Intel has invested $1.5 billion in Tsinghua Unigroup, a state-owned holding company that operates two Chinese chip manufacturers, as part of a plan to accelerate the adoption of Intel’s own chips in the Chinese market. The world’s biggest chip maker said it would take a 20 percent stake of Tsinghua Unigroup, the owner of Spreadtrum Communications and RDA Microelectronics. The deal is subject to regulatory approvals and other closing conditions.