A federal Judge on Thursday rejected some patent claims brought by Google's Motorola Mobility unit against Microsoft, significantly narrowing the patent lawsuit.

US District Court Judge James Robart sided with Microsoft and dismissed 13 claims of infringement on three of Motorola patents involving digital video encoding and decoding.

Microsoft claims Motorola deserves only a small royalty on many of its telecommunications patents. Motorola had sought up to $4 billion a year for its wireless and video patents, while Microsoft argues its rival deserves about $1 million a year, claiming that the specific patents should be considered as "standards-essential" technology.

Microsoft filed its case over the royalty amounts. Motorola's response was to fill a new lawsuit against Microsoft on three patents that cover video technology.

The final ruling is expected to be issued sometime in the next several weeks. The case in U.S. District Court, Western District of Washington is Microsoft Corp. vs. Motorola Inc., 10-cv-1823.