Sand 9, a developer of microelectromechanical systems (MEMS), has raised an additional $4 million in its third round of venture capital, the company disclosed in an amended SEC filing.

Sand 9 develops MEMS resonators for communications timing applications, which the company says has advantages over traditional quartz crystal. Investors in the company include Commonwealth Capital Ventures, Flybridge Capital Partners, General Catalyst Partners, Intel Capital, Khosla Ventures, and Vulcan Capital.