FORT COLLINS — Avago Technologies Ltd. is planning a $57 million expansion at its campus in southeast Fort Collins with the addition of a three-story building and one-story warehouse.

Avago (Nasdaq: AVGO), which makes microchips for mobile telephones, already has a 1.2 million-square-foot campus at 4380 Ziegler Road. The city building permit for which the company applied on June 4 calls for adding a total of 121,767 square feet, consisting of a 23,643-square-foot, one-story warehouse that adjoins a 98,124-square-foot, three-story building that would house offices and a non-hazardous clean-room testing space.

The plan also includes an on-grade link to Avago’s existing Building 1 and a connecting bridge to existing Building 4.

Denver-based J.E. Dunn Construction Co. is the primary contractor for the expansion.

When it decided to expand in Fort Collins in 2011, Avago agreed to add 227 workers by the end of this year in exchange for a series of city economic incentives. The company completed those expansions ahead of schedule and completed two other expansion projects without city aid.

Avago, which is based in both Singapore and San Jose, Calif., employs about 1,300 workers in Fort Collins and also has a Longmont office. It has held two job fairs so far this year, aiming to add 100 and 150 workers respectively.

The company two weeks ago announced a $37 billion acquisition of Irvine, Calif.-based rival chipmaker Broadcom, which also has an office in Fort Collins, and reported quarterly net income of $344 million. Other recent acquisitions include LSI Corp. and PLX Technology.