No father on BC, want husband to adopt.

My son is almost 7 years old. My husband and I have been together since he was 6 weeks old, and married for over 6 1/2 years. He is the only father my son has ever known. There is no father on his birth certificate, and I would like for my husband to adopt him. What do I need to do? How simple is a step parent adoption when there is no father on the BC? We live in Sacramento County.