I am making 6bit R DAC (i.e. 64 resistor) with resistor value 300 ohm. After makin layout of my r string the layout resistor values are slightly different. The top and the bottom resistor values are more different than the pre simulation value. I am using maximum identical contacts and placing to make them matched. I am taking rplpoly for my resistor layout.
Please suggest..How I can make these resistor value identical in the layout.
Case 1: You put in identical schematic values and you
got (SDL synthesis) non-identical layout dimensions.
This would seem improbable.
Case 2: You got identical resistor segment geometries
but the extracted values are off by an integer multiple /
divisor. This might be a hookup error putting two links
in series or parallel.
Case 3: You got identical resistor segment geometries
but the extracted values are off by an arbitrary small
amount. This might be from "too much smarts" in the
layout extraction "doing things" to the extracted value
for stuff like proximity effects. Try putting 66 elements
and tying off the end ones to themselves, as "dummies".
How did you figure out the top and bottom resistance difference, and are those bigger or smaller values? How many contacts you have now, which layer are you using for wiring at the top/middle/bottom?