PORTLAND — Lattice Semiconductor acknowledged late Friday that the mysterious investment firm trying to buy the Portland company is backed by the Chinese government. The disclosure, in a report on the transaction filed Friday evening, is no surprise: Investment analysts have suspected as much since Lattice announced the $1.3 billion deal in November. But both Lattice and its suitor, a newly established firm called Canyon Bridge Capital Partners, had previously said little more than that money for the deal comes from China. The Chinese connection could be an obstacle to getting federal sign-off on the deal, as Lattice acknowledges in Friday’s filing.