Background: Proton has a higher precision in cancer treatment than traditional X or γ radiation because of its Bragg peak feature. Shanghai Institute of Applied Physics is participating in the development of the first proton therapy facility of China. Purpose: Stable and adjustable proton beam extraction is one of the key points of the project. The aim of this work is to design high resolution frequency signal source for slow beam extraction. Methods: A fully digital signal source platform is implemented using FPGA developing board DE2-115 and Direct Digital Synthesizer (DDS) board AD9910/PCBZ. The communication between DE2-115 and AD9910/PCBZ is realized via SPI interface with Verilog HDL programming. Results: High accuracy and flexible frequency signal is obtained through the platform and visualized clearly by oscilloscope and spectrometer

despite a little harmonic. Conclusion: The preliminary results show that scheme design of the project is reasonable and meets the needs of demands although many aspects of the scheme have to be improved further.Cited