Mosaid Technologies asked shareholders on Thursday to take no action on an unsolicited C$480 million ($490 million) offer from rival patent firm WiLan, the latest sign of swelling global interest in increasingly valuable patents.

WiLan on Wednesday offered C$38 a share offer for Mosaid, taking its proposal directly to shareholders after Mosaid rebuffed it in earlier talks. It says a takeover would create a firm with global scope as companies seek to shore up their technology patent portfolios.

Mosaid's board of directors is considering and evaluating Wi-LAN's offer and will respond in due course, the company said in a brief statement in response the WiLan's offer.

Technology giants like Google, Apple, Microsoft and Research In Motion have all been battling to win control of patents as they traverse a maze of litigation related to the use of each others' inventions.

A consortium including Apple, Microsoft and Research In Motion last month paid $4.5 billion for some 6,000 patents of bankrupt Canadian telecoms giant Nortel Networks.

Google, losers in that auction, said on Monday it would pay $12.5 billion for Motorola Mobility, to gain access to one of the mobile phone industry's largest patent libraries.

Both WiLan and Mosaid develop and acquire patents with the main aim of winning licensing deals from companies that use the technology, rather than using the intellectual property in their own products.

Others eye patents more as a way to protect their products from litigation and excessive licensing costs.

Mosaid shares opened sharply higher at C$39.85. The shares closed at C$31.65 before the WiLan offer was announced.

The WiLan offer represents a 20 percent premium to that closing price. WiLan stock was 44 Canadian cents lower at C$6.65.

(Reporting by Pav Jordan and Alastair Sharp; editing by Janet Guttsman)