Re: cell origin
Hi,
Cell origin is the reference point in layout with which position of devices are measured/displayed. If you place the origin of the cell at the left-bottom of the layout, it means entire drawing is in 1st quadrant of layout window. In this case x,y position of any device/routing will be positive and is easy to interpret the location. It is not mandatory to keep the origin at the left-bottom for cells of the chip. But if you are using the cell in 'auto place and route' tool, it would be good to have origin of all the cells at left-bottom.
Also, while mentioning size of the cell, if origin is at the left-bottom you can just specify x,y of rigt-top corener of the cell.