Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
common centroid technique is used for matching purposes. Where, two transistors that need matching .matching means,, the process gradients should be equally felt by the two transistors that need to be matched. For this to be achieved ,, especially in the case of Differential pair matching, common centroid layout techniques are used. Common centroid is analogous to centre of mass. ie,,
if M1 and M2 are two transistors that needed to be matched, then they are digitated to fingers. And the fingers of M1 and fingers of M2 are placed in such a fashion that , the centre of mass of M1 and centre of mass of M2 are both same. This is analogous to common centroid. While providing the interconnects with metals and poly, care has to be taken to ensure that even the mass of the metals also have the same centre of masss. This kind of architecture gives a good matching.
To know what are the various styles of putting it,, refer Alan Hastings Art of Analog Lyout