Santa Rosa’s Keysight Technologies on Monday announced a new offering of $400 million worth of common stock to help fund its purchase of data tech business Ixia.

Keysight, the largest ever company based in Sonoma County, announced in January that it would pay $1.6 billion for Ixia, which provides network “visibility,” testing and security solutions to such customers as Cisco and AT&T.

Keysight said Monday it will combine the proceeds from the stock offering with unsecured debt financing to pay for Ixia.

Keysight stock closed Monday at $38.75, down 27 cents.

Companies involved in underwriting the public offering include Goldman Sachs, B of A Merrill Lynch, Citigroup, BNP Paribas, Barclays, Credit Suisse and Wells Fargo Securities. Keysight plans to grant the underwriters a 30-day option to purchase up to an additional $60 million worth of common shares.