The Development Of High-resolution Low-spurious Frequency Synthesizer

Frequency synthesizer is one of the most important parts used in modern communication and electronic systems. With the development of modern communication techniques, frequency synthesizer is required to have higher performance such as wide band, fast frequency switching speed, low spurious level, pure output spectrum, high resolution , etc. Direct digital synthesis (DDS) is a new frequency synthesis technology coming after direct frequency synthesis (DS) and phase locked loop frequency synthesis (PLL). It's widely used in such fields as radar, communication, electronic warfare and electronic measurement instrument.At first, this paper introduces the basic working principle and characteristics of DDS. The main merits of DDS are high resolution and fast frequency switching speed, but the defects of low output frequency and bad spurious performance restrict the application of DDS. The output frequency can be raised by PLL.This paper analysis it's spurious perfomance.The analysis of the sources of spurious signals and their locations shows that the locations of spurious can be predicted by reference frequency (f_Ck) and DDS output frequency (f_d). So we can combinate DDS and PLL, optimize the spurious characteristics of the comnination frequency synthesizer by choosing proper output frequency of DDS.This paper analyzes some schemes of combination frequency synthesizer of DDS and PLL, and uses the Triple tuned algorithm to achieve high frequency resolution , high output frequency and excellent spurious characteristics. We design a low spurious high resolution triple tuned type frequency synthesizer with AD9850 and PE3336. This frequency synthesizer works at X-band, and demonstrates low spurious level in range of 8.75GHz ± 50MHz , with the frequency step below 0.5MHz (actually the maximum resolution can be 2Hz).