Qualcomm Inc. is preparing to fend off an unsolicited $100 billion takeover bid from Broadcom Ltd. , arguing it undervalues the company, people familiar with the plans said. Qualcomm of Broadcom is preparing a $70-a-share offer for Qualcomm, which could come as soon as Monday, said the people, who asked not to be identified because the plans are private. Qualcomm will argue that the proposal, the largest-ever technology acquisition, is an opportunistic move to buy the chipmaker on the cheap, the people said. While Qualcomm’s board and management will give the offer due consideration, the San Diego-based company will likely recommend that shareholders reject it, the people said. This would force Broadcom to pursue a proxy fight if it wishes to proceed. A Qualcomm spokesman declined to comment, and Broadcom didn’t immediately respond to a request for comment. Shares in Qualcomm were up 3 percent at 6:30 a.m in pre-market trading in New York, while Bro...