In a blender, combine yogurt and ricotta cheese; cover and process until combined.
In a small bowl, combine blueberries and strawberries. Place half the cake cubes in a 2-qt. glass bowl. Layer with 1 cup berries and half the yogurt mixture. Top with remaining cake cubes, 3/4 cup berries and the remaining yogurt mixture. Garnish with remaining berries. Top with whipped topping. Refrigerate leftovers.