Who writes Design Document in an organization?

The person writing the design document is it the project manager or the integrator?

Development of a systyem is team work. Everyone has its own responsibility. Project Manager is responsible to manage project within time and budget, manage development team and communicates between development team and authority. Design document is not responsibility of a project mmanager. For designing, we have architects/designers that develop design of system based on requirements identified and analyzed during requirement analysis phase.