Nikon D80 has a 10.0MP APS-C (23.6 x 15.8 mm ) sized CCD sensor . On the other hand, Nikon D90 has a 12.0MP APS-C (23.6 x 15.8 mm ) sized CMOS sensor .
Below you can see the D80 and D90 sensor size comparison.
Nikon D80 and Nikon D90 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Nikon D80 has 21% larger pixel area compared to Nikon D90, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.