Sony plans to acquire the portion of its optical disc joint venture with NEC that it doesn't already own and make the company a subsidiary, it said Thursday.

Sony already holds 55 percent of Sony NEC Optiarc and will acquire the remaining 45 percent for an undisclosed sum, both companies said in a statement.

Sony NEC Optiarc was formed in 2006 and combined the optical disc drive businesses of the two companies. Sony had a greater strength in the optical pick-up devices used inside drives while NEC's strength was in the chips that control drives.

The merger came at an interesting time as NEC was backing and developing the HD DVD format, which went up and lost against the Sony-backed Blu-ray Disc format in the battle to replace DVD for high-definition video.

The acquisition is scheduled to be completed in December this year at which time the company's approximately 320 employees will become Sony staff.

Following Sony's acquisition of the company NEC will continue to work with what will become Sony's optical drive business by developing some of the chips for the drives.