High-resolution Low Spurious Frequency Synthesizer Developed

Frequency synthesis technology is one of core technologies used in communication and electronic system. With the development of modern communication technology,frequency synthesizers are required to have wide band, high resolution, fast frequency switching speed and low spurious level. DDS (direct digital synthesis ) is a new frequency synthesis technology coming after DS (direct frequency ) and PLL (phase-locked loop frequency synthesis ) and widely applied in communication and radar area .This paper introduces the working principle and characteristics of DDS . DDS is famous for high resolution and fast frequency switching speed, but the flaw of bad spurious performance restricts it's applications. The analysis on sources of the spurious signals and their locations shows that the locations of the spurious can be predicted by ?ck ( reference frequency ) and ?d (DDS output frequency ), so by choosing output frquency of DDS can optimize it's spurious characteristics. Combining the DDS and PLL technology with Triple tuned algorithm promoted by TAJIMA is a method to achieve both high frequency resolution and fast hopping without degradation of spurious characteristics. Based on this method, we design a low spurious and high resolution frequency synthesizer ranged from 92.1MHz to 120.499MHz with AD9850. The synthesizer demonstrated spurious level below -65 dBc with frequency step of 100Hz.