Qualcomm Inc. /zigman2/quotes/206679220/composite QCOM +1.54% said Monday that it was buying the remaining interest in RF360 Holdings Singapore Pte. Ltd., which makes RF frong-end filters. RF360 is a joint venture with Tokyo-based TDK Corp. /zigman2/quotes/201622098/composite TTDKY +0.89% /zigman2/quotes/208948266/delayed JP:6762 +0.20% , with TDK's remaining interest valued at $1.15 billion in August. Qualcomm's stock slipped 0.9% in premarket trading. Qualcomm said the total purchase price, including the initial investment, payments to TDK and development obligations will be about $3.1 billion. Qualcomm said the acquisition strengthens its RF business and helps support the transition to 5G. "Our goal in the formation of this joint venture was to enhance Qualcomm Technologies' front-end solutions to enable us to deliver a truly complete solution to the mobile device ecosystem, and we have done exactly that," said Qualcomm President Cristiano Amon. Qualcomm's stock has soared 37.8% year to date through Friday, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.30% has gained 20.0%.