Olympus SZ-30MR has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features TruePic III+ processor. On the other hand, Sony W620 has a 14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features BIONZ processor.
Below you can see the SZ-30MR and W620 sensor size comparison.
Olympus SZ-30MR and Sony W620 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 Sony W620 has 14% larger pixel area (2.01µm2 vs 1.76µm2) compared to Olympus SZ-30MR, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.