tech: It will determine if your biggest worry are gradients, boundary contitions(that the BJT's or CMOS see the same sorroundings ) or both.
BJTs are MUCH more suceptible than CMOS to noise carried over metal lines, so you want to keep that in mind when routing, and location of terminals in CMOS is diferent than BJTs. Also, CMOSs are much smaller, so are much less suceptable to gradients, and in submicron, much more suceptible to boundary conditions and densitys.
So, if your biggest worry is gradients, a big array helps match them against graidents. If your biggest worry is boundary conditions, a small array is easier to match.
Also, used area is an important concern.. BJTs arrays are big and area hungy, and if you have lots of them, they might use the same area as the rest of your bias cmoses. That is a lot.
Just my 2 cents.