By IAN SHERR AND HARRIET TORRY FEBRUARY 6, 2012

Motorola Mobility Holdings Inc. asked Apple Inc. to pay a potential royalty of 2.25% of sales for some iPhones and iPads last year, representing possibly billions of dollars in licensing fees. 

In a letter filed in a California court last month, a lawyer said Motorola, which is being acquired by Google Inc., had "demanded" the royalty for a license of its patents. The letter, which was dated Oct. 17 of last year, gives a glimpse into the ongoing patent struggles between mobile device makers. Apple in particular has locked horns with titans of industry, including Samsung Electronics Co. Ltd. and HTC Corp, over patents for mobile devices. Each company has suggested much is at stake, but this document gives the first sense of potentially how much. A royalty of 2.25% on Apple's iPhone sales would amount to more than $1 billion in 2011, though the court letter doesn't specify which devices would be affected nor whether it would be retroactive. Apple and Motorola declined to comment. Royalty rates are a closely guarded secret among technology makers, lawyers say, and it is unusual for companies to divulge such information. Additionally, because such rates are so rarely discussed in public, lawyers and industry insiders said it was hard to tell whether the amount Motorola was asked for was reasonable.

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