mburakbaran
Member level 2
Hi all,
I designed a 12bit DAC based on R-2R topology in a 0.18um CMOS tech. It is 8+4bit segmented. The sizes of the switches are increased in a binary weighted manner as the current drawn from each consecutive higher significant bit is going to be double. So, the switch of the LSB is 1 unit, LSB+1 is 2 unit so for and so forth. The segmented parts switch size is equal to each other (4to15 thermometer decoder, thus 15 of them) two times the last non-segmented switch size and 15 is equal. This way, I was able to minimize the systematic mismatch.
Anyways, here comes my question. How do I lay this out? If I go ahead and try to form something like a common-centroid array, the more the fingers gets away from the center, the more rds it will add to that specific finger, and adding yet another systematic mismatch in terms of "Ron" dont you think? How would you suggest I should proceed? (Please bear in mind that the smallest switch is 1 unit, yet the biggest ones (the unary part) are 256 x unit)
Any help is greatly appreciated. Thanks a lot.
I designed a 12bit DAC based on R-2R topology in a 0.18um CMOS tech. It is 8+4bit segmented. The sizes of the switches are increased in a binary weighted manner as the current drawn from each consecutive higher significant bit is going to be double. So, the switch of the LSB is 1 unit, LSB+1 is 2 unit so for and so forth. The segmented parts switch size is equal to each other (4to15 thermometer decoder, thus 15 of them) two times the last non-segmented switch size and 15 is equal. This way, I was able to minimize the systematic mismatch.
Anyways, here comes my question. How do I lay this out? If I go ahead and try to form something like a common-centroid array, the more the fingers gets away from the center, the more rds it will add to that specific finger, and adding yet another systematic mismatch in terms of "Ron" dont you think? How would you suggest I should proceed? (Please bear in mind that the smallest switch is 1 unit, yet the biggest ones (the unary part) are 256 x unit)
Any help is greatly appreciated. Thanks a lot.