Common Centroid for differential pair

[fmfs10]

When I work with differential pairs, I constantly deal with the following transistor construction, for two cut transistors:

AB|BA
BA|AB

But for better matching, I think this one below would be better, giving 2 axis of simmetry, mirroring the x-axis and the y-axis:

AB|AB
-----
BA|BA

Where am I wrong?? Why is the first used more than the second?

 

[dick_freebird]

I don't see the difference, axis-of-symmetry-wise.

It might be as simple as the original form appearing
first in textbooks so lazy readers will not bother past
that point, to see alternatives.

 

[MahmoudHassan]

When I work with differential pairs, I constantly deal with the following transistor construction, for two cut transistors:

AB|BA
BA|AB

But for better matching, I think this one below would be better, giving 2 axis of simmetry, mirroring the x-axis and the y-axis:

AB|AB
-----
BA|BA

Where am I wrong?? Why is the first used more than the second?

For Diff pair

For the input pair that requires good matching don't apply common centroid (AB|BA technique) but do interdigitation ( AB|AB) as this will be better in matching including wiring. (I am talking specifically about this case of simple 4 transistors)

For current mirrors like the load current mirror or biasing current mirrors do common centroid with the middle transistor is the reference transistor.