Both Panasonic LZ20 and Nikon B500 have 16.0 MP resolution sensors but Panasonic LZ20's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Nikon B500's sensor is 1/2.3 (6.17 x 4.55 mm ).
Since Nikon B500's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Panasonic LZ20.
Below you can see the LZ20 and B500 sensor size comparison.
Panasonic LZ20 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.