Nikon P90 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Nikon B500 has a
16.0MP 1/2.3 (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the P90 and B500 sensor size comparison.
Nikon P90 and Nikon B500 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.