Nikon L21 has a
8.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Expeed C2 processor. On the other hand, Canon SX220 HS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 4 with iSAPS technology processor.
Below you can see the L21 and SX220 HS sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon L21 and Canon SX220 HS Cameras
Nikon L21 and Canon SX220 HS 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.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Nikon L21
or the
Canon SX220 HS ,
including hyperfocal distance.