文档介绍：摘要
直接数字频率合成(DDS—Digital Direct Frequency synthesis)是一种新的频率合成方法,是频率合成技术的革命,随着数字集成电路和微电子技术的发展,DDS技术日益显露出它的优越性。直接数字频率合成器是一种全数字化的频率合成器,由相位累加器、波形ROM、D/A转换器和低通滤波器构成,DDS技术具有频率分辨率高、频率切换速度快、频率切换时相位连续、输出相位噪声低和可以产生任意波形等优点。由于上点,DDS技术可被用于雷达、通信、电子对抗和仪器仪表等领域。
论文研究了DDS技术,推导了直接数字频率合成器的数学综合,在理想的条件下分析了直接数字频率合成器的频谱特性,给出了直接数字频率合成器输出信号的时域表达式,对相位截断误差和幅度量化误差的频谱特性进行了分析,并推导出了杂散功率的计算公式,对DAC误差进行了分析,并提出了几种抑制DDS杂散的措施。
最小高斯频移键控(GMSK)是一种典型的连续相位调制方式,具有包络恒定、频谱紧凑、抗干扰能力强等特点,可有效降低邻道干扰,提高非线性功率放大器的效率,已在移动通信(如GSM系统)、航天测控等场合得到广泛应用。传统方法设计的GMSK调制解调器不能很好满足全数字化接收机可编程、多模式等需要。论文还重点研究利用全数字化技术设计GMSK调制解调器,以便更广泛地使用GMSK调制解调技术。还研究了GMSK调制方式的特点及性能;设计了基于DDS技术的GMSK调制的软硬件实验电路。
关键字:直接数字频率合成,高斯最小频移键控,杂散信号,相位截断
ABSTRACT
The Direct Digital Frequency Synthesis (DDS) is a kind of new frequency synthesis method and also a revolution in the frequency synthesis techniques. With the development of digital integrated circuits and microelectronic techniques,DDS exhibits its advantages day by day.
The direct digital frequency synthesizer is a kind of fully digitized frequency synthesizer,which consists of the phase accumulator,the sine look-up table,the digital to analog converter and the low band filter. It is of high frequency resolution,fast frequency switching speed,low phase noise,the ability to switch frequencies while maintaining constant Phase,and the ability to producing arbitrary waveforms. Because of above features,DDS can be used in such fields as munications,electronic warfare and electronic measurement instruments.
Minimum Gaussian frequency shift keying (GMSK) is a typical continuous phase modulation method, which has the characteristics of constant envelope, compact spectrum, and anti-jamming performance. GMSK can effectively reduce inter-channel interference, improve the efficiency of non-linear power amplifier, and has been widely used in munications system (such as GSM system) and others systems. The modulator and demodulator designed in traditional method cannot meet the need of programmable, multi-mode for