Re: Matching Pattern
Hi radram
When it comes to differential amplifier, we expect the current in both the differential pair tx to be the same, that is what it would be designed for in fact. Hence matching becomes critical here. To obtain optimum characteristics from this design, in the layout certain things are to be followed as thumb rule
- common centroid matching for symmetry
- identical routing
-guard ring connected to the corresponding potential.
-adding dummies to achieve poly symmetry as well as continuous diffusion.
Now if u look at AABB--AABB pattern, although there is a uniformity maintained, there is no symmetry, hence process gradients are not nullified.Now you do want your diffential amplifier layout to serve its true purpose right!! Take a look at the ABBA--ABBA pattern and lemme know why thiis is not better than the former combination.
I believe this helps.
Regards
Brittoo