open-source-silicon.dev

is there anyway to size mosfets for a current mirror like,i know w/l ratio i want but how should i chose W and L values,is there any systematic way

You'll want to use the same L and choose the W ratios to match the desired current ratios. I shared a set of gm/Id curves I made for the g5v0d10v5 devices on this channel a while back which you can use to choose the device sizes

The W ratios should be realized as multiples of a single unit transistor width. E.g. choose a per finger width, then choose the number of fingers required to get the desired width per device

Even better for tight matching, you could use multiple instances of a unit device with a fixed number of fingers, leaving mismatches to layout routing and surrounding dummy structures /gradients.