Canon A3100 IS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Canon A2200 has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 4 with iSAPS technology processor.
Below you can see the A3100 IS and A2200 sensor size comparison.
Canon A3100 IS and Canon A2200 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.