Re: Layout Matching
Interdigitation just means that the devices (transistors, resistors, capacitors, diodes) are distributed in an interleaved maner. For instance imagine that you must match two devices (A and B) composed by 4 unit devices each:
ABABABAB
---------> If there is a gradient in this direction component B is more affected than component A
A common centroid structure would be
ABAB|BABA
Notice that in this case there is an axis of symmetry (I added character | for the axis) so any "linear" gradient is compensated. If now A and B are divided into 16 unit devices, a more complex common centroid structure would be
ABAB|BABA
BABA|ABAB
--------------
BABA|ABAB
ABAB|BABA
Notice in this case that the structure has vertical and horizontal symmetry axes, or more general central symmetry.
Have a look at the Hskings book "The Art of Analog Layout"