A Motorola Mobility shareholder has taken the company to court for failing to achieve a sufficient price in its US$12.5 billion sale to Google.

Bloomberg reports that the investor, John Keating, has filed a complaint at the state courthouse in Chicago, saying the price does not adequately compensate shareholders for the company’s intrinsic value.

Google agreed to pay US$40 per share in cash for the company, a 63% premium on its stock price at the time. The deal remains subject to regulatory approval.

The main value of the sale for Google is thought to be Motorola Mobility’s vast patent portfolio, which numbers 17,000 with an additional 7500 pending. Google previously missed out purchasing the patent portfolio of bankrupt tech company Nortel, when it was purchased by a consortium including Microsoft and Apple for US$4.5 billion.

Keating’s reaction to the sale has drawn suggestions there is a ‘patent bubble’ brewing, with companies so desperate to defend themselves in the legal arms race they are vastly overvaluing patent portfolios which would otherwise be worthless.

The full implications of Google's purchase are still being realised - go here for more.