Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; KEK, Tsukuba, Ibaraki 3050801, Japan
STF is a test facility for ILC which is under construction in KEK, Japan. The digital LLRF system is used to control the RF phase and amplitude inside the superconducting cavities. Because there is no real cavity to be controlled, a real time cavity simulator is designed to simulate the cavity response. An FPGA based cavity controller is designed to control the cavities. In the FPGA program, PI feedback and feed forward algorithm are adopted. Measurement shows that both the cavity simulator and the cavity controller work well.