频率合成器中Σ-Δ调制器的设计与实现

摘要

The principle of the sigma-delta modulation technology is introduced first in this paper. Then the first-order and the higher order sigma-delta modulators are analyzed, and finally a method for the sigma-delta modulator based on FPGA is proposed. This design of a sigma-delta modulator is correct and feasible. Simulation results show that the results from the sigma-delta modulator and the fractional-N divider by controling the frequency divider implemented by this method are well in accordance with the simulation results based on Matlab software. Then noise shaping characteristics of the higher-order sigma-delta modulator is further experimentally verified. The fractional spur introduced by the fractional-N frequency synthesizer can be suppressed by the loop filter of the phase-locked-loop,which is highly practicable.%本文首先介绍了Σ-Δ调制技术的基本原理,分析了一阶及高阶Σ-Δ调制器,最后结合一阶Σ-Δ调制器,给出了在FPGA器件上实现Σ-Δ调制器的设计.仿真结果表明,设计实现了Σ-Δ调制器,通过控制分频器实现了小数分频,方法简单易行.与运用Matlab软件仿真的结果完全一致,并进一步证实了高阶数字Σ-Δ调制对量化相位噪声的高通整形特性,从而有效地解决了小数分频频率合成器中的小数杂散问题,具有很高的实用性.