Design Of High Precision Signal Generator Based On DDS

Function signal generator is one of the most commonly used equipment in the field of telecommunications and electronics laboratory,and it also have a wide range of applications in teaching,research,manufacture,biological engineering and remote telemetry areas.With the development of electronictechnology,more and more requires are set on signal source such as higher frequency resolution,wider the frequency range,higher frequeney spectrum purity and so on.However,function signal generators used in scientific research institutes and schools have many defects such as the low frequency accuracy and low resolution,frequency band narrow and a small number kinds of output waveform,and these traditional methods cannot satisfy the request..Our design that multifunctional waveform generator based on DDS is just according to the defects of the signal generators used at present.Direct Digital Frequency Synthesis(DDS) was advanced rapidly in early 1970s.The fully digital DDS technique has such advantages as high frequency resolution,fast frequency switching speed,low phase noise and high stability,overcomes the shortcomings of traditional analog signal sources and is the main content on signal generator research.This article develops a high performance signal generator based on the DDS technique.It uses the AD9852 chip of the AD Inc.as the DDS model kernel and the LPC2138 chip of the Philips Inc.as the control core,and use the touch panel to input and display data.TheμC/OS-Ⅱsystem is also used for software design. Experiments show that the design output frequency bandwidth can be achieved 0.001Hz～50MHz,the frequency resolution 0.001Hz,and a high degree of frequency accuracy and stability.The signal source has been applied in the undergraduate electronics laboratory, achieved with the experimental e-learning requirements.Firstly,the thesis described the histroy and development of frequency synthesis techniques,analyze several principles of frequency synthesizer.,and discuss the advantages and defects of these frequency synthesis techniques,and the design of high-precision signal source based on DDS was given.Then described the principle of DDS.Including the introduction of the composition and structure of DDS,and also the mathematical analysis,spectrum analysis and spurious analysis of DDS.The method of spur suppression for DDS is also given in this paper.The overall design of the signal source system is behind.It included main chips on the system selected,and the overall hardware and software system design were descriped detailed.Hardware design mainly introduced the design of hardware modulars,such as the power supply module,touch panel module,control module of ARM7,signal output of AD9852 and the Low-pass filter module etc.The software design used in signal generator and based onμC/OS-Ⅱsystem were showed in detail,and the method to process 48bit Frequency Control Word in ARM7 are mainly described.Then measured and analyzed the output waveform data,and gived the ways to solve problems encountered in the design,as well as the improvement program for the signal source system.Finally summed up the work of the dissertation,and made some suggestion for further work.