New Fractional-N Synthesizer Used On TT & C Transponder

In the application of satellite monitoring and communication, frequency synthesizers are often used as TT & C transponder’s local oscillator. There is a gap between the traditional integer-N frequency synthesizer’s resolution and the receiving frequency’s accuracy requirement, which affects the adaptability for RF receiver to receive the local oscillator frequency. It is significant to design a new fractional-N frequency synthesizer with certain environmental adaptability, better electrical performance, which can resolve current transponder’s frenquency adaptability, improve its electrical performance stability.This paper introduces the basic theory of the frequency synthesizer, the principle related to the space environment adaptability and the basic theory of fractional PLL frequency. From PLL frequency synthesizer noise and spurious suppression method and DSM noise shaping principle, this paper designed a new fractional-N frequency synthesizer based on DSM MASH structure modulation technique. This paper mainly studies the frequency synthesizer’s design related to the space environment adaptability, noise suppression methods and MASH structure fractional spur’s inhibitory properties. It also processes related theoretical analysis and simulation. In the last, this paper elaborates the design process of digital MASH 1-1-1 structure. The hardware implementation and testing situations are also presented. Finally, measurements from the test indicates that the phase noise is better than -83dBc/Hz @ 10kHz, fractional spurious suppression better than -30dBc, the frequency accuracy reach 100Hz, the hardware operating temperature range up to -40℃～+85℃ the total dose tolerance up to 100 krad (Si), and have a certain resistance to SEU. This design meets the expected target and has good prospects in the satellite engineering applications.