common centroid site:edaboard.com
Hi,
Thanks again. By the way, I wanted to say that your last two posts were helpful, but it doesn't have a button for that. Do you have to start a new thread to be able to say someone's post was helpful?
Anyway, actually as far as M is concerned, I don't really understand how that is decided. In my schematic, I have been simulating using single transistors. But I've seen in one of my books (unfortunately I don't have the book at home with me so I can't tell you exactly what it says) that it is useful when matching large transistors to break them into different strips (and the book gave an equation for determining how many). The bias currents needed by the different parts of the circuit are different so each of those transistors A,B,C,D,E, and F, have the same L but Ws that are integer multiples of the smallest W (E and F are the same size and actually have the smallest Ws). B and C are the largest (but not the same size). I simplified by breaking them each into 2, but actually, B and C will need several strips if they are to have the same W as the other strips. But I was hoping I could still do something like I said, where I cross-couple B's and C's strips and put the others on the sides. A and D are the same size, and I can increase E and F to be the same size as A and D. But I was thinking of making strips where Wstrip=1/2 E's (and F's) W and breaking up B and C into the required number of strips and then intertwining them. I have to check when I get in tomorrow, but if I remember right A=D=2*E=2*F and B=5*E and C=10*E. Or is it possible to do something like this:
DUM BC A1 D1 E DUM
DUM CB A2 D2 F DUM
where BC and CB are actually multiple fingers of each mixed up. Thinking about it now, I see I may need to change B so it is an even multiple of E if I want to do the layout in this way, but is this ok? Or am I misunderstanding something important about layout?
regards,
kris